Active optical switches based on polarization-tuned guided-mode resonance filters for optical communication

A novel polariscope using a liquid crystal (LC) polarization rotator is proposed for full-field subfringe photoelastic stress analysis. The system uses a light-emitting diode-based modified Senarmont polariscope with an added liquid crystal polarization rotator to generate phase shifts by applying suitable voltages to the LC element. Four phase shift polariscope images are captured and analyzed to get the stress distribution. A comparative study with the gray-field polariscope method which uses a rotating analyzer shows good agreement.

A novel optical serial multicast mode scheme using an active vertical coupler optical crosspoint switch matrix has been successfully demonstrated. A fibre delay line has been employed to recirculate optical packets, providing one serial output packet for each recirculation. A minimum Q-factor of 5.68 dB and an optical signal-to-noise-ratio penalty of <2.3 dB are found after nine recirculations.

Due to their narrow reflection peak as well as their compact structure, Guided Mode Resonance Filters (GMRFs) are attractive for many applications. We demonstrate the possibility to modulate the properties of a GMRF by associating with liquid crystals (LCs). By impregnating the diffraction grating with LCs, it is possible to switch between an active and an inactive state depending on the polarization of the light or the applied voltage. In this paper we fabricated and characterized the first diffraction order of LC-impregnated gratings with different periods (0,8 to 5,0µm) and depths (130 to 840nm) to test the ability of liquid crystals to adjust the diffraction properties. Finally, 99.8% of diffraction turn off with a 90° rotation polarization at zero voltage and 90 to 99% by applying a voltage of 30 V according to the grating dimensions. The effect of the grating dimension on the diffraction modulation capacity will be discussed.

This work proposes a mid-infrared polarization rotator that incorporates a twisted nematic liquid crystal (TNLC) cell with a photo-controllable alignment layer. The TNLC device with a sufficient phase retardation can act as an achromic polarization rotation device over a wide wavelengths range and thus can rotate the polarization of a mid-IR laser beam. The photo-alignment technique enables TNLCs with arbitrary twisting angles to be generated by the use of visible polarized addressing light to control the directors of the photo-alignment layer. Therefore, arbitrary rotation angles of the polarization axis of a linearly polarized mid-IR laser beam can be realized. Moreover, the rewritable property and reliability of this polarization rotator are experimentally verified. The flexibility of polarization control for broadband mid-IR opens up a large range of potential mid-IR applications.

A low-crosstalk structure for a 1*2 optical switch using twisted nematic liquid crystal (TN-LC) cells is proposed. Low crosstalk can be obtained by using a walkoff polarizing beam splitter between two TN-LC cells mutually controlled in opposite states. A 1*2 polarization-independent optical switch is assembled using single-mode fibers. Its insertion loss and crosstalk, in both switching modes, are <or=1.6 dB and <or=-37.1 dB, respectively.<<ETX>>

Plasma in low earth orbit can damage electronic components and potentially jeopardize scientific missions in space. Predicting the accumulated damage and understanding components’ radiation tolerance are important in mission planning. In this manuscript, we report on the observed radiation tolerance of single photon detectors and a liquid crystal polarization rotator. We conclude that an uncooled Si APD could continue to operate from more than a month up to beyond the lifetime of the satellite depending on the orbit. The liquid crystal polarization rotator was also unaffected by the exposed dosage.

An optical arrangement for constructing wavelength-tunable spectral filters is presented that makes use of a set of dispersive polarization rotations to select wavelengths. A filter in the arrangement is initially mechanically tunable, requires no achromatic retarder, and can be further electrically tunable, switchable, or both, depending on the elements selected. Test measurements and results are presented and described. Modified arrangements with additional retarder(s) or liquid-crystal polarization rotator(s) are suggested and discussed.

Monolayer MoS2 exhibits interesting optoelectronic properties that have been utilized in applications such as photodetectors and light emitting diodes. For image sensing applications, improving the light sensitivity relies on achieving a low dark current that enables the detection weak light signals. Although previous reports on improving the detectivity have been explored with heterostructures and pn junction devices, some of these approaches lack CMOS compatibility processing and sufficient low dark current suppression. Steep slope transistors that overcome the Boltzmann tyranny can further enhance the performance in photodetectors by providing efficient extraction of photogenerated charges. Here, we report a monolayer MoS2 floating gate negative capacitance phototransistor with the integration of a hafnium-zirconium oxide ferroelectric capacitor. In this study, a SSmin of 30 mV dec-1, very low dark currents of 10-13-10-14 A, and a high detectivity of 7.2 × 1015 cm Hz1/2 W-1 were achieved under weak light illumination due to an enhancement in the photogating effect. In addition, its potential as an optical memory and as an optical synapse with excellent long-term potentiation characteristics in an artificial neural network was also explored. Overall, this device structure offers high photosensitivity to weak light signals for future low-powered optoelectronic applications.

A stereoscopic three‐dimensional (3D) system using a polarization rotator is proposed. The polarization rotator converts the polarizations of different eyes' images in temporal multiplexing. A novel fast nematic liquid crystal mode is also proposed. The new liquid crystal mode has fast response time and high contrast; hence it is a good candidate for polarization rotator. The proposed 3D system utilizes only passive polarized glasses, which are more convenient, light weight and low cost. In addition, the polarization rotator can be applied to current 2D displays and become 3D capable display.

We designed a multifunctional all-dielectric metasurface employing cuboid structures patterned with bow-tie-shaped nanoholes; it exhibits multiple Fano resonances induced by quasi-bound states in the continuum (quasi-BICs) through structural asymmetry. Among them, several resonant modes demonstrated high quality factors in the range of 103–104, along with near-unity modulation depth and strong spectral contrast. The optical responses were analyzed utilizing the finite-difference time-domain (FDTD) method, with Fano profiles fitted to theoretical models and the BIC-governed modes validated via the inverse-square ratio law. Furthermore, multipolar decomposition and electromagnetic spatial field profiles revealed the origins of the resonance, while LC circuit modeling provided additional physical insight into the Fano profiles. The proposed metasurface also exhibited strong polarization dependence, indicating its potential for active optical switching. Finally, the refractive-index sensing performance, including the potential for detecting Vibrio cholerae in an appropriate environment, reached a sensitivity of 342 nm per RIU and a figure of merit of 217.14 RIU−1. Advancing the control of high-Q quasi-BIC Fano resonances, this study highlights Fano resonators’ potential for refractive-index sensing and active switching.

Distinct far field patterns have been demonstrated from grating coupled surface emitting distributed feedback lasers which may therefore be employed as two state spatial optical switches with high speed switching potential.

The new principle of electronic paper that can display two-dimensional (2D) or even stereoscopic three-dimensional (3D) images was developed by us. We review the structure of the display unit that is the light printable rewritable matter with polarization dependent gray scale. It consists of one or two liquid crystal displays based on optical rewritable (ORW) technology. ORW display uses bare plastic or polarizers as substrates, while no conductor is required. Continuous grey image on ORW e-paper maintains proper performance even when the device is bent. The image is changed by light printer. We discuss and experimentally verify the possible design of the light printer device based on polarization rotation. Alternative designs based on twist nematic (TN) or ferroelectric liquid crystals (FLC) operational element are also suggested. Simple construction provides durability and low cost of the ORW e-paper concept, while amazing possibility of 3D picture on ORW electronic paper is principally proved.

A micro-channel plate dynode type image intensifier whose output window is a fibre face plate coated with phosphor on its inner surface has been applied to a low f -number spectroscopic detector for studies of very weak light signals sent from the crossing between an electronic or ionic beam and an atomic or molecular beam. It can reduce long exposures extending over nights for optimum density spectrograms to be obtained in the conventional way, down to scores of minutes and to several seconds. The resolution and sensitivity are both nearly satisfactory, as far as atomic lines, continua, and diatomic band-heads are concerned.

Scientific experiments often demand the detection of very weak light signals at high-speed or to precisely measure the time of arrival of single photons. Arrays of Single-Photon Avalanche Diodes (SPAD) are ideal candidates when high sensitivity is required together with high frame-rate or precise photon-timing resolution. We designed a linear 32x1 SPAD array using a high-voltage CMOS technology able to provide both good SPAD performance and fast electronics. During frame acquisition all pixels work in parallel, each of them being equipped with anything necessary for photon counting. The array architecture is capable of fully parallel operation of all pixels allowing free running acquisition at high frame-rate. With a low-speed 10 MHz clock frequency, one pixel is read out in 100 ns while the whole array is readout in 320 ns, corresponding to a frame-rate of 312.5 kframe/s. The frame-rate can top to 4 Mframe/s with a clock of 128 MHz. The photon timing modality employs the photon time-of-arrival information provided by each of the 32 outputs. All 32 "timing" outputs feed external Time-Correlated Photon Counting boards. The Full-Width at Half- Maximum using very short laser pulses is 55 ps with few kcps counting rate.

Solution-processed flexible broadband ZnO photodetector modified by Ag nanoparticles