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.     

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.     

Guided-wave optical wavelength-division multi/demultiplexer using high-silica channel waveguides

A guided-wave optical waveguide-division multi/demultiplexer for bidirectional transmission at (0.81 ?m, 1.2 ?m)/(0.89 ?m, 1.3 ?m) wavelengths has been realised using high-silica channel waveguides on silicon substrate. The multi/demultiplexer connected with graded-index multi-mode fibres shows a loss of 3.5?5 dB together with far-end and near-end crosstalk levels less than ?30 dB and ?50 dB, respectively.     

A Bayesian Note on Reliability Growth During a Development Testing Program

The problem of estimating the reliability of a system which is undergoing development testing is considered from a Bayesian standpoint. Formally, m sets of binomial trials are performed under conditions which lead to an ordering, ?1 < ?2 < ... < ?m, of the binomial parameters. The parameter of interest is ?m, the final underlying reliability of the system. The marginal posterior pdf for ?m is easily obtained when uniform prior pdf's are assumed. The method is illustrated.     

Low-loss splicing of a 62.4 km single-mode-fibre link

A 62.4 km single-mode-fibre link containing 35 splices has been made in the laboratory using equipment and techniques suitable for landline installations. Mean splice attenuations of 0.1 dB at 1.3 ?m and 0.08 dB at 1.55 ?m were measured. The mean attenuation of the complete spliced link was 0.5 dB/km at 1.3 ?m and 0.34 dB/km at 1.55 ?m. In addition, the attenuations of 200 splices measured at 1.3 ?m are reported.     

Small-active-area germanium avalanche photodiode for single-mode fibre at 1.3 ?m wavelength

A germanium avalanche photodiode of 30 ?m active area diameter has been fabricated and tested. The multiplied dark current is as low as 5 nA at room temperature. A module using this diode and a spherical lens has been assembled and coupled with a single-mode fibre of core diameter 10 ?m. The quantum efficiency of the module is 90% at 1.3 ?m. The sensitivity is measured at 45 Mbit/s and at 1.3 ?m. Minimum detectable powers obtained for 10?11 error rate are ?51.9 dBm and ?50.7 dBm at 25°C and 50°C, respectively.     

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).     

Low-threshold (Ga,In)(As,P) d.h. lasers emitting at 1.55 ?m grown by l.p.e.

Threshold current densities as low as 2.13 kA cm?2 have been achieved in broad-contact double-heterostructure lasers with an emission wavelength of 1.55 ?m. The three-layer structure was grown by liquid-phase epitaxy and contained a quaternary active layer 0.6 ?m thick and a p-type quaternary upper confining layer with a bandgap of 1.05 eV. The normalised threshold current density was 3.5 kA cm?2 ?m?1.     

OH absorption in GeO2-doped fused silica fibres

The OH-ion absorption of SiO2/GeO2-core step-index multimode fibres in the 1.2?1.6 ?m region has been studied in relation to changing GeO2 concentrations. It was found that the OH absorption band at ? 1.4 ?m in SiO2/GeO2-core fibres had two components with maxima at 1.39 ?m and 1.42 ?m related to the first overtone of the fundamental OH vibration in SiO2 and GeO2, respectively.     

High-sensitivity Hi-Lo germanium avalanche photodiode for 1.5 ?m-wavelength optical communication

A high-sensitivity small-detectable-area Hi-Lo germanium avalanche photodiode (Ge APD) was developed for use in 1.55 ?m wavelength optical communication systems. This device has Hi-Lo (p+nn?) impurity profile. Its detectable area is 30 ?m in diameter for single-mode optical-fibre use. The minimum average received signal level obtained was ?40.5 dBm (at 450 Mbit/s, ? = 1.55 ?m, BER = 10?9, return-to-zero). This is 0.7 dB better than the value for the 80?m diameter similar structure Ge APD.     

Short-coupled-cavity (SCC) InGaAsP injection lasers for CW and high-speed single-longitudinal-mode operation

CW and high-speed (100 ps pulse) single-longitudinal-mode operation has been achieved with a short-coupled-cavity (SCC) InGaAsP injection laser (in the 1.3 ?m to 1.55 ?m spectral range) consisting of a short (50?80 ?m) cleaved laser and a short (30?80 ?m) external air resonator with a high-reflectivity mirror. The SCC laser resonator combines the advantages of both a short-cavity laser and a coupled-cavity laser for effective mode selection. Single-mode operation has been maintained at modulation rates of 2 Gbit/s.     

p-i-nf.e.t. hybrid optical receiver for 1.1?1.6 ?m optical communication systems

The fabrication of low capacitance v.p.e. InGaAs/InP p-i-n photodiodes having a high responsivity up to 1.6 ?m wavelength is described. The receiver sensitivities of the p-i-n f.e.t. hybrid receiver for a 280 Mbit/s system, measured at 1.3?m and 1.5 ?m are ?38.9 dBm and ?39.4 dBm,respectively.     

Constraints for fundamental-mode spot size for broadband dispersion-compensated single-mode fibres

Constraints exist for the fundamental-mode spot size for broadband dispersion-compensated fibres because of the relationship between dispersion and spot size. Dispersion compensation between 1.3 and 1.55 ?m is still possible with the usual spot radius of about 5 ?m at ? = 1.3 ?m, while dispersion compensation between 1.3 and 1.8 ?m would require a spot radius of less than 4 ?m.     

Dispersion of pure GeO2 glass core and f-doped GeO2 glass cladding single-mode optical fibre

The letter investigates the dispersion of GeO2 glass core and F-doped GeO2 glass cladding single-mode optical fibre. It is estimated that the total dispersion goes to zero at about ? = 1.77 ?m. The material dispersions of these glasses are also measured. Material dispersion of GeO2 glass, which contains fluorine of 0.41 wt%, vanished at ? = 1.722?m. This occurs at ? = 1.734 ?m for pure GeO2 glass.     

Low crosstalk polarisation-maintaining optical fibre with an 11 km length

An 11 km-long polarisation-maintaining optical fibre with crosstalk up to ?25.2 dB and ?22.5 dB at 1.30 ?m and 1.56 ?m, respectively, is presented. Transmission loss is 1.2 dB/km at 1.3 ?m and has a minimum value of 0.79 dB/km at 1.56 ?m.     

Effect of deposition rate on spectral loss of GeO2-P2O5-SiO2 graded index fibres

Low loss, low OH content 0.23 n.a. graded index germanium phosphosilicate fibres have been fabricated using the m.c.v.d. process at rates up to 0.34 g/min with deposited layer thicknesses up to 16 ?m. The deposition rate did not affect achievement of low loss in the spectral range 0.7 ?m?1.7 ?m.     

GaAs power f.e.t.s with electron-beam-defined gates

The fabrication of GaAs power f.e.t.s having 1 ?m electron-beam-defined gates with 4800 ?m total gatewidth is described. The microwave performance at X-band is compared with that of conventionally defined devices having 2 ?m gate lengths.     

Tailoring zero chromatic dispersion into the 1.5?1.6 ?m low-loss spectral region of single-mode fibres

We have designed and fabricated single-mode silica fibres that have zero chromatic dispersion within the 1.5?1.6 ?m low-loss spectral region by controlling their waveguide dispersion and dopant-dependent material dispersion. These fibres have small core diameters and large core-cladding refractive-index differences, ?n = 0.018, corresponding to a 13 mole % GeO2 dopant concentration in the core. The zero-dispersion wavelength was shifted from ?0 = 1.375 ? to ?0 = 1.54 ? by decreasing the fibre core diameter from 7 ?m to 4.8 ?m. This ability to tailor the minimum dispersion wavelength to the ultra-low-loss region near 1.55 ?m is important for designing single-mode fibres for very long distance and very high capacity optical transmission.     

Low threshold channelled-substrate buried crescent InGaAsP lasers emitting at 1.54 ?m

Double-heterostructure lasers with crescent-shaped InGaAsP active layers have been fabricated with CW emission of 1.54 ?m. Lowest CW thresholds are 45?47 mA for a 200 ?m long cavity at 25°C. The lasing near-field widths are 2.5?3.0 ?m and the spectral widths to 10% of peak are 4?5 nm under both CW conditions and modulation up to 320 Mbit/s.     

Efficient burst-correcting cyclic codes

A class of single burst error-correcting cyclic codes is introduced. The binary version of these codes has block length n = 2m ? 1, number of parity check digits n ? k = 2m?1, and correct bursts of length b = 2m?2, where m is an integer. These codes achieve the upper bound b ?(n ? k)/2, and normally have more information digits than interleaved codes of the same burst-correcting power. The multilevel case is also treated in the letter.