CN117039615A

CN117039615A - Annular photonic crystal microcavity light amplification surface emitting laser

Info

Publication number: CN117039615A
Application number: CN202311159330.0A
Authority: CN
Inventors: 郁骁琦; 杨辉
Original assignee: Su Zhoushiyanshi
Current assignee: Su Zhoushiyanshi
Priority date: 2023-09-08
Filing date: 2023-09-08
Publication date: 2023-11-10

Abstract

An annular photon crystal microcavity light amplifying surface emitting laser is characterized in that an annular photon crystal structure is manufactured on one side of an active layer of a semiconductor laser, the annular photon crystal is provided with a plurality of circles of periodic hollow hole structures, a microcavity structure is formed in the center of the annular photon crystal, and a microcavity mode is obtained. The microcavity mode light field is expanded into the annular photon crystal area, and by utilizing the expanded light field, current is loaded in the photon crystal coverage area, and the active layer photons of the expanded part generate stimulated radiation which is distributed with photons in the microcavity area in the same frequency, same phase and same light field, namely, the microcavity mode light field realizes light amplification in the annular photon crystal, and high-power single-mode laser output is realized.

Description

Annular photonic crystal microcavity light amplification surface emitting laser

1. Background art

The current conventional semiconductor laser structure has: FP, DFB, VCSEL, etc., are hardly compatible with increasing the output laser power and controlling the divergence angle due to the influence of the lateral dimension, the device shape, etc. In 1999, the university of kyoto, noda professor, japan, proposed Photonic Crystal Surface Emitting Lasers (PCSELs), which developed over 20 years, 2023 they made PCSEL devices 3mm in diameter, achieved continuous 50W single mode laser output, with a divergence angle of about 0.05 °. They not only verify the feasibility of the PCSEL technology path, but also will drive the semiconductor laser to further develop, hopefully subvert the development of the semiconductor laser and even the whole laser industry.

The device of the PCSEL structure has several problems: first, in the XY plane where laser resonance occurs, it is difficult to control the laser coupling in the X direction and the Y direction, and when the device is large, linear laser is easily generated in the X direction and the Y direction, respectively, so as to affect the output light field distribution. Second, PCSEL is in a band-edge mode, and a standing wave is generated by using the Γ point of the band edge of the photonic band gap, so that the band gap needs to be opened to better control the mode, and therefore, the refractive index difference between the photonic crystal and the substrate material should be as large as possible. This also results in a stronger in-plane feedback in the X-direction and the Y-direction. If the device is made large, multiple point lasing is likely to occur, resulting in the output laser no longer being single mode.

Annular DFB, annular photonic crystal, etc. structures were studied 20 years ago by the Yariv professor team, california academy of science. Unlike PCSEL analysis in rectangular coordinate system, circular grating and photon crystal are required to be analyzed in cylindrical coordinates, and Bessel function is solved to obtain result. As the adopted annular grating penetrates through the whole device, the grating has strong modulation effect on the light field, and the device is easy to cause multimode after being made large.

In order to make up for the defects of the existing photonic crystal surface-emitting laser, the application provides an annular photonic crystal microcavity light amplification surface-emitting laser so as to realize single-mode high-power laser output. And manufacturing an annular photonic crystal structure on one side of the semiconductor laser active layer, wherein the refractive index of the photonic crystal is smaller than that of the substrate material. The annular photonic crystal has a plurality of circles of periodic hollow hole structures, which are generally more than 1000 circles and even 10000 circles, and a microcavity structure is formed at the center of the annular photonic crystal, so that the optical field distribution of microcavity modes can be obtained correspondingly. When the refractive index of the photonic crystal is larger than that of the substrate material, and the diameter of the microcavity is larger, the microcavity mode light field is limited in the microcavity; when the refractive index of the photonic crystal is smaller than that of the substrate material, or the limiting factor of the photonic crystal layer is smaller, or the diameter of the microcavity is smaller, the microcavity mode light field extends to the periphery of the photonic crystal structure and is attenuated rapidly. By utilizing the expanded light field, the current is loaded in the photon crystal coverage area, and the active layer photons of the expanded part generate stimulated radiation, so that the stimulated radiation is distributed with photons in the microcavity area in the same frequency, same phase and same light field, namely, the microcavity mode light field is amplified in the annular photon crystal. Therefore, the annular photonic crystal structure can be regarded as a reflecting mirror, and a microcavity mode is obtained in the center of the structure; meanwhile, the extended microcavity mode is utilized to realize the optical amplification of the microcavity mode in the coverage area of the annular photonic crystal, so that the high-power single-mode laser output is realized.

2. Summary of the application

Document 1 discloses a ring-shaped photonic crystal resonator for obtaining a wide free spectral range and a high Q value, and comparing the resonant wavelength and mode conditions of photonic crystal voids radially distributed according to Hankel functions with m being 8 and 9, respectively. Because the light field mode is multi-petal, the single-mode laser is not beneficial to being obtained. And only the microcavity mode is output, it is difficult to obtain high power.

Document 2 discloses a laser of an annular DFB, a disk-shaped bragg, and an annular bragg structure, wherein the annular DFB structure is a band-edge mode, and the disk-shaped bragg and the annular bragg structure are forbidden band modes. The structure disclosed in the document has stronger in-plane feedback, so that the number of annular grooves cannot be excessive, otherwise, single-mode output cannot be realized, and therefore, the device is smaller, and the diameter of the 3-class device is 43.6 mu m at the maximum. In addition, the disk-shaped Bragg structure laser has the central microcavity diameter which is half of the diameter of the annular grating structure, the minimum of the central microcavity diameter is about 5.2 mu m, the maximum of the central microcavity diameter is about 12.2 mu m, the threshold value phase difference among a plurality of microcavity modes is small, and the single mode cannot be ensured because the mode is difficult to distinguish and select. Therefore, the designed grating structure cannot realize single-mode high-power laser output.

The structure of the annular photonic crystal microcavity light amplification surface-emitting laser is shown in fig. 1, and is respectively an upper electrode 7, an upper cladding layer 6, an upper waveguide layer 5, an active layer 4, a lower waveguide layer 3 and a lower cladding layer 2 from top to bottom. The annular photonic crystal layer 8 is located on one side of the active layer, and may be located in the upper cladding layer 6, in the upper cladding layer 6 and the upper waveguide layer 5, or may penetrate the upper electrode layer 7 and the upper cladding layer 6.

Preferably, there is a lower electrode 1 below the lower cladding layer 2, and a light hole is left in the middle of the lower electrode 1, and the inner diameter of the lower electrode 1 is larger than the outer diameter of the upper electrode 7, as shown in fig. 1 (a).

Preferably, the lower electrode 1 is also disposed outside the lower cladding layer 2, and the structure is as shown in fig. 1 (b).

Preferably, the upper electrode 7 is ITO.

Preferably, a reflecting layer is further arranged above the upper electrode 7, so that the generated laser light is emitted from the lower part, and the light emitting efficiency is improved.

In order to realize the single-mode high-power laser output of the device, referring to the device structure shown in fig. 1, if the laser emits light from the side of the lower cladding layer 2, the coverage area of the upper electrode 7 should be large enough, so that the active layer 4 within the coverage area of the annular photonic crystal layer 8 obtains electric injection to generate laser. Thus, the coverage of the upper electrode 7 should be comparable to the coverage of the photonic crystal layer 8, or the coverage of the upper electrode 7 should be slightly smaller than the coverage of the annular photonic crystal layer 8, e.g. the diameter of the coverage of the annular photonic crystal layer 8 is about 1.05-1.2 times, preferably 1.1 times the diameter of the upper electrode 7. The lower cladding 2 is a light-emitting surface, a light-emitting hole is reserved in the middle of the lower electrode 1, an electrode part is arranged on the periphery of the lower electrode, the inner diameter of the lower electrode 1 is larger than the outer diameter of the upper electrode 7, and preferably, the inner diameter of the lower electrode 1 is 1.1 times of the outer diameter of the upper electrode 7.

The annular photonic crystal layer 8 is shown in fig. 2 (b) and is composed of a base material 8-1, a photonic crystal 8-2 and a microcavity 8-3. The base material 8-1 refers to the upper cladding layer 6 or the upper waveguide layer 5 or the lower waveguide layer 3 or the lower cladding layer 2. The refractive index of the base material 8-1 is greater than the refractive index of the photonic crystal 8-2. The photonic crystal 8-2 may be hollow or may be filled or partially filled with SiN, ITO, or other materials. An electron blocking layer can be further arranged between the upper cladding layer 6 and the upper waveguide layer 5, and is used for promoting the recombination of electrons and holes at the active layer 4 and avoiding the recombination at the photonic crystal layer.

Fig. 2 shows a ring-shaped photonic crystal pattern arranged according to the zero position of the 1 st order bessel function. Fig. 2 (a) is a complete annular photonic crystal structure, and fig. 2 (b) is an annular photonic crystal including a microcavity structure. For fig. 2 (b), the annular photonic crystal at the periphery of the microcavity can be considered as a mirror, with the optical field concentrated at the center of the annular photonic crystal. By adjusting the circumference size formed by the photonic crystal hollow holes of the innermost ring, microcavity modes with different m values can be obtained, and the high-order microcavity mode can be restrained. Simultaneously, the positions, the sizes and the number of the polarization holes in the microcavity are adjusted, so that the needed microcavity mode can be further controlled and selected.

The scheme of the application is to form a microcavity in the center by utilizing an annular photonic crystal structure. Annular photonic crystal voids are according to the Bessel functionThe solution of the equation (such as a first type Bessel function, a second type Bessel function, a third type Bessel function, etc.) or the solution of the equation of other Bessel functions determines the phase of each circle of photonic crystals, and the phase difference between two adjacent circles of photonic crystals is 2 pi. The Bessel function is preferably a 0-order or 1-order Bessel function, and the 0-order or 1-order Bessel function can be subjected to phase shift. The interval period between two adjacent circles of annular photonic crystals is about a; the spacing between the annular photonic crystal holes of each circle is about a; each photonic crystal void has a diameter of about 0.4a to about 0.6a, preferably about 0.45a to about 0.55a, and more preferably about 0.5a, to reduce the in-plane feedback intensity (see fig. 3 of document 3), which is advantageous in that the device area is large. Considering that the optical field is preferentially distributed in the material with high dielectric constant, in order to reduce the influence of the photonic crystal structure on radial propagation, the optical field mode is better controlled, and the photonic crystal void is preferentially distributed at the zero point of the Bessel function. The a is approximately the wavelength of light in the substrate material, i.e., a=λ/n, and the a is appropriately sized to be consistent with or close to the active layer emission wavelength according to the actual situation. By adjusting the gap period a of the photonic crystal, the resonant frequency of the annular photonic crystal can be adjusted, and the frequency corresponding to the band gap of the annular photonic crystal can be changed.

In the structure of the application, the inner diameter of the lower electrode 1 is slightly larger than the outer diameter of the upper electrode 7, so that the active layer obtains electric injection to realize the inversion of particle number, and a large number of electrons and holes are recombined to form photons. The microcavity formed in the center of the annular photonic crystal structure is easier to excite because the loss of the microcavity mode is smaller than that of the annular photonic crystal mode. Meanwhile, for the microcavity mode, the light intensity is gradually attenuated by the peripheral annular photonic crystal (the resonant frequency of the microcavity mode falls within the band gap of the annular photonic crystal, i.e., light of this frequency is difficult to propagate in the photonic crystal) (see table 1). According to formula r ₂₁ (st)＝B ₂₁ ·f _c ·(1-f _v )·ρ·S(E ₂₁ ) Stimulated radiation Rate r ₂₁ (st) transition probability coefficient B with stimulated radiation ₂₁ Electron at conduction band energy level E ₂ The occupation probability f of (2) _c Energy level E in valence band ₁ Probability of empty (1-f _v ) A reduced density ρ and a photon density S (E ₂₁ ) Proportional to the ratio. The annular photonic crystal region at the periphery of the microcavity still has larger light intensity, namely S (E ₂₁ ) Larger, and therefore the photon stimulated radiation rate r of the region ₂₁ And (st) is larger, and the same frequency, same phase and same optical field of photons in the microcavity mode are distributed, so that the optical amplification of the microcavity mode is realized.

In the scheme of the application, the resonant frequency of the microcavity structure is within the display gain frequency of the active layer, and the resonant frequency of the microcavity structure is within the forbidden band frequency of the annular photonic crystal, so that laser can be formed in the plane to form a microcavity mode; on the other hand, the photon crystal area is filled with carriers, the corresponding active layer area also generates photons, the photons are influenced by laser generated by the microcavity mode, and the photons in the area are stimulated to radiate, so that the optical amplification of the microcavity mode is realized. In addition, since the phase difference between two adjacent circles of the annular photonic crystal is 2pi, light is diffracted in the vertical direction, and thus surface emission can be achieved. The annular photonic crystal microcavity light amplification surface emitting laser realizes that after the area of a semiconductor laser device is made large, the diameter or the side length of the device is more than or equal to 0.5mm, and still single-mode high-power laser output is maintained.

Compared with the prior art, the application has the following beneficial effects:

first, the annular photon crystal structure of the application is beneficial to making the device large due to the design of micro-cavity mode optical amplification, and keeps single-mode laser output to realize single-mode high-power laser output. Second, the annular photonic crystal structure is easier to control microcavity size and is easier to control and select microcavity modes than Fang Jingge, triangular and hexagonal lattices. Thirdly, by additionally arranging a polarized hole structure in the microcavity or controlling the angular period of the annular photonic crystal, the mode of the annular photonic crystal microcavity can be further selected/inhibited, and single-mode output is ensured.

Document 1: jacob Scheuer, ammon Yariv, circular photonic crystal resonators, physical Review E,70,036603 (2004)

Document 2: xiankai Sun, amnon Yariv, surface-emitting circular DFB, disk-, and ring-Bragg resonator lasers with chirped gratings: a unified theory and comparative study, optics Express, vol.16, no.12 (2008)

Document 3: xiankai Sun, jacob Scheuer, amnon Yariv, optimal design and reduced threshold in vertically emitting circular Bragg disk resonator lasers, IEEE Journal of Selected Topics In Quantum Electronics, vol.13, no.2 (2007)

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions of the prior art, the following description will simply refer to the drawings that are required to be used in the description of the technical solutions or the embodiments of the present application.

FIG. 1 is a schematic cross-sectional view of a ring-shaped photonic crystal microcavity light amplifying surface-emitting laser structure according to the present application

FIG. 2 is a diagram showing the comparison of the annular photonic crystal structure and the annular photonic crystal microcavity structure, and FIG. 2 (b) is a cross-sectional view taken along line A-A of FIG. 1 (a)

FIG. 3 is a graph showing distribution of radial components of electric fields in three different microcavity modes according to some embodiments of the present application

FIG. 4 is a block diagram of an optimized annular photonic crystal microcavity according to some embodiments of the present application

FIG. 5 is a diagram illustrating a photonic crystal structure having different rotationally symmetric periodic structures according to some embodiments of the present application

3. Detailed description of the preferred embodiments

Taking a GaN laser as an example, fig. 3 shows electric fields and radial component distribution of the electric fields in three microcavity modes. Fig. 3 (a) and (b) show the electric field and the radial component distribution of the electric field in the microcavity mode with m=1 and n=1, respectively. The light field intensity tapers radially from the center and, because the center is a singular point, the mode is exactly linear polarized. Fig. 3 (c) and (d) show the electric field and the radial component distribution of the electric field in the microcavity mode with m=0 and n=1, respectively. The light field is in a ring shape, and if the light spot obtained after focusing by using the lens is smaller than the light spot obtained after focusing by using the Gaussian beam, the light field is suitable for laser processing. Fig. 3 (e) and (f) show the electric field and the radial component distribution of the electric field in the microcavity mode with m=2 and n=1, respectively. The mode has 4 lobes radially, belongs to a high order mode, and should be avoided for single mode output. Therefore, the first two modes are the most valuable modes for application to semiconductor lasers. The size of the circumference (i.e. the size of the microcavity) formed by the annular photonic crystal holes at the innermost ring can be controlled, and the diameter, arrangement, refractive index, photonic crystal layer limiting factors and the like of the annular photonic crystal holes can be controlled to obtain a required mode.

R is the radius of the central microcavity, a is the period of the spacing between the voids, and the diameter of the device is about 0.5mm, i.e., about 2800a, for the example of a GaN-based laser. Table 1 shows the relationship between different microcavity radii to obtain the light field modes. When the microcavity radius is small, the microcavity mode is a linear polarization mode with m=1 and n=1. When the microcavity radius increases to 4.38a, the microcavity mode increases by 4 modes, namely, m=0, n=1 radial polarization and angular polarization modes, and 2 m=2, n=1 modes. Therefore, the size of the central microcavity of the annular photonic crystal can be controlled to control microcavity mode and optical field distribution, and the generation of a higher-order mode is restrained.

TABLE 1 microcavity radius versus light field mode

As can be seen from Table 1, microcavity modes usually occur in pairs, with the two degenerate mode polarizations being perpendicular to each other. If the polarization direction of the light emitted by the laser can be controlled, the subsequent optical regulation and control processing is facilitated. Therefore, the application designs two modes, which can be used independently or in combination:

firstly, a plurality of polarization holes are added in the microcavity, so that the polarization direction of the mode can be controlled. For example, for a microcavity structure with r=2.38a, 2 polarized holes are placed in the microcavity, with the center of the microcavity on the line of the 2 polarized holes, as shown in fig. 4. This structure limits the direction of the radial and angular components of the electric field so that the polarization direction is controllable.

Secondly, the hollow holes of each circle of the annular photonic crystal are circumferentially distributed, so that the annular photonic crystal has rotational symmetry. The arrangement of each circle is controlled, so that when the rotation symmetry period of the whole photonic crystal structure is 2 pi, the polarization direction of the low-order mode is randomly generated, and the laser polarization generated by each laser is difficult to control to be the same. When rotational symmetry is introduced into the photonic crystal structure, and the period is pi, the polarization direction of the low-order mode is controlled. These two structures are shown in fig. 5, where the period of rotational symmetry in fig. 5 (a) is 2 pi and the period of rotational symmetry in fig. 5 (b) is pi. If the rotation period is pi/2, pi/3, etc., it is difficult to control the polarization directions to be uniform or perpendicular to each other due to the presence of a plurality of symmetries.

Claims

1. An annular photonic crystal microcavity light amplification surface emitting laser, includes upper electrode, upper cladding, upper waveguide layer, active layer, lower waveguide layer, lower cladding, when the carrier is injected into the active layer, the active layer emits light, its characterized in that:

and a two-dimensional annular photonic crystal structure is arranged on one side of the active layer, the two-dimensional annular photonic crystal is formed into an annular lattice, and the annular lattice formed by the two-dimensional annular photonic crystal forms a microcavity structure at the center.

2. The annular photonic crystal microcavity light amplification surface emitting laser of claim 1, wherein the two-dimensional annular photonic crystal forms an annular lattice, and each ring of annular photonic crystals is distributed according to a solution of a bessel function or other form of bessel function equation;

the active layer emits light to resonate in the microcavity structure to form a microcavity mode;

the active layer emits light in the annular photonic crystal, and the microcavity mode is optically amplified;

the coverage area of the upper electrode is smaller than or equal to that of the annular photonic crystal structure.

3. The annular photonic crystal microcavity light-amplifying surface-emitting laser of claim 1, wherein the diameter of the annular photonic crystal microcavity light-amplifying surface-emitting laser is 0.5mm or more or the side length is 0.5mm or more.

4. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 1 wherein the resonant frequency of the annular photonic crystal microcavity structure is within the frequency at which the active layer exhibits gain.

5. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 4 wherein the resonant frequency of the annular photonic crystal microcavity structure is within the forbidden band frequency of the annular photonic crystal.

6. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 2, wherein two adjacent turns of the annular photonic crystal are out of phase by 2Ω.

7. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 6 wherein adjacent turns of the annular photonic crystal have a pitch period of a.

8. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 7, wherein the voids comprising the annular photonic crystal lattice are spaced apart by a.

9. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 8 wherein the diameter of the void is 0.4a to 0.6a.

10. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 9 wherein the diameter of the void is 0.45a to 0.55a.

11. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 10, wherein the diameter of the void is 0.5a.

12. The annular photonic crystal microcavity optically amplified surface-emitting laser of claim 2 wherein the rings of annular photonic crystals are distributed according to a zero-order or first-order bessel function.

13. The annular photonic crystal microcavity optically amplified surface-emitting laser of claim 12 wherein the annular photonic crystals of each ring are distributed according to the zero location of the bessel function.

14. The annular photonic crystal microcavity optically amplified surface-emitting laser of claim 12 wherein the zero-order or first-order bessel function is phase shifted.

15. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 2 wherein a plurality of polarized hole structures are provided in the microcavity structure.

16. The annular photonic crystal microcavity light amplifying surface emitting laser of any of claims 1-15, wherein the annular photonic crystal has rotational symmetry.

17. The annular photonic crystal microcavity light-amplified surface-emitting laser of claim 16, wherein the period of rotational symmetry is 2 pi or pi.

18. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 1, wherein the two-dimensional annular photonic crystal structure is in an upper cladding layer, or in an upper waveguide layer, or in both an upper cladding layer and an upper waveguide layer.

19. The annular photonic crystal microcavity light amplifying surface emitting laser of claim 18, wherein a light hole is left in the middle of the lower electrode, and the inner diameter of the lower electrode is larger than the outer diameter of the upper electrode.