Optical Receiver Intensity Correction via Feedback
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Solution Overview
Problem
Existing optical receivers for RZ-DPSK and coherent optical systems face challenges in automatically correcting intensity differences due to variations in optical signal intensity and path, leading to degraded CMRR and waveform distortion.
Innovation Solution
Incorporating a differential transimpedance amplifier with closed feedback loops and a level adjustment unit that detects photoelectric currents to adjust signal levels automatically, ensuring equal intensity for both optical signals before demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a balanced receiver using a delayed interferometer is applied for RZ-DPSK or RZ-DQPSK modulation at high transmission rates, then the optical noise tolerance is improved, but the received intensity of two optical signals cannot be kept equal due to intensity or optical path differences, degrading CMRR and causing waveform distortion
Solution Approach 1:
The patent introduces a feedback mechanism where the received optical signals are fed back through variable optical attenuators to the input of the delayed interferometer. This feedback loop automatically adjusts the intensity balance between the two optical signals by controlling the attenuation levels, thereby maintaining equal received intensities and improving CMRR without compromising the optical noise tolerance provided by the balanced receiver structure
Solution Approach 2:
The system employs self-service through automatic intensity balancing where the received signals themselves are used to control the variable optical attenuators in the feedback path. The system automatically compensates for intensity differences without requiring external control, making the intensity equalization process self-regulating and adaptive to changing conditions
2Device complexity
If the intensity difference between two optical signals is not corrected, then the device complexity is reduced, but the CMRR is degraded and waveform distortion increases
Solution Approach 1:
The patent achieves multi-functionality by using the same delayed interferometer structure for both demodulation and intensity balancing purposes. The feedback path utilizing variable optical attenuators serves dual functions: maintaining intensity equality for CMRR improvement and providing automatic gain control, thereby improving reliability without significantly increasing device complexity
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
This configuration allows for automatic correction of intensity differences, improving CMRR and maintaining signal quality by adjusting signal levels based on detected photoelectric currents, thereby enhancing demodulation accuracy and reducing waveform distortion.
Implementation Method 1
The photodiodes (PD) 611 and 612 convert two optical signals outputted from the 1-bit delayed interferometer 650 into intensity modulated signals
Data Source
AI summary
In the optical receiver available for the RZ-DPSK modulation system, the difference in the received intensity due to the difference in the intensity or optical path of the optical signal cannot be corrected automatically, therefore, an optical receiver according to an exemplary aspect of the invention includes a first photodiode receiving a normal phase optical signal from a first output of a 1-bit delayed interferometer and outputting a positive signal; a second photodiode receiving a reversed phase optical signal from a second output of the 1-bit delayed interferometer and outputting a complementary signal; a differential transimpedance amplifier inputting the positive signal and the complementary signal and including a closed feedback loop for each input of the positive signal and the complementary signal; a level adjustment unit adjusting a signal level in the closed feedback loop; a photoelectric current detection unit detecting a photoelectric current generated in each of the first photodiode and the second photodiode; and wherein the level adjustment unit adjusts the signal level on the basis of an output of the photoelectric current detection unit.