Coherent Optical IF Calibration for Tx-Rx Transfer Decomposition
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Solution Overview
Problem
Existing methods for calibrating transmitter and receiver analog chains in optical modems are costly, complex, and inefficient, failing to accurately measure crosstalk and nonlinearities under nominal operating conditions, and require external detectors and sampling oscilloscopes.
Innovation Solution
Implementing a method called TRIAD that uses an acousto-optical modulator to introduce an intermediate frequency (IF) between the transmitter and receiver, allowing for a single measurement to calibrate both chains, including crosstalk and nonlinearities, under both factory and operational conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external optical detectors and digital sampling oscilloscopes are used for calibration, then measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an acousto-optical modulator as an intermediary device that converts optical signals to acoustic signals, enabling the use of standard acoustic measurement equipment instead of specialized optical measurement devices. This mediator allows calibration to be performed with simpler, more affordable hardware while maintaining measurement capability.
Solution Approach 2:
The patent replaces complex optical measurement systems with a simplified acoustic-based measurement system. By using an acousto-optical modulator to convert optical signals to acoustic signals, the system substitutes sophisticated optical detection hardware with more common acoustic measurement equipment, reducing overall system complexity and cost.
2Reliability
If traditional calibration methods are used, then calibration can be performed, but calibration time and throughput are slow
Solution Approach 1:
The patent employs periodic test signals and repeated measurements to efficiently characterize transmitter and receiver impairments. By using periodic acoustic test signals that modulate the optical carrier, the system can rapidly gather calibration data through repeated cycles, significantly improving throughput while maintaining accuracy through statistical analysis of multiple measurements.
Solution Approach 2:
The patent changes the measurement parameters by operating in the acoustic frequency domain rather than the optical domain. This parameter transformation allows for faster measurement speeds because acoustic signals can be generated and detected more rapidly than optical signals, thereby improving calibration throughput while preserving measurement accuracy through the acousto-optical conversion process.
3Measurement precision
If calibration is performed under different operating modes, then comprehensive characterization is achieved, but calibration complexity increases
Solution Approach 1:
The patent creates a universal calibration methodology that works across different operating modes (factory calibration and field calibration) using the same acousto-optical measurement approach. The single-sideband modulation technique and acoustic test signal generation provide a unified framework that can characterize various impairments (crosstalk, nonlinearities, polarization effects) without requiring mode-specific procedures, thereby reducing calibration process complexity while maintaining comprehensive characterization capability.
Solution Approach 2:
The acousto-optical modulator serves as a universal intermediary that enables consistent measurement across different operating conditions. Whether performing factory calibration or field calibration, the same acousto-optical conversion mechanism translates optical impairments into measurable acoustic signals, providing a unified approach that simplifies the calibration process while achieving comprehensive impairment characterization.
4Measurement precision
If polarization lockers are used for alignment, then receiver alignment is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical polarization alignment systems (polarization lockers) with an acoustic-based measurement and alignment approach. By converting optical polarization information into acoustic domain measurements through the acousto-optical modulator, the system eliminates complex mechanical polarization control hardware while achieving equivalent or superior alignment accuracy through acoustic signal analysis.
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
Facilitates fast and accurate calibration of transmitter and receiver chains, reducing hardware complexity and costs, while enabling real-time impairment characterization and correction, even under nominal operating conditions.
Implementation Method 1
Implementing a method called TRIAD that uses an acousto-optical modulator to introduce an intermediate frequency (IF) between the transmitter and receiver
Data Source
AI summary
Aspects of the subject disclosure may include, for example, based on a transmission of a transmit (Tx) signal from a coherent optical transmitter to a coherent optical receiver, extracting a transfer function of the coherent optical transmitter, a transfer function of the coherent optical receiver, one or more impairments associated with the coherent optical transmitter, one or more impairments associated with the coherent optical receiver, or a combination thereof to facilitate calibration or impairment characterization of one or more of the coherent optical transmitter and the coherent optical receiver, wherein an offset between a laser frequency of the coherent optical transmitter and a laser frequency of the coherent optical receiver satisfies a threshold so as to enable the extracting. Other embodiments are disclosed.