K.I. Kang

Comparison of Sagnac and Mach-Zehnder ultrafast all-optical interferometric switches based on a semiconductor resonant optical nonlinearity

We present a theoretical analysis of recently demonstrated ultrafast all-optical interferometric switching devices (based on Sagnac and Mach-Zehnder interferometers) that use a large optical nonlinearity in a resonant regime. These devices achieve ~10-ps switching windows and do not require high-energy optical control pulses. We theoretically analyze and compare one Sagnac and two Mach-Zehnder switching configurations.

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.

DEMONSTRATION OF ULTRAFAST, ALL-OPTICAL, LOW CONTROL ENERGY, SINGLE WAVELENGTH, POLARIZATION INDEPENDENT, CASCADABLE, AND INTEGRATABLE SWITCH

A new type of ultrafast all optical switch based on a Mach–Zehnder interferometer is demonstrated with a 10 ps switching window which requires only 0.65 pJ of control pulse energy. The optical nonlinearity which is utilized is associated with the gain compression of semiconductor optical amplifiers, and the switching turnoff transition does not depend on the slow amplifier recovery time. Both data and control pulses are at the same wavelength of 1.313 μm, and are not polarized orthogonal to each other. The device configuration and the semiconductor amplifiers allow for small scale integration and data output cascadability.

An analysis of signal-to-noise ratio and design parameters of a terahertz optical asymmetric demultiplexer

Analysis of the signal-to-noise ratio (SNR) as a function of the component parameters in a terahertz optical asymmetric demultiplexer (TOAD) can help optimize its performance as a demultiplexer or as a router in an optical time division multiplexed network. The analysis presented here accounts for crosstalk due to deviation from a perfect 3 dB splitting ratio in the TOADs 2/spl times/2 coupler, and the degradation of SNR due to fluctuations in the control pulse energy. The spontaneous emission noise output of the semiconductor optical amplifier (SOA) contained in the TOAD is simulated under different degrees of saturation. The analysis indicates that leakage due to the asymmetric placement of the SOA contributes significantly to the crosstalk. To achieve a SNR of 21.5 dB or higher in a 100 Gb/s system, one must use a 2/spl times/2 coupler that deviates less than 1% from a perfect 3 dB splitting ratio. Also, control pulse energy fluctuations must be less than 10% for a 20-GHz bandwidth electronic receiver. Novel crosstalk-free designs are proposed and analyzed which meet the stringent requirements of current TOAD devices. A significant enhancement in SNR is predicted when the SOA is operated near the optimal saturation point.

Ultrafast optical time demultiplexers using semiconductor optical amplifiers

The operating principle of the utilization of resonant optical nonlinearities in recently demonstrated ultra-fast all-optical interferometric switching devices is presented. Optimum switching windows expected from these devices are investigated with a simple theoretical analysis. The experimental results of these devices are presented along with the nonlinear optical properties of a semiconductor optical amplifier. The information from the experimental results of the nonlinear optical properties are used to address a problem associated with a saturation of the semiconductor optical amplifier by an incoming ultra-high bit rate data stream. We also discuss the advantages and disadvantages in different operation modes — same or different wavelengths for the control and data signals. Finally, we discuss the relative advantages and disadvantages among these devices.

Ultrafast photonic packet switching with optical control

We report the first demonstration of all-optical multi-bit address recognition at 250 Gb/s using a self-routing scheme. With bit period being only 4 ps, two address bits from each packet header were used for routing. Photonic packets can be removed(dropped) by a routing switch from network traffic at their destination. The packet-switching bit-error rate was measured to be less than 10(-9) .

Nonlinear-index-of-refraction measurement in a resonant region by the use of a fiber Mach–Zehnder interferometer

The nonlinear index of refraction in a resonant region has been determined by the use of a fiber-based Mach--Zehnder interferometer to measure the temporal fringe shift between two signals. The measurement technique is direct and does not require additional amplitude information for the extraction of the nonlinear index of refraction. This technique has been used to measure the temporal response of an InGaAsP semiconductor optical amplifier at 1.313 µm.

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.