Photonic Crystal Surface Emitting Laser

Abstract

The present invention provides a photonic crystal surface emitting laser, which relates to the technical field of semiconductor lasers. The photonic crystal surface emitting laser comprises: an excitation part for exciting laser; an emission part for causing the laser to resonate and outputting the laser in the normal direction of the resonance surface by diffraction, wherein the emission part comprises a plurality of photonic crystal units arranged in an array, each of which is used to form a plurality of different resonance modes when the laser resonates, and two resonance modes with symmetric electric field vectors in the plurality of resonance modes are degenerately coupled at energy band points through a specific cross-section of the photonic crystal unit.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, and in particular to a photonic crystal surface emitting laser. Background Art

[0002] Laser is another major invention of mankind since the 20th century, following atomic energy, electronic computers, and semiconductors. Surface-emitting semiconductor lasers have the advantages of high power, long life, low cost, and easy array integration, and have received widespread attention and application in many fields.

[0003] In addition to the vertical cavity surface emitting (VCSEL) structure, the commonly used surface emitting solutions can also use distributed feedback gratings or photonic crystals to achieve vertical emission. The photonic crystal surface emitting structure (PCSEL) can increase the emission aperture on a single chip while reducing the impact of lateral multi-mode oscillation caused by increasing size, meeting the requirements of high output power, narrow divergence and high-speed operation, and does not require external optical path modulation, greatly reducing optical loss.

[0004] In traditional photonic crystal structures, there are usually two or more high-quality factor modes at the Γ2 point. When the gain increases and external factors change, the single-mode performance and single-mode stability deteriorate due to mode competition and other reasons. Summary of the invention

[0005] In view of this, the present invention provides a photonic crystal surface emitting laser, which realizes large-area surface emission, reduces far-field divergence angle and optimizes beam shape by designing the shape of the photonic crystal and adjusting the band structure while improving single-mode performance.

[0006] An embodiment of the present invention provides a photonic crystal surface emitting laser, comprising: an excitation section for exciting laser; an emission section for causing the laser to resonate and output the laser in the normal direction of the resonance surface through diffraction, wherein the emission section comprises a plurality of photonic crystal units arranged in an array, each of which is used to form a plurality of different resonance modes when the laser resonates, and through the specific shape cross-section of the photonic crystal unit, two resonance modes with symmetric electric field vectors in the plurality of resonance modes are degenerately coupled at energy band points.

[0007] According to the embodiment of the present invention, the specific shape cross section of each photonic crystal unit is formed by connecting a first circular arc and a second circular arc end to end, and the first circular arc and the second circular arc have the same orientation.

[0008] According to an embodiment of the present invention, the radian of the first circular arc is greater than π, and the radian of the second circular arc is less than π.

[0009] According to an embodiment of the present invention, the radius of the first arc is greater than the radius of the second arc.

[0010] According to an embodiment of the present invention, a plurality of photonic crystal units are arranged in an array in a specific lattice type manner.

[0011] According to an embodiment of the present invention, the specific lattice type includes a tetragonal lattice.

[0012] According to an embodiment of the present invention, a photonic crystal surface emitting laser includes a cladding layer, and a plurality of photonic crystal units are formed on the cladding layer.

[0013] According to an embodiment of the present invention, the inside of a specific cross-section of the photonic crystal unit is air and the outside is a cladding layer; or the inside of a specific cross-section is a cladding layer and the outside is air.

[0014] According to an embodiment of the present invention, the photonic crystal surface emitting laser also includes a substrate layer, a second confinement layer, an active layer, and a first confinement layer stacked in sequence, a cladding layer is arranged on the first confinement layer, and each photonic crystal unit formed on the cladding layer is also continuously formed on one or more layers of the first confinement layer, the active layer, the second confinement layer, and the substrate layer.

[0015] According to an embodiment of the present invention, the material of the photonic crystal unit includes Group II-VI system materials and Group III-V system materials.

[0016] According to an embodiment of the present invention, the photonic crystal surface emitting laser provided by the present invention adjusts the energy band structure to achieve degenerate coupling of high quality factor (Q) mode A and low Q mode E2 at the energy band Γ2 point, resulting in a reduction in the Q value of mode A, and only retaining one high Q mode B at the Γ2 point, which is beneficial to improving the single-mode characteristics. The photonic crystal surface emitting laser provided by the present invention breaks the symmetry of the circular photonic crystal structure, achieves symmetry breaking, realizes beam shaping, and improves beam quality. The photonic crystal surface emitting laser provided by the present invention can realize a laser light source with high single-mode characteristics, high beam quality, and high brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0018] Figure 1 A schematic top view of a photonic crystal surface emitting laser according to an embodiment of the present invention is shown;

[0019] Figure 2 Schematically showing a formation diagram of a photonic crystal unit according to an embodiment of the present invention;

[0020] Figure 3 A schematic diagram showing the structure of a photonic crystal surface emitting laser according to an embodiment of the present invention;

[0021] Figure 4A schematic diagram showing the structure of a photonic crystal surface emitting laser according to yet another embodiment of the present invention;

[0022] Figure 5 Schematically showing the electric field mode distribution diagram of Γ2 band edge modes A, B, E1, and E2 in a single period photonic crystal according to an embodiment of the present invention;

[0023] Figure 6 A diagram schematically shows the relationship between the quality factor of the Γ2 band edge mode of the photonic crystal structure according to an embodiment of the present invention and the change in the distance from the arc center when the arc radius is fixed;

[0024] Figure 7 A diagram schematically shows the relationship between the minimum Q value of the photonic crystal structure and the corresponding arc center distance as a function of the arc radius according to an embodiment of the present invention;

[0025] Figure 8 A schematic diagram showing an energy band comparison diagram of a photonic crystal structure according to an embodiment of the present invention and some traditional photonic crystal structures;

[0026] Fig. 9 A comparison diagram of far-field distribution images of a photonic crystal according to an embodiment of the present invention and a traditional circular photonic crystal is schematically shown.

[0027] Description of reference numerals:

[0028] 1-first electrode layer; 2-cladding layer; 3-first confinement layer; 4-active layer; 5-second confinement layer; 6-substrate layer; 7-second electrode layer; 10, 10'-emitting part; 20, 20'-excitation part; 11-photonic crystal unit. DETAILED DESCRIPTION

[0029] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0030] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0031] In the description of the present invention, “several” means one or more, “more” means more than two, “greater than”, “less than”, “exceed”, etc. are understood as not including the number itself, and “above”, “below”, “within”, etc. are understood as including the number itself.

[0032] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0034] Figure 1 The figure schematically shows a top view of a photonic crystal surface emitting laser according to an embodiment of the present invention.

[0035] like Figure 1 As shown, the photonic crystal surface emitting laser may include an emitting unit 10 and an exciting unit 20. The exciting unit 20 is used to excite the laser. The emitting unit 10 is used to resonate the laser and output the laser in the normal direction of the resonance surface by diffraction. The emitting unit 10 may include a plurality of photonic crystal units 11 arranged in an array, each photonic crystal unit 11 having a specific cross-section shape, each photonic crystal unit 11 being used to form different multiple resonance modes when the laser resonates, and the specific cross-section shape of the photonic crystal unit 11 makes the two resonance modes with symmetric electric field vectors in the multiple resonance modes degenerately coupled at the energy band point. In the laser resonance process, there may be two high quality factor (Q value) modes, A and B modes, and the Q value of the A mode is higher than the Q value of the B mode. With different pumping conditions and external influences, mode conversion may occur in the mode competition, which is not conducive to the single-mode characteristic. The resonance mode E2 has a symmetric relationship with the resonance mode A in the electric field vector. Through the degenerate coupling between the resonance mode A and the resonance mode E2, the resonance mode A with a high Q value can be reduced, and the resonance mode B with a low Q value can be retained, which is conducive to improving the single-mode characteristic.

[0036] In some embodiments, the specific shape cross-section of each photonic crystal unit 11 can be formed by connecting the first arc and the second arc end to end, and the first arc and the second arc have the same orientation. It is understandable that the first arc and the second arc can form a crescent-like shape. Compared with traditional photonic crystals such as circular, elliptical, triangular and other structures, crescent-shaped photonic crystals can break the symmetry of the circular photonic crystal structure and achieve symmetry breaking. While the unit breaks the symmetry and realizes a single-petal circular far-field spot, the degenerate coupling of the high-quality factor mode A and the low-Q mode E2 at the energy band Γ2 point is achieved, resulting in a reduction in the Q value of mode A, and only one high-Q mode B is retained at the Γ2 point, which is beneficial to improving the single-mode characteristics. The advantages of the crescent-shaped photonic crystal unit and the comparison with some traditional photonic crystal units will be further explained later.

[0037] The degenerate coupling effect is related to the radius, arc center distance, and curvature of the first arc and the second arc in the crescent shape. To further enhance the single-mode characteristics, the crescent shape can be further optimized. In some embodiments, the curvature of the first arc can be greater than π, and the curvature of the second arc can be less than π. Further, in some embodiments, the radius of the first arc can be greater than the radius of the second arc.

[0038] Figure 2 The diagram schematically shows the formation of a photonic crystal unit according to an embodiment of the present invention.

[0039] like Figure 2 As shown, on the basis of the above embodiment, the cross section of the photonic crystal unit can be formed by cutting a large circle 11a and a small circle 11b. The large circle 11a can be used as the initial circle, and the small circle 11b can be used as the cutting circle. By cutting off a small section of the arc of the large circle 11a with the small circle 11b, the cross section of the photonic crystal unit can be obtained. The arc of the large circle 11a after being cut is used as the first arc in the above, and the arc of the small circle 11b falling inside the large circle 11a is used as the second arc in the above. The distance between the centers of the large circle 11a and the small circle 11b can be recorded as d, the spacing between the two photonic crystal units, that is, the lattice constant can be recorded as a, the radius of the large circle 11a is recorded as r0, and the radius of the small circle 11b is recorded as r, and the following relationship can be obtained:

[0040]

[0041] Wherein, m and n are parameters to be determined. The specific values ​​are related to factors such as the material and depth of the photonic crystal unit, and the present invention does not further limit them. The lattice constant a and the radius of the large circle r0 mainly determine the working wavelength of the photonic crystal unit, and the radius of the small circle r and the distance from the center of the circle d determine the position where the mode degeneration occurs. This will be further explained below.

[0042] Figure 3The structure of a photonic crystal surface emitting laser according to an embodiment of the present invention is schematically shown.

[0043] like Figure 3 As shown, the photonic crystal surface emitting laser may include a first electrode layer 1, a cladding layer 2, a first confinement layer 3, an active layer 4, a second confinement layer 5, a substrate layer 6, and a second electrode layer 7 arranged from top to bottom. An array of photonic crystal units 11 may be formed on the cladding layer 2. For example, the photonic crystal unit 11 may be prepared on the cladding layer 2 by an etching method. In some embodiments, the photonic crystal unit 11 may be etched only on the cladding layer 2. In some embodiments, etching may be continued downward along the etched area of ​​the cladding layer 2 until the first confinement layer 3, the active layer 4, the second confinement layer 5, and the substrate layer 6. In other words, in addition to being formed on the cladding layer 2, the photonic crystal unit 11 may be further formed on the first confinement layer 3, the active layer 4, the second confinement layer 5, or the substrate layer 6. The depth of the photonic crystal unit 11 is different, and the modulation intensity is also different accordingly. For example, when etching to a depth close to the active layer 4, a stronger modulation effect can be obtained. The present invention does not limit the specific depth of the photonic crystal unit 11.

[0044] Figure 4 The structure of a photonic crystal surface emitting laser according to another embodiment of the present invention is schematically shown. Figure 4 Can include Figure 3 The first electrode layer 1, the cladding layer 2, the first restriction layer 3, the active layer 4, the second restriction layer 5, the substrate layer 6 and the second electrode layer 7 are arranged from top to bottom. Figure 4 The details of each layer are omitted. Figure 4 The description of each layer is omitted in Figure 3 The content will not be repeated here.

[0045] The photonic crystal unit 11 can be formed in many ways. Figure 3 As shown, the cladding layer 2 outside the cross section of the photonic crystal unit 11 can be etched to form the photonic crystal unit 11. At this time, the photonic crystal unit 11 is a dielectric column structure, and the surrounding area can be air. Figure 4 As shown, the cladding layer 2 on the inner side of the cross section of the photonic crystal unit 11 in the emission part 10' can be etched to form the photonic crystal unit 11. At this time, the photonic crystal unit 11 can be an air column structure, which is surrounded by the cladding layer 2. The emission part 10' can be connected to the cladding layer 2 of the excitation part 20'. In this way, the preparation of the photonic crystal unit of the embodiment of the present invention can adapt to different preparation conditions and preparation processes. It should be emphasized that no matter what etching method is used, the band structure can be adjusted through the specific shape of the cross section of the photonic crystal unit 11, while improving the single-mode performance, achieving large-area surface emission, reducing the far-field divergence angle, and optimizing the beam shape.

[0046] It can be understood that when the photonic crystal unit 11 is formed on the first confinement layer 3, the active layer 4, the second confinement layer 5 or the substrate layer 6, the photonic crystal unit 11 can be formed according to Figure 3 or Figure 4 The first confinement layer 3, the active layer 4, the second confinement layer 5 or the substrate layer 6 within the cross section of the photonic crystal unit 11 is etched in a certain manner, or the first confinement layer 3, the active layer 4, the second confinement layer 5 or the substrate layer 6 outside the cross section of the photonic crystal unit 11 is etched to form photonic crystal units 11 of different depths.

[0047] like Figure 3 and Figure 4 As shown, a plurality of photonic crystal units 11 may be arranged in an array in a specific lattice type manner, which may be a tetragonal lattice.

[0048] The materials of the photonic crystal unit 11 include but are not limited to II-VI system materials and III-V system materials. According to the different material systems, the wavelength band of the photonic crystal surface emitting laser can cover the visible light, near infrared band and even mid- and far-infrared band.

[0049] As an example, the pumping method of the photonic crystal surface emitting laser structure can be electrical injection.

[0050] Figure 5 The electric field mode distribution diagram of Γ2 band edge modes A, B, E1, and E2 in a single period photonic crystal according to an embodiment of the present invention is schematically shown.

[0051] like Figure 5 As shown, it is the electric field mode distribution diagram of a single period Γ2 band edge mode of a photonic crystal structure with a crescent-shaped cross-section according to an embodiment of the present invention calculated by COMSOL. Among them, the horizontal and vertical coordinates represent the spatial position, and the grayscale represents the relative size of the electric field. In a crescent-shaped photonic crystal structure with mirror symmetry about the y=x axis, two modes (mode A and mode E2) are symmetric modes, and their electric field vectors are symmetric about the y=x axis; the remaining two modes (mode B and mode E1) are antisymmetric modes, and their electric field vectors are antisymmetric about the y=x axis. According to the 3D coupled mode theory and the finite element method, in the surface photonic crystal structure, mode A has the smallest radiation constant, and mode B has the second smallest radiation constant. Mode A and mode B do not have a large gap, resulting in a large mode competition between them, which deteriorates the single-mode performance. The present invention uses the shape parameters of the crescent structure to modify the energy band, and can find the point where the symmetric mode energy band is degenerate. At this point, coupling occurs between the symmetric modes, resulting in degenerate coupling of the high Q mode A and the low Q mode E2 at the Γ2 point, causing the Q value of the A mode to decrease, and only one high Q mode, mode B, is retained at the Γ2 point. At this time, there is only one minimum radiation constant mode B in the band edge mode.

[0052] Figure 6 A diagram schematically shows the relationship between the quality factor of the Γ2 band edge mode of the photonic crystal structure according to an embodiment of the present invention and the change in the arc center distance when the arc radius is fixed, Figure 7 The diagram schematically shows the relationship between the minimum Q value of the photonic crystal structure and the corresponding arc center distance as a function of the arc radius according to an embodiment of the present invention.

[0053] like Figure 6 As shown, it shows the relationship between the quality factor of the Γ2 band edge mode of the crescent-shaped photonic crystal structure calculated by COMSOL and the distance d between the center of the small circle 11b and the center of the large circle 11a when the radius of the small circle 11b is fixed. The small circle 11b and the large circle 11a can be seen in Figure 2 As shown in the figure, the horizontal axis represents the value of the center distance d, and the vertical axis represents the quality factor. It can be seen from the figure that the quality factor is related to the center distance d.

[0054] like Figure 7 As shown, the horizontal axis represents the ratio of the radius of the large circle 11a to the radius of the small circle 11b, the left vertical axis represents the ratio of the center distance d to the lattice constant a, and the right vertical axis represents the quality factor. It can be seen that the center distance d is linearly related to the radius ratio r / r0, and the minimum Q value of the A mode after coupling decreases as the radius ratio r / r0 increases.

[0055] Figure 8 The energy band comparison diagram of the photonic crystal structure according to the embodiment of the present invention and some traditional photonic crystal structures is schematically shown.

[0056] like Figure 8 As shown, (a) shows a specific crescent-shaped structure (e.g. Figure 2 (b) represents the photonic crystal band diagram of a non-specific crescent-shaped structure, (c) represents the photonic crystal band diagram of a circular structure, and (d) represents the photonic crystal band diagram of an elliptical structure. In the figure, the symbols M, X and Γ represent different energy band points, respectively. This embodiment adopts the Γ2 band edge mode. This band edge mode is a symmetry-protected in vivo bound state (BIC) mode of the continuum. Since it can effectively suppress leakage, it theoretically has an extremely high quality factor and is an ideal mode for laser excitation. A, B, E1, and E2 represent four band edge modes, respectively. From Figure 8As can be seen in the figure (c), when the graph is a complete circle, the E1 mode and the E2 mode are degenerate at the Γ2 point; as shown in the figure (b), when the graph begins to break, the E1 mode and the E2 mode are degenerate, the E2 mode frequency increases, and the A mode frequency decreases; as shown in the figure (a), when a specific point is reached, the A mode and the E2 mode overlap at the Γ2 point; beyond the specific point, the A mode and the E2 mode are separated again. As shown in the figure (d), it is an elliptical photonic crystal structure band diagram, which has the advantages of a symmetry-breaking photonic crystal structure, but due to mode separation, it is weaker than the specific crescent-shaped structure with symmetry mode degeneration in mode distinction of high Q modes. It can be found from the figure that compared with the traditional photonic crystal structure and the non-specific crescent-shaped structure, the specific crescent-shaped structure has the characteristics of symmetry mode degeneration while realizing the symmetry breaking of the photonic crystal.

[0057] Fig. 9 A comparison diagram of far-field distribution images of a photonic crystal according to an embodiment of the present invention and a traditional circular photonic crystal is schematically shown.

[0058] like Fig. 9 As shown, the far-field distribution image of a circular photonic crystal (left figure) and the far-field distribution image of a crescent-shaped photonic crystal (right figure) are respectively. The horizontal and vertical coordinates represent the spatial position, and the grayscale represents the relative size of the electric field. It can be seen that for a circular photonic crystal with a high degree of symmetry, the far-field image of the high-quality factor pattern usually presents a donut-shaped spot. Compared with the traditional circular photonic crystal, the crescent-shaped photonic crystal of the embodiment of the present invention can reduce the far-field divergence angle, optimize the beam shape, and make the beam more concentrated.

[0059] So far, the present embodiment has been described in detail in conjunction with the accompanying drawings. According to the above-mentioned multiple embodiments, the photonic crystal surface emitting laser proposed in the present invention, in view of the problem that the existing photonic crystal structure is not conducive to single-mode characteristics, designs a photonic crystal unit with a specific cross-section shape (for example, a crescent-shaped cross-section formed by shearing two circles of different sizes). By designing the parameters of the cross-section, it is possible to achieve degenerate coupling of the high-quality factor band edge mode A and the low-quality factor band edge mode E2 at the energy band Γ2 point. While the unit breaks the symmetry and realizes a single-petal circular far-field spot, it realizes the degenerate coupling of the high-quality factor (Q) mode A and the low-Q mode E2 at the energy band Γ2 point, resulting in a reduction in the Q value of mode A, and only retaining one high-Q mode B at the Γ2 point, which is conducive to improving the single-mode characteristics.

[0060] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination advantageously. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A photonic crystal surface emitting laser, characterized in that: include: An excitation unit, used for exciting laser; An emitting unit is used to make the laser resonate and output the laser in the normal direction of the resonance surface by diffraction, wherein: The transmitting part includes a plurality of photonic crystal units arranged in an array, each of the photonic crystal units having a specific cross-section shape, each of the photonic crystal units being used to form a plurality of different resonance modes when the laser resonates, and through the specific cross-section shape of the photonic crystal unit, two resonance modes with symmetric electric field vectors in the plurality of resonance modes are degenerately coupled at an energy band point, and the specific cross-section shape of each photonic crystal unit is formed by a first circular arc and a second circular arc connected end to end, and the first circular arc and the second circular arc have the same orientation.

2. The photonic crystal surface emitting laser according to claim 1, characterized in that: The radian of the first circular arc is greater than π, and the radian of the second circular arc is less than π.

3. The photonic crystal surface emitting laser according to claim 2, characterized in that: The radius of the first circular arc is greater than the radius of the second circular arc.

4. The photonic crystal surface emitting laser according to claim 1, characterized in that: The plurality of photonic crystal units are arranged in an array in a specific lattice type manner.

5. The photonic crystal surface emitting laser according to claim 4, characterized in that: The specific lattice type includes a tetragonal lattice.

6. The photonic crystal surface emitting laser according to claim 1, characterized in that: The photonic crystal surface emitting laser includes a cladding layer, and a plurality of the photonic crystal units are formed on the cladding layer.

7. The photonic crystal surface emitting laser according to claim 6, characterized in that: The specific cross-section of the photonic crystal unit has air inside and the cladding layer outside; or The inner side of the specific shape cross section is the coating layer, and the outer side is air.

8. The photonic crystal surface emitting laser according to claim 6, characterized in that: The photonic crystal surface emitting laser also includes a substrate layer, a second confinement layer, an active layer, and a first confinement layer stacked in sequence, the cladding layer is arranged on the first confinement layer, and each of the photonic crystal units formed on the cladding layer is also continuously formed on one or more layers of the first confinement layer, the active layer, the second confinement layer, and the substrate layer.

9. The photonic crystal surface emitting laser according to claim 1, characterized in that: The materials of the photonic crystal unit include II-VI group system materials and III-V group system materials.

Images