Elephant coupler: Vertically curved Si waveguide with wide and flat wavelength window insensitive to coupling angle

Akizuki

IEEE Photon. Technol. Lett.

et al. 2020

For input coupling from single-mode optical fibers to photoreceivers made with silicon photonics integrated circuits (Si-PICs), we constructed a polarization-insensitive optical surface coupler with a vertically curved silicon waveguide. The polarization insensitivity was attained by the equalization of the radiative transmission losses of TE and TM polarizations in the vertically curved waveguide (VCW) structure while keeping the straight structure of the spot-size converter (SSC) connected above the curved structure. Numerical simulations revealed that the radius of curvature of 6 µm or larger nearly enabled the equalization, and thus we developed a bending technology using ion implantation to realize simultaneously a VCW radius of curvature of 6 µm and a straight SSC of length 7 µm by varying the implantation angles. The bent silicon core was subsequently coated with SiO 2 by plasma-enhanced chemical vapor deposition to function as a collimation lens. The coupling properties of the fabricated coupler and the single-mode fiber with a mode-field diameter of 5 µm exhibited a polarization dependence loss of less than 0.25 dB, a 1-dB bandwidth of 180 nm, and coupling losses of about 1.6 dB at 1550 nm wavelength. A sharp inversely tapered Si waveguide that affects these characteristics significantly can be formed by applying ArF-immersion lithography on the 45-nm-node and hence fabrication is compatible with mass production processes.

Section: Introductionmentioning

confidence: 99%

Polarization-Insensitive Vertically Curved Si Surface Optical Coupler Bent by Ion Implantation

Akizuki

IEEE Photon. Technol. Lett.

et al. 2020

“…[5][6][7][8] Recently, we developed an alternative surface coupler consisting of a vertically curved silicon waveguide at the terminal of Si-PIC. [9][10][11][12][13][14][15] This coupler (called "elephant coupler") bends the propagating direction of light to vertical angle from the Si-PIC plane with broad spectrum bandwidth and polarization-insensitive nature. In addition, since multiple elephant couplers can be placed two-dimensionally on a Si-PIC chip, elephant coupler is suited for the attachment of multiple fiber lines using V-grooved fiber arrays and multicore fibers.…”

mentioning

confidence: 99%

“…In this method, stress generation and relaxation in the Si waveguide cantilever suspended in free space become the driving force of bending. [9][10][11][12][13][14][15] The bending occurs only in the implanted and suspended region and the bending structure is very sensitive to the length of this region. However, in the IIB process, [16][17][18][19][20] isotropic wet etching required for cantilever formation can only guarantee uniformity and reproducibility on the order of micrometers.…”

mentioning

confidence: 99%

Improvement of fabrication accuracy of vertically curved silicon waveguide optical coupler using hard mask shielded ion implantation bending

Akizuki

et al. 2020

Jpn. J. Appl. Phys.

To obtain high device fabrication uniformity and reproducibility for vertically curved silicon waveguide optical coupler, we developed the high accuracy ion implantation bending (IIB) method by incorporating a tungsten mask that can partially shield the ion implantation. The developed IIB method improved the positional accuracy of the origin of vertically curved Si wire bending from a wet etching-level of 1 μm order to a dry etching-level of several 100 nm order, and we obtained a fabrication accuracy of about less than ±0.4 μm of the tip position of the Si-wire vertically curved structures.

“…13,15) Recently, an alternative type of surface optical coupler configured with a vertically curved Si waveguide has been demonstrated. [16][17][18][19] To obtain very small curvature, we demonstrated that the ion implantation method is effective, as illustrated in Fig. 1, and we nicknamed the fabricated coupler an elephant coupler because it resembles a raised elephant trunk.…”

mentioning

confidence: 99%

“…1, and we nicknamed the fabricated coupler an elephant coupler because it resembles a raised elephant trunk. [17][18][19] We experimentally achieved the miniaturization of the bending radius to several micrometers by controlling implantation conditions such as ion species, acceleration voltage, and dose. The elephant coupler shows broadband operation because it changes the direction of propagating light along the waveguide.…”

mentioning

confidence: 99%

Design of compact surface optical coupler based on vertically curved silicon waveguide for high-numerical-aperture single-mode optical fiber

Atsumi

et al. 2017

Jpn. J. Appl. Phys.

A surface optical coupler based on a vertically curved Si waveguide was designed for coupling with high-numerical aperture single-mode optical fibers with a mode-field diameter of 5 µm. This coupler has a quite small device size, with a height of approximately 12 µm, achieved by introducing an effective spot-size converter configured with the combination of an extremely short Si exponential-inverse taper and a dome-structured SiO2 lens formed on the coupler top. The designed coupler shows high-efficiency optical coupling, with a loss of 0.8 dB for TE polarized light, as well as broad-band coupling with a 0.5-dB-loss band of 420 nm.