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A simple device to allow enhanced bandwidths at 850 nm in multimode fibre links for gigabit LANs

Summary form only given. There is currently much interest in gigabit/s datacommunication links for computer LANs. However, due to the low modal bandwidth of installed multimode fibre (MMF), the achievable link lengths are limited. At an operating wavelength of 1300 nm, greater link lengths can be achieved with mode conditioning patch cords which generate an offset launch into the MMF. However, at the alternative operating wavelength of 850 nm, there is currently no equivalent low cost commercial method available that allows restricted mode launch to be achieved. Therefore, there is considerable interest in developing techniques for generating conditioned launch in MMF which can be implemented in a cost-effective manner. A device has been previously reported that used focused ion beam etching to suppress the emission at the centre of the output aperture. However, this technique requires additional processing steps and results in non planar devices. This paper therefore demonstrates a simpler approach for enhancing the performance of these links.

Subcarrier modulation for transmission of 1-Gbit/s channels over 500 m of 62.5-/spl mu/m multimode fiber

Summary form only given. The growing demand for high-speed interconnects for LAN applications makes it interesting to study alternative modulation formats to increase the transmission capacity of widely installed 62.5-/spl mu/m multimode fiber (MMF). Subcarrier multiplexing (SCM) is an attractive technique for increasing the data capacity of existing multimode fiber links. In this paper we report the use of two different subcarriers at frequencies up to 5.5 GHz each transmitting 1 Gbit/s over 500 m of MMF. Using conventional NRZ modulation a data channel is limited in bandwidth by the modal dispersion inherent in multimode fiber. Subcarrier multiplexing presents a way to overcome this limitation by using the regions of fairly flat response at frequencies beyond the fibers 3-dB frequency. By transmitting several narrowband channels in the passband regions, rather than a single broadband channel, a significant increase in the data transmission capacity of MMF is possible.

Material gain comparison for InGaAsP, AlGaInAs and InGaAsN for 1.3 micron laser diode

Summary form only given. Recently, AlGaInAs and InGaAsN have received much interest as materials for 1.3 micron laser applications in competition with traditional InGaAsP. Both AlGaInAs and InGaAsN have the advantage of large conduction band offsets leading to superior electron confinement. We compare the gain and transparency carrier density at two temperatures to determine best the modulation response as well as the lowest possible threshold carrier density for uncooled laser applications. It is predicted that AlGaInAs has the highest peak differential gain for both room temperature and high temperature operation hence showing much potential for high speed response. AlGaInAs also has the lowest predicted transparency carrier density that may lead to low threshold currents, further enhancing its promise for 1.3 micron laser diode applications.

Novel constant output power control of a semiconductor optical amplifier based switch

Summary form only given. A novel semiconductor optical amplifier (SOA ) output modulation power monitor and control scheme has been proposed which avoids the need for optical power monitoring. A demonstration of this technique to control output power in an N x N crosspoint switch is presented.

Performance of 10 Gbit/s VCSELs operating at 85/spl deg/C

Summary form only given.Vertical cavity surface emitting lasers (VC SELs) are regarded as a key enabling technology for broadband low-cost optical interconnects. Future applications such as 10 Gigabit ethernet will demand that these devices operate at minimum modulation rates of 10 Gbit/s. A number of groups have reported VCSELs that are capable of these data rates. However, to the best of the authors knowledge there is no published work that shows that these devices are capable of operating at the high temperatures required for commercial applications. This paper demonstrates the first 10 Gbit/s modulation of an oxide-confined VCSEL operating at temperatures up to 85/spl deg/C.

Field trial of a QKD and high-speed classical data hybrid metropolitan network (Conference Presentation)

Quantum Key Distribution (QKD) is attracting much interest for the distribution of cryptographic keys using single photon signals. Currently QKD is often used to provide secure distribution of cryptographic keys for the encryption of data transmitted using conventional classical communication systems.nThis paper reports major field trials carried out over several months on the Cambridge UK Quantum Network showing the operation of QKD systems alongside high-speed classical transmission systems encrypted QKD derived with AES keys. Quantum Key transmission at record secure key rates of 3.3Mbps, 3.2Mbps and 2.5Mbps has been achieved over 5km, 9.5km and 10.5km long links respectively with corresponding average Quantum bit error rates (QBER) of 2.9%, 2.4% and 3%. nUsing a 33km link attached to the network with a loss of 7.5 dB, a secure key rate of 1.4 Mbps is achieved with an average QBER of 3.4%. Under loop back conditions this link provides a 66 km transmission path with a 16dB fibre loss, enabling a field trial using the QKD signals multiplexed with two wavelengths each transmitting 100Gb/s classical data to be carried out. This achieves an average secure key rate of 80.2 kbps and a mean QBER of 6.6%, in line with theoretical predictions. During the trial duration, the statistics of the QBER were found to be Gaussian distributed with a standard deviation of 0.5. The results of the field trial suggest that the system works stably and has considerable potential for applications in metropolitan networks. Further measurements will be reported at the conference.

Regenerative optical routing using a combined sampled-grating DBR laser and 16/spl times/16 arrayed waveguide grating

Summary form only given. In this work, for the first time, a regenerative wavelength routing switch has been constructed using tuneable lasers to implement regenerative wavelength conversion. Both laser and integrated laser amplifier components have been shown to allow combined wavelength conversion and regeneration. In this paper, a tunable SG-DBR laser is used to allow prototype testing of one input path to the switch. The laser has a broad tuning range of about 40 nm, the output wavelength being tuned by the selection of bias current to four different sections. A 16 /spl times/ 16 AWG is then used to provide the full routing function. Q factor measurements as a function of received power show that for low received power where the S/N ratio is poor, a good improvement in the signal quality is achieved because of regeneration. An IPDR of about 10 dB has been demonstrated for the router.

Demonstration of four wave mixing in an integrated pump laser and semiconductor optical amplifier for midspan spectral inversion dispersion compensation

Summary form only given. For the first time, an integrated DFB/SOA laser has been shown to operate as an MSSI dispersion compensator via NDFWM with a 10 GHz pulse train and 2.5 Gb/s data. Although the former does show some degradation, it is believed that further optimisation of the device (such as reduced DFB linewidth) will lead to far superior performance.

Optical Fiber Communication Conference and the International Conference on Integrated Optics and Optical Fiber Communications (OFC/IOOC'99), San Diego, USA

A novel dual-purpose vertical-cavity optoelectronic component, functioning either as a laser or as an avalanche photodetector, is employed in a link as a transceiver unit allowing ping-pong communications. Successful system performance is demonstrated at bit rates up to 1.244 Gbit/s.

Trends in Laser Diodes

This paper will review the recent rapid advances in the field of diode lasers, and overview their importance, not only in applications in optical communications, storage and printing, but also in more recent applications using high optical powers, as in machining, medicine and pumping. The paper will also address the new forms of laser diode, recently developed for operation at new lasing wavelengths, from the UV to the mid-infra red, concluding with comments relating to future projections for the field.