Method for designing freeform concave grating imaging spectrometer

Patent metadata

Field	Value
Publication number	US-11614617-B2
Application number	US-202117235096-A
Country	US
Kind code	B2
Filing date	Apr 20, 2021
Priority date	Feb 5, 2021
Publication date	Mar 28, 2023
Grant date	Mar 28, 2023

Abstract

A method for designing a freeform concave grating imaging spectrometer includes selecting a series of light rays incident from different positions of a slit as characteristic light rays. The coordinates and normal directions of characteristic data points at intersections of the characteristic light rays and a surface of a freeform concave grating are calculated. A freeform surface shape of the freeform concave grating is obtained by fitting, so that an initial structure is obtained. Then the initial structure is optimized.

First claim

What is claimed is:

1. A method for manufacturing a freeform concave grating imaging spectrometer, comprising:
S 1 , selecting a series of light rays incident from different positions of a slit as characteristic light rays;
S 2 , calculating coordinates and normal directions of characteristic data points at intersections of the characteristic light rays and a surface of a freeform concave grating, wherein a line space of the freeform concave grating is constant;
S 3 , obtaining a freeform surface shape of the freeform concave grating by fitting, so that an initial structure is obtained;
S 4 , optimizing the initial structure; and
S 5 , manufacturing a freeform concave grating imaging spectrometer according to, parameters output in the step S 4 , wherein the freeform concave grating imaging spectrometer is a physical element; and the freeform concave grating imaging spectrometer comprises a slit, a concave grating, and an image surface.

2. The method of claim 1 , wherein a method for calculating normal direction of each characteristic data point on a surface of the freeform concave grating comprises:
S 21 ′, according to system spectral dispersion and a distance between the surface of the freeform concave grating and an image surface, calculating an angle of dispersion of a chief ray in a center of the slit;
S 22 ′, according to the angle of dispersion and spectral range, calculating a grating line distance d0; and
S 23 ′, solving R according to a formula

(

S
′

-
S

)

×
R

=

n
⁢
λ

d

⁢
G
×
R

,

wherein
n represents an order of diffraction, λ represents a wavelength of the light, G represents a normal direction of a grating generating surface, R represents the normal direction of the characteristic data point on the surface of the freeform concave grating, d represents a distance between two adjacent grating lines at a light incident point, S represents a direction vector of an incident light at the corresponding characteristic data point on the surface of freeform concave grating, and S′ represents a direction vector of an outgoing light at the corresponding characteristic data point on the surface of the freeform concave grating.

3. The method of claim 1 , wherein in the step S 4 , the initial system is optimized by using an optical design software.

4. The method of claim 1 , further comprising a step of processing according to parameters output in the step S 4 , so that a physical element of the freeform concave grating imaging spectrometer is obtained.

5. A method for making a freeform concave grating imaging spectrometer comprising:
S 1 , selecting a series of light rays incident from different positions of a slit as characteristic light rays;
S 2 , calculating coordinates and normal directions of characteristic data points at intersections of the characteristic light rays and a surface of a freeform concave grating, wherein a line space of the freeform concave grating is constant;
S 3 , obtaining a freeform surface shape of the freeform concave grating by fitting, so that an, initial structure is obtained; and
S 4 , optimizing the initial structure; and
S 5 , manufacturing a freeform concave grating imaging spectrometer according to parameters output in the step S 4 , wherein the freeform concave grating imaging spectrometer is a physical element; and the freeform concave grating imaging spectrometer consisting of a slit, a freeform concave grating, an image surface, and a detector; wherein the freeform concave grating is positioned to disperse and reflect a light beam irradiated from the slit, to form a reflected light beam, and the image surface is positioned to form an image from the reflected light beam irradiated from the freeform concave grating.

6. The method of claim 5 , wherein a method for calculating normal direction of each characteristic data point on a surface of the freeform concave grating comprises:
S 21 ′, according to system spectral dispersion and a distance between the surface of the freeform concave grating and an image surface, calculating an angle of dispersion of a chief ray in a center of the slit;
S 22 ′, according to the angle of dispersion and spectral range, calculating a grating line distance d0; and
S 23 ′, solving R according to a formula

(

S
′

-
S

)

×
R

=

n
⁢
λ

d

⁢
G
×
R

,

wherein
n represents an order of diffraction, λ represents a wavelength of the light, G represents a normal direction of a grating generating surface, R represents the normal direction of the characteristic data point on the surface of the freeform concave grating, d represents a distance between two adjacent grating lines at a light incident point, S represents a direction vector of an incident light at the corresponding characteristic data point on the surface of freeform concave grating, and S′ represents a direction vector of an outgoing light at the corresponding characteristic data point on the surface of the freeform concave grating.

7. A method for manufacturing a freeform concave grating imaging spectrometer, comprising:
S 1 , selecting a series of light rays incident from different positions of a slit as characteristic light rays;
S 2 , calculating coordinates and normal directions of characteristic data points at intersections of the characteristic light rays and a surface of a freeform concave grating, wherein a line space of the freeform concave grating is variable;
S 3 , obtaining a freeform surface shape of the freeform concave grating by fitting, so that an initial structure is obtained;
S 4 , optimizing the initial structure; and
S 5 , manufacturing a freeform concave grating imaging spectrometer according to parameters output in the step S 4 , wherein the freeform concave grating imaging spectrometer is a physical element; and the freeform concave grating imaging spectrometer comprises a slit, a concave grating, and an image surface.

8. The method of claim 7 , wherein a method for calculating the normal direction of each characteristic data point on a surface of the freeform concave grating comprises:
S 21 , setting a surface shape of the freeform concave grating to a spherical surface, wherein an inters

Assignees

• Univ Tsinghua
• Hon Hai Prec Ind Co Ltd

Inventors

• Zhang Ben-Qi
• Zhu Jun
• Tan yi-lin
• Jin Guo-Fan
• Fan Shou-Shan

Classifications

• G01J3/2823 Primary

  Imaging spectrometer · CPC title

• G01J3/18

  using diffraction elements, e.g. grating (gratings per se G02B) · CPC title

• G02B5/1861

  Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials (G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence) · CPC title

• G02B27/0012 Primary

  Optical design, e.g. procedures, algorithms, optimisation routines · CPC title