高橋 浩

We review recent progress on our integrated-optic OFDM demultiplexers fabricated with silica PLC technology. We detail the configuration, operating principle, and characteristics of the demultiplexers, which are based on optical FFT and DFT. (C)2011 Optical Society of America

A flexible and compact hierarchical optical cross-connect (HOXC) node that considers a practical waveband add/drop restriction is proposed. We introduce a prototype HOXC system and verify its technical feasibility and transmission characteristics.

Both high density multiplexing and high speed transmission are required for large capacity networks supporting broadband service penetration. This paper reviews recent progress on key devices based on silica waveguide lightwave circuits for such systems.

We propose a compact hierarchical optical cross-connect architecture with modular growth capability utilizing newly developed waveband selective switches with dedicated waveband drop ports for grooming. 10-degree HOXC prototype systems are developed and their feasibility verified.

The signal transmission characteristics of the first practical hierarchical optical cross-connect with a terabit-scale throughput are clarified experimentally employing 10-Gb/s wavelength-division-multiplexed signals. The observed power penalty was less than 0.9 dB after a 4-hop signal transmission.

A compact polarisation-multiplexed differential quadrature phase-shift keying (DQPSK) demodulator achieved by integrating a polarisation beam splitter and two DQPSK demodulators consisting of a delay interferometer and a 90 degrees-hybrid using silica-based planar lightwave circuit technology is demonstrated. The optical characteristics of the fabricated demodulator were sufficient for the direct detection of 100 Gbit/s polarisation-multiplexed DQPSK signals.

We present a full description of a polarization-independent athermal differential quadrature phase shift keying (DQPSK) demodulator that employs silica-based planar lightwave circuit (PLC) technology. Silica-based PLC DQPSK demodulator has good characteristics including low polarization dependence, mass producibility, etc. However delay line interferometer (DLI) of demodulator had the large temperature dependence of its optical characteristics, so it required large power consumption to stabilize the chip temperature by the thermo-electric cooler (TEC). We previously made a quick report about an athermal DLI to reduce a power consumption by removing the TEC. In this paper, we focus on the details of the design and the fabrication method we used to achieve the athermal characteristics, and we describe the thermal stability of the signal demodulation and the reliability of our demodulator. We described two athermalization methods; the athermalization of the transmission spectrum and the athermalization of the polarization property. These methods were successfully demonstrated with keeping a high extinction ratio and a small footprint by introducing a novel interwoven DLI configuration. This configuration can also limit the degradation of the polarization dependent phase shift (PDf) to less than 1/10 that with the conventional configuration when the phase shifters on the waveguide are driven. We used our demodulator and examined its demodulation performance for a 43 Gbit/s DQPSK signal. We also verified its long-term reliability and thermal stability against the rapid temperature change. As a result, we confirmed that our athermal demodulator performed sufficiently well for use in DQPSK systems.

We have successfully demonstrated an AWG with a wide and rectangular passband by introducing a new concept using 0th and 1st order modes. An interference circuit consisting of a tandem MZI and a mode converter at the entrance of the 1st slab waveguide perturbs the input light field, thus attaining a 0.5-dB bandwidth of 69% relative to its channel spacing.

An integrated-optic demultiplexer is realised for use with 8 x 10 Gbaud orthogonal frequency division multiplexed subcarrier channels. The device is composed of an 8 x 8 optical fast Fourier transform circuit and an array of optical gates, and is used to demultiplex a 160 Gbit/s polarisation multiplexed signal in the optical domain.

We propose and demonstrate a novel technique for interconnecting arrayed-waveguide-grating-based wavelength routing networks. Experiments reveal that this technique enables us to establish full-mesh wavelength paths between arbitrary nodes in two networks.

We describe a technique for reducing the wavelength-dependent phase-difference deviation between in-phase and quadrature components in an 90 degrees optical hybrid consisting of four 3-dB couplers and a phase shifter. We fabricated the 90 degrees hybrid with our proposed technique, which uses silica-based planar lightwave circuit technology. The fabricated 90 degrees hybrid exhibits a low phase-difference deviation from 90 degrees of less than 0.7 degrees over the C- and L-bands, and will be useful in a digital coherent receiver for transmission systems operating at 100 Gbit/s or more.

This paper investigates the performances of recently developed ultra-compact waveband cross-connect modules that will play a key role in the creation of hierarchical optical path networks. We confirm negligible coherent crosstalk effects and good cascadability.

This paper discusses practical applications of the frequency band starting at 100 GHz-a band that has yet to be fully exploited. It considers the feasibility of future applications driven by the sub-terahertz and terahertz bands, examining this feasibility from two perspectives: (1) market needs and the standards being released to meet these needs mainly in the area of communications applications, and (2) advances in semiconductor technologies and their peripheral technologies. To discuss approaches to implementing these applications, we present two transmission technologies that we are developing.

We demonstrate a compact wavelength/waveband selective switch based hierarchical optical cross-connect (HOXC) system for the first time. Its performance confirms that the HOXC will be applied to create cost-effective metro-core and metro-edge ring interconnections. (C) 2010 Optical Society of America

Described is a compact dual polarisation optical hybrid (DPOH) that has been achieved by integrating polarisation beam splitters and 908-hybrids fabricated with silica-based planar lightwave circuit technology. The fabricated DPOH worked completely passively without any adjustments and its optical characteristics were sufficient for the coherent detection of 111 Gbit/s DPQPSK signals.

The first practical hierarchical optical cross-connect system is developed and its feasibility confirmed using field-installed fibers. Fully-implemented equipment requires a 16-U chassis to manage 4.8-Tbit/s signals from 8 WDM lines and 160 client ports. (C) 2010 Optical Society of America

An integrated-optic demultiplexer for 8 x 10 Gbaud OFDM sub-carrier channels is realized, which comprises a PLC-based 8 x 8 optical FFT circuit. It is successfully used to demultiplex a 160 Gbit/s OFDM signal optically. (C) 2010 Optical Society of America

We propose and demonstrate a novel wide passband MZI-synchronized AWG and a simple way to eliminate its group delay ripple. We obtained a 0.5-dB passband of 69 GHz and a 0.5 ps total GDR for a dispersion balanced out pair.

We present a novel optical OFDM demultiplexer with a silica-PLC-based optical DFT circuit. This compact device can process an arbitrary number of subcarriers. The operation of a ten-channel device is demonstrated by demultiplexing a 100-Gbit/s (10-subcarrier x 10-Gbit/s) OFDM signal.

A tunable optical dispersion compensator that uses cascaded arrayed-waveguide gratings and integrated phase shifter is reported. It is reflective configuration but does not require a circulator. The dispersion is successfully controlled from +142 to +1148 ps/nm.

We describe a silica-based arrayed-waveguide grating (AWG) with low channel-dependent loss variation achieved by using mode-field converters designed with the wavefront matching method. This mode-field converter converts the fundamental mode of the arrayed waveguide into the field distribution with a flat-top far field at the interface between the slab and output waveguides. We applied our mode-field converters to an AWG with a 100-GHz channel spacing and reduced the loss deviations experimentally from 2.4 to 0.7 dB over one free spectral range. Moreover, we confirmed that the introduction of our mode-field converters had no adverse effects on the AWG demultiplexing characteristics. It is notable that the loss uniformity was improved solely by replacing the conventional tapered waveguide between the arrayed waveguides and output slab waveguide with our mode-field converter without sacrificing the fabrication manageability or AWG design flexibility.

This paper describes a waveguide crossing design that uses the wavefront matching (WFM) method. The WFM method enables us to design waveguide crossings with lower loss than simple crossings composed of two straight waveguides, without any crosstalk degradation. We report the procedure for designing waveguide crossings based on the WFM method and some experimental results. For experimental confirmation, we made a waveguide crossing test circuit using silica-based planar lightwave circuit (PLC) technology. By comparing the results obtained with samples constructed with different waveguides, we show that our design method is very efficient for higher waveguides suitable for high-density integration. In addition, we describe an example application of our designed crossings to an integrated PLC device, namely a wavelength multiplexer with a variable optical attenuator. We show that waveguide crossings designed by the WFM method are useful for improving the loss characteristic of highly integrated PLC devices.

We propose a novel reconfigurable AWG-STAR (physical star topology network with arrayed-waveguide grating router) that employs two kinds of cyclic-frequency arrayed-waveguide gratings whose repetition channel numbers are coprime. We demonstrate that all the wavelength paths can be assigned independently with excellent transmission characteristics.

A 43-Gb/s differential quadrature phase-shift keying demodulator is demonstrated with a wide operation range enhanced by birefringence control achieved by using stress release grooves. The fabricated demodulator realizes a sufficiently low polarization-dependent frequency shift of less than 150 MHz over the C- and L-bands. In addition, we report an experimental result showing the reduction in the power consumption of a thermooptic effect-based phase shifter achieved by introducing the grooves.

We demonstrate a low power consumption differential quadrature phase-shift keying (DQPSK) demodulator using silica-based planar lightwave circuit (PLC) technology. A reduction of the power consumption is achieved by suppressing the temperature dependence of the circuit characteristic and eliminating a thermo-electric cooler (TEC) device. The maximum power consumption of the fabricated demodulator with an operating temperature range of -5 degrees C to 70 degrees C is 1.4 W, which is 60% lower than that of a conventional PLC demodulator with TEC. We report experimental results that demonstrate its good demodulation performance for a 43-Gb/s DQPSK system.

An integrated-optic device for demultiplexing optical orthogonal frequency-division-multiplexed signals is described that consists of an optical fast-Fourier-transform circuit and optical gates. The fast-Fourier-transform circuit is composed of symmetrical Mach-Zehnder interferometers that are suitable for precisely adjusting filter characteristics. This device can process four or more channels with a relatively simple configuration and reduced size. An optical demultiplexer for four subcarrier channels is realized and used to demultiplex 4 X 10 Gbit/s signals. (C) 2009 Optical Society of America

In this paper, we describe the procedure for designing low-loss Y-branch waveguides by the wavefront matching (WFM) method, and report experimental results as proof of concept. The designed Y-branches were fabricated using silica-based planar lightwave circuit (PLC) technology. A Y-branch fabricated with a 0.45%-Delta waveguide exhibited a low excess loss of less than 0.2 dB over a wide wavelength range of 1250 to 1650 nm. In addition, we demonstrate that the WFM-designed Y-branches enable us to provide compact 1 x 32 splitters with an average insertion loss of 16.0 dB at a wavelength of 1550 nm. In addition, we present some experimental results obtained using samples with different Delta values, and show that our design method is more efficient for a higher Delta waveguide suitable for functional PLC devices.

A planar lightwave circuit based device is proposed that can recognise optical multiwavelength pulse patterns based on digital-to-analogue conversion. The device consists of a splitter with variable splitting ratios, delay lines and an arrayed-waveguide grating based wavelength multiplexer, and requires no optical gates. 80 Gbit/s and four-bit label recognition experiments were successfully carried out with the device.

We propose an integrated-photonic device for demultiplexing optical OFDM signals that consists of an optical FFT circuit. An optical demultiplexer for four OFDM sub-carriers is realized, and used to demultiplex 4 x 10 Gbit/s signals. (C)2009 Optical Society of America

A low power consumption DQPSK demodulator is realized with a PLC with resin-filled grooves. The power consumption from -5 to 70 degrees C is 1.4W, which is 60% lower than for a conventional demodulator with TEC control. (C)2008 Optical Society of America

We propose a novel flexible AWG-STAR system that employs two kinds of cyclic-frequency AWGs whose repetition channel numbers are coprime. We demonstrate that we can reconfigure all the wavelength paths in a network independently. (C)2008 Optical Society of America

We demonstrate a compact dual polarization optical hybrid achieved by the integration of polarization beam splitters and 90 degrees-hybrids using silica-based planar lightwave circuit. The fabricated device exhibited sufficient characteristics for coherent systems such as DP-QPSK.

We demonstrate a compact waveband cross-connect switch module that will be utilized for creating cost-effective multi-degree optical cross-connect nodes. Its measured performance confirms that it can be applied to metro-edge/ metro-access networking in the future.

An efficient ROADM-ring connecting node architecture is proposed that utilizes waveband routing and achieves small footprint and cost-effectiveness. The key component devices are implemented using PLC technologies and the system performance is experimentally verified.

An AWG-based tunable dispersion compensator with integrated silicone lenses is fabricated. Its tuning range runs from +47 to +410 ps/nm and error-free dispersion compensation is confirmed fir 42.7-Gbps CSRZ-DQPSK optical signals.

We propose and demonstrate a novel technique for interconnecting AWG-based wavelength routing networks. Experiments successfully demonstrated that this enables us to establish full-mesh wavelength paths between arbitrary nodes in two networks.

Silica waveguide planar lightwave circuit (PLC) technology is very useful for fabricating compact and high performance optical devices for optical communication. Wavelength multiplexers and optical switches for ROADM and OXC are still being developed to improve performance further. New devices for an advanced modulation format can also be fabricated with PLC technology. © 2009 SPIE-OSA-IEEE.

We developed an 8x8 wavelength router incorporating two AWGs and multiple 4x4 matrix switches to allocate WDM channels for each route flexibly. We describe the design principles of the router and its basic transmission characteristics. (C) 2007 Optical Society of America.