Coherent Optical Transceiver Self-Calibration for Path Droop Correction
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Solution Overview
Problem
Coherent optical transceivers in LEO satellite modems face non-idealities and RF losses that cause higher frequencies to be attenuated relative to lower frequencies, leading to non-linear phase responses and inter-symbol-interference, which are not effectively corrected by existing calibration methods.
Innovation Solution
A self-calibrating transceiver system that measures separate path droops using a calibration comb waveform, allowing for the mathematical separation of droops and calculation of filter coefficients to correct for these impairments through a series of N unique signal paths, enabling in-field calibration without specialized equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing calibration methods are used, then the system can perform basic calibration, but it cannot effectively correct non-linear phase responses and RF losses caused by non-idealities
Solution Approach 1:
The patent segments the calibration process by measuring droop separately for N unique signal paths (I/Q paths, X/Y polarization paths) rather than treating them as a single combined response. This allows the system to solve N simultaneous equations to obtain independent filter coefficients for each path, enabling precise correction of non-linear phase responses and RF losses that cannot be corrected by conventional single-step calibration methods.
2Manufacturing precision
If filter coefficients are calculated to correct RF losses, then frequency response can be improved, but the complexity of measuring and calculating separate path droops increases
Solution Approach 1:
The transceiver performs self-calibration by using its own internal components (DACs, IQ modulators, photodetectors, ADCs) to measure and correct its own droop characteristics. The system generates calibration signals, measures the complete lineup response through N unique paths, calculates filter coefficients, and applies corrections without requiring external calibration equipment, thereby achieving frequency response flatness while managing calibration complexity through self-contained operations.
3Ease of operation
If in-field calibration is performed without specialized equipment, then ease of operation is improved, but measurement precision may be compromised
Solution Approach 1:
The patent uses a calibration comb waveform as an intermediary signal that contains multiple frequency components. By measuring the response to this structured calibration signal across N unique paths, the system can mathematically separate and precisely characterize droop in each path. The comb waveform serves as a mediator that enables accurate measurement without requiring specialized external equipment, as the transceiver's own signal generation and detection capabilities are sufficient when processed through the calibration algorithm.
Data Source
AI summary
A self-calibrating transceiver includes a set of digital to analog converters configured to process a comb calibration waveform, at least one IQ modulator configured to generate at least one optical signal comprising I and Q components operably coupled from the set of digital to analog converters. A receiver photonics circuit is configured to convert the coupled optical signals to electrical signals. The receiver photonics circuit includes a set of analog to digital converters coupled to convert the electrical signals to digital signals representative of the comb calibration waveform in cartesian IQ format. Processing circuitry is coupled to determine at least magnitude and/or phase of the digital signals and generate filter coefficients based on a comparison of at least magnitude and/or phase to the comb calibration waveform.