Coherent Optical Receiver Gain Balancing for Stable CMRR
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Solution Overview
Problem
The common mode rejection ratio (CMRR) in coherent optical receivers decreases due to differences in receiving intensity or photoelectric conversion efficiency between photodiodes, leading to waveform distortion and reduced signal quality in high-speed optical communication systems.
Innovation Solution
An optical receiver configuration that includes a first and second photodiode, a differential transimpedance amplifier, and a gain adjustment unit to equalize the voltage amplitudes of the output signals from both photodiodes, ensuring that the gains of the differential transimpedance amplifier for each photodiode are adjusted to match, thereby compensating for differences in receiving intensity and photoelectric conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single optical receiver is used to receive optical signals, then the device complexity is reduced, but the common mode rejection ratio (CMRR) deteriorates due to differences in receiving intensity or photoelectric conversion efficiency between photodiodes
Solution Approach 1:
The patent introduces a feedback control mechanism where the output signals from the first and second photodiodes are fed back to a gain adjustment unit. This unit continuously monitors the voltage amplitudes and adjusts the gains of the differential transimpedance amplifier to equalize the output levels, thereby maintaining high CMRR despite variations in photodiode characteristics.
Solution Approach 2:
The patent dynamically changes the gain parameter of the differential transimpedance amplifier based on the detected voltage amplitude differences between the two photodiode outputs. By adjusting the gain in real-time, the system compensates for manufacturing variations and maintains equal voltage amplitudes, thus preserving CMRR performance.
2Productivity
If the bit rate per wavelength increases to exceed 40 Gbit/s, then the productivity of optical communication is improved, but the signal quality deteriorates due to waveform distortion from chromatic dispersion and polarization mode dispersion
Solution Approach 1:
The patent employs feedback control where the received optical signal is continuously monitored and the gain adjustments are made based on the detected signal characteristics. This feedback mechanism enables real-time compensation for waveform distortion caused by chromatic dispersion and polarization mode dispersion, maintaining signal quality at high bit rates.
3Reliability
If gain adjustment is applied to equalize voltage amplitudes from both photodiodes, then the common mode rejection ratio is improved, but the device complexity increases due to additional gain adjustment means
Solution Approach 1:
The patent merges the gain adjustment function with the existing differential transimpedance amplifier structure. The gain adjustment unit is integrated into the signal processing path, combining multiple functions (amplification, differential operation, and gain control) into a unified structure that minimizes additional complexity while achieving CMRR improvement.
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 effectively suppresses the decline in CMRR, ensuring accurate waveform equalization and improved signal quality by maintaining equal voltage amplitudes for the output signals from both photodiodes, enhancing the reliability of high-speed optical communication systems.
Implementation Method 1
a first photodiode receiving a first optical signal and outputting a positive signal; a second photodiode receiving a second optical signal and outputting a complementary signal
Implementation Method 2
a differential transimpedance amplifier receiving the positive signal and outputting an amplified positive signal voltage, and receiving the complementary signal and outputting an amplified complementary signal voltage
Data Source
AI summary
The common mode rejection ratio (CMRR) decreases due to the difference in receiving intensity of the optical signal or in photoelectric conversion efficiency of the photodiode in the related coherent optical receiver, therefore, an optical receiver according to an exemplary aspect of the present invention includes a first photodiode receiving a first optical signal and outputting a positive signal; a second photodiode receiving a second optical signal and outputting a complementary signal; a differential transimpedance amplifier receiving the positive signal and outputting an amplified positive signal voltage, and receiving the complementary signal and outputting an amplified complementary signal voltage; and a gain adjustment means for adjusting a first gain of a gain of the differential transimpedance amplifier for the positive signal and a second gain of a gain of the differential transimpedance amplifier for the complementary signal.