Takahashi Hiroshi

Over 1000 channel, 6.25 GHz spaced ultra-dense WDM transmission is achieved over 126 km field-installed fibers in the test bed of JGN II by employing single supercontinuum multi-carrier source. We also investigate the influence of four-wave-mixing that occurred in the ultra-dense WDM transmission.

We describe a compact 1.5%-Delta athermal silica-based 100-GHz-spacing 16-channel arrayed-waveguide grating (AWG) multi/demultiplexer with a modified groove design for a very low excess loss. We propose new approaches for modifying the shape of the grooves and the arrayed waveguides and optimize the shape modifications for 1.5%-Delta waveguides. By employing this modified groove design, we greatly reduced the groove excess loss from 1.9 to 0.4 dB in the 1.5%-Delta athermal AWG.

Over 1000-channel DWDM transmission experiment has been achieved. A 1046 x 2.67 Gbit/s, 6.25 GHz-spaced DWDM signal is successfully transmitted over 126 kin field-installed fibres in the test-bed of JGN II by employing a single supercontinuum lightwave source, which generates more than 1000 carriers and uniform precise channel spacing of 6.25 GHz.

Over 1000-channel DWDM transmission experiment has been achieved. A 1046 x 2.67 Gbit/s, 6.25 GHz-spaced DWDM signal is successfully transmitted over 126 kin field-installed fibres in the test-bed of JGN II by employing a single supercontinuum lightwave source, which generates more than 1000 carriers and uniform precise channel spacing of 6.25 GHz.

We have realized a novel Mach-Zehnder interferometer (MZI) thermo-optic switch that can operate over a much wider wavelength range than a conventional MZI switch. We constructed the novel MZI switch by incorporating a phase-generating coupler (PGC) as an optical coupler. The PGC generates a nonlinear wavelength-dependent phase, which functions as a virtual wavelength-dependent delay part that cancels out the wavelength dependence of a MZI. We fabricated the novel MZI switch on a silica-based planar fight-wave circuit and achieved a low insertion loss of less than 1.6 dB and a high extinction ratio of 30 dB over a wide wavelength range of 160 nm. (C) 2005 Optical Society of America.

We propose a new way for designing optical waveguides with the optimum shape. This approach is called the wavefront matching method and we describe its fundamental aspects and report some experimental results. © 2005 IEEE.

We review recent progress on optical switches that employ silica-based planar lightwave circuits (PLC) including a 16 x 16 matrix switch, a 1 x 128 switch, an 8-channel 1 x 8 switch array, and a 32-channel 2 x 2 switch array. These switches are composed of silica-based waveguides and have a solid-state structure with no moving parts, thus they exhibit low insertion loss, high repeatability, and excellent long-term reliability. We also describe IC-on-PLC technology, where IC chips are integrated on the PLC surface for higher functionality and greater compactness. We report the results of reliability tests on the PLC switches, and show that they can put to practical use.

We propose and fabricate planar waveguide type optical tweezers that use arrayed waveguide gratings as waveguide lenses. We confirm in experiments that the proposed tweezers can manipulate several particles simultaneously without mechanical movable parts. (c) 2004 Optical Society of America.

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. (c) 2005 Optical Society of America.

We report experimental results for small-angle waveguide crossings designed with our recently proposed wavefront matching method. We successfully obtained lower loss and crosstalk values than conventional straight waveguide crossings.

We propose a novel compact optical circuit arrangement for a matrix switch. The fabricated 8 x 8 silica-based PLC switch is half the size of a previously reported switch and exhibits an insertion loss as low as 2.5 dB.

We propose a new way for designing optical waveguides with the optimum shape. This approach is called the wavefront matching method and we describe its fundamental aspects and report some experimental results.

This paper presents a 10-Gb/s wireless link system that uses a 120-GHz-band sub-terahertz electro-magnetic waves. In the transmitter photonic techniques are used for generation, modulation, and emission of the sub-THz signals, while the receiver is composed of all-electronic devices using InP-HEMTs.

We review the athermalization techniques that have been proposed for AWGs and discuss the advantages and disadvantages provided by each approach. We then describe our recent progress on the design and fabrication of a silica-based athermal AWG with a 1.5%-Δ waveguide and report its compactness and excellent optical characteristics including its extremely low insertion loss.

A differential-phase-shift quantum key distribution experiment was carried out with a planar light-wave circuit (PLC) Mach-Zehnder interferometer. This scheme has two advantages: it requires no polarization control and has a high repetition frequency, provided that a stable interferometer is available. Stable polarization-insensitive operation was achieved with an interferometer fabricated by PLC technology. Raw key creation at a rate of 3076 bits/s with a 5.0% quantum bit-error rate was achieved over 20 km of fiber. The stability of the PLC interferometer was examined. (C) 2004 Optical Society of America.

We applied a super-multi-fiber PLC connector for connecting up to 64 ch to the board packaging of an 8 × 8 delivery and coupling switch (DC-SW) module with a fiber sheet. The DC-SW module is composed of plural PLCs and needs a large amount of fiber crossing. The PLC connector can attach fibers to and remove them from a PLC endface and realizes a PLC receptacle module instead of a PLC pigtail module. The fiber sheet resolves the problem of fiber congestion. We demonstrate the smart optical fiber wiring and board packaging of a DC-SW whose optical performance matches that of a conventional switch in which the pigtail fibers of the PLC modules are fusion spliced and squeezed into a package.

A low loss wavelength-selective switch is proposed and demonstrated. The switch has a 1 x 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.

In this paper, we report a wavelength-selective switch which consists of AWGs and an optical 1 x N spatial switch based on transversal filter configuration. The transversal type switch is advantageous, when we integrate thermally sensitive components such as AWGs or LDs with it, because the switch always consumes constant power, regardless of the output selection. We fabricated a wavelength-selective optical 1 x 4 spatial switch with 5 channel AWGs, and confirmed its operating principle. Also, we obtained extinction ratio of 20 dB. We believe that this kind of wavelength-selective switch is applied to wavelength router or optical cross connect system.

Optical circuits composed of delay lines and couplers are widely used in optical signal processing. However, optical component that employs such a circuit is not suitable in a system whose channel arrangement is periodic with respect to wavelength, since the transmission spectra of the circuit are theoretically periodic with respect to frequency. In this paper, we show that optical circuits with a uniform wavelength period can be realized by generating a wavelength dependent phase with the phase-generating coupler (PGC) that we propose. We have applied our method to a Mach-Zehnder interferometer (MZI) as an example of an optical circuit and obtained excellent transmission spectra with a uniform wavelength period.

Pulse waveform shaping with a silica-waveguide-based circuit employing an arrayed-waveguide grating pair and an array of amplitude and phase controllers is demonstrated. The frequency components of a modelocked laser have been flexibly synthesised to produce 40 GHz square pulses with various widths.

We have realized a first optical filter composed of optical delay lines and couplers that has a periodic response with respect to wavelength, whereas a conventional optical filter is known to have a periodic response to relative optical frequency. This new filter can be constructed by using a phase-generating coupler (PGC) that supplies the optical delay lines with a wavelength-dependent nonlinear phase. The PGC, which is also composed of optical delay lines and couplers, can simultaneously provide a desired phase and an arbitrary amplitude coupling ratio. We applied our transformation method to a conventional Mach-Zehnder interferometer (MZI) as an-example of an-optical frequency filter and converted it to an optical wavelength filter. We fabricated the designed MZI on a silica-based planar lightwave circuit and successfully realized what is believed to be the first MZI with a uniform wavelength period. (C) 2004 Optical Society of America.

We demonstrate the generation of 90-125 GHz inillimeter-wave signal with a phase noise of less than -75 dBc/Hz at 100 Hz; by using optical heterodyning that employs an arrayed-waveguide grating (AWG) integrated with 3-dB combiners.

Optical switches based on silica-based planar lightwave circuit (PLC) technology are promising devices for use in constructing optical switching systems because they have the advantages of a low insertion loss, high integration and high reliability. We have successfully fabricated a 32-channel 2×2 optical PLC switch array that is suitable for OADM systems. This switch was realized by using a new circuit configuration for OADM systems and a low power consumption technique to provide higher integration. We report the circuit configuration and good optical performance of this switch.

Optical switches based on silica-based planar lightwave circuit (PLC) technology are promising devices for use in constructing optical switching systems because they have the advantages of a low insertion loss, high integration and high reliability. We have successfully fabricated a 32-channel 2×2 optical PLC switch array that is suitable for OADM systems. This switch was realized by using a new circuit configuration for OADM systems and a low power consumption technique to provide higher integration. We report the circuit configuration and good optical performance of this switch.

A novel optical bandpass filter is proposed that consists of an arrayed-waveguide grating pair and an optical slit. A 200 GHz cyclic and 40 GHz passband optical filter using the proposed configuration, which is useful for WDM single sideband filtering, is successfully demonstrated.

We investigated two types of novel sliess controlling waveguide structure with a view lo realizing a polarization-insensitive silica-based AWG. We clarified the relationship between the polarization sensitivity and waveguide structure by using stress analysis. We experimentally confirmed that both waveguide structures successfully provide polarization-insensitive characteristics (AX<0.01 nm) without any optical degradation.

Optical switches based on silica glass waveguide planar lightwave circuit are promising devices for constructing a large-scale optical switching system because a lot of switch elements can be integrated and they have high reliability. This report describes the structure of the switch element, the design of whole switch circuit and new methods for improving their optical characteristics. Experimental results of 16 x 16 matrix switch, 1 x 128 selection switch, 8-array 1 x 8 switch and 8 x 8 DC switch are shown as application examples of this technology.

The planar lightwave circuit type optical switch (PLC-SW) is highly reliable and suitable for functionality integration. We have applied the PLC-SW to the lambda label routing unit or optical path cross-connect (OPXC) of a photonic multi-protocol label switching router that we have been developing since 2000. We developed a compact optical switch package in the OPXC with high-density PLC-SW devices implemented with high functionality. In this report, we briefly describe the OPXC, which is now a mature system. We then describe the optical switch package, its characteristics, and related reliability test results.

An optical switch based on a transversal filter configuration is demonstrated. The switch consists of cascaded 3 dB optical power splitters and a phase shifter array. By using a silica-based planar lightwave circuit, a 1 x 4 optical switch was realised. A characteristic of the switch is that its power consumption is constant regardless of the output selection.

Optical cross-connects and optical add-drop multiplexers are essential for the construction of WDM network system with larger capacity and higher performance. Optical switches attract much attention because they will act as key devices in the network. Silica-based PLC optical switches we have developed have excellent optical characteristics and are near practical use. Among those optical switches, 8-arrayed 2x2 and 8-arrayed 1x2 optical switches was investigated in terms of reliability. Through a set of reliability tests based on Telcordia standards, we confirmed the sufficient mechanical strength and the long-term reliability of the switches.

We have developed planar lightwave circuit type switches (PLC-SWs) that offer the advantages of a low insertion loss and long-term stability, and which are useful for photonic network systems based on WDM technologies such as optical cross connect systems. This switch consists of a Mach-Zehnder interferometer and thin film heaters, and operates via the thermo-optic effect. Advances in WDM photonic networks have led to a need for more data channels. We have to develop a compact and large-scale optical switch and realize low power consumption. This paper describes a compact and low driving power PLC-SW that employs super high delta waveguides and heat insulating grooves. We have realized a very compact switch element that is l/3 smaller than a conventional element, and which uses 1/10 the driving power. We also report the applications of these configurations to IxN type switches, which are very useful for practical systems.

Silica-based planar lightwave circuits (PLC) are key components of functional devices designed for use in optical fiber communication systems because, compared with bulk optics devices, they offer compactness, excellent stability and reliability in addition to high functionality. This talk reviews the current status of PLC development. The fabrication process, basic characteristics, packaging and reliability are. presented, many device applications are described, and experimental results related to optical switches, interleave filters, chromatic/polarization dispersion compensators, gain spectrum equalizers and wavelength multiplexers are reported. Finally, the history of PLC development is summarized, and future target devices are described along with the kind of development needed for such devices designed for use in the next generation of optical communication systems.

By optimizing the structure of the Mach-Zehnder interferometer made of silica-based waveguide and the lightwave circuit, it is shown that it is possible to obtain an optical switch with high extinction even if there is process variation in waveguide optical length and coupling ratio of directional coupler. We designed and fabricated 8-array 1 × 8 switch chips with this optimization and the chips exhibited average extinction of 56 dB without optical length adjustment after fabrication. It is also shown that the characteristics of the switch maintain in wide environmental temperature range with theoretical consideration on temperature dependence.

A novel method of flattening the passband of an arrayed waveguide grating with a small excess loss, which employs a new concept that uses the assist of the weak first-order mode, is described. A 16-channel 100 GHz-spacing demultiplexer with a fibre-to-fibre loss of less than 3.6 dB and a flattened excess loss of 1.85 dB is demonstrated. The I dB down passband is widened 2.2 times.

A novel method of flattening the passband of an arrayed waveguide grating with a small excess loss, which employs a new concept that uses the assist of the weak first-order mode, is described. A 16-channel 100 GHz-spacing demultiplexer with a fibre-to-fibre loss of less than 3.6 dB and a flattened excess loss of 1.85 dB is demonstrated. The I dB down passband is widened 2.2 times.