Optical filter and spectrometer

Patent metadata

Field	Value
Publication number	US-9625628-B2
Application number	US-201514608356-A
Country	US
Kind code	B2
Filing date	Jan 29, 2015
Priority date	Jan 31, 2014
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

An optical filter is disclosed including two laterally variable bandpass filters stacked at a fixed distance from each other, so that the upstream filter functions as a spatial filter for the downstream filter. This happens because an oblique beam transmitted by the upstream filter is displaced laterally when impinging on the downstream filter. The lateral displacement causes a suppression of the oblique beam when transmission passbands at impinging locations of the oblique beam onto the upstream and downstream filters do not overlap.

First claim

What is claimed is:

1. An optical filter comprising:
an upstream laterally variable bandpass optical filter; and
a downstream laterally variable bandpass optical filter;
wherein the downstream laterally variable bandpass optical filter is sequentially disposed downstream of the upstream laterally variable bandpass optical filter and separated by a distance L along an optical path of an optical beam,
wherein the upstream and downstream laterally variable bandpass optical filters each have a bandpass center wavelength that gradually varies in a mutually coordinated fashion along a first direction transverse to the optical path, thereby providing for each bandpass center wavelength having a same dependence, and
wherein a dependence of spectral selectivity of the optical filter on a degree of collimation of the optical beam is less than a corresponding dependence of spectral selectivity of the downstream laterally variable bandpass optical filter on the degree of collimation of the optical beam.

2. The optical filter of claim 1 , wherein the bandpass center wavelengths of the upstream and downstream laterally variable bandpass optical filters are monotonically increasing in the first direction.

3. The optical filter of claim 1 , wherein the bandpass center wavelengths of the upstream and downstream laterally variable bandpass optical filters are non-linearly increasing in the first direction.

4. The optical filter of claim 1 , wherein the bandpass center wavelengths of the upstream and downstream laterally variable bandpass optical filters have a substantially identical dependence of the bandpass center wavelength on an x-coordinate along the first direction.

5. The optical filter of claim 1 , wherein a lateral distance Δx 1 along the first direction, corresponding to a bandwidth of the upstream laterally variable bandpass optical filter, is larger than a lateral distance Δx 2 along the first direction, corresponding to a bandwidth of the downstream laterally variable bandpass optical filter.

6. The optical filter of claim 1 , further comprising:
a transparent medium having a refractive index n between the upstream and downstream laterally variable bandpass optical filters.

7. The optical filter of claim 6 , wherein L/n is greater than 0.2 mm and less than 15 mm.

8. The optical filter of claim 6 , wherein L/n=Δx 1 /0, wherein Δx 1 is a lateral distance along the first direction, corresponding to a bandwidth of the upstream laterally variable bandpass optical filter, and 0 is an angle of acceptance of the optical filter.

9. The optical filter of claim 6 , wherein
the transparent medium comprises a transparent substrate, and
the upstream and downstream laterally variable bandpass optical filters are disposed on opposite sides of the transparent substrate.

10. The optical filter of claim 6 , wherein the refractive index n varies along the first direction.

11. The optical filter of claim 1 , wherein the bandpass center wavelengths of the upstream and downstream laterally variable bandpass optical filters are aligned with each other, such that a line connecting positions corresponding to a same bandpass center wavelength of the upstream and downstream laterally variable bandpass optical filters forms an angle of less than 45 degrees with a normal to the downstream laterally variable bandpass optical filter.

12. The optical filter of claim 11 , wherein the angle varies along the first direction.

13. The optical filter of claim 1 , wherein the upstream and downstream laterally variable bandpass optical filters are disposed at an angle to each other, so that the distance L varies along the first direction.

14. The optical filter of claim 1 , further comprising:
an aperture, disposed in the optical path, having a width varying in the first direction.

15. The optical filter of claim 1 , further comprising:
a spectral response flattening filter disposed in the optical path for flattening a spectral response of the optical filter.

16. The optical filter of claim 15 , wherein the spectral response flattening filter is disposed on the upstream or downstream laterally variable bandpass optical filter or therebetween.

17. The optical filter of claim 1 , further comprising:
an additional laterally variable bandpass optical filter in the optical path,
the additional laterally variable bandpass optical filter having a bandpass center wavelength varying in a coordinated fashion with the bandpass center wavelengths of the upstream and downstream laterally variable bandpass optical filters.

18. The optical filter of claim 1 , wherein the upstream and downstream laterally variable bandpass optical filters each comprise a bandpass center wavelength and a 3 dB passband no greater than 10% of a corresponding center bandpass wavelength.

19. The optical filter of claim 1 , wherein at least one of the upstream or downstream laterally variable bandpass optical filters comprises thin film layers comprising three or more different materials.

20. The optical filter of claim 1 , wherein at least one of the upstream or downstream laterally variable bandpass optical filters comprises:
a thin film layer stack,
a sub-wavelength grating, or
a dichroic polymer.

21. An optical spectrometer comprising:
an optical filter comprising:
an upstream laterally variable bandpass optical filter;
a downstream laterally variable bandpass optical filter;
wherein the downstream laterally variable bandpass optical filter is sequentially disposed downstream of the upstream laterally variable bandpass optical filter and separated by a distance L along an optical path of an optical beam,
wherein the upstream and downstream laterally variable bandpass optical filters each have a bandpass center wavelength that gradually varies in a mutually coordinated fashion along a first direction transverse to the optical path, thereby providing for each bandpass center wavelength having a same dependence, and

wherein a dependence of spectral selectivity of the optical filter on a degree of collimation of the optical beam is less than a corresponding dependence of spectral selectivity of the downstream laterally variable bandpass optical filter on the degree of collimation of the optical beam; and
an optical sensor disposed in the optical path downstream of the downstream laterally variable bandpass optical filter.

22. The optical spectrometer of claim 21 , further comprising:
a light source for providing the optical beam, wherein the optical beam comprises converging or diverging rays.

23. The optical spectrometer of claim 21 , further comprising:
a diffuser disposed in the optical path upstream of the upstream laterally variable bandpass optical filter for increasing uniform intensity distribution of the optical beam on the upstream laterally variable bandpass optical filter.

24. The optical spectrometer of claim 21 , wherein the optical sensor comprises a photodetector array having pixels disposed along the first direction.

25. The optical spectrometer of claim 24 , wherein
the photodetector array comprises a two-dimensional array of pixels disposed so that when the optical beam is monochromatic,
a spectral line is formed on the photodetector array, and
the spectral line forms an acute angle with rows of the photodetector array.

26. The optical spectrometer of claim 24 , wherein
the photodetector array comprises a two-dimens

Assignees

• Jds Uniphase Corp
• Viavi Solutions Inc

Inventors

• Hruska Curtis R
• Catching Benjamin F
• Smith Paula

Classifications

• G01J3/2803

  using photoelectric array detector · CPC title

• G02B5/285 Primary

  comprising deposited thin solid films (G02B5/281 - G02B5/289 take precedence; multilayered film filters for fibre optic multiplexing G02B6/29361) · CPC title

• G01J2003/2813

  2D-array · CPC title

• G01J3/0229 Primary

  using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters · CPC title

• G01J3/0262

  Constructional arrangements for removing stray light · CPC title