Optical circuit for sensing a biological entity in a fluid and method of configuring the same

1. An optical circuit for sensing a biological entity in a fluid, comprising:

a sensing arrangement comprising:

a reference arm having a reference waveguide;

a sensing arm having a waveguide;

a sensing window extending across the reference arm and the sensing arm; and

a further sensing arrangement coupled to the sensing arrangement, the further sensing arrangement comprising:

a reference arm having a reference waveguide; and

a sensing arm having a waveguide;

wherein lengths of the reference waveguide and the waveguide of the sensing arrangement are configured in accordance with a temperature dependency reduction criterion, and

wherein the further sensing arrangement is covered with a cladding layer.

2. The optical circuit of claim 1 , wherein the lengths of the reference waveguide and the waveguide of the sensing arrangement are further configured in accordance with refractive indices of the reference waveguide and the waveguide of the sensing arrangement.

3. The optical circuit of claim 1 , wherein the sensing arm of the sensing arrangement further comprises a further waveguide coupled in series with the waveguide of the sensing arrangement.

4. The optical circuit of claim 3 , wherein a length of the further waveguide is configured in accordance with the temperature dependency reduction criterion.

5. The optical circuit of claim 4 , wherein the length of the further waveguide is further configured in accordance with the refractive index of the reference waveguide, the refractive index of the waveguide and a refractive index of the further waveguide of the sensing arrangement.

6. The optical circuit of claim 1 , wherein the reference waveguide of the sensing arrangement comprises a core layer disposed above a first cladding layer and a second cladding layer disposed above the core layer and the first cladding layer.

7. The optical circuit of claim 1 ,

wherein the waveguide of the sensing arrangement comprises a core layer disposed above a cladding layer;

wherein the core layer of the waveguide of the sensing arrangement comprises a first portion and a second portion; and

wherein the first portion is arranged adjacent to the second portion such that a slot is formed between the first portion and the second portion such that the waveguide of the sensing arrangement constitutes a slot waveguide.

8. The optical circuit of claim 3 , wherein the further waveguide comprises a core layer disposed above a first cladding layer and a second cladding layer disposed above the core layer and the first cladding layer.

9. The optical circuit of claim 1 , wherein the sensing arrangement further comprises:

an input port coupled to a first end of the reference arm and a first end of the sensing arm of the sensing arrangement; and

an output port coupled to a second end of the reference arm and a second end of the sensing arm of the sensing arrangement.

10. The optical circuit of claim 9 ,

wherein the input port is configured to direct an optical signal to the first end of the reference arm and the first end of the sensing arm of the sensing arrangement; and

wherein the output port is configured to combine an optical signal from the second end of the reference arm and an optical signal from the second arm of the sensing arrangement and to output the combined optical signal.

11. The optical circuit of claim 1 , wherein the lengths and cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement are configured based on the temperature dependency reduction criterion.

12. The optical circuit of claim 11 ,

wherein the lengths and the cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement are further configured based on Vernier effect whereby the lengths and the cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement are further configured based on a free spectral range of the sensing arrangement and a free spectral range of the further sensing arrangement.

13. A method of configuring an optical circuit for sensing a biological entity in a fluid, the optical circuit comprising:

a sensing arrangement comprising a reference arm having a reference waveguide, a sensing arm having a waveguide, and a sensing window extending across the reference arm and the sensing arm, and

a further sensing arrangement coupled to the sensing arrangement, the further sensing arrangement comprising a reference arm having a reference waveguide, and a sensing arm having a waveguide, wherein the further sensing arrangement is covered with a cladding layer

the method comprising:

determining lengths of the reference waveguide and the waveguide of the sensing arrangement based on a temperature dependency reduction criterion.

14. The method of claim 13 , wherein the temperature dependency reduction criterion is to minimize the temperature dependency of the optical circuit.

15. The method of claim 14 , wherein the temperature dependency of the optical circuit is minimized to zero.

16. The method of claim 13 , further comprising determining the lengths of the reference waveguide and the waveguide of the sensing arrangement based on refractive indices of the reference waveguide and the waveguide of the sensing arrangement.

17. The method of claim 13 ,

wherein the sensing arm of the sensing arrangement of the optical circuit further includes a further waveguide coupled in series with the waveguide of the sensing arrangement; and

wherein the method further comprises determining a length of the further waveguide based on the temperature dependency reduction criterion.

18. The method of claim 17 , further comprising determining the length of the further waveguide based on the refractive index of the reference waveguide, the refractive index of the waveguide and a refractive index of the further waveguide.

19. The method of claim 13 ,

wherein the method further comprises:

determining lengths and cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement based on the temperature dependency reduction criterion, and

determining the lengths and the cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement based on Vernier effect.

20. The method of claim 19 , wherein determining the lengths and the cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement based on Vernier effect comprises determining the lengths and the cross-sectional areas of the reference arm and the sensing arm of the further sensing arrangement based on a free spectral range of the sensing arrangement and a free spectral range of the further sensing arrangement.