Dual wavelength surface emitting InGaAsP l.e.d.s

Surface emitting l.e.d.s capable of simultaneous emission near 1.14 ?m and 1.3 ?m wavelengths, from an area 75 ?m × 75 ?m. have been fabricated and tested. Outputs of 0.5 mW and 0.8 mW, respectively, were obtained at the two wavelengths in initial devices driven at 50 mA d c. The measured crosstalk was ?23.9 dB (electrical).     

Growth of Ga0.47In0.53As on InP by low-pressure m.o. c.v.d.

The first heteroepitaxy is reported of Ga0.47In0.53As on InP by low-pressure metalorganic chemical vapour deposition (m.o. c.v.d.). Triethylindium (t.e.i.) and triethylgallium (t.e.g) were used as group III sources, and arsine as the group V source. These Ga0.47In0.53As epilayers exhibit high electron mobility (7.74 cm2 V?1 s?1 for a total impurity concentration of 2.5 × 1016 cm?3 at 300 K) and a photoluminescence efficiency comparable to l.p.e. layers. The lattice mismatch is only ?a0/a0 ? 4 × 10?4. Our mobility measurements indicate that m.o. c.v.d. Ga0.47In0.53As is a promising material for microwave device applications.     

Phosphor-doped silica cladding v.a.d. fibres

Loss reduction of v.a.d. (vapour-phase axial deposition) fibres at wavelengths of 1.3 ?m and 1.6 ?m was investigated. The infrared absorption loss was reduced by applying SiO2-P2O5 cladding instead of SiO2-B2O3 cladding and by minimising the waveguide imperfection loss. The minimum losses of the fabricated v.a.d. fibre were 0.5 dB/km and 0.28 dB/km at wavelengths of 1.3 ?m and 1.6 ?m, respectively. This fact indicates that fibres fabricated by the soot process, like those made by the vapour-phase axial-deposition process, can be used as long-wavelength optical transmission media. We have also found the OH absorption abnormality at wavelengths of 0.95, 1.24 and 1.39 ?m, and the loss peak values are different from those reported.     

Mg-doped InGaAsP/InP l.e.d.s for high-bit-rate optical-communication systems

The design criteria for high-speed luminescent diodes are applied to realise InGaAsP/InP l.e.d.s at 1.26 ?m wavelength. By highly doping the active region with Mg, a modulation bandwidth in excess of 1 GHz is achieved.     

Ultralow-loss 220 km-long single-mode-fibre cable link in 1.5 ?m wavelength region

Ultralow-loss single-mode-fibre cables specially designed for the 1.5 ?m region were fabricated. The fibre parameters are a mode-field radius of 6 ?m and an effective cutoff wavelength of 1.4 ?m. The average loss is 0.19 dB/km at 1.55 ?m. The total loss of a 216 km-long cable link consisting of 2 km-long fibres with 107 splices was 46.3 dB. The cables also show a good loss stability at 1.55 ?m in long-term use.     

Low-power CMOS switched-capacitor lowpass filter using current conveyors

A new approach is proposed to the design of high-order switched-capacitor LPFs of megahertz cutoff frequency for communications channel selection. It essentially uses current conveyors instead of op amps to achieve low power consumption. A fifth-order Chebyshev LPF with a 1-MHz cutoff frequency is thus synthesized and fabricated in a 0.35-μm CMOS technology. The LPF consumes less than 10 mW from a 3-V power supply and exhibits a third harmonic distortion better than ?54 dB in response to a 1-V sinusoidal input at the cutoff frequency. The rms noise voltage is at most 1.9 mV in a 2-MHz bandwidth.     

Material-dispersion-limited operation of high-bit-rate optical-fibre data links using l.e.d.s

Material dispersion generally limits the transmission capacity of optical-fibre data links using l.e.d.s. A 137 Mb/s data link has been operated by using either AlGaAs or InGaAsP l.e.d.s at 0.89 or 1.20 ?m, respectively. `Eye? diagrams of the received signal for transmission over different lengths of a graded-index germanium borosilicate fibre illustrate the effects of material dispersion.     

1.1 Gb/s pseudorandom pulse-code modulation of 1.27 ?m wavelength c.w. InGaAsP/InP d.h. lasers

Pulse-code modulation of InGaAsP/InP d.h. injection lasers at a 1.1. Gb/s rate in a room-temperature environment has been demonstrated. The operating wavelength was 1.27 ?m. Fabrication and characteristics of the lasers, design of the 1.1 Gb/s circuitry, and performance of the experimental transmitter are described briefly.     

GaAs m.e.s.f.e.t. prepared by organometallic chemical vapour deposition

GaAs m.e.s.f.e.t.s with gate dimensions of 1.5 ?m × 300 ?m were fabricated in the epitaxial layers grown by organometallic chemical vapour deposition (o.m.c.v.d.) technique. The average saturation velocity in the channel was deduced to be 1.3 × 107 cm/s and is equal to that of epitaxial layers grown by AsCl3 chemical vapour deposition (c.v.d.). The velocity degraded region was confined to within about 350 ? of the interface. A gain of 10 dB and a noise figure of 3 dB with an associated gain of 5.5 dB at 8 GHz were measured.     

Threshold dependence on active-layer thickness in InGaAsP/InP d.h. lasers

Room-temperature threshold current density Jth against active-layer thickness d is reported for pulsed InGaAsP/InP double-heterostructure lasers operating at wavelengths near 1.23 ?m. For d ? 1 ?m, Jth/d is 5.0 kA cm?2 ?m?1, whereas the lowest threshold is 1.6 kA cm?2 for d ? 0.2 ?m. The threshold dependence is fitted by a numerical calculation based on a two-parameter gain model.     

Error performance of frequency-hopped d.p.s.k. system

In order to accurately evaluate bit error rates for a frequency-hopped d.p.s.k. system, digital computer experiments were performed. The value of Eb/N0 at the 10?3 error rate without fading was 8.4 dB.     

Fabrication of single-mode fibres by v.a.d.

A 21 km long single-mode fibre with loss values of 0.6 dB/km at 1.2 and 1.55 ?m, and 0.7 dB/km at 1.3 ?m, has been made by the v.a.d. method. This indicates the high potential of this method in the production of long low-loss single-mode fibres.     

Microwave InxGa1?xAsyP1?y/InP f.e.t

Microwave performance of InxGa1?xAsyP1?y quaternary alloy metal-semiconductor field effect transistors (m.e.s.f.e.t.s) is reported. Liquid-phase epitaxy (l.p.e.) using a step cooling technique has been employed to grow submicrometre quaternary layers having room-temperature bandgaps of 0.9, 1.0, 1.05, 1.15 and 1.2eV. F.E.T.s having gate dimensions of 1×200 ?m and a channel length of 5 ?m have been fabricated using 1.15 and 1.2 eV quaternary alloys. A maximum d.c. transconductance of about 10 mS and a maximum available gain of about 7 dB at 10 GHz have been obtained.     

ZOGMOST: an improved m.o.s.t. for c.c.d. peripheral circuits

An improved formation for m.o.s. transistors fabricated with the `shadow-etch? c.c.d. process is reported. The narrow self-aligned gaps produced by the process are used to provide an additional screen gate, which allows the gate-drain overlap capacitance to be minimised, thereby improving the frequency characteristics of linear and digital m.o.s. circuits. Depending on the gain of the stage involved, an improvement in the frequency performance of up to 5 times is expected, and practical results for the modified m.o.s.t. agree with this prediction.     

New estimate of the minimum noise figure of a m.e.s.f.e.t.

New estimates of the drain and gate noise multiplication parameters, the correlation coefficient and the minimum noise figure for a m.e.s.f.e.t. are advanced. For an uncooled GaAs m.e.s.f.e.t. having a 1 ?m gate length, a minimum possible noise figure of 1 dB at 10 GHz is predicted. InP is only marginally better.     

p-i-n/f.e.t. hybrid optical receiver for longer-wavelength optical communication systems

Preliminary results are reported on the first GaInAs p-i-n/f.e.t. hybrid optical receiver for longer-wavelength optical communication systems. The GaInAs photodiode has a capacitance of 0.3 pF and quantum efficiency of 25%, and gives a receiver sensitivity for a 140 Mbit/s n.r.z. system at 1.24 ?m of ?40.7 dBm for a 10?9 error rate.     

OH-ion reduction in v.a.d. optical fibres

The dehydration effect of SOCl2 on v.a.d. optical-fibre preforms has been investigated. The OH content of the graded-index fibres obtained was reduced to the level of 0.05 p.p.m. (the lowest value was 0.03 p.p.m.), resulting in the minimum loss of 0.60 dB/km at 1.3 ?m.     

13 ?m wide stripe c.w. GaAs/GaAlAs d.h. lasers linear to more than 10 mW

By using a very uniform device structure it has been possible to fabricate stripe contact d.h. GaAs/GaAlAs injection lasers with linear continuous output power exceeding 10 mW from one facet independent of stripe width in the range 10?14 ?m. These results predict that there is no fundamental mechanism that gives a nonlinearity at a few milliwatts output power which could explain earlier published results, and that increased maximum linear output power could be achieved by further improving the uniformity of the device structure.     

Ultimately low OH content v.a.d. optical fibres

Ultimately low OH content optical fibres with 1.2% refractive-index difference and 80 ?m core diameter have been successfully obtained by dehydrating a v.a.d.-made porous preform under optimised conditions. The loss increase at 1.39 ?m due to residual OH ions was only 0.04 dB/km. Accordingly, the measured attenuation curve can be resolved into contribution from the intrinsic loss mechanism with the additional low waveguide imperfection loss.     

A new d.h. laser configuration with passive transverse field confinement

A new geometry is proposed which significantly improves the characteristics of single mode d.h. stripe geometry lasers, with regard to astigmatism of the near field, transverse field confinement, modal gain and threshold current. The advantages over other devices are discussed. Numerical results are presented for 5 and 10 ?m stripe lasers.