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 propose a novel directional coupler type switch based on mode transfer by thermo-optic effect. In our design, the directional coupler switch maintains the anti-coupling by changing the refractive index in ON state and the coupling in OFF state. In this paper, the directional coupler switch consisted of only one single electrode on the opposite side of input waveguide in the coupling region. The coupling region was designed to have the coupling length for perfect optical coupling. Polymer materials with large thermo-optic coefficient were adopted for the change of the refractive index
profiles of two waveguides. As the thermo-optic coefficient of polymer materials is negative, the refractive index decreases by applied voltage. When the electrode is sufficiently powered, the incident light only propagates along the input waveguide due to breaking the symmetry. For the optimized switch design, our simulating study shows the extinction ratios of -21.2 and -28.3 dB in OFF and ON states, respectively. The required variation of the refractive index for switching is only order of 10<sup>-3</sup>. This concept is expected to improve the power consumption and the extinction ratio of a directional coupler switch.
We designed and fabricated a 1310 nm/1550 nm demultiplexer with a directional coupler for optical fiber communication systems with much increased transmission capacity. We also propose novel design methods to reduce its length and improve its performance. First, the device length was reduced by using the generalized extinction ratio curve, which was normalized by the normalized frequency (v). Second, the lateral shift and the curved waveguide for the optimization of input region were adopted to improve the extinction ratio, and the shift is to outward of a directional coupler. Lateral shift reduces discrepancy between the two transfer coefficients, Cve and Cvo, and curved input waveguide controls mode profile asymmetrically to minimize the effect of these without serious decrease in transfer efficiency. For a given interaction length of 1.948 mm, the 1310 nm and 1550 nm wavelength light transfer to the cross state and the bar state, respectively. Above results are used to fabricate of a demultiplexer operating at 1310 nm and 1550 nm with the extinction ratios of -29.64 dB at 1310 nm and -20.32 dB at 1550 nm, respectively. The demultiplexer device was fabricated with polymer materials on a fused glass substrate. The core of the device was formed by micro-transfer molding technique with the polydimethylsiloxane (PDMS) mold. We found that these novel devices can be formed in optical fiber communication systems.
A vertically interconnected structure is a key feature of a photonic integrated circuit application, like an optical printed circuit board. Conventional vertical interconnecting structures have a 45 degree mirror, with or without metal coating to enhance its reflectance. We have designed a curved-shape semi-spherical type vertical interconnecting structure to enhance vertical interconnecting efficiency, and also developed simple fabrication procedure to realize it.