F.S. Yang

Broadband fiber-optical parametric amplifiers and wavelength converters with low-ripple Chebyshev gain spectra

We have shown that the propagation constant mismatch /spl Lambda//spl beta/ for a 2-pump fiber OPA can be well approximated by a fourth-order Chebyshev polynomial, by adjusting /spl omega//sub c/, near /spl omega//sub 0/, and the pump spacing. Very low gain ripple can be obtained over tens of nanometer. This level of performance is not available with any other type of optical amplifier. It could make fiber OPAs and related wavelength converters attractive when multiple stages are required.

Nonlinear crosstalk and two countermeasures in SCM-WDM optical communication systems

We investigate, theoretically and experimentally, crosstalk between wavelengths in subcarrier-multiplexed (SCM) wavelength-division multiplexed (WDM) optical communication systems. Crosstalk arises mainly from interactions between subcarriers on one wavelength and the optical carrier of another wavelength. In a dispersive fiber, crosstalk can be attributed to stimulated Raman scattering (SRS) and cross-phase modulation (XPM) combined with group velocity dispersion (GVD). We investigate the phase relationship between SRS-induced and XPM-induced crosstalks. Crosstalks induced by SRS and XPM add in the electrical domain and can interfere constructively or destructively. Experimental results show that the combined crosstalk level can be as high as 40 dBc after 25 km of SMF with two wavelengths and 18 dBm per wavelength of transmitted power. We propose two crosstalk countermeasures. The first countermeasure uses parallel fiber transmission. We show theoretically that both SRS-induced and XPM-induced crosstalks can be cancelled to the first order. We present an experimental demonstration of concept which has achieved 15 dB of crosstalk cancellation over 200 MHz. The second countermeasure uses optical carrier suppression. We show, theoretically and experimentally, that by suppressing the optical carrier, we can significantly reduce crosstalk while maintaining the same link budget and carrier-to-noise ratio (CNR) at the receiver, 20 dB of crosstalk reduction over 2 GHz has been demonstrated experimentally.

High-nonlinearity fiber optical parametric amplifier with periodic dispersion compensation

Theory shows that the maximum gain and bandwidth of one-pump fiber optical parametric amplifiers made from high-nonlinearity fiber, operated with a pump wavelength /spl lambda//sub p/ far from the fiber zero-dispersion wavelength /spl lambda//sub 0/ can greatly be improved by periodic dispersion compensation. We have performed experiments and obtained good agreement with theory: for /spl lambda//sub p/=1542 and /spl lambda//sub 0/=1591 nm, we have increased the bandwidth from 7 to 28 nm, and the maximum gain from 15 to 20 dB, by splicing three pieces of standard fiber at regular intervals in a 40-m long nonlinear fiber.

CORD : Optical packet-switched network testbed

Abstract We are implementing and investigating CORD, a 2.5 Gbit/s/λ WDM packet-switched network testbed. CORD features: (i) contention resolution optics (CRO), which consist of optical switches and delay lines to perform all-optical packet contention resolution; (ii) multichannel subcarrier multiplexed (MSCM) signaling to transmit an 80 Mbit/s control channel and 2.5 Gbit/s payload data on the same wavelength; (iii) networkwide distributed slot synchronization technique with maximum slot jitter of ± 6.5 ns; (iv) novel ultrafast signaling synchronization using delay-line phase alignment for data recovery within 4 bits; and (v) pilot-tone payload data synchronization for clock recovery within 16 ns. In this article, we describe the CORD network testbed and discuss the performance and scaling potential of the technologies developed for CORD.

Idler spectral broadening suppression in two-pump fiber optical parametric amplifier

We have demonstrated the suppression of idler broadening in a two-pump fiber optical parametric amplifier by dithering the two pumps with out-of-phase signals. Idler spectrum linewidth almost the same as signal linewidth is observed.

Suppression of fiber nonlinearities in HFC systems by distributed fiber Raman amplification

We study in detail the two types of nonlinear crosstalk which cause severe problems in WDM AM CATV systems. They are respectively due to stimulated Raman scattering (SRS), and cross-phase modulation (XPM) interacting with group-velocity dispersion.

WDM routers based on hierarchic optical discrete Fourier transform matrices

We have introduced the possibility of synthesizing WDM routers based on N X N hierarchic star couplers. We have examined how the required phase shifts can be introduced by means of path length differences, and studied in detail the crosstalk introduced by the frequency dependence of these phases. We have found that crosstalk levels are moderate, even in units designed for a wavelength range as large as 64 nm. Additional opportunities exist for improving performance further, by implementing the phases by different path differences. The many degrees of freedom of hierarchic star couplers could also be used for making versatile reconfigurable routers.

Cancellation of SRS cross talk in an analog WDM optical communication system by a parallel technique

Summary form only given. Stimulated Raman scattering (SRS) cross talk has been identified as a major obstacle to the implementation of analog wavelength-division multiplexing (WDM) optical communication systems. Here we report, for the first time to our knowledge, a SRS crosstalk reduction obtained by a cancellation technique. The experimental setup is shown. An optical carrier, was intensity-modulated at the frequency (signal) by a Mach-Zehnder interferometric modulator.

Nonlinear crosstalk and SBS reduction by carrier suppression in an analog WDM optical communication system

Nonlinear cross talk and stimulated Brillouin scattering (SBS) reduction are demonstrated in an analog wavelength-division multiplexing (WDM) optical communication system using optical carrier suppression. Cross talk reduction by 20 dB over 2 GHz is achieved. SBS is negligible without employing any frequency or phase dithering.

Fiber optical parametric amplifier: bandwidth expansion by dispersion compensation

We demonstrate an optical fibre parametric amplifier concept by measuring the parametric gain on three different combination of fibers including nonlinear fibre and dispersion shifted fibre.