We proposed a novel grating design of an out-of-plane coupler with non-uniform duty ratio operating at a wavelength of
1.55 μm for the highly efficient coupling from a waveguide to an optical fiber. In order to evaluate the coupling
performance, the diffracted output beam profile and the focusing performance due to the variations of duty ratio
configuration were investigated by a 2D Bloch-wave analysis. In addition, a simple fabrication method was proposed to
realize the grating by the Near-Field Holographic lithography system with variable aperture unit.
We propose and demonstrate a photonic crystal optical group delay device, in which two dimensional photonic crystal line
defect waveguide with chirped hole, induces sequential optical group delays for time-spreading/wavelength-hopping optical
code division multiple access (O-CDMA). The photonic crystal line defect waveguide allows ultrasmall size of device due to
its strong optical confinement by the photonic bandgap. And chirped photonic crystal waveguides, in which radius of holes are
gradually changed so that the photonic bands are smoothly shifted to the higher frequency side. When a short pulse signal with
a wide spectrum comes into this device, the guided light is localized at specific position depending on wavelength. This
concept is suitable to realize a pulse waveform synthesizer and an en/decoder for time-spreading/wavelength-hopping O-CDMA.
We have confirmed that this device has a chromatic temporal dispersion of ~ 33-fs/nm, corresponding to the repetition
rate of ~ 1-ps for pulses with wavelength-interval of 30-nm, by two dimensional finite difference time domain simulation.
We fabricated an arrayed waveguide grating (AWG) demultiplexer for optical fiber communication systems and
photonic integrated circuits. We also used an embossing technique to fabricated the AWG instead of traditional
semiconductor technologies, such as photolithography and etch process. UV curable polymers (ZPU 12-47 and ZPU 12-
45) were used as the core and upper cladding layers. The polydimethylsiloxane (PDMS) mold used for the embossing
process is manufactured by a photoresist structure formed on a silicon wafer. We tried the embossing onto a fused silica
glass using the PDMS mold. After UV curing, the PDMS mold was peeled away carefully, and a pattern of the AWG
demultiplexer was left on the surface of that substrate. The upper cladding layer was coated over the patterned structure.
The fabrication of the AWG demultiplexer was completed by a cleaving process. The residual layer produced after an
embossing process was adjusted by the volume of polymer droplet. The embossing technique will have the potential for
broad applications in fabrication of photonic devices.
We designed a compact wavelength-splitter using self-collimated diffraction in two-dimensional polymeric photonic crystal (PhC). In a three-dimensional finite difference time-domain (3-D FDTD) simulation, the beams of two different wavelengths (1043-nm and 1550-nm) are separated at an angle of 15 degrees in the PhC region. And, we fabricated this device using ultra-violet (UV) embossing technique that can be simply performed at room temperature with a silicon mold. We expect that this design concept and low-cost mass production method of a PhC-based device enable us to realize a very high-density integrated circuits due to its simple fabrication process and compact size.