Active Phase Modulation for Circular Ranging OCT Demodulation
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Solution Overview
Problem
Existing coherent circular ranging (CR) systems in optical coherence tomography suffer from RF errors that cause artifacts due to imaging at multiples of the frequency comb free spectral range, necessitating complex optical circuits and frequent recalibration, limiting their practical application.
Innovation Solution
Implement active phase modulation methods using a phase modulator to generate stable I/Q demodulation of detected signals, enabling high-speed acquisition of complex interference signals up to 1 MHz, simplifying system construction and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive polarization-based optical quadrature demodulation is used, then artifacts are reduced by more than 50 dB, but the optical circuit becomes relatively complex and frequent recalibration is required
Solution Approach 1:
The patent replaces the passive polarization-based optical quadrature demodulation system with an active phase modulation system using an electro-optic phase modulator. This substitution eliminates the need for complex polarization optics and frequent recalibration while achieving similar artifact reduction performance. The active phase modulator dynamically introduces phase shifts without requiring the complex optical circuitry of the passive polarization system.
Solution Approach 2:
The patent changes the demodulation approach from passive polarization-based to active phase modulation-based, fundamentally altering the operating parameters of the system. By using temporal phase modulation at the laser repetition rate rather than polarization optics, the system achieves stable I/Q demodulation without the complexity and recalibration requirements of the previous approach.
2Productivity
If frequency combs are used for coherent circular ranging, then imaging speed and range are enhanced, but RF errors cause artifacts at multiples of the free spectral range
Solution Approach 1:
The patent implements active feedback through the electro-optic phase modulator that dynamically adjusts the phase of the reference beam based on the laser repetition rate. This feedback mechanism continuously compensates for RF errors and maintains stable interference patterns, enabling the system to operate at high speeds without generating artifacts at multiples of the free spectral range.
Solution Approach 2:
The patent introduces dynamic phase modulation at the laser repetition rate to actively manage the interference patterns. By making the phase shifting dynamic rather than static, the system can adapt to temporal variations and maintain stable demodulation across the full imaging range, eliminating the harmful RF error artifacts that plague static frequency comb systems.
3Reliability
If active phase modulation is used, then stable I/Q demodulation is achieved, but the phase modulator must operate at high laser repetition speeds up to and beyond 1 MHz
Solution Approach 1:
The patent employs dynamic phase modulation at the laser repetition rate, using the electro-optic phase modulator to introduce precise phase shifts that track the temporal frequency of the laser. This dynamic approach allows the system to maintain stable I/Q demodulation even at high repetition rates up to and beyond 1 MHz, as the phase modulation continuously adapts to the laser's temporal characteristics.
Solution Approach 2:
The patent utilizes periodic phase modulation synchronized with the laser repetition rate. By applying phase shifts at the same periodicity as the laser pulses, the system creates stable interference patterns that can be reliably demodulated. This periodic action allows the phase modulator to operate at high speeds while maintaining demodulation stability through consistent temporal synchronization.
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
Stable I/Q demodulation reduces artifacts by more than 50 dB, facilitating robust and efficient CR systems suitable for clinical and industrial applications.
Implementation Method 1
applying, using a phase modulator, a phase shift including a first phase shift and a second phase shift to at least one of the reference portion or the sample portion of the electro-magnetic radiation source
Implementation Method 2
acquiring in-phase data based on a first interference between first backscattered electro-magnetic radiation during the first time period and the at least one of the reference portion or the sample portion subjected to the first phase shift
Data Source
AI summary
A method including: scanning a sample over a period of time using an electro-magnetic radiation source, the period of time including a first time period and a second time period, a sample portion of the electro-magnetic radiation source being directed to the sample in a sample arm of an optical interferometric system, and a reference portion of the electro-magnetic radiation source being directed to a reference arm of the optical interferometric system; applying, using a phase modulator, a phase shift comprising a first phase shift and a second phase shift to at least one of the reference portion or the sample portion of the electro-magnetic radiation source, the first phase shift being applied during the first time period and the second phase shift being applied during the second time period, the second phase shift having a difference of 90 degrees from the first phase shift.