Optical performance monitor built into EDFA repeaters for WDM networks

Abstract

Wavelength-division multiplexing (WDM) technology is considered to have great potential for use in such optical networks as optical crossconnect systems and optical add-drop multiplexing (ADM) systems."' But the issue of monitoring (to ensure effective system maintenance in the practical operation of such networks) has yet to be fully resolved. Specifically, while effective monitoring is available for the regenerators SDH/SONET Regenerator A 1 EDFA Repeater Tho2 Fig. 1. Supervision and control for SDH/SONET regenerator and EDFA repeater. SDH synchronous digital hierarchy; SONET: synchronous optical network; O/E optical-electrical converter; RST regenerator section termination; E/O: electrical-optical converter; OA&M: operation, administration and maintenance; EDFA erbium-doped fiber amplifier; SNR signal-to-noise ratio.used in SDH/SONET system^,^ the only available performance monitors for Er-doped fiber amplifiers (EDFAs) in WDM systems are spectrum analyzers, which are neither fast nor reliable enough. And just as the monitoring of bit errors is important for guaranteeing quality in SDH/ SONET systems, so signal-to-noise ratio (SNR) is important to EDFA monitoring in WDM systems.Tn this paper, we present an optical performance monitor that employs an acousto-optic tunable filter (AOTF), which has previously been utilized as a wavelength channel counter for per-channel output power control in an EDFA repeater? This monitor, which features low cost, high reliability, and high-speed operations, can detect SNRs, output levels per channel, and the number of channels, information which can be used in the supervision and control of EDFA repeaters. Figure 2 shows the optical performance monitor, which employs a polarization-independent AOTF that operates over a wide tunable wavelength range (>110 nm), with a high extinction ratio (>15 dB). The AOTF is driven by pulses ranging in frequencyfrom 172-178 MHz (from Tho2 Fig. 2. Optical performance monitor built-in EDFA repeater. EDFA erbium-doped fiber amplifier; AOTF: acousto-optic tunable filter; PD: photo diode; S(xi): signal power of channel A, ; total power; PXi-bar: channel Xi removed power; N: noise power. 2 -40 -30 -20 -1 0 EDFA Input Power per Channel :Pin [dBm] Tho2 Fig. 3. Experimental setup and results. AWG: arrayed wave guide; LN Mod: LiNb03 external modulator; ATT: optical attenuator; EDFA erbiumdoped fiber amplifier; Pin: EDFA input power per channel; Rx: optical receiver.

Improved optical spectral monitoring using regularization

“…Various optical channel monitoring techniques have been proposed [2][3][4]. One commonly used technique is to scan the spectrum with a narrow band-pass tuneable filter [5].…”