J.E. McGeehan

All-optical signal processing using /spl chi//sup (2)/ nonlinearities in guided-wave devices

The authors present a review of all-optical signal-processing technologies based on /spl chi//sup (2)/ nonlinear interactions in guided-wave devices and their applications for telecommunication. In this study, the main focus is on three-wave interactions in annealed proton-exchanged periodically poled lithium niobate waveguides due to their suitable properties with respect to nonlinear mixing efficiency, propagation loss, and ease of fabrication. These devices allow the implementation of advanced all-optical signal-processing functions for next-generation networks with signal bandwidths beyond 1 THz. In this paper, integrated structures that will allow for improvements of current signal-processing functions as well as the implementation of novel device concepts are also presented.

All-optical address recognition for optically-assisted routing in next-generation optical networks

Optical fiber communication technology enabled high-speed, long-distance capacity in todays networks. The packet switching functions such as address recognition and routing are performed in the electrical domain after optical-to-electrical conversion. As more real-time applications come online, demand for bandwidth increases, and electronic processing may potentially become a bottleneck at the intermediate nodes along the network. We introduce some optical address recognition schemes for optically-assisted routing that may decrease the processing delay at these nodes.

Degree-of-polarization-based PMD monitoring for subcarrier-multiplexed signals via equalized carrier/sideband filtering

We demonstrate a method for differential-group-delay (DGD) and polarization-mode-dispersion (PMD) monitoring using the degree-of-polarization (DOP) in subcarrier-multiplexed (SCM) systems. Traditional SCM signal show very little DOP sensitivity to DGD/PMD due to the low modulation depth used for generating SCM signals. We use a narrow-band optical filter to equalize the power of the carrier and one of the sidebands by offsetting the filter from the carrier, enabling PMD and DGD monitoring and more than tripling the DOP sensitivity to DGD/PMD. Our technique is simple, uses only a single optical filter, and can be applied to both single- and double-sideband (SSB and DSB) SCM signals as well as single and multisubcarrier systems. Additionally, we show that our monitoring technique is robust to the chromatic dispersion-induced radio-frequency (RF) power fading effect seen in DSB SCM signals. Using this technique to enhance the DOP sensitivity to DGD/PMD and generate a feedback signal to a PMD compensator (PMDC), we obtain an 11-dB improvement in the 5% RF power tail.

All-optical decrementing of a packet's time-to-live (TTL) field and subsequent dropping of a zero-TTL packet

We demonstrate an optical time-to-live (TTL) decrementing module for optical packet-switched networks. Our module acts on a standard NRZ-modulated binary TTL field within a 10 Gb/s packet and decrements it by one if the TTL is nonzero. If the TTL of the incoming packet is zero, the module signals an optical switch to drop the packet. Our technique is independent of the TTL length, does not require the use of ultrashort RZ optical pulses, requires no guard time between the end of the TTL field and the packet data, and has only a 2.4 dB power penalty at 10/sup -9/ bit-error rate.

All-optical chromatic dispersion monitoring of a 40-Gb/s RZ signal by measuring the XPM-generated optical tone power in a highly nonlinear fiber

We experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique potential for ultrahigh-speed systems. A monochromatic continuous wave probe is coupled with the tapped-off data signal into a highly nonlinear fiber. An optical tone that is sensitive to CD is generated near the probe wavelength due to the cross-phase modulation effect and is used for CD monitoring. The monitoring window is /spl plusmn/42 ps/nm for 40-Gb/s return-to-zero systems. This monitoring technique is simple and needs no modification at the transmitter.

Performance optimization of RZ data format in WDM systems using tunable pulse-width management at the transmitter

Tunable pulse-width management is one of the efficient methods to enhance the robustness of return-to-zero (RZ) data formats for long-haul transmission systems. We demonstrate both single channel and 4 /spl times/ 10-Gb/s wavelength-division-multiplexed performance optimization using tunable pulse-width management. Pure RZ single with tunable pulse-width is generated by changing the driving voltages on a phase modulator and the dispersion values of a tunable dispersion element simultaneously according to our simulation results. Varying the pulse width from 50 to 10 ps at the transmitter can almost double the transmission distance with 4% variation in the residual link dispersion.

First-order PMD monitoring for NRZ data using RF clock regeneration techniques

We propose and demonstrate two novel techniques for 10 Gb/s polarization-mode-dispersion (PMD) monitoring for NRZ signals that use a regenerated RF clock tone as a monitoring signal. Our techniques regenerate the RF clock tone that is usually absent after square-law detection in the electrical NRZ data spectrum (in the absence of dispersion). Our first technique uses a dispersive element in the monitoring tap-line to put the beat terms between the optical clock sidebands and the carrier in phase and thus regenerates the RF clock tone after detection. Our second technique involves the use of an optical filter that is centered at the bit rate frequency on either the upper or lower sideband of the optical spectrum, removing one of the sidebands and thus preventing the beating that normally cancels the RF clock tone. We show (theoretically, via simulation, and experimentally) the effect that PMD has on these regenerated RF clock tones. We also demonstrate PMD compensation at 10 Gb/s using these techniques for monitoring and show a 6-dB improvement in the 1% power penalty tail. Our techniques are simple, do not require modification at the transmitter, and can be applied to WDM systems via the use of a multichannel dispersive element or a tunable filter swept across all channels.

Theoretical and experimental analysis of the dependence of a signal's degree of polarization on the optical data spectrum

We show theoretically and experimentally the relationship between a signals degree of polarization (DOP), all-order polarization mode dispersion (PMD), and the optical spectrum (and hence the data modulation format and pulse width), and that these effects must be taken into account when using the DOP for differential group delay (DGD) monitoring. We explain the theory behind how all-order PMD affects a signals DOP, and observe the pulse-width dependence for 10-, 20-, and 40-Gb/s return-to-zero (RZ) systems as the duty cycle changes. We then analyze and show (via simulation and experimentation) the effects of different data modulation formats (RZ, carrier-suppressed RZ, alternate-chirped RZ, and differential phase-shift keying) on the DOP in a DGD monitor. We conclude that the measurable DGD range and DOP sensitivity in DOP-based DGD monitors are dependent on a signals pulse width and the data modulation format. We also show the theory behind the effects of first- and second-order PMD on the maximum and minimum DOP.

Wavelength-Shift-Free 3R Regenerator for 40-Gb/s RZ System by Optical Parametric Amplification in Fiber

We demonstrate wavelength-shift-free 3R-regenerator for 40-Gb/s optical return-to-zero (RZ) system by optical parametric amplification (OPA) with a clock-modulated pump in highly nonlinear fiber. The power penalty is improved by 2.6 dB, and the signal power is amplified by 7 dB

Multiwavelength-channel header recognition for reconfigurable WDM networks using optical correlators based on sampled fiber Bragg gratings

We demonstrate a tunable, multiwavelength optical correlator that uses an array of sampled fiber Bragg gratings (FBGs) as the correlating element. The incoming wavelength-division-multiplexing (WDM) data streams are tapped off and the packet headers on each 10-Gb/s channel are simultaneously recognized and correlated to a reconfigurable header code. The correlation output for each channel is compared to a threshold level, and simple decision electronics are used to drive a set of switches to route the individual WDM packets accordingly. Using this technique, we recognize two WDM 10-Gb/s packet headers simultaneously, with a negligible power penalty when switching packets to the appropriate output port. Moreover, we tune the gratings for reconfigurable routing.