High-Speed Electroabsorption Modulators And MSM Photodetectors

Since the introduction of the Internet, the average growth of data traffic has doubled every year over the past 30 years, and is expected to continue to do so also for the next decade. Due to its advantage of high bandwidth, reliability, low cost and little interference, optical fiber communication system constitute the backbone of the Internet and have experienced a tremendous growth in transmission capacity. In commercial optical fiber transmission system, the electronic time-division multiplexing (ETDM) channel data rates of 40Gb/s has been achieved and the next generation transmission system operating beyond 40Gb/s will be deployed soon.The high speed ETDM transmission system is based on data modulation using external optical modulators in transmitters and the deployment of high speed photodetectors in receivers. Electroabsorption modulators (EAM) based on quantum-confined Stark effect in multiple-quantum wells have advantages for high-speed, low drive voltage, and high extinction ratio applications. They are compact in size and can be monolithically integrated with source lasers. Thus, for ETDM systems with data rates beyond 40Gb/s, the high speed EAM integrated with a laser could be a promising candidate. On the other hand, MSM photodetectors have the advantage of low capacitance, high bandwidth, low dark current, and in ease of fabrication. The planar structure of MSM photodetector is also suitable for monolithic integration and could be the key components in optical receivers.This thesis presents the theoretical study, design optimization and characterizationof high speed electroabsorption modulator. An electroabsorption modulator with a bandwidth of 100GHz, the return loss less than -12dB up to 60GHz and an dynamic extinction ratio of 10.7dB at 50Gb/s with a drive voltage of 3V_p-p has been demonstrated. The good performance of the device is due to the optimized design of InGaAsP/InGaAsP multiple-quantum-wells, optical waveguide and the deployment of segmented traveling-wave electrodes.An ETDM fiber optical transmitter with Non-Return-to-Zero(NRZ) optical output signal was assembled with a high speed electroabsorption modulator and a 80Gb/s multiplexer. Clear eye openings have been demonstrated at 80Gb/s for ETDM. This is also the first ETDM transmitter with NRZ optical output signal ever been demonstrated to operate over 80Gb/s. The temperature-dependent effects in a high speed electroabsorption modulator were analyzed. Operating uncooled between 10-50 ℃ for the high speed electroabsorption modulator was achieved by choosing optimum operation voltages with the highest modulation efficiency at different temperatures as the applied DC voltages. At 50Gb/s, the dynamic extinction ratio is >8.4dB with 3V_p-p drive voltage over the entire temperature range.An Asymmetric Fabry-Perot modulator/detector (AFPMD) was employed in a full-duplex radio-over-fibre system, in which the AFPMD works both as a modulator and simultaneously as a photodetector so as to achieve low cost electrical-optical conversion. For the first time, the property of intermodulation distortion in a full-duplex radio-over-fibre system using AFPMD has been investigated. The employment of balanced RF input powers over modulators provides the feasibility to suppress the intermodulation distortion and enhance the spurious free dynamic range (SFDR) in a full-duplex radio-over-fibre system.A 2D finite-difference method is developed to study the MSM photodetector. The time-domain numerical simulation is based on the Poisson equation and continuity equations for electrons and holes. The distributions of the electrical field, the carriers and the current density in the MSM photodetector were calculated, and the DC characteristics and transient response of the photodetector have been analyzed. An optimized design of Si based MSM photodetector was given to achieve a fastresponse while keeping a satisfactory responsivity.