D. T. Mayweather

Implementation of STARNET: a WDM computer communications network

STARNET is a broadband backbone optical wavelength-division multiplexing (WDM) local area network (LAN). Based on a physical passive star topology, STARNET offers all users two logical subnetworks: a high-speed reconfigurable packet-switched data subnetwork and a moderate-speed fix-tuned packet-switched control subnetwork. Thus, STARNET supports traffic with a wide range of speed and continuity characteristics. We report the analysis and implementation of an entire STARNET two-node network, from the optical to the computer layer, at the Optical Communications Research Laboratory (OCRL) of Stanford University. To implement the two logical subnetworks, we designed and implemented two different techniques: combined modulation and multichannel subcarrier multiplexing (MSCM). OCRL has already demonstrated several combined modulation techniques such as phase shift-keyed and amplitude shift-keyed (PSK/ASK), and differential phase shift-keyed and amplitude shift-keyed (DPSK/ASK), yielding combined ASK/DPSK modulation receiver sensitivities better than -32 dBm. OCRL has designed and implemented a high-speed high-performance packet-switched STARNET computer interface which enables high-throughput transfer to/from host computer, low latency switching, traffic prioritization, and capability of multicasting and broadcasting. With this interface board, OCRL has achieved average transmit and receive throughputs of 685 Mb/s and 571 Mb/s, respectively, out of the 800 Mb/s theoretical maximum of the host computer bus. The incurred packet latency due to the interface for a specified multihop network configuration has been simulated to be 24 /spl mu/s. Using simulation and experimental results, it is shown that STARNET is highly suitable for high-speed multimedia network applications.

Wavelength tracking of a remote WDM router in a passive optical network

We propose, analyze, and demonstrate a simple, robust method which enables a laser to track uncontrolled changes in a remotely located WDM device. As opposed to locking to a wavelength standard, our method locks the wavelength comb of a tunable DBR to a waveguide grating router (200-GHz channel spacing). We have demonstrated tracking at a 1 C/min temperature slew rate without requiring sacrificial channels, a pilot tone, or analog dithering circuitry. We discuss tradeoffs between step size, slew rate, measurement accuracy, and power penalty.

Parametric analysis of semiconductor-doped glasses for all-optical switching

We use the basic physical parameters of semiconductor-doped glasses (SDGs) to compute the dependence of their nonlinear index n/sub 2/ due to the bandgap resonant effect on pump intensity and to predict the power and length requirements of an all-optical SDG waveguide switch. The main conclusions are that (1) the pump and signal wavelengths should be in specific and different ranges to minimize the switching power and signal loss, (2) for CdSSe- and CdTe-doped glasses, n/sub 2/ is relatively small, (3) their power requirements are consequently quite high (2-100 W), although (4) much lower than in a comparable device operated near the half-bandgap. We provide evidence that this weak nonlinearity, compared to that of semiconductors in bulk, is due to the strong nonradiative recombination of carriers arising from the small size of the semiconductor microcrystallites. Projections indicate a reduction in switching power by up to a factor of 1000 by increasing the microcrystallite size, thus producing a slower (ns) but more power efficient switch.

WDM laser tracking of an uncontrolled, remote router suitable for local loop applications

We demonstrate a new and robust digital method to remotely track rapid (1 C/min) uncontrolled environmental changes in a WDM device. Our method requires no RF circuitry, wavelength standard, or analog dithering. Our method enables a multiwavelength source to track a multi-channel WDM component in the field within a local loop environment which is characterized by large temperature and received power variations, hardware limitations, and power fluctuations.

Combined optical modulation formats and their applications

The realization of high-speed optical networks hinges on the efficient use of network resources. To optimize the utilization of the limited network resources, we have developed novel combined optical modulation formats. Combined optical modulation allows the transmission of two independent data streams simultaneously on the same optical carrier using a separate modulation format for each stream. Each individual data stream is then received separately with a separate optical receiver. The use of combined optical modulation optimizes the utilization of network resources by allowing the transmission of two separate data streams with a single transmitter laser.

Power and length requirements for all-optical switching in semiconductor-doped glass waveguides

We present a theoretical model that computes the nonlinear index (n2) of semiconductor- doped glasses (SDG), based on the materials properties, and predicts the power and length requirements, as well as the optimum operating wavelengths, for an all-optical SDG waveguide switch. The main conclusions are that (1) n2 depends strongly on pump intensity, which partly explains the large disparity in reported values of n2, (2) the pump and signal wavelengths should be in specific and different ranges to minimize switching power and signal loss, (3) for CdSSe- and CdTe-doped glasses, n2 is relatively small, and the switching power requirement for these two SDGs is consequently quite high (2 - 16 W). We provide evidence that this weak nonlinearity, compared to that of similar semiconductors in bulk, is due to the strong nonradiative recombination of carriers arising from the small size of the semiconductor microcrystallites. Projections indicate that the switching power would be reduced by up to three orders of magnitude by increasing the microcrystallite size, thus producing a slower (ns) but more power-efficient switch.