Low Loss Vertical Optical Path Conversion Using 45° Mirror for Coupling between Optical Waveguide Devices and Planar Devices

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To realize low loss optical interconnects between optical waveguide devices and two dimensional array-type devices, we investigated a novel 45° mirror device buried by index matching epoxy resin and coated with an anti-reflection layer. A groove with an isosceles right triangle cross section was formed using a dicing saw so as to cut into the single-mode optical waveguide, and aluminum thin film was obliquely deposited on the 45° side wall of the groove to increase the reflectance. The groove was filled with a spin-coating of UV-curable epoxy resin to planarize the top surface, and low index polymer (Teflon) was formed on the top surface as the anti-reflection layer. The optimum depth of the groove for reducing shadowing of the deflected beam was analyzed. As a result the insertion loss of the 45° mirror was reduced 1.3 dB compared to the insertion loss of straight waveguide. In addition, a novel optical tap device is proposed and demonstrated using a similar fabrication process to that of the 45° mirror device. The isosceles right triangle-shaped groove was formed on the upper cladding layer so as to almost touch the core layer. After filling it in and finishing it with the epoxy resin and AR coating used in the 45° mirror device, the loss of the through port was reduced 0.5 dB compared to the insertion loss of straight waveguide and -14 dB (4.0%) of the optical power was transmitted to the tap port. Lastly as a model of the coupling between waveguide devices and two-dimensional arrayed devices such as vertical cavity surface emitting lasers (VCSEL's), the vertical port of the 45° mirror device was connected to a single mode fiber with a very small mode field diameter (3.6 µm). This configuration transmitted -11.8 dB (6.6%) of the input power from the input port to the vertical tap port and vice versa.