Compact Littrow Spectrometer with Common Lens for SD-OCT
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Solution Overview
Problem
High-speed spectral domain optical coherence tomography (SD-OCT) systems face challenges due to the large size of spectrometers and sensitivity to mechanical vibrations and temperature variations, as well as distortions caused by conical diffraction in Littrow configurations, which affect the accuracy and stability of the spectrometer output.
Innovation Solution
A compact Littrow spectrometer design is implemented, using a common lens to focus both incoming and diffracted beams and employing conical diffraction to separate them vertically, with optical corrections such as aberrant lenses and field flattening lenses to mitigate distortions and stabilize the system, while also incorporating polarization-independent grating designs to reduce sensitivity to polarization changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a classical in-plane diffraction configuration is used with separate lenses for incident and diffracted beams, then off-axis distortion is reduced, but the spectrometer size becomes large
Solution Approach 1:
The patent merges the functions of the incident beam lens and diffracted beam lens into a single common lens. This common lens focuses both the incident beam onto the grating and the diffracted spectral components onto the detector array, thereby reducing the number of optical elements and compacting the spectrometer size while maintaining acceptable distortion levels through optimized optical geometry
Solution Approach 2:
The patent transitions from a two-dimensional in-plane diffraction configuration to a three-dimensional conical diffraction configuration. By tilting the grating to create conical diffraction, the spectral components are dispersed in a conical pattern rather than a planar pattern, allowing the use of a common lens while maintaining spectral separation and reducing off-axis distortion effects
2Volume of stationary object
If the spectrometer output is made compact with small pixel height, then the system becomes more sensitive to mechanical vibration and temperature variation
Solution Approach 1:
The patent creates an optical system where the spectral line focus is positioned at the detector plane with minimized curvature and distortion. By optimizing the conical diffraction geometry and common lens positioning, the system achieves a more uniform optical path and focus position across the spectral range, reducing the impact of small displacements caused by vibration and thermal expansion on the detection accuracy
Solution Approach 2:
The patent changes the diffraction geometry parameters by introducing conical diffraction through grating tilt. This parameter change transforms the spectral dispersion from a planar to a conical pattern, which when combined with the common lens, creates a more stable focus position on the detector that is less sensitive to mechanical and thermal variations
3Ease of operation
If conical diffraction is used to separate incoming and diffracted beams vertically, then beam separation is achieved, but distortion is introduced to the spectral line
Solution Approach 1:
The patent converts the distortion introduced by conical diffraction into a beneficial effect by using a specifically designed aberrant lens. This lens introduces opposite distortion that compensates for the conical diffraction distortion, thereby straightening the spectral line on the detector. The harmful distortion is thus transformed into a means for achieving accurate spectral measurement
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
The design results in a more compact, stable, and polarization-independent spectrometer that improves the accuracy and robustness of SD-OCT systems by reducing distortions and sensitivity to mechanical and thermal variations, enabling high-speed and high-resolution imaging.
Implementation Method 1
a grating for dispersing an incoming light beam into its spectral components
Implementation Method 2
using a common lens to focus both incoming and diffracted beams
Implementation Method 3
employing conical diffraction to separate them vertically
Implementation Method 4
with optical corrections such as aberrant lenses and field flattening lenses to mitigate distortions
Data Source
AI summary
A compact conical diffraction Littrow spectrometer is disclosed. The distortion of the conically diffracted spectral component beams is compensated and as a result, the diffracted spectral beams can still be focused into a substantially straight line to shine onto a detector array. A spectral domain optical coherence tomography (SD-OCT) system incorporating a Littrow spectrometer or a spectrometer having one or more shared focusing element(s) and an SD-OCT system incorporating a spectrometer that is substantially polarization independent are also disclosed.