Pulsed Diode Laser Interferometry for Low-Cost Broad Bandwidth OCT
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Solution Overview
Problem
Current interferometric imaging systems, such as OCT, face challenges with high costs due to expensive light sources and detectors, particularly in achieving broad bandwidth and high power while maintaining low duty cycle requirements for field illumination OCT systems.
Innovation Solution
A semiconductor diode laser is operated under non-traditional conditions with pulses of drive current to achieve a spectral output bandwidth at least two times larger than equilibrium conditions, combined with a multiple point imaging spectrometer for hybrid SS/SD-OCT systems, utilizing consumer-grade 2D array sensors and optimized for low-cost, high-power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional broad bandwidth light sources (superluminescent diodes or swept sources) are used, then spectral bandwidth and power are improved, but system cost increases significantly
Solution Approach 1:
The patent applies parameter changes by operating the diode laser in pulsed mode rather than continuous wave mode, and by controlling the pulse width and repetition rate to achieve spectral broadening through dynamic effects. This transforms a standard narrow-bandwidth laser into a broad-bandwidth source without requiring expensive specialized components.
2Measurement precision
If longer exposure times are used to improve signal-to-noise ratio, then measurement sensitivity is improved, but phase washout increases due to axial/lateral motion
Solution Approach 1:
The patent employs periodic pulsed illumination where each pulse is short enough to minimize phase washout but the repetition rate allows sufficient signal accumulation. This periodic action enables longer effective exposure times for improved signal-to-noise ratio while maintaining phase stability within each individual pulse.
3Power
If high power light sources are used to achieve sufficient signal from weakly reflecting samples, then signal intensity is improved, but source cost and complexity increase
Solution Approach 1:
The patent uses a standard, inexpensive diode laser that is widely available and simple in design, rather than copying or adapting complex expensive sources like superluminescent diodes or swept sources. The simplicity of the diode laser platform reduces both cost and complexity while achieving the required performance through clever operational techniques.
4Ease of manufacture
If consumer-grade 2D array sensors are used to reduce detector cost, then detector cost decreases, but frame rate is limited to less than 200Hz
Solution Approach 1:
The patent performs preliminary spectral dispersion of the light before detection, so that each pixel in the 2D array sensor receives light at a specific wavelength. This allows the use of slower frame rate sensors because the spectral information is already separated and can be processed more efficiently, compensating for the limited frame rate of consumer-grade sensors.
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 enables longer exposure times with minimal phase washout, reducing costs and enhancing the signal-to-noise ratio in interferometric imaging, particularly suitable for field illumination OCT and self-interference interferometry.
Implementation Method 1
Rapidly tunable intracavity filters, which precisely restrict the longitudinal mode of the laser, are standard in swept source OCT (see for example, US Patent No. 5,949 801), where it is desirable to smoothly sweep a narrow laser line across a broad bandwidth.
Implementation Method 2
Non-equilibrium thermal effects and carrier density effects can create small changes in refractive index of the laser cavity.
Implementation Method 3
OCDR is an interferometric imaging method that determines the scattering profile of a sample along the beam by detecting light reflected from a sample combined with a reference beam.
Data Source
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AI summary
Various optical systems equipped with diode laser light sources are discussed in the present application. One example system includes a diode laser light source for providing a beam of radiation. The diode laser has a spectral output bandwidth when driven under equilibrium conditions. The system further includes a driver circuit to apply a pulse of drive current to the diode laser. The pulse causes a variation in the output wavelength of the diode laser during the pulse such that the spectral output bandwidth is at least two times larger the spectral output bandwidth under the equilibrium conditions.