Swept Source OCT Phase-Locked Detection Synchronization
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Solution Overview
Problem
Swept-source OCT systems face challenges in maintaining image quality at high wavelength sweep rates, leading to blurring and artifacts due to fluctuations in the ratio of sweep and sampling frequencies, especially when using a single trigger for an entire data frame.
Innovation Solution
Establishing a phase-locked relationship between the sweep control signal and the detection clock signal, either through hardware phase-locking or software resampling, to ensure precise synchronization and reduce phase jitter, thereby improving image quality and coherence at higher sweep rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wavelength sweep rate is increased to improve imaging speed, then productivity is improved, but image quality deteriorates due to blurring and artifacts caused by frequency ratio fluctuations
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the detection clock signal frequency to maintain a constant ratio with the sweep control signal frequency. When the sweep rate changes, the detection clock frequency is proportionally adjusted to preserve the sampling-to-sweep frequency ratio, thereby preventing image degradation while enabling high-speed imaging
Solution Approach 2:
The patent implements feedback control by continuously monitoring the sweep control signal frequency and adjusting the detection clock signal frequency accordingly. The system uses the frequency ratio information as feedback to maintain synchronous sampling, ensuring that the detection clock remains locked to the sweep rate variations and preventing artifacts caused by frequency drift
2Loss of time
If the wavelength sweep rate is increased to reduce scanning time, then loss of time is reduced, but measurement precision deteriorates due to phase jitter
Solution Approach 1:
The patent changes the detection clock frequency parameter in proportion to the sweep rate to maintain a constant frequency ratio. This ensures that even at high sweep rates, the sampling remains synchronized with the optical frequency changes, preserving depth measurement precision without increasing scanning time
Solution Approach 2:
The patent makes the detection clock signal dynamic by allowing its frequency to change in response to sweep rate variations. This dynamic adjustment ensures that the sampling rate adapts to the instantaneous sweep conditions, maintaining measurement precision across varying scan speeds
3Device complexity
If independent oscillators are used for sweep control and detection clock to simplify the system, then device complexity is reduced, but reliability deteriorates due to frequency ratio fluctuations
Solution Approach 1:
The patent merges the sweep control and detection clock functions by establishing a phase-locked relationship between them. The detection clock is derived from or synchronized to the sweep control signal, ensuring that both functions share a common frequency reference and maintain a constant ratio, thereby improving reliability while maintaining reasonable system complexity
Solution Approach 2:
The patent introduces a phase-locked loop or frequency synthesis mechanism as an intermediary between the sweep control signal and detection clock. This intermediary ensures that the detection clock frequency is always a precise multiple or fraction of the sweep rate, maintaining reliability without requiring direct coupling of the oscillators
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 significantly reduces blurring and artifacts, allowing for high-quality imaging even at higher sweep rates, enabling deeper scans with improved signal-to-noise ratio and reduced phase jitter, while maintaining coherence for accurate depth information.
Implementation Method 1
The tunable light source 12 carries out wavelength sweeps with a specific repetition rate f sweep, in which it generates optical signals in which the wavelength of the signal changes over time. Such signals are also referred to as 'chirps'.
Implementation Method 2
The optical signals in the two interferometer arms 16 and 18 are superimposed, for example with the aid of a 50/50 coupler 25, and an interference signal 34 is generated
Implementation Method 3
an interference signal 34 is generated, for example with the aid of photodetectors 26 and a differential amplifier 28
Implementation Method 4
the sweep control signal 30 and the detection clock signal 38 are phase-locked, in particular with the aid of a phase-locked loop 46
Data Source
Figure 1~2
Figure 3~5
Figure 6a~6b
AI summary
A swept source OCT system and related method are disclosed. The system comprises a control device for operating a tunable light source in response to an electronic sweep control signal such that the tunable light source carries out wave length sweeps with a repetition rate fsweep, which depends on the frequency of the sweep control signal. The system further comprises a detection device for the time-resolved detection of an interference signal from a sample beam and a reference beam with the help of a detection cycle signal. The sweep control signal and the detection cycle signal are phase-locked, or means for creating a signal or signal sequence are provided, said signal or signal sequence being characterising for the frequency relationship and/or the relative phase position of the sweep control signal and detection cycle signal.