High Speed Photonic Integrated Circuits For On-Chip Optical Interconnects

With the rapid development of the information and communication technology, higher demands are required for the communication networks, good performance computers and servers. More and more attentions are paid to integrated optics in the applications such as optical interconnects and optical communication owing to its advantages of compactness, lower power consumption and larger bandwidth. To achieve lower cost and better performance, higher integration density is desirable for photonic integrated devices. On one hand, high refractive index contract Si is adopted to reduce the sizes of the devices; on the other hand, more functionalities are integrated on Si substrate by monolithic or hybrid integration. Silicon based photonic integrated circuits not only have the advantages of high bandwidth, fast transmission speed, immune of electromagnetic interference and low power consumption, but also be compatibile with CMOS technology, which makes it more possible for ultracompact, high density optical system and breaks the bottleneck of the electrical interconnects in terms of the speed, power consumption for the on-chip interconnect and intra-chip interconnect. In this thesis, we are focusing on the study of high speed photonic integrated circuits for on-chip optical interconnects.Firstly, in passive components area, we propose three methods for reducing the size of the arrayed waveguide grating(AWG). The first one is AWG with periodic microbends structures in the arrayed waveguide region. The bending radius is 5μm. In this way, we can achieve greater length difference in the limited space. The fabricated 15-channel 400 GHz microbend-type AWG has overlapped free propagation region and 34 wavguides with microbends in arrayed waveguide region. The footprint of the device is merely 163μm×14μm. The second one is photonic crystal reflective type AWG. The reflectivity is more than 90% in the wide range from 1450 nm to 1650 nm. A 9-channel 400 GHz AWG with photonic crystal reflectors has a size of only 134μm× 125μm. The third one is Bragg grating reflective type AWG. The grating period is 370 nm with the gap 150 nm and 10 periods in total. The reflectivity is greater than 95% in 300 nm wide wavelength range. The footprint of the 9-channel 400 GHz AWG with Bragg grating reflectors is 130μm×00μm.Secondly, in active components area, a Ⅲ-Ⅴ/Si heterogeneously integrated EAM with lumped-type electrodes is designed and fabricated. The length of the modulation area is 100μm, and an ultrashort two-stage taper of 45μm with evanescent coupling efficiency greater than 98% is invented. We develop the fabrication process for hybrid Ⅲ-Ⅴ/Si active devices based on BCB adhesive bonding technology. Then we build the measurement setup and achieve a E/O response bandwidth of 17 GHz, as well as good back-to-back eye diagram at 10 Gb/s,20 Gb/s 30 Gb/s. It can also be used as a photodetector by applying a sufficient reverse bias voltage, and the responsivity is 0.72 A/W.Thirdly, in terms of on-chip optical interconnect, the passive AWG and active EAM are integrated together. We develop a 5-channel,200GHz channel-spacing,20 Gb/s per channel heterogeneously integrated electro-absorption modulator array with a total capacity of 100 Gb/s.Finally, by further optimization, we achieve a 180 Gb/s high-speed heterogeneously integrated electro-absorption modulator array and a 180 Gb/s high-speed heterogeneously integrated detector array. Also, we build a high speed on-chip optical interconnect system that allows light modulated by a modulator, go through the multiplexer, demultiplexer, and then detected by the photodector at the end. By now, some preliminary results are obtained.