We present a new thresholding device consisting of a double phase conjugate mirror (DPCM) combined with a phase conjugate mirror resulting in superior thresholding characteristics compared to that of a DPCM alone.
{"title":"New Thresholding Device using a Double Phase Conjugate Mirror with Phase Conjugate Feedback","authors":"P. Tayebati, L. H. Domash","doi":"10.1364/pmed.1991.tub6","DOIUrl":"https://doi.org/10.1364/pmed.1991.tub6","url":null,"abstract":"We present a new thresholding device consisting of a double phase conjugate mirror (DPCM) combined with a phase conjugate mirror resulting in superior thresholding characteristics compared to that of a DPCM alone.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117059069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have investigated 2WM and 4WM processes in photorefractive crystals in the nonsaturated regime, i.e. when the coupling between beams and the absorption depend on the light intensity. Different models of saturable absorption in 2WM via reflection grating are considered, and the corresponding wave equations are solved exactly. The solutions are written in terms of hypergeometric functions or in quadratures. From the solutions it was found that the energy transfer between the waves is less effective in the nonsaturated stage of the process.
{"title":"Phase Conjugation with Saturable Gain and Saturable Absorption","authors":"M. Belic, D. Timotijević, R. Boyd","doi":"10.1364/pmed.1991.wc20","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc20","url":null,"abstract":"We have investigated 2WM and 4WM processes in photorefractive crystals in the nonsaturated regime, i.e. when the coupling between beams and the absorption depend on the light intensity. Different models of saturable absorption in 2WM via reflection grating are considered, and the corresponding wave equations are solved exactly. The solutions are written in terms of hypergeometric functions or in quadratures. From the solutions it was found that the energy transfer between the waves is less effective in the nonsaturated stage of the process.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"272 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116263600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Absorption gratings can cause significant beam coupling in photorefractive crystals;1,2 in the case of BaTiO3, we found gains as large as 1 cm−1.3 This coupling is caused by the variation in absorption created by the spatially periodic distribution of empty and full trap sites throughout the crystal and it requires only one active level. There is also evidence that there are two or more photoactive levels in BaTiO3, as well as in other photorefractive crystals. In BaTiO3, these extra levels explain the sublinear intensity dependence of the photoconductivity,4,5 as well as light-induced absorption.6,7 Here we study the effects that multiple photo-active levels have on absorption grating coupling. We derive expressions for the two-beam absorption coupling gain vs. the magnitude of the grating wavevector k g and show that it does not vanish as kg tends to zero, in contrast to the single photo-active level case. This effect is verified experimentally and is used to evaluate the donor-to-acceptor density ratio in a BaTiO3 crystal.
{"title":"Absorption Gratings with Multiple Levels","authors":"R. Cudney, R. Pierce, G. D. Bacher, J. Feinberg","doi":"10.1364/pmed.1991.mc4","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc4","url":null,"abstract":"Absorption gratings can cause significant beam coupling in photorefractive crystals;1,2 in the case of BaTiO3, we found gains as large as 1 cm−1.3 This coupling is caused by the variation in absorption created by the spatially periodic distribution of empty and full trap sites throughout the crystal and it requires only one active level. There is also evidence that there are two or more photoactive levels in BaTiO3, as well as in other photorefractive crystals. In BaTiO3, these extra levels explain the sublinear intensity dependence of the photoconductivity,4,5 as well as light-induced absorption.6,7 Here we study the effects that multiple photo-active levels have on absorption grating coupling. We derive expressions for the two-beam absorption coupling gain vs. the magnitude of the grating wavevector k\u0000 g\u0000 and show that it does not vanish as kg tends to zero, in contrast to the single photo-active level case. This effect is verified experimentally and is used to evaluate the donor-to-acceptor density ratio in a BaTiO3 crystal.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"377 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115787594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Compound semiconductors such as GaAs are known to be very fast photorefractive materials. However, due to their relatively small electro-optic coefficient, their diffraction efficiency is much smaller than that of most oxide materials such as BaTiO3. Even so, easily detectable signal with fairly good signal to noise ratio can be usually achieved in a GaAs based application without the aid of an external electric field due to the cross-polarization coupling1 capability of GaAs and the high sensitivity of modern video cameras. For example, in a recently demonstrated real-time optical image correlator2, the correlation output was normally strong enough to saturate the vidicon camera used. On the other hand, in some applications such as the ring oscillator, the double phase conjugate mirror, and the self-pumped phase conjugator, a sufficiently large net two-beam coupling gain is needed. In compound semiconductors, net gain had been achieved by applied electric field techniques. However, in general, these techniques have two side effects, namely the Schottky-barrier effect3 and the low-frequency current oscillation effect4. Depending on the particular requirement of an application, these effects may or may not be a problem. But, they are not desired in general. In this paper, we report the results of a study on the electrode material dependence of the Schottky-barrier effect in the undoped GaAs crystal. In particular, the widely-used silver-paste electrodes are compared with thermally-evaporated alloy electrodes.
{"title":"Applied Electric Field Effect on Photorefractive GaAs","authors":"Duncan T. H. Liu, Li-Jen Cheng, Jaehoon Kim","doi":"10.1364/pmed.1991.tua5","DOIUrl":"https://doi.org/10.1364/pmed.1991.tua5","url":null,"abstract":"Compound semiconductors such as GaAs are known to be very fast photorefractive materials. However, due to their relatively small electro-optic coefficient, their diffraction efficiency is much smaller than that of most oxide materials such as BaTiO3. Even so, easily detectable signal with fairly good signal to noise ratio can be usually achieved in a GaAs based application without the aid of an external electric field due to the cross-polarization coupling1 capability of GaAs and the high sensitivity of modern video cameras. For example, in a recently demonstrated real-time optical image correlator2, the correlation output was normally strong enough to saturate the vidicon camera used. On the other hand, in some applications such as the ring oscillator, the double phase conjugate mirror, and the self-pumped phase conjugator, a sufficiently large net two-beam coupling gain is needed. In compound semiconductors, net gain had been achieved by applied electric field techniques. However, in general, these techniques have two side effects, namely the Schottky-barrier effect3 and the low-frequency current oscillation effect4. Depending on the particular requirement of an application, these effects may or may not be a problem. But, they are not desired in general. In this paper, we report the results of a study on the electrode material dependence of the Schottky-barrier effect in the undoped GaAs crystal. In particular, the widely-used silver-paste electrodes are compared with thermally-evaporated alloy electrodes.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"IA-14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126557150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
What are the defects responsible for the photorefractive effect in BaTiO3? What charge con version processes involving these defects are taking place during illumination? Along which energetic paths are charges transported? These questions have to be answered if one wants to understand the outstanding photorefractive properties of BaTiO3 on a microscopic basis.
{"title":"Identification of light induced charge transfer processes in BaTiO3 by combined ESR and optical measurements","authors":"O. Schirmer, E. Possenriede, H. Kröse, P. Jacobs","doi":"10.1364/pmed.1991.wb1","DOIUrl":"https://doi.org/10.1364/pmed.1991.wb1","url":null,"abstract":"What are the defects responsible for the photorefractive effect in BaTiO3? What charge con version processes involving these defects are taking place during illumination? Along which energetic paths are charges transported? These questions have to be answered if one wants to understand the outstanding photorefractive properties of BaTiO3 on a microscopic basis.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131405343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Control and optimization of the behavior of photorefractive crystals requires first, a thorough understanding of the nature (charge state, local symmetry, and electronic structure) of the defects/impurities present in these materials, and of their interaction with light.1,2,3 Toward this end, we have carried out electron paramagnetic resonance (EPR), photo-EPR, and optical absorption measurements on a variety of BaTiO3 samples doped with transition metal ions. These crystals were grown by top-seeded solution growth from a melt with an excess of TiO2.
{"title":"Spectroscopy of Light Sensitive Defect/Impurity Centers in Photorefractive BaTiO3","authors":"R. Schwartz, B. Wechsler, R. McFarlane","doi":"10.1364/pmed.1991.wb2","DOIUrl":"https://doi.org/10.1364/pmed.1991.wb2","url":null,"abstract":"Control and optimization of the behavior of photorefractive crystals requires first, a thorough understanding of the nature (charge state, local symmetry, and electronic structure) of the defects/impurities present in these materials, and of their interaction with light.1,2,3 Toward this end, we have carried out electron paramagnetic resonance (EPR), photo-EPR, and optical absorption measurements on a variety of BaTiO3 samples doped with transition metal ions. These crystals were grown by top-seeded solution growth from a melt with an excess of TiO2.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132817032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Undoped semi-insulating GaP is photorefractive material which is sensitive to the laser light of the wavelength between 0.6 μm and 0.9 μm1). He-Ne lasers and GaAlAs laser diodes belong to this spectral region. This material is important for constructing compact systems with laser diodes.
{"title":"Temperature dependence of the two beam coupling gain coefficient of photorefractive GaP","authors":"K. Kuroda, Y. Okazaki, T. Shimura, M. Itoh","doi":"10.1364/pmed.1991.tuc5","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc5","url":null,"abstract":"Undoped semi-insulating GaP is photorefractive material which is sensitive to the laser light of the wavelength between 0.6 μm and 0.9 μm1). He-Ne lasers and GaAlAs laser diodes belong to this spectral region. This material is important for constructing compact systems with laser diodes.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130783970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reconfigurable volume holograms are important for a wide range of multiple data storage applications, including optical interconnection systems, image processing and neural network models. Therefore, there has been much previous work on multiplexing techniques to obtain a large number of stored images which can be recalled independently. But even the most promising of these multiplexing techniques, angular multiplexing using the selectivity of the Bragg-condition, revealed to be limited primarily because of cross-correlation noise. Moreover, mechanically changing the incident angle of the reference beam1,2 requires a high reliability in the positioning and is therefore inherently slow. To overcome these problems, an intensity spatial light modulator can be used to define the various angular multiplexed incident directions3.
{"title":"Phase-coded hologram multiplexing for high capacity optical data storage","authors":"C. Denz, G. Pauliat, G. Roosen","doi":"10.1364/pmed.1991.md1","DOIUrl":"https://doi.org/10.1364/pmed.1991.md1","url":null,"abstract":"Reconfigurable volume holograms are important for a wide range of multiple data storage applications, including optical interconnection systems, image processing and neural network models. Therefore, there has been much previous work on multiplexing techniques to obtain a large number of stored images which can be recalled independently. But even the most promising of these multiplexing techniques, angular multiplexing using the selectivity of the Bragg-condition, revealed to be limited primarily because of cross-correlation noise. Moreover, mechanically changing the incident angle of the reference beam1,2 requires a high reliability in the positioning and is therefore inherently slow. To overcome these problems, an intensity spatial light modulator can be used to define the various angular multiplexed incident directions3.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115122976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
There is a spatial phase shift between a sinusoidal light intensity pattern and the resulting refractive index grating formed in a photorefractive crystal. For crystals where diffusion is the dominant mechanism for charge migration, this spatial shift is 1/4 of the grating spacing. Any deviation from this value implies some other transport mechanism, such as an applied or internally developed electric field, or the photogalvanic effect, in which optically excited charges preferentially move in one direction in the crystal. Due to its relevance to beam coupling, this spatial shift has been studied extensively using a variety of methods, most of them interferometric in nature1-5. However, interferometric methods only reveal the phase of the complex beam coupling coefficient, which is not necessarily the spatial phase shift of the electro-optically induced grating. Other effects, such as trap grating coupling, can affect the phase of the total coupling coefficient, and thereby prevent a measurement of the spatial phase shift.
{"title":"Origins of the Photorefractive Phase Shift","authors":"R. Cudney, G. D. Bacher, R. Pierce, J. Feinberg","doi":"10.1364/pmed.1991.tua2","DOIUrl":"https://doi.org/10.1364/pmed.1991.tua2","url":null,"abstract":"There is a spatial phase shift between a sinusoidal light intensity pattern and the resulting refractive index grating formed in a photorefractive crystal. For crystals where diffusion is the dominant mechanism for charge migration, this spatial shift is 1/4 of the grating spacing. Any deviation from this value implies some other transport mechanism, such as an applied or internally developed electric field, or the photogalvanic effect, in which optically excited charges preferentially move in one direction in the crystal. Due to its relevance to beam coupling, this spatial shift has been studied extensively using a variety of methods, most of them interferometric in nature1-5. However, interferometric methods only reveal the phase of the complex beam coupling coefficient, which is not necessarily the spatial phase shift of the electro-optically induced grating. Other effects, such as trap grating coupling, can affect the phase of the total coupling coefficient, and thereby prevent a measurement of the spatial phase shift.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124122636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Shimura, H. Miao, M. Itoh, H. Okamura, K. Kuroda
In photorefractive two wave mixing (TWM) using a BaTiO3, output power of amplified signal beam is often fluctuating. The amplification factor is very sensitive to disturbances such as mechanical vibration and fluctuation of the wavelength of the laser. It becomes a serious problem when we use TWM in optical information processing systems. We tried to stabilize the output power of the probe beam using a laser diode (LD) and feedback loop.
{"title":"Power stabilization in photorefractive two wave mixing by frequency tuning of laser diode","authors":"T. Shimura, H. Miao, M. Itoh, H. Okamura, K. Kuroda","doi":"10.1364/pmed.1991.tub5","DOIUrl":"https://doi.org/10.1364/pmed.1991.tub5","url":null,"abstract":"In photorefractive two wave mixing (TWM) using a BaTiO3, output power of amplified signal beam is often fluctuating. The amplification factor is very sensitive to disturbances such as mechanical vibration and fluctuation of the wavelength of the laser. It becomes a serious problem when we use TWM in optical information processing systems. We tried to stabilize the output power of the probe beam using a laser diode (LD) and feedback loop.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124424618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：