TDMA fibre-optic network with optical processing

A fibre-optic network with time-division multiple access (TDMA) is implemented using optical processing. The network is capable of accommodating 50 stations transmitting at 10Mbit/s. Synchronisation is achieved using a central optical source with 2ns pulses. Integrated electro-optic modulators and optical fibre delay lines are used to multiplex the stations.     

Computer model of a superluminescent LED with lateral confinement

We present a computer simulation of a strip-geometry superluminescent light emitting diode (SLD). One end of the strip waveguide has a finite reflectivity while the reflectivity vanishes at the other end because it is assumed that the strip waveguide terminates in a high-loss region. The gain of the structure is computed from the drive current and several intrinsic device parameters; gain saturation is taken into account. We discuss the dependence of the light power coupled into a fiber from an InGaAsP SLD at 1.3 μm as a function of the driving current, the reflectivity of one end of the strip waveguide, its numerical aperture (NA), and its length and width. A considerable improvement in power coupling efficiency can be realized when the waveguide NA equals the fiber NA or, in the absence of lateral confinement, when the fiber NA is much larger than the half-width to length ratio (times the refractive index) of the strip waveguide. Previous analyses have ignored lateral waveguiding effects.     

FDMA-FSK star network with a tunable optical filter demultiplexer

An optical frequency-division-multiple-access (FDMA) star network is analyzed and demonstrated experimentally using two 45-Mb/s frequency-shift-keyed (FSK) laser channels at 1.5 μm. A tunable fiber Fabry-Perot (FFP) filter is used to select channels and convert FSK to intensity modulation for direct detection. The analysis predicts and experiment supports a minimum channel spacing of about six times bit rate B for a single FFP. These constraints are similar to those for more complex heterodyne demultiplexing. Estimates show that a network with 1000 users, independent of bit rate, is feasible with a tandem FFP. For B=1 Gb/s per channel the network capacity would be 1 Tb/s     

Optimization of the stimulated Raman scattering threshold

A theoretical analysis of the threshold condition for stimulated Raman oscillation is presented. The treatment, similar to that applied recently to optical parametric generation, assumes that a low loss resonator is provided for the Stokes radiation and accordingly pump depletion is neglected in the threshold calculation. Diffraction effects are included in detail, within the paraxial ray limits of Gaussian beam theory. The oscillation threshold for the fundamental resonator mode is expressed as a function of resonator losses, focusing conditions of pump and Stokes waves, and the length of the active medium.     

1 Gbit/s transmission experiment over 101 km of single-mode fibre using a 1.55 ?m ridge guide C3 laser

Using a cleaved-coupled-cavity (C3) ridge guide laser which oscillates in a single longitudinal mode at 1.55 ?m wavelength, we report the first lightwave transmission experiment exploying single-frequency lasers at speeds above 500 Mbit/s. We have achieved digital transmission with a bit-error rate of 2 × 10?10 at 1.0 Gbit/s over 101 km of single-mode fibre. This represents a record for the length of unrepeatered optical transmission for bit rates greater than 500 Mbit/s. Evidence for an error-rate floor, presumably due to residual partition noise, is observed. No such floor was observed in an 84 km?1 Gbit/s experiment using the same C3 laser.     

Non-coherent photonic frequency-multiplexed access networks

Noncoherent WDMA/FDMA (wavelength-division multiaccess/frequency-division multiaccess) networks that use tunable filters to select channels are considered. They have the same sensitivity as direct-detection networks, which is about 10 dB less than coherent networks. However, the noncoherent networks are much less complicated, which makes them interesting for multiaccess applications, where cost is more important than sensitivity. The direct-detection sensitivity is sufficient to allow as many as 1000 channels. Some recent research network experiments and progress on essential components for realizing noncoherent FDMA networks are reviewed     

The Internet and Society

As technology comes to dominate our economy and our lives, government is having a greater impact for good and bad on its directions and benefits. Government funding, regulation, and legislation can stimulate or stifle new technology. The explosion of the Internet is a perfect example of the effects of government policy on the interactions between technology and society, as I had the opportunity to discover during a year in Washington.     

Mechanism of refractive index increase in photosensitized poly(methyl methacrylate)

Poly(methyl methacrylate) prepared under special circumstances exhibits a substantial increase in refractive index after irradiation with ultraviolet light. The essential step in the preparation is peroxidation of the monomer prior to polymerization. This increase in refractive index results from a photo-induced polymerization of unreacted monomer (1-2 percent) within the film which produces an increase in density (and hence refractive index) in the irradiated region. It is believed that peroxides, both polymeric and monomeric, act as photoinitiators. Sensitivity depends on the concentration of photoinitiator but the absolute value of Δn depends on the amount of unreacted monomer.     

Amplitude fluctuations and photon statistics of InGaAsP injection lasers

We experimentally show that the statistical distribution of the light output from an injection laser can be adequately described by the superposition of a coherent electric field and narrow-band Gaussian noise. A technique for measuring these fluctuations in the time domain with a resolution of 120 ps is described. The results for several InGaAsP lasers show that intensity fluctuations in an injection laser are rather large, so that the probability of finding the output below 50 percent of the average power in a 120 ps time interval can be as high as 10^-5.     

FSK with direct detection in optical multiple-access FDM networks

High-performance optical data networks of the future may interconnect hundreds of users at gigabit rates for a reasonable cost. A novel approach is described that utilizes a passive star coupler for distribution, a multiplicity of frequency-shift keyed (FSK) tunable lasers to provide a frequency division multiplexed (FDM) network, and a tunable optical fiber Fabry-Perot filter to select the channels and convert the FSK signal to ASK (amplitude-shift keying) for direct detection. The design of high-speed FDM-FSK direct detection networks and the performance of critical devices, such as tunable FM lasers, tunable filters, integrated star couplers, and optical amplifiers, are reviewed and discussed