Multiplexed Volume Bragg Gratings Research Articles

End-to-end simulations of exoplanet detection with multiplexed volume Bragg gratings

Context. 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. Aims. 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. Methods. 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. Results. We find that exoplanet signals can be recovered down to contrasts of 10−6−10−7, 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. Conclusions. 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.

Angle amplifier in a 2D beam scanning system based on peristrophic multiplexed volume Bragg gratings

Abstract 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 the grating, whereas there is 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 incidence and exit angles from the expected values is less than 0.07°. It is believed that the proposed 2D angle amplifier has the potential to realize high-performance and large-angle beam steering in high-power laser beam scanning systems.

High efficiency multiplexed volume Bragg gratings for angle deflection at 1064nm

The volume Bragg grating (VBG) recorded in the photo-thermo-refractive (PTR) glass has high diffraction efficiency (DE), excellent angle selectivity, multiplexed and flexible design, which is an ideal device to achieve the angle magnification of beam scanning. In this study, a 4-channel multiplexed VBGs with the average relative diffraction efficiency (RDE) greater than 96% at 1064 nm and the maximum discrete angle deflection of 12° was designed and fabricated. And the angle deviation of experiments and design schemes were controlled less than 0.3°. The laser damage of PTR glass and multiplexed VBGs were also tested at 1064 nm. Laser damage tests were performed with a beam diameter of 0.3 mm by 1-on-1 mode. It showed that the laser damage threshold of PTR glass and multiplexed VBGs were 44.33J/cm2 and 30.15 J/cm2 respectively.

Augmented reality display based on photo-thermo-refractive glass planar waveguide.

An augmented reality display based on a planar waveguide made in photo-thermo-refractive glass had been demonstrated. The monolithic integration of multiplexed volume Bragg gratings with the waveguide platform provided in/out-coupling and image transmission from a portable projector. Design and calculation of the grating configuration was performed. The optical replication method was simulated and implemented for manufacturing the multiplexed coupling elements. Resulted field of view was limited by the projection system of the prototype, however can be expanded beyond 50o.

Design and fabrication of multiplexed volume Bragg gratings as angle amplifiers in high power beam scanning system.

In this study, the realization of multiplexed volume Bragg gratings (VBGs) working as angle amplifiers in high power beam scanning system is theoretically and experimentally investigated. The design of the multiplexed VBG for the working wavelength of 1064 nm is described. We propose a cascaded multiplexed VBGs scheme that consists of 12 grating channels. Three 4-channel multiplexed VBGs were fabricated inside photo-thermo-refractive (PTR) glasses by multiple exposures and subsequent heat treatment. The test results show that this angle amplifier can achieve discrete angle deflection ranging from -45° to + 45°. The relative diffraction efficiency of all the grating channels is more than 80% and is almost polarization independent.

Off-axis digital holography with multiplexed volume Bragg gratings.

We report on an optical imaging design based on common-path off-axis digital holography, using a multiplexed volume Bragg grating. In the reported method, a reference optical wave is made by deflection and spatial filtering through a volume Bragg grating. This design has several advantages, including simplicity, stability, and robustness against misalignment.

Wavelength beam combining of VECSELs using multiplexed volume Bragg gratings in a compound cavity

A method of wavelength beam combining to enhance the total output brightness of vertical external cavity surface emitting lasers (VECSELs) using multiplexed volume Bragg gratings (MVBGs) is presented. The MVBGs are designed to introduce wavelength-specific feedback for the 1020 nm near-infrared wavelength VECSELs to achieve both spectral stabilisation and beam combining effects. In conjunction with the compound cavity arrangement, a combined output of >6 W is achieved with >98% combining efficiency using two VECSELs. The beam combining scheme produces near-diffraction limited output with enhanced spectral density and wavelength-stabilised characteristics.

Spectral interference in multiplexed volume Bragg gratings: theoretical calculations and experimental verification.

Multiplexed volume Bragg gratings can be applied to many types of broad- and narrowband spectral systems. However, there are often deleterious side effects to combining several gratings into a single holographic optical element, including loss of efficiency in diffracted waves of interest and the introduction of spurious waves. Design of these spectral systems requires analysis methods that are flexible and efficient and that take these side effects into account. We present a matrix-based algorithm for determining diffraction efficiencies of significant coupled waves in these multiplexed grating Holographic optical elements (HOEs). Several carefully constructed experiments with spectrally multiplexed gratings in dichromated gelatin verify our conclusions.

Scaling the spectral beam combining channels in a multiplexed volume Bragg grating

In order to generate high power laser radiation it is often necessary to combine multiple lasers into a single beam. The recent advances in high power spectral beam combining using multiplexed volume Bragg gratings recorded in photo-thermo-refractive glass are presented. The focus is on using multiple gratings recorded within the same volume to lower the complexity of the combining system. Combining of 420 W with 96% efficiency using a monolithic, multiplexed double grating recorded in PTR glass is demonstrated. A multiplexed quadruple grating that maintains high efficiency and good beam quality is demonstrated to pave a way for further scaling of combining channels.