Mirror-Based Broadband Silicon-Photonics Vertical I/O With Coupling Efficiency Enhancement for Standard Single-Mode Fiber

• Published in: Journal of lightwave technology Vol. 38; no. 12; pp. 3147 - 3155
• Main Authors: Noriki, Akihiro, Tamai, Isao, Ibusuki, Yasuhiro, Ukita, Akio, Suda, Satoshi, Shimura, Daisuke, Onawa, Yosuke, Yaegashi, Hiroki, Amano, Takeru
• Format: Journal Article
• Language: English
• Published: New York IEEE 15.06.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Broadband; Coupled modes; Couplers; Couplings; Curved beams; Design optimization; Micro-mirrors; Micrometers; Mirrors; Misalignment; Optical coupling; Optical polarization; Optical waveguides; Photonics; Silicon; Silicon photonics; Tapering; Tolerances; Vertical polarization; Wave division multiplexing; Waveguides; Wavelength division multiplexing
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2020.2995915

The broadband vertical optical coupling of silicon (Si) photonics poses significant challenges regarding the use of wavelength division multiplexing (WDM). The grating coupler, a type of vertical optical coupling device, strongly depends on the wavelength. As an alternative, we developed another vertical optical coupling device using a 45° curved micro-mirror. To experimentally demonstrate the broadband vertical optical coupling, the curved micro-mirror was designed based on a measured optical beam output from a Si inverse taper waveguide and integrated on a Si photonic chip to experimentally demonstrate the broadband vertical optical coupling. Without using the use of additional lenses, the Si waveguides were coupled with standard single-mode fiber (SMF) by applying fabricated mirrors. Owing to its lens function, the coupling efficiency was enhanced by 1.4 and 3.4 dB for TE and TM polarization. Over the entire O-band, low-wavelength dependent losses of 1 dB were also obtained. Misalignment tolerances were evaluated and 1-dB tolerances of approximately plus or minus 2 micrometers were obtained. By optimizing the design of the Si inverse taper waveguide, a low-polarization dependent loss of 0.3 dB on average was also obtained for the O-band. The average loss was 3.3 dB. Compared with grating couplers, a broadband and low polarization-dependent Si-photonics vertical coupling was demonstrated using an integrated curved mirror.