Optical Amplifier Pre-emphasis for Gain Ripple Compensation
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Solution Overview
Problem
Conventional optical communications systems face the optical amplifier gain ripple penalty due to non-flat gain spectra of optical amplifiers, leading to degraded bit error rate performance, which is compounded by the use of multiple amplifiers and is costly to address with dynamic gain equalizers and optical performance monitors.
Innovation Solution
The method involves storing gain ripple information in optical amplifier modules, using system software to compute pre-emphasis or equalization requirements, and applying corrections using existing Variable Optical Attenuators (VOAs) and reconfigurable blocking filters (RBFs) to achieve a flat signal-to-noise ratio at the receiver, without the need for expensive feedback mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dynamic gain equalizers (DGE) and optical performance monitors (OPM) are used to alleviate gain ripple penalty, then bit error rate performance is improved, but system cost increases significantly
Solution Approach 1:
The patent uses a copy of the amplifier gain ripple characteristics (stored in lookup tables) to predict and compensate for gain ripple effects without requiring expensive real-time measurement hardware. Instead of using actual OPM measurements, the system uses pre-characterized ripple patterns from factory calibration to compute pre-emphasis settings.
Solution Approach 2:
The system performs preliminary characterization of each amplifier's gain ripple characteristics during factory calibration and stores this information in lookup tables. This pre-computed data is then used during operation to determine pre-emphasis settings, eliminating the need for real-time measurement and feedback hardware.
2Length of stationary object
If multiple optical amplifiers are used to extend transmission distance, then system reach is improved, but gain ripple penalty increases linearly
Solution Approach 1:
The system pre-characterizes the gain ripple properties of each amplifier during factory calibration and stores this information in lookup tables. During operation, the controller retrieves these pre-computed characteristics and automatically calculates the appropriate pre-emphasis settings to compensate for the cumulative ripple effects of multiple amplifiers in the chain.
Solution Approach 2:
The system implements a computational feedback mechanism where the controller uses stored amplifier characteristics and actual operating conditions (temperature, gain settings) to dynamically adjust pre-emphasis settings. This closed-loop approach compensates for ripple accumulation without requiring expensive physical feedback hardware.
3Reliability
If conventional gain equalization methods are used, then signal-to-noise ratio is improved, but additional expensive hardware is required
Solution Approach 1:
The patent replaces expensive physical measurement and equalization hardware with computational models stored in lookup tables. The system uses pre-characterized gain ripple patterns (copies of actual amplifier behavior) to predict required equalization settings, eliminating the need for expensive DGE and OPM hardware while achieving the same signal-to-noise ratio improvement.
Solution Approach 2:
The patent substitutes physical hardware-based equalization mechanisms (DGE, OPM) with a software-based computational system. The controller uses stored lookup table data and mathematical computations to determine pre-emphasis settings, replacing mechanical/optical feedback systems with an electronic software solution that achieves the same equalization effect.
Data Source
AI summary
The present invention provides an optical amplifier pre-emphasis and equalization method that alleviates the optical amplifier gain ripple penalty experienced in conventional optical communications systems. This method includes storing measured communications channel signal gain ripple information, acquired during factory calibration, in the internal memory of each optical amplifier module. When the optical amplifiers are assembled into a chain, system software retrieves this communications channel signal gain ripple information from each optical amplifier module and computes the pre-emphasis or equalization required for each channel in order to obtain a flat SNR at a receiver. The method also includes measuring the ambient temperature of each optical amplifier module and applying a correction based on the expected change in gain response of each optical amplifier. The method further includes, for Raman amplifiers and the like, applying a fiber type, gain setting, GFF error, etc. correction based on the expected change in gain response of each optical amplifier. The method relies on using VOAs at the sources or DGEs/RBFs in the optical signal path to pre-emphasize or equalize the optical channels.