Optical polarisation control utilising an optical heterodyne detection scheme

An optical polarisation control scheme utilising optical heterodyne detection for coherent transmission is proposed and demonstrated at a wavelength of 1.5 ?m. It converts an arbitrary polarisation state to a linear state at a received optical power level of less than ?70 dBm.     

Low-noise optical detection of a 1.1 Gb/s optical data stream

A low-noise, 1.1 Gb/s optical receiver has been built using a silicon a.p.d. and a GaAs f.e.t. The receiver sensitivity was evaluated using error-rate measurements, and for a bit error rate of 10?9, with no fibre, the measured optical sensitivity was ?37.0 dBm. These results are used as a basis for the calculation of maximum repeater spacings for 1.1 Gb/s systems operating at 0.85 ?m and 1.25 ?m wavelengths.     

Wavelength-division-multiplexed optical transmission system with single-mode fibre and a dual-wavelength hybrid laser light source

Wavelength-division-multiplexed optical fibre transmission over a 45km single-mode fibre using a hybrid dual-wavelength InP CSBH laser light source emitting at 1.3 ?m and 1.5 ?m has been demonstrated. This simple and economic system provides two distinct optical data channels without requiring electronic or optical multiplexing. Optical crosstalk was unobservable while operating the separate optical channels at 1.5 Gbit/s and 90 Mbit/s, respectively. The use of a single light source eliminates multiple fibre-to-source alignments, reducing transmitter packaging costs.     

800 Mbit/s optical transmission experiments with dispersion-free fibres at 1.5 ?m

By using dispersion-free single-mode fibres at 1.5 ?m, where silica fibres have minimum loss, an optical transmission experiment was successfully carried out at 800 Mbit/s with 20 km repeater spacing. Error rate against receiving optical level characteristics showed that the optical power penalty caused by fibre dispersion is negligible after long line transmission at 1.5 ?m.     

Demonstration of high capacity in the LAMBDANET architecture: a multiwavelength optical network

The letter presents transmission measurements in a multi-wavelength optical network, using 18 channels spaced 2 nm around 1.55 ?m. Each channel was modulated at 1.5G bit/s and transmitted through 57.8 km of single-mode optical fibre. Experimental results demonstrate a bandwidth-distance product of l.56 Tbit s?1 km and a point-to-multipoint figure of merit of 21.5 Tbit s?1 km node.     

Coherent optical receiver for 680 Mbit/s using phase diversity

A coherent optical receiver using a multiport optical coupler to provide phase diversity is described. By this means, only homodyne bandwidth is required in the signal processing, but with tolerances on the frequency tracking typical of heterodyne systems. Measured sensitivities with limited local-oscillator power are ?47.5 dBm at 320 Mbit/s and ?42 dBm at 680 Mbit/s. The results at the higher bit rate are strongly influenced by limited receiver module bandwidth.     

Spectral- and length-dependent losses in optical fibres investigated by a two-channel backscatter technique

Spectral- and length-dependent losses in optical fibres have been investigated using a two-channel technique for back-scatter-waveform analysis. Results are compared with measurements obtained by the `cutback? method over the wavelength range 0.82?1.07 ?m. Attenuation measurements at 0.95 ?m show a significant variation in OH- concentration along the fibre.     

Detailed evaluation of an attainable repeater spacing for fibre transmission at 1.3 ?m and 1.55 ?m wavelengths

An attainable repeater spacing at 1.3 ?m and 1.55 ?m wavelengths using a step-index monomode fibre cable is given, after detailed consideration of total loss as well as total dispersion of an optical fibre. The longest attainable repeater spacing at 1 Gb/s is about 100 km at 1.55 ?m wavelength using a single-mode laser diode and a monomode fibre with a relatively small core-cladding refractive index difference, e.g. about 0.2%.     

Long-range 1.5 ?m OTDR in a single-mode fibre using A D2 gas-in-glass laser (100 km) or a semiconductor laser (60 km)

We have observed Rayleigh backscatter in a single-mode fibre in optical time domain refiectometry at 1.56 ?m wavelength to a range of 100 km using a D2 gas-in-glass laser, and to 60 km at 1.53 ?m using an injection laser. The low-noise receiver used an InGaAs PIN photodiode and a FET-input operational amplifier with averaging of 1000 times to provide signal/noise enhancement.     

Measurement of nonlinear distortion in photodiodes

The 2nd-order nonlinear distortion of avalanche photodiodes (TIXL-55, C-20817) was found to be less than ?60 dB for an incident average optical power of ?20 dBm modulated at a peak depth of 75%. p-i-n photodiodes (HP 5082-4207) were found to have 2nd-order-distortion levels below the noise level. A method using three independent optical signal sources was employed in the measurement.     

All-Optical Modulation-Format Convertor Employing Polarization-Rotation-Type Nonlinear Optical Fiber Loop Mirror

An all-optical modulation-format convertor with regenerative function based on fiber nonlinearity is proposed and demonstrated. The convertor was formed utilizing polarization- rotation-type nonlinear optical fiber loop mirror and could operate at both on–off keying (OOK) to OOK and OOK to phase-shift keying (PSK) format conversions only by simply rotating the optical axis of the intra $lambda/2$ waveplate, without excess-loss generation and realignment of the driving conditions of control optical signals in the format exchange. The 40-Gb/s OOK to OOK/PSK format conversions were successfully performed utilizing this new type of the all-optical convertor. The results also revealed that this convertor has a reshaping function to degraded control signals as an inline all-optical regenerator.      

New optical fibre fabrication method

A new method for optical fibre fabrication has been found. The method is based on the so-called `sol-gel process?, which enables one to produce a core rod for optical fibre. Pure silica core fibre fabricated using this method exhibits an optical attenuation characteristic as low as 6 dB/km at a wavelength of 0.85 ?m.     

1.6 Gbit/s optical receiver at 1.3 ?m with SAW timing retrieval circuit

The performance of a 1.6 Gbit/s optical receiver employing a s.a.w. filter as a timing tank is reported. The error-rate characteristics in a p.c.m. transmission system using a 1.3 ?m In-GaAsP laser and single-mode fibres were studied. The average received optical power at a 10?9 error rate was ?28 dBm. In a 15 km transmission experiment, the receiving level was degraded by 2 dB owing to fibre dispersion. Timing phase margin of 75 degrees after 12 km transmission was confined with the self-timed receiver.     

Wideband 1.5?m optical receiver using travelling-wave laser amplifier

A high-sensitivity, wideband optical receiver using a travelling-wave laser amplifier in conjunction with a PIN photodiode and commercial 50? amplifier is described. A sensitivity of ?37 dBm at 1 Gbit/s has been achieved, with a 17dB net amplifier gain.     

40-Gb/s Polarization-Insensitive All-Optical Clock Recovery Using a Quantum-Dot Fabry–PÉrot Laser Assisted by an SOA and Bandpass Filtering

We experimentally demonstrate polarization- insensitive all-optical clock recovery using a passively mode-locked quantum-dot Fabry–PÉrot (QD-FP) semiconductor laser at 40 Gb/s. Polarization insensitivity is achieved by using a wavelength conversion stage based on cross-phase modulation in a semiconductor optical amplifier and optical bandpass filtering. A clock signal with a root-mean-square timing jitter of 300 fs is recovered for an input data signal with a scrambled state-of- polarization (SOP). This is comparable to that from the QD-FP laser alone for an input signal with a fixed SOP. Moreover, an improvement in the tolerance to a degradation in the optical signal-to-noise ratio of the input signal is achieved by the use of the wavelength conversion stage.      

Simple common-collector full-monolithic preamplifier for 560 Mbit/s optical transmission

A simple common-collector full-monolithic preamplifier is developed using an advanced 3 ?m Si-bipolar IC technology SICOS. The amplifier characteristics are a 650 MHz bandwidth and a 5.2 pA/?(Hz) equivalent input noise current at a 3 k? transimpedance. Measured optical sensitivity of a front end consisting of the amplifier and a Ge-APD is ?36.2 dBm for an error rate of 10?9 at a 560 Mbit/s bit rate and 1.3 ?m wavelength.     

Unrepeatered video transmission using pulse frequency modulation over 100 km of monomode optical fibre

Unrepeatered transmission of 625-line colour video signals using PFM over monomode optical fibre is reported. The results show that a received video signal/noise ratio better than 53 dB unified weighted was achieved over 68 km of fibre at 1.3 ?m and 102 km at 1.52 ?m.     

140 Mbit/s optical FSK fibre heterodyne experiment at 1.54 ?m

An optical fibre heterodyne experiment using 2-FSK modulation at 140 Mbit/s has been operated in the 1.5 ?m loss window. A receiver sensitivity of ?55 dBm has been obtained; operation over a fibre link of 199.7 km showed no additional system degradation.     

Linewidth requirement evaluation and 290 km transmission experiment for optical CPFSK differential detection

The linewidth requirement for CPFSK differential detection is evaluated. CPFSK modulation of DFB-LD is confirmed from the spectrum correlation between an output spectrum and calculated results. In a 1.55 ?m 400 Mbit/s transmission experiment using a 290 km pure-silica-core fibre, average received optical power at a 10?9 bit error rate is ?49.9 dBm.     

Waveform shaping of chirp-controlled signal by semiconductoroptical amplifier using Mach-Zehnder frequency discriminator

The optical output waveform of a semiconductor optical amplifier (SOA) is shaped using a Mach-Zehnder interferometer (MZI) as a frequency discriminator in order to suppress its distortion at high SOA input powers. This technique is applied to chirp control of an optical signal using an SOA, and the chirp control with waveform shaping greatly improves the transmission performance of a positively chirped optical signal in standard single-mode fiber over a wide range of SOA input powers. We also demonstrate that the chirp control with waveform shaping can be achieved without changing the drive settings of the SOA and MZI, even when the optical frequency is switched to another channel located on the wavelength-division-multiplexing frequency grid