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Abstract We report a 1 × N hybrid radio frequency (RF) photonic splitter with arbitrary phase shift and amplitude ratio using a dual-polarization dual-parallel Mach Zehnder modulator (DP-DPMZM). The DP-DPMZM is properly set to generate an orthogonally polarized single-sideband (SSB) modulated optical signal. By controlling a polarization controller (PC) and a polarizer (Pol.) that cascaded behind the modulator, an RF photonic splitter with arbitrary phase and amplitude ratio can be realized. Compared with previous reported works, the proposed RF splitter can be operated in a wide bandwidth since no optical or electrical filters are involved. The proposed scheme is theoretically analyzed and experimentally verified. [ABSTRACT FROM AUTHOR]

Abstract An all-optical image-reject frequency down-converter based on cascaded modulators and a wavelength demultiplexer is presented. The radio-frequency (RF) and the local-oscillator (LO) signal are fed to a phase modulator and a dual-parallel Mach–Zehnder modulator, respectively. Using a wavelength demultiplexer, two down-conversion channels can be obtained. Quadrature phase difference between the two down-converted signals is achieved by properly setting the modulator bias. Image rejection can thus be realized based on Hartley architecture. Experimental results show that image rejection ratios of 32.5 dB in a 10-MHz instantaneous bandwidth and over 50 dB for a single frequency can be obtained. The scheme can be applied to antenna remoting applications, and a 25-km fiber transmission is demonstrated. Highlights • Cascaded structure enables the proposed system to be applied to antenna remoting applications. • Image-reject frequency down-conversion can be all-optically implemented, no RF 90-degree hybrid coupler is required. • Quadrature LO signals is realized by simply adjusting the modulator bias, which supports wideband and accurate phase tuning. [ABSTRACT FROM AUTHOR]

In this paper, a projection-type dual-view holographic three-dimensional (3D) display consisting of a single spatial light modulator (SLM) and a grating light-guide plate is proposed and implemented. A synthetic phase-only hologram of two different 3D objects is calculated by the layer-based Fresnel diffraction method and uploaded onto the SLM for 3D reconstruction. A grating with special design and fabrication is used as the light-guide plate to re-direct the two reconstructed 3D images into the two separated viewing zones simultaneously. Optical experiments demonstrate that the proposed system can realize the function of dual-view holographic 3D display, and it can present 3D images to the human eye with sufficient depth cues, which enables the observers free of the accommodation-vergence conflict and visual fatigue problem. Furthermore, the proposed dual-view holographic 3D display system is applied to the see-through display for augmented reality (AR) applications, and the performance of this system is also tested in the experiments and the results show that the system can provide the dual-view AR 3D sensation successfully. [ABSTRACT FROM AUTHOR]

We report a reconfigurable microwave photonic mixer with multiple functions and wide bandwidth. By changing the photodetection configuration, the mixer can be conveniently reconfigured to realize four functions: single-ended mixing, I/Q mixing, double balanced mixing and image rejection mixing. Furthermore, the filter-free system has a wide bandwidth and the ability to perform both frequency up-conversion and down-conversion. The proposed reconfigurable mixer is based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The optical signal is modulated by the DP-DPMZM and split into two orthogonally polarized signals, which are combined by a 90° optical hybrid and detected by photodetectors. The experimental results show that the mixer has a wide bandwidth from 2 GHz to 30 GHz with a 30 dB spur suppression, and the image rejection ratio of the image rejection mixer is over 30 dB. [ABSTRACT FROM AUTHOR]

We present a common path interference setup for detection of surface depth differences of the order of 200 nm, using a vortex and a Gaussian beam generated with a spatial light modulator. The phase of a vortex with a topological charge +1 and the phase of a lens are encoded next to each other onto the spatial light modulator. Both beams are incident onto a surface with a step feature; the Gaussian beam is incident onto a flat mirrored surface, while the vortex beam scans through the step. Upon interaction with the testing surface, both beams are superposed and their interference pattern is captured, collecting a set of images as a result of the scanning process. A phase detection algorithm is applied to these images and by tracking the vertical positions of the phase singularity along the scanning, the depth variations are estimated. The proposed set up is able to detect a 179 nm step feature, working with light at a wavelength of 830 nm and using a vortex with a diameter of 177 μ m. [ABSTRACT FROM AUTHOR]

Graphene has become an ideal material in terahertz domain due to its linear band-structure and extraordinary carrier transport properties as well as the variable carrier density which can be modified by bias voltage. A high-performance modulator based on double-layer graphene was proposed here which was composed of graphene–silica–silicon–silica–graphene five layers. The equivalent circuit method was used to calculate its 3dB bandwidth, modulation speed, insertion loss and modulation depth. The results show its 3dB bandwidth is approximately 264 KHz, the modulation speed can reach 151 KHz and insertion loss is about 0.3 dB. The modulator was fabricated by chemical vapor deposition method and measured using terahertz-time domain spectroscopy system which was produced by Zomega Terahertz company of America. The experimental results show a best measured modulation depth of 61% can be achieved with a bias voltage of 32 V. The proposed modulator here has many advantages such as fast modulation rate, high modulation depth, wide bandwidth as well as easy to fabricate which provides an effective method to the terahertz communications and imaging systems. [ABSTRACT FROM AUTHOR]

A theoretical investigation of a suspended self-biasing graphene waveguide for electro-optical modulators is presented. The light–matter interaction can be enhanced by suspending the waveguide. For electro-absorptive modulation, the normalized modulation depth can be 0.54 dB/ μ m with a 3-dB footprint of only 1.5 μ m 2 . The insertion loss is extremely low ∼ 0.002 dB, with the figure of merit of ∼ 2700. For the electro-refractive modulation, a 100% modulation can be achieved with much smaller π -phase shift length of only 18.0 μ m. The modulators also show great potential for high-speed ( ∼ 559.2 GHz) modulation. The compromise between modulation speed and modulation efficiency is reduced significantly and the design is near-optimal to its fundamental limits. Moreover, a verification simulation by COMSOL is also given. This suspended graphene modulator can pave the way to practical high-speed, compact-footprint, and high-efficiency devices. [ABSTRACT FROM AUTHOR]

Variable optical attenuation and optical modulation are essential operations in integrated photonic circuits. A new graphene plasmonic gap waveguide structure, which possesses the functions of variable optical attenuator and modulator, is proposed and numerically investigated. The propagation and attenuation modes of the structure can be realized by tuning the gate-voltage. The result shows that it can achieve great modulation depth per micrometer and the working frequency range of 8 THz or more for the variable optical attenuator and the modulator. It also has the advantages of high tolerance, large attenuation range/ modulation depth, wide bandwidth and high integration without crosstalk, which would be promising for high integrated optical circuits. [ABSTRACT FROM AUTHOR]

A novel photonic scheme of microwave waveforms generator based on a dual-loop optoelectronic oscillator (OEO) is experimentally verified. A 10-GHz microwave signal generated by OEO is modulated onto the directly modulated laser (DML) and the phase modulator (PM) simultaneously. By adjusting the driven power of the DML and the PM and the phase difference between the pulse signal inputted into the PM and the PM’s driven signal, the desired optical spectrum is obtained. By passing appropriate dispersion, the optical spectrum can be converted into desired waveform. In this experiment, a series of waveforms with the shapes of sawtooth/reversed-sawtooth, triangle, and pulse are generated. [ABSTRACT FROM AUTHOR]

In this paper, we numerically demonstrated a dynamically tunable implementation of electromagnetically induced transparency (EIT) response with two coupling graphene-nanostrips in terahertz region. Compared to the metal-based structures or separated graphene structures, the Fermi energies of proposed two coupling graphene-nanostrips can be independently tuned by changing bias voltage between the metallic pads and substrate, the EIT window which appears from the near-field coupling between two resonators can be dynamically tuned without reoptimizing and refabricating the structures. As a result, the EIT window has a significant tunable capacity which can realize a higher frequency modulation depth and control the amplitude of transmission peak at a fixed frequency; moreover, the group delay of transmission peak at a fixed frequency with the amplitude of over 0.95 could be dynamically tuned. These results would exhibit potential applications in modulators and tunable slow light devices. [ABSTRACT FROM AUTHOR]

Edge detection is one of the most important tools to recognize the features of an object. In this paper, we propose an optical edge detection method based on computational ghost imaging (CGI) with structured illuminations which are generated by an interference system. The structured intensity patterns are designed to make the edge of an object be directly imaged from detected data in CGI. This edge detection method can extract the boundaries for both binary and grayscale objects in any direction at one time. We also numerically test the influence of distance deviations in the interference system on edge extraction, i.e., the tolerance of the optical edge detection system to distance deviation. Hopefully, it may provide a guideline for scholars to build an experimental system. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP), a rising two-dimensional material with a layer-number-dependent direct bandgap of 0.3–1.5 eV, is very interesting for optoelectronics applications from near- to mid-infrared wavebands. In the atmosphere, few-layer BP tends to be oxidized or degenerated during interacting with lasers. Here, we fabricate few-layer BP nanosheets based on a liquid exfoliation method using N-methylpyrrolidone as the dispersion liquid. By incorporating BP nanosheets with polymers (polyvinyl alcohol or high-melting-point polyimide), two flexible filmy BP saturable absorbers are fabricated to realize passive mode locking in erbium-doped fiber lasers. The polymer-BP saturable absorber, especially the polyimide-BP saturable absorber, can prevent the oxidation or water-induced etching under high-power laser illuminations, providing a promising candidate for Q-switchers, mode lockers, and light modulators. [ABSTRACT FROM AUTHOR]

A novel structure of double-ring slow-light gyroscope with two input–output waveguides is studied. We utilize interferometric detection method, and sufficiently combine the advantages of Interferometric Fiber Optic Gyro (I-FOG) and Resonator Optic Gyro (ROG). The responses of the structure are derived and simulated. Here two experimental schemes are also proposed. By applying a square wave to the integrated phase modulator, we can make the structure work at the highest sensitivity. After applied the square wave, the system runs at linear zone, thus the angular velocity can be obtained according to the linear relationship between the phase difference and the angular velocity. The optimal parameters for the largest phase difference of light signal monitored at different output ports are investigated. Some comparisons are done in the condition of various values of transmission loss coefficients. [ABSTRACT FROM AUTHOR]

In this paper, a photonic microwave waveform generator based on a dual-parallel Mach–Zehnder modulator is proposed and experimentally demonstrated. In this reported scheme, only one radio frequency signal is used to drive the dual-parallel Mach–Zehnder modulator. Meanwhile, dispersive elements or filters are not required in the proposed scheme, which make the scheme simpler and more stable. In this way, six variables can be adjusted. Through the different combinations of these variables, basic waveforms with full duty and small duty cycle can be generated. Tunability of the generator can be achieved by adjusting the frequency of the RF signal and the optical carrier. The corresponding theoretical analysis and simulation have been conducted. With guidance of theory and simulation, proof-of-concept experiments are carried out. The basic waveforms, including Gaussian, saw-up, and saw-down waveforms, with full duty and small duty cycle are generated at the repetition rate of 2 GHz. The theoretical and simulation results agree with the experimental results very well. [ABSTRACT FROM AUTHOR]

A method has been proposed to generate complex periodic discrete non-diffracting beams (PDNBs) via superposition of two identical simple PDNBs at a particular angle. As for special cases, we studied the superposition of the two identical squares (“4+4”) and two hexagonal (“6+6”) periodic wave fields at specific angles, respectively, and obtained a series of interesting complex PDNBs. New PDNBs were also obtained by modulating the initial phase difference between adjacent interfering beams. In the experiment, a 4 f Fourier filter system and a phase-only spatial light modulator imprinting synthesis phase patterns of these PDNBs were used to produce desired wave fields. [ABSTRACT FROM AUTHOR]

Perfect absorption in graphene-based nanostructures has attracted much attention due to its potential applications in novel photodectors and light modulators with high integrability. Based on critical coupling theory, we propose a graphene-based dielectric metasurface, demonstrating graphene-assisted single-band to multi-band perfect absorption with independent band selectivity in the near-infrared range. The proposed graphene-metasurface absorber can support a delocalized guided mode resonance and a series of localized cavity modes with different order, which can be selectively excited at will by simply tuning the geometry of the system, thus realizing an independent control of single-band to multi-band perfect absorption at critical coupling condition. The proposed hybrid structure possesses simple structural configuration and is easily accessible by standard nano-fabrication technique. Our results may find potential applications in the design of novel photoelectronic devices such as graphene-based photodectors or light modulators with flexible multi-band selectivity for desired wavelength. • We propose a graphene-based all-dielectric metasurface, demonstrating graphene-assisted single-band to multi-band perfect absorption with independent band selectivity in the near-infrared wavelength range. • The proposed graphene-metasurface absorber can be selectively excited at will by simply tuning the geometry of the system, thus realizing an independent control of single-band to multi-band perfect absorption at critical coupling condition. • The proposed hybrid structure possesses simple structural configuration and is easily accessible by standard nano-fabrication technique. • Our results may find potential applications in the design of novel photoelectronic devices such as graphene-based photodectors or light modulators with flexible multi-band selectivity for desired wavelength. [ABSTRACT FROM AUTHOR]

While projecting a Gaussian beam onto the spatial light modulator (SLM) which has loaded a composite hologram, several vortex beams can be generated at one time. On the contrary, while projecting the corresponding vortex beam onto the hologram, the Gaussian beam can be restored, realizing the demodulation of vortex beam. In traditional optical communication systems, a hologram can only demodulate one incident vortex beam. In this paper, a vortex beam demodulation method based on composite diffraction hologram is proposed, which can demodulate several incident vortex beams with only one hologram. An experimental system is set up in this paper which achieves the generation, transmission and demodulation experiments of vortex beams with 64QAM-OFDM signals. After a series of offline processing on the demodulated Gaussian beam, constellation and bit error rates (BER) of each subcarrier for OFDM signals are acquired. The experimental results show that good system performance can be achieved with this method as the BERs of all subcarriers are under the FEC threshold. [ABSTRACT FROM AUTHOR]

This study presents a new method to develop a thin controllable retarder/modulator with spatial axial symmetry by rotating a freely suspended of 4-Cyano-4- n -pentylbiphenyl (5CB) and N -(4-methoxybenzylidene)-4-butylaniline (MBBA) liquid crystal films using mechanical method or as a liquid film motor. [ABSTRACT FROM AUTHOR]

The performance of radio over fiber (RoF) system with dual drive Mach Zehender modulator has been optimized against third order intermodulation distortion by using 120° hybrid coupler in transmission system. Signal to Noise Distortion ratio (SNDR) has been evaluated and a performance comparison is also drawn for the systems based on 90° and 120° hybrid coupler in both noise and intermodulation distortion dominant environment. The SNDR is efficiently improved by employing 120° hybrid coupler in noise dominant and intermodulation distortion dominant environment. An improvement of 4.86 dB is obtained in the maximum SNDR with 120° hybrid coupler is obtained over at 20 km optical fiber length compared with a 90° hybrid coupler based system. A significant reduction of third order intermodulation power at receiver has also been observed with 120° hybrid coupler. [ABSTRACT FROM AUTHOR]

This paper presents an analysis, simulation and comparison of the performance of Optical single sideband (OSSB) radio over fiber (RoF) system based on a dual drive Mach Zehender modulator (DD-MZM) using 90 o and 120 o hybrid coupler including the effects of phase noise from RF signal oscillator and laser source, input RF signal power and fiber dispersion. Signal to Noise ratio (SNR) is significantly influenced by phase noise from RF signal oscillator and input RF signal power. On comparison with conventional 90 o hybrid coupler system, the performance of the considered system improves by 5.64 and 0.67 dB in terms of SNR, when RF and laser phase noises are increased. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a spatial beam shaping method to achieve high-quality near-field for a high-power frequency tripling laser system by using a liquid crystal spatial light modulator (SLM). Considering the nonlinear relationship between the output 3 ω intensity and the input 1 ω intensity of the frequency conversion system and the transmittance nonuniformity of the whole laser system, we introduce an efficient spatial beam shaping method that improves the output near-field beam quality of frequency tripling laser dramatically. Results show that the near-field peak-to-mean value of the frequency tripling laser improves from 1.83:1 to 1.42:1 after spatial beam shaping within four shots. This method provides effective guidance for spatial beam shaping of high-power frequency tripling laser systems. [ABSTRACT FROM AUTHOR]

Liquid crystal on silicon (LCoS) spatial light modulators have been considered for a wide variety of scientific applications, due to their phase modulation capability and high spatial resolution. Nevertheless, their intrinsic characteristics, like the extensively studied depolarization and phase shift fluctuations, can make their behavior significantly distant from the ideal and somewhat unpredictable. Here, we present the characterization of a different source of uncertainty: the non-uniform spatial response of the LCoS, which is fundamentally different to the static aberrations of the panel. We measured local deviations of ±22% from the expected phase shift, resulting in non-negligible effects for phase modulation measurements, phase shifting interferometry, wavefront correction, and speckle interferometry. [ABSTRACT FROM AUTHOR]

In this paper, we present the experimental generation of Airy beams via computational and photorefractive holography. Experimental generation of Airy beams using conventional optical components presents several difficulties and a practically infeasible. Thus, the optical generation of Airy beams has been made from the optical reconstruction of a computer generated hologram implemented by a spatial light modulator. In the photorefractive holography technique, being used for the first time to our knowledge, the hologram of an Airy beam is constructed (recorded) and reconstructed (read) optically in a nonlinear photorefractive medium. The Airy beam experimental realization was made by a setup of computational and photorefractive holography using a photorefractive Bi 12 TiO 20 crystal as holographic recording medium. Airy beams and Airy beam arrays were obtained experimentally in accordance with the predicted theory; with excellent prospects for applications in optical trapping and optical communications systems. [ABSTRACT FROM AUTHOR]

Irradiance fluctuations of a pseudo Multi-Gaussian Schell Model beam propagating in the maritime environment is explored as a function of spatial light modulator cycling rate and estimated atmospheric turnover rate. Analysis of the data demonstrates a strong negative correlation between the scintillation index of received optical intensity and cycling speed for the estimated atmospheric turnover rate. [ABSTRACT FROM AUTHOR]

We propose and investigate a novel frequency shift keying (FSK) format for 40-Gb/s transmission system. In this paper, we present the generation, the dispersion compensation, the detection and the performance evaluation of the proposed FSK format. FSK signal is generated based on the bias voltages of a novel external FSK modulator, which is consisting of two LiNbO 3 Mach–Zehnder (MZ) modulators. By numerical simulation, the transmission performance and the different dispersion compensation schemes of the FSK signal are discussed. [ABSTRACT FROM AUTHOR]

A new photonic approach for triangular waveform generation by making full use of the polarization sensitive characteristic of the single-drive Mach–Zehnder modulator (MZM) is proposed and experimentally demonstrated. In this method, the MZM is biased at minimum transmission point and its best modulation axis has an angle with the polarization direction of injection continuous wave (CW). Due to the polarization dependent modulation efficiency of a MZM, the odd-order modulation sidebands can be generated on the parallel polarization component but only the optical carrier is presented on the orthogonal direction. After a polarizer, the required Fourier components can be projected on the same polarization direction, which contribute a triangular pulse stream by photodetection. In the experimental demonstration, triangular waveforms with repetition frequencies of 8, 10, and 12 GHz are successfully generated, respectively. [ABSTRACT FROM AUTHOR]

Photonic generation of arbitrary waveform microwave pulse with tunable carrier frequency and phase based on tunable optoelectronic oscillator (TOEO) and a dual-drive Mach–Zehnder modulator (DDMZM) is proposed. Utilizing the frequency tunability of TOEO, the carrier frequency of the microwave signal can be tuned by adjusting the wavelength of the tunable laser source (TLS) and the tunable range can be as large as tens of GHz. By controlling the signals applied to DDMZM, the generation of arbitrary waveform microwave pulse with tunable phase in the range of −180° to 180° is achieved. The proposed scheme can realize the integration of frequency tuning, phase tuning, pulse modulation and radar transmitted waveform generation in the optical domain, which provides a guarantee of transmitting high-quality microwave signal in radar systems. [ABSTRACT FROM AUTHOR]

By means of the variational approach, three classes of azimuthally modulated vortex solitons are constructed for the (2+1)-dimensional nonlinear Schrödinger equation with a type of transverse nonperiodic modulation. These solutions include numerical single layer azimuthal vortex solitons in the medium with Gaussian type modulation and analytical azimuthons in medium with the anharmonic potential. We present the results for two types of nonlinearities which are common in optical materials. The properties of vortex solitons, which are characteristic of the topological charge m , propagation constant k 0 , angular velocity ω and radial quantum number L , are studied. The numerical simulations are used to verify the propagation properties of these vortex solitons. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate a novel approach to realize tunable optical carrier-to-sideband ratio (OCSR) by introducing two radiofrequency (RF) signals with phase difference to drive a Mach-Zehnder modulator. Stimulated Brillouin scattering is adopted to remove the undesirable sideband, converting double sideband (DSB) to single sideband (SSB). By altering RF signal phase difference, wide ranges of OCSR from −23 to 44 dB and −21 to 44 dB are obtained for the DSB and SSB modulation, respectively. The operation frequency bandwidth covers from 5 to 42.3 GHz. The optimum OCSR to maximize the output RF power is also presented for the best transmission behavior. The proposed approach will be vital for optimizing the transmission performance by improving modulation efficiency and receiver sensitivity. [ABSTRACT FROM AUTHOR]

An optically controllable terahertz wave modulator based on the electromagnetically induced transparency-like effect (EIT-like) of the metamaterial structures is proposed and demonstrated. A modulation depth of 63% was measured at 0.33 THz in our study. The modulation action arises from the destructive interference between the resonators composed of high-resistivity silicon and gold resonators. Utilizing terahertz time domain spectrometer (THz-TDS), we show that the transmission properties of the structures can be tuned by an externally applied pump beam. By comparing the modulation depth with and without the structures producing EIT-like behavior, and the bare silicon's modulation depth, it is found that the modulation performance can be significantly improved with employment of EIT effect. Our study provides an alternative route to facilitate potential applications in terahertz range. [ABSTRACT FROM AUTHOR]

We report the measurement of a large optical reflection matrix (RM) of a highly disordered medium. Incident optical fields onto a turbid sample are controlled by a spatial light modulator, and the corresponding fields reflected from the sample are measured using full-field Michelson interferometry. The number of modes in the measured RM is set to exceed the number of resolvable modes in the scattering media. We successfully study the subtle intrinsic correlations in the RM which agrees with the theoretical prediction by the random-matrix theory when the effect of the limited numerical aperture on the eigenvalue distribution of the RM is taken into account. The possibility of the enhanced delivery of incident energy into scattering media is also examined from the eigenvalue distribution which promises efficient light therapeutic applications. [ABSTRACT FROM AUTHOR]

The Generalized Phase Contrast (GPC) method has been demonstrated to reshape light efficiently to match the input beam profile requirements of different illumination targets. A spatially coherent beam can be GPC-shaped into a variety of static and dynamic profiles to match e.g. fixed commercially available modulation systems or for more irregular and dynamic shapes such as found in advanced optogenetic light-excitations of neurons. In this work, we integrate a static GPC light shaper to illuminate a phase-only spatial light modulator encoding dynamic phase holograms. The GPC-enhanced phase-holograms are encoded to create reconfigurable spot arrays and arbitrary extended patterns. For a given laser power, our experimental results show a significant intensity gain in the resulting diffraction patterns when we illuminate the holograms with a GPC-shaped beam as compared to the more common practice of hard truncation. The phase flatness of the GPC-enhanced readout beam has also been investigated. [ABSTRACT FROM AUTHOR]

A novel linearized single-sideband modulator is proposed and demonstrated to generate optical single-sideband (OSSB) signal and improve the dynamic range of microwave photonic links. The modulator is composed of a dual-electrode Mach–Zehnder modulator (DEMZM) lying on the top branch and a phase shifter (PS) lying on the bottom branch. By optimizing the optical power split ratio of the linearized modulator and the phase shift of the PS, the third-order inter-modulation distortion (IMD3) can be efficiently suppressed while the second-order distortion components are eliminated simultaneously. It is a multi-octave linearization technique which can be applied for broadband systems. Simulation results show that, the linearized modulator can provide a spurious-free dynamic range (SFDR) of 130 dB for a bandwidth of 1 Hz at the received optical power of 2 dBm assuming shot noise is the dominant noise contribution, which is 22 dB higher than the conventional DEMZM. The effects of the finite extinction ratio of modulator, the phase deviation of PS and the dispersion of fiber on the linearization performance are also investigated. [ABSTRACT FROM AUTHOR]

We demonstrate large-contrast, low-crosstalk, low-power, and broadband spatial light modulators (SLMs) for operation at terahertz (THz) frequencies. The electro-thermally activated SLMs rely on the insulator–metal-phase transition of two VO 2 thin films deposited on opposite sides of a sapphire substrate. We validated the effectiveness of our approach by fabricating and testing 2×2 pixel SLM prototypes. Record high amplitude modulation depth of 96%, −30 dB pixel-to-pixel crosstalk and precise THz transmission control was determined for the fabricated SLMs over a broad range of THz frequencies. Raster scanning THz transmission revealed excellent pixel uniformity with very large on/off contrast. These attributes are fundamental for high-contrast THz imaging and spectroscopy applications. [ABSTRACT FROM AUTHOR]

We propose an optical multicarrier generation technique using silicon micro-ring modulator (MRM) and analyze the scheme. Numerical studies have been done for three types MRMs having different power coupling coefficients. The proposed scheme is found to generate four optical carriers having 12.5 GHz spacing. According to simulation, the maximum side-mode-suppression ratio (SMSR) of ~16.3 dB with flatness of ~0.2 dB is achieved by using this scheme. The minimum extinction ratio (ER) of the generated carriers is found to be more than 35 dB. We also propose modulator driver circuit to generate RF signal, which is needed to generate multicarrier using MRM. The effect of coupling coefficient on the SMSR of the generated carriers is also investigated. [ABSTRACT FROM AUTHOR]

We report an effective phase modulation for transverse magnetic (TM) waves in Mach–Zehnder modulators constructed by gain quantum well nanostructures on the basis of resonantly enhanced Pockels effect. The numerical results show that the optical gain coefficient is very large in the vicinity of the optical communication wavelength, and it is accessible to obtain a very large refractive index change of 10 −2 order of magnitude, and a very small voltage–length product for π phase shift with V π × L 0 = 0.156 V mm at the working wavelength λ = 1.55 μ m by a suitable bias electric field, which is over ten times less than the previous best report. These properties have a great potential for device application in high-performance and high-miniaturization electro-optical switches and phase modulators at the optical communication window. [ABSTRACT FROM AUTHOR]

A prototype of full-duplex wavelength-division-multiplexing-based radio-over-fiber (WDM-RoF) system using a single continuous wave (CW) laser at central station (CS) is proposed and investigated. In the proposal, the tunable optical frequency comb (OFC) generator is performed by cascading an electro-absorption modulator (EAM), a phase modulator (PM) and a Mach–Zehnder intensity modulator (IM). Then the proposed OFC is used as the source of WDM-RoF network. The base station (BS) is simplified by using central carrier along with downlink multi-frequency millimeter-wave signals (MMWs). In the scheme, we obtain 21 comb lines within 0.2 dB power deviation with an interval about 10 GHz. Then we apply it to a bidirectional 1:7 WDM-RoF cellular network. For the downlink, three MMWs with frequencies of 40 GHz, 60 GHz and 80 GHz are obtained. For the uplink, 7 WDM channels carrying upstream signal are converted simultaneously. Both down and uplink delivery over 20 km transmission with less than 1 dB power penalty, which shows high spectral-efficiency and good performance over long-distance delivery. [ABSTRACT FROM AUTHOR]

A novel single sideband (SSB) radio-over-fiber (ROF) system based on a dual-electrode dual-parallel Mach–Zehnder modulator (DE-DPMZM) is proposed, in which the Mach–Zehnder modulator (MZM) is used to produce a single sideband signal and the dual-parallel structure is used to suppress the third-order intermodulation distortion (IMD3) to improve the spurious-free dynamic range (SFDR) of the ROF system. A theoretical analysis is given and simulation experiment is carried out. The results show that the proposed scheme can improve 25 dB in SFDR which is up to 127.854 dB Hz 2 / 3 compared with the conventional SSB ROF system. In addition, the single sideband modulation can extend the transmission distance of optic signal. [ABSTRACT FROM AUTHOR]

Two modulator drivers in 0.25 μm SiGe:C BiCMOS, which are integrated each together with a Mach–Zehnder modulator for electro-optical modulation (optical C-band) are presented. The fully integrated modulator occupies an area of 12.3 mm 2 . Carrier depletion in reverse biased pn junctions is used to adjust the refractive index in both arms of the Mach–Zehnder modulator (dual-drive configuration). The first integrated driver has a low power consumption of 0.68 W but a high gain of S 21 =37 dB and delivers an inverted as well as a non-inverted output data signal between 0 V and 2.5 V (5 V pp differential). The driver circuit is supplied with 2.5 V and at the output stage with 3.5 V. Bit-error-ratio (BER) measurements with a pseudo-random-bit-sequence (PRBS 2 31 −1) resulted in a BER better than 10 −12 for input voltage differences down to 50 mV pp . A second adapted driver is supplied with 2.5 V and 4.2 V, consumes 0.87 W and delivers a differential data signal with 5.6 V pp having a gain of S 21 =40 dB. The fully integrated modulator achieved at an optical wavelength of 1540 nm and 10 Gb/s data rate an extinction ratio of 3.3 dB for a 1 mm long modulator ( V π L π ≈2 V cm) with driver variant 1 and 8.4 dB for a 2 mm long modulator with driver variant 2. [ABSTRACT FROM AUTHOR]

A programmable liquid crystal beam-shaping system was installed for a 200-mJ optical parametric chirped-pulse amplification (OPCPA) system front end and was applied to dramatically improve the beam uniformity in the subsequent amplifier. A highly nonuniform beam profile caused by gain inhomogeneity in the amplifier was pre-compensated by the beam shaping system using significantly improved open-loop and closed-loop algorithms. The details of the improved algorithms will be described. The issues of running a liquid crystal device with a high-energy, ultrashort-pulse laser, such as damage risk and temporal contrast degradation, will be addressed. [ABSTRACT FROM AUTHOR]

Abstract: The investigation of few-layer graphene embedded in silicon waveguide (GESW) exhibits it has a superior performance than monolayer GESW where the effective mode index variation ( ) at the given chemical potential change and the number of graphene layers N (N<5) shows in a linear relationship. The results from modal analysis show that the of quadri-layer GESW can be as large as 0.047, based on which a Mach–Zehnder modulator has been proposed with the advantages of only 16.5μm arm length, low energy consumption (8fJ/bit), high extinction ration (31.8dB) and small applied voltage (<1V). Furthermore, the working temperature of the proposed modulator can span in a large range from 300K to 400K and the modulation performance stays almost unchanged when the input wavelength varies from 1520nm to 1580nm. [Copyright &y& Elsevier]

Abstract: The modulated pyramid wavefront sensor is known for its high sensitivity and adjustable dynamic range. The need for mechanically moving parts in a modulated pyramid wavefront sensor can be overcome by using the recently proposed digital pyramid wavefront sensor. In this paper, a digital multi-faceted pyramid wavefront sensor is demonstrated with the use of a reflecting phase-only spatial light modulator. The four-pupil digital pyramid wavefront sensor with 4-facets is extended to 6 and 8-facets. It is noted from the experiments performed under identical low-noise conditions that the performance of the wavefront sensor in terms of the root mean square wavefront error remains nearly the same in cases of four, six and eight pupil configurations. Under the circumstances elucidated here, the results of simulations indicate that in the presence of scatter noise, the pyramid wavefront sensor with greater number of pupils could lead to an improvement over the standard four-pupil pyramid wavefront sensor. Noise from scattering makes the choice of optimal modulation radius critical while sensing in open-loop adaptive optics systems. [Copyright &y& Elsevier]

Abstract: By combining broadband common-path spectral interferometry with an iterative fitting algorithm the phase response of a liquid-crystal spatial light modulator has been characterized from 400 to 770nm, equivalent to a frequency bandwidth of 0.36PHz. The resulting calibration not only maps the response of the device as a function of wavelength and voltage, but also provides sufficient information to recover the thickness of the liquid-crystal cell and the wavelength dependent refractive index of the liquid-crystal. The technique has applications in amplitude and phase shaping of pulses from broadband super-continuum and optical parametric oscillator/amplifier sources. [Copyright &y& Elsevier]

Abstract: A simple scheme for the ultra-wideband (UWB) pulse generation based on a phase modulator and programmable filter is proposed and experimentally demonstrated. By locating the center wavelength of two tunable lasers at left and right linear slope of the filter, polarity-reversed monocycle pluses are generated. A section of single mode fiber is utilized to introduce proper time delay between the pair of UWB monocycle pulses. By switching the programmable filter between bandpass filter and notch filter, positive and negative doublet pulse can be obtained additionally. The generated UWB pulses are measured in both time and frequency domain. [Copyright &y& Elsevier]

Abstract: We propose and demonstrate a novel and cost efficient method to generating a frequency quadrupling optoelectronic oscillator (OEO) using a single polarization modulator (PolM) in a Sagnac loop. The OEO loop and the Sagnac loop share the same PolM. In the OEO loop, the PolM is used to generate the fundamental microwave signal. In the Sagnac loop, the joint use of the PolM, a polarization controller (PC), and a polarization beam splitter (PBS) is equivalent to an intensity modulator. The odd order sidebands of the modulated signal are suppressed by biasing the equivalent intensity modulator at the maximum transmission point. Moreover, the undesired optical carrier is also eliminated by bidirectional use of the PolM. As a result, only the two second order sidebands are left. The beating between the two second order sidebands in a photodetector (PD) generates a microwave signal at the frequency corresponding to four times of the fundamental tone. A frequency quadrupling microwave signal at the frequency of 39.74GHz with a phase noise of −100.14dBc/Hz at 10kHz frequency offset was experimentally generated. [Copyright &y& Elsevier]

Abstract: We propose an approach by reducing the distortion to signal ratio (DSR) of Mach–Zehnder modulator (MZM) to improve the bit error rate (BER) performance in intensity modulated and direct detected (IM/DD) optical orthogonal frequency division multiplexing (OOFDM) system. The DSR of the MZM, which is a measurement of nonlinear distortions induced by MZM, can be correctly evaluated by building an equivalent polynomial model, and then minimized with partial transmit sequence (PTS) technique without over-sampling. Experimental results demonstrate that compared to the original scheme and peak to average power ratio (PAPR) reduction with PTS scheme, the improvement of the receive sensitivity by the proposed scheme is 2.8dB and 1.2dB, respectively, at the BER of 1×10−3 after transmission over 100km standard single-mode fiber. The theory analysis also shows the proposed scheme can reduce computational complexity significantly compared to the PAPR-PTS scheme. [Copyright &y& Elsevier]

Abstract: Longitudinal electric field illumination is greatly effective for enhancing the local electric field and Raman signal at the tip apex in tip-enhanced Raman spectroscopy (TERS). In this work, the optical field distribution of tightly focused radially polarized (RP) beam on the focal plane is calculated according to vector diffraction theory and the effectiveness of longitudinal field excitation on Raman signal enhancement is experimentally verified. An RP beam generated by a liquid crystal spatial light modulator is focused via a high numerical-aperture objective lens to form a strong longitudinal electric field at the focus. The focused field is utilized to excite single-walled nanotubes sample in TERS experiments. The experimental results demonstrate that the enhancement factor of RP excitation is obviously higher compared with linearly polarized illumination. And then, the corresponding TERS mapping and topography are simultaneously characterized. [Copyright &y& Elsevier]

Abstract: A novel approach to generating ultra-wideband (UWB) impulses based on a Mach–Zehnder modulator (MZM) and a Fabry–Pérot semiconductor optical amplifier (FP-SOA) is proposed and demonstrated. Both the carrier dynamic behavior of SOA and the feedback of FP cavity are exploited to generate a pair of polarity-reversed doublet-like impulses. Simulations and experiments are carried out to verify the UWB generation. In the experiment, the fractional bandwidths of the negative-doublet-like and the positive-doublet-like impulses are 100% and 108%, respectively. The bit error rate (BER) performance of the UWB before and after a span of 19-km standard single mode fiber (SSMF) transmission is also investigated and error-free performance can be achieved for each condition. Finally the UWB wireless transmission over a span of 10cm is investigated. [Copyright &y& Elsevier]

The modulating retro-reflector (MRR) communication is developed to solve the problem of insufficient terminal power in underwater optical communication (UOC) where size, weight and power are severely restricted. Here, we propose a new MRR link scheme using the optical orbital angular momentum (OAM) for such scenarios to realize high-order coding. Furthermore, we simulate the OAM MRR link in the oceanic turbulence channel and use the convolutional neural network (CNN) to classify OAM patterns. The simulation results show that the OAM MRR link can realize error-free image transmission under weak turbulence strength of C n 2 = 1 0 − 15 K 2 m − 2 / 3 within 15 m distance using 8/16-ary OAM superposed modes, and with the increasing of the distance and the turbulence strength, the performance is decreasing, where the 16-ary format has a higher coding efficiency but lower performance than the 8-ary format. An experiment of the OAM MRR link using CNN to classify 16-ary OAM superposed modes is also demonstrated, where two space light modulators (SLMs) are used to simulate the short-distance oceanic turbulence channel and modulate the OAM beam, respectively. Our experiment result shows the recognition rate of 16-ary OAM set with different types of channel conditions. Our work may provide a novel way for high-order coding MRR links in underwater channels and hopefully increase the data rate of the MRR link in the future. • A new modulating retro-reflector (MRR) link scheme using the optical orbital angular momentum (OAM) is proposed. • We simulate the OAM MRR link in the ocean turbulent channel and use the convolutional neural network (CNN) to classify OAM patterns, which can realize error-free image transmission under weak turbulence strength of C n 2 = 1 0 − 15 K 2 m − 2 / 3 within 15 m distance using 8/16-ary OAM superposed modes. • An experiment of the OAM MRR link using CNN to classify 16-ary OAM superposed modes is also demonstrated, where two space light modulators (SLMs) are used to simulate the short-distance ocean turbulence channel and modulate the OAM beam, respectively. • Our work may provide a novel way for high-order coding MRR links in underwater channels and hopefully increase the data rate of the MRR link in the future. [ABSTRACT FROM AUTHOR]

Abstract: A novel and simple remote up conversion (RUC) scheme is proposed to provide wired service and 60GHz dispersion-robust wireless service in a radio-over-fiber (RoF) system based on electrical tones injection (ETI). According to our knowledge, the RUC scheme with only one modulator is proposed for the first time. The ETI is utilized to simplify the traditional RUC scheme by simultaneously using one modulator for both the modulation of baseband data millimeter wave. Moreover, such scheme can provide both wired and wireless service without any additional device. Experimental results show that 2.5Gbps wired service and 2.5Gbps wireless service at 60GHz are successfully delivered over 50km SMF with power penalty less than 0.3dB. [Copyright &y& Elsevier]