Jih-Run Tsai

Two-dimensional analytical modeling of a linear variable filter for spectral order sorting.

A two-dimensional thin film thickness model based on the geometry of a commercial coater which can calculate more effectively the profiles of linear variable filters (LVFs) has been developed. This is done by isolating the substrate plane as an independent coordinate (local coordinate), while the rotation and translation matrices are used to establish the coordinate transformation and combine the characteristic vector with the step function to build a borderline which can conclude whether the local mask will block the deposition or not. The height of the local mask has been increased up to 40 mm in the proposed model, and two-dimensional simulations are developed to obtain a thin film profile deposition on the substrate inside the evaporation chamber to achieve the specific request of producing a LVF zone width in a more economical way than previously reported [Opt. Express23, 5102 (2015)OPEXFF1094-408710.1364/OE.23.005102].

The hyperspectral imaging achieved by aberration-corrected freeform concave blaze grating with variable line spacing

To design a concave grating for a hyperspectral imaging (HSI) system, it is critical to achieve flat field focusing in both the horizontal and vertical directions on the image sensor. We have developed a generalized automation aberration reduction procedure (ARP) that can be applied in any cases of a concave grating spectrometer. The concave grating, which has a free-form profile with blaze grating pitch and variable line spacing [3], is fabricated using five-axis CNC machine with nanometer machining precision for hyperspectral imaging. In order to evaluate the performance, an optical system is designed and setup to measure the focused spot size, spectral resolution and diffraction efficiency.

Design and verification of an aberration-corrected free-form concave blaze grating with variable line spacing for hyperspectral imaging (Conference Presentation)

A flat-field aberration corrected concave blaze grating for 400-1100nm is designed and fabricated. The concave grating, which has a free-form profile with blaze grating pitch and variable line spacing, is fabricated using five-axis CNC machine with nanometer machining precision. An optical system is setup to measure the focused spot size, spectral resolution and diffraction efficiency to evaluate the performance of aberration-corrected concave grating. The blaze grating reaches a diffraction efficiency of 70%. The focused vertical spot size is 50µm, which indicates a 50µm spatial resolution at the image plane. The focused horizontal spot size is 300µm, which converts to a spectral resolution of 6nm. The design methodology can be applied to an Offner type hyperspectral imager with a free-form convex grating and variable line spacing to achieve high efficiency and high spatial and high spectral resolving power.

Design and verification of a flat-field aberration-corrected concave blaze grating for hyperspectral imaging

An optimization process to control the aberration of a concave grating is developed. The approach has a dramatic reduction in aberration and great improvement in spectral resolution.

Two-dimensional analytical modeling of a linear variable filter for spectral order sorting

A two-dimensional thin film thickness model based on the geometry of a commercial coater which can calculate more effectively the profiles of linear variable filters (LVFs) has been developed. This is done by isolating the substrate plane as an independent coordinate (local coordinate), while the rotation and translation matrices are used to establish the coordinate transformation and combine the characteristic vector with the step function to build a borderline which can conclude whether the local mask will block the deposition or not. The height of the local mask has been increased up to 40 mm in the proposed model, and two-dimensional simulations are developed to obtain a thin film profile deposition on the substrate inside the evaporation chamber to achieve the specific request of producing a LVF zone width in a more economical way than previously reported.

Analytical Modeling of a Linear Variable Filter for Computational Hyperspectral Imaging

An analytical thin film thickness model calculates the profiles of linear variable filters, which perform spectral filtering. Coupled with an image sensor and using a computational algorithm, this device becomes a LVF-hyperspectral imager.

Aberration Control of a Concave Grating for Hyperspectral Imager

An optimization process to control the aberration of a concave grating is developed. The approach has a dramatic improvement in aberration reduction and spectral resolution. Calculated result is in good agreement with measurement.

Generalized Aberration Reduction Procedure of a Concave Grating for Hyperspectral Imaging

A generalized optimization process for reducing the aberration of a concave grating is developed. Our aberration reduction process is to minimize the root-mean-square spot sizes for the spectral range on the detector plane. To evaluate the performance, a model based on a previous concave grating designed for a mid-infrared (7.5 μm ~13.5 μm) spectrometer is built. The result shows that the current new approach has a dramatic improvement in aberration reduction and yields better spectral resolution.