J.W. Lou

All-optical packet-drop demonstration using 100-Gb/s words by integrating fiber-based components

Packet-drop function for a time-division multiplexing network using 100-Gb/s, 8-b words is experimentally demonstrated by integrating all-optical header processing and payload demultiplexing with electrooptic packet routing. The header processor consists of two levels of all-optical logic gates based on low birefringent nonlinear optical loop mirrors (NOLMs), and the payload demultiplexer is a two-wavelength NOLM. Both devices are driven by synchronized lasers with timing jitter under 1 ps. The contrast ratios for both header processor and demultiplexer are 10:1 and that of the packet router is 17 dB. The switching energies for header processing and payload reading are 10 and 1 pJ/pulse, respectively.

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5??dB by use of 550??m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24??turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel- and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5??dB for nontwisted fiber to 0.5??dB for fiber that is twisted at a rate of 8??turns/m, and the twist rate should be more than 4??turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8??turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4??pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.

Polarization insensitive demultiplexing of 100-Gb/s words using a twisted fiber nonlinear optical loop mirror

We demultiplex 100-Gb/s words using a two-wavelength nonlinear optical loop mirror (NOLM) with polarization sensitivity <0.5 dB obtained by using fiber twisted at eight turns/m. This polarization insensitive demultiplexer is more suitable than conventional nontwisted fiber NOLMs for use in high-speed all-optical networks where the input states of polarization are arbitrary. The demultiplexer consists of synchronized erbium-doped fiber lasers, a 100-Gb/s fixed word encoder, and a NOLM using 450 m of twisted fiber with /spl lambda//sub 0/=1518 mn. For inputs of arbitrary polarization, we measure a/spl sim/5.5-ps timing window and contrast ratio >15 dB. To understand the improvement in performance of the system due to the polarization insensitivity, we apply a statistical method of measuring the Q for the twisted and nontwisted fiber demultiplexers. The Q of /spl sim/15 for the twisted fiber NOLM is improved over that of the NOLM with nontwisted fiber (Q/spl sim/10), and is consistent with an increased minimum nonlinear transmission.

Demonstration and performance analysis for the off-ramp portion of an all-optical access node

Ultrafast processing of packets is demonstrated and the performance analyzed for the off-ramp portion of an all-optical access node. The off-ramp consists of synchronized fiber lasers driving an all-optical header processor that includes nonlinear optical loop mirrors (NOLM), electrooptic router, and demultiplexer in the form of a two-wavelength NOLM. We achieve switching contrasts of 10:1 for the header processor and demultiplexer with switching energies of 10 pJ and 1 pJ, respectively. Also, a proposed measurement technique to obtain eye diagrams is used to analyze the all-optical header processor using the synchronized lasers. Using this technique, we obtain an eye diagram with a Q value of 7.1/spl plusmn/0.36, which corresponds to a worst case BER value of 8.8/spl times/10/sup -12/ for a 95% confidence level. Finally, simulation models are used to verify and compare the experimental results, and we find good agreement. We also use the model to study the various causes for the degradation of the Q value through our system.

Broader and flatter supercontinuum spectra in dispersion-tailored fibers

In summary, we find experimentally that dispersion decreasing (DD) fiber produces broader and smoother supercontinuum (SC) spectra than dispersion increasing (DI) or constant dispersion fiber. At 24.3 W peak input power, the SC spectrum of DD fiber is over 100 nm wide, over twice that created by constant dispersion fiber. The spectrum is also relatively flat over the 20-nm range from 1545-1565 nm. We will also report applications of the multiwavelength SC source to erbium doped fiber amplifiers and wavelength-division multiplexed fiber characterization.

Path average measurements of optical fiber nonlinearity using solitons

This paper experimentally demonstrates a new method to determine the optical nonlinearity of single-mode optical fiber. The technique takes advantage of the well-known nonlinear response of optical fibers and well-developed models for soliton pulse propagation to extract information about the fiber characteristics. Fiber nonlinearity can degrade the performance of communication systems by, for example, causing crosstalk and signal distortions. Measuring the fiber nonlinearity would greatly aid system designers in building and upgrading communication systems. The method is utilized to determine values for n/sub 2//A/sub eff/, where n/sub 2/ is the nonlinearity of the glass and A/sub eff/ is effective area of the core. On various lengths of Corning SMF-28 fiber and Corning SMF-DS fiber. Experimentally measured propagation results for short (/spl ap/2 ps) optical pulses are compared to computer simulated models to determine the fiber nonlinearity. The method finds n/sub 2//A/sub eff/=3.0/spl times/10/sup -10/ W/sup -1/ values for short lengths (/spl ap/400 m) of Corning SMF-28 fiber and values of 2.7/spl times/10/sup -10/ W/sup -1/ for longer lengths (/spl ap/6.5 km and /spl ap/20 km). The difference is expected due to the 8/9 polarization scrambling factor, and the values are in agreement with reported literature [1]. The method also determines n/sub 2//A/sub eff/=5.6/spl times/10/sup -10/ W/sup -1/ for a /spl ap/12 km Corning dispersion shifted fiber. The method has two major regimes of operation based on the soliton period, a characteristic length for solitons. For few soliton periods (Z/Z/sub 0/ /spl sim/4) the output pulsewidth is measured as a function of launched power. The methods major advantage is its capability to measure long lengths of standard fiber, where it uses only standard diagnostic tools such as autocorrelation and optical power measurements. However, the method is only applicable in the soliton regime of fibers.

System performance measurements for an all-optical header processor using 100-Gb/s packets

We experimentally measure the eye diagram of an all-optical header processor using a crosscorrelator to achieve picosecond resolution. By varying 100-Gb/s header packets, we measure an eye diagram with a Q-value of 7.1 at 12-pJ packet pulse energy for the all-optical header processor consisting of all-optical logic gates and synchronized fiber lasers. From the Q-value, we also statistically calculate the potential bit-error-rate performance of 7.0/spl times/10/sup -13/. By measuring the change in Q-values as a function of input power, we find that input power fluctuations degrade the performance of the header processor by reducing the switching contrast of the logic gates in the header processor.

Self-synchronization of 100-Gbit/s TDM packets using a semiconductor laser amplifier and an intensity discriminator

Using a semiconductor laser amplifier followed by an intensity discriminator, we demonstrate packet clock extraction from a 100-Gbit/s eight-bit packet where the first pulse is 20 dB higher than the remaining bits. This extracted pulse can be used to process high-speed packets with low timing jitter within each packet frame. Previous demonstrations of self-synchronization have involved marker pulses at different wavelengths, polarization, intensity, or bit period. Our scheme allows all pulses in the packet to be identical, which simplifies packet generation and propagation in high-speed TDM systems.

All-optical 100-gbit/s word packet time-division-multiplexed access node in a looped-back configuration: enabling technologies for sequential add–drop functionality

We experimentally demonstrate the adding, dropping, and passing through of 100-Gbit/s word packets in a looped-back all-optical time-division-multiplexed (TDM) access node. Packets are routed with a 17-dB contrast ratio and demultiplexed with a 20-dB contrast ratio. This node uses short 100-Gbit/s words to demonstrate its potential to process data packets from multiple sources and to perform packet switching in a multinode ring network configuration. The ability to tolerate timing jitter as well as varying input signal characteristics is essential to an all-optical access node in a multinode network. For 2-ps input pulses, the header processor has a timing window of approximately 5 ps, and the demultiplexer has a timing window of approximately 5.5 ps. This allows for tolerance to bit-to-bit timing jitters or to an increase in the pulse width of as much as 3 ps. Packet-to-packet timing jitter is detected and compensated by the technique used to synchronize the local source to each packet. The key enabling technologies of an all-optical TDM packet add-drop multiplexer are discussed, including an erbium-doped fiber laser, a nonlinear optical loop mirror logic gate, self-synchronization to incoming packets with a fast-saturation/slow-recovery gain element followed by an intensity discriminator, a two-wavelength nonlinear optical loop mirror demultiplexer, and synchronization of new packets to the network packet rate with a phase-locked loop. The local source is automatically synchronized to the incoming packet, because it uses an extracted pulse from the packet, which has a contrast ratio of >20 dB to the rest of the packet. Finally, new packets are added by use of a local laser and a synchronization method, which gives a timing jitter of approximately 1 ps. Using a statistical method of measuring Q value with picosecond resolution, we show that a header processor with two cascaded logic gates has a Q value of 7.1 with a 95% confidence level.

Demultiplexing of arbitrarily polarized 100 Gb/s words using a twisted fiber nonlinear optical loop mirror

Summary form only given. We demonstrate a 100 Gb/s demultiplexer for data with arbitrary input states of polarization using a polarization insensitive, two-wavelength, nonlinear optical loop mirror (2/spl lambda/ NOLM). The device uses 450 m of twisted fiber to achieve polarization sensitivity 15 dB, and Q-parameter >15. Our demultiplexer combines the 2/spl lambda/ NOLM with a local laser and synchronization circuit based on a phase-locked-loop and an acousto-optic modulator and grating in the laser.