Abstract
We report the design of a high-efficiency spectral-domain spectrometer with cylindrical optics for line scanning optical coherence tomography (OCT). The spectral nonlinearity in k space (wavenumber) lowers the depth-dependent signal sensitivity of the spectrometers. For linearizing, in this design, grating and prism have been introduced. For line scanning, a cylindrical mirror is utilized in the scanning part. Line scanning improves the speed of imaging compared to fly-spot scanning. Line scanning OCT requires a spectrometer that utilizes cylindrical optics. In this work, an optical design of a linear wavenumber spectrometer with cylindrical optics is introduced. While there are many works using grating and prism to linearize the K space spectrometer design, there is no work on linearizing the k-space spectrometer with cylindrical optics for line scanning that provides high sensitivity and high-speed imaging without the need for resampling. The design of the spectrometer was achieved through MATLAB and ZEMAX simulations. The spectrometer design is optimized for the broadband light source with a center wavelength of 830 ± 100 nm (8.607 m− 6.756 m in k-space). The variation in the output angle with respect to the wavenumber can be mentioned as a nonlinearity error. From our design results, it is observed that the nonlinearity error reduced from 147.0115 to 0.0149 *m within the wavenumber range considered. The use of the proposed reflective optics for focusing reduces the chromatic aberration and increases image quality (measured by the Strehl ratio (SR)). The complete system will provide clinicians a powerful tool for real-time diagnosis, treatment, and guidance in surgery with high image quality for in-vivo applications.
Highlights
There is considerable interest in designing ultra-broadband optical coherence tomography, which is a low coherence interferometric 3D imaging technique that provides cross-sectional views of the subsurface microstructure of biological tissue with micrometer resolution for clinical studies [1,2]
In SD-optical coherence tomography (OCT), the depth profile is constructed by inverse Fourier transform (FT) of the interferograms, and it is mandatory to rescale the output from the wavelength to the wavenumber space
The Strehl ratio is above the Marechal criterion for both transmission grating and reflective grating with prism spectrometers
Summary
There is considerable interest in designing ultra-broadband optical coherence tomography, which is a low coherence interferometric 3D imaging technique that provides cross-sectional views of the subsurface microstructure of biological tissue with micrometer resolution for clinical studies [1,2]. To reduce the signal sensitivity fall-off, the linear k-space spectrometer has been introduced [5,13] This spectrometer uses a prism to offset the nonlinearity caused by the grating. In [8], two systems were designed, the first one has a center wavelength of 1270 nm with a bandwidth of 70 nm, and the second one has a center wavelength of 830 nm with a bandwidth of 40 nm In these works, linearizing the k space spectrometer shows a significant improvement in signal sensitivity [7,8]. There is an increasing demand for ultra broadband OCT systems with a higher axial resolution to distinguish smaller structures [16] It causes more difficulties for k-space spectrometer design in the nonlinearity error correction and the aberration correction for focusing lens. The complete system will allow clinicians a powerful tool for real-time diagnosis, treatment, and guidance in surgery with high image quality for in-vivo applications
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