Xiangjun Zhao

An optical packet switch based on WDM technologies

Dense wavelength-division multiplexing (DWDM) technology offers tremendous transmission capacity in optical fiber communications. However, switching and routing capacity lags behind the transmission capacity, since most of todays packet switches and routers are implemented using slower electronic components. Optical packet switches are one of the potential candidates to improve switching capacity to be comparable with optical transmission capacity. In this paper, we present an optically transparent asynchronous transfer mode (OPATM) switch that consists of a photonic front-end processor and a WDM switching fabric. A WDM loop memory is deployed as a multiported shared memory in the switching fabric. The photonic front-end processor performs the cell delineation, VPI/VCI overwriting, and cell synchronization functions in the optical domain under the control of electronic signals. The WDM switching fabric stores and forwards cells from each input port to one or more specific output ports determined by the electronic route controller. We have demonstrated with experiments the functions and capabilities of the front-end processor and the switching fabric at the header-processing rate of 2.5 Gb/s. Other than ATM, the switching architecture can be easily modified to apply to other types of fixed-length payload formats with different bit rates. Using this kind of photonic switch to route information, an optical network has the advantages of bit rate, wavelength, and signal-format transparencies. Within the transparency distance, the network is capable of handling a widely heterogeneous mix of traffic, including even analog signals.

Performance analysis of nonlinear semiconductor optical amplifier devices operated near 100 Gb/s speed

By utilizing the gain decompression effect, nonlinear semiconductor-optical-amplifier devices are possible to operate at more than 100 Gb/s speeds. We study conditions how we can achieve such a high speed operation for ultrafast TDM applications.

Adaptive equalization approach for canceling the multipath effect in multimode fibers

The main source of bit errors in multi-mode fibers (MMF) transmission systems is the inter-symbol interference (ISI) caused by the differential mode dispersion (DMD) generated multi-path effects. The DMD creates inter-symbol interference and limits the transmission distance-bandwidth product of a MMF to 3OO MHz-km. Hence, at 10 Gb/s data rate, the transmission distance is only -3O meters, which is not very useful for networking. In this work, we propose to utilize the adaptive equalization technique to combat the DMD and increase the transmission distance to almost the desired length. With this technique, we not only obtain MMF-based 10 Gb/s gigabit Ethernets (GE) but also upgrade all the already installed MMFs (OC-3 backbones) to higher-speed pipes. We present simulation results that show the success of our proposed adaptive equalization approach in canceling the DMD generated multi-path effect in MMF transmissions.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Selective-area-growth materials for widely tunable semiconductor lasers

We report preliminary results ofwidely tunable semiconductor laser materials using selective area growth techniques. This material has very broad gain profiles ofmore than 250 nm and is promising to be used as widely tunable laser diodes for future broadband wavelength division multiplexed (WDM) access networks.

Transparent all-optical packet network using digital header and arbitrary payload

Optical packet networks have the advantages of high efficiency and transparency. It can take care of a heterogeneous mix of traffic. We demonstrated bit-rate and signal-format transparent operations of an all-optical packet-switched network.

Wavelength division multiplexed (WDM) data-block switching for parallel computing and interconnects

We report a new generation switch, the data-block switch, which can greatly increase the capacity and reduce the complexity of the interconnect network of a parallel computing system. By using WDM techniques, parallel data can be multiplexed and transmitted through a single fiber. By using photonic switching techniques, we can switch a block of parallel data in one switch operation to any site desired. In this work, we demonstrate such an operation with our fabricated 1 X 2 semiconductor optical amplifier (SOA) switch. This integrated device is an active/passive Y- junction waveguide device with a passive waveguide region in the middle and 3 active waveguide regions at each end. The amplified spontaneous emission spectrum of the SOA shows that this broadband switch can easily cover a wavelength range of more than 64 ITU wavelength grids (100 GHz). The switch operation of multiple wavelengths and the switching speed of the device were studied. A switching time of around 400 ps was achieved.

The effect of contact resistance in a broadband semiconductor optical amplifier using SAG techniques

Ultra-broadband gain materials can be made by using selected area growth (SAG) techniques. Material gain peak along the waveguide can vary as much as 300nm (from 1300nm to 1600 nm) in InGaAsP/InP quantum well waveguides. This gain peak variation is obtained by both material composition changes and quantum well width changes. This kind of broad band materials can be used to make ultra broad tunable lasers, amplifiers, and wavelength converters. Due to large band gap variation, the current injection will not be constant along the waveguide. The average serial resistance perpendicular to the waveguide direction will play an important role in the current distribution. In our simulation, a large serial resistance device will have a uniform current injection, therefore a uniform carrier distribution. But for a small serial resistance device, the carrier distribution along the waveguide is mainly decided by the local waveguide material bandgaps.

Growth and fabrication of an integrated DFB laser and EA modulator

By using the selective area growth (SAG) technique, the grating over growth technique, and the buried hetero-structure (BH) regrowth technique, we have successful fabricated integrated distributed feedback laser and electro-absorption modulator. A suitable tensile strain is introduced during the multiple quantum well (MQW) growth to compensate the compressive strain caused by the SAG effect. To obtain better control on the growth condition and grating coupling coefficient, a quaternary grating laser is used. The best DFB laser shows a threshold current of around 12 mA and slope efficiency up to 0.13 mW/mA from one facet.

All-optical HIPPIs using photonic switches and optical buffer memories

We propose an all-optical parallel interface based on the HIPPI-6400 protocol [1]. WDM techniques and optical switches asawellas buffers are used to implement the parallel interface. Optical switches can switch all wavelengths in one switching operation, so the switch fabrics can be simplified. Since the information is kept in the optical domain, the cost and latency can be reduced. Through the optical transparency, variable bit rates of data micropackets can be used in different connections.

Theoretical analysis of semiconductor-optical-amplifier-based wavelength converters

We analyzed the key design parameters of semiconductor optical amplifiers (SOAs) based wavelength converters. Simple analytical equations to calculate the rise and fall time of the converted signals in a long SOA (>5OOim) are derived.