GaAs VCSEL's at λ=780 and 835 nm for short-distance 2.5-Gb/splastic optical fiber data links

Selectively oxidized GaAs vertical-cavity surface-emitting lasers for λ=780- and 835-nm emission wavelength and 120-μm-core diameter step index plastic optical fiber (POF) are investigated for short distance interconnects. 2.5-Gb/s pseudorandom data transmission over up to 2.5 m of plastic fiber is demonstrated with a bit-error rate (BER) of better than 10^-11. Furthermore, bias-free data transmission at 2.5 Gb/s over 1-m fiber length again at a BER of better than 10^-11 is reported     

Single-transverse-mode 3.4-mW emission of oxide-confined 780-nmVCSELs

The authors have fabricated oxide-confined vertical-cavity surface-emitting lasers with metal apertures exhibiting a spatial mode filtering effect. Single-mode continuous-wave output is enhanced up to 3.4 mW by this effect for AlGaAs-based 780-nm vertical-cavity surface-emitting lasers with a 3.5-μm-diameter oxide aperture. From numerical calculations, the round-trip loss difference between zeroth- and first-order optical modes as a function of metal aperture size indicates that there is an optimum point; a 4-μm metal aperture size is suitable for higher order mode suppression of a 3.5-μm oxide aperture device     

Application of Raman-distributed amplification to WDM transmissionsystems using 1.55-μm dispersion-shifted fiber

A numerical design method for wavelength division multiplexing (WDM) transmission systems employing distributed Raman amplification (DRA) is proposed. This method evaluates fiber nonlinear effects by considering the equivalent fiber loss with DRA. The method is used to evaluate the performance of WDM transmission systems in which DRA is employed in a 1.55-μm dispersion-shifted fiber (DSF) transmission line. Transmission limit and the optimum fiber input powers for 1550-nm band (C-band) and 1580-nm band (L-band) transmission are investigated. Results show that bidirectional pumping is the best approach to extending transmission distance. Furthermore, the transport limits of optical transport networks that use DRA and optical add/drop multiplexers are analyzed     

Design optimization for efficient erbium-doped fiber amplifiers

The gain and pumping efficiency of aluminosilicate erbium-doped fiber amplifiers (EDFAs) are analyzed as a function of guiding parameters and Er-doping profile for two pump wavelengths of λ _p=980 nm and λ_p=1.47 μm. Three designs of fiber-amplifier waveguides are considered: one with the same mode size as standard 1.5-μm communication fibers (type 1); one with the same mode size as standard 1.5-μm dispersion-shifted fibers (type 2); and one with mode size smaller than those of communication fibers (type 3). For the 1.47-μm pump, fundamental LP₀₁ mode excitation is assumed, while for the λ_p=980-nm pump, concurrent excitation of LP₁₁ modes is considered. It is shown that excitation of higher-order pump modes at 980 nm does not significantly affect the amplifier gain performance. The effect of concentrating the Er³⁺ doping near the center of the fiber core is shown to increase the amplifier gain coefficients by a factor of 1.5 to 2     

Strong fiber Bragg grating fabrication by hybrid 157- and 248-nmlaser exposure

A permanent 248-nm photosensitivity response was locked into hydrogen-loaded standard telecommunication fiber by uniform 157-nm F₂-laser pre-exposure. Strong (>30 dB) fiber Bragg gratings were efficiently generated after hydrogen out-diffusion, improving the thermal stability. The 157-mn radiation produced weakly absorbing Si-OH and Ge-OH absorption bands at 1.39-μm     

Simultaneous distribution of multichannel analog and digital videochannels to multiple terminals using high-density WDM and a broad-bandin-line erbium-doped fiber amplifier

The simultaneous amplification of 16 distributed feedback (DFB) lasers over a 34-nm spectral range in an erbium-doped fiber amplifier is reported. Sixteen DFB lasers spaced at approximately 2-nm intervals and covering 34 nm in the 1.55-μm band were modulated with a total of 100 studio-quality analog FM-TV channels and six 622-Mb/s channels     

Small-signal analysis of 1.3-μm microcavity light-emittingdiodes

The modulation speed of 1.3-μm microcavity light-emitting diodes (MCLEDs) has been measured using a small-signal modulation analysis. A speed of 260 MHz using a 25-μm diameter sample at current density of 10 kA/cm² has been achieved. The carrier confinement has been calculated for several carrier densities in order to investigate the origin of the speed limitation. By comparing the performance of the 1.3-μm MCLEDs with that of the 990-nm devices we conclude that the limiting factor on the speed seems to be a lack of carrier confinement in the quantum wells and not a cavity effect     

0.18-μm fully-depleted silicon-on-insulator MOSFET's

High-performance 0.18-μm gate-length fully depleted silicon-on-insulator (FD-SOI) MOSFET's were fabricated using 4-nm gate oxide, 35-nm thick channel, and 80-nm or 150-nm buried oxide layer. An elevated source/drain structure was used to provide extra silicon during silicide formation, resulting in low source/drain series resistance. Nominal device drive currents of 560 μA/μm and 340 μA/μm were achieved for n-channel and p-channel devices, respectively, at a supply voltage of 1.8 V. Improved short-channel performance and reduced self-heating were observed for devices with thinner buried oxide layers     

Translation of Gbps Phase-Modulated Optical Signal From Near-Infrared to Visible Band

Phase-coded optical signal was spectrally translated from the conventional near-infrared communication band to the visible band. Spectrally narrow 780-nm pump was combined with phase-modulated 1575-nm signal in a small core photonic crystal fiber (PCF), to generate 518-nm idler through parametric process. The phase-modulated idler carrying 1-Gbps information was received in an error-free manner. The onset of the stimulated Brillouin scattering (SBS) was found to be a major limitation for conversion efficiency and noise performance. The SBS effect and the birefringence properties of the small core PCF were studied at both 780 and 1550 nm and their impact on the parametric process was analyzed.     

The investigation of key technologies for sub-0.1-μm CMOS devicefabrication

The fabrication of sub-0.1-μm CMOS devices and ring oscillator circuits has been successfully explored. The key technologies include: lateral local super-steep-retrograde (SSR) channel doping with heavy ion implantation, 40-nm ultrashallow source/drain (S/D) extension, 3-nm nitrided gate oxide, dual p⁺/n⁺ poly-Si gate electrode, double sidewall scheme, e-beam lithography and RIE etching for sub-0.1-μm poly-Si gate pattern, thin and low sheet resistance SALICIDE process, etc. By these innovations in the technologies, high-performance sub-0.1-μm CMOS devices with excellent short-channel effects (SCEs) and good driving ability have been fabricated successfully; the shortest channel length is 70 nm. 57 stage unloaded 0.1-μm CMOS ring oscillator circuits exhibiting delay 23.8 ps/stage at 1.5 V, and 17.5 ps/stage and 12.5 ps/stage at 2 V and 3 V, respectively, are achieved     

Cutoff frequency and propagation delay time of 1.5-nm gate oxideCMOS

The high-frequency AC characteristics of 1.5-nm direct-tunneling gate SiO₂ CMOS are described. Very high cutoff frequencies of 170 GHz and 235 GHz were obtained for 0.08-μm and 0.06-μm gate length nMOSFETs at room temperature. Cutoff frequency of 65 GHz was obtained for 0.15-μm gate length pMOSFETs using 1.5-nm gate SiO₂ for the first time. The normal oscillations of the 1.5-nm gate SiO₂ CMOS ring oscillators were also confirmed. In addition, this paper investigates the cutoff frequency and propagation delay time in recent small-geometry CMOS and discusses the effect of gate oxide thinning. The importance of reducing the gate oxide thickness in the direct-tunneling regime is discussed for sub-0.1-μm gate length CMOS in terms of high-frequency, high-speed operation     

Er3+-doped fiber amplifier pumped by 0.98 μm laserdiodes

The performance of an Er³⁺-doped fiber amplifier pumped by 0.98 μm InGaAs laser diodes (LDs) is reported. By using a fiber with low Er³⁺ content and optimizing the fiber length, a maximum signal gain of 37.8 dB at 30-mW pump power was realized at a signal wavelength of 1.536 μm. A maximum gain coefficient of 1.9 dB/mW at 14 mW pump power was achieved. It was found that the fiber amplifier pumped by the 0.98-μm LDs is twice as efficient as that pumped by 1.48-μm LDs, from the viewpoint of both required fiber length and the attained gain     

Semiconductor pump laser technology

Recent progress in high-power semiconductor lasers for erbium-doped fiber amplifiers is described, focusing on 1.48-μm InGaAsP/InP lasers and 0.98-μm InGaAs/GaAs lasers. The experimental output powers exceed 200 mW (the maximum power was 325 mW) for 1.48-μm lasers, and simulation results indicate that over 400 mW could be obtained by optimizing parameters in strained-layer (SL) multiple-quantum-well (MQW) lasers. Stable operation over a few thousand hours under 100-mW power is demonstrated for liquid-phase-epitaxy-grown lasers, MQW lasers, and SL-MQW lasers grown by all-metal organic vapor-phase epitaxy (MOVPE). For 0.98-μm lasers, improvement in the fiber coupling efficiencies and long-term reliabilities are described. Their power coupled into a single-mode fiber has reached over 100 mW, with coupling efficiencies of approximately 40%. Although reliability seems to be one of the drawbacks compared with 1.48-μm lasers, stable operation for over 10,000 h at 50°C and 30 mW has been reported     

Chromatic dispersion measurement in 1.55 μm narrow-band regionusing a tunable external-cavity laser

Measurement of the chromatic dispersion of an 80.6-km-long, concatenated, dispersion-shifted, single-mode fiber (DSF) with a tunable 1.55-μm external-cavity laser diode, using the phase-shift technique at 1.55 μm over 80-nm bandwidth, is discussed. It is shown that the technique does not need intricate curve-fitting equations or a large number of laser sources with specified wavelengths. As a result, the measurement configuration and procedure are relatively simple. The technique is useful for measuring the chromatic dispersion of future advanced fibers such as dispersion flattened fibers with various refractive index profiles     

A scaled 0.25-μm bipolar technology using full e-beamlithography

The full leverage offered by electron-beam lithography has been exploited in a scaled 0.25-μm double polysilicon bipolar technology. Devices and circuits were fabricated using e-beam lithography for all mask levels with level-to-level overlays tighter than 0.06 μm. Ion implantation was used to form a sub-100-nm intrinsic base profile, and a novel in-situ doped polysilicon emitter process was used to minimize narrow emitter effects. Transistors with 0.25-μm emitter width have current gains above 80 and cutoff frequencies as high as 40 GHz. A record ECL gate delay of 20.8 ps at 4.82 mW has been measured together with a minimum power-delay product of 47 fJ (42.1 ps at 1.12 mW). These results demonstrate the feasibility and resultant performance leverage of aggressive scaling of conventional bipolar technologies     

A widely tunable narrow linewidth semiconductor fiber ring laser

We have demonstrated a novel approach to obtain a 0.1-nm line width laser with 38-dB sidemode suppression by utilizing a 1.3-μm semiconductor optical amplifier in a fiber unidirectional ring that consists of a linear polarizer and polarization controllers. The laser has a low-threshold current of 22.5 mA as well as a wide tuning range of 28 nm. The new approach is applicable to the 1.55-μm region as well. It is expected that nanosecond wavelength tuning speed is feasible using this approach in conjunction with fast electrooptic polarization controllers, short cavities and low-cavity losses     

A narrow beam 1.3-μm-super luminescent diode integrated with aspot-size converter and a new type rear absorbing region

The device structure and performance of 1.3-μm narrow beam superluminescent diodes (NB-SLD's), which consist of a spot-size converter and a new type rear absorbing region, are reported. A butt-jointed selectively grown spot-size converter (SSC) is employed to realize the narrow beam characteristics. The rear absorbing region is designed as a taper structure with a part of the region is inclined from the active-stripe axes. In order to investigate the effects of both SSC length and active-region length on device performance, two types of NB-SLDs, whose SSC and active-region lengths differ, are fabricated. An electrode to sweep out photoexcited carriers in the absorption region is formed on one device. By comparing the characteristics of these devices, we clarify that a 500-μm-active-region device is suitable for high-output power operation, and a 400-μm-active-region device is suitable for realizing short coherent length. The light-output power is 13.9 mW at 200-mA-injection current for the former device, and the full-width at half-maximum (FWHM) of the spectrum is 62.6 nm (calculated coherence length is 26.5 μm) for the latter device. Very small spectral modulation index (0.015 at 5 mW-output power) is attained by grounding the absorption-region electrode. For the SSC length, a 300-μm SSC device shows very narrow far-field patterns (FFPs) and very good fiber-coupling characteristics. The FWHM of horizontal and vertical FFPs are 8.9 and 10.6°, respectively. Because of this narrow beam divergence, the coupling efficiency of -1.9 dB to a flat-end 4-μm spot-size fiber is obtained without lenses. The alignment tolerance of this device to the fiber for both horizontal and vertical direction is more than 3 μm at a loss of when -1 dB from the optimum coupling     

Design and fabrication of double modulation dopedInAlAs/lnGaAs/InAs heterojunction FETs for high-speed andmillimeter-wave applications

We report the design, fabrication, and characterization of InP-based double-sided-doped (DSD) MODFETs with InAs-layer-inserted channels. Devices based on optimized structures show a significant improvement in the effective saturation velocity, from 2.4×10⁷ cm/s for lattice-matched MODFETs to 3.1×10⁷ cm/s for InAs MODFETs. This leads to a maximum extrinsic transconductance of 1.95 S/mm and excellent high-speed performance of f_T=265 GHz for 0.13-μm T-gates. A f_max higher than 300 GHz can be achieved by fabricating a wide lateral recess groove, which simultaneously results in an improved breakdown voltage of 6.7 V. The excellent RF performance is primarily due to the reduction of Coulomb scattering from donor layers, especially under the channel, and to the reduction of scattering caused by the interface roughness. This improvement is achieved by inserting a 4-nm InAs layer, which better confines the two-dimensional electron gas (2DEG) at the center of the channel of MODFET's     

Manufacturing study of yield and performance dependence on gatelength of submicron AlInAs-GaInAs HEMTs

The fabrication, characterization, and statistical analysis of the performance and yield of AlInAs-GaInAs on InP low-noise high electron mobility transistors (HEMTs) with subquarter-micron T-gates fabricated with electron beam lithography are reported. This was undertaken to establish the manufacturability of submicron AlInAs-GaInAs HEMT technology for various low-noise microwave receiver applications. Excellent DC device yield (up to 90%) was obtained from devices to gate widths 300 μm and 1000 μm. A range of minimum noise figures between 0.026 to 0.5 dB at 2 GHz and 0.39 to 0.8 dB at 12 GHz were obtained for 0.15-μm and 0.20-μm gate length devices. The results establish the correlation between the noise figure and yield for this new class of microwave devices     

All-optical 1300-nm to 1550-nm wavelength conversion using cross-phase modulation in a semiconductor optical amplifier

All-optical 1300-nm to 1550-nm wavelength converters may be important components in lightwave networks which use both the 1300-nm and the 1550-nm low-loss transmission windows of silica optical fiber. We describe a new all-optical 1300-nm to 1550-nm wavelength converter, based on cross-phase modulation in a 1300-nm semiconductor optical amplifier. We demonstrate operation of the wavelength converter at 1.25 Gb/s, and present bit-error rate measurements. The wavelength converter demonstrated here potentially operates at high speed, with low input power and low polarization-sensitivity.