Temperature insensitive filter

Patent metadata

Field	Value
Publication number	US-11360262-B2
Application number	US-201816958476-A
Country	US
Kind code	B2
Filing date	Dec 31, 2018
Priority date	Dec 29, 2017
Publication date	Jun 14, 2022
Grant date	Jun 14, 2022

Abstract

An integrated wavelength-selective filter device comprises a first optical element, for directing received radiation into a direction defined by a first angle, and a second optical element being a diffractive element configured for diffracting the directed radiation under a second angle. The second angle is such that for a single reference wavelength the diffracted radiation is directed into a propagation medium for advancing therein towards a predetermined position on the first optical element or on a further optical element for filtering radiation having a wavelength substantially matching the reference wavelength from radiation having a substantially different wavelength. The propagation medium is formed from a material that is different from any material of the substrate of the first and the second optical element.

First claim

The invention claimed is:

1. An integrated wavelength-selective filter device comprising:
a first optical element patterned in or on a substrate, the first optical element being configured for receiving radiation incident thereon and for directing at least partially said received radiation into a direction defined by a first angle,
a second optical element patterned in or on a substrate, the second optical element being a diffractive element and extending longitudinally and arranged distantly to the first optical element, the second optical element being configured for receiving said directed radiation under an angle of incidence and adapted for diffracting said directed radiation under a second angle, said second angle depending on wavelength,
wherein the first optical element directs said received radiation into a propagation medium, said directed radiation propagating solely through the propagation medium until being received at the second optical element, the propagation medium being formed from a material being different from any material of said substrate of said first and said second optical element, and
wherein the second optical element is configured such that the second angle is such that, for a single reference wavelength, the diffracted radiation is directed into said propagation medium for advancing in said propagation medium towards a predetermined position on the first optical element or on a further optical element for filtering radiation having a wavelength substantially matching the reference wavelength from radiation having a substantially different wavelength, wherein the reference wavelength is uniquely determined for the entire device.

2. The integrated wavelength-selective filter device according to claim 1 , wherein said propagation medium is formed from a material with substantially smaller thermo-optic refractive index coefficient as compared to the respective thermo-optic refractive index coefficient of any material of said substrate of said first and said second optical element.

3. The integrated wavelength-selective filter device according to claim 1 , wherein the second optical element is adapted for back-reflecting into said propagation medium said directed radiation for advancing in said propagation medium along the same elevation angular direction but with opposite propagation sense as compared to the radiation incident on the second optical element, said elevation angular direction being defined with respect to a flat surface of the substrate of the second optical element.

4. The integrated wavelength-selective filter device according to claim 1 , wherein the second optical element is configured in an off-axis configuration so as to diffract backwards the radiation incident on the second optical element along a different azimuthal angular direction as compared to the azimuthal angular direction of the incident radiation incident on the second optical element, an azimuthal angular direction being defined with respect to a flat surface of the substrate of the second optical element, the filter device further comprising a further optical element having similar characteristics as the first optical element and being configured for coupling out the filtered radiation.

5. The integrated wavelength-selective filter device according to claim 3 , wherein the second optical element is configured in an off-axis configuration so as to diffract backwards the radiation incident on the second optical element along a different azimuthal angular direction as compared to the azimuthal angular direction of the incident radiation incident on the second optical element, an azimuthal angular direction being defined with respect to a flat surface of the substrate of the second optical element, the filter device further comprising a further optical element having similar characteristics as the first optical element and being configured for coupling out the filtered radiation.

6. The integrated wavelength-selective filter device according to claim 1 , wherein the filter device comprises at least one material with a thermal expansion coefficient or design, such that, for a change in at least the second angle caused by a change in the temperature of the device, the length of a path of said directed radiation propagating in said propagation medium from the first optical element to the second optical element is adapted automatically by thermal expansion of the device due to the temperature change, such that for the reference wavelength, the diffracted radiation again is directed to the predetermined position.

7. The integrated wavelength selective filter device according to claim 1 , wherein the first optical element and the second optical element are patterned in or on the same substrate or wherein the first optical element and the second optical element are formed in a semiconductor or dielectric substrate of a chip.

8. The integrated wavelength-selective filter device according to claim 1 , wherein the filter device comprises a reflective element so that on the path of said directed radiation propagating in said propagation medium from the first optical element to the second optical element, the radiation is reflected by a reflective surface of the reflective element.

9. The integrated wavelength-selective filter device according to claim 8 ,
wherein the first optical element and the second optical element are both formed on a same flat surface of the device, and
wherein the reflective element is positioned above or below said flat surface.

10. The integrated wavelength-selective filter device according to claim 9 , wherein the device furthermore comprises at least one stand-off for supporting the reflective element being positioned above or below said flat surface.

11. The integrated wavelength-selective filter device according to claim 10 ,
wherein the filter device comprises at least one material with a thermal expansion coefficient or design, such that, for a change in at least the second angle caused by a change in the temperature of the device, the length of a path of said directed radiation propagating in said propagation medium from the first optical element to the second optical element is adapted automatically by thermal expansion of the device due to the temperature change, such that for the reference wavelength, the diffracted radiation again is directed to the predetermined position, and
wherein the adapting of a path length is obtained by thermal expansion of the at least one stand-off.

12. The integrated wavelength-selective filter device according to claim 11 ,
wherein both the first optical element and the second optical element are patterned in or on the same substrate material, and
wherein the stand-off comprises at least one material selected in such a way that its overall thermal expansion coefficient is approximately three times larger than the thermal expansion coefficient of the substrate material of the first and second optical element.

13. The integrated wavelength-selective filter device according to claim 10 , wherein the at least one stand-off is at least partially formed from a material of the substrate of the first and second optical element by locally removing a portion of said material of the substrate.

14. The integrated wavelength-selective filter device according to claim 12 , wherein temperature insensitivity is less than 1 pm/K over a temperature range of 100 K.

15. The integrated wavelength-selective filter device according to claim 1 , wherein the first optical element and the second optical element are positioned above one another and wherein the propagation path for the diff

Assignees

• Univ Gent
• Imec Vzw

Inventors

• Baets Roeland
• Ryckeboer Eva
• Rahim Abdul
• Vasiliev Anton
• Nie Xiaomin

Classifications

• G02B6/124

  Geodesic lenses or integrated gratings · CPC title

• G01J3/22

  Littrow mirror spectrometers · CPC title

• G02B6/29326

  Diffractive elements having focusing properties, e.g. curved gratings (Rowland circle spectrometers G01J3/20) · CPC title

• G02B6/12007 Primary

  forming wavelength selective elements, e.g. multiplexer, demultiplexer · CPC title

• G02B6/29398

  Temperature insensitivity · CPC title