Abstract

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.

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