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Laser cladding is one of the most useful surface coating methods for improving the wear and corrosion resistance of material surfaces. Although the heat input associated with laser cladding is small, a heat affected zone (HAZ) is still generated within the substrate because this is a thermal process. In order to reduce the area of the HAZ, the heat input must therefore be reduced. In the present study, we examined the effects of the powdered raw material particle size on the heat input and the extent of the HAZ during powder bed laser cladding. Ni–Cr–Si–B alloy layers were produced on C45 carbon steel substrates in conjunction with alloy powders having average particle sizes of 30, 40 and 55 µm, while measuring the HAZ area by optical microscopy. The heat input required for layer formation was found to decrease as smaller particles were used, such that the HAZ area was also reduced.

A Ni-Cr-Si-B alloy layer was produced on a type 304 stainless steel plate by laser cladding. In order to produce cladding layer with smooth surface and low dilution, influence of laser beam profile on cladding layer was investigated. A laser beam with a constant spatial intensity at the focus spot was used to suppress droplet formation during the cladding layer formation. This line spot, formed with a focussing unit designed by our group, suppressed droplet generation. The layer formed using this line spot with a constant spatial intensity had a much smoother surface compared to a layer formed using a line spot with a Gaussian-like beam. In addition, the dilution of the former layer was much smaller. These results indicated that a line spot with a constant spatial intensity was more effective in producing a cladding layer with smooth surface and low dilution because it suppressed droplet generation.

Laser cladding is one of the useful surface coating methods for improving the quality of wear and corrosion resistance of material surface. Compared with other conventional surface coating methods, such as thermal spray and plasma transferred arc welding (PTA), laser cladding can produce much better coatings with minimum dilution and well bond to the substrate. Ni-Cr-Si-B alloy is widely used as a hard facing material. However hardness of this layer produced by PTA is decreased due to dilution. In this study, we investigated the influence of power density and heat input on hardness of the Ni-Cr-Si-B alloy layer. We revealed the combination of laser parameters which can produce cladding layer with Ra of under 8 μ m and upper the hardness of 820 HV.Laser cladding is one of the useful surface coating methods for improving the quality of wear and corrosion resistance of material surface. Compared with other conventional surface coating methods, such as thermal spray and plasma transferred arc welding (PTA), laser cladding can produce much better coatings with minimum dilution and well bond to the substrate. Ni-Cr-Si-B alloy is widely used as a hard facing material. However hardness of this layer produced by PTA is decreased due to dilution. In this study, we investigated the influence of power density and heat input on hardness of the Ni-Cr-Si-B alloy layer. We revealed the combination of laser parameters which can produce cladding layer with Ra of under 8 μ m and upper the hardness of 820 HV.

In order to investigate the influence of beam profile on laser cladding phenomena, Ni-Cr-Si-B alloy coating was produced on type 304 stainless steel plate with two types of beam profile, Gaussian-like and flat-top type. High speed observation revealed that Gaussian-like beam profile generated the droplets near the molten pool. These droplets caused the rough cladding layer. Droplets were not generated by using flat-top beam profile. These droplets caused the rough cladding layer. Flat-top beam profile suppressed the droplets formation and smooth cladding layer was produced.In order to investigate the influence of beam profile on laser cladding phenomena, Ni-Cr-Si-B alloy coating was produced on type 304 stainless steel plate with two types of beam profile, Gaussian-like and flat-top type. High speed observation revealed that Gaussian-like beam profile generated the droplets near the molten pool. These droplets caused the rough cladding layer. Droplets were not generated by using flat-top beam profile. These droplets caused the rough cladding layer. Flat-top beam profile suppressed the droplets formation and smooth cladding layer was produced.

The surfaces of many engineering components requires the quality of wear and corrosion resistance in order to extend the service life. Laser cladding is one of the surface modification methods to produce high quality, metallurgically bonded coatings on substrates with a minimal heat input into the substrate. Recently, weight reduction and energy consumption of engineering components is required because of resource depletion. One approach for meeting this demand is formation of thin cladding layer on thin substrate. Powder material with small particles are needed in order to form thin cladding layer. The effect of particle diameter on powder melting process is important in laser cladding. In this study, Ni-Cr-Si-B alloy coating was produced in order to investigate the effect of the particle diameter on powder melting process.

This paper presents a fully electrical 40-Gb/s time-division-multiplexing (TDM) system prototype transmitter and receiver. The input and output interface of the prototype are four-channel 10-Gb/s signals. The prototype can be mounted on a 300-mm-height rack and offers stable 40-Gb/s operation with a single power supply voltage. InP high-electron mobility transistor (HEMT) digital IC's perform 40-Gb/s multiplexing/demultiplexing and regeneration. In the receiver prototype, unitraveling-carrier photodiode (UTC-PD) generates 1 V/sub pp/ output and directly drives the InP HEMT decision circuit (DEC) without any need for an electronic amplifier. A clock recovery circuit recovers a 40-GHz clock with jitter of 220 fs/sub pp/ from a 40-Gb/s nonreturn-to-zero (NRZ) optical input. The tolerable dispersion range of the prototype within a 1-dB penalty from the receiver sensitivity at zero-dispersion is as wide as 95 ps/nm, and the clock phase margin is wider than 70/spl deg/ over almost all the tolerable dispersion range. A 100-km-long transmission experiment was performed using the prototype. A high receiver sensitivity [-25.1 dBm for NRZ (2/sup 7/-1) pseudorandom binary sequence (PRBS)] was obtained after the transmission. The 40-Gb/s regeneration of the InP DEC suppressed the deviation in sensitivity among output channels to only 0.3 dB. In addition, four-channel 40-Gb/s wavelength-division-multiplexing (WDM) transmission was successfully performed.

This paper reports on 20- and 40-Gbit/s differential precoder modules for optical duobinary transmission systems. These precoder modules overcome the speed limit of a conventional precoder by parallel processing. The proposed precoders handle two or four parallel signals before multiplexing with data rates of one-half or one-quarter the transmission bit rate, and the final preceded signal is obtained by multiplexing the precoder output bit by bit, production-level 0.2-/spl mu/m gate-length GaAs MESFET's were used to fabricate the precoders. The precoders are mounted in an RF package. They successfully performed 20- and 40-Gbit/s precoding for the first time, and the 20-Gbit/s precoder achieved a maximum precoding rate of 22 Gbit/s, which is 76% faster than that of the conventional circuit using the same MESFETs. The 40-Gbit/s precoder performs 40-Gbit/s precoding when combined with a 40-Gbit/s multiplexer unit. Twenty-Gbit/s optical duobinary transmitter and receiver circuits using the 20-Gbit/s precoder module successfully generate fully encoded optical duobinary signal at this rate for the first time. These circuits show a receiver sensitivity of -28.6 dBm for a bit error rate of 1/spl times/10/sup -9/.

This paper describes a 4O-Gbit/s decision integrated circuit (IC) fabricated with 0.12-/spl mu/m gate length GaAs metal-semiconductor field-effect transistors (MESFET's). A superdynamic flip-flop circuit and a wide-band amplifier were applied in order to attain 40-Gbit/s operation. A conventional static decision IC was also fabricated for comparison. The dynamic decision IC operated up to 40 Gbit/s, which is twice as fast as the conventional static decision IC. Error-free 40-Gbit/s operation is the fastest among GaAs MESFET decision IC's.

This paper describes an optical repeater circuit that uses an InAlAs/InGaAs HEMT digital integrated circuit (IC) chip set. The chip set includes a 64-Gb/s 2:1 multiplexer (MUX), a 40-Gb/s demultiplexer (DEMUX), a 46-Gb/s decision circuit (DEC), and a 48-GHz frequency divider (DIV). Electrically multiplexed and demultiplexed 40-Gb/s 300-km transmission is successfully demonstrated.

This paper describes the device, circuit design, and packaging technologies applicable to 40-Gb/s-class future lightwave communications systems. A 0.1-/spl mu/m gate InAlAs-InGaAs high electron mobility transistors (HEMTs) with InP recess etch stopper was adopted mainly for IC fabrication. Fabricated ICs demonstrate excellent data-multiplexing, demultiplexing, and amplifying operation at 10 Gb/s.

Formation phenomena of cladding layers were observed with high speed video camera to analyze the cladding layer formation process. The influence of the overlap rate and laser beam profile were also investigated on formation process of cladding layer. High speed video revealed that the bottom of the laser beam having low power intensity melted only powder material without melting the substrate and gathered powder to be a globular shape. This caused the lack of powder material, melting of the substrate and mixing substrate to cladding layer by the following laser irradiation. The gathering of powder material was suppressed by using a copper slit to shape laser beam profile. It was found that the laser beam profile strongly affected the laser cladding process.

A pulse-rate-tunable, electrooptic pulse-pattern generator and a wideband high-efficiency optical-to-electrical (OE) conversion stimulus probe have been developed. Sinusoidal electrooptic amplitude/phase modulation and chirp compensation were used to provide picosecond pulsation, and the relationship between pulse-rate tunability and the extinction ratio has been studied analytically and experimentally. Return-to-zero (RZ) pylse patterns of 10–72 Gb s−1 have been generated by using LiNbO3 amplitude/phase modulators with a bandwidth of 18 GHz, a single dispersion shifted fibre, and a time-division multiplexer. A 1.55 μm waveguide p-i-n photodiode yielded high responsivity (0.75 A W−1) and a saturation peak voltage of 200 mV at the probe tip. The measured effective 3 dB bandwidth exceeds 50 GHz, which is currently limited by the frequency dispersion of the coplaner waveguide (CPW) used in the probe. Use of this generator and probe, in combination with electrooptic sampling, for on-wafer characterization of a broadband distributed amplifier revealed the amplifier's saturation characteristics and waveform distortion under actual operating conditions with a 64 Gb s−1, 120 mV per probe, RZ pulse-pattern input.

This paper proposes a novel model for estimating power dissipation of optical/electrical interconnections as a function of transmission bit error rate. This model is applied to a simplified optoelectronic transmitter and receiver configuration in which a photodetector is directly connected to the decision circuit. It is analytically verified that this configuration can achieve error-free operation with low power under practical operating conditions. A comparison between optical and electrical interconnections based on this simplified configuration is performed. This result shows the interconnection length and bit rate at which optical interconnection is superior in terms of power dissipation to electrical interconnection, Only optical interconnections achieve error-free operation with 40 mW power dissipation at a transmission bit rate of 10 Gb/s and an interconnection length over 7 m.

By reducing optical path length with a light collection system, we achieved the smallest dual-rate triplexer for use in 10G-EPON OLT XFP transceivers, while maintaining performance high enough to meet IEEE specifications.

We offer an isolator-free EA-DFB module by employing forward error correction. We analyze the behavior of a laser under optical feedback and the error occurrence mechanism. We obtain error-free operation at the receiver sensitivity of −31 dBm.

A low-cost and small BOSA achieves excellent optical transmission waveforms with a >40% mask margin in a wide temperature range (−10 to 85 oC) by using impedance matching circuits in a low-cost TO CAN package.

NRZ operation at 40 Gb/s has been successfully performed using a very compact module of a multiple-quantum-well (MQW) electroabsorption modulator integrated with a distributed-feedback (DFB) laser. While the DFB laser is injected with a constant current, the integrated MQW electroabsorption modulator is driven with a 10-Gb/s electrical NRZ signal. A clearly opened eye diagram has been observed in the modulated light from the modulator. And a receiver sensitivity of -27.2 dBm at 10/sup -9/ has been experimentally confirmed in the bit-error-rate (BER) performance.

In high-speed and/or long-haul transmission systems with data rates of 40 Gbit/s and beyond, the system degradation due to 1st- and also higher-order polarization mode dispersion (PMD) is a significant issue. So far, PMD compensators have been proposed for 1st- and higher-order PMD. In this paper, we focus on two types of optical PMD compensators, single-stage first-order compensator and double-stage compensator with higher-order canceller, and estimate their performances. Moreover, we propose a single-stage first & higher-order compensator as a “degenerate” version of the double-stage one by reducing the number of monitoring parameters (circuit) and the number of controllers (PCs). The functions of 1st- and higher-order PMD compensators are integrated into a single-stage configuration, with signal distortion monitoring at the output of the polarizer. The compensation performance of three PMD compensators is investigated in a 10.7 Gbit/s NRZ transmission system. The results show that the proposed single-stage compensator can effectively suppress the degradation due to 2nd-order PMD.

A joint field trial on 40G transmission was conducted, where Deutsche Telekom's and NTT's R&D groups got involved. 43-Gbit/s/ch CS-RZ signals of the NTT G.709-OTN system were transmitted over selected high-PMD fiber links in DT's actual field environment. The advantage of CS-RZ modulation format was confirmed in comparison with conventional NRZ against all-order (first- and higher-order) PMD. Moreover, we introduced a new scheme for an accelerated determination of outage probability due to PMD that is adapted to practical field conditions in an operated fiber network with buried fibers and in-line operational optical elements.

This paper reports on precoder IC modules for 20 Gbit/s and 40 Gbit/s optical duobinary transmission systems that uses production-level 0.2 /spl mu/m gate-length GaAs MESFETs. The transmitter using the precoder module generates fully encoded 20 Gbit/s optical duobinary signals for the first time and achieves a high receiver sensitivity of -28.6 dBm.

A 120 Gbit/s transmission system prototype that uses optical time-division multiplexing is successfully demonstrated. Independently modulated, four 20 Gbit/s and one 40 Gbit/s channels in 120 Gbit/s signal are transmitted through a 160 km dispersion shifted fiber.

We demonstrate 1.04-Tbit/s (13-channel) dense-WDM transmission experiment based on alternate-polarization 80-Gbit/s signals with 0.4-bit/s/Hz spectrum efficiency, over a 89-km zero-dispersion-flattened transmission line using a Mach-Zehnder modulator pulse generator.

This paper presents the recent progress of 40-Gbit/s time division multiplexing (TDM) transmission technologies based on 0.1-/spl mu/m InP HEMT ICs and new optical devices operating at 40 Gbit/s and beyond. System experiments demonstrate that the 40-Gbit/s TDM system is very attractive for upgrading transmission capacity into the Tbit/s range.

This paper describes an InAlAs/InGaAs HEMT digital IC chip set which includes a multiplexer, demultiplexer, decision circuit, and frequency divider. Electrically multiplexed and demultiplexed 40-Gbit/s transmission is successfully performed.

This paper describes a 40 Gbit/s decision IC using 0.15-/spl mu/m gate length GaAs MESFETs. A super-dynamic flip-flop circuit and wideband amplifier were applied in order to attain 40 Gbit/s operation. The IC is the first to provide an error-free 40 Gbit/s decision operation.

We propose a simple reshaping and regenerating (2R) repeater. We show that it reduces the power penalty that arises from ASE noise at 10 Gbit/s. The repeating performance is investigated both experimentally and numerically.

A 43 Gbit/s CS-RZ OTN system in a PMD-limited transmission line in an actual field environment has been tested. The advantage of CS-RZ modulation in comparison with conventional NRZ against all-order PMD is confirmed. Also, ITU-T G.709 FEC performance against all-order PMD is clarified. High second-order PMD of 200 ps/sup 2/ was accommodated with the FEC.

The authors demonstrate a 40 Gbit/s simple optical receiver that uses a uni-travelling-carrier photodiode as a decision IC driver. The photodiode drives the decision circuit directly with 1 Vp-p without any electrical amplifier. Receiver sensitivity of –27.8 dBm was obtained at 40 Gbit/s.

The authors demonstrate the high dispersion tolerance of a 40 Gbit/s optical duobinary signal. The tolerable dispersion range of the signal was 175 ps/nm. This dispersion range is more than twice that obtained using a binary non-return-to-zero intensity modulated signal.

The authors report a new transmission scheme in which bandwidth-weighted TDM and WDM signals are optimised against dispersion of a transmission fibre. Using a wideband optical amplifier, simultaneous transmission of 40 Gbit/s TDM signals and 4 channel /spl times/20 Gbit/s WDM signals is successfully demonstrated.

The authors propose a simple optical gate that uses an electroabsorption modulator driven by a high-speed and high-saturation output photodiode. The photodiode generates a 10 GHz short electrical pulse larger than 2 Vpp and directly drives the modulator. The optical gate demonstrates as 40 Gbit/s 4:1 demultiplexing operation.

Summary form only given. This paper demonstrates 160-Gbit/s wavelength-division multiplexing (WDM) transmission using a four-channel multiplexed 40-Gbit/s optical duobinary signal. Four-channel WDM transmission without individual-channel dispersion compensation is possible because of the high dispersion tolerance of the optical duobinary signal. To our knowledge, this is the first demonstration of 40-Gbit/s optical duobinary transmission.

A simple wavelength converter is proposed in which the optical modulator is directly driven by a high-speed and high-output current photodiode. The converter is capable of 10 Gbit/s operation with a wavelength conversion range from 1.53 to 1.56 µm.

The authors describe an approach for realising a single-channel 40 Gbit/s optical repeater system using InP-based HEMTs. A fundamental optical repeater circuit using the HEMT IC modules successfully demonstrates 40 Gbit/s, 300 km transmission.

The authors describe a 46 Gbits super-dynamic type decision circuit module that uses InAlAs/InGaAs HEMTs. At a data rate of 40 Gbit/s, the module shows an input data sensitivity of 104 mV/sub pp/ and a clock phase margin of 212.

The authors report a 2–46.5 GHz quasi-static frequency divider IC using InAlAs/InGaAs/InP HEMTs. Wideband clock/data buffers and an HLO (high-speed latching operation)-type T-FF were incorporated to enhance the operating range. The IC was mounted on a dedicated IC package and operated up to 45.2 GHz.

A 64 Gbit/s 2:1 selector-type multiplexer IC using InAlAs/InGaAs/InP HEMTs is reported. The record operating data rate was measured on a wafer. The IC was mounted on a dedicated IC package and operated beyond 52 Gbit/s.

A 40 Gbit/s, fully-integrated 1:2 demultiplexer IC using InAlAs/InGaAs/InP HEMTs is reported. The IC integrates the full functionality for 40 Gbit/s data and 40 GHz regenerated clock inputs, including output bit alignment.

The authors report 46 Gbit/s 2:1 multiplexer and 40 Gbit/s 1:2 demultiplexer IC modules using InAlAs/InGaAs/InP HEMTs. Each chip is mounted on a dedicated broadband chip-size cavity package. These modules are the first to provide an error-free 40 Gbit/s multiplex/demultiplex operation.