Y. Hibino

Recent advances in high-density and large-scale AWG multi/demultiplexers with higher index-contrast silica-based PLCs

This paper reviews recent progress on high-density and large-scale arrayed-waveguide-grating (AWG) multi/demultiplexers, which have been developed for wavelength division multiplexing (WDM)-based photonic networks. The AWG has been the key to the construction of flexible and large-capacity WDM networks. This is because, compared with conventional filters consisting of thin-film interference filters and microoptics, the AWG offers the advantages of low loss, high port counts, and mass productivity. To improve such characteristics further, low-loss, higher index-contrast (super-high /spl Delta/) planar lightwave circuits (PLCs) with a bending radius of 2 mm have recently been developed. It has been shown that these PLCs are effective for use in constructing a compact AWG module with 1/5 the volume of a conventional module and large-scale AWGs with 256 and 400 channels. Three techniques for low-loss fiber connection with spot-size converters have also been developed for the super-high /spl Delta/ PLCs, and it has been confirmed that these techniques can be applied to the fabrication of AWG modules. Furthermore, two-stage tandem AWG-type multi/demultiplexers with more than 1000 channels have been demonstrated. This paper describes the progress that has been made on these high-density and large-scale AWGs, which are expected to contribute greatly to the construction of future photonic networks including optical add/drop multiplexing systems and optical crossconnect systems.

Silica-based waveguide-type 16 x 16 optical switch module incorporating driving circuits

We developed a 16/spl times/16 optical matrix switch module in which we incorporated a silica-based thermooptic switch chip and driving circuits. The module exhibited excellent levels of performance, namely a low insertion loss and a high extinction ratio. This is the largest scale waveguide-type matrix switch module yet reported. Driving circuits with a serial-to-parallel control signal conversion function enabled us to realize a new module structure that is both simple and flexible for use with larger scale switches.

Passband-width broadening design for WDM filter with lattice-form interleave filter and arrayed-waveguide gratings

We successfully fabricated a high channel count and flat-top wavelength-division-multiplexing filter by integrating a waveguide-type interleave filter and two arrayed-waveguide grating on one chip. Optimizing the loss ripple of the interleave filter, we realized a 50-GHz spacing, 102-channel ports, a 1-dB passband of 30 GHz, and an insertion loss of 4 dB.

Low loss fully reconfigurable wavelength-selective optical 1/spl times/N switch based on transversal filter configuration using silica-based planar lightwave circuit

A low loss wavelength-selective switch is proposed and demonstrated. The switch has a 1/spl times/4 transversal filter configuration that includes arrayed waveguide gratings and thermooptic phase shifters, and can route arbitrary wavelength input light to arbitrary outputs with no loss variation. We confirmed its operating principle and obtained an average loss of 2.7 dB and a worst extinction ratio of more than 20 dB.

Athermal arrayed-waveguide grating multi/demultiplexers composed of TiO/sub 2/--SiO/sub 2/ waveguides on Si

We have successfully demonstrated a novel athermal arrayed-waveguide grating (AWG), which is composed of highly TiO/sub 2/-doped SiO/sub 2/ glass rib waveguides on a silicon substrate. We found that the wavelength temperature coefficients of the athermal AWG depend not only on the TiO/sub 2/ concentration but also on the annealing temperature after fabrication. We obtained a center wavelength temperature coefficient of 0.7 pm//spl deg/C at a TiO/sub 2/ concentration of 66 mol% and an annealing temperature of 900/spl deg/C.

100-GHz spacing 8-channel light source integrated with external cavity lasers on planar lightwave circuit platform

We have successfully fabricated a 100-GHz spacing 8-channel light source using hybrid integration technologies based on planar lightwave circuits (PLCs). The light source was composed of UV-written Bragg gratings and laser diode (LDs) on PLC platforms. To adjust the Bragg wavelength to the ITU-T grid, we used a precise phasemask with eight different pitches. Moreover, to suppress temperature-dependent mode hopping, we tuned the longitudinal mode wavelength so that it became stable by photosensitively modifying the waveguide refractive index in the cavity, which we achieved using an ArF excimer laser, in addition to inserting silicone in the cavity. As a result, we obtained eight lasing wavelengths controlled to those of the ITU-T grids and optical powers of more than 1.5 mW at an injection current of 80 mA without any temperature dependent mode hopping in the 8-channel light source. We also confirmed direct modulation at 2.5 Gb/s in every channel and we showed that we could modulate two adjacent channels simultaneously without any interference effect. These results show that the compact PLC-type integrated light source is promising for use in WDM systems.

12.5-GHz spacing compact and low-loss interleave filter using 1.5% /spl Delta/ silica-based waveguide

We describe the fabrication of a compact lattice-form waveguide interleave filter with a narrow channel spacing of 12.5 GHz. The circuit size was reduced to 1/4 the size of the original circuit by employing a novel folding layout and a waveguide with a high refractive index difference (/spl Delta/) of 1.5% that can reduce the minimum bending radius to 2 mm. The 12.5-GHz spacing interleave filter was fabricated on a single chip by using silica-based planar lightwave circuit technology. We achieved a low insertion loss of <2.3 dB, a wide 1-dB passband width of >8.1 GHz, a 20-dB stopband width of >7.3 GHz, a low crosstalk of <-25 dB, and a low chromatic dispersion of within /spl plusmn/300 ps/nm.

Novel birefringence compensating AWG design

We propose a novel birefringence compensating arrayed waveguide grating (AWG) design that utilizes birefringence dependence on core width. We successfully demonstrated a polarization insensitive 100 GHz-spaced 16-channel multiplexer with a polarization dependent wavelength shift of 0.01 nm.

Crosstalk reduction in arrayed-waveguide grating multiplexer/demultiplexer using cascade connection

This paper proposes a cascade-connected arrayed-waveguide grating (AWG) as a solution to the problem of crosstalk accumulation in a large-scale AWG multiplexer/demultiplexer (MUX/DEMUX) and demonstrates a 64-channel cascaded AWG module with a very low background crosstalk of less than -80 dB and a total crosstalk of about -34 dB. In this paper, the authors densely integrate 64 additional compactly designed crosstalk-suppressing AWGs whose bandwidths were carefully optimized and directly attach them to a conventional 64-channel AWG. Consequently, in addition to a very low crosstalk, a low insertion loss and a compact size without passband shape distortion are achieved with this module. Based on the performance of the cascaded AWG module, it is then estimated that it is possible to realize a 1000-channel AWG MUX/DEMUX that is free from the problem of crosstalk accumulation.

Compactly folded waveguide-type interleave filter with stabilized couplers

We employed our proposed stabilized coupler and folded configuration for use as a 50 GHz channel spacing waveguide-type interleave filter. In spite of its compact layout, it exhibited satisfactory demultiplexing properties including chromatic dispersion.