Research On Integrated Semiconductor Devices For All-Optical Signal Processing

Nowadays, the signal processing for IP packet routing and switching at the routers are carried out with electronic devices, which are impossible to meet today’s rapidly increasing demands on bandwidths and capacity. This is because the so-called "the electronic bottleneck". Thus, the information processing capabilities, at the nodes of optical networks, do not match the ultra-broadband transmission capacity, which has already become a serious problem. In addition, the optical-electrical-optical conversion and electronic processing at the nodes consume large amounts of power. If the ultrafast optical signals could be processed without converting to electrical signals, the power consumption of networks will be reduced greatly. Consequently, development of ultrafast all-optical devices is very important for the future low power-consumption "all-optical networks", in which the electronic devices are replaced by photonic devices.In view of the above, this thesis addresses researches concerning three all integrated semiconductor devices for optical signal processing: multimode interference (MMI) couplers, side-ported MMI coupler based wavelength multiplexers/demultiplexers (MUXs/DMUXs) and all-optical analog-to-digital converters (ADC). Details are as follows:In this thesis, a new approach, which agrees with the fabrication progress, is proposed to evaluate the performances of general-interference (GI)3-dBMMI coupler, paired-interference (PI)3-dBMMI coupler and symmetric interference (SI)3-dBMMI coupler. Applications, which are suitable for the previous three kinds of3dB-MMI couplers, are discussed.The above three3-dB MMI couplers with spot-size converters (SSC) based on InP and SOI substrates are designed and fabricated respectively. The results show that3-dB GI-MMI and3-dB PI-MMI couplers based on InP/InGaAsP materials show good performances on the imbalance (IM), which is low than1dB/0.5dB, and excess losses (EL), which is approximately-3.2dB/-2.7dB in1540～1560nm wavelength range. Performances of the three types of3-dB MMI couplers based on SOI platform are not very good. Within the range of1530～1570nm, IMs of GI/PI/SI3-dB MMI couplers change during [-2.7dB,1.3dB],[-4.8dB,2dB] and [-1dB, OdB], respectively.A novel side-ported MMI coupler based wavelength MUX/DMUX is proposed and demonstrated. The devices are designed and fabricated on InP and SOI platform, respectively. InP-based demultiplexer chip has successfully split the combined incident signals at1310/1550nm to different ports with extinction ratios (ER) of22.6/15.36dB, respectively. Size of the multimode section is5μm×280.6μm For SOI-based demultiplexer, the measured ERs for signals around1310/1555.3nm are more than8/18dB, respectively. The overall chip size is less than100μm×100μm, and size of the multimode section is1.35μm×22.3μm. Meanwhile, an improved asymmetrical multi-section GI-MMI coupler based1310/1550-nm wavelength splitter is also designed and produced. The measured results show the ERs of14.1dB and35.7dB at1.55μm and1.31μm, respectively.A novel phase-shifted optical quantization scheme for an all-optical ADC, which uses4×4MMI couplers, is proposed. The factors that limit the performances of the proposed photonic ADC are investigated, including the intensity jitter of the sampling pulses, phase and intensity splitting imbalance of the MMI couplers. The bandwidth limitations are discussed. On the SOI substrate, a4×4MMI coupler is designed and fabricated.