Single-crystal modifications of the Mach-Zehnder electro-optic modulator

Two single-crystal modifications of the Mach-Zehnder electro-optic modulator are described. Preliminary theoretical estimates show that these variants are capable of ensuring the amplitude modulation of laser beams with elevated power (no less than several watts) at frequencies up to 4 GHz. The obtained modulation characteristics show that the modulation depth in the proposed devices reaches 50–80% and a half-wave voltage of these devices amounts to 100–160 V.     

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.     

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.     

Analysis and optimum design of a polymer Y-fed coupler electro-optic switch using double-section reversed electrodes

A packaged polymer electro-optic switch using double-section reversed electrodes based on the Y-fed coupler structure is investigated in terms of the conformal transforming method, image method, coupled mode theory and electro-optic modulation theory. The structure and principle are described, and unique formulations are proposed for simulating the device, including the amplitude transfer matrix, propagation powers and output powers. Design and optimization are performed, and characteristics are analyzed. Under the central operation wavelength of 1550 nm, the coupling region length is 4391.5 µm, the driving voltages of the upper and lower branches are as low as +0.633 and ?0.633 V, respectively; the insertion loss and crosstalk are less than 2.04 and ?30 dB, respectively, within the relative large ranges of fabrication error and wavelength shift. The proposed analysis and formulations are proved to be sufficiently accurate by comparison with the beam propagation method (BPM). The designed switch with the above waveguide and electrode structure shows lower switching voltage compared to our previous reported switches.     

Efficient Single-Mode GaAs/AlGaAs W Waveguide Phase Modulator with a Low Propagation Loss

We report a single-mode P-P-p-i-n-N-N GaAs/AlGaAs W waveguide phase modulator with a high phase modulation efficiency and a low propagation loss. The phase modulator with a W-shaped refractive-index profile utilizes a novel epilayer structure to reduce the propagation loss associated with doped layers and to obtain a phase modulation efficiency larger than those of P-i-N double heterostructure modulators. The phase shift and propagation loss were measured with a Fabry-Perot resonance method at 1.31-mum wavelength. A phase modulation efficiency as high as 34.6 degrees /V mm was measured for TE polarized light. Also propagation losses of less than 0.6 dB/cm were achieved. As a result, the W waveguide phase modulator that exhibits a high phase modulation efficiency and a low propagation loss have been experimentally realized for the first time as far as we know.     

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.     

Design and analysis of a phase modulator based on a metal-polymer-silicon hybrid plasmonic waveguide

A plasmonic-hybrid-waveguide-based optical phase modulator is proposed and analyzed. The field enhancement in the low-index high-nonlinear polymer layer provides nanoscale optical confinement and a fast optical modulation speed. At 2.5 V drive voltage, a π phase shift can be obtained for a 13-μm-long plasmonic waveguide. Because of its small capacitance and parasitic resistance, the modulation bandwidth can reach up to 100 GHz with a low power consumption of ～9 fJ/bit. The plasmonic waveguide is connected to a silicon wire waveguide via an adiabatic taper with a coupling efficiency of ～91%. The phase modulator can find potential applications in optical telecommunication and interconnects.     

Linear electro-optic effect in the organic crystal 4-aminobenzophenone

The linear electro-optic effect in single crystals of 4-aminobenzphenone (ABP) is reported together with calibration data on LiNbO(3). For ABP the linear electro-optic coefficients r(22) and r(32) at 488 nm were found to be 2.12 and 5.05 pm/V, respectively, with the corresponding reduced half-wave voltages being 49.4 +/- 0.1 and 9.3 +/- 0.1 kV. For LiNbO(3) the half-wave voltage was found to be 4.0 +/- 0.1 kV at 632.8 nm and 2.4 +/- 0.1 kV at 488 nm.     

Quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics under both DC and AC bias

The basic quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) transparent ceramics have been studied under both DC and AC electric field bias. The contribution of piezoelectric resonance to electro-optic effect for this quadratic electro-optic ceramics material has been experimentally demonstrated and theoretically analyzed. It is found that, at the piezoelectric resonance frequencies, the piezoelectric induced electro-optic effect dominates and leads to a dramatically high sensitivity for weak electric signal detection. About 20 dB signal-to-noise ratio is attained when detecting AC electric field strength of 1 V/m with optimized DC bias. Besides, the effects of AC frequency and amplitude on halfwave voltage V(π) of PMN-PT are investigated.     

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).     

Design of integrated 1×2, 1×4 low driving voltage polymer electro-optic switches based on Y-fed directional couplers

Two integrated 1 × 2 and 1 × 4 polymer electro-optic switches based on Y-fed directional couplers are designed and optimized in terms of the coupled mode theory, electro-optic modulation theory, conformal transforming method and image method. The principle of the 1 × 2 electro-optic switch is described. Parameters including the core size, buffer layer thickness, electrode thickness, electrode width and electrode gap are optimized. Simulation results show that the length of the designed 1 × 2 switch is about 3.126 mm, the driving voltages of the two branches are as low as 0.891 and ?0.891 V, respectively, the crosstalk and insertion loss are less than ?30 and 1.42 dB, respectively, within the operation wavelength from 1527 to 1574 nm. Under the same driving voltages, the 1 × 4 optical switch with a total length of less than 7 mm can be switched by altering the voltages applied on the electrodes of the three Y-fed directional couplers. Simulation results from the beam propagation method (BPM) indicate that the two designed devices exhibit favorable switching functions.     

Linearized electro-optic modulators based on a two-section Y-fed directional coupler

We experimentally demonstrate a linearized Y-fed directional coupler (DC) modulator based on an electro-optic (EO) polymer waveguide. The spurious free dynamic range of 119 dB/Hz2/3, which is 11 dB higher than that of the conventional Mach-Zehnder modulator, is achieved by introducing the reversed Δβ technique in the two-section Y-fed DC. The in-device EO coefficient (r33) of the fabricated device is as high as 79 pm/V in 1.55 μm wavelength, which is 88% of a single film r33 of LPD-80/APC.     

Simulation of cross-talk reduction in multimode waveguide-based micro-optical switching systems by use of single-mode filters

We propose a method to reduce cross talk by using single-mode filters, namely, extracting the fundamental mode from a multimode optical network (EFMON). The EFMON effect is evaluated for a three-step switching system consisting of cascade electro-optic (EO) waveguide prism deflector (WPD) micro-optical switches (MOSs) and a multimode waveguide network. The WPD MOS is optimized for single-mode operation in lead lanthanum zirconate titanate thin films as EO slab waveguides with a driving voltage of 12 V, a length of 310 microm, and a channel distance of 20 microm. Beam propagation method simulation reveals that mode disturbance, higher-order modes, and cross talk are accumulated by switching steps. A single-mode filter for EFMON in the output region of the switching system reduces cross talk to below -20 dB at a propagation length of 2000 microm in the single-mode filter and below -30 dB at 20000 microm.     

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.     

All-optical modulation with anomalous photovoltaic film on a Ti:LiNbO(3) waveguide modulator

An anomalous photovoltaic film formed by simultaneous oblique sputter deposition of CdTe and CdS from different directions was integrated onto LiNbO(3) and combined with a Mach-Zehnder-type interferometric waveguide modulator. Irradiation by 830-nm laser light with low intensity near 1 mW of the photovoltaic film induced anomalous photovoltages of ~5 V, which is as high as the half-wave voltage. This photovoltage was used to control the signal light in the waveguide. Modulation by external light was demonstrated with a response time of 0.1 s. Because of the presence of CdS with a photoconductive effect, the response time was much faster than that of conventional anomalous photovoltaic films formed by oblique deposition of CdTe.     

The enhanced phase modulation ability of optical modulator based on bi-layer graphene-silicon waveguide

We demonstrate that by inserting bi-layer graphene inside silicon waveguide, the modulation ability of the overall waveguide can be greatly enhanced. Moreover, the modulation ability of the waveguide remains stable under the variations of the temperature and the wavelength of the incident light. A Mach–Zehnder modulator based on this structure is proposed and the calculated results show that the modulator exhibits an excellent performance in terms of short length arm (7 μm), low energy consumption (8 fJ/bit) and high extinction ratio (31 dB). Besides, it requires low applied voltage and can be compatible with CMOS technology.     

光电集成加速度地震检波器中声光波导相位调制器的设计与实验

提出了一种新型的光电集成加速度地震检波器,这是一种全新的微光机电系统(MOEMS),为实现硅基底上的光波导M-Z干涉仪的相位调制,采用了声光相位调制的方法,该相位调制器利用叉指换能器(IDT)激发出声表面波(SAW)实现对光波导的相位调制,在对光波导声光相位调制机理深入研究的基础上,设计并制作了器件,实验结果与理论相一致。     

Tunable power splitter based on an electro-optic multimode interference device

Power splitters based on multimode interference (MMI) devices that offer the possibility of dynamically tuning the power-splitting ratio using electro-optic (EO) polymers are presented. The so-called 1 x 2 electro-optic MMI (EO-MMI) is demonstrated to provide a tuning range of 6 dB at approximately 54 V as theoretically predicted. Also a method is discussed to reduce the driving voltage by generating multiple beats, which provide 15 V for a tunable range of 10 dB for r(33)=15 pm/V at wavelength 1.55 microm.     

Low frequency linear electro-optic effect in PbTa2O6

The transverse linear electro-optic coefficients of PbTa₂O₆ crystals, grown from solution in Pb₂V₂O₇, have been measured. A half-wave voltage of 600 V applied along the [010] axis, has been determined.     

Microwave characteristics of polymer electro-optic modulators

The finite difference method is employed for the Laplace equation to calculate the microwave properties of polymer-based electro-optic modulators. The finite difference scheme uses a nonequidistant grid for fast calculation of the mode index and characteristic impedance of an open micro striplike modulator with a thick electrode as well as for a shielded micro striplike structure. It is demonstrated that the finite thickness of the electrode must be taken into consideration when optimizing the design of an electro-optic modulator. It is shown that by using a shielded microstrip configuration the modulator may be optimized and simultaneously pacified with regard to environmental influence.