Absolute linear-in-k spectrometer

Patent metadata

Field	Value
Publication number	US-12085445-B2
Application number	US-202017603487-A
Country	US
Kind code	B2
Filing date	Apr 3, 2020
Priority date	Apr 16, 2019
Publication date	Sep 10, 2024
Grant date	Sep 10, 2024

Abstract

A detector system for Fourier spectroscopy such as a spectral domain optical coherence tomography instrument includes a diffractive optic for diffracting the interfering light into angularly dispersed wavenumbers, a prism for reduces a nonlinear angular dispersion among the wavenumbers, and a focusing optic for converting the angularly dispersed wavenumbers from the prism into spatially distributed wavenumbers along a detector having an array of pixels. A field lens between the focusing optic and the detector has a freeform surface for more evenly distributing the wavenumbers along the array of pixels.

First claim

The invention claimed is:

1. An absolute linear-in-K spectrometer comprising:
a diffractive optic for diffracting collimated light from an entrance aperture into angularly dispersed wavenumbers;
a prism for reducing a nonlinear angular dispersion among the wavenumbers;
a focusing optic for converting the angularly dispersed wavenumbers from the prism into spatially distributed wavenumbers along a detector; and
a field lens between the focusing optic and the detector having a freeform surface with a surface geometry that reduces field dependent aberrations introduced by the prism and more linearly distributes the wavenumbers along the detector;
wherein a sag of the freeform surface is defined by a plurality of polynomial terms in which coefficients of the polynomial terms are constrained so that chief rays of evenly spaced wavenumbers are distributed along the detector in a form that is maximized toward an even spacing of the chief rays along the detector, such that a residual nonlinearity RN of the wavenumbers distributed along the detector is less than 10 −4 percent, where the residual nonlinearity RN as a percent is determined in accordance with the following expression:

R
⁢

N
[
%
]

=

(

∫

k
min

k
max

[

f
⁡
(
k
)

-

g
⁡
(
k
)

]

2

⁢
dk

)

/

(

k
max

-

k
min

)

f
⁡
(

k
max

)

-

f
⁡
(

k
min

)

×
1
⁢
0
⁢
0

where k max and k min are respective maximum and minimum wavenumbers distributed along the detector, f(k) is a function of calibration relating wavenumbers to pixels of the detector, and g(k) is the linear approximation of f(k) with the least root mean square error.

2. The spectrometer of claim 1 in which the freeform surface has a sag z defined in accordance with the following expression:

z
=

c
⁢

r
2

1
+

1
-

(

1
+

k
c

)

⁢

c
2

⁢

r
2

+

∑
j

⁢

C
j

⁢

Z
j

⁡

(

ρ
,
φ

)

,

where r is a radial coordinate of the surface, cis a curvature of a base sphere, k c is a conic constant, ρ and φ are normalized radial and azimuthal components in an aperture, and C j is a weight factor of a j th Zernike term, Z j , where the weight factor C j is determined in a way that chief rays of evenly spaced wavenumbers are distributed along the detector in a form that is maximized toward an even spacing of the chief rays along the detector.

3. The spectrometer of claim 2 in which the expression for the sag z includes 16 Zernike terms Zj.

4. The spectrometer of claim 1 in which the prism is a Brewster-angled prism that is oriented and spaced between the diffractive optic and the focusing optic for reducing the nonlinear angular dispersion among the wavenumbers.

5. The spectrometer of claim 4 in which the field lens has front surface facing the fo

Assignees

• Univ Rochester

Inventors

• Yoon Changsik
• Rolland-Thompson Jannick P
• Bauer Aaron

Classifications

• G01J2003/1208

  Prism and grating · CPC title

• G01J3/0208

  using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction · CPC title

• G01B9/02091

  Tomographic interferometers, e.g. based on optical coherence · CPC title

• G01B9/02044

  Imaging in the frequency domain, e.g. by using a spectrometer · CPC title

• G01J3/2803

  using photoelectric array detector · CPC title