Terahertz-wave element, terahertz-wave detecting device, terahertz time-domain spectroscopy system, and tomography apparatus

1. A terahertz-wave element comprising:

a waveguide that includes an electro-optic crystal and allows light to propagate therethrough; and

a coupling member that causes a terahertz wave to enter the waveguide,

wherein a propagation state of the light propagating through the waveguide changes as the terahertz wave enters the waveguide via the coupling member,

wherein the waveguide includes a core layer and a cladding layer,

wherein the cladding layer is interposed between the coupling member and the core layer, and

wherein a<d<λ eq /10 is satisfied where d denotes a thickness of the cladding layer, a denotes a thickness corresponding to 1/e 2 of a light intensity of the light in the core layer, e being the base of natural logarithm and λ eq denotes an equivalent wavelength in the cladding layer with respect to a wavelength corresponding to a maximum frequency of the terahertz wave.

2. The terahertz-wave element according to claim 1 , wherein the waveguide includes a core layer and a cladding layer, and

wherein a thickness of the core layer is smaller than or equal to half a length of an equivalent wavelength in the core layer, corresponding to a maximum frequency of the terahertz wave.

3. The terahertz-wave element according to claim 1 , wherein an angle θ c formed between the light and the terahertz wave satisfies the following equation:

cos

⁢

⁢

θ

c

=

n

g

n

THz

where ng denotes an effective group refractive index of the light, and n THz denotes an effective refractive index of the terahertz wave.

4. A terahertz-wave detecting device comprising:

the terahertz-wave element according to claim 1 ; and

a detecting unit configured to detect the light propagating through the waveguide of the terahertz-wave element.

5. The terahertz-wave detecting device according to claim 4 , wherein the detecting unit detects a polarization state of the light.

6. The terahertz-wave detecting device according to claim 5 , wherein the electro-optic crystal includes Y-cut lithium niobate,

wherein if a propagating direction of the light in the waveguide is defined as an X axis and a direction orthogonal to the propagating direction is defined as a Z axis, the light input to the waveguide is polarized light including a Y-axis component and a Z-axis component of an electric field, and

wherein the detecting unit includes a polarization splitter that splits the light propagating through the waveguide into linearly-polarized light components polarized in different directions, and a light detector that detects the linearly-polarized light components.

7. The terahertz-wave detecting device according to claim 6 , wherein the polarization splitter, the light detector, and the waveguide are formed on a single substrate, and wherein the polarization splitter and the light detector are coupled to each other by the waveguide.

8. The terahertz-wave detecting device according to claim 5 , wherein the detecting unit detects a phase state of the light.

9. A terahertz time-domain spectroscopy system comprising the terahertz-wave detecting device according to claim 4 .

10. A tomography apparatus comprising the terahertz time-domain spectroscopy system according to claim 9 .

11. The terahertz-wave element according to claim 1 , wherein, in a cross section taken in a direction orthogonal to a propagating direction of the light in the waveguide, the coupling member has a curve in a portion thereof other than a surface thereof that is in contact with the electro-optic crystal.

12. A terahertz-wave element comprising:

a first waveguide including an electro-optic crystal;

a second waveguide including an electro-optic crystal;

a first coupling member that extracts a terahertz wave, which is generated from the electro-optic crystal due to light propagating through the first waveguide, to a space; and

a second coupling member that causes the terahertz wave to enter the second waveguide from the space.

13. A terahertz-wave detecting device comprising:

i) a terahertz-wave element including:

a waveguide that includes an electro-optic crystal and allows light to propagate therethrough; and

a coupling member that causes a terahertz wave to enter the waveguide,

wherein the waveguide includes a core layer, and

wherein a thickness of the core layer is smaller than or equal to half a length of an equivalent wavelength in the core layer, corresponding to a maximum frequency of the terahertz wave; and

ii) a detecting unit configured to detect the light propagating through the waveguide of the terahertz-wave element.

14. The terahertz-wave detecting device according to claim 13 , wherein the detecting unit detects a polarization of the light.

15. The terahertz-wave detecting device according to claim 13 , wherein the detecting unit detects a phase state of the light.

16. A terahertz-wave element comprising:

a waveguide that includes an electro-optic crystal and allows light to propagate therethrough; and

a coupling member that causes a terahertz wave to enter the waveguide,

wherein a propagation state of the light propagating through the waveguide changes as the terahertz wave enters the waveguide via the coupling member,

wherein the waveguide includes a core layer,

wherein a thickness of the core layer is smaller than or equal to half a length of an equivalent wavelength in the core layer, corresponding to a maximum frequency of the terahertz wave.