Pub Date : 2023-12-14DOI: 10.3390/photonics10121376
Wei-Chao Zhang, Lin-Heng Li, Tao Zhang
In order to improve the sensitivity and accuracy of the giant magnetostrictive material-fiber Bragg gratings’ (GMM-FBG) current sensor, in which the magnetostrictive modulator is Terfenol-D, the temperature effects on the FBG center wavelength and GMM magnetostriction coefficient are investigated to initiate an amending scheme in which temperature parameters are introduced into a GMM-FBG sensing model so as to calibrate current values. Based on electromagnetism theory, the magnetic structure is optimized in design to significantly increase the magnetic coupling efficiency and to homogenize magnetic distribution, employing finite element simulations of the electromagnetic field. The relevant experimental platform is constructed with a wavelength demodulation system. At the temperature range of 20~70 °C, response amplitudes of the current sensor are tested under various current values. The experimental results indicate that the sensitivity of the GMM-FBG current sensor decreases with the temperature increment and is also positively correlated to the target current. Through analyzing the response characteristics of the current sensor to temperature variation, a reasonable GMM-FBG sensing amelioration model with a temperature compensation coefficient is established based on a mathematical fitting method, according to which the current detecting accuracy can be increased by 4.8% while measuring 60 A current at the representative working temperature of 40 °C.
为了提高巨磁致伸缩材料-光纤布拉格光栅（GMM-FBG）电流传感器（其中的磁致伸缩调制器为Terfenol-D）的灵敏度和精确度，研究了温度对FBG中心波长和GMM磁致伸缩系数的影响，从而提出了一种修正方案，即在GMM-FBG传感模型中引入温度参数，以校准电流值。基于电磁学理论，利用电磁场的有限元模拟对磁结构进行了优化设计，以显著提高磁耦合效率并均匀磁分布。利用波长解调系统搭建了相关实验平台。在 20~70 °C 的温度范围内，测试了电流传感器在不同电流值下的响应振幅。实验结果表明，GMM-FBG 电流传感器的灵敏度随温度升高而降低，并且与目标电流呈正相关。通过分析电流传感器对温度变化的响应特性，基于数学拟合方法建立了一个合理的带有温度补偿系数的 GMM-FBG 传感改进模型，根据该模型，在 40 °C 的代表性工作温度下测量 60 A 电流时，电流检测精度可提高 4.8%。
{"title":"Structural Optimization and Temperature Compensation of GMM-FBG Fiber Current Transducer","authors":"Wei-Chao Zhang, Lin-Heng Li, Tao Zhang","doi":"10.3390/photonics10121376","DOIUrl":"https://doi.org/10.3390/photonics10121376","url":null,"abstract":"In order to improve the sensitivity and accuracy of the giant magnetostrictive material-fiber Bragg gratings’ (GMM-FBG) current sensor, in which the magnetostrictive modulator is Terfenol-D, the temperature effects on the FBG center wavelength and GMM magnetostriction coefficient are investigated to initiate an amending scheme in which temperature parameters are introduced into a GMM-FBG sensing model so as to calibrate current values. Based on electromagnetism theory, the magnetic structure is optimized in design to significantly increase the magnetic coupling efficiency and to homogenize magnetic distribution, employing finite element simulations of the electromagnetic field. The relevant experimental platform is constructed with a wavelength demodulation system. At the temperature range of 20~70 °C, response amplitudes of the current sensor are tested under various current values. The experimental results indicate that the sensitivity of the GMM-FBG current sensor decreases with the temperature increment and is also positively correlated to the target current. Through analyzing the response characteristics of the current sensor to temperature variation, a reasonable GMM-FBG sensing amelioration model with a temperature compensation coefficient is established based on a mathematical fitting method, according to which the current detecting accuracy can be increased by 4.8% while measuring 60 A current at the representative working temperature of 40 °C.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"1 4","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138972620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-14DOI: 10.3390/photonics10121378
Xiayin Liu, Zhiyu Cai, Xiaogang Wang, Bijun Xu
A model of a generalized pulse source, whose complex degree of temporal coherence is described by a function of the nth power difference of two instants, was constructed. As examples, we consider the generalized Gaussian and multi-Gaussian Schell-model pulse sources and study their propagation in dispersive media. It is indicated that such pulse beams present unique self-focusing, off-axis self-shifting and asymmetric self-splitting characteristics by adjusting the power exponent and phase parameters. Further, we explicitly discuss how the coherence time, summation factor as well as the dispersive coefficient significantly affect the self-focusing and self-shifting behaviors of the pulse beam. The results will benefit some applications involving pulse shaping, optical trapping and remote sensing.
我们构建了一个广义脉冲源模型，其复杂的时间相干度由两个时刻的 n 次幂差函数来描述。我们以广义高斯和多高斯谢尔模型脉冲源为例，研究了它们在色散介质中的传播。结果表明，通过调整功率指数和相位参数，这类脉冲光束会呈现出独特的自聚焦、离轴自偏移和非对称自分裂特性。此外，我们还明确讨论了相干时间、求和因子以及色散系数如何显著影响脉冲光束的自聚焦和自位移行为。这些结果将有利于一些涉及脉冲整形、光学捕获和遥感的应用。
{"title":"Propagation Properties of Generalized Schell-Model Pulse Sources in Dispersive Media","authors":"Xiayin Liu, Zhiyu Cai, Xiaogang Wang, Bijun Xu","doi":"10.3390/photonics10121378","DOIUrl":"https://doi.org/10.3390/photonics10121378","url":null,"abstract":"A model of a generalized pulse source, whose complex degree of temporal coherence is described by a function of the nth power difference of two instants, was constructed. As examples, we consider the generalized Gaussian and multi-Gaussian Schell-model pulse sources and study their propagation in dispersive media. It is indicated that such pulse beams present unique self-focusing, off-axis self-shifting and asymmetric self-splitting characteristics by adjusting the power exponent and phase parameters. Further, we explicitly discuss how the coherence time, summation factor as well as the dispersive coefficient significantly affect the self-focusing and self-shifting behaviors of the pulse beam. The results will benefit some applications involving pulse shaping, optical trapping and remote sensing.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"13 3","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138972562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-14DOI: 10.3390/photonics10121375
A. Pushkin, F. Potemkin
The chirped pulse amplification (CPA) systems based on transition-metal-ion-doped chalcogenide crystals are promising powerful ultrafast laser sources providing access to sub-TW laser pulses in the mid-IR region, which are highly relevant for essential scientific and technological tasks, including high-field physics and attosecond science. The only way to obtain high-peak power few-cycle pulses is through efficient laser amplification, maintaining the gain bandwidth ultrabroad. In this paper, we report on the approaches for mid-IR broadband laser pulse energy scaling and the broadening of the gain bandwidth of iron-doped chalcogenide crystals. The multi-pass chirped pulse amplification in the Fe:ZnSe crystal with 100 mJ level nanosecond optical pumping provided more than 10 mJ of output energy at 4.6 μm. The broadband amplification in the Fe:ZnS crystal in the vicinity of 3.7 μm supports a gain band of more than 300 nm (FWHM). Spectral synthesis combining Fe:ZnSe and Fe:CdSe gain media allows the increase in the gain band (~500 nm (FWHM)) compared to using a single active element, thus opening the route to direct few-cycle laser pulse generation in the prospective mid-IR spectral range. The features of the nonlinear response of carbon nanotubes in the mid-IR range are investigated, including photoinduced absorption under 4.6 μm excitation. The study intends to expand the capabilities and improve the output characteristics of high-power mid-IR laser systems.
{"title":"Refining the Performance of mid-IR CPA Laser Systems Based on Fe-Doped Chalcogenides for Nonlinear Photonics","authors":"A. Pushkin, F. Potemkin","doi":"10.3390/photonics10121375","DOIUrl":"https://doi.org/10.3390/photonics10121375","url":null,"abstract":"The chirped pulse amplification (CPA) systems based on transition-metal-ion-doped chalcogenide crystals are promising powerful ultrafast laser sources providing access to sub-TW laser pulses in the mid-IR region, which are highly relevant for essential scientific and technological tasks, including high-field physics and attosecond science. The only way to obtain high-peak power few-cycle pulses is through efficient laser amplification, maintaining the gain bandwidth ultrabroad. In this paper, we report on the approaches for mid-IR broadband laser pulse energy scaling and the broadening of the gain bandwidth of iron-doped chalcogenide crystals. The multi-pass chirped pulse amplification in the Fe:ZnSe crystal with 100 mJ level nanosecond optical pumping provided more than 10 mJ of output energy at 4.6 μm. The broadband amplification in the Fe:ZnS crystal in the vicinity of 3.7 μm supports a gain band of more than 300 nm (FWHM). Spectral synthesis combining Fe:ZnSe and Fe:CdSe gain media allows the increase in the gain band (~500 nm (FWHM)) compared to using a single active element, thus opening the route to direct few-cycle laser pulse generation in the prospective mid-IR spectral range. The features of the nonlinear response of carbon nanotubes in the mid-IR range are investigated, including photoinduced absorption under 4.6 μm excitation. The study intends to expand the capabilities and improve the output characteristics of high-power mid-IR laser systems.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"22 5","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138972404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In shallow tissues of the human body, pathological changes often occur, and there are several kinds of scattering media, such as mucosa, fat, and blood, present on the surface of these tissues. In such scattering environments, it is difficult to distinguish the location of the lesions using traditional attenuation-based imaging methods, while polarization-based imaging methods are more sensitive to this information. Therefore, in this paper, we conducted experiments using diluted milk to simulate biological tissues with scattering effects, illuminated with non-polarized light sources, and used an optimized robust polarization de-scattering algorithm for image processing. The results were qualitatively and quantitatively analyzed through local intensity comparison and visual fidelity functions, verifying the effectiveness of this algorithm under specific conditions.
{"title":"Polarization-Based De-Scattering Imaging in Turbid Tissue-like Scattering Media","authors":"Shirong Zhang, Jian Liang, Yanru Jiang, Liyong Ren","doi":"10.3390/photonics10121374","DOIUrl":"https://doi.org/10.3390/photonics10121374","url":null,"abstract":"In shallow tissues of the human body, pathological changes often occur, and there are several kinds of scattering media, such as mucosa, fat, and blood, present on the surface of these tissues. In such scattering environments, it is difficult to distinguish the location of the lesions using traditional attenuation-based imaging methods, while polarization-based imaging methods are more sensitive to this information. Therefore, in this paper, we conducted experiments using diluted milk to simulate biological tissues with scattering effects, illuminated with non-polarized light sources, and used an optimized robust polarization de-scattering algorithm for image processing. The results were qualitatively and quantitatively analyzed through local intensity comparison and visual fidelity functions, verifying the effectiveness of this algorithm under specific conditions.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"22 6","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139002790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-14DOI: 10.3390/photonics10121379
Jiajing Lang, Cheng Chen, Pu Zhang, Mei Qi, Haowei Chen
We report a single-wavelength tunable mode-locked fiber laser. The single wavelength can be tuned from 1537.49 nm to 1608.06 nm by introducing a Sagnac loop filter. As far as we know, this is the widest single-wavelength tuning range achieved in an erbium-doped mode-locked all-fiber laser based on nonlinear amplifying loop mirror (NALM). The laser’s pulse width changes from 549 fs to 808 fs throughout the tuning process, the maximum average output power is 5.72 mW, and the single-pulse energy is 0.34 nJ at a central wavelength of 1556.53 nm. This laser source can serve as an efficient tool for applications that require a broad tunability range. The combination of femtosecond pulses and extensive wavelength tuning capabilities makes this laser system highly valuable in fields such as fiber optic communications, spectroscopy, sensing, and other applications that benefit from ultrafast and tunable laser sources.
{"title":"C- and L-Bands Wavelength-Tunable Mode-Locked Fiber Laser","authors":"Jiajing Lang, Cheng Chen, Pu Zhang, Mei Qi, Haowei Chen","doi":"10.3390/photonics10121379","DOIUrl":"https://doi.org/10.3390/photonics10121379","url":null,"abstract":"We report a single-wavelength tunable mode-locked fiber laser. The single wavelength can be tuned from 1537.49 nm to 1608.06 nm by introducing a Sagnac loop filter. As far as we know, this is the widest single-wavelength tuning range achieved in an erbium-doped mode-locked all-fiber laser based on nonlinear amplifying loop mirror (NALM). The laser’s pulse width changes from 549 fs to 808 fs throughout the tuning process, the maximum average output power is 5.72 mW, and the single-pulse energy is 0.34 nJ at a central wavelength of 1556.53 nm. This laser source can serve as an efficient tool for applications that require a broad tunability range. The combination of femtosecond pulses and extensive wavelength tuning capabilities makes this laser system highly valuable in fields such as fiber optic communications, spectroscopy, sensing, and other applications that benefit from ultrafast and tunable laser sources.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"14 11","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139003052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3390/photonics10121369
Mariya Degtereva, Yevgeniy Levin, Anastasia Gubina, Aleksandr E. Degterev, Ivan Lamkin, G. Konoplev, Sergey Tarasov, Andrei Whaley, A. Whaley, I. Suloev, A. Danilova, K. Gusev, D. Maimistov
Precise adaptation of the greenhouse lighting spectrum to basic photophysiological processes can effectively and directionally stimulate plant growth and development. The optimal spectrum depends on the plant species and the stage of development and could be assessed empirically. The aim of this study is to determine the LED illumination spectrum that provides a significant improvement in the growth rate and accumulation of biologically active compounds for basil plants (Ocimum basilicum L.) under hydroponic cultivation compared to more traditional lighting sources. The following light sources with various emission spectra were used: an LED lamp within a spectral range of 400–800 nm (B:G:R 15%:5%:80%); a high-pressure sodium lamp (HPS) (B:G:R 5%:45%:50%); a compact fluorescent lamp (B:G:R 20%:40%:40%); a grow LED strip (B:G:R 15%:40%:45%); a white LED lamp (B:G:R 30%:45%:25%); a customized LED lighting setup in color ratios 100%B, 75%B + 25%R, 50%B + 50%R, 25%B + 75%R, 100%R, and natural lighting. A photosynthetic photon flux density (PPFD) of 150 μmol∙m−2∙s−1 was provided with all the sources. It was demonstrated reliably that employing the LED strip as an illumination device gives a 112% increase in basil plant yield compared to the HPS; the transpiration coefficient for the LED strip is six times lower than for the HPS. The content of flavonoids in the basil aerial parts on the 30th, 50th, and 70th days of development is 3.2 times higher than for the HPS; the metabolite composition is also more uniform for LED strip lighting.
根据基本光生理过程精确调整温室照明光谱，可以有效地定向刺激植物生长和发育。最佳光谱取决于植物种类和生长发育阶段，可根据经验进行评估。本研究的目的是确定 LED 照明光谱，与更传统的照明光源相比，该光谱能显著提高水培罗勒植物（Ocimum basilicum L.）的生长速度和生物活性化合物的积累。使用了以下具有不同发射光谱的光源：400-800 纳米光谱范围内的 LED 灯（B:G:R 15%:5%:80%）；高压钠灯（HPS）（B:G:R 5%:45%:50%）；紧凑型荧光灯（B：G:R 20%:40%:40%）；生长 LED 灯带（B:G:R 15%:40%:45%）；白光 LED 灯（B:G:R 30%:45%:25%）；颜色比例为 100%B 、75%B + 25%R、50%B + 50%R、25%B + 75%R、100%R 的定制 LED 照明装置，以及自然光。所有光源的光合光通量密度（PPFD）均为 150 μmol∙m-2∙s-1。实验可靠地证明，使用 LED 灯带作为照明设备，罗勒的产量比使用 HPS 时提高了 112%；LED 灯带的蒸腾系数比 HPS 低六倍。罗勒气生部分在生长第 30、50 和 70 天的黄酮类化合物含量比 HPS 高 3.2 倍；LED 灯带照明的代谢物组成也更均匀。
{"title":"Influence of the Spectral Composition of Illuminating Light Sources on Biometric and Phytochemical Characteristics of Ocimum basilicum L.","authors":"Mariya Degtereva, Yevgeniy Levin, Anastasia Gubina, Aleksandr E. Degterev, Ivan Lamkin, G. Konoplev, Sergey Tarasov, Andrei Whaley, A. Whaley, I. Suloev, A. Danilova, K. Gusev, D. Maimistov","doi":"10.3390/photonics10121369","DOIUrl":"https://doi.org/10.3390/photonics10121369","url":null,"abstract":"Precise adaptation of the greenhouse lighting spectrum to basic photophysiological processes can effectively and directionally stimulate plant growth and development. The optimal spectrum depends on the plant species and the stage of development and could be assessed empirically. The aim of this study is to determine the LED illumination spectrum that provides a significant improvement in the growth rate and accumulation of biologically active compounds for basil plants (Ocimum basilicum L.) under hydroponic cultivation compared to more traditional lighting sources. The following light sources with various emission spectra were used: an LED lamp within a spectral range of 400–800 nm (B:G:R 15%:5%:80%); a high-pressure sodium lamp (HPS) (B:G:R 5%:45%:50%); a compact fluorescent lamp (B:G:R 20%:40%:40%); a grow LED strip (B:G:R 15%:40%:45%); a white LED lamp (B:G:R 30%:45%:25%); a customized LED lighting setup in color ratios 100%B, 75%B + 25%R, 50%B + 50%R, 25%B + 75%R, 100%R, and natural lighting. A photosynthetic photon flux density (PPFD) of 150 μmol∙m−2∙s−1 was provided with all the sources. It was demonstrated reliably that employing the LED strip as an illumination device gives a 112% increase in basil plant yield compared to the HPS; the transpiration coefficient for the LED strip is six times lower than for the HPS. The content of flavonoids in the basil aerial parts on the 30th, 50th, and 70th days of development is 3.2 times higher than for the HPS; the metabolite composition is also more uniform for LED strip lighting.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"56 5","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138976493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mode-division multiplexing (MDM) is a promising multiplexing technique to further improve the transmission capacity of optical communication and on-chip optical interconnection systems. Furthermore, the multimode optical switch is of great importance in the MDM system, since it makes the MDM system more flexible by directly switching multiple spatial signals simultaneously. In this paper, we proposed a mode-independent optical switch based on the graphene–polymer hybrid waveguide platform that could process the TE11, TE12, TE21 and TE22 modes in a few-mode waveguide. The presented switch is independent of the four guided modes, optimizing the buried position of graphene capacitors in the polymer waveguide to regulate the coplanar interaction between the graphene capacitors and spatial modes. The TE11, TE12, TE21 and TE22 modes can be regulated simultaneously by changing the chemical potential of graphene capacitors in a straight waveguide. Our presented switch can enable the independent management of the spatial modes to be more flexible and efficient and has wide application in the MDM transmission systems.
{"title":"Mode-Independent Optical Switch Based on Graphene-Polymer Hybrid Waveguides","authors":"Tianhang Lian, Yuhang Xie, Qidong Yu, Shijie Sun, Xiaoqiang Sun, Xi-bin Wang, Daming Zhang","doi":"10.3390/photonics10121372","DOIUrl":"https://doi.org/10.3390/photonics10121372","url":null,"abstract":"Mode-division multiplexing (MDM) is a promising multiplexing technique to further improve the transmission capacity of optical communication and on-chip optical interconnection systems. Furthermore, the multimode optical switch is of great importance in the MDM system, since it makes the MDM system more flexible by directly switching multiple spatial signals simultaneously. In this paper, we proposed a mode-independent optical switch based on the graphene–polymer hybrid waveguide platform that could process the TE11, TE12, TE21 and TE22 modes in a few-mode waveguide. The presented switch is independent of the four guided modes, optimizing the buried position of graphene capacitors in the polymer waveguide to regulate the coplanar interaction between the graphene capacitors and spatial modes. The TE11, TE12, TE21 and TE22 modes can be regulated simultaneously by changing the chemical potential of graphene capacitors in a straight waveguide. Our presented switch can enable the independent management of the spatial modes to be more flexible and efficient and has wide application in the MDM transmission systems.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"183 S477","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139006451","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, the refractive index and extinction coefficient of ferroelectric liquid crystals have been examined by the terahertz time-domain spectroscopy system. Two modes of ferroelectric liquid crystal materials, deformed helix ferroelectric liquid crystal (DHFLC), and electric suppressed helix ferroelectric liquid crystal (ESHFLC) are tested as experimental samples. Nematic liquid crystal (NLC) was also investigated for comparison. The birefringence of DHFLC 587 slowly increases with the growth of frequency, and it averages at 0.115. Its extinction coefficients gradually incline to their stable states at 0.06 for o-wave and 0.04 for e-wave. The birefringence of ESHFLC FD4004N remains between around 0.165 and 0.175, and both of its e-wave and o-wave extinction coefficients are under 0.1, ranging from 0.05 to 0.09. These results of FLC will facilitate the examination and improve the response performance of THz devices using fast liquid crystal materials.
{"title":"The Birefringence and Extinction Coefficient of Ferroelectric Liquid Crystals in the Terahertz Range","authors":"Ying Ma, Yuhang Shan, Yongning Cheng, Ruisheng Yang, H. Kwok, Jianlin Zhao","doi":"10.3390/photonics10121368","DOIUrl":"https://doi.org/10.3390/photonics10121368","url":null,"abstract":"In this paper, the refractive index and extinction coefficient of ferroelectric liquid crystals have been examined by the terahertz time-domain spectroscopy system. Two modes of ferroelectric liquid crystal materials, deformed helix ferroelectric liquid crystal (DHFLC), and electric suppressed helix ferroelectric liquid crystal (ESHFLC) are tested as experimental samples. Nematic liquid crystal (NLC) was also investigated for comparison. The birefringence of DHFLC 587 slowly increases with the growth of frequency, and it averages at 0.115. Its extinction coefficients gradually incline to their stable states at 0.06 for o-wave and 0.04 for e-wave. The birefringence of ESHFLC FD4004N remains between around 0.165 and 0.175, and both of its e-wave and o-wave extinction coefficients are under 0.1, ranging from 0.05 to 0.09. These results of FLC will facilitate the examination and improve the response performance of THz devices using fast liquid crystal materials.","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"134 3","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139006220","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3390/photonics10121370
A. Czerwinski
The realm of quantum engineering has undergone a remarkable transformation in recent years [...]
近年来，量子工程领域发生了巨大变化 [...]
{"title":"Special Issue on Photonic State Tomography: Methods and Applications","authors":"A. Czerwinski","doi":"10.3390/photonics10121370","DOIUrl":"https://doi.org/10.3390/photonics10121370","url":null,"abstract":"The realm of quantum engineering has undergone a remarkable transformation in recent years [...]","PeriodicalId":20154,"journal":{"name":"Photonics","volume":"135 6","pages":""},"PeriodicalIF":2.4,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139006216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3390/photonics10121371
Payam Parvizi, Runnan Zou, Colin Bellinger, R. Cheriton, Davide Spinello
Optical satellite communications (OSC) downlinks can support much higher bandwidths than radio-frequency channels. However, atmospheric turbulence degrades the optical beam wavefront, leading to reduced data transfer rates. In this study, we propose using reinforcement learning (RL) as a lower-cost alternative to standard wavefront sensor-based solutions. We estimate that RL has the potential to reduce system latency, while lowering system costs by omitting the wavefront sensor and low-latency wavefront processing electronics. This is achieved by adopting a control policy learned through interactions with a cost-effective and ultra-fast readout of a low-dimensional photodetector array, rather than relying on a wavefront phase profiling camera. However, RL-based wavefront sensorless adaptive optics (AO) for OSC downlinks faces challenges relating to prediction latency, sample efficiency, and adaptability. To gain a deeper insight into these challenges, we have developed and shared the first OSC downlink RL environment and evaluated a diverse set of deep RL algorithms in the environment. Our results indicate that the Proximal Policy Optimization (PPO) algorithm outperforms the Soft Actor–Critic (SAC) and Deep Deterministic Policy Gradient (DDPG) algorithms. Moreover, PPO converges to within 86% of the maximum performance achievable by the predominant Shack–Hartmann wavefront sensor-based AO system. Our findings indicate the potential of RL in replacing wavefront sensor-based AO while reducing the cost of OSC downlinks.
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