Fabrication and analysis of a low-loss in-fiber active polymer waveguide

We present a method for fabricating an in-fiber electro-optic polymer waveguide within a D-shaped optical fiber. A combined process of selective chemical etching and spin coating creates a 2-cm in-fiber poly(methyl methacrylate)-DR1 dye polymer waveguide section with an overall insertion loss of micro 1.6 dB at 1550 nm. Numerical simulations show that, for in-fiber polymer waveguides to have low loss, the polymer layer's thickness must be kept below a certain value so that it will not support slab waveguide modes. Long transition regions between the unetched fiber and the polymer waveguide section also reduce loss. We analyze the efficiency of an in-fiber polymer waveguide by simulating its theoretical performance as an electro-optic modulator.     

High-Contrast Spatial Light Modulator by use of the Electroabsorption and the Electro-Optic Effects in a GaAs Single Crystal

A new spatial light modulator that uses the electroabsorption and the electro-optic effects in a GaAs single crystal is proposed. The device has the same structure as a Pockels readout optical modulator and can be operated at a frame rate higher than 500 Hz. When the electroabsorption and the electro-optic effects are combined, the dynamic range (contrast ratio) becomes larger than that which results when either effect is used singly. It was experimentally confirmed that the modulator has a high contrast ratio (greater than 2000:1), high sensitivity, and consequently large gamma characteristics.     

Optical stress sensor based on electro-optic compensation for photoelastic birefringence in a single crystal

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3?m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement.     

100-megabit-per-second resonant-cavity phase modulator for coherent optical communications

A resonant-cavity electro-optic phase modulator is designed, implemented, and experimentally verified to operate at a data rate of 100 Mbits/s. The cavity is made up of a highly reflective backmirror and the partially reflective end of an electro-optic crystal. A voltage signal applied to the electro-optic crystal erturbs the effective optical path length inside the cavity and hence its resonance frequency. Because the phase of the reflected optical signal from the cavity is highly dispersive when the cavity is tuned near resonance, a cw incident signal will experience a large phase shift as the cavity is electro-optically tuned on and off resonance. This phase-dispersion effect can be used in the construction of an optical phase modulator capable of modulating the signal at data rate in excess of 100 Mbits/s. The performance of the modulator was measured by first heterodyne detecting the signal to an intermediate frequency andthen measuring the spectral characteristics with a radio frequency spectrum analyzer. The measured phase shift is shown to be in good agreement with theoretical predictions.     

Theory of the basic optoelectronic behavior of a tunnel diode

The basic behavior of a tunnel diode when it is used as an optoelectronic device is presented. It is shown that a tunnel diode can be used as an electro-optic modulator, as a device that exhibits self-induced transparency, or as a wavelength converter (for both upconversion and downconversion). The tunnel diode has optical bistability even if it is not placed inside a Fabry-Perot resonator. Numerical estimations are made for some of the parameters of interest for an optoelectronic device and are compared with those of other existing semiconductor-based optoelectronic devices. As the numerical estimates show, a tunnel diode can be a highly efficient optoelectronic device with an extremely wide area of application.     

极化聚合物薄膜电光系数的实时测量

提出了一种极化聚合物薄膜电光系数的实时测量方法。实验结构由耦合棱镜和依次制备在棱镜底面的四层薄膜组成,这四层薄膜分别是金属层（作为上电极）、极化聚合物,缓冲层和下电极。包含导波共振角并具有一定角度的入射光线会聚于棱镜底面,然后用CCD探测拍摄反射光斑,当外加电场作用于上下电极时,就可从光斑暗线位置的变化测量极化聚合物薄膜的电光系数。在测量过程中,使用了计算机图像处理方法和光学空间滤波技术。     

Characterization of the phase modulation property of a free-space electro-optic modulator by interframe intensity correlation matrix

Characterization of a phase modulator or phase shifter has always been an integral part of phase-modulating or phase-adjusting applications. We propose a simplified approach to characterize a phase modulator by investigating the performance of phase shifts from grabbed interferograms using the phase extraction method. After reviewing some phase analysis techniques, the interframe intensity correlation (IIC) matrix method is introduced to the investigation. The proposed strategy is illustrated by the measurement of a free-space electro-optic modulator (EOM). Placing the modulator in one arm of a Michelson interferometer, the global phase shifts are estimated by the IIC method from the phase-stepped interferograms. Experimental results demonstrate the tested EOM has a phase modulation response of at least 2π rad with a π/20 rad modulation precision for λ=1064 nm. In addition, our method is applicable to various types of phase modulator or phase shifter calibration, e.g., electro-optic phase modulator, spatial light modulator, or piezoelectric transducer (PZT).     

衰减全反射结构的双通道聚合物电光调制器

近年来,反射结构的电光调制器由于其特殊性质,已引起了人们的极大兴趣。提出一种双通道衰减全反射电光调制器,该调制器含有两对电极,当两束光以一定的角度平行入射棱镜底面时,两束反射光的强度就会被加于两对电极上的电信号分别调制,这样在一个棱镜上可实现两束光信号的同时调制。     

Electro-optic polymer light modulator based on surface plasmon resonance

The first experimental results, to our knowledge, for an optical modulator that makes use of an electro-optic polymer located between two thin silver films are presented. The methods used to fabricate the modulator are discussed. Initial results show 18.5% modulation in the intensity of the light reflected off of the modulator at a wavelength of 6328 ?.     

Electro-optic modulation in an anisotropic artificial Kerr medium

We describe the performance of intensity and phase modulators that use an aqueous suspension of polytetrafluoroethylene (PTFE) microparticles. In this medium, the electro-optic effect is caused by the reorientation of anisotropic microparticles in an applied electric field. The intensity modulator was constructed in the Kerr geometry by the use of a sample path length of 20 μm. The response time of the modulator is less than 25 ms, and the depth of modulation was measured to be 28 dB for a switching voltage of 134 V(rms). The switching voltage necessary to achieve a π-phase shift with the phase modulator is less than 30 (Vrms).     

Time-resolved fluorescence-decay measurement and analysis on single cells by flow cytometry

A novel method is described for the measurement and analysis of fluorescence decays of individual cells and particles in flow. It combines the rapid measurement capabilities of a flow cytometer and the robust measurement and analysis procedures of time-domain fluorescence-lifetime spectroscopy. For excitation we use a cw laser that is pulse modulated by an electro-optic modulator. The characteristics and the repetition rate of the excitation pulses can be easily adjusted to accommodate fluorescence decays with a wide range of lifetimes.     

Large-area Fabry-Perot modulator based on electro-optic polymers

We present a large-area electro-optic Fabry-Perot modulator utilizing a photoaddressable bis-azo polymer placed between two dielectric mirrors with an open aperture of 2 cm. A modulation efficiency of 1% at an effective modulation voltage of 20 V for a wavelength of 1.55 microm is demonstrated. By comparing distance tuning of the cavity with wavelength tuning, an effective electro-optic coefficient of -7 pm/V is measured.     

Athermal design for the potassium titanyl phosphate electro-optical modulator

An athermal design for the KTP electro-optical modulator is presented. By using the wave coupling theory of linear electro-optic effect and taking account of thermal expansion, the more accurate athermal static phase retardation (ASPR) directions in potassium titanyl phosphate (KTP) are found, and the optimized design for a transverse amplitude modulator at ASPR orientation is obtained. The numerical results show that the modulator with an athermal Soleil-Babinet compensator is of excellent thermal stability, and the acceptable error of the ASPR direction is less than 0.1 degrees.     

Theoretical and experimental studies of polarization mode dispersion of an electro-optic Mach-Zehnder modulator

A theoretical model is developed to study the polarization mode dispersion effect in an electro-optic Mach-Zehnder interferometric (MZI) modulator. The Stokes parameters and differential group delay (DGD) of the output light of a MZI modulator can be analytically derived with the proposed model, which is based on a three-dimensional Maxwell's wave equation approach. The theoretical model is validated to the extent possible by comparing the theoretical results of the Stokes parameters and DGD with experimental measurements that are based on the wavelength-scanning method and the Jones matrix eigenanalysis method.     

Acoustic vibrations in integrated electro-optic modulators on substrates of lithium niobate

The processes of the excitation of acoustic vibrations and their influence on the optical signals in integrated electro-optic modulators on substrates of lithium niobate have been investigated. The resonant frequencies of the excitation of substrate vibrational modes have been determined. It has been shown that acoustic vibrations can make a significant contribution to the modulator transfer characteristic at frequencies up to several hundred megahertz, which should be taken into account when using the modulators at low frequencies, for example, as a part of fiber-optic sensors.     

Ferroelectric liquid-crystal waveguide modulation based on a switchable uniaxial-uniaxial interface

Liquid crystals have effective electro-optic coefficients that are orders of magnitude larger than other integrated optical materials such as lithium niobate. However, previous studies of liquid-crystal waveguides have mainly focused on nematic liquid crystals, which exhibit impractically large scattering losses as waveguides. Studies of smectic liquid crystals and liquid crystals under strong confinement suggest the losses in these materials may be more manageable. In this study, the possibility of using ferroelectric liquid crystals in active waveguide modulators is explored through the analysis of several modulator configurations: a cutoff modulator, a deflection modulator, and an input coupler. As a way to study these structures, a mode-matching technique was developed to analyze the effects of a discontinuity in a uniaxial slab waveguide whose optic axis is in the plane of the waveguide. The results from the mode-matching technique were compared with those from simple bulk models. The analysis shows that ferroelectric liquid-crystal modulators have many desirable performance characteristics and could form the basis for practical waveguide modulators.     

Electro-optic heterodyne interferometer

We propose a new configuration for using a triangle-wave signal to drive the electro-optic modulator in an electro-optic heterodyne interferometer system. The new configuration is adapted to measure the phase retardation of a wave plate and the optical rotation angle of a chiral medium. By adding optic elements, the second-harmonic component amplitude of the interferometer photodetector output signal became proportional to the phase retardation or optical rotation angle of the samples being tested.     

Time-division multiplexing of large serial fiber-optic Bragg grating sensor arrays

Time-division multiplexing is a promising method for the interrogation of fiber-optic Bragg grating sensors arrays for measurement of strain and temperature. We examine the performance of these systems to determine the parameters for high-sensitivity, low-cross-talk operation. It is shown that the performance can be greatly improved by use of a short time resolution in the demultiplexing process. We propose a new method of demultiplexing with an electro-optic modulator to read out the sensor pulses by gating the signal with 400-ps resolution. The system is demonstrated experimentally to provide 0.15-muepsilon/ radicalHz strain resolution in a 50-Hz bandwidth within a full-scale range of 8000 muepsilon. The system parameters are capable of handling at least 50 time-addressed sensors on a single fiber.     

Velocity matching of a GaAs electro-optic modulator

New designs for the velocity matching of a deep-etched semiconductor electro-optic modulator are presented. A tantalum pentoxide (Ta2O5) coating is considered here for achieving velocity matching between the microwave and the optical signals. The effects of the velocity mismatch, the conductor loss, the dielectric loss, and the impedance mismatch are studied in relation to the optical bandwidth of a high-speed semiconductor modulator. It is shown that both the dielectric loss and the impedance matching play key roles for velocity-matched high-speed modulators with low conductor loss. The effects of Ta2O5 thickness on the overall bandwidth and on the half-wave voltage-length product VpiL are also reported.     

铌酸锂光纤型行波调制器研究

以LiNbO3光纤作为通光部分,Si2N2O为衬底分别取代了传统波导电光调制器的中Ti:LiNbO3波导和铌酸锂衬底设计了带宽为95.49 GHz铌酸锂光纤型调制器.今利用有限元法分析SCPS电极结构下该铌酸锂光纤调制器的性能.研究结果表明,该新型调制器可以在很宽的频带内实现调制速度的匹配和阻抗匹配,半波驱动电压为2.56 V,特性阻抗为55.3Ω.