Optical Phase Distortion Measurement Circuit
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Solution Overview
Problem
Existing broadband phase distortion measurement techniques face challenges in accurately measuring phase relationships due to unknowns such as delay and phase offset drift, which affect the stability and accuracy of phase distortion measurements in receivers.
Innovation Solution
A test circuit and method utilizing a first and second laser, a photo diode, and a receiver-under-test (RUT) to generate and measure 3-tone signals with known phase relationships, eliminating the impact of delay and phase offset drift by calculating phase deviations between measured phasors and comparing them with known phase relationships.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing broadband phase distortion measurement techniques are used, then phase distortion can be measured, but measurement accuracy is degraded due to unknown delay and phase offset drift
Solution Approach 1:
The patent introduces an optical domain as an intermediary to generate the test signal. By using optical frequency combs and photodetection, the system creates electrical tones with precisely known phase relationships, eliminating the need for direct electrical signal generation that suffers from phase drift. The optical domain acts as a stable reference that mediates between the test source and the receiver under test.
Solution Approach 2:
The patent replaces traditional electrical signal generation and distribution systems with an optical-based system. Instead of using electrical oscillators and signal distributors that are susceptible to phase drift, the system uses optical frequency combs and photodetection to generate the multi-tone test signal, substituting the mechanical/electrical domain with the optical domain for more stable phase relationships.
2Measurement precision
If traditional phase distortion measurement methods are used, then measurements can be performed, but delay variations affect measurement accuracy
Solution Approach 1:
The optical domain serves as an intermediary that generates test signals with inherently stable phase relationships. The optical frequency comb provides a natural reference that is insensitive to delay variations in the electrical domain, allowing accurate phase distortion measurements even when delay varies across the bandwidth.
3Productivity
If phase offset drift is present in the measurement system, then measurements can proceed, but measurement stability deteriorates
Solution Approach 1:
By introducing the optical domain as an intermediary, the system generates test signals whose phase relationships are determined by optical frequencies rather than electrical oscillators. This intermediary reference is stable and does not suffer from the same drift problems as electrical systems, enabling continuous measurements without recalibration.
Solution Approach 2:
The system performs preliminary phase relationship establishment in the optical domain before the signals enter the receiver under test. The optical frequency comb pre-establishes known phase relationships among multiple tones, so that when these tones pass through the device under test, any phase deviations can be directly attributed to the device rather than to drift in the test equipment.
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 approach allows for accurate characterization and measurement of phase distortion in high-frequency broadband receivers, eliminating the dependency on unknown phase drift and delay, resulting in invariant phase distortion measurements.
Implementation Method 1
The photo diode receives and mixes the first optical signal and the second optical signal, and produces a first tone at a third frequency f3
Implementation Method 2
The second laser is tuned to a second frequency f2 and generates a second optical signal and phase modulates the second optical signal with a periodic signal with a repetition frequency fM
Data Source
AI summary
A test circuit for measuring phase distortion includes a first laser, a second laser and a photo diode. The first laser is tuned to a first frequency f1 and generates a first optical signal. The second laser is tuned to a second frequency f2 and generates a second optical signal and phase modulates the second optical signal with a periodic signal with a repetition frequency fM. The photo diode receives and mixes the first optical signal and the second optical signal, and produces a first tone at a third frequency f3, which is a carrier frequency equal to an absolute value of a difference between the second frequency f2 and the first frequency f1, a second tone at a fourth frequency f4 at a difference between the third frequency f3 and the repetition frequency fM, and a third tone at a fifth frequency f5 at a sum of the third frequency f3 and the repetition frequency fM.