Belgian chip research center imec has demonstrated a net 400-gigabit-per-second optical link using an avalanche photodiode that operates at 5 volts. The detector amplifies the electrical signal produced by incoming light, helping a receiver pick up weaker signals while maintaining the speed needed for data-center connections.
A photodiode converts light into electrical current. An avalanche photodiode (APD) adds internal amplification, which can improve sensitivity but has traditionally cost bandwidth, required a higher operating voltage, or both. Imec says its germanium-on-silicon APD combines a 100 GHz bandwidth with a responsivity of 1.8 amperes per watt at 5 volts. It reports comparable performance in two optical wavelength bands used for communications, the O-band and C-band.
Imec changed the amplifying region
The researchers began with a design that normally separates light absorption, charge control and amplification. They narrowed the amplification layer to less than 100 nanometers in a recessed germanium-on-silicon structure and removed the charge layer. Imec says the resulting responsivity corresponds to roughly twofold internal gain. The detector was made on its 300 mm silicon-photonics platform.
Receiving weaker signals at 400 Gbps
For the link demonstration, imec paired the new detector with a C-band electro-absorption modulator it reported at last year's European Conference on Optical Communication. The combined setup reached a net data rate of 400 gigabits per second. Imec also reports a 3 dB improvement in receiver sensitivity compared with a conventional photodiode. That comparison concerns sensitivity in its reported test, not a measured reduction in the power consumed by a complete data-center link.
Greater sensitivity could let a system designer use less laser power or tolerate more optical loss, depending on the link. It plans to test reliability across a wider range of temperatures and optical input powers and to integrate the APD with high-speed receiver electronics.
