Ting-Kuang Chiang

BROADBAND FIBER OPTICAL PARAMETRIC AMPLIFIERS

The bandwidth of a single-pump fiber optical parametric amplifier is governed by the even orders of fiber dispersion at the pump wavelength. The amplifier can exhibit gain over a wide wavelength range when operated near the fibers zero-dispersion wavelength. It can also be used for broadband wavelength conversion,with gain. We have experimentally obtained gain of 10-18 dB as the signal wavelength was tuned over a 35-nm bandwidth near 1560 nm.

Cross-phase modulation in fiber links with multiple optical amplifiers and dispersion compensators

We have theoretically and experimentally investigated the cross-phase modulation (XPM) effect in optical fiber links with multiple optical amplifiers and dispersion compensators. Our theory suggests that the XPM effect can be modeled as a phase modulator with inputs from the intensity of copropagating waves. The frequency response of the phase modulator corresponding to each copropagating wave depends on fiber dispersion, wavelength separation, and fiber length. The total XPM-induced phase shift is the integral of the phase shift contributions from all frequency components of copropagating waves. In nondispersive fibers, XPM is frequency-independent; in dispersive fibers, XPMs frequency response is approximately inversely proportional to the product of frequency, fiber dispersion, and wavelength separation. In an N-segment amplified link, the frequency response of XPM is increased N-fold, but only in very narrow frequency bands. In most other frequency bands, the amount of increase is limited and almost independent of N. However, in an N-segment amplified link with dispersion compensators, the frequency response of XPM is increased N-fold at all frequencies if the dispersion is compensated for within each fiber segment. Thus, the XPM-induced phase shift is smaller in systems employing lumped dispersion compensation than in systems employing distributed dispersion compensation.

Implementation of STARNET: a WDM computer communications network

STARNET is a broadband backbone optical wavelength-division multiplexing (WDM) local area network (LAN). Based on a physical passive star topology, STARNET offers all users two logical subnetworks: a high-speed reconfigurable packet-switched data subnetwork and a moderate-speed fix-tuned packet-switched control subnetwork. Thus, STARNET supports traffic with a wide range of speed and continuity characteristics. We report the analysis and implementation of an entire STARNET two-node network, from the optical to the computer layer, at the Optical Communications Research Laboratory (OCRL) of Stanford University. To implement the two logical subnetworks, we designed and implemented two different techniques: combined modulation and multichannel subcarrier multiplexing (MSCM). OCRL has already demonstrated several combined modulation techniques such as phase shift-keyed and amplitude shift-keyed (PSK/ASK), and differential phase shift-keyed and amplitude shift-keyed (DPSK/ASK), yielding combined ASK/DPSK modulation receiver sensitivities better than -32 dBm. OCRL has designed and implemented a high-speed high-performance packet-switched STARNET computer interface which enables high-throughput transfer to/from host computer, low latency switching, traffic prioritization, and capability of multicasting and broadcasting. With this interface board, OCRL has achieved average transmit and receive throughputs of 685 Mb/s and 571 Mb/s, respectively, out of the 800 Mb/s theoretical maximum of the host computer bus. The incurred packet latency due to the interface for a specified multihop network configuration has been simulated to be 24 /spl mu/s. Using simulation and experimental results, it is shown that STARNET is highly suitable for high-speed multimedia network applications.

Widely tunable spectrum translation and wavelength exchange by four-wave mixing in optical fibers

Summary form only given. Wavelength conversion has been the subject of much research in recent years. Various methods have been studied with use of optical nonlinearities in either semiconductors or fibers. We introduce a novel technique based on four-wave mixing (FWM) in fibers, which has the potential for achieving unit conversion efficiency. It involves only spectrum translation, not inversion or phase conjugation. It is widely tunable and can, in principle, shift wavelengths by tens and even hundreds of nanometers. It can also perform a novel optical function, namely, complete exchange of optical power between two wavelengths.

Optimizing the location of dispersion compensators in periodically amplified fiber links in the presence of third-order nonlinear effects

In order to minimize third-order nonlinear effects while compensating dispersion in a periodically amplified link, it is more effective to place a single dispersion compensator at the end of the link than to individually compensate each segment. The improvement obtained by using the former approach instead of the latter one, defined as the ratio of the powers of the four-wave mixing products in the two cases, is (sin N u/N sin u)/sup 2/ where N is the number of segments, and u represents phase mismatch. We have experimentally verified this conclusion, by performing a cross-phase modulation experiment in a two-segment link.

Cancellation of third-order nonlinear effects in amplified fiber links by dispersion compensation, phase conjugation, and alternating dispersion.

We show that in principle it is possible to cancel third-order nonlinear effects in optical fiber links. The necessary conditions exist in two-segment links, with dispersion compensation, phase conjugation, and amplification between the two, as well as opposite chromatic dispersion coefficients in the segments. The cancellation is independent of loss, modulation format, and modulation frequency.

Cross phase modulation in fiber links with optical amplifiers

Summary form only given. In WDM optical communication systems, nonlinear effects in optical fibers can lead to crosstalk between channels . It has been reported that cross phase modulation (XPM) induced by residual intensity modulation causes penalty in multi-channel PSK and FSK systems. Previously we have shown that chromatic dispersion has a significant impact on the magnitude of XPM in a single segment of fiber. In this paper, we investigate experimentally and theoretically XPM in systems where multiple optical amplifiers are used as repeaters.

Fiber-optical parametric amplifier with 35-nm bandwidth

Summary form only given. We show that the bandwidth of a fiber-optical parametric amplifier (OPA) depends only on the even orders of fiber dispersion at the pump wavelength, and can reach tens of nanometers when operating near the zero-dispersion wavelength. Theory and experimental results show that fiber OPAs can exhibit bandwidths exceeding that of EDFAs, and could find applications as broadband amplifiers, or as broadband wavelength converters with high conversion efficiency.

Compensation of cross-phase modulation in periodically amplified CPFSK optical communication systems

In long-distance periodically amplified systems, dispersion compensation is highly beneficial. In this paper, we show that compensating the dispersion in each segment (type-A systems) still leads to significant cross phase modulation (XPM) induced penalty even when high dispersion fiber is used, but the penalty is greatly reduced by concentrating the dispersion compensation at one place (type-B systems).

Impact Of Four Wave Mixing On Optical FSK WDM Communication Systems

The performance of optical wavelength-division-multiplexed (WDM) systems may be degraded by four wave mixing (FWM) due to the fiber nonlinearities [ 11. The impact of FWM on system performance depends on the modulation technique and receiver structure. The frequency-shift-keying (FSK) heterodyne system using nonsynchronous demodulation with single-filter envelope detection (SFED) is relatively easy to implement, and has been used in many experiments [2]. The impact of FWM on heterodyne FSK systems employing dual-filter envelope detection has been analyzed in [3], but the impact of FWM on FSK WDM systems employing SFED receivers is yet to be analyzed.