Figure 2 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Schematic of the spectrometer using grating and prism (two wavelengths, orange longer and purple shorter).
Source publication
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 s...
Context in source publication
Context 1
... linearity will reduce sensitivity fall-off and computing time. A prism will be inserted in the proposed design between the grating and the focusing mirror, as shown in Figure 2. If the prism and grating angles are set up such that the center wavelength will propagate parallel to the base of the prism, linearity can be ensured [14]. ...
Citations
... To improve the axial resolution by a factor of 2, we simulate a multirate SD-OCT with a delay line. We use the filters in Equation (43)- (45) and to set up the two channels filter bank. The image after passing through the multirate filter bank is shown in Figure 7(b). ...
... The resolution and bandwidth of the SD-OCT system are often limited by the spectrometer. Grating spectrometers are widely used in SD-OCT [45] and its performance is determined by various physical parameters such as grating length, number of gratings, material used, wavelengths, etc. [46]. Often these parameters are interdependent and are restricted by technology and feasibility. ...
Optical coherence tomography is state-of-the-art in non-invasive imaging of biological structures. Spectral Domain Optical Coherence Tomography is the popularly used variation of this technique, but its performance is limited by the bandwidth and resolution of the system. In this work, we theoretically formulate the use of phase modulators and delay lines to act as filters on the tomography system and scan multiple channels. Various channels are then combined in a digital computer using filter bank theory to improve the sampling rate. The combination of multiple channels allows for increasing the axial resolution and maximum unambiguous range beyond the Nyquist limit. We then simulate the multirate spectral domain optical coherence tomography with 2 channels. We show that a single delay line can improve the axial resolution while a pair of phase modulators can improve the maximum unambiguous range of the system. We also show the use of multirate filter banks to carry out this process. Thus, by using a few extra components in the spectral domain optical coherence tomography, its performance can be increased manifold depending on the number of channels used. The extra cost is the time taken to perform the extra scans that is trivial for stationary objects like biological tissues.
... Spectrometer records intensity of all wavelengths. The recorded spectral information in converted to k-space and then an inverse Fourier transform is applied to extract depth versus intensity profile also known as A-scan [2]. ...
... where =2 +1 and () z is given by Similarly, the spectrometer can have resolution M time worse than required so the frequency resolution is downsampled by M. Hence, the block diagram can be again applicable to this case but with inverted domains. Analysis filter () m Hz can be calculated using equation (26) and (40) depending on the tunable delay line/phase modulation given and synthesis filter () m Fz can be calculated using equation (41) and (42). We stress that although equation (26) and equation (39) look the same for both the delay line and cross-arm phase modulation scenarios, it is important to know that their domain is opposite (specifically frequency and length respectively). ...
... The resolution and bandwidth of the SD-OCT system are often limited by the spectrometer. Grating spectrometers are widely used in SD-OCT [42] and its performance is determined by various physical parameters such as grating length, number of gratings, material used, wavelengths, etc. [43]. Often these parameters are interdependent and are restricted by technology and feasibility. ...
Optical coherence tomography is state-of-the-art in non-invasive imaging of biological structures. Spectral Domain Optical Co-herence Tomography is the popularly used variation of this technique, but its performance is limited by the bandwidth and res-olution of the system. In this work, we theoretically formulate the use of phase modulators and delay lines to act as filters on the tomography system and scan multiple channels. Various channels are then combined in a digital computer using filter bank theory to improve the sampling rate . The combination of multiple channels allows for increasing the axial resolution and maximum unambiguous range beyond the Nyquist limit. We then simulate the multirate spectral domain optical coherence tomography with 2 channels. We show that a single delay line can improve the axial resolution while a pair of phase modulators can improve the maximum unambiguous range of the system. We also show the use of multirate filter banks to carry out this process. Thus, by using a few extra components in the spectral domain optical coherence tomography, its performance can be increased manifold de-pending on the number of channels used. The extra cost is the time taken to perform the extra scans that is trivial for stationary objects like biological tissues.
... An additional advantage of the k-mapping technique is that it allows the nonlinear K space signal to be sampled and then converted back to the linear k form during post-processing. Increasing the amount of pixels may also help to counteract this loss of sensitivity [11,14,15]. More pixels in the same region decrease the pixel size, which results in a lot of distortion because of the smaller pixels. ...
... More pixels in the same region decrease the pixel size, which results in a lot of distortion because of the smaller pixels. The scattered spectrum's point spread function (PSF) will be greater than the spectrometer's pixel size in this situation, limiting its performance [15][16][17]. As the number of pixels rises, so do the system costs and processing times, both of which are increasing exponentially. ...
... For better signal sensitivity, researchers developed the linear k-space spectrometer. The nonlinearity of the grating is compensated by using a prism to linearize the spectrometer [7,15,16]. Grisms [18] may be created by placing a diffraction grating in front of a prism with an optimal angle between them. Signal sensitivity has been significantly improved by linearizing the k space spectrometer in these studies [4,5]. ...
Optical coherence tomography (OCT) has a wide range of uses in bioimaging and nondestructive testing. Larger bandwidth light sources have recently been implemented to enhance measurement resolution. Increased bandwidth has a negative impact on spectral nonlinearity in k space, notably in the case of spectral domain OCT (SD-OCT). This nonlinearity reduces the depth-dependent signal sensitivity of the spectrometers. A grating and prism combination is extensively used for linearizing. In an earlier study, we used a combination of the reflective grating and prism, as well as a cylindrical mirror with a radius of 180 mm, to achieve a high SR ratio with low nonlinearity. A creative design for a spectrometer with a cylindrical mirror of radius 50 mm, a light source with a center wavelength of 830 ± 100 nm (μm−1 − 6.756 μm−1 in k-space), and a grating of 1600 lines/mm is presented in this work. The design optimization is performed using MATLAB and ZEMAX. In the proposed design, the nonlinearity error reduced from 157∘× μm to 10.75∘× μm within the wavenumber range considered. The sensitivity research revealed that, with the new design, the SR ratio is extremely sensitive to the imaging optics’ angles. To resolve this, a spectrometer based on Grism is introduced. We present a Grism-based spectrometer with an optimized SR ratio of 0.97 and nonlinearity of 0.792∘× μm (Δθ/Δk). According to the sensitivity study, the Grism-based spectrometer is more robust.
With the performance of optical films is required to be higher and higher in optical instruments. The design of optical thin films optical instruments. The optical characteristics of the film system are determined quantitatively by the evaluation function in the film system design. The is a method to solve the problem. This method has been applied in many fields such as engineering, economics and biology. The main idea of this method is to use ants to find the shortest path between two points. In other words, ants move from one place to another to obtain food or other resources. If there are many ants moving around, they will form a path, which can be called the best solution to the current problem. In this paper, some new ideas thin optimization design are proposed.
