A terahertz quantum cascade laser generating a radially polarized cylindrical vector beam

Abstract

The application relates to a terahertz quantum cascade laser for generating a radially polarized cylindrical vector beam. The structure is sequentially arranged from bottom to top as a substrate layer, a lower electrode layer and an active region layer. The active region layer is provided with a circular first upper electrode layer located at the center, a circular ring-shaped second upper electrode layer surrounding the first upper electrode layer and a circular ring-shaped absorption boundary layer surrounding the second upper electrode layer. The structure of the junction between the active region layer and the first upper electrode layer is a first-order concentric circular metal buried grating, and the structure of the second upper electrode layer is a second-order concentric circular metal-air grating. The centers of the first-order concentric circular metal buried grating and the second-order concentric circular metal-air grating coincide. The first-order concentric circular metal buried grating excites an angular mode, and generates isotropic cylindrical wave radiation in the waveguide; the second-order concentric circular metal-air grating couples the light in the waveguide into a radially polarized cylindrical vector beam emitted vertically. Finally, the device can be monolithically integrated to obtain a radially polarized cylindrical vector beam.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology and relates to a terahertz quantum cascade laser that generates radially polarized column vector beams. Background Technology

[0002] Vector beams possess rich spatial degrees of freedom and have wide applications in optical interaction, optical communication, and optical imaging. Cylindrical vector beams, a special type of vector beam, exhibit a hollow, circularly symmetrical optical field distribution; two specific examples are radially polarized and tangentially polarized cylindrical vector beams. With the increasing demands in communication and imaging, many reports have described the generation of vector beams using passive discrete components through cascading (Naidoo, Darryl, et al. Nature Photonics 10.5 (2016): 327-332., Cai, Xinlun, et al. Science 338.6105(2012): 363-366., etc.). However, with the development of modern information technology, optical systems increasingly demand miniaturization, low power consumption, and stability from optoelectronic devices.

[0003] Recently, in the visible and near-infrared bands, there have been reports of generating vector beams through on-chip integration without relying on external optical components. Examples include optically pumped on-chip vector beam semiconductor lasers for near-infrared optical communication (Miao, Pei, et al. Science 353.6298 (2016): 464-467.) and electrically pumped radially polarized vector beam lasers (Zhang, Juan, et al. Nature Communications 9.1 (2018): 2652.). In the terahertz band, Elvis Mujagić generated vector beams using angularly distributed feedback gratings (Mujagić, Elvis, et al. Applied Physics Letters 95.1 (2009): 011120.). Wang Qijie's research group attempted to generate vector beams using a second-order concentric circular feedback grating (Liang, Guozhen, et al. ACS photonics 2.11(2015): 1559-1566., Liang, Guozhen, et al. Optics express 21.26 (2013): 31872-31882.). However, they were unable to successfully observe a hollow circularly symmetrical light field distribution in the experiment because their laser resonator could not effectively distinguish between the fundamental mode and the second-order angular mode. Summary of the Invention

[0004] In view of the prior art described above, the present invention proposes a terahertz quantum cascade laser for generating radially polarized column vector beams. By combining a first-order concentric metal buried grating with a second-order concentric metal-air grating, a novel method is proposed to obtain radially polarized column vector beams emitted from the vertical plane on-chip.

[0005] The terahertz quantum cascade laser that generates radially polarized column vector beams has the following structure from bottom to top: a substrate layer 1, a lower electrode layer 2, and an active region layer 3. The active region layer 3 has a centrally located circular first upper electrode layer 5, a ring-shaped second upper electrode layer 6 surrounding the first upper electrode layer 5, and a ring-shaped absorption boundary layer 4 surrounding the second electrode layer 2.

[0006] At the junction of the active region layer 3 and the first upper electrode layer 5, an annular groove is etched on the upper surface. The first upper electrode layer 5 fills the etched groove to form a first-order concentric circular metal buried grating, wherein the thickness of the first upper electrode layer 5 is equal to the depth of the groove.

[0007] The first-order concentric metal buried grating is aligned with the center of the second-order concentric metal-air grating structure of the second upper electrode layer 6.

[0008] The lower electrode layer 2 is a Ti and Au composite material layer, with the thickness of Ti being 10 nm – 20 nm and the thickness of Au being 0.8 μm – 1 μm, wherein Ti is on top of Au.

[0009] The first upper electrode layer 5 is a circular Ti and Au composite material layer with a thickness of 10 nm – 20 nm for Ti and a thickness of 1.5 μm – 2.5 μm for Au. The radius of the circle with Ti below Au is 80 μm – 130 μm.

[0010] The first-order concentric circular metal buried grating has a period along the radial direction that is half the wavelength of light in the medium at the operating frequency, corresponding to a period of 12.1 μm; the radius of the innermost ring of the grating is three-quarters of the grating period, corresponding to a radius of 9 μm; the grating duty cycle is 50%, the number of grating periods is 6–10, and the grating depth is 1.5 μm–2.5 μm.

[0011] The second upper electrode layer 6 is a ring-shaped Ti and Au composite material layer. The thickness of Ti is 10 nm – 20 nm, and the thickness of Au is 0.8 μm – 1 μm, with Ti below Au. The size of the ring along the radial direction is 150 μm – 250 μm. The structure of the second upper electrode layer 6 is a second-order concentric metal-air grating. The period of the second-order concentric metal-air grating along the radial direction is one wavelength of light in the medium at the operating frequency, corresponding to a period of 24.2 μm, with 6-10 periods and a duty cycle of 50%.

[0012] The absorbing boundary layer 4 is a ring-shaped n-type heavily doped GaAs material layer with a doping concentration of 10. 18 cm -3 The material thickness is 0.6 μm, and the size of the ring along the radial direction is 200 μm – 300 μm.

[0013] This invention can directly generate a radially polarized cylindrical vector beam emitted from a vertical plane by an on-chip electric pump. The beam presents a ring-shaped far-field spot with polarization characteristics along the radius of the ring. It has the advantages of high integration, high stability, and high excitation efficiency. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the device of the present invention. 1 is the substrate layer, 2 is the lower electrode layer, 3 is the active region layer, 4 is the absorption boundary layer, 5 is the first upper electrode layer, and 6 is the second upper electrode layer.

[0015] Figure 2 This is a cross-sectional schematic diagram of the device of the present invention. Detailed Implementation

[0016] To further illustrate the technical means and effects of the present invention, the following detailed description is provided in conjunction with the preferred embodiments of the present invention and their accompanying drawings. Specific Implementation

[0017] The terahertz quantum cascade laser that generates radially polarized column vector beams has the following structure from bottom to top: a substrate layer 1, a lower electrode layer 2, and an active region layer 3. The active region layer 3 has a centrally located circular first upper electrode layer 5, a ring-shaped second upper electrode layer 6 surrounding the first upper electrode layer 5, and a ring-shaped absorption boundary layer 4 surrounding the second upper electrode layer 6.

[0018] At the junction of the active region layer 3 and the first upper electrode layer 5, an annular groove is etched on the upper surface, and the first upper electrode layer 5 fills the etched groove to form a first-order concentric circular metal buried grating.

[0019] The first-order concentric metal buried grating is aligned with the center of the second-order concentric metal-air grating structure of the second upper electrode layer 6.

[0020] The lower electrode layer 2 is a Ti and Au composite material layer, with a Ti thickness of 15 nm and an Au thickness of 0.9 μm, wherein Ti is on top of Au.

[0021] The active region material of the active region layer 3 comprises 90 periodically repeating modules, each module containing 9 overlapping GaAs potential wells and 9 Al layers. 0.15 Ga 0.85 The GaAs barrier has the following thicknesses starting from GaAs: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3, 2.7 (nm). The first two GaAs layers are doped, with an n-type doping concentration of 10. 16 cm -3 .

[0022] The first upper electrode layer 5 is a circular Ti and Au composite material layer with a thickness of 15 nm for Ti and a thickness of 2 μm for Au, wherein Ti is below Au and the radius of the circle is 110 μm.

[0023] The first-order concentric circular metal buried grating has a period of 12.1 μm along the radial direction; the radius of the innermost ring of the grating is 9 μm; the grating duty cycle is 50%; the number of grating periods is 8; and the grating depth is 2 μm.

[0024] The second upper electrode layer 6 is a ring-shaped Ti and Au composite material layer. The thickness of Ti is 15 nm, and the thickness of Au is 0.9 μm, with Ti below Au. The ring has a radial dimension of 200 μm. The structure of the second upper electrode layer 6 is a second-order concentric metal-air grating. The second-order concentric metal-air grating has a radial period of 24.2 μm, 8 periods, and a duty cycle of 50%.

[0025] The absorbing boundary layer 4 is a ring-shaped n-type heavily doped GaAs material layer with a doping concentration of 10. 18 cm -3 The material thickness is 0.6 μm, and the size of the ring along the radial direction is 250 μm. Specific Implementation

[0026] The terahertz quantum cascade laser that generates radially polarized column vector beams has the following structure from bottom to top: a substrate layer 1, a lower electrode layer 2, and an active region layer 3. The active region layer 3 has a centrally located circular first upper electrode layer 5, a ring-shaped second upper electrode layer 6 surrounding the first upper electrode layer 5, and a ring-shaped absorption boundary layer 4 surrounding the second electrode layer 2.

[0027] At the junction of the active region layer 3 and the first upper electrode layer 5, an annular groove is etched on the upper surface, and the first upper electrode layer 5 fills the etched groove to form a first-order concentric circular metal buried grating.

[0028] The first-order concentric metal buried grating is aligned with the center of the second-order concentric metal-air grating structure of the second upper electrode layer 6.

[0029] The lower electrode layer 2 is a Ti and Au composite material layer, with a Ti thickness of 10 nm and an Au thickness of 0.8 μm, wherein Ti is on top of Au.

[0030] The active region material of the active region layer 3 comprises 90 periodically repeating modules, each module containing 9 overlapping GaAs potential wells and 9 Al layers. 0.15 Ga 0.85 The GaAs barrier has the following thicknesses starting from GaAs: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3, 2.7 (nm). The first two GaAs layers are doped, with an n-type doping concentration of 10. 16 cm -3 .

[0031] The first upper electrode layer 5 is a circular Ti and Au composite material layer with a thickness of 10 nm for Ti and a thickness of 1.5 μm for Au, wherein Ti is below Au and the radius of the circle is 130 μm.

[0032] The first-order concentric circular metal buried grating has a period of 12.1 μm along the radial direction; the radius of the innermost ring of the grating is 9 μm; the grating duty cycle is 50%; the number of grating periods is 10; and the grating depth is 1.5 μm.

[0033] The second upper electrode layer 6 is a ring-shaped Ti and Au composite material layer. The thickness of Ti is 10 nm, and the thickness of Au is 0.8 μm, with Ti below Au. The ring has a radial dimension of 150 μm. The structure of the second upper electrode layer 6 is a second-order concentric metal-air grating. The second-order concentric metal-air grating has a radial period of 24.2 μm, a number of periods of 6, and a duty cycle of 50%.

[0034] The absorbing boundary layer 4 is a ring-shaped n-type heavily doped GaAs material layer with a doping concentration of 10. 18 cm -3 The material thickness is 0.6 μm, and the size of the ring along the radial direction is 200 μm. Specific Implementation

[0035] The terahertz quantum cascade laser that generates radially polarized column vector beams has the following structure from bottom to top: a substrate layer 1, a lower electrode layer 2, and an active region layer 3. The active region layer 3 has a centrally located circular first upper electrode layer 5, a ring-shaped second upper electrode layer 6 surrounding the first upper electrode layer 5, and a ring-shaped absorption boundary layer 4 surrounding the second electrode layer 2.

[0036] At the junction of the active region layer 3 and the first upper electrode layer 5, an annular groove is etched on the upper surface, and the first upper electrode layer 5 fills the etched groove to form a first-order concentric circular metal buried grating.

[0037] The first-order concentric metal buried grating is aligned with the center of the second-order concentric metal-air grating structure of the second upper electrode layer 6.

[0038] The lower electrode layer 2 is a Ti and Au composite material layer, with a Ti thickness of 20 nm and an Au thickness of 1 μm, wherein Ti is on top of Au.

[0039] The active region material of the active region layer 3 comprises 90 periodically repeating modules, each module containing 9 overlapping GaAs potential wells and 9 Al layers. 0.15 Ga 0.85 The GaAs barrier has the following thicknesses starting from GaAs: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3, 2.7 (nm). The first two GaAs layers are doped, with an n-type doping concentration of 10. 16 cm -3 .

[0040] The first upper electrode layer 5 is a circular Ti and Au composite material layer with a thickness of 20 nm for Ti and a thickness of 2.5 μm for Au, wherein Ti is below Au and the radius of the circle is 80 μm.

[0041] The first-order concentric circular metal buried grating has a period of 12.1 μm along the radial direction; the radius of the innermost ring of the grating is 9 μm; the grating duty cycle is 50%; the number of grating periods is 6; and the grating depth is 2.5 μm.

[0042] The second upper electrode layer 6 is a ring-shaped Ti and Au composite material layer. The thickness of Ti is 20 nm, and the thickness of Au is 1 μm, with Ti below Au. The ring has a radial dimension of 250 μm. The structure of the second upper electrode layer 6 is a second-order concentric metal-air grating. The second-order concentric metal-air grating has a radial period of 24.2 μm, 10 periods, and a duty cycle of 50%.

[0043] The absorbing boundary layer 4 is a ring-shaped n-type heavily doped GaAs material layer with a doping concentration of 10. 18 cm -3 The material thickness is 0.6 μm, and the size of the ring along the radial direction is 300 μm.

[0044] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. All technical content not described in detail in this invention is conventional.

Claims

1. A terahertz quantum cascade laser for generating radially polarized column vector beams, comprising a substrate layer (1), a lower electrode layer (2), and an active region layer (3); characterized in that: The structure of the terahertz quantum cascade laser that generates radially polarized column vector beams, from bottom to top, is as follows: The active region layer (3) consists of a substrate layer (1), a lower electrode layer (2), and an active region layer (3). The active region layer (3) has a centrally located circular first upper electrode layer (5), an annular second upper electrode layer (6) surrounding the first upper electrode layer (5), and an annular absorption boundary layer (4) surrounding the second upper electrode layer (6). The upper surface of the active region layer (3) at the junction with the first upper electrode layer (5) is etched with an annular groove. The first upper electrode layer (5) fills the etched groove to form a first-order concentric metal buried grating, wherein the thickness of the first upper electrode layer (5) is equal to the depth of the groove. The first-order concentric metal buried grating is aligned with the center of the second-order concentric metal-air grating structure of the second upper electrode layer (6).

2. The terahertz quantum cascade laser for generating radially polarized column vector beams according to claim 1, characterized in that: The lower electrode layer (2) is a Ti and Au composite material layer, with a thickness of 10nm–20nm for Ti and a thickness of 0.8μm–1μm for Au, wherein Ti is on top of Au.

3. A terahertz quantum cascade laser for generating radially polarized column vector beams according to claim 1, characterized in that: The first upper electrode layer (5) is a circular Ti and Au composite material layer with a thickness of 10nm–20nm and a thickness of 1.5μm–2.5μm. The Ti layer is below the Au layer, and the radius of the circle is 80μm–130μm.

4. A terahertz quantum cascade laser for generating radially polarized column vector beams according to claim 1, characterized in that: The first-order concentric circular metal buried grating has a period along the radial direction that is half the wavelength of light in the medium at the operating frequency, corresponding to a period of 12.1 μm; the radius of the innermost ring of the grating is three-quarters of the grating period, corresponding to a radius of 9 μm; the grating duty cycle is 50%, the number of grating periods is 6–10, and the grating depth is 1.5 μm–2.5 μm.

5. A terahertz quantum cascade laser for generating radially polarized column vector beams according to claim 1, characterized in that: The second upper electrode layer (6) is a ring-shaped Ti and Au composite material layer. The thickness of Ti is 10nm–20nm and the thickness of Au is 0.8μm–1μm. Ti is below Au, and the size of the ring along the radial direction is 150μm–250μm. The structure of the second upper electrode layer (6) is a second-order concentric metal-air grating. The period of the second-order concentric metal-air grating along the radial direction is one wavelength of light in the medium at the working frequency, corresponding to a period of 24.2μm, a number of periods of 6-10, and a duty cycle of 50%.

6. A terahertz quantum cascade laser for generating radially polarized column vector beams according to claim 1, characterized in that: The absorbing boundary layer (4) is a ring-shaped n-type heavily doped GaAs material layer with a doping concentration of 10. 18 cm -3 The material thickness is 0.6 μm, and the size of the ring along the radial direction is 200 μm–300 μm.

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