Down Conversion Receiver for Distortion-Free Phase Recovery
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Solution Overview
Problem
Conventional down-conversion techniques distort phase modulated signals, leading to loss of phase information and reduced spur free dynamic range (SFDR) in optical links, especially at high frequencies.
Innovation Solution
A method for down-converting phase modulated optical signals by optically coupling the signal with a local oscillator and differentially photodetecting to generate a differentially photodetected signal, which is then processed using quadrature signals to recover phase information without distortion, employing a phase tracker and modulators to accurately replicate the phase information in a sub-band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional down-conversion techniques are used to recover phase modulated signals, then the signal can be processed at lower frequencies, but phase information is lost and distortion increases
Solution Approach 1:
The patent employs a phase tracker that continuously monitors the phase of the down-converted signal and feeds back control signals to adjust the local oscillator frequency, ensuring the oscillator remains locked to the signal carrier. This feedback mechanism prevents phase information loss by dynamically compensating for frequency offsets and phase drift during the down-conversion process.
Solution Approach 2:
The patent replaces conventional electronic down-conversion methods with an optical-domain approach using photodetectors and local optical oscillators. By performing the down-conversion optically before electrical detection, the system avoids the distortion and phase information loss inherent in purely electronic conversion methods, while still achieving lower frequency processing.
2Speed
If conventional down-conversion is used for phase modulated signals, then frequency conversion is achieved, but spur free dynamic range is reduced
Solution Approach 1:
The phase tracker continuously adjusts the local oscillator frequency based on feedback from the photodetector output, maintaining precise frequency alignment. This feedback mechanism suppresses spurious signals and improves the spur-free dynamic range by preventing frequency mismatch and phase distortion that would otherwise generate unwanted spectral components.
Solution Approach 2:
The patent dynamically changes the frequency parameter of the local oscillator to match the incoming signal frequency, enabling accurate down-conversion across a wide frequency range. By continuously adjusting this parameter through the phase tracker, the system maintains high spur-free dynamic range while achieving flexible frequency conversion capability.
3Ease of operation
If phase modulated signals are down-converted using standard methods, then the signal can be processed, but distortion is introduced
Solution Approach 1:
The patent substitutes electronic down-conversion with optical-domain processing, using photodetectors to convert the optical signal to electrical signals after optical mixing with the local oscillator. This substitution eliminates the distortion introduced by conventional electronic conversion methods while maintaining ease of signal processing through the optical-hybrid approach.
Solution Approach 2:
The phase tracker provides continuous feedback to adjust the local oscillator frequency, ensuring precise frequency alignment during down-conversion. This feedback mechanism maintains signal fidelity by preventing frequency mismatch and phase distortion, while still enabling straightforward signal processing operations.
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
Achieves high-fidelity phase recovery with SFDR greater than 140 dBm Hz2/3, maintaining signal integrity and reducing distortion across a wide frequency band.
Implementation Method 1
optically coupling a phase modulated optical signal and a local oscillator signal
Implementation Method 2
differentially photodetecting the optically coupled phase modulated optical signal and local oscillator signal to generate a differentially photodetected signal
Data Source
AI summary
In one embodiment, a down conversion receiver is provided for a phase modulated optical signal. This may include an optical coupler coupled to be capable of receiving a phase modulated signal and a local oscillator signal, and a modulator coupled to an input of the optical coupler so as to be capable of modulating one of: (1) a phase modulated signal; or (2) a local oscillator signal. A photodetector circuit is located to be capable of detecting signals coupled by the optical coupler, with a sub-band selector circuit coupled to be capable of receiving signals from the photodetector circuit. The sub-band selector circuit has an output coupled to a modulating input of the modulator.