JP6116367B2 - Semiconductor laser device - Google Patents

Description

  The present invention relates to a semiconductor laser device that emits terahertz waves.

  The terahertz cascade laser is expected as a terahertz light source that is small and easy to drive. However, since the wavelength of the terahertz wave emitted from the emission end face of the terahertz cascade laser is very long with respect to the emission region at the emission end face, the influence of diffraction appears remarkably and the spread angle becomes large. It is difficult to increase the ratio (extraction efficiency) that can be effectively used as the oscillation light of the cascade laser.

  As a method for suppressing the spread angle of a terahertz wave, a method is known in which a ring-shaped diffraction grating structure is formed on the surface of a terahertz cascade laser and a higher-order diffraction mode emitted from the surface is used (non-patent document). Reference 1 and 2). As another method for suppressing the spread angle of the terahertz wave, a method of combining a terahertz cascade laser and a one-dimensional leaky wave antenna with a metamaterial structure is known (see Non-Patent Documents 3 and 4).

L. Mahler et al., "Distributed feedback ring resonators for vertically emitting terahertzquantum cascade lasers", Optics Express, 17, 13031 (2009). M. S. Vitiello et al., "Highefficiency coupling of Terahertz micro-ring quantum cascade lasers to thelow-loss optical modes of hollow metallic waveguides", Optics Express, 19,1122 (2011). A. A. Tavallaee et al., "Zero-Index Terahertz Quantum-Cascade Metamaterial Lasers", IEEE Journal of Quantum Electronics, 46, 1091 (2010). A. A. Tavallaee et al., "Terahertz quantum-cascade laser with active leaky-wave antenna", Applied Physics Letters, 99, 141115 (2011).

  However, in the methods described in Non-Patent Documents 1 and 2, since a higher-order diffraction mode is used, the terahertz wave extraction efficiency is not necessarily high. In the methods described in Non-Patent Documents 3 and 4, since the one-dimensional leaky wave antenna of the metamaterial structure is used, the spread angle of the terahertz wave can only be suppressed in the one-dimensional direction.

  Accordingly, an object of the present invention is to provide a semiconductor laser device that can emit a terahertz wave whose divergence angle is suppressed in a two-dimensional direction with high extraction efficiency.

  The semiconductor laser device of the present invention has a quantum cascade laser structure, a semiconductor laminate that oscillates terahertz waves, and a plurality of transmission line type metamaterial unit structures arranged in a ring, and is incident from the semiconductor laminate A transmission line type metamaterial leakage wave structure that emits leakage waves to the outside while guiding terahertz waves in a ring shape.

  In this semiconductor laser device, since the transmission line type metamaterial unit structures are arranged in a ring shape, the electric field strengths of leakage waves strengthen each other in the direction perpendicular to the plane in which the transmission line type metamaterial unit structures are arranged, and the spread angle Will be suppressed in the two-dimensional direction. Therefore, according to this semiconductor laser device, the terahertz wave whose divergence angle is suppressed in the two-dimensional direction can be emitted with high extraction efficiency.

  Here, the optical path length in the transmission line type metamaterial leakage wave structure may be 70 to 130% of the wavelength of the terahertz wave. In this case, in a plurality of transmission line type metamaterial unit structures arranged in a ring shape, the position where the electric field strength that contributes most to the radiation intensity occupies the opposite position with respect to the center portion of the ring, and thus the terahertz that was originally in antiphase The waves are phased. For this reason, the electric field strengths further strengthen each other, and the spread angle is suppressed in the two-dimensional direction.

  The plurality of transmission line type metamaterial unit structures are separated from the first transmission line type metamaterial unit structure which is a starting point of terahertz wave guiding and the first transmission line type metamaterial unit structure, A plurality of third transmission line type metamaterial unit structures connecting the second transmission line type metamaterial unit structure serving as an end point of the wave, the first transmission line type metamaterial unit structure, and the second transmission line type metamaterial unit structure. And a material unit structure. According to this, the terahertz wave is guided and emitted to the outside in the transmission line type metamaterial leakage wave structure.

  The plurality of transmission line type metamaterial unit structures may be arranged in a circular shape. According to this, a terahertz wave forming a circular pattern can be emitted.

  The plurality of transmission line type metamaterial unit structures may be arranged with a period of less than a quarter of the wavelength of the terahertz wave. Thereby, it can function effectively as a metamaterial.

  The transmission line type metamaterial leaky wave structure includes a first electrode for applying a voltage to the semiconductor multilayer body, an annular body provided on the first electrode among the second electrodes, a first electrode, A plurality of third electrodes provided on the annular body so as to face each other in an annular manner, a fourth electrode electrically connecting each of the third electrodes and the first electrode, In this case, the fourth electrode may be formed on the outer side surface of the transmission line type metamaterial leakage wave structure. The annular body may be made of a dielectric. In the present invention, since these configurations can be appropriately selected, there is a high degree of freedom in adjusting whether the dispersion characteristic of the terahertz wave is a balanced system or an unbalanced system and adjusting the phase constant.

  Here, the annular body may have the same stacked structure as the semiconductor stacked body. According to this, at the time of manufacturing the semiconductor laser device, the semiconductor stacked body and the annular body can be manufactured in the same process.

  The semiconductor laser device of the present invention may further include a substrate that supports the semiconductor laminate and the transmission line type metamaterial leakage wave structure, and the first electrode may be provided on the substrate. According to this, each component of the semiconductor laser device can be stabilized.

  According to the present invention, it is possible to provide a semiconductor laser device that can emit a terahertz wave whose divergence angle is suppressed in a two-dimensional direction with high extraction efficiency.

1 is a plan view of a semiconductor laser device according to an embodiment of the present invention. FIG. 2 is a side view of the semiconductor laser device of FIG. It is sectional drawing along the III-III line of FIG. It is a figure which shows the optical path length of a transmission line type | mold metamaterial leaky wave structure. FIG. 2 is an equivalent circuit diagram of a transmission line type metamaterial unit structure in the semiconductor laser device of FIG. 1. 2 is a graph showing dispersion characteristics of a transmission line type metamaterial unit structure in the semiconductor laser device of FIG. 1. It is the top view and side view of the semiconductor laser apparatus of other embodiment of this invention. It is the top view and side view of the semiconductor laser apparatus of other embodiment of this invention. It is the top view and side view of the semiconductor laser apparatus of other embodiment of this invention. It is the top view and side view of the semiconductor laser apparatus of other embodiment of this invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same part or an equivalent part, and the overlapping description is abbreviate | omitted.

  As shown in FIGS. 1 and 2, the semiconductor laser device 1 includes a rectangular plate-like substrate 2 made of InP. A common electrode (first electrode) 3 made of gold and indium is provided on the surface 2 a of the substrate 2. On the surface 3 a of the common electrode 3, a semiconductor laminate 4 and a substantially circular transmission line type metamaterial leakage wave structure 11 are provided. That is, the substrate 2 supports the semiconductor laminate 4 and the transmission line type metamaterial leakage wave structure 11.

  The semiconductor stacked body 4 has a quantum cascade laser structure made of InGaAs / InAlAs. The semiconductor stacked body 4 is disposed on the surface 2 a of the substrate 2 with its longitudinal direction coinciding with the longitudinal direction of the substrate 2. A counter electrode (second electrode) 6 made of gold is provided on the surface 4 a of the semiconductor stacked body 4 so as to face the common electrode 3. The semiconductor laminate 4 is sandwiched between the common electrode 3 and the counter electrode 6 to form a Fabry-Perot resonator using a metal waveguide, and a voltage is applied between the common electrode 3 and the counter electrode 6. Thus, a terahertz wave is oscillated from the emission end face 4b. In addition, a reflection film that totally reflects the terahertz wave may be formed on the end surface on the opposite side of the emission end surface 4b among the both end surfaces of the semiconductor stacked body 4.

  The transmission line type metamaterial leaky wave structure 11 has an annular body 50 provided on the common electrode 3. The annular body 50 is made of a dielectric such as InP, and is disposed on the surface 2 a of the substrate 2 so as to be adjacent to the semiconductor stacked body 4. The annular body 50 includes an introduction portion 51 that is a portion where a terahertz wave is incident from the semiconductor stacked body 4, and a main body portion 52 that integrally extends from the introduction portion 51 and forms a path through which the terahertz wave is guided. The main body 52 extends and circulates so as to draw a circular shape in plan view with the introduction portion 51 as a starting point, and its end portion remains at a position close to the introduction portion 51. That is, the main body 52 has a circular shape with a part missing.

  Here, of the both end faces of the annular body 50, the end face 50a on the side where the introduction portion 51 is provided faces the emission end face 4b of the semiconductor stacked body 4 so that the optical axis of the terahertz wave passes. Of both end portions of the annular body 50, the end surface 50b on the side where the introduction portion 51 is not provided is subjected to antireflection coating or oblique processing so that the guided terahertz wave is not reflected. The distance between the emission end face 4b and the end face 50a of the annular body 50 is set to be smaller than the radial thickness of the annular body 50.

  As shown in FIGS. 1 to 3, a plurality of divided electrodes (third electrodes) made of gold are arranged on the surface 52 a of the main body 52 so as to face the common electrode 3 and are arranged in an annular shape. ) 8 is provided. The divided electrodes 8 are separated from each other by a gap 9. Further, a split electrode 8 made of gold is also provided on the surface 51 a of the introduction part 51 so as to face the common electrode 3.

  A plurality of connection electrodes (fourth electrodes) 10 made of gold are formed on the outer side surface 52 b of the main body 52. Each connection electrode 10 electrically connects each divided electrode 8 (excluding the divided electrode 8 on the introduction part 51) and the common electrode 3. That is, the connection electrode 10 short-circuits each divided electrode 8 to the common electrode 3.

  A transmission line type metamaterial unit structure (hereinafter simply referred to as “a”) is constituted by the common electrode 3, one divided electrode 8, a part of the main body 52 sandwiched between the common electrode 3 and the divided electrode 8, and one connection electrode 10. Also referred to as “unit structure”). And the transmission line type | mold metamaterial leaky wave structure 11 is comprised by arranging the several unit structures 7 in cyclic | annular form. Here, the unit structure 7 includes a first unit structure serving as a starting point of the terahertz wave guide, a second unit structure provided at a position separated from the first unit structure and serving as an end point of the terahertz wave guiding, And a plurality of third unit structures connecting the unit structures.

  The period in which the plurality of unit structures 7 are arranged in a ring is set to be less than a quarter of the wavelength of the target terahertz wave. Here, the period corresponds to the total value of the size of one divided electrode 8 and one gap 9 in the circumferential direction in which each divided electrode 8 and gap 9 are arranged, that is, the length ΔZ of the unit structure 7. For example, it can be said that it is a value obtained by dividing the length of the circumference passing through the center of the main body 52 of the annular body 50 by the number of the divided electrodes 8 (or gaps 9) (however, the portion where the introduction portion 51 is provided is calculated). Except from).

  The optical path length in the transmission line type metamaterial leakage wave structure 11 is the optical length of the path through which the terahertz wave is guided in the transmission line type metamaterial leakage wave structure 11, and is indicated by a one-dot chain line in FIG. 4. As described above, it is a value obtained by multiplying the distance from the end surface 50a of the annular body 50 to the opposite end surface 50b through the introduction portion 51 and the main body portion 52, by the refractive index. This optical path length is the length of the wavelength of the terahertz wave. Here, the optical path length is the length when passing through the central portion of the annular body 50 in the radial direction. Moreover, in FIG. 4, the arrow has shown the direction where a terahertz wave guides.

  Next, the dispersion characteristic of the transmission line type metamaterial leakage wave structure 11 will be described.

FIG. 5 shows an equivalent circuit of the unit structure 7 constituting the transmission line type metamaterial leakage wave structure 11. The equivalent circuit of the unit structure 7 includes a series capacitance C _L formed between adjacent divided electrodes 8 (that is, a gap 9), a parallel inductance L _L corresponding to the connection electrode 10, the divided electrodes 8, and the common electrode 3. and parallel capacitance C _R formed between consists of four elements of the series inductance L _R corresponding to the segmented electrodes 8. This equivalent circuit can be considered as a left-handed / right-handed composite line, and can be said to be a unit cell of a so-called transmission line type metamaterial.

This unit cell can control the dispersion characteristics by adjusting the above four elements (C _L , L _L , C _R , L _R ). Here, the dispersion characteristic is a characteristic representing the relationship between the phase constant β and the angular frequency ω of the terahertz wave, and the dispersion characteristic of the unit cell (length is ΔZ) is expressed by the following equation (1). The

The outline of the graph when the horizontal axis is β · ΔZ and the vertical axis is ω is as shown in FIG. Also, as shown in FIG. 6, depending on the value of each element, the right-handed branch (first quadrant side) and the left-handed branch (second quadrant side) are balanced systems in which there is no gap when β = 0 (ie, C _L · L _R = and dispersion characteristics of _C if the R · _{L L),} can take the dispersion characteristics of the non-equilibrium systems that there is a gap (i.e. if the _{C L · L R ≠ C R} · L L). In the region (radiation region) surrounded by “air line” (light dispersion characteristics in the atmosphere) in FIG. 6, the absolute value of the refractive index becomes smaller than 1, and the radiation to the outside is caused as a leakage mode. It becomes possible. By utilizing this characteristic, the transmission line type metamaterial leakage wave structure 11 can be operated as a leakage wave antenna.

  Specifically, the shape and material of the members constituting the common electrode 3, the annular body 50, the divided electrode 8 and the connection electrode 10, the distance between adjacent divided electrodes 8 (that is, the width of the gap 9), etc. The dispersion characteristics can be changed by various changes. For example, if the height, width, and length of the unit structure 7 are 10 μm, the width of the gap 9 is 0.2 μm, and the width of the connection electrode 10 is about 2 μm, a leakage mode is formed in a region around 2 THz and radiation is performed. Since the optical path length of the transmission line type metamaterial leakage wave structure 11 in which a plurality of unit structures 7 are formed side by side is about the wavelength of the incident terahertz wave, the surface 2a of the substrate 2 on which the unit structures 7 are arranged. The terahertz wave can be emitted in a direction perpendicular to the plane (a direction perpendicular to the plane formed by the circular shape of the annular body 50).

  In the semiconductor laser device 1 configured as described above, when a voltage is applied between the common electrode 3 and the counter electrode 6, a terahertz wave is oscillated from the semiconductor stacked body 4 having the quantum cascade laser structure, and the terahertz A wave enters the transmission line type metamaterial leakage wave structure 11. At this time, in the transmission line type metamaterial leaky wave structure 11, the unit structures 7 are arranged in a ring and the optical path length is about the wavelength of the incident terahertz wave. A terahertz wave is emitted to the outside as a leakage wave in a vertical direction. At this time, the electric field strengths of the leaky waves in the emission direction are strengthened with each other, and the spread angle is suppressed in the two-dimensional direction. Therefore, according to this semiconductor laser device, the terahertz wave whose divergence angle is suppressed in the two-dimensional direction can be emitted with high extraction efficiency.

  Further, at this time, the semiconductor laminate 4 and the transmission line type metamaterial leakage wave structure 11 are arranged so as to be adjacent to each other, and the end face 50a on the side where the introduction part 51 is provided among the end faces of the annular body 50. Is opposed to the emission end face 4b of the semiconductor laminate 4, and therefore, the terahertz wave is incident on the transmission line type metamaterial leakage wave structure 11 from the semiconductor laminate 4 with high efficiency. For this reason, according to this semiconductor laser device 1, it is possible to emit the terahertz wave with higher extraction efficiency.

  Further, since the terahertz wave emitted to the outside has a circular pattern, the coupling with the hollow fiber is good.

  Further, since the optical path length in the transmission line type metamaterial leakage wave structure 11 is the length of the wavelength of the terahertz wave, in the plurality of unit structures 7 arranged in a ring shape, as shown in FIG. The position where the electric field intensity E that contributes most is the largest, occupies the opposite position with respect to the center of the ring, and the terahertz wave that was originally in antiphase is phased. For this reason, the electric field strengths further strengthen each other, and the spread angle is suppressed in the two-dimensional direction.

  The transmission line type metamaterial leakage wave structure 11 includes an annular body 50, a plurality of divided electrodes 8, and a connection electrode 10, and the connection electrode 10 is a transmission line type metamaterial leakage wave structure. 11, the shape and material of these members are appropriately selected to adjust whether the terahertz wave dispersion characteristics are balanced or unbalanced, and the phase The constant can be adjusted. That is, the degree of freedom in designing the transmission line type metamaterial leakage wave structure 11 is high.

  Further, in the semiconductor laser device 1, since the plurality of unit structures 7 are arranged with a period of less than one quarter of the wavelength of the terahertz wave, it can function effectively as a metamaterial.

  The semiconductor laser device 1 further includes a substrate 2 that supports the semiconductor laminate 4 and the transmission line type metamaterial leakage wave structure 11, and the common electrode 3 is provided on the surface 2 a of the substrate 2. Each component of the laser device 1 is stabilized.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the above embodiment, the annular body 50 is made of a dielectric, but the annular body 50 may have the same stacked structure as the semiconductor stacked body 4. In this case, when the semiconductor laser device 1 is manufactured, the semiconductor stacked body 4 and the annular body 50 can be manufactured in the same process.

  Moreover, in the said embodiment, although the optical path length was made into the length of the wavelength of a terahertz wave, this may be made into the length of 70 to 130% of a wavelength. Even when the optical path length is within this range, the electric field strengths of the leaky waves strengthen each other, and the radiation strength in the direction perpendicular to the plane on which the unit structures 7 are arranged increases.

  In addition, as shown in FIG. 7, the transmission line type metamaterial leakage wave structure 11 may be provided also on the end face side opposite to the emission end face 4 b of the semiconductor stacked body 4 in the above embodiment. In this case, terahertz waves can be emitted from two locations simultaneously.

  Further, as shown in FIG. 8, the transmission line type metamaterial leakage wave structure 11 may be a hexagon or another polygon. In this case, the emission shape of the terahertz wave corresponds to the shape of the transmission line type metamaterial leakage wave structure 11.

Further, the unit structure 7 is not necessarily provided with both the series capacitance C _L and the parallel inductance L _L. For example, as shown in FIG. 9, the connection electrode 10 that constitutes the parallel inductance L _L in the above embodiment may be omitted. In this case, the dispersion characteristic is only the right-handed branch. Further, for example, as shown in FIG. 10 may be configured without a gap 9 which constituted the series capacitance C _L in the above embodiment. In this case, the dispersion characteristic is only the right-handed branch.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser apparatus, 2 ... Board | substrate, 3 ... Common electrode (1st electrode), 4 ... Semiconductor laminated body, 6 ... Counter electrode (2nd electrode), 7 ... Transmission line type | mold metamaterial unit structure, 8 ... Divided electrode (third electrode), 9 ... gap, 10 ... connecting electrode (fourth electrode), 11 ... transmission line type metamaterial leakage wave structure, 50 ... annular body.

Claims (10)

A semiconductor laminate having a quantum cascade laser structure and emitting terahertz waves;
A transmission line type metamaterial leakage wave structure having a plurality of transmission line type metamaterial unit structures arranged in a ring and emitting a leakage wave to the outside while guiding the terahertz wave incident from the semiconductor laminate in a ring shape With body ,
The semiconductor stacked body and the transmission line metamaterial leaky wave structure, that is separate from each other, the semiconductor laser device.   The semiconductor laser device according to claim 1, wherein an optical path length in the transmission line type metamaterial leakage wave structure is 70 to 130% of a wavelength of the terahertz wave. The plurality of transmission line type metamaterial unit structures are:
A first transmission line type metamaterial unit structure that is a starting point of the terahertz wave guide;
A second transmission line type metamaterial unit structure that is spaced apart from the first transmission line type metamaterial unit structure and serves as an end point of the terahertz wave guide;
3. A plurality of third transmission line type metamaterial unit structures connecting the first transmission line type metamaterial unit structure and the second transmission line type metamaterial unit structure, according to claim 1 or 2. Semiconductor laser device.   The semiconductor laser device according to claim 1, wherein the plurality of transmission line type metamaterial unit structures are arranged in a circular shape.   5. The semiconductor laser device according to claim 1, wherein the plurality of transmission line type metamaterial unit structures are arranged with a period of less than a quarter of the wavelength of the terahertz wave. 6. The transmission line type metamaterial leakage wave structure is
An annular body provided on the first electrode among the first electrode and the second electrode for applying a voltage to the semiconductor laminate;
A plurality of third electrodes provided on the annular body so as to be opposed to the first electrode and arranged in an annular shape;
The semiconductor laser device according to claim 1, further comprising a fourth electrode that electrically connects each of the third electrodes and the first electrode.   The semiconductor laser device according to claim 6, wherein the fourth electrode is formed on an outer side surface of the transmission line type metamaterial leakage wave structure.   8. The semiconductor laser device according to claim 6, wherein the annular body is made of a dielectric.   The semiconductor laser device according to claim 6, wherein the annular body has the same stacked structure as the semiconductor stacked body. Further comprising a substrate for supporting the semiconductor laminate and the transmission line type metamaterial leakage wave structure,
The semiconductor laser device according to claim 6, wherein the first electrode is provided on the substrate.

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