Polygonal Microcavity Chaotic Laser and Its Regulation Method

Abstract

The present disclosure provides a polygon microcavity chaotic laser and a control method thereof. The laser includes: a whispering gallery cavity (1) with a cross-section being a regular polygon or an arc-edge regular polygon for forming total internal reflection of light; a hole (2) disposed inside the whispering gallery cavity (1) for suppressing high-order transverse modes and regulating the number of modes; an annular ohmic contact window (3) located at the upper end of the whispering gallery cavity (1) for non-uniform injection of current to achieve non-linear interaction of modes to generate chaotic laser; and a waveguide (4) for directionally outputting the chaotic laser. The laser has a simple structure, does not require external optical injection, external optical feedback or optoelectronic feedback, solves the problem that the mode regulation of a large-size microcavity laser is uncontrollable due to the increase in the number of modes, which destroys the generation of chaotic light, has a higher output power, and a wider chaotic operating current range.

Description

Technical Field

[0001] The present disclosure relates to the fields of semiconductor optoelectronics, optical computing, and optical detection, and particularly relates to a polygonal microcavity chaotic laser and a control method thereof. Background Art

[0002] Due to characteristics such as initial value sensitivity, randomness, and large spectral bandwidth, chaotic lasers have important application values in the fields of true random number generation, secure communication, chaotic radar, optical time domain reflectometry, and reservoir photon computing. Traditional semiconductor lasers introduce perturbations through optical injection, optical feedback, or optoelectronic feedback to achieve chaos. This kind of chaotic laser based on discrete devices has a complex structure and poor system stability. The on-chip photonic integrated or hybrid integrated chaotic laser based on optical feedback has a small size, but complex processes, high production costs, and cannot avoid the weak periodicity caused by optical feedback, reducing the application quality. In 2018, the Institute of Semiconductors, Chinese Academy of Sciences reported a microcavity chaotic laser based on an arc-edge hexagon, which achieved the output of spontaneous chaotic signals without external optical injection and external optical feedback. When the size of the microcavity laser increases or the arc-edge deformation is relatively large, multimode lasing will occur, making mode control uncontrollable and destroying chaotic output. This makes the size of the laser under the existing scheme not too large, the output power relatively low, and the working current range where chaos can be achieved relatively small, restricting its further application. Therefore, it is necessary to propose a large-size whispering gallery mode semiconductor chaotic laser that can improve the laser power and the chaotic state working range. Summary of the Invention

[0003] In view of the above problems, the present invention provides a polygonal microcavity chaotic laser and a control method thereof to solve at least one of the above technical problems.

[0004] One aspect of the present disclosure provides a polygonal microcavity chaotic laser, including: a whispering gallery mode cavity 1 with a cross-section being a regular polygon or an arc-edge regular polygon; a hole 2 coaxial with the whispering gallery mode cavity 1 and disposed inside the whispering gallery mode cavity 1 for suppressing high-order transverse modes and regulating the number of modes; an annular ohmic contact window 3 coaxial with the whispering gallery mode cavity and located at the upper end of the whispering gallery mode cavity 1 for non-uniform injection of current to achieve non-linear interaction of modes to generate chaotic laser; and a waveguide 4 in contact connection with the outer wall of the whispering gallery mode cavity 1 for outputting the chaotic laser.

[0005] Further, the whispering gallery mode cavity 1 is an active cavity, and its material structure is a quantum well or a quantum dot structure.

[0006] Further, the whispering gallery mode cavity 1 has a square, hexagonal, octagonal, arc-edge quadrilateral, arc-edge hexagonal, or arc-edge octagonal structure.

[0007] Further, the cross-section of the hole 2 includes triangular, quadrilateral, pentagonal, hexagonal, elliptical, and circular structures.

[0008] Further, the light output port of the waveguide 4 is a cleavage plane or an end-face coating structure.

[0009] On the other hand, the present disclosure provides a method for controlling a polygonal microcavity chaotic laser, the method including: increasing the size of the polygonal microcavity chaotic laser to increase the output chaotic laser power; adjusting the shape and size of the hole 2 in the polygonal microcavity chaotic laser to suppress different high-order transverse modes; and adjusting the connection position between the waveguide 4 and the whispering gallery cavity 1 to optimize the coupling output efficiency.

[0010] The above at least one technical solution adopted in the embodiments of the present disclosure can achieve the following beneficial effects:

[0011] (1) For this polygonal microcavity chaotic laser, by introducing the central hole design, the high-order modes of the whispering gallery cavity laser can be suppressed, effectively controlling the number of modes, solving the problem that the mode control is uncontrollable due to the increase in the number of modes at large sizes and destroying the generation of chaotic laser. Compared with the existing microcavity chaotic laser scheme without holes, it is beneficial to design the resonator size in a larger direction, thereby facilitating the increase of the output optical power.

[0012] (2) For this polygonal microcavity chaotic laser, by changing the position of the output waveguide, more efficient mode coupling between the waveguide and the whispering gallery cavity can be achieved, which is beneficial to improving the coupling output efficiency and increasing the output optical power.

[0013] (3) For this polygonal microcavity chaotic laser, compared with the traditional chaotic laser scheme, it does not require external optical injection, external optical feedback or optoelectronic feedback, has a simple system, high stability, no feedback delay peak in the chaotic signal, and high chaotic signal quality.

[0014] (4) For this polygonal microcavity chaotic laser, the manufacturing process is simple, without secondary epitaxy, without complex active and passive integration technologies, without hybrid integration technologies, low cost, and has important application values in true random number generation, secure communication, chaotic radar, chaotic detection, and photonic computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] To more fully understand the present disclosure and its advantages, reference will now be made to the following description in conjunction with the accompanying drawings, in which:

[0016] Figure 1 Schematically shows a schematic plan view of a polygonal microcavity chaotic laser provided by an embodiment of the present disclosure;

[0017] Figure 2Schematically shows a three-dimensional structural schematic diagram of a polygonal microcavity chaotic laser provided by an embodiment of the present disclosure;

[0018] Figure 3 Schematically shows the variation of the Q values of the fundamental mode, first-order mode, and second-order mode and the mode interval between the fundamental mode and the first-order mode with the inner diameter of the hole of an arc-edge quadrilateral cavity with a side length of 20 μm, a deformation amount of 2.17 μm, and a waveguide width of 1.5 μm obtained by using the finite element numerical calculation method according to an embodiment of the present disclosure;

[0019] Figure 4 Schematically shows the variation of the coupling efficiency with the waveguide translation distance of an arc-edge quadrilateral cavity with a side length of 20 μm, a deformation amount of 2.17 μm, a waveguide width of 1.5 μm, and an inner diameter of the hole of 6.5 μm obtained by using the finite element numerical calculation method according to an embodiment of the present disclosure;

[0020] Figure 5 Schematically shows the voltage-current and power-current curve graphs of a polygonal microcavity chaotic laser according to an embodiment of the present disclosure;

[0021] Figure 6 Schematically shows the chaotic signal spectrogram measured under a current of 17 - 22 mA of a polygonal microcavity chaotic laser according to an embodiment of the present disclosure;

[0022] Figures 7A to 7F Schematically shows the chaotic signal frequency spectrum diagram measured under a current of 17 - 22 mA of a polygonal microcavity chaotic laser according to an embodiment of the present disclosure;

[0023] Description of reference numerals:

[0024] 1 - Whispering gallery cavity, 2 - hole, 3 - annular ohmic contact window, 4 - waveguide;

[0025] 101 - N electrode layer, 102 - N-type substrate, 103 - lower confinement layer, 104 - active region layer, 105 - upper confinement layer, 106 - ohmic contact layer, 107 - P electrode layer. Detailed implementation manners

[0026] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0027] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0028] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0029] To solve the problems of low output power and small chaotic operating current range of existing microcavity chaotic lasers, the present disclosure proposes a polygonal microcavity chaotic laser, which can effectively increase the size of the whispering gallery cavity, suppress high-order transverse modes, improve the waveguide coupling output efficiency of the laser, increase the output power of the chaotic laser, and expand the chaotic operating current range while meeting the requirements for generating chaotic laser.

[0030] Figure 1 Schematically shows a schematic plan view of a polygonal microcavity chaotic laser provided by an embodiment of the present disclosure. Figure 2 Schematically shows a schematic three-dimensional view of a polygonal microcavity chaotic laser provided by an embodiment of the present disclosure.

[0031] As Figure 1 、 Figure 2 shown, the entire laser material layer can include an N electrode layer 101, an N-type substrate layer 102, a lower limit layer 103, an active region layer 104, an upper confinement layer 105, an ohmic contact layer 106, and a P electrode layer 107 from bottom to top. A whispering gallery cavity 1, a hole 2, an annular ohmic contact window 3, and a waveguide 4 are etched on the above material layer. Among them, the whispering gallery cavity 1 has a cross-section that is a regular polygon or an arc-edge regular polygon. The whispering gallery cavity 1 is an active cavity, and its material structure is a quantum well or quantum dot structure, which can form total internal reflection of light; the hole 2 is coaxial with the whispering gallery cavity 1 and is arranged inside the whispering gallery cavity 1 for suppressing high-order transverse modes and regulating the number of modes; the annular ohmic contact window 3 is located at the upper end of the whispering gallery cavity 1 and is coaxial with the whispering gallery cavity for non-uniform injection of current to achieve non-linear interaction of modes to generate chaotic laser; the waveguide 4 is in contact connection with the outer wall of the whispering gallery cavity 1 for outputting chaotic laser.

[0032] Optionally, the whispering gallery cavity 1 has a square, hexagonal, octagonal, arc-edge quadrilateral, arc-edge hexagonal, or arc-edge octagonal structure, etc., and is not specifically limited.

[0033] Optionally, the cross-section of the hole 2 includes a triangular, quadrilateral, pentagonal, hexagonal, elliptical, or circular structure.

[0034] In this embodiment, the ohmic contact window 3 is in a ring shape. In this embodiment, the waveguide 4 is linear and perpendicular to a diagonal of the whispering gallery cavity 1. The light output port of the waveguide 4 is a cleavage surface or an end face coating structure. Optionally, the waveguide 4 can also be arc-shaped, spiral-shaped, etc. Another embodiment of the present disclosure provides a method for regulating a polygonal microcavity chaotic laser, and the method includes steps S1 to S3.

[0035] S1, in order to increase the chaotic optical power, increase the size of the polygonal microcavity chaotic laser to enhance the output chaotic laser power.

[0036] S2, adjust the shape and size of the hole 2 in the polygonal microcavity chaotic laser to achieve the suppression of different high-order transverse modes.

[0037] S3, adjust the connection position of the waveguide 4 and the whispering gallery cavity 1 to optimize the coupling output efficiency.

[0038] According to the regulation method provided by the embodiment of the present disclosure, the chaotic optical power is increased by increasing the size of the polygonal microcavity chaotic laser; in order to solve the problem that multimode lasing caused by increasing the size cannot generate chaotic laser, the number of modes can be reduced by digging the hole 2 in the whispering gallery cavity 1, and by adjusting the shape and size of the hole 2, the suppression degree of the high-order transverse modes can be further determined to ensure the output of high-power chaotic laser; furthermore, by adjusting the connection position of the waveguide 4, the coupling output efficiency of the laser can be improved.

[0039] The regulation method of the polygonal microcavity chaotic laser has a simple process, does not require secondary epitaxy, does not require complex active and passive integration technologies, does not require hybrid integration technologies, has a low cost, and has important application values in aspects such as true random number generation, secure communication, chaotic radar, chaotic detection, and photonic computing.

[0040] Reference Figure 1 shows a schematic plan view of an arc-edge regular polygonal microcavity chaotic laser, where a is the original side length of the square, d is the waveguide width, δ is the arc-edge deformation amount (i.e., the maximum distance between the arc edge and the adjacent square side length), r is the arc-edge radius, Rin is the inner diameter of the hole, h is the waveguide translation distance, and w is the width of the annular ohmic contact window.

[0041] Figure 3Schematically shows the variation of the Q values of the fundamental mode, the first-order mode, and the second-order mode, and the mode interval between the fundamental mode and the first-order mode of an arc-edge quadrilateral cavity with side length a = 20 μm, deformation δ = 2.17 μm, and waveguide width d = 1.5 μm obtained by using the finite element numerical calculation method according to an embodiment of the present disclosure, as the inner diameter Rin of the hole changes. It can be found from the figure that as the inner diameter increases, the Q values of each order mode decrease, indicating that the hole digging can effectively suppress the high-order transverse modes and regulate the number of modes. The size of the inner diameter can be determined by simulation optimization, and then the suppression degree of the high-order transverse modes can be determined. The mode interval between the fundamental mode and the first-order mode remains basically unchanged as the inner diameter increases, and suddenly increases to 40 GHz at 7 μm. Because when the mode interval is too large, the laser will not be able to enter the spontaneous chaotic state through the nonlinear interaction between modes. Considering the requirements of the mode interval and the mode Q value, the selected inner diameter Rin of the circular hole in this example is 6.5 μm.

[0042] Figure 4 Schematically shows the variation of the coupling efficiency with the waveguide translation distance h of an arc-edge quadrilateral cavity with side length 20 μm, deformation 2.17 μm, waveguide width 1.5 μm, and inner diameter of the hole 6.5 μm obtained by using the finite element numerical calculation method according to an embodiment of the present disclosure. In this example, the waveguide is translated upward or downward along the direction perpendicular to the horizontal diagonal, and always remains connected to the whispering gallery mode cavity during the translation process. By translating the waveguide, more efficient coupling between the whispering gallery mode cavity fundamental mode and the first-order mode and the waveguide mode field can be achieved. It can be seen from the figure that at different waveguide translation distances, different coupling output efficiencies can be obtained. By optimizing the waveguide translation position, the maximum coupling output efficiency can be obtained. As Figure 4 can be seen, when the optimized waveguide translation distance h in this example is 4√2 μm, the maximum coupling output efficiency of the fundamental mode and the first-order mode is obtained. At other positions, it is impossible to achieve the maximum coupling output efficiency of the fundamental mode while ensuring a relatively high coupling output efficiency of the first-order mode.

[0043] In the central-hole-digging whispering gallery mode cavity chaotic laser in the embodiments of the present disclosure, the whispering gallery mode cavity and the waveguide can be made of the same material and the same process, or can be prepared from different materials. The active region layer of the whispering gallery mode cavity has a quantum well structure or a quantum dot structure, and injecting current into it can provide optical gain.

[0044] In one example, the substrate material is InP, the active layer is an AlGaInAs multi-quantum well structure, the whispering gallery cavity is an arc-edge quadrilateral cavity with a side length of 20 μm and a deformation amount of 2.17 μm, the waveguide width is 1.5 μm, the holes are circular with an inner diameter of 6.5 μm, and they are located within the arc-edge quadrilateral cavity. The hole-drilling operation can be achieved within the arc-edge quadrilateral cavity through semiconductor standard lithography and etching processes, or other processes. The waveguide and the arc-edge quadrilateral cavity use the same material and the same process, and the waveguide is translated upward by 4√2 μm along the direction perpendicular to the horizontal diagonal. In this example, the light-emitting surface of the waveguide uses a natural cleavage surface, but the method of coating the end face is not excluded. In order to achieve non-uniform current injection, a ring-shaped ohmic contact window structure is designed in this example, which is located on top of the arc-edge quadrilateral cavity, and the width of the ring-shaped window is 3 μm.

[0045] Performance tests were carried out on the central-hole-drilled whispering gallery cavity chaotic laser shown in this example.

[0046] Figure 5 The voltage-current and power-current curves of the polygon microcavity chaotic laser according to an embodiment of the present disclosure are given; these curves show that the laser realizes continuous electrical lasing at room temperature, and the maximum output optical power of the laser is more than three times higher than that of the previously reported non-hole-drilled chaotic laser with the maximum output optical power.

[0047] Figure 6 The chaotic signal spectrogram measured by the polygon microcavity chaotic laser according to an embodiment of the present disclosure at a current of 17 - 22 mA is given. It can be seen from the spectrogram that the spectrum broadens, showing a broadened chaotic spectrum, and the chaotic working current range further increases.

[0048] Figures 7A to 7F The spectrogram measured by the spectrum analyzer after passing through the detector of the polygon microcavity chaotic laser according to an embodiment of the present disclosure at a current of 17 - 22 mA is given. The gray part is the noise floor of the spectrum analyzer, and the black part is the power spectrum curve. This result proves that the central-hole-drilled whispering gallery laser in this example generates chaotic output, and the chaotic working current range further increases.

[0049] In summary, the present disclosure provides a central-hole-drilled whispering gallery cavity chaotic laser. By drilling a hole in the center of the whispering gallery cavity, the high-order transverse mode lasing of the large-size whispering gallery cavity can be effectively suppressed according to the size of the aperture, thereby realizing an increase in the size of the whispering gallery cavity, improving the output power of the chaotic laser; at the same time, the method of waveguide translation is adopted to improve the coupling output efficiency of the waveguide, further improving the output power of the laser and increasing the chaotic working current range. This central-hole-drilled whispering gallery cavity semiconductor self-generated chaotic laser without external optical feedback, external optical injection, and optoelectronic feedback has simple process fabrication, low cost, and good reliability, and has important application values in the fields of random number generation, secure communication, chaotic radar, chaotic detection, and photonic computing.

[0050] Those skilled in the art will understand that the features recited in the various embodiments and / or claims of the present disclosure can be combined or / and combined in various ways, even if such combinations or combinations are not explicitly recited in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features recited in the various embodiments and / or claims of the present disclosure can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present disclosure.

[0051] Although the present disclosure has been shown and described with reference to specific exemplary embodiments thereof, those skilled in the art should understand that various changes in form and detail can be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the present disclosure should not be limited to the above embodiments, but should be determined not only by the appended claims but also by the equivalents of the appended claims.

Claims

1. A polygon microcavity chaotic laser, characterized in that, Including: A whispering gallery cavity (1) with a regular polygon cross-section or an arc-edge regular polygon cross-section for forming total internal reflection of light; A hole (2) coaxial with the whispering gallery cavity (1) and disposed inside the whispering gallery cavity (1) for suppressing high-order transverse modes and regulating the number of modes; An annular ohmic contact window (3) located at the upper end of the whispering gallery cavity (1) and coaxial with the whispering gallery cavity (1) for non-uniform current injection to achieve non-linear interaction of modes to generate chaotic laser; A waveguide (4) in contact connection with the outer wall of the whispering gallery cavity (1) for directionally outputting the chaotic laser. The waveguide (4) is perpendicular to a diagonal of the whispering gallery cavity (1), and the waveguide (4) is translated upward or downward along a direction perpendicular to the horizontal diagonal to improve the coupling output efficiency.

2. The polygon microcavity chaotic laser according to claim 1, characterized in that, The whispering gallery cavity (1) is an active cavity, and its material structure is a quantum well or a quantum dot structure.

3. The polygon microcavity chaotic laser according to claim 1, characterized in that, The whispering gallery cavity (1) has a square, hexagonal, octagonal, arc-edge quadrilateral, arc-edge hexagonal or arc-edge octagonal structure.

4. The polygon microcavity chaotic laser according to claim 1, characterized in that, The cross-section of the hole (2) includes a triangle, quadrilateral, pentagon, hexagon, ellipse or circular structure.

5. The polygon microcavity chaotic laser according to claim 1, characterized in that, The light output port of the waveguide (4) is a cleavage plane or an end-face coating structure.

6. A method for regulating a polygon microcavity chaotic laser, applied to the polygon microcavity chaotic laser according to any one of claims 1-5, characterized in that, The method includes: Increasing the size of the polygonal microcavity chaotic laser to increase the output power of the chaotic laser; Adjusting the shape and size of the hole (2) in the polygonal microcavity chaotic laser to achieve suppression of different high-order transverse modes; Adjusting the connection position between the waveguide (4) and the whispering gallery cavity (1) in the polygonal microcavity chaotic laser to optimize the coupling output efficiency.

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