T. Saida

Optical spotsize converter using narrow laterally tapered waveguide for planar lightwave circuits

We present a full description of the design and fabrication of a compact laterally tapered spotsize converter (SSC) that provides both low-loss coupling and large fabrication tolerances. The SSC is based on a laterally tapered waveguide with a narrow core width that can be fabricated simply by using the usual fabrication process. We discuss the design concept of the SSC in detail and provide a simple design procedure with which to obtain the optimum SSC design parameters. We also investigate the fiber misalignment tolerance and mode field diameter of the SSC and confirm that it is suitable for integration with large-scale optical devices. Furthermore, we examine the performance of the SSC for higher refractive index difference (/spl Delta/) of 2.0% and 2.5% with a smaller bending radius. We fabricated the 2-mm-long SSC using 1.5%-, 2.0%-, and 2.5%-/spl Delta/ silica-based planar lightwave circuits. This enabled us to reduce the single-mode fiber coupling loss to 0.4 dB at a single waveguide junction with a low polarization-dependent loss of 0.05 dB regardless of the /spl Delta/ values, while providing a core width fabrication tolerance of /spl plusmn/0.3 /spl mu/m, and an endface position tolerance of /spl plusmn/0.2 mm.

Fabrication of silica-on-Si waveguide with higher index difference and its application to 256 channel arrayed waveguide multi/demultiplexer

Improved techniques were used to fabricate a silica-on-Si waveguide with a higher core-to-cladding index difference and a 2 mm bending radius. A 256 channel and 25 GHz spacing arrayed-waveguide multiplexer with low loss and low crosstalk was successfully fabricated for the first time using the waveguides.

16-wavelength 10-GHz actively mode-locked fiber laser with demultiplexed outputs anchored on the ITU-T grid

We propose and demonstrate a 16-wavelength polarization-maintaining fiber laser, actively mode-locked at 10 GHz. The fiber laser includes a 16-channel 100-GHz-spaced arrayed waveguide grating (AWG) in the laser cavity; therefore, the outputs are demultiplexed and the lasing wavelengths are anchored at the ITU-T grid. The multiwavelength lasing has been achieved by cooling the erbium-doped fiber in liquid nitrogen. Generation of simultaneous multiwavelength short pulses was demonstrated.

Y-branch waveguides with stabilized splitting ratio designed by wavefront matching method

We designed optical Y-branch waveguides with a stabilized splitting ratio by using a new design approach based on the wavefront matching method. The designed Y-branches were fabricated using silica-based planar lightwave circuit technology. We suppressed any variation in the splitting ratio of the Y-branch experimentally and obtained excess losses of <0.35 dB over a wide wavelength range of 1.3-1.7 /spl mu/m.

Compact and low-loss arrayed waveguide grating module with tolerance-relaxed spot-size converter

A compact, low-loss arrayed waveguide grating (AWG) module was achieved by adopting a novel optical spot-size converter (SSC) to planar lightwave circuits (PLCs). The SSC is a laterally tapered waveguide that can be fabricated simply by the conventional fabrication process. The structure is composed of a core width converting region where the spot-size is converted efficiently, and a core width fine-tuning region where the cut-position tolerance is relaxed. We have applied this structure to a 1.5%-/spl Delta/ silica-based waveguides and reduced the single-mode fiber coupling loss to less than 0.5 dB/point. The SSC provides a large cut-position tolerance that enables angle polishing of the PLC endfaces to prevent reflection and low-loss connection of pigtail fibers. The center channel insertion loss of the AWG module was reduced from 4.2 to 2.2 dB, and the reflection was less than -60 dB.

Dual-Carrier Dual-Polarization IQ Modulator Using a Complementary Frequency Shifter

We discuss the detailed characteristics of a dual-carrier dual-polarization (DP) in-phase-and-quadrature (IQ) modulator. As the dual-carrier generator, we used a complementary frequency shifter (CFS), which generates two frequency-spacing-locked optical subcarriers and outputs each of them from different output ports without any optical demultiplexers. We fabricated the modulator, which integrates a CFS, a quad-parallel IQ modulator, and a polarization-multiplexing circuit, with a hybrid configuration of silica planar lightwave circuits and a LiNbO3 chip. With the fabricated modulator, we demonstrated that the CFS enables us to flexibility change the relative and absolute optical frequencies of the subcarriers with a high isolation ratio of about 40 dB. We generated a 400-Gb/s dual-carrier DP 16-level quadrature amplitude modulation (16QAM) signal by driving the modulator with high-speed digital-to-analog converters.

Optical waveguide lens with modulated width designed by wavefront matching method

We use our recently proposed wavefront matching method to design waveguide lenses with modulated widths. We fabricated a waveguide lens pair in a silica waveguide, and confirmed its operational principle experimentally.

Multiwavelength, actively mode-locked polarization maintaining fiber laser at 10 GHz

We demonstrate a multiwavelength actively mode-locked polarization maintaining fiber laser at 10 GHz. Stable generation of 13-wavelength short pulses was demonstrated by cooling the erbium-doped fiber in liquid nitrogen.

Optical pulse pattern recognition circuit based on an optical digital-to-analog converter on a planar lightwave circuit

A 4-bit optical digital-to-analog converter for use in optical pulse pattern recognition has been fabricated on a silica-based planar light-wave circuit. We successfully confirmed the recognition of various kinds of 4-bit pulse sequence at 10 Gb/s.

Low-loss 1.5% /spl Delta/ arrayed waveguide grating with spot-size converters

We achieved a very low insertion loss of 0.7 dB in a 1.5% /spl Delta/ arrayed-waveguide grating by successfully fabricating spot-size converters that reduced single-mode fiber coupling loss from 1.6 to 0.2 dB/point.