Design and Fabrication of a Compact 2-D Photonic Crystal Collimating 1043-nm/1550-nm Wavelength Demultiplexer and Its Application to Photonic Integration

초록

We designed and fabricated a compact (~8-μm×13-μm) 1043-nm/1550-nm wavelength demultiplexer using the self-collimation phenomena of 2-dimensional (2D) photonic crystal (PC). We analyzed the equi-frequency surfaces (EFSs) of the first and second bands using a plane-wave expansion method. We also used a 3-dimnsional (3D) finite difference time-domain code to estimate the characteristics. Then, we fabricated the finite 2D PC using nanoimprint method and reactive ion etching process. The structure of this device consists of a 2-μm-thick SU-8 2000 (MicroChem Corp., refractive index n=1.561 at 1.55-μm) core layer placed over a 3-μm-thick fused silica (refractive index n=1.45 at 1.55-μm) substrate layer. It is patterned with a 2D square lattice holes of radius r=0.3a, where “a” is the PC lattice constant, 540-nm. The hole array has 15 columns by 23 rows. In order to launch the light, we truncate the crystal at a (10) surface, and place an external dielectric waveguide having a width of 2-μm, tilted at 22.5°. We then attached two external output dielectric waveguides having a width of 4-μm. Finally, to preserve the vertical symmetry, we etched substrate with an etch depth of 500-nm. In our devices, the beams of two different wavelengths (1043-nm and 1550-nm) are separated at an angle of 15 degrees in the PC region. We also designed, fabricated and tested an optical circuit board on which this PC device is integrated with conventional input and output waveguides. We expect that this integrated module would allow for high-density miniaturized integrated circuits with simple fabrication process.