Optical Output Module Bias Control for DQPSK Phase Shift
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Solution Overview
Problem
In DQPSK optical communication systems, adjusting the bias voltage for phase shift is challenging due to temperature and time drifts, requiring additional hardware and increasing manufacturing costs, especially when using RF power detectors.
Innovation Solution
An optical output module with phase modulating means, phase shift means, and bias control means that adjust the bias voltage based on inherent modulation signals and low-frequency signals, detecting power differences at specific voltage conditions to achieve the desired phase shift without a pilot signal, reducing hardware complexity and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pilot signal is given to the bias voltage for phase shift adjustment, then the phase shift amount can be accurately controlled, but additional RF power detector hardware is required which increases device complexity and manufacturing cost
Solution Approach 1:
The invention extracts and utilizes the inherent low-frequency signal components already present in the modulation signals applied to the phase modulators. By detecting these existing signal components through synchronous detection, the system eliminates the need for separate pilot signals and RF power detectors, thereby reducing hardware complexity while maintaining phase shift control accuracy
Solution Approach 2:
The invention makes the existing modulation signals serve dual purposes: their primary function of modulating the optical signal and an additional function of providing reference signals for phase shift detection and control. This multi-functionality eliminates the need for dedicated pilot signals and simplifies the overall system architecture
2Measurement precision
If a pilot signal is given to the bias voltage for phase shift adjustment, then the phase shift amount can be accurately controlled, but manufacturing cost increases due to additional hardware
Solution Approach 1:
The invention extracts and utilizes the inherent low-frequency signal components already present in the modulation signals applied to the phase modulators. By detecting these existing signal components through synchronous detection, the system eliminates the need for separate pilot signals and RF power detectors, thereby reducing hardware complexity while maintaining phase shift control accuracy
Solution Approach 2:
The invention replaces expensive RF power detector hardware with a cost-effective synchronous detection circuit that utilizes existing signal components. This substitution significantly reduces manufacturing costs while achieving the same phase shift control functionality
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise adjustment of phase shift without a pilot signal, reducing hardware complexity and manufacturing costs while maintaining optical transmission quality, allowing for efficient phase shift control in DQPSK systems.
Implementation Method 1
a laser;
Implementation Method 2
first phase modulating means for modulating a phase of an optical signal output from the laser based on a first bias voltage in which a first modulation signal is inherent
Data Source
AI summary
The I phase modulator modulates a phase based on the bias voltage in which a first modulation signal and a first pilot signal are inherent and the Q phase modulator modulates a phase based on the bias voltage in which a second pilot signal different from the first pilot signal and a second modulation signal are inherent. A time-average power synchronous detection unit detects an optical power at a timing at which the positivity and negativity of the voltages of both pilot signals become the same, and an optical power when the positivity and negativity of the voltages of both pilot signals are opposite. The bias voltage control unit controls the bias voltage so that the difference between both the optical powers becomes small based on the detection result of the time-average power synchronous detection unit.