Planar optical waveguide with core of low-index-of-refraction interrogation medium

1. A sample cartridge comprising:

a first substrate formed of a first material and a second substrate formed of a second material that is different from the first material, the second substrate having an inner surface facing the first substrate;

the first and second substrates being spaced apart from each other to partly define a volume for confining a sample therein,

the second substrate further comprising a refractive element that couples external collimated light propagating parallel to the inner surface of the second substrate and offset from an optical axis of the second substrate, through the inner surface of the second substrate and to the first substrate to illuminate at least a portion of the sample.

2. The sample cartridge of claim 1 , wherein the first and second materials have different indices of refraction.

3. The sample cartridge of claim 1 , wherein at least one of the first and second materials is formed of a plurality of disparate layers having an effective refractive index that is greater than a refractive index of a surrounding medium.

4. The sample cartridge of claim 1 , wherein the second substrate and the refractive element are integrally formed from a single, injection molded piece of the second material.

5. The sample cartridge of claim 1 , wherein the refractive volume forms a curved aspheric surface to minimize an optical aberration.

6. The sample cartridge of claim 1 , wherein the first and second substrates cooperate to uniformly illuminate the portion of the sample.

7. The sample cartridge of claim 1 , wherein reflections cause the light to pass through the portion of the sample multiple times.

8. The sample cartridge of claim 7 , wherein the reflections include total internal reflection at an outer surface of the first and second substrates.

9. A cartridge for illuminating a sample with a light beam from a light source, the cartridge comprising:

a first substrate including a first outer surface and a first inner surface, and a second substrate including a second outer surface and a second inner surface in a planar region along an optical axis thereof, the first and second inner surfaces being spaced apart from each other to form a planar waveguide and partly defining a volume for confining the sample therein;

the second substrate further including a cylindrical lens portion for refracting the light beam into the waveguide, the cylindrical lens portion being outwardly convex from the second outer surface and having a longitudinal axis that is perpendicular to a normal vector of the waveguide;

such that when the light source directs the light beam toward the cylindrical lens portion in a propagation direction that is parallel to and offset from the optical axis, the light beam optically couples to and is contained within the waveguide between the outer surfaces of the first and second substrates, while illuminating at least a portion of the sample confined within the volume.

10. The cartridge of claim 9 , wherein

the cylindrical lens portion has a refractive index n and a radius R, and a location on the lens portion that is furthest from the second inner surface is defined as the apex; and

when the light beam strikes the cylindrical lens portion at a height y from the apex, the light beam refracts through an angle β in accordance with the condition

y

=

R

⁡

[

1

-

n

⁢

⁢

sin

⁢

⁢

β

1

-

2

⁢

n

⁢

⁢

cos

⁢

⁢

β

+

n

2

]

.

11. The cartridge of claim 10 , wherein

the apex is at a height t relative to the second inner surface, and

the light beam focuses on the second inner surface at a distance L from the apex in accordance with the condition

L

=

t

-

y

tan

⁢

⁢

β

-

2

⁢

yR

-

y

2

.

12. The cartridge of claim 11 , wherein the cylindrical lens portion is truncated such that it does not extend along the second substrate beyond distance L from the apex in the propagation direction.

13. The cartridge of claim 11 , wherein the cylindrical lens portion does not include material in at least a portion of an optical deadzone formed within the cylindrical lens portion from the apex to the second outer surface at distance L therefrom in the propagation direction.

14. The sample cartridge of claim 9 , wherein the second substrate and the cylindrical lens portion are integrally formed from a single, injection molded material.

15. An apparatus for illuminating a sample, the apparatus comprising:

a waveguide including

a first substrate including a first outer surface and a first inner surface, one of the first outer surface and the first inner surface comprising a reflective layer,

a second substrate including a second outer surface and a second inner surface, the first and second inner surface of the first and second substrates, respectively, being spaced apart from each other and partly defining a volume for confining the sample therein; and

a light source for directing collimated light toward the waveguide, at an angle parallel to and offset from the second inner surface, such that the light optically couples to, and is contained within, the waveguide at and between the reflective layer and the second outer surface, while illuminating at least a portion of the sample confined within the volume;

wherein the waveguide and the light source cooperate to uniformly illuminate the portion of the sample.

16. The sample cartridge of claim 15 , wherein reflections cause the light to pass through the portion of the sample multiple times.

17. The sample cartridge of claim 16 , wherein the reflections include total internal reflection at the second outer surface.

18. The sample cartridge of claim 15 , the second substrate further comprising a curved refractive element that couples external light that is directed towards the refracted element, to the first and second substrates to illuminate at least a portion of the sample, wherein when the external light is provided as collimated light, the refractive element diverges the collimated light within the cartridge.