Jun Ping Zhang

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.

A low-crosstalk semiconductor optical amplifier

A new type of semiconductor optical amplifiers (SOAs) that can have a very low-channel crosstalk is proposed and demonstrated. By arranging the order of the gain materials with different saturation power, the SOA crosstalk is greatly reduced. This new type of SOA can be an ideal gain material for wavelength division multiplexed (WDM) amplification and integration in the access and metro environment.

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.

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.

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.

Design, growth, and characterization of GaAs/AlAs type-II superlattices

We report our recent results on characterization of GaAs/AlAs superlattices exhibiting evidence of a quasi- indirect transition between minibands. These structures have potential applications in semiconductor optical amplifiers with greatly-reduced cross-talk at high bit rates and Q-switched lasers.

Adiabatic mode expansion laser diodes fabricated by selective area growth

Adiabatic mode expansion laser diodes (AME-LDs) with small beam divergence fabricated by selective area growth (SAG) are described. The AME-LDs have low thresholds of around 12 mA. The lateral and vertical far field angles (FWHM) are reduced from 25° and 300 to 8° and 14°, respectively. The measured alignment tolerance to a cleaved single mode fiber (SMF) is 3 pm.

A dynamically refreshable optical fiber loop memory

An optical fiber loop memory can be used in a packet switched optical network to resolve the contention problems and increase the system flexibility. We report a multi- wavelength optical fiber loop memory with in-loop waveguide grating router. Bit error rate of stored packets is analyzed both experimentally and theoretically. A new refreshable multi-wavelength loop memory configuration is proposed and experimentally demonstrated. With this refreshable optical memory, which works like a DRAM (dynamic random access memory), optical signal can be stored as long as system required.