Journal articles: 'Coherent Beam Multiplexing. Spectral Multiplexing'

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Feng, Y., R. Alonso-Mori, T. R. M. Barends, V. D. Blank, S. Botha, M. Chollet, D. S. Damiani, et al. "Demonstration of simultaneous experiments using thin crystal multiplexing at the Linac Coherent Light Source." Journal of Synchrotron Radiation 22, no. 3 (April 10, 2015): 626–33. http://dx.doi.org/10.1107/s1600577515003999.

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Multiplexing of the Linac Coherent Light Source beam was demonstrated for hard X-rays by spectral division using a near-perfect diamond thin-crystal monochromator operating in the Bragg geometry. The wavefront and coherence properties of both the reflected and transmitted beams were well preserved, thus allowing simultaneous measurements at two separate instruments. In this report, the structure determination of a prototypical protein was performed using serial femtosecond crystallography simultaneously with a femtosecond time-resolved XANES studies of photoexcited spin transition dynamics in an iron spin-crossover system. The results of both experiments using the multiplexed beams are similar to those obtained separately, using a dedicated beam, with no significant differences in quality.

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Jiang, Cheng, Hongpei Wang, Hongmei Chen, Hao Dai, Ziyang Zhang, Xiaohui Li, and Zhonghui Yao. "Broadband Quantum Dot Superluminescent Diode with Simultaneous Three-State Emission." Nanomaterials 12, no. 9 (April 22, 2022): 1431. http://dx.doi.org/10.3390/nano12091431.

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Semiconductor superluminescent light-emitting diodes (SLEDs) have emerged as ideal and vital broadband light sources with extensive applications, such as optical fiber-based sensors, biomedical sensing/imaging, wavelength-division multiplexing system testing and optoelectronic systems, etc. Self-assembled quantum dots (SAQDs) are very promising candidates for the realization of broadband SLED due to their intrinsic large inhomogeneous spectral broadening. Introducing excited states (ESs) emission could further increase the spectral bandwidth. However, almost all QD-based SLEDs are limited to the ground state (GS) or GS and first excited state (ES1) emission. In this work, multiple five-QD-layer structures with large dot size inhomogeneous distribution were grown by optimizing the molecular beam epitaxy (MBE) growth conditions. Based on that, with the assistance of a carefully designed mirror-coating process to accurately control the cavity mirror loss of GS and ESs, respectively, a broadband QD-SLED with three simultaneous states of GS, ES1 and second excited-state (ES2) emission has been realized, exhibiting a large spectral width of 91 nm with a small spectral dip of 1.3 dB and a high continuous wave (CW) output power of 40 mW. These results pave the way for a new fabrication technique for high-performance QD-based low-coherent light sources.

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Zhang, Chenghong, Fangrui Qu, Peiwen Ou, Haoqi Sun, Shi He, and Bo Fu. "Recent Advances and Outlook in Single-Cavity Dual Comb Lasers." Photonics 10, no. 2 (February 18, 2023): 221. http://dx.doi.org/10.3390/photonics10020221.

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Dual-comb spectroscopy as an emerging tool for spectral analysis has been investigated in a wide range of applications, including absorption spectroscopy, light detection and ranging, and nonlinear spectral imaging. Two mutually coherent combs facilitate high-precision, high-resolution, and broadband spectroscopy. Recently, dual combs generated from a single cavity have become compelling options for dual-comb spectroscopy, enabling huge simplification to measuring systems. Here, we review the progress of single-cavity dual comb lasers in recent years and summarize the distinctive advantages of single-cavity dual combs. First, the principles of optical frequency comb and dual-comb spectroscopy are introduced in time and frequency domains. Then, the implementation techniques and typical applications of single-cavity dual comb lasers are discussed, including directional multiplexing, wavelength multiplexing, polarization multiplexing, and space multiplexing. Finally, an outlook on the development of single-cavity dual combs is presented.

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Wang, Fanggang, and Xiaodong Wang. "Coherent Optical DFT-Spread OFDM." Advances in Optical Technologies 2011 (March 31, 2011): 1–4. http://dx.doi.org/10.1155/2011/689289.

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We consider application of the discrete Fourier transform-spread orthogonal frequency-division multiplexing (DFT-spread OFDM) technique to high-speed fiber optic communications. The DFT-spread OFDM is a form of single-carrier technique that possesses almost all advantages of the multicarrier OFDM technique (such as high spectral efficiency, flexible bandwidth allocation, low sampling rate, and low-complexity equalization). In particular, we consider the optical DFT-spread OFDM system with polarization division multiplexing (PDM) that employs a tone-by-tone linear minimum mean square error (MMSE) equalizer. We show that such a system offers a much lower peak-to-average power ratio (PAPR) performance as well as better bit error rate (BER) performance compared with the optical OFDM system that employs amplitude clipping.

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Dong, Siyuan, Radhika Shiradkar, Pariksheet Nanda, and Guoan Zheng. "Spectral multiplexing and coherent-state decomposition in Fourier ptychographic imaging." Biomedical Optics Express 5, no. 6 (May 9, 2014): 1757. http://dx.doi.org/10.1364/boe.5.001757.

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Boutet, Sébastien, Lutz Foucar, Thomas R. M. Barends, Sabine Botha, R. Bruce Doak, Jason E. Koglin, Marc Messerschmidt, et al. "Characterization and use of the spent beam for serial operation of LCLS." Journal of Synchrotron Radiation 22, no. 3 (April 11, 2015): 634–43. http://dx.doi.org/10.1107/s1600577515004002.

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X-ray free-electron laser sources such as the Linac Coherent Light Source offer very exciting possibilities for unique research. However, beam time at such facilities is very limited and in high demand. This has led to significant efforts towards beam multiplexing of various forms. One such effort involves re-using the so-called spent beam that passes through the hole in an area detector after a weak interaction with a primary sample. This beam can be refocused into a secondary interaction region and used for a second, independent experiment operating in series. The beam profile of this refocused beam was characterized for a particular experimental geometry at the Coherent X-ray Imaging instrument at LCLS. A demonstration of this multiplexing capability was performed with two simultaneous serial femtosecond crystallography experiments, both yielding interpretable data of sufficient quality to produce electron density maps.

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Wipfler, Alexander, Tiago Buckup, and Marcus Motzkus. "Multiplexing single-beam coherent anti-stokes Raman spectroscopy with heterodyne detection." Applied Physics Letters 100, no. 7 (February 13, 2012): 071102. http://dx.doi.org/10.1063/1.3680209.

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Kadhim, Muthanna Ali, Ali Yousif Fattah, and Atheer Alaa Sabri. "Spectral efficiency and performance improvement of coherent optical transmission system." Indonesian Journal of Electrical Engineering and Computer Science 27, no. 1 (July 1, 2022): 290. http://dx.doi.org/10.11591/ijeecs.v27.i1.pp290-300.

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This paper presents an orthogonal frequency division multiplexing (OFDM) for a long-haul optical transmission system with high-rate transferability to alleviate dispersion effects. In addition, we suggest combining polarization division multiplexing (PDM) with coherent OFDM (CO-OFDM) to increase spectral efficiency (SE). Based on OptiSystem (2021) version 18.0" software package, a 100 Gbps single-channel PDM-CO-OFDM transmission system is investigated using different modulation formats; bipolar phase keying (BPSK), quadrature phase shift keying (QPSK), Eight-Phase-Shift Keying modulators (8-PSK), and quadrature amplitude modulation (16-QAM). A 60 km span of standard single-mode fiber (SSMF) cable is employed in this investigation. The system's performance and spectral efficiency have been evaluated by comparing against the different modulation schemes. The outcomes that were got show that the BPSK modulation scheme has the longest transmission distance and requires a lesser level of optical signal to noise ratio (OSNR) at the receiver side. Concerning spectral efficiency, 16-QAM outperforms the others. Farther, the impact of employing ultra-low loss and large effective area fiber in reducing loss and nonlinear effects in the optical channel for 16-QAM modulation formats is examined. The result found that the system with advanced fiber has superior performance than the SSMF. The bit error rate (BER) of 0.033 (20% concatenated forward error correction (FEC) threshold) is used as a baseline.

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Yu, Tian-You, Marko B. Orescanin, Christopher D. Curtis, Dusan S. Zrnić, and Douglas E. Forsyth. "Beam Multiplexing Using the Phased-Array Weather Radar." Journal of Atmospheric and Oceanic Technology 24, no. 4 (April 1, 2007): 616–26. http://dx.doi.org/10.1175/jtech2052.1.

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Abstract The recently installed S-band phased-array radar (PAR) at the National Weather Radar Testbed (NWRT) offers fast and flexible beam steering through electronic beam forming. This capability allows the implementation of a novel scanning strategy termed beam multiplexing (BMX), with the goal of providing fast updates of weather information with high statistical accuracy. For conventional weather radar the data acquisition time for a sector scan or a volume coverage pattern (VCP) can be reduced by increasing the antenna’s rotation rate to the extent that the pedestal allows. However, statistical errors of the spectral moment estimates will increase due to the fewer samples that are available for the estimation. BMX is developed to exploit the idea of collecting independent samples and maximizing the usage of radar resources. An improvement factor is introduced to quantify the BMX performance, which is defined by the reduction in data acquisition time using BMX when the same data accuracy obtained by a conventional scanning strategy is maintained. It is shown theoretically that a fast update without compromising data quality can be achieved using BMX at small spectrum widths and a high signal-to-noise ratio (SNR). Applications of BMX to weather observations are demonstrated using the PAR, and the results indicate that an average improvement factor of 2–4 can be obtained for SNR higher than 10 dB.

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MYARA, M., P. SIGNORET, J. P. TOURRENC, B. ORSAL, and J. JACQUET. "1/f NOISE IN DBR TUNABLE LASERS." Fluctuation and Noise Letters 06, no. 01 (March 2006): L35—L43. http://dx.doi.org/10.1142/s0219477506003124.

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Tunable Lasers are key-components for Wavelength Division Multiplexing optical communication applications at 1.55μm. In this paper, we compare a rate equation model with measurements performed in order to study the Bragg section contribution in the 1/f-optical-beam noise power spectral density.

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Steinbrück, A., J. W. Choi, S. Fasold, C. Menzel, A. Sergeyev, T. Pertsch, and R. Grange. "Plasmonic heating with near infrared resonance nanodot arrays for multiplexing optofluidic applications." RSC Adv. 4, no. 106 (2014): 61898–906. http://dx.doi.org/10.1039/c4ra13312a.

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In this work, we show local laser-induced heating in fluids with gold nanodot arrays prepared by electron-beam lithography that cover resonances in the near infrared spectral range from 750 nm to 880 nm.

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Et. al., Keshav N,. "Millimetre Wave Communication with Spatial Division Multiplexing for 5G systems." Turkish Journal of Computer and Mathematics Education (TURCOMAT) 12, no. 7 (June 5, 2021): 2609–16. http://dx.doi.org/10.17762/turcomat.v12i7.3632.

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The point of this paper is to combination of spatial division multiplexing (SDMA) along with NOMA improves the performance of the system. This paper is done with multibeam forming for performance enhancement, Analog beam forming is done along with the digital beam forming to increase the spectral efficiency and also the user count increases so that we could able to achieve high throughput. In this paper the design problems of mm wave NOMA due to beamforming is focused so that achievable data rate is high. This is due to the number of RF chains. We analyses the demanding joint plan of the intertwined power distribution and client matching for mm Wave-SDMA. Some problems are talked about and a few arrangements are proposed in detail in mm Wave communications.

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Joseph, Nisha Mary, and Puttamadappa C. "Highly Accurate Technique for CO-OFDM Channel Estimation Technique Using Extreme Learning Machine (ELM)." WSEAS TRANSACTIONS ON ELECTRONICS 14 (March 9, 2023): 7–23. http://dx.doi.org/10.37394/232017.2023.14.2.

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In wireless systems, channel estimation is considered a problematic technology, due to the fact of the difference in time between wireless channels and the noise effect. Orthogonal frequency-division multiplexing (OFDM) is a promising candidate for future optical communications and has received wide concern. The article proposed a Coherent Optical (CO) orthogonal frequency division multiplexing (OFDM) scheme, which gives a scalable and flexible solution for increasing the transmission rate, being extremely robust to chromatic dispersion as well as polarization mode dispersion. Nevertheless, both coherent detection and OFDM are prone to phase noise due to the phase mismatch between the laser oscillators at the transmitter and receiver sides and the relatively long OFDM symbol duration compared to that of single carrier communications. An Extreme Learning Machine (ELM) with Pilot Assisted Equalization (PEM) is proposed for compensation of impairments caused by fibre nonlinearity in coherent optical communication systems. Channel estimation using ELM and the value of distortion is sent to the OSTBC receiving end based on the distortion information the data is decoded and pilot data is removed. FFT is applied to the data and QPSK demodulation is done in the data to get its original form. In addition, the article utilized a free-space optical communication system of multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) with a modified receiver structure. Simulation reveals that the proposed model exhibits significant BER (0.0112) performance and provides better spectral efficiency as compared with conventional systems and less computational complexity. This suggested that the proposed method shows better performance by using the CO-OFDM-FSO-MIMO-ELM-based channel estimation technique for high-speed data communication networks in real-time scenarios respectively.

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Zhu, Diling, Yiping Feng, Stanislav Stoupin, Sergey A. Terentyev, Henrik T. Lemke, David M. Fritz, Matthieu Chollet, et al. "Performance of a beam-multiplexing diamond crystal monochromator at the Linac Coherent Light Source." Review of Scientific Instruments 85, no. 6 (June 2014): 063106. http://dx.doi.org/10.1063/1.4880724.

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Yousif, Raghad Zuhair, Yazen Saifuldeen Almashhadani, and Basud Mohammed Rasool. "Performance Evaluation of Dispersion Compensation Fiber-based Coherent Optical OFDM-WDM for Long Haul RoF." Al-Kitab Journal for Pure Sciences 6, no. 2 (November 3, 2022): 1–13. http://dx.doi.org/10.32441/kjps.06.02.p1.

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Demanding extra Bandwidth and high data rates has been meet by the integration both of wired and wireless communication systems. For that the Radio over Fiber (RoF) technology has gained a traction. In this article a Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) is proposed as the main wired system for transmitting data at high rates suffers from the polarization mode dispersion and chromatic dispersion of the optical channel which mitigates the data rates. Thus, to combat these limitations a Desperation Compensation Fiber (DCF) which adds negative attenuation to the optical signals transmitted in optical fiber is suggested. Moreover, the addition of Wavelength- Division- Multiplexing (WDM) to the system of transmission provides better bandwidth saving, high data rates, and better spectral efficiency, and power utilization. The efficiency of high data rate CO-OFDM integrated with RoF for long haul transmission between 100km and 450km with data rates up to 10 Gbps have been investigated in this article with SMF-DCF with 16 DPSK and 16-QAM modulations schemes respectively. The simulation results showed that the proposed system can achieve a high data rate up to 55 Gbps but when integrated with WDM, with a fiber link length can be increased to up to 6600 kilometers, with highest data rate up to 1.65 Tbps.

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Monga, Himanshu, and R. S. Kaler. "Implementation and performance analysis of a new family of coherent 3-dimensional space/phase/frequency spread optical code for OCDMA networks." JOURNAL OF SOCIAL SCIENCE RESEARCH 3, no. 2 (March 28, 2014): 232–39. http://dx.doi.org/10.24297/jssr.v3i2.3106.

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In his paper, we have demonstrated the feasibility of a spectrally efficient wavelength-division-multiplexing-compatible optical code-division multiple-access system using 16 phase-locked laser lines within a 40-GHz tunable window as frequency and an ultrahigh frequency resolution spectral phase encoderâ€“decoder. Coding and decoding slots using binary [0,Ï€ ] phase chips were demonstrated for four users at 5 Gb/s, and a single coded signal was separated from four copropagating signals, with bit-error rate <10 -9.

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Giacoumidis, Elias, Yi Lin, Jinlong Wei, Ivan Aldaya, Athanasios Tsokanos, and Liam Barry. "Harnessing machine learning for fiber-induced nonlinearity mitigation in long-haul coherent optical OFDM." Future Internet 11, no. 1 (December 20, 2018): 2. http://dx.doi.org/10.3390/fi11010002.

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Coherent optical orthogonal frequency division multiplexing (CO-OFDM) has attracted a lot of interest in optical fiber communications due to its simplified digital signal processing (DSP) units, high spectral-efficiency, flexibility, and tolerance to linear impairments. However, CO-OFDM’s high peak-to-average power ratio imposes high vulnerability to fiber-induced non-linearities. DSP-based machine learning has been considered as a promising approach for fiber non-linearity compensation without sacrificing computational complexity. In this paper, we review the existing machine learning approaches for CO-OFDM in a common framework and review the progress in this area with a focus on practical aspects and comparison with benchmark DSP solutions.

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Shi, Chengzhi, Marc Dubois, Yuan Wang, and Xiang Zhang. "High-speed acoustic communication by multiplexing orbital angular momentum." Proceedings of the National Academy of Sciences 114, no. 28 (June 26, 2017): 7250–53. http://dx.doi.org/10.1073/pnas.1704450114.

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Long-range acoustic communication is crucial to underwater applications such as collection of scientific data from benthic stations, ocean geology, and remote control of off-shore industrial activities. However, the transmission rate of acoustic communication is always limited by the narrow-frequency bandwidth of the acoustic waves because of the large attenuation for high-frequency sound in water. Here, we demonstrate a high-throughput communication approach using the orbital angular momentum (OAM) of acoustic vortex beams with one order enhancement of the data transmission rate at a single frequency. The topological charges of OAM provide intrinsically orthogonal channels, offering a unique ability to multiplex data transmission within a single acoustic beam generated by a transducer array, drastically increasing the information channels and capacity of acoustic communication. A high spectral efficiency of 8.0 ± 0.4 (bit/s)/Hz in acoustic communication has been achieved using topological charges between −4 and +4 without applying other communication modulation techniques. Such OAM is a completely independent degree of freedom which can be readily integrated with other state-of-the-art communication modulation techniques like quadrature amplitude modulation (QAM) and phase-shift keying (PSK). Information multiplexing through OAM opens a dimension for acoustic communication, providing a data transmission rate that is critical for underwater applications.

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Zhang, Jun, Hangyu Peng, Jingbo Wang, Jiye Zhang, Li Qin, Yongqing Ning, and Lijun Wang. "Dense spectral beam combining of quantum cascade lasers by multiplexing a pair of blazed gratings." Optics Express 30, no. 2 (January 3, 2022): 966. http://dx.doi.org/10.1364/oe.446124.

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Han, Jinliang, Jun Zhang, Xiaonan Shan, Yawei Zhang, Hangyu Peng, Li Qin, and Lijun Wang. "High-power narrow-linewidth diode laser based on external cavity feedback technology for Yb: YAG pumping." Japanese Journal of Applied Physics 61, no. 12 (November 24, 2022): 120903. http://dx.doi.org/10.35848/1347-4065/aca247.

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Abstract An external cavity feedback structure based on volume Bragg grating is introduced to realize the spectral stabilization and linewidth narrowing of a diode laser with a central wavelength of 968.668 nm and a spectral linewidth of 0.405 nm. A diode laser source producing 1.443 kW power from an output fiber with a core diameter of 1000 μm is achieved by using a spatial beam, combining, and polarization multiplexing technologies. The external cavity feedback and fiber coupling efficiencies exceed 93% and 90%, respectively. Such a high-power narrow-linewidth diode laser can be applied in Yb: YAG pumping efficiently and stably.

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Du, Jinzhi, Weijia Cui, Bin Ba, Chunxiao Jian, and Liye Zhang. "Joint Estimation for Time Delay and Direction of Arrival in Reconfigurable Intelligent Surface with OFDM." Sensors 22, no. 18 (September 19, 2022): 7083. http://dx.doi.org/10.3390/s22187083.

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Recently, the joint estimation for time delay (TD) and direction of arrival (DOA) has suffered from the high complexity of processing multi-dimensional signal models and the ineffectiveness of correlated/coherent signals. In order to improve this situation, a joint estimation method using orthogonal frequency division multiplexing (OFDM) and a uniform planar array composed of reconfigurable intelligent surface (RIS) is proposed. First, the time-domain coding function of the RIS is combined with the multi-carrier characteristic of the OFDM signal to construct the coded channel frequency response in tensor form. Then, the coded channel frequency response covariance matrix is decomposed by CANDECOMP/PARAFAC (CPD) to separate the signal subspaces of TD and DOA. Finally, we perform a one-dimensional (1D) spectral search for TD values and a two-dimensional (2D) spectral search for DOA values. Compared to previous efforts, this algorithm not only enhances the adaptability of coherent signals, but also greatly decreases the complexity. Simulation results indicate the robustness and effectiveness for the proposed algorithm in independent, coherent, and mixed multipath environments and low signal-to-noise ratio (SNR) conditions.

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Ahmed, Bashar M., and Raad S. Fyath. "Effect of Fiber Nonlinearity on the Performance of WDM Dual-Polarization Coherent Optical OFDM Systems." INTERNATIONAL JOURNAL OF COMPUTERS & TECHNOLOGY 13, no. 9 (September 30, 2014): 4943–64. http://dx.doi.org/10.24297/ijct.v13i9.2397.

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In recent years, there is increasing interest in using dual-polarization (DP) technique to enable future systems with at least 100 Gb/s rate per channel to operate over existing optical networks. The performance of these advanced systems can be enhanced further by using coherent optical orthogonal multiplexing (CO-OFDM) technique which offers high spectral efficiency and outstanding tolerance of fiber dispersion. This paper addresses the effect of fiber nonlinear optics on the performance of dual-polarization wavelength-division multiplexing (WDM) CO-OFDM systems operating with 100 Gb/s per channel. Different modulation formats, namely BPSK, QPSK and 16-QAM, are used. First, the performance of a single-channel system is investigated in the absence and presence of fiber nonlinearity. The results are compared with a conventional (single-polarization) system to identify the key role played by the DP technique. The investigation is then extended to WDM systems incorporating DP-OFDM technique. The results reveal that the effect of fiber nonlinearity can be reduced by using optimum transmitter laser power Popt. Further, the value of Popt is a function of transmission distance, number of multiplexed channels, and modulation formats. Popt of -11, -12, and -5 dBm is needed for a ten-channel DP system operating with BPSK, QPSK, and 16-QAM formats, respectively. Simulation results presented in this work are obtained using Opti System (version 11.1) which is a commercial software package

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Stoupin, S., S. A. Terentyev, V. D. Blank, Yu V. Shvyd'ko, K. Goetze, L. Assoufid, S. N. Polyakov, et al. "All-diamond optical assemblies for a beam-multiplexing X-ray monochromator at the Linac Coherent Light Source." Journal of Applied Crystallography 47, no. 4 (August 1, 2014): 1329–36. http://dx.doi.org/10.1107/s1600576714013028.

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A double-crystal diamond (111) monochromator recently implemented at the Linac Coherent Light Source (LCLS) enables splitting of the primary X-ray beam into a pink (transmitted) and a monochromatic (reflected) branch. The first monochromator crystal, with a thickness of ∼100 µm, provides sufficient X-ray transmittance to enable simultaneous operation of two beamlines. This article reports the design, fabrication and X-ray characterization of the first and second (300 µm-thick) crystals utilized in the monochromator and the optical assemblies holding these crystals. Each crystal plate has a region of about 5 × 2 mm with low defect concentration, sufficient for use in X-ray optics at the LCLS. The optical assemblies holding the crystals were designed to provide mounting on a rigid substrate and to minimize mounting-induced crystal strain. The induced strain was evaluated using double-crystal X-ray topography and was found to be small over the 5 × 2 mm working regions of the crystals.

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Anand, Vijayakumar, Tomas Katkus, and Saulius Juodkazis. "Randomly Multiplexed Diffractive Lens and Axicon for Spatial and Spectral Imaging." Micromachines 11, no. 4 (April 21, 2020): 437. http://dx.doi.org/10.3390/mi11040437.

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A new hybrid diffractive optical element (HDOE) was designed by randomly multiplexing an axicon and a Fresnel zone lens. The HDOE generates two mutually coherent waves, namely a conical wave and a spherical wave, for every on-axis point object in the object space. The resulting self-interference intensity distribution is recorded as the point spread function. A library of point spread functions are recorded in terms of the different locations and wavelengths of the on-axis point objects in the object space. A complicated object illuminated by a spatially incoherent multi-wavelength source generated an intensity pattern that was the sum of the shifted and scaled point spread intensity distributions corresponding to every spatially incoherent point and wavelength in the complicated object. The four-dimensional image of the object was reconstructed using computer processing of the object intensity distribution and the point spread function library.

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Zhang, Zhen, Emma Snively, Valery Dolgashev, and Zhirong Huang. "Fast and flexible control of beam longitudinal phase space for high-repetition-rate x-ray free-electron lasers." Review of Scientific Instruments 94, no. 2 (February 1, 2023): 024706. http://dx.doi.org/10.1063/5.0135658.

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The wide-ranging requirements for the photon properties from multiple beamlines in superconducting based free-electron lasers (FELs) demand more challenging beam manipulation techniques. Shot-by-shot control of electron beam bunch length and peak current at high repetition rate up to megahertz is highly desired. In this paper, we present a comprehensive study of a method based on a 2-m-long normal conducting radio-frequency cavity to achieve fast and flexible control of beam compression and realize the full potential of the facility, including theoretical analysis, beam dynamics simulations, and conceptual cavity design for the Linac Coherent Light Source II and its high-energy upgrade. We illustrate the physical mechanism of the chirping cavity on the control of the final beam compression and propose methods to lower the requirements for the cavity parameters. The application of this method will allow tailored photon properties of individual beamlines to optimize their performance and drastically improve the multiplexing capabilities of a high-repetition rate FEL facility.

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Allen, B., D. Simmons, T. D. Drysdale, and J. Coon. "Performance analysis of an orbital angular momentum multiplexed amplify-and-forward radio relay chain with inter-modal crosstalk." Royal Society Open Science 6, no. 1 (January 2019): 181063. http://dx.doi.org/10.1098/rsos.181063.

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The end-to-end spectral efficiency and bit error rate (BER) of an amplify-and-forward (AF) radio relay chain employing orbital angular momentum (OAM) multiplexing is presented. The inherent divergence of a beam carrying OAM is overcome by means of a lens. Modelled and measured inter-modal crosstalk levels are incorporated into the analysis. The results show that an end-to-end spectral efficiency of up to 8 bits s −1 Hz −1 is achievable using four OAM modes to multiplex four parallel data streams over 20 hops, provided that the detrimental effects of inter-modal crosstalk are mitigated. The spectral efficiency is expected to scale further by using more OAM modes. The BER profile along the relay chain is analysed for each of the four OAM modes.

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Gorkunov, Maxim V., Artur R. Geivandov, Alena V. Mamonova, Ivan V. Simdyankin, Irina V. Kasyanova, Alexander A. Ezhov, and Vladimir V. Artemov. "Non-Mechanical Multiplexed Beam-Steering Elements Based on Double-Sided Liquid Crystal Metasurfaces." Photonics 9, no. 12 (December 15, 2022): 986. http://dx.doi.org/10.3390/photonics9120986.

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We propose, optimize, fabricate and test beam-steering elements based on double-sided liquid-crystal (LC) metasurfaces allowing for diffractive and spectral multiplexing, and thus covering three different beam deflection directions each. While straightforward parallel design requires one diffractive beam-steering element per a direction determined by Bragg’s law, double-sided LC-metasurfaces are remarkably flexible and allow optimization for three operation modes at different applied voltages: zero-voltage mode with dominant +1 order red light and +2 order blue light diffraction; intermediate mode at 1.4–1.6 V voltage with dominant +1 order blue light diffraction; and transparent mode at 5 V voltage. We comprehensively study three such elements with 6, 8 and 10 micrometer periods and verify their capability of deflecting blue and red light beams with 40–70% efficiencies in nine target directions with 10 ms characteristic switching times.

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Li, Xuan, Junce Shi, Long Wei, Keke Ding, Yuhang Ma, Zaijin Li, Lin Li, et al. "Research on Silicon-Substrate-Integrated Widely Tunable, Narrow Linewidth External Cavity Lasers." Crystals 12, no. 5 (May 8, 2022): 674. http://dx.doi.org/10.3390/cryst12050674.

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Widely tunable, narrow linewidth external cavity lasers on silicon substrates have many important applications, such as white-light interferometry, wavelength division multiplexing systems, coherent optical communication, and optical fiber sensor technology. Wide tuning range, high laser output power, single mode, stable spectral output, and high side-mode suppression ratio external cavity lasers have attracted much attention for their merits. In this paper, two main device-integrated structures for achieving widely tunable, narrow linewidth external cavity lasers on silicon substrates are reviewed and compared in detail, such as MRR-integrated structure and MRR-and-MZI-integrated structure of external cavity semiconductor lasers. Then, the chip-integrated structures are briefly introduced from the integration mode, such as monolithic integrated, heterogeneous integrated, and hybrid integrated. Results show that the silicon-substrate-integrated external cavity lasers are a potential way to realize a wide tuning range, high power, single mode, stable spectral output, and high side-mode suppression ratio laser output.

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Liao, Chien-Sheng, Pu Wang, Ping Wang, Junjie Li, Hyeon Jeong Lee, Gregory Eakins, and Ji-Xin Cheng. "Spectrometer-free vibrational imaging by retrieving stimulated Raman signal from highly scattered photons." Science Advances 1, no. 9 (October 2015): e1500738. http://dx.doi.org/10.1126/sciadv.1500738.

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In vivo vibrational spectroscopic imaging is inhibited by relatively slow spectral acquisition on the second scale and low photon collection efficiency for a highly scattering system. Recently developed multiplex coherent anti-Stokes Raman scattering and stimulated Raman scattering techniques have improved the spectral acquisition time down to microsecond scale. These methods using a spectrometer setting are not suitable for turbid systems in which nearly all photons are scattered. We demonstrate vibrational imaging by spatial frequency multiplexing of incident photons and single photodiode detection of a stimulated Raman spectrum within 60 μs. Compared to the spectrometer setting, our method improved the photon collection efficiency by two orders of magnitude for highly scattering specimens. We demonstrated in vivo imaging of vitamin E distribution on mouse skin and in situ imaging of human breast cancerous tissues. The reported work opens new opportunities for spectroscopic imaging in a surgical room and for development of deep-tissue Raman spectroscopy toward molecular level diagnosis.

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Stepanov, Ivan V., Denis M. Fatkhiev, Vladimir S. Lyubopytov, Ruslan V. Kutluyarov, Elizaveta P. Grakhova, Niels Neumann, Svetlana N. Khonina, and Albert K. Sultanov. "Wavelength-Tunable Vortex Beam Emitter Based on Silicon Micro-Ring with PN Depletion Diode." Sensors 22, no. 3 (January 25, 2022): 929. http://dx.doi.org/10.3390/s22030929.

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Herein we propose a design of a wavelength-tunable integrated vortex beam emitter based on the silicon-on-insulator platform. The emitter is implemented using a PN-depletion diode inside a microring resonator with the emitting hole grating that was used to produce a vortex beam. The resonance wavelengths can be shifted due to the refractive index change associated with the free plasma dispersion effect. Obtained numerical modeling results confirm the efficiency of the proposed approach, providing a resonance wavelength shift while maintaining the required topological charge of the emitted vortex beam. It is known that optical vortices got a lot of attention due to extensive telecommunication and biochemical applications, but also, they have revealed some beneficial use cases in sensors. Flexibility in spectral tuning demonstrated by the proposed device can significantly improve the accuracy of sensors based on fiber Bragg gratings. Moreover, we demonstrate that the proposed device can provide a displacement of the resonance by the value of the free spectral range of the ring resonator, which means the possibility to implement an ultra-fast orbital angular momentum (de)multiplexing or modulation.

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Hu, Hao, and Leif K. Oxenløwe. "Chip-based optical frequency combs for high-capacity optical communications." Nanophotonics 10, no. 5 (February 3, 2021): 1367–85. http://dx.doi.org/10.1515/nanoph-2020-0561.

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AbstractCurrent fibre optic communication systems owe their high-capacity abilities to the wavelength-division multiplexing (WDM) technique, which combines data channels running on different wavelengths, and most often requires many individual lasers. Optical frequency combs, with equally spaced coherent comb lines derived from a single source, have recently emerged as a potential substitute for parallel lasers in WDM systems. Benefits include the stable spacing and broadband phase coherence of the comb lines, enabling improved spectral efficiency of transmission systems, as well as potential energy savings in the WDM transmitters. In this paper, we discuss the requirements to a frequency comb for use in a high-capacity optical communication system in terms of optical linewidth, per comb line power and optical carrier-to-noise ratio, and look at the scaling of a comb source for ultra-high capacity systems. Then, we review the latest advances of various chip-based optical frequency comb generation schemes and their applications in optical communications, including mode-locked laser combs, spectral broadening of frequency combs, microresonator-based Kerr frequency combs and electro-optic frequency combs.

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Li, Xiangzhi, Weijia Cui, Haiyun Xu, Bin Ba, and Yankui Zhang. "A Novel Method for DOA and Time Delay Joint Estimation in Multipath OFDM Environment." International Journal of Antennas and Propagation 2020 (January 30, 2020): 1–11. http://dx.doi.org/10.1155/2020/3952175.

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Joint time delay and direction of arrival estimation based on uniform linear arrays in Orthogonal Frequency Division Multiplexing (OFDM) systems has to face the problems posed by coherent multipath environments and high computational complexity. In this paper, a novel fast method is proposed to achieve a joint direction-of-arrival (DOA) and time-dealy (TD) estimation of multipath OFDM signals by fully using space-frequency characteristics. Firstly, we construct an extended virtual array by combining the array structure and frequency-domain information. Then, we calculate the extended channel frequency response matrix and adopt smoothing processing to eliminate the multipath effect. Next, we get the result of DOA estimation by using a closed-form solution, which costs little complexity and can achieve fast estimation. Finally, we conduct a one-dimensional spectral search using the obtained DOA values to estimate time delays. Simulation results show that our proposed methods have excellent performance even under low SNR conditions in different multipath environments. Furthermore, methods proposed in this paper have much less computational complexity and better estimation performance compared with the multidimensional spectral peak search methods.

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Liu, Ning, Xuewen Wang, Jinpeng Yuan, Liantuan Xiao, Suotang Jia, and Lirong Wang. "Manipulation of the orbital angular momentum via four-wave mixing in Rb vapor." Laser Physics Letters 20, no. 3 (January 31, 2023): 035204. http://dx.doi.org/10.1088/1612-202x/acb43d.

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Abstract The manipulation of the orbital angular momentum (OAM) contributes to understand the OAM multiplexing, is significant in free-space optical communication and information processing. We theoretically simulate and experimentally demonstrate the regularity of the OAM transfer, including the angular and radial modes, of Laguerre–Gaussian beam via four-wave mixing process in 85Rb vapor. The 420 nm coherent blue light output field inherits the phase characteristic of 780 nm and 776 nm beams with different OAM modes. The output field OAM modes show the transfer as a typical arithmetic operation of the input field OAM modes with equal-handed angular indice l, while, the conversion between angular and radial modes occurs with the opposite angular indice l. Such rules of the OAM transfer and manipulation have implications on the research of high-capacity information transfer and quantum communication.

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Zang, Zihan, Zhi Li, Yi Luo, Yanjun Han, Hongtao Li, Xuanyi Liu, and H. Y. Fu. "Ultrafast parallel single-pixel LiDAR with all-optical spectro-temporal encoding." APL Photonics 7, no. 4 (April 1, 2022): 046102. http://dx.doi.org/10.1063/5.0071885.

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Light detection and ranging (LiDAR) with scanning beam has been widely used in autonomous driving and large-scale manufacturing, where the fast-changing scene is of great interest. However, the acquisition rate of current LiDAR is limited by beam steering speed and the round-trip delay, hindering the development of video-rate LiDAR. Here, we uniquely combine all-optical encoders with wavelength-division multiplexing devices to implement spectro-temporal encoding on the illumination light. Parallel detection and fast spectral scanning can be achieved with only one laser and one single photodetector. Our result shows the fastest single-pixel LiDAR to date, and the detection speed can be multiplied with scalability. We demonstrate 3.56-fold improvement of speed for a maximum of 75 m detection range compared with a serial LiDAR. A record acquisition rate of 21.38 MHz for a maximum of 25 m detection range is obtained. This approach has the potential to break the limitation on current ultrafast single-pixel LiDAR and opens a new paradigm for ultrafast-frame-rate imaging systems.

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Bernal, M.-P., G. W. Burr, H. Coufal, R. K. Grygier, J. A. Hoffnagle, C. M. Jefferson, R. M. Macfarlane, R. M. Shelby, G. T. Sincerbox, and G. Wittmann. "Holographic-Data-Storage Materials." MRS Bulletin 21, no. 9 (September 1996): 51–60. http://dx.doi.org/10.1557/s088376940003637x.

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In holographic data storage, a photo-sensitive medium is exposed to the interference pattern that is generated when an object beam, with an input data page encoded in the spatial profile of the beam, is intersected by a second, coherent laser beam. The photosensitive medium replicates these interference fringes as a change in optical absorption, refractive index, or thickness. Data are retrieved from the medium by exposing it to light from just one of the beams, which is then diffracted from the stored fringe pattern to reconstruct the other beam, including all the information that had been in the input data page. For a material of sufficient thickness, a large number of interference patterns, each identified by a different grating vector, can be stored or “multiplexed” in the same volume element, with negligible crosstalk between the individual interference patterns. Multiplexing of a large number of pages in the same volume element of the recording medium can be accomplished in several ways—for example by varying the angle between object and reference beam or the wavelength of both beams. Given no other limiting factors, the number of holograms that can be multiplexed in one volume element is directly proportional to the product of the thickness of the medium and its refractive index—that is, materials with optical thicknesses of the order of several millimeters are desirable.By its very nature, the holographic-storage mechanism distributes the stored information redundantly throughout the recording volume.

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Verma, Deepika, Rahul Bosu, and Shanthi Prince. "Performance Investigation of WDM based hybrid RF-FSO Link with Unmanned Aerial Vehicles based Optical Relays." Journal of Physics: Conference Series 2335, no. 1 (September 1, 2022): 012015. http://dx.doi.org/10.1088/1742-6596/2335/1/012015.

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Abstract The paper presents the design of wavelength division multiplexing (WDM) based hybrid radio frequency-free space optical communication (RF-FSOC) system for high data rate transmission in the scenarios where the direct line-of-sight (LOS) view between the end-to-end communication nodes is unavailable. As such, a simulation model of unmanned aerial vehicle (UAV) based parallel relaying mechanism incorporating amplify and reflection (AR) technique is presented for establishing a point-to-point FSOC link between UAV and ground base station. Furthermore, the power spectral characteristics of the WDM optical signals modulated by 8-PAM signalling scheme at the transmitter node of the proposed model is simulated and analysed in the Optisystem 16. The simulation results illustrate that the overall link length of the proposed UAV based hybrid system with 1 Gbps data rate and transmitted beam divergence angle of 10 mrad extends upto a maximum range of 200 m in light fog condition.

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Rahmani, Mohamed, Abdelhamid Cherifi, Abdullah S. Karar, Ghoutia Naima Sabri, and Boubakar S. Bouazza. "Contribution of New Three-Dimensional Code Based on the VWZCC Code Extension in Eliminating Multiple Access Interference in Optical CDMA Networks." Photonics 9, no. 5 (May 3, 2022): 310. http://dx.doi.org/10.3390/photonics9050310.

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In order to solve the problem of one-dimensional code length, two-dimensional code spatial length, phase induced intensity noise PIIN effect, improved system capacity, and increased the number of simultaneous users, a new three-dimensional spectral/time/spatial variable weight zero cross correlation code for non-coherent spectral amplitude coding-optical code division multiple access (3D-VWZCC-SAC-OCDMA) is proposed in this paper. Its construction is based on a one-dimensional (1D) spectral sequence and two-dimensional (2D) temporal/spatial sequences, which are characterized by the property of zero cross correlation ZCC. The simulation results demonstrate that our code proves high immunity against PIIN noise and shot noise, it increases multiplexing ability when the passage is from (1D) and (2D) to (3D) up to 5.112 and 2.248 times, and it saves −7.04 dBm and −5.9 dBm of the receiver power due to simple detection at the receiver; furthermore, the 3D-VWZCC system capacity has outperformed the 3D-PD, 3D-PD/MD and 3D-DCS/MD codes, which reach 3686, 2908, and 3234 times, respectively. Moreover, our code offers better performance, in terms of data rates, with up to 2 Gbps compared to previous codes, which makes the system meet the requirements of optical communication networks. Further, 3D-VWZCC is also simulated in Optisystem software, where our code offers a transmission quality Q reaching 11.56 with a bit error rate BER of 1.99 × 10−31 despite a high number of users.

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Zhao, Peiqian, V. Coudé Du Foresto, J. M. Mariotti, P. Lena, and Bifang Zhou. "Stellar Diameter Measurements with Fiber Optic Double Fourier Interferometry—Experimental Study." Symposium - International Astronomical Union 166 (1995): 362. http://dx.doi.org/10.1017/s0074180900228453.

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Long baseline optical interferometry has been successfully employed to measure the diameters of stars. In this technique, bandwidth smearing can affect the measurement accuracy. These bandwidth smearing effects can be, to some extent, eliminated by dividing the whole observing spectral band into sub-bands and calculating the star's diameter based on the visibilities and spatial frequencies at the corresponding sub-bands. In the visible range, dividing the whole spectral band can be implemented by introducing a spectrograph, while in the IR domain, this operation can be performed efficiently with the technique of double Fourier interferometry (DFI) without losing the advantage of multiplexing. In particular, the use of IR single-mode fiber optics for DFI will make the interferometer extremely compact, light, insensitive to surrounding conditions, etc. We established an IR single-mode fiber optic double Fourier interferometer in the laboratory, in which the optical path difference modulations are generated by stretching fiber arms and the beam combination is carried out with a fiber optic directional coupler. In this paper, we report on experiments and experimental results from measurements of the diameter of an artificial star with the technique of fiber optic DFI.

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Nieborek, Mateusz, Katarzyna Rutkowska, Tomasz Ryszard Woliński, Bartosz Bartosewicz, Bartłomiej Jankiewicz, Dariusz Szmigiel, and Anna Kozanecka-Szmigiel. "Tunable Polarization Gratings Based on Nematic Liquid Crystal Mixtures Photoaligned with Azo Polymer-Coated Substrates." Crystals 10, no. 9 (August 31, 2020): 768. http://dx.doi.org/10.3390/cryst10090768.

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Liquid crystal polarization gratings are of great interest for optical communications as elements performing beam steering, splitting, multiplexing or beam combining. Material birefringence, cell thickness or a period of the liquid crystal director pattern influence, among other features, spectroscopic and electro-optical characteristics of fabricated devices, determining thus their functionality and applicability. Here, we report on liquid crystal polarization gratings that allow for complete maximization of the first-order diffraction efficiency (resulting in total elimination of the zeroth-order diffraction) for any wavelength of an incident beam from green to the near-infrared spectral region by applying a low electric voltage. The gratings with periods as small as 10 μm were obtained by holographic exposure of the cell substrates coated with light-sensitive azo polymer alignment layers, and then filled with three different liquid crystal mixtures. The influence of gold nanoparticle dopants in the liquid crystalline mixtures on spectroscopic and electro-optical properties of the devices is presented. Moreover, on the basis of the measured transmittance spectra of the fabricated gratings, the unknown birefringence of liquid crystal mixtures as well as their effective birefringence due to molecular reorientation in the electric field in the visible and near IR region were determined.

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Li, Xuan, Junce Shi, Long Wei, Keke Ding, Yuhang Ma, Kangxun Sun, Zaijin Li, et al. "Research Progress of Wide Tunable Bragg Grating External Cavity Semiconductor Lasers." Materials 15, no. 22 (November 21, 2022): 8256. http://dx.doi.org/10.3390/ma15228256.

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In this paper, we review the progress of wide tunable Bragg grating external cavity semiconductor lasers (BG-ECSLs). We concentrate on BG-ECSLs based on the wide tunable range for multicomponent detection. Wide tunable BG-ECSLs have many important applications, such as wavelength-division multiplexing (WDM) systems, coherent optical communications, gas detection and atom cooling. Wide tunability, narrow linewidth and a high side-mode suppression ratio BG-ECSLs have attracted much attention for their merits. In this paper, three main structures for achieving widely tunable, narrow linewidth, high side-mode suppression ratio BG-ECSLs are reviewed and compared in detail, such as the volume Bragg grating (VBG) structure, fiber Bragg grating (FBG) structure and waveguide Bragg grating (WBG) structure of ECSLs. The advantages and disadvantages of different structures of BG-ECSLs are analyzed. The results show that WBG-ECSLs are a potential way to realize the integration, small size, wide tuning range, stable spectral output and high side-mode suppression ratio laser output. Therefore, the use of WBG as optical feedback elements is still the mainstream direction of BG-ECSLs, and BG-ECSLs offer a further new option for multicomponent detection and multi-atoms cooling.

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Jabar, Hashem A., and Rashid A. Fayadh. "Implement Algorithm to Reduce Effect of Snowy Weather in North of Iraq on Fso Signal." Science Journal of University of Zakho 6, no. 3 (September 30, 2018): 130–34. http://dx.doi.org/10.25271/sjuoz.2018.6.3.520.

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Free space optic (FSO) is now a well-established access technology that commonly start using in wireless data transmission because of its large advantage like cost effective and Line-Of-Sight (LOS) permission which lead this technology to be more secure and get own to everyone. While radio frequency (RF) travels using optical fiber through weather atmospheric, large phenomena like (Rain-fog/haze-snow and temperature) works to block laser beam from reaching its receiver. Optical code division multiple access (OCDMA) is a hot topic due to its large advantage such as permitting large number of user to transmit large amount of data using single optical laser beam , but multiple users share single laser beam lead to increase multiple access interference (MAI) which primary deteriorates the performance of OCDMA. Sub-Carrier Multiplexing (SCM) is used in the system to multiplex multiple data stream on single laser beam. Spectral Amplitude Coding (SAC) technique used to enhance FSO signal by allocate own spectrum to each user, this technique generate code called Multi-Diagonal (MD) code that allow zero interaction between user data. This paper focused on the effect of snowy weather in north of Iraq on the FSO signal by using (SCM-SAC-OCDMA) based on multi-diagonal code and determined the distance between the transverse with approach bit error rate (BER) in the receiver side. Based on the system result data can travel through [0.4 - 4] Km as transmission distance under different snow rate with BER between [].

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Makarov, S. B., S. V. Zavjalov, D. C. Nguyen, and A. S. Ovsyannikova. "Coherent Detection of Non-Orthogonal Spectrally Efficient Multicarrier Signals Using a Decision Feedback Algorithm." Journal of the Russian Universities. Radioelectronics 24, no. 5 (November 29, 2021): 22–35. http://dx.doi.org/10.32603/1993-8985-2021-24-5-22-35.

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Introduction. Spectrally efficient frequency division multiplexing (SEFDM) is a promising technology for improving spectral efficiency. Since SEFDM signals transmitted on subcarriers are not orthogonal, interchannel interference occurs due to the mutual influence of signals transmitted on adjacent subcarriers. Algorithms for receiving SEFDM signals can be distinguished into element-by-element coherent detection and maximum-likelihood sequence estimation (MLSE). The former method, although being simpler, is characterized by a low bit error rate performance. The latter method, although providing for a higher energy efficiency, is more complicated and does not allow high absolute message rates.Aim. To consider a trade-off solution to the problem of coherent detection of SEFDM signals under the condition of significant interchannel interference, namely, the use of an iterative algorithm of element-by-element processing with decision feedback at each subcarrier frequency.Materials and methods. Analytical expressions for the operation of a demodulator solver were derived. A simulation model for transmission of SEFDM signals was built in the MatLab environment, including element-by-element detection with decision feedback.Results. The simulation results confirmed the efficiency of the proposed algorithm. For error probabilities p =102…103, the energy gains reach values from 0.2 to 7.5 dB for different values of the non-orthogonal subcarrier spacing. At the same time, the efficiency of the detection algorithm with decision feedback turns out to be significantly lower than that when using the detection algorithm MLSE.Conclusion. The proposed detection algorithm can be used in future generations of mobile communications, which require high transmission rates. By reducing the computational complexity of the algorithm, it is possible to provide for a lower power consumption of mobile devices.

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Hussein Ali, Adnan, Hayder Jasim Alhamdane, and Begared Salih Hassen. "Design analysis and performance evaluation of the WDM integration with CO-OFDM system for radio over fiber System." Indonesian Journal of Electrical Engineering and Computer Science 15, no. 2 (August 1, 2019): 870. http://dx.doi.org/10.11591/ijeecs.v15.i2.pp870-878.

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<span>The optical communication and wireless networks can be integrated to increase the capacity and mobility with decrease the costs in the access networks. Optical communication is considered a Fiber optic communication that can be used for wired and wireless communication. The problems of Fiber optic communication have a solution represented by Radio over fiber (RoF) which can control many base stations (BSs) that connect to a central station (CS) with an optical fiber. The Coherent optical OFDM (CO-OFDM) have concerned a great interest due to the high spectral efficiency and strength to the fiber dispersion, also it can be considered as a promising candidate when used in long haul optical fiber transmission systems. The integration of the wavelength division multiplexing system (WDM) with (CO-OFDM) system for increasing the system performance as well as achieving high data rates. The simulation of WDM-ROF and (WDM-CO-OFDM) with an optisystem simulator to analyze the RF spectrum, spectrum signal visualizers, and constellation diagrams. The proposed of integration of WDM and RoF-OFDM system is to achieve 100 km fiber length using 4QAM sequence bit, and the received power with electrical and optical amplifications by using 10 Gbps data signal.</span>

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Ito, Shota, Hideki Kandori, and Victor A. Lorenz-Fonfria. "Potential Second-Harmonic Ghost Bands in Fourier Transform Infrared (FT-IR) Difference Spectroscopy of Proteins." Applied Spectroscopy 72, no. 6 (February 13, 2018): 956–63. http://dx.doi.org/10.1177/0003702818757521.

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Fourier transform infrared (FT-IR) difference absorption spectroscopy is a common method for studying the structural and dynamical aspects behind protein function. In particular, the 2800–1800 cm−1 spectral range has been used to obtain information about internal (deuterated) water molecules, as well as site-specific details about cysteine residues and chemically modified and artificial amino acids. Here, we report on the presence of ghost bands in cryogenic light-induced FT-IR difference spectra of the protein bacteriorhodopsin. The presence of these ghost bands can be particularly problematic in the 2800–1900 cm−1 region, showing intensities similar to O–D vibrations from water molecules. We demonstrate that they arise from second harmonics from genuine chromophore bands located in the 1400–850 cm−1 region, generated by double-modulation artifacts caused from reflections of the IR beam at the sample and at the cryostat windows back to the interferometer (inter-reflections). The second-harmonic ghost bands can be physically removed by placing an optical filter of suitable cutoff in the beam path, but at the cost of losing part of the multiplexing advantage of FT-IR spectroscopy. We explored alternatives to the use of optical filters. Tilting the cryostat windows was effective in reducing the intensity of the second harmonic artifacts but tilting the sample windows was not, presumably by their close proximity to the focal point of the IR beam. We also introduce a simple numerical post-processing approach that can partially, but not fully, correct for second-harmonic ghost bands in FT-IR difference spectra.

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Dinc, Niyazi Ulas, Joowon Lim, Eirini Kakkava, Christophe Moser, and Demetri Psaltis. "Computer generated optical volume elements by additive manufacturing." Nanophotonics 9, no. 13 (June 25, 2020): 4173–81. http://dx.doi.org/10.1515/nanoph-2020-0196.

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AbstractComputer generated optical volume elements have been investigated for information storage, spectral filtering, and imaging applications. Advancements in additive manufacturing (3D printing) allow the fabrication of multilayered diffractive volume elements in the micro-scale. For a micro-scale multilayer design, an optimization scheme is needed to calculate the layers. The conventional way is to optimize a stack of 2D phase distributions and implement them by translating the phase into thickness variation. Optimizing directly in 3D can improve field reconstruction accuracy. Here we propose an optimization method by inverting the intended use of Learning Tomography, which is a method to reconstruct 3D phase objects from experimental recordings of 2D projections of the 3D object. The forward model in the optimization is the beam propagation method (BPM). The iterative error reduction scheme and the multilayer structure of the BPM are similar to neural networks. Therefore, this method is referred to as Learning Tomography. Here, instead of imaging an object, we reconstruct the 3D structure that performs the desired task as defined by its input-output functionality. We present the optimization methodology, the comparison by simulation work and the experimental verification of the approach. We demonstrate an optical volume element that performs angular multiplexing of two plane waves to yield two linearly polarized fiber modes in a total volume of 128 μm by 128 μm by 170 μm.

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Macedo, Leandro, Edson A. Souza, Anselmo Frizera, Maria José Pontes, Carlos Marques, and Arnaldo Leal-Junior. "Static and Dynamic Multiparameter Assessment of Structural Elements Using Chirped Fiber Bragg Gratings." Sensors 23, no. 4 (February 7, 2023): 1860. http://dx.doi.org/10.3390/s23041860.

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This paper presents the development, analysis, and application of chirped fiber Bragg gratings (CFBGs) for dynamic and static measurements of beams of different materials in the single-cantilever configuration. In this case, the beams were numerically analyzed using the finite-element method (FEM) for the assessment of the natural frequencies and vibration modes of the beam for the dynamic analysis of the structural element. Furthermore, the static numerical analysis was performed using a load at the free end of the beam, where the maximum strain and its distribution along the beam were analyzed, especially in the region at which the FBG was positioned. The experimental evaluation of the proposed CFBG sensor was performed in static conditions for forces from 0 to 50 N (in 10 N steps) applied at the free end of the beam, whereas the dynamic evaluation was performed by means of positioning an unbalanced motor at the end of the beam, which was excited at 16 Hz, 65 Hz, 100 Hz, and 131 Hz. The results showed the feasibility of the proposed device for the simultaneous assessment of the force and strain distribution along the CFBG region using the wavelength shift and the full-width at half-maximum (FWHM), respectively. In these cases, the determination coefficients of the spectral features as a function of the force and strain distribution were higher than 0.99 in all analyzed cases, where a potential resolution of 0.25 N was obtained on the force assessment. In the dynamic tests, the frequency spectrum of the sensor responses indicated a frequency peak at the excited frequency in all analyzed cases. Therefore, the proposed sensor device is a suitable option to extend the performance of sensors for structural health assessment, since it is possible to simultaneously measure different parameters in dynamic and static conditions using only one sensor device, which, due to its multiplexing capabilities, can be integrated with additional optical fiber sensors for the complete shape reconstruction with millimeter-range spatial resolution.

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Ulanowski, Alexander, Benjamin Merkel, and Andreas Reiserer. "Spectral multiplexing of telecom emitters with stable transition frequency." Science Advances 8, no. 43 (October 28, 2022). http://dx.doi.org/10.1126/sciadv.abo4538.

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In a quantum network, coherent emitters can be entangled over large distances using photonic channels. In solid-state devices, the required efficient light-emitter interface can be implemented by confining the light in nanophotonic structures. However, fluctuating charges and magnetic moments at the nearby interface then lead to spectral instability of the emitters. Here, we avoid this limitation when enhancing the photon emission up to 70(12)-fold using a Fabry-Perot resonator with an embedded 19-micrometer-thin crystalline membrane, in which we observe around 100 individual erbium emitters. In long-term measurements, they exhibit an exceptional spectral stability of <0.2 megahertz that is limited by the coupling to surrounding nuclear spins. We further implement spectrally multiplexed coherent control and find an optical coherence time of 0.11(1) milliseconds, approaching the lifetime limit of 0.3 milliseconds for the strongest-coupled emitters. Our results constitute an important step toward frequency-multiplexed quantum-network nodes operating directly at a telecommunication wavelength.

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"PAPR Reduction in Coherent Optical OFDM System using Modified Sliding Norm Transformer." Iraqi Journal of Computer, Communication, Control and System Engineering, December 10, 2018, 33–42. http://dx.doi.org/10.33103/uot.ijccce.18.3.4.

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Orthogonal Frequency Division Multiplexing is one of the most important multiple carrier modulation format, which has many applications in wireless communication and optical communication. It is considered as an excellent method for fast optical communication inferable from its high spectral efficiency and its strength to path losses. Peak to average power ratio is regarded as one of the main problems that are experienced by the optical orthogonal frequency division multiplexing system, which directly affects the characteristics of the system. The current paper proposes an efficient technique to reduce Peak to Average Power Ratio by the modified Dursun’s method or the so called modified discrete sliding norm transformer in coherent optical orthogonal frequency division multiplexing system for the first time to the base of our knowledge consequently. The proposed technique does not need to send side information to the receiver; also, it does not degrade bandwidth. This algorithm lessens Peak to Average Power Ratio in the optical coherent Orthogonal Frequency Division Multiplexing system to about 4.15 dB at complementary cumulative distribution function (CCDF) probability of 10-3 and improves the system performance.

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Shri, Tanu, Anita Suman, and Parveen Kumar. "Performance investigation of free space optics link employing polarization division multiplexing and coherent detection-orthogonal frequency division multiplexing under different link parameters." Journal of Optical Communications, August 24, 2020. http://dx.doi.org/10.1515/joc-2020-0148.

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AbstractFree space optics (FSO) is a novel transmission technique capable of providing high-capacity links with large bandwidth and robustness against electromagnetic waves interference. In this work, we demonstrate the development of a 100 Gbps FSO link which employs the hybridization of polarization division multiplexing technique and coherent detection-orthogonal frequency division multiplexing technique. Further, we have investigated the system performance by varying different parameters like the input power, the size of the receiver antenna, wavelength of laser beam, the angle of beam divergence, and the additional losses. The proposed system has been modeled and analyzed over Optisystem test bed.

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Tawade, Laxman, Umesh Pinjarkar, Kavita Awade, Abida Bapu Aboobacker, Manisha Gosavi, and Yogeshwari Bhatlawande. "An Optical OFDM Modem with Adaptive Volterra Equalizer." Journal of Optical Communications 36, no. 1 (January 1, 2015). http://dx.doi.org/10.1515/joc-2014-0043.

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Abstract:

AbstractIt addresses orthogonal frequency division multiplexing (OFDM) transmission over optical links with high spectral efficiency, i.e. by using high-order quadrature amplitude modulation (QAM) schemes as a mapping method prior to the OFDM multicarrier representation. Here we address especially coherent optical OFDM modem in long distance which is affected by nonlinear distortion caused by fiber nonlinearity. Fiber nonlinearity is a majo performance-limiting factor in advanced optical communication systems. We proposed a nonlinear electrical equalization scheme based on the Volterra model. To compare with other popular linear compensation technique such as the least mean square (LMS), simulation results are presented to demonstrate the capability of a Volterra model based electrical equalizer used in a coherent optical orthogonal frequency division multiplexing system. It is shown that the Volterra model based equalizer can significantly reduce nonlinear distortion.

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Journal articles on the topic 'Coherent Beam Multiplexing. Spectral Multiplexing'

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