Optical Amplifier Dynamic Range Extension via PWM and Lookup Table
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Solution Overview
Problem
Conventional optical amplifier systems face instability and limited dynamic range due to fluctuations in pump power at low operation levels and non-linear characteristics at high power levels, particularly near the lasing threshold, which affects the stability and efficiency of the amplifier.
Innovation Solution
The method involves operating the optical amplifier using pulse width modulation (PWM) to maintain the pump laser above the kink region, with a lookup table to compensate for non-linearities, ensuring stable operation by varying the duty cycle and using a combination of PWM and lookup table to linearize the output power, thereby avoiding the adverse effects of the kink region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the pump laser is operated near its lasing threshold to reduce power consumption, then energy efficiency is improved, but pump power stability deteriorates due to reflections and fluctuations
Solution Approach 1:
The patent applies pulse width modulation (PWM) to periodically switch the pump laser between on and off states, avoiding continuous operation near the unstable threshold region. By using periodic pulsing with duty cycle control, the system achieves stable average power output while keeping the pump operating point away from the problematic threshold region, thus resolving the contradiction between energy efficiency and power stability.
2Power
If the pump laser operates at high power levels to increase amplifier output, then signal gain is improved, but non-linear characteristics and kinks in the L-I curve limit further power increase
Solution Approach 1:
The patent uses PWM to operate the pump laser in periodic pulses rather than continuous DC mode. This allows the system to achieve high average output power by increasing the peak pulse power without suffering from the non-linear kink region effects that plague continuous operation. The periodic switching avoids the unstable operating points in the L-I curve while maintaining high overall power output through duty cycle control.
3Ease of operation
If conventional DC drive current control is used to maintain a fixed power set point, then power control simplicity is improved, but dynamic range is limited due to instability at low powers and non-linearities at high powers
Solution Approach 1:
The patent replaces conventional DC drive control with PWM-based periodic control. By varying the duty cycle of the PWM signal, the system can achieve a wide dynamic range from very low to very high average power levels while avoiding the instability regions. This maintains operational simplicity through a single control parameter (duty cycle) while dramatically extending the usable dynamic range compared to DC control.
Data Source
AI summary
The present invention generally relates to the operation of optical network equipment such as optical amplifiers. In one aspect, a method of operating an optical amplifier is provided such that output of the optical amplifier avoids the effects of operating an optical gain medium in a non-linear (kink) region of an L-I curve. The method generally includes operating an optical gain medium in a fully off state or fully on state above the kink region with a PWM signal. In another aspect, the effects of the kink region may be compensated for by utilizing a lookup table. A sample of the optical power of an amplified optical signal may be used to select an entry in the lookup table that compensates for non-linearities in the kink region. In yet a further aspect, a lookup table may be used to control a pulse modulator to compensate for non-linearites in the kink region of the L-I curve.