# Development Status of Key Technologies for Optoelectronic Integrated Circuit Manufacturing
## 3 Manufacturing of Optoelectronic Integrated Circuits
### Optical Interconnect  
With the increasing demand and miniaturization of transistors, the data transmission between chips and within chips requires higher bandwidth and speed and lower power consumption. Optical interconnects with low power consumption and interference have numerous advantages [59]. In the future, optoelectronic integrated circuits will replace conventional electrical interconnects with optical interconnects. Studies have focused on optical interconnect [60; 61; 62; 63]. In 1982, Fujitsu devised a silicon-based waveguide to simplify the device structure and reduce the device size and cost [64]. In 1984, [PERSON] et al. [65] proposed to replace conventional electrical interconnection with optical interconnection technology. In 1987, [PERSON] et al. [66] proposed an optical waveguide based on the SOI platform. The SOI material exhibits excellent core-cladding refractive index difference and mitigates loss. Subsequently, this method was used to develop silicon-based waveguides. In 1993, [PERSON] et al. [67] prepared porous Si optical waveguides by varying the current intensity in the electrochemical etching process used to fabricate porous Si, which affects the porosity of the monolayer and the optical properties in a simple manner. In 2004, Sun Yat-Sen University [68] proposed an integrated optical waveguide device based on the principle of multi-mode interference, with a structural unit of 3 \(\times\) 2 for optical power separation and optical cross-interconnection. By introducing the MMI region near the crossover point, the crosstalk characteristics of the crossover waveguide improved considerably. In 2015, IBM [69] used the effect of grain size on optical loss to propose a low-loss large-grain polysilicon waveguide with a high refractive index to integrate various small photonic components. Furthermore, the use of small optical components improves performance. In 2018, the University of Arizona [70] introduced a waveguide that includes a thin waveguide core and a tapered structure design that provides previously unachievable performance, including efficient coupling with considerably reduced footprint, loose alignment tolerances, and low polarization dependence. These features are critical for high-volume manufacturing using low-cost, low-accuracy assembly tools. Generally, the optical interconnection system consists of light sources, electro-optic modulators, optical waveguides, optical switches, filters, wavelength division multiplexing, and optical detectors. The interconnection process includes the light emitted by the light source being used as a data transmission carrier. The electro-optic modulator loads the electrical signal to be transmitted on the optical carrier, transmits it to the interconnection terminal through the optical waveguide, and, finally, receives and demodulates it into an electrical signal via the detector [71; 72]. Structurally, optical interconnects include intra-chip interconnects, inter-chip interconnects, inter-module interconnects, inter-board interconnects, and interconnects between communication devices [39]. The optical interconnection technology is mature and has been commercialized. The optical interconnection technology between circuit boards, modules, and chips is developing, whereas the optical interconnection within the chip is in the application basic research stage, and the optical interconnection technology is accelerating to in-chip development. From the transmission channel, optical interconnection includes free space interconnection, waveguide interconnection, and optical fiber interconnection. Among them, free space interconnection exhibits optical path alignment, and waveguide interconnection provides high-density interconnection channels, which are suitable for interconnection within chips or between chips. They are crucial in optoelectronic integrated circuits and are a current research focus in optical interconnection.