Дисертації з теми "Acousto-optic tunable filter"

Spectroscopy is a powerful tool for analysis in a widerange of scientific and industrial fields. Spectroscopic measurements obtaininformation about the interaction between matter and radiated energy.This information may be utilized for detection and classification of objectsand substances. There is a wealth of different methods and technologiesdeveloped for different applications, from space- and air-borne remotesensing to medical sample analysis.In this report we present a spectral imaging system consisting of a digitalcamera with an acousto-optical tunable filter (AOTF) as the spectralband selective element. An evaluation of the properties of the imager ispresented, and we investigate the feasibility of real-time spectral imagingvideo based on this system. A comparison with other spectral imagingtechnologies is made. Custom application software for camera control andimage acquisition is presented. A special optical layout that minimizes theoptical aberrations produced by the diffraction process in the AOTF is alsopresented.The system produce a stack of monochrome images at different wavelength bandsforming an "image cube" containing a combinationof spatial an spectral information. The system uses the visible part ofthe electromagnetic spectrum to collect spectral information at every pointin an image plane. Our results show that the camera have good lightsensitivity and a high signal-to-noise ratio, but that the image throughputand spatial resolution is not optimal for a high image rate. The AOTFis a highly flexible device with random access to wavelength bands andselectable band-pass shape. But the many configurable parameters of thesystem also complicates usage. Many parameters need to be calibrated,and we present some methods on this. A major challenge in an spectralimaging system is to get enough light through to the sensor, and we findthat there is high loss of light caused by the diffraction process in the filter.It will be shown that the system is not suitable for real-time spectral videoimaging because of the low frame rate. Suggestions for improvements aregiven.

Thesis (M.S. in Systems Technology (Space Operations) Naval Postgraduate School, September 1993.
Thesis advisor(s): Philip A. Durkee. "September 1993." Includes bibliographical references. Also available online.

L’imagerie hyperspectrale et de polarimétrie est un domaine en plein essor qui présente de nombreuses applications. Ce contexte pousse à améliorer sans cesse les filtres, notamment en termes de résolution spectrale. Il est utile par exemple d’augmenter le nombre de bandes spectrales et leurs finesses pour permettre une meilleure caractérisation des éléments de la scène observée. Dans ce contexte, nous présentons les possibilités offertes par l’interaction acousto-optique dans la paratellurite. Les filtres accordables acousto-optiques (AOTF) sont utilisés pour l’imagerie hyperspectrale et la polarimétrie pour leurs nombreux avantages : leur accord rapide et l’adressage arbitraires, leur robustesse, leur efficacité et leur bonne résolution spectrale. La biréfringence du matériau permet d’obtenir deux faisceaux diffractés ayant deux polarisations linéaires orthogonales en sortie, permettant une potentielle mesure polarimétrique. Dans le cadre de cette thèse portant sur les filtres acousto-optiques accordables à sélection de polarisation pour l’imagerie hyperspectrale, nous étudions plusieurs systèmes utilisant un filtre acousto-optique travaillant sur de larges bandes spectrales. Nous démontrons la capacité qu’offre un AOTF en tant qu’analyseur de polarisation linéaire à haut rendement de diffraction. Nous présentons une méthode d’apodisation du signal (avec amélioration de la résolution spectrale) en utilisant un AOTF mono-transducteur dans un système « double pass », permettant de garder plus de 90 % d’efficacité. Nous avons enfin réalisé les phases de conception, de caractérisation et de validation d’un AOTF original, multi-électrodes (5 électrodes) pour l’imagerie hyperspectrale et de polarimétrie permettant d’homogénéiser la bande passante (<10 nm) sur une large bande de fonctionnement [450 nm - 800 nm]
Hyperspectral and polarimetric imaging shows numerous applications and is rapidly developing. This context encourages continuous improvement of filters, particularly for the spectral resolution. For instance, it can be useful to increase the number of spectral bands and reduce the spectral bandwidth to improve the characterization of the observed elements in the scene. In this context, we present the different possibilities offered by the acoustooptic interaction in paratellurite. Acousto-Optic Tunable Filters (AOTF) are used for hyperspectral and polarimetric imaging because of their numerous advantages: their fast tuning and arbitrary addressing, robustness, efficiency, and good spectral resolution. The birefringence of the material makes it possible to obtain two diffracted beams with two orthogonal linear polarizations at the output, allowing a potential polarimetric measurement. As part of this thesis on acousto-optical tunable filters with polarization selection for hyperspectral imaging, we are studying several systems using an acousto-optical filter working on broad spectral bands. We demonstrate the ability of an AOTF as a high diffraction efficiency linear polarization analyzer. We present a method of apodisation of the signal (with improvement of the spectral resolution) by using a mono-transducer AOTF in a “double pass” system able to maintain more than 90% efficiency. We performed the design, characterization, and validation phases of an original, multi-electrode (5 electrodes) AOTF for hyperspectral and polarimetric imaging to homogenize the bandwidth (<10 nm) over a wide operating band [450 nm - 800 nm]

The design and application of high performance Acousto-Optic Tunable Filters (AOTFs) is the topic of this thesis. The most common material commercially used to build AOTFs is Tellurium Dioxide because of its extended wavelength range from 380 nm up 4.5 μm, a good acousto-optic figure of merit, and the availability in crystal of large di- mension with good optical quality. The performance of an AOTF can be summarized by passband versus wavelength, RF power to achieve peak diffraction efficiency and tuning range. One of the most relevant parameters which limits AOTF performance is the RF power versus diffraction efficiency, which increases with 2. A practical limi- tation has been imposed to 50mW /mm2 , above these level thermal gradient affects the performance. This level is easy reached for conventional AOTF for wavelength above 2.5 μm. The reduction of RF power requirement is achieved by means of acous- tic resonant cavities. The theoretical development and subsequent design of the first resonant AOTF developed inside Gooch and Housego is carried out, and the exper- imental results are in good agreement with the predicted performances. The results obtained from the experience with resonant AOTFs lead to extending the wavelength range from 180 nm up to 10 μm using different acousto-optic materials with limited performance with conventional configuration. Crystal quartz is investigated to extend the wavelength range down to 180 nm, this material is well known in acousto-optic applications. The resonant configuration is particularly suitable for this crystal since the advantage factor is particularly high thanks to the low acoustic attenuation. The experimental results show good agreement with the predicted performances, leading to a large aperture AOTF operating between 180 nm and 380 nm with RF power for peak diffraction efficiency below 8 W. This is the first time that a resonant imaging AOTF made of crystal quartz is reported in literature, to the best of the authors knowledge. Calomel single crystal is investigated to realise an AOTF operating between 4.5 μm and 10 μm. Due to its physical properties which are incompatible with conventional manufacturing processes, different challenges (such as bonding the ultrasonic trans- ducer) are solved by the author in order to build a high performance AOTF. Despite the preliminary results showing promise, the acousto-optic properties of the material are limiting the achievable performance, at least for acousto-optic tunable filters, a fact that does not seem to have been widely appreciated , and which cannot solved by just optimising the design. From the application point of view an optical spectrum analyser based on AOTF technology is investigated, where a dual polarization AOTF is developed in order to realize a spectrometer with a competitive price operating in the wavelength range between 2.5 μm and 4.5 μm. The effects of the acoustic attenuation on a large aperture AOTF is investigated theoretically and experimentally since the performance is affected in the UV range leading to non-ideal operating condition, and a solution is proposed to overcome this issue The results obtained will allow the design of high performance AOTFs in the industrial environment leading to a new types of devices with enhanced performance.

碩士
國立臺灣科技大學
電子工程技術研究所
86
The linewidth properties of an acousto-optic tunable filter for light with arbitrary polarization are studied. The input light which interacts colinearly or noncolinearly with sound inside an AOTF is assumed to be arbitrarily polarized. A set of coupled equations which can describe the interaction inside an AOTF are derived from the vector wave equation.The uniform coupling coefficient equations can not be applied to the apodized AOTF case for the codirectional Bragg interaction.We add the off-Bragg condition in the uniform coupling equations to account for apodized ones. The apodized equations can be applied to analyzing any AOTF.Finally, the numerical results of linewidth response for different conditions are presented .

碩士
國立臺灣科技大學
電子工程系
93
Polarization-mode dispersion is one of the most critical problems for the high-speed wavelength-division-multiplexed system. For a given transmission path, the difference in propagation time experienced by the two polarization modes at a given wavelength is called the differential group delay(DGD) or first-order PMD. We can select the wavelength using the acousto-optic tunable filter and measure the frist-order PMD by the Fixed Analyzer Technique and the data modulation after transmission through a long single mode fiber which causes depolarization. We can determine the different group delay with the relationship between DOP and DGD. Thus, we may measure and compensation it in-time.

Wavelength tunable sources find applications in areas of laser surgery, optical coherence tomography, material processing, and differential absorption light detection and ranging. Acousto-optic tunable filters (AOTFs) are wavelength selective devices which allow for better stability than mechanical tuning due to their lack of mechanical movement. Agile tunability is achieved by avoiding inertial effects. The aim of this thesis was to investigate the performance and limitations of AOTF wavelength controlled external semiconductor laser cavities. The three key components of a typical tunable source are outlined. Conventional tuning mechanisms are compared with AOTFs, and different gain media discussed, with semiconductors being identified as suitable for building AOTF tuned sources. Initially, two diffraction grating tuned sources were constructed. The first was a Thulium doped fibre laser which produced >1.3 W over 1920 – 2060 nm wavelength range which has since been delivered to OzGrav for characterising the absorption of low hydroxide OH bulk fused silica. The second source was constructed from a superluminescent diode with an Indium Phosphide (InP) active layer and produced >5 mW over 1650 – 1750 nm. This source was subsequently used for characterising a frequency shifting, quasi-collinear AOTF for its tuning relation, response to different driving conditions, and temporal response. Two tunable laser cavities were built using the quasi-collinear AOTF. The first was based on the InP superluminescent diode and demonstrated >10 mW over 1615 – 1775 nm. However, the laser displayed significant etalon effects in its spectral output. This motivated the construction of a ring-cavity based on an InP semiconductor optical amplifier. This laser produced >5 mW over 1600 – 1750 nm, with ~0.3 nm linewidths and no etalon effects observed in the output. Sweep rates of 10⁵ nm/s were demonstrated for both lasers without significant spectral broadening or power modulation. This is of similar magnitude to the fastest previously reported quasi-collinear AOTF tuned semiconductor lasers. Wavelength agility was demonstrated by switching between any two wavelengths in the gain band within the 29 μs interaction time of the AOTF. Finally, a frequency compensating AOTF device was utilised in the ring-cavity to investigate the effect of frequency shift on laser performance. Operating with no frequency shift allowed for a reduction in linewidth, but made the laser more sensitive to residual etalon effects which had not previously been observed with the frequency shifting AOTF ring-cavity. A +30 kHz frequency shift was significant enough to disturb these intracavity interference effects while being small enough to reduce the linewidth from the 0.3 nm observed with the frequency shifting AOTF to <0.1 nm. Future directions of research are discussed. These include operation at other wavelengths, and investigating dual wavelength operation.
Thesis (MPhil) -- University of Adelaide, School of Physical Sciences, 2019

Stimulated Raman Scattering (SRS) is a Coherent Raman microscopy method that has been increasingly employed in recent years for highly-specific, label-free, and high-speed bioimaging. Compared to a similar Coherent Raman method, the so-called Coherent Anti-Stokes Scattering (CARS) microscopy, it exhibits advantages such as the absence of nonresonant background (NRB) and the linearity of the signal intensity on the concentration of molecules of interest. However, SRS can be affected by unwanted background signals that hinder the acquisition of an accurate Raman information. These unwanted signals are generated by parasitic effects that are difficult to suppress in standard SRS setups. Here, I present a frequency-modulation (FM) SRS technique via an Acousto-Optic Tunable ioilter (AOTF), describing its implementation on Vibra Lab setup and assessing its efficiency with imaging results. The FM technique provides a cancellation of the unwanted background signals, maintaining intact the SRS information. It is based on the weak spectral dependence of the parasitic effects as compared to the high spectral specificity of the SRS signal. The proposed scheme presents a few advantages when compared with other solutions presented in the literature. In particular, it doesn't require a complex setup configuration, and it can be used seamlessly in a very broad range of the vibrational spectrum.

碩士
國立臺灣科技大學
電子工程系
93
Polarization-mode dispersion (PMD) is an obstacle in many fiber-optic transmission systems, and as the bit rates increase to 40Gb/s and beyond, its impact will be even more great. Consequently, there is a large interest in techniques to compensate or mitigate the effects of the PMD, and a number of methods have been proposed. Acousto-optic tunable filters (AOTF) are very attractive system components in wavelength division multiplexing (WDM) networks because of their broad continuous electronic wavelength tunability and narrow filter bandwidth. The unique multiwavelength filtering capability further adds a new dimension of flexibility to network design that cannot be achieved by any other kind of optical filter. An variable delay time of the AOTF can be generated when we changed the amplitude of acoustic wave. In this paper, we use AOTF to compensate the effects of the PMD. The proposed technique is verified by the computer simulation.

碩士
國立臺灣科技大學
電子工程系
89
Polarization mode dispersion causes an increasing interest in the last few years because of it is a major limitation to the transmission capabilities of high bit rate digital optical transmission system. PMD is generated when a lightwave opagates through a birefringence medium, such as noncollinear TeO2 AOTF. A vertical polarized light incident into the anisotropic medium which is perturbed by a shear sound wave generates an orthogonal polarized light at the output region. During the AO interaction, both the ordinary and extraordinary diffracted light in an anisotropic medium can be described by the Maxwell's equations. Under the kDB coordinate systems, a set of vectorial coupled wave equations that can be described between the ordinary and extraordinary light can be derived. Due to the AO interaction, the light with one polarized can be coupled into another polarized light, hence cause polarization change. A PMD is therefore induced. The polarization of a monochromatic light can be described by three unit stokes vectors, s1, s2, s3, and from the defining relation between stokes vectors and polarization dispersion vector, the differential group delay can be derived. The mean differential group delay of the AOTF device can be determined by counting the number of extreme per unit wavelength internal in the transmission spectrum as a wavelength-dependent state of polarization. An experiment is set up to check the validity of our theoretics. The theoretical and experimental results can be computed. Certain identical patterns are observed.

博士
國立臺灣科技大學
電子工程系
95
We propose an on-line, wide-band, adaptive, and no data traffic interruption polarization mode dispersion (PMD) monitoring system based on the modulated amplified spontaneous emission (ASE) and cascaded acousto-optics tunable filters (AOTFs) techniques. This method is applicable to a long-haul, multiple erbium-doped fiber amplifiers (EDFAs), dense wavelength division multiplexing (DWDM) optical transmission system. Due to the unique properties of the non payload signal bearing and wide-band existence, the ASE noise of one of the EFDAs is employed as the supervisory (SV) signal and becomes traceable during transmission by modulating it with low-frequency rf signal. In addition, the AOTFs are used seriously at the receiver side due to its prominently refractive-index adjustability and wide channel scanning properties. This method is based on frequency domain measurement, which has many advantages for implementation. Using the fixed-analyzer method, PMDs of different wavelength bands which range from 1545-1580nm of an DWDM optic-fiber communication system can be found by adaptively changing the radio frequency of the AOTF. The resolution of the proposed monitoring system can be improved by cascading the AOTFs at the receiver side. To prove the validity of our method, the theoretical results are compared with the experimental data. A high degree of agreement is observed.

The mid-infrared spectral region between 3 μm and 5 μm contains the absorption features of many different organic and biological compounds, which leads to a wide range of potential applications for sources of mid-infrared radiation. Historically, this part of the spectrum has been difficult to access, which has limited the development of these applications. Fibre based lasers offer long gain lengths, effective thermal management and robustness. This thesis explores pulsed operation of fibre lasers using the ⁴F(9/2) → ⁴I(9/2) transition in erbium, which is currently the only fibre laser source to directly generate light in the 3.4 μm to 3.8 μm region. This thesis explores lasers that generate pulses in the nanonsecond, picosecond and femtosecond regimes through use of both Q-switching and mode-locking techniques. The Q-switched systems utilise acousto-optic devices to modulate the resonator losses and produce pulsed laser output. These systems included the first actively Q-switched fibre laser at 3.5 μm. Mode-locked pulses with electronically tunable wavelength were generated via the frequency shifted feedback technique, using an acousto-optic tunable filter. The non-linear polarisation rotation method was used to generate ultrafast mode-locked pulses. This was the first time that this technique had been used on the 3.5 μm erbium transition, which resulted in the first subpicosecond pulses from a fibre laser at this wavelength, with a duration of 580 fs and an energy of 3.2 nJ. The resulting peak power of 5.5kW is the highest of any 3.5 μm fibre laser system. The ultrashort pulses are used to demonstrate non-linear spectral broadening in a highly non-linear fibre. This thesis concludes with a summary of results and suggestions for future work.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2021

by Changsong Qin.
Thesis (Ph.D.)--Chinese University of Hong Kong, 1997.
Includes bibliographical references (p. 128-139).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.

碩士
國立臺灣科技大學
電子工程系
93
The crystal of an acousto-optic tunable filter (AOTF) is an anisotropic medium. When the light traveling in the medium, the refractive index would be different in different polarization. It makes a time delay, which is called differential group delay (DGD) and the phenomenon used in transmission is called polarization-mode dispersion (PMD). 　　PMD causes the signal distortion and is a major limitation to the bandwidth of the optical transmission system. A set of coupled equations can be derived from Maxwell's equations and kDB system, and can describe the relation between lightwaves of AOTF. An analytical expression of the lightwaves and Stokes parameters, can be found. The DGD could hance be derived. A computer simulations of state of polarization (SOP) changing and experiments are provided to check to validity of our theory.