Kung-Li Deng

Unbalanced TOAD for optical data and clock separation in self-clocked transparent OTDM networks

We simulate and demonstrate a single-beam intensity-thresholding all-optical switch by modifying a terahertz optical asymmetric demultiplexer (TOAD) with an uneven power splitting in the loop. An optimized set of parameters used in the demonstration is found from the simulations considering the saturation of the semiconductor optical amplifier. With 8.7-dB input clock-to-data ratio, the clock-to-data ratio can be suppressed down to -7.4 dB at the reflected (data) port. An amplified output with 3.0 dB clock-to-data ratio improvement was achieved in the transmitted (clock) port at a low switching energy of 150 fJ. The device can be used for clock recovery in self-clocked optical networks.

A 1024-channel fast tunable delay line for ultrafast all-optical TDM networks

Based on a passive k-stage feed-forward delay line structure, this letter presents a novel scheme which allows fast tuning among as many as 2/sup k//spl times/2/sup k/ ultrafast time-division multiplexed (TDM) channels in all-optical networks. At a lower speed, a simple selection rule is applied at the input and output of the structure to set the state of the delay. In the experimental demonstration, the delay line can be tuned to any of the 1024 50-Mb/s channels in a 50-Gb/s all-optical TDM network with a five-stage structure and two E/O modulators. The average reconfiguration time is about 20 ns.

Single-shot optical sampling oscilloscope for ultrafast optical waveforms

We present an all-optical technique for measuring single-shot optical pulse phenomena using a feed-forward pulse replicator and a compact, nonlinear loop mirror called the terahertz optical asymmetric demultiplexer (TOAD). By exploiting the fast nonlinearity of a semiconductor optical amplifier (SOA) placed asymmetrically within the loop, a sampling window on the order of a few picoseconds can be used to detect features in low-energy (<pJ) optical waveforms. We successfully demonstrate a sampling system with 10-ps resolution capable of sampling single-shot optical waveforms up to 160 ps in duration. The sampled real-time pulsewidth agrees well with standard, long-range space autocorrelation.

Routing of 100 Gb/s words in a packet-switched optical networking demonstration (POND) node

This paper presents the design and experimental results of an optical packet-switching testbed capable of performing message routing with single wavelength time division multiplexed (TDM) packet bit rates as high as 100 Gb/s. The physical topology of the packet-switched optical networking demonstration (POND) node is based on an eight-node ShuffleNet architecture. The key enabling technologies required to implement the node such as ultrafast packet generation, high-speed packet demultiplexing, and efficient packet routing schemes are described in detail. The routing approach taken is a hybrid implementation in which the packet data is maintained purely in the optical domain from source to destination whereas control information is read from the packet header at each node and converted to the electrical domain for an efficient means of implementing routing control. The technologies developed for the interconnection network presented in this paper can be applied to larger metropolitan and wide area networks as well.

A highly-scalable, rapidly-reconfigurable, multicasting-capable, 100-Gb/s photonic switched interconnect based upon OTDM technology

We describe an ultrafast photonic switched interconnect based upon technologies developed for optical time division multiplexing (OTDM). The system uses a time-interleaved broadcast-and-select star architecture that is functionally equivalent to a crossbar switch. The interconnect offers full connectivity and low uniform latency among the input and output ports. The enabling technologies include ultrafast gated time slot tuners and all-optical demultiplexers. By utilizing these advanced optical technologies, it is possible to construct a highly scalable, rapidly reconfigurable, ultra-high-speed switch with performance beyond the capacity of current electronics. In the experimental demonstration, we constructed an interconnect with a peak bit rate of 100 Gh/s and the capability of connecting 16 OTDM ports. The system successfully demonstrated error-free operation of 100 Gb/s-multiplexing and demultiplexing in addition to rapid inter-channel switching capability on the order of the single channel bit period. The system also supports multicasting functions among many nodes. To scale the system to accommodate a large number of ports, we provide an analysis of the coherent crosstalk requirements through the network to show the potential to support hundreds of ports within practical constraints of the optical components. We believe that this system offers an approach to meet the demands of high bandwidth and fast switching capability required in current high-speed lightwave networks.

Packet-switched optical networks

We describe a testbed to study both the theoretical aspects and physical implementation issues associated with high-bit-rate, multihop, packet-switched OTDM networks. We have found that using optical time-division-multiplexed (OTDM) techniques can greatly increase the bandwidth of a single-wavelength channel. Ultrafast OTDM networks are excellent candidates for meeting the system requirements for massively parallel processor interconnects, which include low latency, high bandwidth, and immunity to electromagnetic interference. High-bit-rate transparent optical networks (or TONs) for multiprocessor interconnects will be best realized with an OTDM network architecture. To fully use the bandwidth of optical fiber, we spaced the picosecond pulses closely together (about 10 ps) and typically applied a return-to-zero modulation format. While the total capacity of TDM and wavelength division multiplexing (WDM) networks may essentially be the same, TDM systems have better throughput delay performance. They also have faster, single-channel access times for high-data-rate end users such as HDTV video servers, terabyte-media data banks, and supercomputers.

Fabrication of precision fiber-optic time delays with in situ monitoring for subpicosecond accuracy

We have developed a technique to produce precise fiber-optic time delays with subpicosecond accuracy and <0.1-dB loss by heating and stretching optical fiber in a fusion splicer. A fiber Mach-Zehnder interferometer allows in situ measurement of these precise delays using a simple alignment process and requiring only a weak optical signal. To demonstrate this capability, we assembled a six-stage feed-forward delay line that can be used to generate 64 optical pulses with 9.5 +/- 0.8-ps pulse spacings and 4.8-dB total insertion loss.

Influence of crosstalk on the scalability of large OTDM interconnects using a novel rapidly reconfigurable highly scalable time-slot tuner

We studied the coherent crosstalk properties of a novel time-slot tuner and its implications on the scalability of large-scale OTDM interconnects. A statistical model for the coherent crosstalk was used to evaluate the performance degradation which arises from the coherent interference between signal and crosstalk fields. Based upon this highly scalable, rapidly tunable channel selector, large all-optical TDM switching interconnects up to 100 nodes with an aggregate bandwidth of hundreds of Gb/s can be feasible, using off-the shelf electro optical (E/O) modulators with on/off extinction ratios of 30 dB. The results show the potential to further scale the size of the system up to hundreds of nodes, given on/off extinction ratios of 35-40 dB for the modulators.

Signal processing in high speed OTDM networks

This paper presents the design and experimental results of an optical packet-switching testbed capable of performing message routing with single wavelength TDM packet bit rates as high as 100 Gb/s.

All-optical clock extraction for self-clocked demultiplexing at 100 Gb/s

The polarization of polarization and wavelength independent clock and data separation of ultrafast optical time-division-multiplexed systems is demonstrated using an intensity-dependent all-optical switch. The clock and data separation is achieved by all-optical intensity switching based on the nonlinearity of the semiconductor optical amplifier asymmetrically placed in an unbalanced loop. With the proper power splitting ratio, clock pulse, and amplification, the signal can be extracted. The signals from the separator are directly used in the terahertz optical asymmetric demultiplexer.