Photodetector

Photodetectors convert the received high-speed optical signals into electrical signals. However, since silicon is transparent to light waves above 1.1 μm, detectors cannot be made from silicon alone. Currently, the high-frequency detectors integrated on silicon substrates mainly include hybrid integrated III-V and silicon-germanium hybrid detectors.

The detector shown below is a vertical PN diode structure.

The hybrid integrated III-V detector has high coupling efficiency, high sensitivity and fast response; the performance of the silicon germanium detector is also excellent, and the device preparation technology is compatible with the CMOS process, which is more suitable for large-scale integration and is the current mainstream solution. Silicon germanium detection chips are divided into PIN and APD. PIN diodes have relatively low sensitivity and are used for medium and short distance optical communication transmission; APD has higher detection sensitivity and is suitable for longer distances.

Passive Multiplexing Technology

In order to improve communication capacity, multiplexing technology is usually used to combine multiple low-speed channels into a high-speed channel. Common multiplexing methods include wavelength division multiplexing, polarization multiplexing, mode multiplexing, etc.

Wavelength division multiplexing technology has been used in current silicon photonic chip products to generate multiple communication channels based on beam interference. The most common multi-beam interference wavelength division multiplexing devices mainly include arrayed waveguide grating (AWG), etched diffraction grating (EDG), micro ring resonator (MRR), echelle grating (EG), etc. In order to obtain a flat-top passband for a microring resonator, it is usually necessary to cascade multiple microrings to form a high-order microring resonator.

Compared with other types of multiplexing devices, microrings are more sensitive to temperature. AWG and EDG are based on the principle of multi-beam interference, but currently there are many limitations, such as high insertion loss, large device size, and thermal crosstalk in each channel that will seriously degrade device performance.