Abstract:Recording of volume Bragg gratings (VBGs) in photo-thermo-refractive glass is limited to a maximum refractive index change about 0.002. We discuss various saturation curves and their influence on the amplitudes of recorded gratings. Special attention is given to multiplexed VBGs aimed at recording several gratings in the same volume. The best shape of the saturation curve for production of the strongest gratings is the threshold-type curve. Two-photon absorption as a mechanism of recording also allows increasi… Show more
“…The total RIM of a sample would be calculated by summing the RIM of each channel, which is 1.16 × 10 –3 for VBG1, 1.57 × 10 –3 for VBG2 and 1.37 × 10 –3 for VBG3. Since the upper limit of the dynamic range of PTR glass is about 2 × 10 –3[ 34 , 41 ] , it is possible to have DE increased as long as the sample reaches a higher RIM. Figure 7 The RIM fitting curve of the first channel of each monolithic VBG and the corresponding picture. The total RIM of a sample would be calculated by summing the RIM of each channel, which is 1.16 × 10 –3 for VBG1 (a), 1.57 × 10 –3 for VBG2 (b) and 1.37 × 10 –3 for VBG3 (c).…”
Section: Resultsmentioning
confidence: 99%
“…The total RIM of a sample would be calculated by summing the RIM of each channel, which is 1.16 × 10 -3 for VBG1, 1.57 × 10 -3 for VBG2 and 1.37 × 10 -3 for VBG3. Since the upper limit of the dynamic range of PTR glass is about 2 × 10 -3 [34,41] , it is possible to have DE increased as long as the sample reaches a higher RIM.…”
Section: Resultsmentioning
confidence: 99%
“…The DE given by Kogelnik’s coupled wave theory [ 32 ] is as follows:where is the phase mismatch factor and is the RIM. Considering the upper limit of the dynamic range of PTR glass, one grating channel should achieve as high a DE as possible with lower RIM [ 34 ] . In the case of and , the DE in Equation (10) will reach 100%, and accordingly we have the following:which represents the rapidly decreased red line in Figure 3.…”
Section: Theoretical Design Of Volume Bragg Gratingsmentioning
confidence: 99%
“…Considering the upper limit of the dynamic range of PTR glass, one grating channel should achieve as high a DE as possible with lower RIM [34] . In the case of δ = 0 and ν = π/2, the DE in Equation (10) will reach 100%, and accordingly we have the following:…”
In this paper, a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared, in which a calculation method is firstly proposed to optimize the number of channels to a minimum. The induction of peristrophic multiplexing reduces the performance difference in one bulk of grating whereas no need to deliberately optimize the fabrication process. It is revealed that a discrete 2D angle deflection range of ±30° is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55% with a Root-Mean-Square deviation of less than 3.4% in the same grating. The deviation of the Bragg incident and exit angle from the expected values is less than 0.07°. It is believed that the proposed 2D angle amplifier has the potential to realize
“…The total RIM of a sample would be calculated by summing the RIM of each channel, which is 1.16 × 10 –3 for VBG1, 1.57 × 10 –3 for VBG2 and 1.37 × 10 –3 for VBG3. Since the upper limit of the dynamic range of PTR glass is about 2 × 10 –3[ 34 , 41 ] , it is possible to have DE increased as long as the sample reaches a higher RIM. Figure 7 The RIM fitting curve of the first channel of each monolithic VBG and the corresponding picture. The total RIM of a sample would be calculated by summing the RIM of each channel, which is 1.16 × 10 –3 for VBG1 (a), 1.57 × 10 –3 for VBG2 (b) and 1.37 × 10 –3 for VBG3 (c).…”
Section: Resultsmentioning
confidence: 99%
“…The total RIM of a sample would be calculated by summing the RIM of each channel, which is 1.16 × 10 -3 for VBG1, 1.57 × 10 -3 for VBG2 and 1.37 × 10 -3 for VBG3. Since the upper limit of the dynamic range of PTR glass is about 2 × 10 -3 [34,41] , it is possible to have DE increased as long as the sample reaches a higher RIM.…”
Section: Resultsmentioning
confidence: 99%
“…The DE given by Kogelnik’s coupled wave theory [ 32 ] is as follows:where is the phase mismatch factor and is the RIM. Considering the upper limit of the dynamic range of PTR glass, one grating channel should achieve as high a DE as possible with lower RIM [ 34 ] . In the case of and , the DE in Equation (10) will reach 100%, and accordingly we have the following:which represents the rapidly decreased red line in Figure 3.…”
Section: Theoretical Design Of Volume Bragg Gratingsmentioning
confidence: 99%
“…Considering the upper limit of the dynamic range of PTR glass, one grating channel should achieve as high a DE as possible with lower RIM [34] . In the case of δ = 0 and ν = π/2, the DE in Equation (10) will reach 100%, and accordingly we have the following:…”
In this paper, a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared, in which a calculation method is firstly proposed to optimize the number of channels to a minimum. The induction of peristrophic multiplexing reduces the performance difference in one bulk of grating whereas no need to deliberately optimize the fabrication process. It is revealed that a discrete 2D angle deflection range of ±30° is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55% with a Root-Mean-Square deviation of less than 3.4% in the same grating. The deviation of the Bragg incident and exit angle from the expected values is less than 0.07°. It is believed that the proposed 2D angle amplifier has the potential to realize
“…Due to the incoherent addition the refractive index modulation grows linearly with the number of spectral lines, quickly saturating the writing material [19,20]. This can be circumvented by coherently writing the gratings that create a refractive index profile as determined by Eq.…”
Detecting and monitoring gas species is an important part of remote sensing because the state of the environment can be retrieved from the state of the gas species. This can be used to track temperature and pressure structures in the atmosphere for weather predictions, or monitor the air quality. Discriminating different species is easier at higher spectral resolution when the spectral lines are clearly resolved. The need to do this at high spatial resolution and over large fields of view leads to a trade-off between spectral and spatial resolution and spectral bandwidth. We propose to use a highly multiplexed Bragg grating that can optically combine the relevant information from the spectrum without the need to disperse the whole spectrum. This allows us to circumvent the spatial and spectral trade-off and therefore substantially increase the field of view compared to conventional hyperspectral imagers. A dynamic implementation based on acousto-optical filters that can be adapted on the fly is discussed as an easy and flexible way to create the multiplexed gratings. We describe the details of multiplexed Bragg gratings and show that we can retrieve the spatial distribution of individual species abundances in gas mixtures, and we show that we can even do this for the atmospheres of exoplanets orbiting faraway stars.
Direct imaging of exoplanets greatly enhances our ability to spectroscopically detect molecules in their atmospheres, but requires both excellent angular and spectral resolution. A highly promising approach uses multiplexed transmission gratings to achieve compressed sensing, but the published theoretical calculations are not realistic enough to determine whether the approach is feasible. We aim to determine the performance of recovering exoplanet signals of an instrument with multiplexed volume Bragg gratings in a full, detailed numerical simulation, specifically examining any effects caused by multiplexing several gratings. Our end-to-end simulation includes realistic stellar and planetary spectra, a closed-loop adaptive optics simulation, and rigorous coupled wave analysis to model the multiplexed gratings. We chose 20 passbands around expected methane absorption features that were optically combined using 20 gratings. We find that exoplanet signals can be recovered down to contrasts of $10^ $, without the addition of a coronagraph. Multiplexing a larger number of gratings improves the deepest recovered contrast, if photon noise is the dominant noise source. When residuals from our simple post-processing approach are the largest noise source, a larger number of multiplexed gratings decreases the performance, due to the stacking of the PSFs at different wavelengths. This is an artifact of our data reduction approach. We conclude that multiplexed Bragg gratings are a viable method to look for exoplanets with a compressed sensing approach and additional gains may be made in post-processing.
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