Cryogenic Thermo-Optical Coefficient of SU-8 Measured Using a Racetrack Resonator at 850 nm
SU-8 is an emerging polymer material for integrated optical circuits that has demonstrated good structural properties in a cryogenic environment. In this article, we investigate the thermo-optical properties of SU-8 for a wavelength <inline-formula><math xmlns="http://www.w3.org/1998/M...
Saved in:
| Main Authors: | , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-08-01
|
| Series: | Photonics |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2304-6732/11/9/800 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | SU-8 is an emerging polymer material for integrated optical circuits that has demonstrated good structural properties in a cryogenic environment. In this article, we investigate the thermo-optical properties of SU-8 for a wavelength <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>λ</mi><mo>=</mo><mn>850</mn><mtext> </mtext><mi mathvariant="normal">n</mi><mi mathvariant="normal">m</mi></mrow></semantics></math></inline-formula>, from room temperature to cryogenic temperature down to 14 K. To measure the material properties, we designed and fabricated SU-8 racetrack resonators via electron beam lithography. While cooling the device in a closed-cycle cryostat, we measured the resonance spectrum as a function of the temperature from which we determined the temperature-induced variations of the group and effective indices of the waveguide. With the aid of waveguide eigenmode simulations, we used these data to derive the temperature dependence of the SU-8 refractive index <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>n</mi></mrow><mrow><mi>S</mi><mi>U</mi><mo>−</mo><mn>8</mn></mrow></msub><mfenced separators="|"><mrow><mi>T</mi></mrow></mfenced></mrow></semantics></math></inline-formula>. At room temperature (T~295 K), the thermo-optic coefficient <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mrow><msub><mrow><mi>d</mi><mi>n</mi></mrow><mrow><mi>S</mi><mi>U</mi><mo>−</mo><mn>8</mn></mrow></msub></mrow><mo>/</mo><mrow><mi>d</mi><mi>T</mi></mrow></mrow><mo>=</mo><mo>−</mo><mn>5.3</mn><mo>±</mo><msup><mrow><mn>0.2</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mtext> </mtext><mi mathvariant="normal">K</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>. At low temperature (T~14 K), <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mrow><msub><mrow><mi>d</mi><mi>n</mi></mrow><mrow><mi>S</mi><mi>U</mi><mo>−</mo><mn>8</mn></mrow></msub></mrow><mo>/</mo><mrow><mi>d</mi><mi>T</mi></mrow></mrow><mo>=</mo><mo>−</mo><mn>1.27</mn><mo>±</mo><msup><mrow><mn>0.05</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mi mathvariant="normal">K</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>. Our research shows the potential of SU-8 photonics in a cryogenic environment, suitable for the integration with quantum light sources emitting in the near infrared (NIR). |
|---|---|
| ISSN: | 2304-6732 |