Diplexer With Integrated Filters and Photodetector in Ge-Si Using \Gamma- and \Gamma- Directions in a Grating Coupler

• Published in: IEEE photonics technology letters Vol. 21; no. 22; pp. 1698 - 1700
• Main Authors: Doerr, C.R., Long Chen, Rasras, M.S., Young-Kai Chen, Weiner, J.S., Earnshaw, M.P.
• Format: Journal Article
• Language: English
• Published: New York IEEE 15-11-2009; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Coupling circuits; Fiber gratings; Fiber lasers; Filters; Germanium; grating; integrated optics; Optical coupling; Optical fiber couplers; Optical fiber polarization; photodetector; Photodetectors; photonic crystal; Photonic integrated circuits; Silicon on insulator technology; silicon photonics
• ISSN: 1041-1135; 1941-0174
• DOI: 10.1109/LPT.2009.2031820

We demonstrate a central-office-type diplexer in which the filter and photodetector are monolithically integrated on a silicon-on-insulator substrate. The photonic integrated circuit receives a 1577-nm signal from an external laser and sends it to the fiber link using a two-dimensional grating coupler. The same grating coupler receives a 1270-nm signal from the fiber link and sends it to a monolithically integrated germanium photodetector using a polarization-diversity scheme to achieve polarization independence. The grating coupler is novel in that both the Gamma- X and Gamma- M directions are employed. This allows the grating coupler to couple both the 1577- and 1270-nm wavelengths with a small fiber tilt angle and hence have low polarization-dependent loss.