Daiki Tanaka

Ultra-small, self-holding, optical gate switch using Ge 2 Sb 2 Te 5 with a multi-mode Si waveguide

We report a multi-mode interference-based optical gate switch using a Ge(2)Sb(2)Te(5) thin film with a diameter of only 1 µm. The switching operation was demonstrated by laser pulse irradiation. This switch had a very wide operating wavelength range of 100 nm at around 1575 nm, with an average extinction ratio of 12.6 dB. Repetitive switching over 2,000 irradiation cycles was also successfully demonstrated. In addition, self-holding characteristics were confirmed by observing the dynamic responses, and the rise and fall times were 130 ns and 400 ns, respectively.

Low loss, small crosstalk offset crossing structure for large-scale planar lightwave circuits

A low loss, small crosstalk offset crossing structure for a Si wire waveguide is proposed. We analyzed the properties of the structure for both the TE and TM modes by 2-D FDTD (two-dimensional finite difference time domain) simulation. By optimizing the offset crossing structure, a transmission loss of 0.021dB, and crosstalk of -55.0dB was achieved with a crossing angle of 20 degrees for the TE mode. A transmission loss of 0.070dB, and crosstalk of -48.6dB was also achieved with the same crossing angle for the TM mode. The low losses achieved with a small crossing angle makes this structure very useful for highly integrated optical matrix switches, etc.

Ultra-compact, self-holding asymmetric Mach-Zehnder interferometer switch using Ge2Sb2Te5 phase-change material

An asymmetric Mach-Zehnder interferometer optical switch using phase-change material (PCM) is reported. In this switch, two Ge2Sb2Te5 thin films, each 1μm in diameter, are deposited on a Si waveguide, and are used as phase shifters. The PCM can be reversibly switched between the amorphous and crystalline states. The difference in refractive index between the two states is very large, typically more than 2. Therefore, an optical switch using the PCM can be very small. The switching operation is successfully demonstrated by laser pulse irradiation. The maximum extinction ratio is 26.7 dB, and 2.2-nm peak wavelength shift is verified.

Stripe-based collimating silica planar waveguide for a free-space wavelength selective cross connect

We propose an integrated beam collimating silica waveguide with stripe-based structure for the use in wavelength selective cross connect (WSXC). The coupling loss of the device is below 0.15 dB within the ideal propagation distance.

Phase change characteristics of Ge2Sb2Te5 thin film for a self-holding optical gate switch

Fast and low power consumption optical switches are required for photonic networks. To this end, we proposed the optical gate switch using phase change material (PCM) and silicon waveguides. This switch had low power consumption because it consumed power only when the state was changed. Furthermore, the chip size is very small due to the large refractive index change of PCM. In this paper, we studied the phase-change characteristics of various kinds of thin GST film on SOI (silicon-oninsulator). A laser diode (LD) with a wavelength of 660 nm was used to irradiate the material. We compared the optical responses by laser pulse irradiation on GST films, and concluded GST-147 was the most suitable material for the optical switch because it had the lowest phase change threshold. The phase-change characteristics of GST-225 films with thickness of 25 nm, 50 nm and 75 nm were also examined. Thicker GST films had lower phase change thresholds. However, thermal simulations showed that the phase of the bottom part of thicker films may not be changed. Therefore, we concluded that GST films with thicknesses between 25 nm to 50 nm are the most suitable for optical switches.

Comparative simulation of three types of 3-dB coupler using a Si wire waveguide

We have proposed a cross gap coupler (CGC), which has an X-junction with an internal mirror at the cross section. We compared the splitting properties of three types of 3-dB coupler using a silicon wire waveguide; a CGC, a directional coupler (DC), and a multimode interference (MMI) coupler. The wavelength dependences of these structures were simulated (or evaluated) by two-dimensional finite-difference time-domain (2-D FDTD) method. The CGC showed smaller wavelength dependence in comparison to the other types of coupler.

Reversible Switching of an Optical Gate Using Phase-Change Material and Si Waveguide

Optical gate switch that uses Ge2Sb2Te5 phase-change material was fabricated and the reversible switching has been achieved for the first time. The switch is only 5-µm long and laser pulse irradiation was used for switching.

Low loss, small crosstalk offset crossing structure of si wire waveguide

Low loss, small crosstalk offset crossing structure of Si wire waveguide is proposed. The transmission loss of 0.018 dB, and the crosstalk of -49.1 dB are achieved with a crossing angle of 20 degrees.

Low Crosstalk Design of an Optical Matrix Switch Using Phase-Change Material

A crossbar type optical matrix switch using phase-change material was designed to have low crosstalk. The crosstalk of less than -49.1 dB was achieved for a 4×4 matrix switch by adjusting a unit switch structure.

Reversible switching of an optical gate based on Si rib waveguides with a Ge 2 Sb 2 Te 5 thin film

Reversible switching of an optical gate based on Si rib waveguides with a Ge2Sb2Te5 thin film is reported. We demonstrated four cycles of switching by pulsed laser irradiation. The average extinction ratios of each switching event were 9.1, 10.7, 11.6 and 11.7 dB, respectively. The extinction ratio of this optical gate was more than 5.9 dB over the wide wavelength range from 1525 nm to 1600 nm.