Laser module
The laser module includes a QCL element and a light source. The QCL element includes a substrate, a lower clad layer provided on the substrate, an active layer that is provided on an opposite side of the lower clad layer from the substrate and generates a first terahertz wave, an upper clad layer provided on an opposite side of the active layer from the lower clad layer, and a first electrode provided on an opposite side of the upper clad layer from the active layer. The second terahertz wave from the light source enters the active layer through the substrate, is reflected by the first electrode, and is amplified or wavelength-converted. The third terahertz wave amplified or wavelength-converted in the active layer is emitted to the outside through the substrate.
1 . A laser module comprising:
a quantum cascade laser element configured to generate a first terahertz wave having a difference frequency between a first frequency and a second frequency; and
a light source configured to emit a second terahertz wave that is different from the first terahertz wave to the quantum cascade laser element, wherein
the quantum cascade laser element includes:
a substrate;
a first clad layer provided on the substrate;
an active layer that is provided on an opposite side of the first clad layer from the substrate, constitutes a resonator that oscillates a light of the first frequency and a light of the second frequency, and generates the first terahertz wave;
a second clad layer provided on an opposite side of the active layer from the first clad layer; and
a metal electrode provided on an opposite side of the second clad layer from the active layer,
the second terahertz wave enters the active layer through the substrate, is reflected by the metal electrode, and is amplified or wavelength-converted, and
a third terahertz wave, which is the second terahertz wave after being amplified or wavelength-converted in the active layer, is emitted to the outside through the substrate.
2 . The laser module according to claim 1 , wherein
the substrate is formed of InP or Si.
3 . The laser module according to claim 1 , wherein
a length of the active layer in a first direction which is a resonance direction of the quantum cascade laser element is 100 μm to 3 mm.
4 . The laser module according to claim 1 , wherein
the substrate is formed of Si,
the substrate includes:
a first main surface facing the first clad layer; and
a second main surface located on an opposite side of the first main surface,
after the second terahertz wave is first reflected by the metal electrode and before the second terahertz wave is emitted to the outside as the third terahertz wave, the second terahertz wave is reflected by the second main surface of the substrate at least once or more and re-enters the active layer.
5 . The laser module according to claim 1 , wherein
the substrate includes:
a first end surface located on a first side in a first direction which is a resonance direction of the quantum cascade laser element; and
a second end surface located on a second side opposite to the first side in the first direction,
the active layer includes:
a third end surface located on the first side in the first direction; and
a fourth end surface located on the second side in the first direction, and
the second terahertz wave is incident on the first end surface along a direction inclined with respect to the first direction so as to approach the active layer from the first side toward the second side in the first direction.
6 . The laser module according to claim 5 , wherein
the third terahertz wave is emitted from the second end surface along a direction inclined with respect to the first direction so as to move away from the active layer from the first side toward the second side in the first direction.
7 . The laser module according to claim 5 , wherein
the substrate includes:
a first main surface facing the first clad layer; and
a second main surface located on an opposite side of the first main surface,
the first end surface is inclined with respect to a second direction orthogonal to the first main surface so as to approach the second end surface from the first main surface toward the second main surface along the second direction.
8 . The laser module according to claim 7 , wherein
an inclination angle of the first end surface with respect to a plane orthogonal to the first direction substantially coincides with an angle at which an emission direction of the first terahertz wave is inclined with respect to the first direction.
9 . The laser module according to claim 5 , wherein
the substrate includes:
a first main surface facing the first clad layer; and
a second main surface located on an opposite side of the first main surface,
the second end surface is inclined with respect to a second direction orthogonal to the first main surface so as to approach the first end surface from the first main surface toward the second main surface along the second direction.
10 . The laser module according to claim 9 , wherein
an inclination angle of the second end surface with respect to a plane orthogonal to the first direction substantially coincides with an angle at which an emission direction of the first terahertz wave is inclined with respect to the first direction.
11 . The laser module according to claim 5 , further comprising an incident lens that includes an incident surface on which the second terahertz wave is incident and a facing surface facing the first end surface, wherein the facing surface of the incident lens is in direct or indirect contact with the first end surface.
12 . The laser module according to claim 11 , wherein
the incident lens is formed of Si.
13 . The laser module according to claim 11 , wherein
the incident lens is a meta-lens in which an uneven structure is formed on the incident surface.
14 . The laser module according to claim 5 , further comprising an exit lens that includes an exit surface that emits the third terahertz wave and a facing surface facing the second end surface, wherein the facing surface of the exit lens is in direct or indirect contact with the second end surface.
15 . The laser module according to claim 14 , wherein
the exit lens is formed of Si.
16 . The laser module according to claim 14 , wherein
the exit lens is a meta-lens in which an uneven structure is formed on the exit surface.
17 . The laser module according to claim 7 , wherein
the first end surface of the substrate protrudes to the first side more than the third end surface of the active layer in the first direction.
18 . The laser module according to claim 9 , wherein
the second end surface of the substrate protrudes to the second side more than the fourth end surface of the active layer in the first direction.
19 . The laser module according to claim 1 , wherein
the substrate includes:
a first end surface located on a first side in a first direction which is a resonance direction of the quantum cascade laser element; and
a second end surface located on a second side opposite to the first side in the first direction,
the active layer includes:
a third end surface located on the first side in the first direction; and
a fourth end surface located on the second side in the first direction,
the substrate includes:
a first main surface facing the first clad layer; and
a second main surface located on an opposite side of the first main surface,
the first end surface is inclined with respect to a second direction orthogonal to the first main surface so as to approach the second end surface from the first main surface toward the second main surface along the second direction,
the first end surface of the substrate protrudes to the first side more than the third end surface of the active layer in the first direction, and
the second terahertz wave is incident on the first main surface along the second direction, passes through an inside of the substrate, and is reflected by the first end surface and the second main surface to be incident on the active layer.
20 . The laser module according to claim 1 , wherein
the substrate includes:
a first end surface located on a first side in a first direction which is a resonance direction of the quantum cascade laser element; and
a second end surface located on a second side opposite to the first side in the first direction,
the active layer includes:
a third end surface located on the first side in the first direction; and
a fourth end surface located on the second side in the first direction,
the substrate includes:
a first main surface facing the first clad layer; and
a second main surface located on an opposite side of the first main surface,
the first end surface is inclined with respect to a second direction orthogonal to the first main surface so as to approach the second end surface from the second main surface toward the first main surface along the second direction,
the first end surface of the substrate protrudes to the first side more than the third end surface of the active layer in the first direction, and
the second terahertz wave is incident on the second main surface along the second direction, passes through an inside of the substrate, and is reflected by the first end surface to be incident on the active layer.