Frequency Offset Compensating Apparatus for Optical Coherent Receiver
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Solution Overview
Problem
Optical coherent receivers face difficulties in accurately compensating for frequency and phase offsets due to technological restrictions, particularly in high-frequency offset scenarios, which affect the performance of the receiver.
Innovation Solution
A frequency offset compensating apparatus is introduced, comprising a front end processor, a frequency offset estimator, and a series of integrators and multipliers that convert the optical signal into a base band digital electric signal, estimate phase offset changes, and correct these changes to produce a compensated base band electric signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If digital phase recovery technology is used to remove phase offset, then the receiver can operate without a phase locked loop, but the technology fails when frequency offset exceeds tens of MHz
Solution Approach 1:
The patent segments the phase offset compensation process into two distinct stages: coarse frequency offset compensation using a frequency offset compensator, and fine phase offset compensation using digital phase recovery. This segmentation allows each stage to handle specific ranges of offset, enabling the system to operate reliably even when total frequency offset exceeds tens of MHz.
Solution Approach 2:
The patent applies preliminary action by performing frequency offset compensation before phase offset recovery. The frequency offset compensator预先 removes the large frequency offset component, creating a precondition where the subsequent digital phase recovery can effectively handle the remaining small phase offsets without being overwhelmed by large frequency drifts.
2Measurement precision
If phase locked loop is used to control local oscillator laser, then precise frequency and phase control can be achieved, but implementation is very difficult due to technological restrictions
Solution Approach 1:
The patent replaces the mechanical/optical phase locked loop system with a fully digital signal processing approach. Instead of using a phase locked loop to physically control the local oscillator laser frequency and phase, the system uses digital signal processing algorithms (frequency offset compensator and digital phase recovery) to electronically remove offsets from the received signal, achieving the same precision without the complexity of optical feedback control.
Solution Approach 2:
The patent introduces an intermediary frequency offset compensator between the optical front-end and the digital phase recovery stage. This intermediary component handles the large frequency offset that would otherwise overwhelm the digital phase recovery algorithm, acting as a bridge that prepares the signal for successful phase recovery while maintaining full digital control.
3Reliability
If frequency offset is kept extremely low (MHz level), then digital phase recovery can operate properly, but this limits the operating range and adaptability of the receiver
Solution Approach 1:
The patent makes the system dynamic by implementing adaptive frequency offset compensation that can handle varying frequency offsets in real-time. The frequency offset compensator continuously estimates and compensates for frequency offsets, allowing the receiver to adapt to different operating conditions and frequency drift scenarios, thereby expanding the operational range while maintaining reliability.
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 solution effectively compensates for frequency offsets in optical coherent receivers, improving signal quality and enabling operation even in high-frequency offset conditions, thus enhancing the performance and reliability of optical communication systems.
Implementation Method 1
an optical frequency mixer 107, and photoelectric detectors (PD) 108 and 109 in FIG. 1 constitute a front end processor for converting an inputted optical signal 101 into a base band electric signal
Data Source
AI summary
The present invention relates to a frequency offset compensating apparatus and method, and an optical coherent receiver. The optical coherent receiver includes a front end processor and a frequency offset estimator, of which said front end processor converts an inputted optical signal into a base band digital electric signal, and said frequency offset estimator estimates a phase offset change introduced by a frequency offset in said base band digital electric signal; said frequency offset compensating apparatus comprises an M output integrator, for integrating the phase offset change introduced by the frequency offset to acquire M inverse numbers of the phase offset introduced by the frequency offset, where M is an integer greater than 1; a series-parallel converting device, for dividing said base band digital electric signal into M sub base band digital electric signals; M complex multipliers, for constructing the corresponding inverse numbers in the M inverse numbers to be complex numbers, and multiplying them with the corresponding sub base band digital electric signals in the M sub base band digital electric signals; and a parallel-series converting device, for converting the M sub base band digital electric signals multiplied by said complex multipliers into a base band electric signal.