We show that achromatic grating techniques can suppress beam fanning while still allowing two beam coupling to occur.
我们表明消色差光栅技术可以抑制光束扇动，同时仍然允许两束耦合发生。
{"title":"Photorefractive Noise Suppression using Achromatic Gratings","authors":"W. Rabinovich, G. C. Gilbreath, B. Feldman","doi":"10.1364/pmed.1991.mc8","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc8","url":null,"abstract":"We show that achromatic grating techniques can suppress beam fanning while still allowing two beam coupling to occur.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"15 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":"116394514","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}
The light-induced scattering is observed in photorefractive crystals due to noise hologram recording characterized by a complex angular spectrum1. The formation of such holograms in planar waveguides has a number of peculiarities because the recording speed of a waveguide holographic grating depends on its period2.
{"title":"Light-Induced Scattering in Planar Photorefractive Waveguides","authors":"A. Bashkirov, G. Glazov, I. Itkin","doi":"10.1364/pmed.1991.wc26","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc26","url":null,"abstract":"The light-induced scattering is observed in photorefractive crystals due to noise hologram recording characterized by a complex angular spectrum1. The formation of such holograms in planar waveguides has a number of peculiarities because the recording speed of a waveguide holographic grating depends on its period2.","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":"122553702","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}
The experimental set-up of our photorefractive incoherent to coherent converter 1 is shown in figure 1. With two interfering Ar-ion-laser beams (λ=514.5 nm) we write a phase hologram into a photorefractive KNbO3 crystal. Using anisotropic Bragg diffraction 2 we choose the direction of the diffracted beam (λ=632.8 nm) perpendicular to the crystal surface. The input image is projected into the crystal plate anti-parallel to the diffracted beam. A short wavelength transmitting dichroitic beam splitter is used to separate the incoherent light from the diffracted beam. This set-up shows highest resolution 3.
{"title":"Resolution limit of photorefractive spatial light modulators","authors":"P. Amrhein, P. Günter","doi":"10.1364/pmed.1991.mb8","DOIUrl":"https://doi.org/10.1364/pmed.1991.mb8","url":null,"abstract":"The experimental set-up of our photorefractive incoherent to coherent converter 1 is shown in figure 1. With two interfering Ar-ion-laser beams (λ=514.5 nm) we write a phase hologram into a photorefractive KNbO3 crystal. Using anisotropic Bragg diffraction 2 we choose the direction of the diffracted beam (λ=632.8 nm) perpendicular to the crystal surface. The input image is projected into the crystal plate anti-parallel to the diffracted beam. A short wavelength transmitting dichroitic beam splitter is used to separate the incoherent light from the diffracted beam. This set-up shows highest resolution 3.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"66 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":"125827860","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}
Many optical image processing operations such as edge enhancement may be performed by suitable linear spatial filters. A broader class of operations is made available by extending this technique to nonlinear filters. An example of this is the use of a logarithmic nonlinearity for conversion of multiplicative to additive noise [1]. In this work, we demonstrate that phase preserving thresholding in the Fourier plane which linearly transmits signals above a certain intensity, reduces additive signal dependent noise, such as noise from coherent artifacts, image defects and uniformity noise.
{"title":"Photorefractive Deamplification for Artifact Noise Reduction","authors":"J. Khoury, M. Cronin-Golomb","doi":"10.1364/pmed.1991.wc12","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc12","url":null,"abstract":"Many optical image processing operations such as edge enhancement may be performed by suitable linear spatial filters. A broader class of operations is made available by extending this technique to nonlinear filters. An example of this is the use of a logarithmic nonlinearity for conversion of multiplicative to additive noise [1]. In this work, we demonstrate that phase preserving thresholding in the Fourier plane which linearly transmits signals above a certain intensity, reduces additive signal dependent noise, such as noise from coherent artifacts, image defects and uniformity noise.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"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":"126809974","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}
Due to their large potential storage capacity, photorefractive crystals are an attractive medium for a variety of optical computing architectures[1]. The actual capacity of such storage systems is determined by the minimum acceptable diffraction efficiency for a given system design[2] and the maximum number of holograms that can be recorded with this efficiency in photorefractive crystals.
{"title":"Diffraction Efficiency Dynamics in Photorefractive Crystals","authors":"E. Maniloff, K. Johnson","doi":"10.1364/pmed.1991.md6","DOIUrl":"https://doi.org/10.1364/pmed.1991.md6","url":null,"abstract":"Due to their large potential storage capacity, photorefractive crystals are an attractive medium for a variety of optical computing architectures[1]. The actual capacity of such storage systems is determined by the minimum acceptable diffraction efficiency for a given system design[2] and the maximum number of holograms that can be recorded with this efficiency in photorefractive crystals.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"40 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":"114623605","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}
When photorefractive materials are included as elements in image and signal processing systems, the dynamic range of the photorefractive element has a significant impact on the overall performance of the system. Evaluating the Emits on this dynamic range is of particular importance if we hope to provide a realistic comparison of photorefractive devices such as spatial light modulators1,2 or integrating correlators 3 with similar devices based on competing opto-electronic technologies. We must thus determine the range of signal beam intensities which may be used to write a holographic grating with a reference beam of some fixed intensity, or in other words, the maximum beam ratio that will cause a detectable refractive index grating to be written within the photorefractive material.
{"title":"Fundamental Noise Limits in Photorefractive Systems","authors":"F. Vachss, C. Gu, John H. Hong, T. Chang","doi":"10.1364/pmed.1991.mc7","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc7","url":null,"abstract":"When photorefractive materials are included as elements in image and signal processing systems, the dynamic range of the photorefractive element has a significant impact on the overall performance of the system. Evaluating the Emits on this dynamic range is of particular importance if we hope to provide a realistic comparison of photorefractive devices such as spatial light modulators1,2 or integrating correlators 3 with similar devices based on competing opto-electronic technologies. We must thus determine the range of signal beam intensities which may be used to write a holographic grating with a reference beam of some fixed intensity, or in other words, the maximum beam ratio that will cause a detectable refractive index grating to be written within the photorefractive material.","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":"131390522","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}
In photorefractive two-beam coupling the interference of two optical beams creates a refractive index grating resulting in energy transfer between the two beams. In models describing this effect it is usually assumed that both beams have perfect spatial coherence. For some applications such as achromatic volume holography [1], multimode fiber gyroscopes and optical phase conjugation through turbulence, spatial coherence effects may become important in the coupling process. Reduced spatial coherence leads to lower contrast interference fringes in an interference fringe region smaller than that of the perfectly coherent case. In recent work, we have made a quantitative study of the influence of these effects on coupling under the assumption that the coherence properties of the interacting beams do not change during the coupling [2]. In the present work, we include the influence that beam coupling has on spatial coherence of the interacting beams. It is worth noting that the problem of spatial coherence in nonlinear wave mixing has been studied earlier [3-5]. However, all of these studies referred to the case of fast Kerr-medium. Photorefractive materials are much slower and cannot follow fast changes of the phases of interacting beams. Thus description of the mixing process will be different.
{"title":"Two-Beam Coupling with Partially Coherent Light","authors":"H. Kong, W. Krolikowski, M. Cronin-Golomb","doi":"10.1364/pmed.1991.mc9","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc9","url":null,"abstract":"In photorefractive two-beam coupling the interference of two optical beams creates a refractive index grating resulting in energy transfer between the two beams. In models describing this effect it is usually assumed that both beams have perfect spatial coherence. For some applications such as achromatic volume holography [1], multimode fiber gyroscopes and optical phase conjugation through turbulence, spatial coherence effects may become important in the coupling process. Reduced spatial coherence leads to lower contrast interference fringes in an interference fringe region smaller than that of the perfectly coherent case. In recent work, we have made a quantitative study of the influence of these effects on coupling under the assumption that the coherence properties of the interacting beams do not change during the coupling [2]. In the present work, we include the influence that beam coupling has on spatial coherence of the interacting beams. It is worth noting that the problem of spatial coherence in nonlinear wave mixing has been studied earlier [3-5]. However, all of these studies referred to the case of fast Kerr-medium. Photorefractive materials are much slower and cannot follow fast changes of the phases of interacting beams. Thus description of the mixing process will be different.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"12 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":"130940884","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}
O. P. Nestiorkin, Y. Shershakov, B. Zel'dovich, N. Bogodaev, L. Ivleva
Holographic grating in a photorefractive crystal may be recorded due to the diffusion of electrons or their drift in external or intrinsic photovoltaic dc field as a result of illumination by a static interference pattern. Those traditional mechanisms are well studied [1]. Running interference pattern may be registered by the phase-locked detection in the externally applied ac field. That mechanism was realized in the paraelectric crystal Bi12TiO20 (BTO) [2,3]. In this work we have performed the phase-locked detection mechanism in the ferroelectric photorefractive crystal SBN:Ce.
{"title":"Phase-locked detection of running interference pattern in photorefractive SBN","authors":"O. P. Nestiorkin, Y. Shershakov, B. Zel'dovich, N. Bogodaev, L. Ivleva","doi":"10.1364/pmed.1991.wc10","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc10","url":null,"abstract":"Holographic grating in a photorefractive crystal may be recorded due to the diffusion of electrons or their drift in external or intrinsic photovoltaic dc field as a result of illumination by a static interference pattern. Those traditional mechanisms are well studied [1]. Running interference pattern may be registered by the phase-locked detection in the externally applied ac field. That mechanism was realized in the paraelectric crystal Bi12TiO20 (BTO) [2,3]. In this work we have performed the phase-locked detection mechanism in the ferroelectric photorefractive crystal SBN:Ce.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"28 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":"132616688","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}
N. Bogodaev, L. Ivleva, A. Korshunov, N. Polozkov, V. Shkunov
Two-wave mixing allows one to change effectively Intensities, phases, space profiles, polarizations and time evolution of interacting beams [1,21. We will show, that two-wave mixing of partially coherent beams may be used to increase degree of coherence of these beams. The physics of the effect under discussion is as follows: two partially coherent beams write a refraction index grating in a nonlinear medium whose position and profile are practically stationary. Scattering of strong beam on this grating in the direction of the weak one means that this weak beam acquires an addition, that is coherent with the strong beam, thereby increasing degree of coherence of the beams. Similar effects were discussed in connection with scattering of different frequency components at the common running grating [3] and with Interaction of different polarization components [4,5].
{"title":"Increase of mutual coherence of light beams in two-wave interaction in photorefractive crystals","authors":"N. Bogodaev, L. Ivleva, A. Korshunov, N. Polozkov, V. Shkunov","doi":"10.1364/pmed.1991.mc10","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc10","url":null,"abstract":"Two-wave mixing allows one to change effectively Intensities, phases, space profiles, polarizations and time evolution of interacting beams [1,21. We will show, that two-wave mixing of partially coherent beams may be used to increase degree of coherence of these beams. The physics of the effect under discussion is as follows: two partially coherent beams write a refraction index grating in a nonlinear medium whose position and profile are practically stationary. Scattering of strong beam on this grating in the direction of the weak one means that this weak beam acquires an addition, that is coherent with the strong beam, thereby increasing degree of coherence of the beams. Similar effects were discussed in connection with scattering of different frequency components at the common running grating [3] and with Interaction of different polarization components [4,5].","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"7 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132063463","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 investigate the properties of a laser-induced interference filter in photorefractive BaTiO3. The filter has several control parameters for the reflectance and its high wavelength selectivity makes the filter suited as output mirror of a tuneable single mode infrared semiconductor laser. Furthermore, the interference filter represents a unique simple method for probing higher spatial harmonics in the photorefractive grating.
{"title":"Laser-Induced Interference Filters in Photorefractive Materials","authors":"P. Petersen, P. Johansen, T. Skettrup","doi":"10.1364/pmed.1991.tub7","DOIUrl":"https://doi.org/10.1364/pmed.1991.tub7","url":null,"abstract":"We investigate the properties of a laser-induced interference filter in photorefractive BaTiO3. The filter has several control parameters for the reflectance and its high wavelength selectivity makes the filter suited as output mirror of a tuneable single mode infrared semiconductor laser. Furthermore, the interference filter represents a unique simple method for probing higher spatial harmonics in the photorefractive grating.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"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":"126663590","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}
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