Optical time-division multiplexing signal processing using electro-optic modulators

We present some optical signal processing methods for optical time-division multiplexing, based on electro-optic modulators. Dual-parallel Mach–Zehnder modulator and time-lens-based signal processing for optical frequency comb generation, optical Nyquist pulse generation and time-domain demultiplexing are realized. Multifunctional optoelectronic oscillators which are capable of performing simultaneous electrical clock recovery, optical clock recovery and demultiplexing are demonstrated with modulators embedded as the key components.     

High-speed electro-optic analogue-digital conversion

An experimental electro-optic analogue-digital convertor based on a diffraction modulator is described to illustrate the principle that direct analogue-digital conversion can be performed at high speeds with electro-optic devices.     

Optimisation of electro-optic crystal modulators

A general method is given for the optimum design of electro-optic light modulators in respect of minimum halfwave voltage for crystals of any class. Examples are given for materials of class 42m (XDP).     

Temperature tuning of LiNbO3 electro-optic waveguide TE/TM mode convertors

A novel temperature tuning technique for LiNbO3 electro-optic waveguide mode convertors is described. Operation of both X- and Z-cut LiNbO3 devices with greater than 99% conversion efficiency at the fixed wavelength of 1.52 ?m is reported and tuning rates of ?0.9 nm°C?1 and ?1.0 nm°C?1, respectively, demonstrated.     

Floating-impedance convertors using current conveyors

A floating-negative-impedance convertor and a generalised impedance convertor are described. The circuits use a practical realisation of the CCII+ type current conveyor, the design being based on a differential input/output transadmittance cell.     

Limitations of zinc sulphide leaky waveguide electro-optic modulators

Design criteria for relative-phase optical-waveguide modulators are established for single-crystal thin films of zinc sulphide grown on silicon. It is found that the minimum guide length is limited by voltage breakdown to 2 mm while for high frequency applications, because of the leaky nature of the guiding region, the maximum available length and thickness of zinc sulphide are the limiting factors.     

High-speed electrooptic phase modulators using InGaAs/InAlAsmultiple quantum well waveguides

High-speed phase modulation of waveguided InGaAs/InAlAs multiple-quantum-well optical modulators operating at 1.55 μm is described. The modulator requires a low voltage for π-phase-shift ( V_π=2.5 V) as well as a small intensity modulation depth of 1 dB. The measured electrical 3-dB bandwidth is 10 GHz, giving a bandwidth-to-voltage ratio of 4 GHz/V     

Electrooptic light modulators

The field of electrooptic light modulation by means of the Pockels and Kerr effects in crystals is summarized with particular attention to communications applications using the optical maser. AH available data on electrooptic materials are tabulated, and design considerations and operating principles for various modulator configurations are outlined.     

Spatial light modulators

Near real-time reusable spatial light modulators for coherent optical data processing are reviewed. The PROM, liquid crystal, and electron beam addressed DKDP and oil film light valves appear to be the most promising devices for coherent optical data processing.     

聚合物波导电光调制器阵列的研究及其应用

基于衰减全反射结构,提出了一种聚合物电光调制器阵列,该调制器含有多对电极,且多对电极可同时极化并可以独立工作.目前我们已在实验室成功制备了双通道聚合物波导电光调制器,并利用此调制器实现两路视频信号的同时调制.     

High-speed power-efficient indoor wireless infrared communication using code combining .II

For pt.I see ibid., vol.50, no.7, p.1098-1109 (2002). We examine an infrared link composed of a multibeam transmitter and a direction-diversity receiver, employing code combining. The latter represents an added dimension to the conventional diversity concepts, which are limited to combining the individual received symbols. Rate-compatible punctured convolutional codes are used to encode intensity-modulated on-off keying (OOK) optical power, to create an adaptive environment for efficient utilization of channel spectral bandwidth, to provide a means for accurate channel estimation, and to maintain a guaranteed bit error rate (BER) performance at all receiver positions. It is shown that a BER not exceeding 10/sup -9/ with 99% probability can be achieved at bit rates up to a few hundreds of megabits per second, at very low transmitted power levels.     

High-speed power-efficient indoor wireless infrared communication using code combining .I

While use of power-efficient signaling schemes appears to be effective at compensating for the inherent high path-loss associated with pure diffuse infrared links, it begins to lose its effectiveness as the data rate is increased. At very high data rates, intersymbol interference (ISI) can result in a very high and sometimes irreducible power penalty, preventing the system from operating at a low bit-error probability. We use a link design employing a multibeam transmitter in conjunction with a narrow field-of-view (FOV) direction diversity receiver. The design goal is to eliminate the effect of ISI so that power-efficient signaling schemes such as pulse-position modulation (PPM) can be employed at very high data rates. We also use high-rate Reed-Solomon codes to further increase the power efficiency of PPM signals. The proposed system can be made rate-adaptive through varying modulation level L and/or code rate R without increasing the complexity significantly. This provides a dynamic range large enough to allow efficient utilization of available bandwidth, i.e., to allow portable terminals to communicate at their highest permitted data rate, without sacrificing the quality of service. It is shown that a bit error rate not exceeding 10/sup -9/ can be achieved within the link coverage area with 99% probability at bit rates up to a few hundreds of megabits per second, using transmitted power levels well below 1 W.     

Picosecond signal sampling and multiplication by using integrated tandem light modulators

A picosecond signal sampling experiment was performed successfully by using integrated optic technologies. Two interferometric modulators of the traveling-wave and lumped types were integrated in series on a LiNbO3crystal surface. The traveling-wave modulator was oprated as a sampling gate activated by an electrical pulse train of 1-GHz repetition from a comb generator, while the lumped one was driven by a 2-GHz CW signal. The aperture time of the gate was estimated about 52 ps from the measurement using the image tube streak camera modified to sinusoidal scan at 1 GHz. Also a signal multiplication experiment was carried out using 100- and 10-MHz CW signals.     

Integration of GaAS MESFET drivers with GaAs directional-coupler electro-optic modulators

We demonstrate the first integration of active electronic devices with semiconductor waveguide modulators. By combining ion-implanted GaAs MESFET amplifiers with directional-coupler electro-optic modulators, the DC drive voltage has been reduced by a factor of ?v = 9, making an effective electro-optic figure-of-merit ?vn3r41 for GaAs superior to that of LiNbO3     

High-speed electroabsorption modulators buried with ruthenium-doped SI-InP

InGaAlAs-InAlAs electroabsorption modulators are successfully fabricated using ruthenium (Ru)-doped semi-insulating (SI)-InP burying technology. A comparison of measured and calculated microwave characteristics reveals that there is no additional microwave loss because zinc diffusion is inhibited by the use of Ru-doped SI-InP layers. A small-signal electrooptical response with a -3-dB electrical bandwidth of over 50 GHz is demonstrated.     

High-speed MQW electroabsorption optical modulators integrated withlow-loss waveguides

An MQW electro-absorption optical modulator integrated with low-loss input and output waveguides is proposed to achieve larger modulation bandwidth with a shorter modulation region, keeping the total device length large enough for easy fabrication and packaging. A fabricated 1-mm-long modulator with a modulation-region length of 50 μm shows a low insertion loss (7 dB), low driving voltage (V_{10 dB}=2.6 V), and large modulation bandwidth f_{3 dB} =40 (GHz) extrapolated from measurements up to 20 GHz. This modulator is suitable for application to ultra-high-speed fiber transmission systems     

Efficient octave-bandwidth microwave light modulators

The use of wide-bandwidth interdigital microwave circuits to provide electrooptic modulation of light is discussed. Two models employing lithium niobate crystals of different aspect ratios have been constructed and tested. Both have nominal bandwidth from 1.0 to 2.0 GHz but actually give somewhat greater modulation bandwidth. Single-pass modulation tests made using 6328-Å light at RF drive power level of 5 watts show that 30 percent modulation depth over a 1.5-GHz frequency band is obtained for one model while approximately 50 percent modulation depth over a 1.1-GHz band is obtained for the other. These results show excellent agreement with analytical predictions. Measurement techniques are also discussed.     

New active RC synthesis procedure using negative-impedance convertors

A new network configuration is introduced which may be used in active RC network synthesis. It uses a voltage-controlled voltage amplifier having negative gain equal to unity and a voltage- or current-inversion negative-impedance convertor. A synthesis procedure is eventually described using the new configuration.     

Switched-capacitor immittance convertors using a single operational amplifier

The improved switched-capacitor immittance convertors using a single operational amplifier are proposed. The general scheme which enables the conversion of the capacitive (n + 1)-terminal networks into the corresponding bilinearly equivalent networks consisting of LC parallel branches is also proposed.     

High-speed spatial light modulator

A high-speed, coherent spatial light modulator is under development. It is based on the coupling of a silicon photodiode and electrooptic crystal. The design criteria and theoretical performance are presented. Optical quality oflambda/20rms atlambda = 500nm over a 1 in aperture has been demonstrated. Submicrosecond write and erase rates are predicted. Heat dissipation limits the predicted continuous rate to 2.5 kHz or higher, depending on required optical quality. Calculated phase MTF is 50 percent at 10 cycles/mm.