Ryuzo Iga

Quantum Wire Fabrication by E-Beam Elithography Using High-Resolution and High-Sensitivity E-Beam Resist ZEP-520

We have evaluated the resolution of the positive electron-beam (E-beam) resist ZEP-520 using finely focused E-beam exposure for the application of quantum wire fabrication in a large area. Compared with the poly-methylmethacrylate (PMMA) resist conventionally used for nanofabrication, ZEP resist shows almost the same resolution under sensitivity improvement of one order of magnitude, and the throughput is increased by a factor of more than 100 by introducing a highly bright Zr/O/W thermal field emitter as an E-beam source. Other excellent performance characteristics, such as high dry-etching durability and process stability, allow us to apply ZEP resist for larger-area, high-density quantum wire fabrication. By both wet chemical etching and dry-etching combined with CBE selective growth, InGaAs nanostructures as small as 15 nm can be obtained with a pitch of 70 nm over several hundred µm squares.

Facet growth of InP/InGaAs layers on SiO2-masked InP by chemical beam epitaxy

Abstract Selective area growth of periodic InP/InGaAs heterostructure layers by chemical beam epitaxy are studied. The layers are grown in windows ranging in width from 0.1 to 5 μm under various substrate temperature and mask stripe direction conditions. Mesa-like structures bounded by a (100) top surface and two (111)B sidewalls are selectively grown for InP and InGaAs. An analysis of the time evolution of the mesa cross-section areas reveals that 100% of the metalorganic molecules impinging on the (111)B planes migrate to the (100) plane in InP facet growth, while only 40% of them migrate in InGaAs growth. Cathodoluminescence measurement indicates that the peak wavelengths of the selectively grown InGaAs/InP superlattice shift to longer wavelength as the stripe window width decreases. A 450 A wide InGaAs quantum wire is buried in InP layers in a single growth step. A simple model explaining the facet growth mechanism is also proposed.

A 40-gb/s InGaAlAs-InAlAs MQW n-i-n Mach-Zehnder Modulator with a drive Voltage of 2.3 V

We have developed a traveling-wave Mach-Zehnder modulator using an n-i-n heterostructure fabricated on an InP substrate. We obtained an extremely small /spl pi/ voltage (V/spl pi/) of 2.2 V, even for a short signal-electrode length of 3 mm. We confirmed that the device has an impedance-matched electrode and operates at 40 Gb/s with a single-ended drive voltage of 2.3 V.

1.3-

A 1.3- monolithically integrated light source for metro area 100-Gb/s Ethernet is developed. Four 25-Gb/s electroabsorption modulators integrated with distributed-feedback lasers and their multiplexer are monolithically integrated on one chip. A shallow ridge waveguide is used for lasers and modulators for large modulation bandwidth, and a deep ridge waveguide is used for the multiplexer region due to its low bending and radiation losses. The integration of hetero-waveguide devices enables the very small chip size of 22.6 . With the device, 100-Gb/s (4 25-Gb/s simultaneous) operation is demonstrated with the clear eye-openings, and error-free 40-km single-mode fiber transmission is achieved for the first time.

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We present a multi-channel modulation circuit monolithically integrated with one 25-GHz-spacing AWG for both MUX and DEMUX and eight channels of SOAs and EAMs. The circuit can generate individual optical signals for each DWDM channel with a high extinction ratio of >20 dB and loss compensation. The circuit size can be reduced to 15 /spl times/ 7 mm/sup 2/.

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A compact electroabsorption modulators integrated distributed feedback (EADFB) laser array module has been developed for 100-Gb/s Ethernet. Four 25-Gb/s EADFB lasers and an optical multiplexer are monolithically integrated on one chip in an area of only 2 mm × 2.6 mm. As a result, a compact 12 mm × 20 mm EADFB laser array module is achieved. A bridge-type RF circuit board is employed to transmit high-frequency, 4 × 25-Gb/s, electrical signals effectively in a narrow package and improve the electrical/optical response of the module. The module has a 3-dB frequency bandwidth of 20 GHz for the four lanes assigned in 100-Gb/s Ethernet. Furthermore, the possibility of realizing low-driving voltage operation is investigated to reduce the power consumption of the module. An error-free transmission through 10 km of single-mode fiber at 100 Gb/s with a modulation voltage of only 1 V is demonstrated.

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The first ultra-compact transmitter optical sub-assembly (TOSA) has been developed for the metro-area 100 Gbit/s Ethernet (100 GbE) system. Four DFB lasers integrated with electro-absorption modulators (EADFB lasers) operated at 25.8 Gbit/s and an optical multiplexer are monolithically integrated on one chip. The chip was assembled in the compact TOSA using a three-dimensional (3D) RF circuit board supported by a spacer. The new structure provides compact and high-density interconnection with low crosstalk between RF signal lines. The TOSA is very small at just 8.0 mm × 35 mm × 6.5 mm including the receptacle and the flexible printed circuit (FPC) and could be installed in next-generation small form 100 GbE transceivers. In addition, an error-free transmission is demonstrated through 40 km of single-mode fiber at 100 Gbit/s with a modulation voltage of 2 V.

25-Gb/s Monolithically Integrated Light Source for Metro Area 100-Gb/s Ethernet

We have developed a monolithic integrated device consisting of an electroabsorption modulator and a semiconductor optical amplifier (SOA) connected by a deep-ridge passive waveguide by means of butt-joint selective area growth. Lossless operation with a high extinction ratio of 32 dB and clear eye opening at 10 Gb/s are successfully achieved. We confirm that the optical injection should be from the SOA side of the device to obtain a wide error-free range of incident optical power from -20 to +10 dBm. Our device could lead to richly functional photonic integrated circuits comprising arrayed waveguide gratings (AWGs) for advanced wavelength-division-multiplexing networks, since the passive waveguide has the same structure as AWGs.

Multi-channel modulation in a DWDM monolithic photonic integrated circuit

In this letter, we report the single-mode operation of 1.55-/spl mu/m buried heterostructure vertical-cavity surface-emitting lasers (VCSELs) fabricated on a GaAs-AlAs distributed Bragg reflector using thin-film wafer fusion. A 7-/spl mu/m VCSEL exhibits a single transverse mode at up to about 0.1-mW maximum optical output power and 75/spl deg/C maximum operation temperature under continuous-wave operation.

A Compact EADFB Laser Array Module for a Future 100-Gb/s Ethernet Transceiver

Selective growth of GaAs using an Ar+ laser beam is reported. The laser irradiation during growth in the substrate temperature range 400–525 °C forms a GaAs spot of 400 μm in diameter. The spot growth rate increases up to 1.3 μm/h with laser power and does not depend on the type of substrate conductivity. Temperature rise due to the irradiation is revealed to be 7° at 120 °C for the laser power of 500 mW (laser beam diameter 400 μm). A concentric circle pattern can be formed by diffracting a laser beam. These results strongly suggest that the growth rate enhancement arises from the photodissociation of metalorganic molecules.