Vertical cavity surface emitting laser based on coupled cavity and preparation method thereof

Abstract

The invention provides a vertical cavity surface emitting laser based on a coupled cavity and a preparation method thereof, and relates to the technical field of semiconductor lasers. The vertical cavity surface emitting laser based on the coupled cavity comprises a central cavity used for generating a first light beam; n coupling cavity groups, each coupling cavity group comprising two coupling cavities, and the two coupling cavities are symmetrically distributed at two sides of the central cavity and are in coupling connection with the central cavity; each coupling cavity is configured to receive the first light beam, reflect the first light beam for multiple times and then output a second light beam to the central cavity; wherein the phases of the 2N second light beams are regulated and controlled to be matched with the phase of the first light beam by controlling the phase of the second light beam corresponding to each coupling cavity, so that the 2N second light beams and the first light beam generate a photon-photon resonance effect.

Description

Technical Field

[0001] The present disclosure relates to the technical field of semiconductor lasers, and more specifically, to a vertical cavity surface emitting laser based on a coupled cavity and a preparation method thereof. Background Art

[0002] Vertical-Cavity Surface-Emitting Lasers (VCSELs) have the advantages of low threshold current, high transmission rate, high power conversion efficiency, low electrical power loss, high operating temperature, and high reliability. Moreover, its circular output spot has incomparable advantages such as high coupling efficiency with optical fibers, easy to form a two-dimensional array, and in-situ detection, which is suitable for large-scale production and has also become the core light source for short-distance optical interconnection recognized internationally. Currently, the main wavelength is 850 nm, which plays an important role in the development and application of short-distance, optical interconnection big data centers and supercomputer technologies. In recent years, such lasers have developed rapidly under the traction of the development needs of new generation information technologies. Single The direct modulation 3 dB bandwidth of a single chip can reach 30 GHz.

[0003] However, affected by the carrier-photon resonance effect, thermal effect, parasitic resistance, capacitance, and non-linear gain effect (such as relaxation oscillation), the 3 dB bandwidth ability of traditional structure direct modulation 850 nm VCSELs is limited; on the other hand, in a single-mode fiber link for long-distance transmission, the frequency chirping phenomenon caused by modulation limits the transmission distance of the VCSEL light source in the optical fiber due to the existence of dispersion. Summary of the Invention

[0004] In view of this, the present disclosure provides a vertical cavity surface emitting laser based on a coupled cavity and a preparation method thereof.

[0005] On the one hand, the present disclosure provides a vertical cavity surface emitting laser based on a coupled cavity, including: a central cavity for generating a first light beam; N coupled cavity groups, each coupled cavity group including two coupled cavities, the two coupled cavities being symmetrically distributed on both sides of the central cavity and coupled to the central cavity; each coupled cavity being configured to receive the first light beam, output a second light beam to the central cavity after multiple reflections of the first light beam; wherein, by controlling the phase of the second light beam corresponding to each coupled cavity, the phases of the 2N second light beams are adjusted to match the phase of the first light beam, so that the 2N second light beams and the first light beam generate a photon-photon resonance effect.

[0006] According to an embodiment of the present disclosure, each coupled cavity is further configured to: control the slow light delay time of each coupled cavity to adjust the phase of the corresponding second light beam.

[0007] According to an embodiment of the present disclosure, controlling the slow light delay time corresponding to each coupled cavity includes: controlling the injection current corresponding to each coupled cavity to regulate the corresponding slow light delay time.

[0008] According to an embodiment of the present disclosure, controlling the injection current corresponding to each coupled cavity to regulate the corresponding slow light delay time includes: controlling the carrier concentration in the active region corresponding to each coupled cavity by controlling the injection current corresponding to each coupled cavity; determining the corresponding slow light delay time according to the carrier concentration in the active region.

[0009] According to an embodiment of the present disclosure, each coupled cavity includes: an oxidation confinement hole configured to regulate the phase of the second light beam corresponding to each coupled cavity by controlling the aperture size of the oxidation confinement hole.

[0010] According to an embodiment of the present disclosure, N coupled cavity groups are symmetrically distributed around the central cavity.

[0011] According to an embodiment of the present disclosure, it further includes: a radio frequency electrode connected to the central cavity; at least two DC electrodes, one DC electrode connected to one coupled cavity; wherein, the radio frequency electrode and the at least two DC electrodes are coplanar.

[0012] According to an embodiment of the present disclosure, it further includes: at least two ground electrodes, one ground electrode connected to one coupled cavity.

[0013] According to an embodiment of the present disclosure, it further includes: an epitaxial structure, and the central cavity and N coupled cavity groups are disposed on the epitaxial structure.

[0014] A second aspect of the present disclosure provides a method for manufacturing a vertical cavity surface emitting laser based on coupled cavities, including: epitaxially growing to prepare an epitaxial structure; etching and processing on the epitaxial structure to prepare a central cavity and N coupled cavity groups, wherein the central cavity is used to generate a first light beam; N coupled cavity groups, each coupled cavity group includes two coupled cavities, and the two coupled cavities are symmetrically distributed on both sides of the central cavity and are coupled to the central cavity; each coupled cavity is configured to receive the first light beam, and after multiple reflections of the first light beam, output a second light beam to the central cavity; wherein, by controlling the phase of the second light beam corresponding to each coupled cavity, the phases of the 2N second light beams are regulated to match the phase of the first light beam, so that the 2N second light beams and the first light beam generate a photon-photon resonance effect.

[0015] The vertical cavity surface emitting laser based on coupled cavities and the method for manufacturing the same provided by the embodiments of the present disclosure at least have the following beneficial effects:

[0016] By providing N coupled cavity groups, each coupled cavity group includes two coupled cavities, and the two coupled cavities are symmetrically distributed on both sides of the central cavity, so that the N coupled cavity groups generate a uniform feedback intensity, improving the stability of the laser and achieving stable single-mode emission.

[0017] Meanwhile, by controlling the slow light delay times corresponding to various N coupled cavity groups, the photon-photon resonance effect is further controlled, effectively improving the modulation bandwidth and extending the modulation bandwidth beyond the limit of the relaxation oscillation frequency. Description of the Drawings

[0018] Through the following description of the embodiments of the present disclosure with reference to the drawings, the above and other objects, features and advantages of the present disclosure will become clearer. In the drawings:

[0019] Figure 1 Schematically shows a flowchart of a method according to an embodiment;

[0020] Figure 2 Schematically shows a structural diagram of a vertical cavity surface emitting laser based on coupled cavities according to an embodiment of the present disclosure;

[0021] Figure 3 Schematically shows a flowchart of a method according to an embodiment of the present disclosure. Detailed Embodiments

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, it should be understood that these descriptions are exemplary only 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 thorough understanding of the embodiments of the present disclosure. However, obviously, one or more embodiments can be implemented without these specific details. In addition, in the following description, descriptions of well-known systems and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0023] 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 features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0024] 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.

[0025] In the case of using expressions such as "at least one of A, B, and C", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, and C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0026] In multimode, low-cost vertical-cavity surface-emitting lasers (VCSELs) fiber optical interconnections, common modulation coding techniques include Multi-Pulse Amplitude Modulation, Carrier-less Amplitude and Phase Modulation, and Discrete Modulation. However, these techniques are not applicable to the transmission of 850 nm single-mode VCSELs.

[0027] Another technique to effectively increase the modulation bandwidth is through external feedback, which is considered a cost-effective method to increase the mode bandwidth in directly modulated semiconductor lasers. This technique effectively improves the mode bandwidth of VCSELs by exciting the photon-photon resonance (PPR) between the modulation field and the external cavity, which appears as a secondary resonance in the modulation spectrum. Figure 1 A flowchart of a method according to an embodiment is schematically shown.

[0028] As Figure 1 shown, the manufacturing process of traditional 850 nm VCSELs is as follows:

[0029] Step 1: Perform an epitaxial growth to prepare an epitaxial structure, which includes a lower DBR, an n-type waveguide confinement layer, an active region, a p-type waveguide confinement layer, an oxidation layer, an upper DBR, and a p-type cap layer.

[0030] Step 2: Etch the epitaxial structure through lithography and other process technologies. Determine the etch mesa size based on the front electrode size and the light-emitting hole size.

[0031] Step 3: Use the wet oxidation method to prepare the oxidation aperture.

[0032] Step 4: Continue to deposit the front electrode, thin the substrate on the back, and deposit the back electrode.

[0033] Figure 2 A structural diagram of a vertical-cavity surface-emitting laser based on a coupled cavity according to an embodiment of the present disclosure is schematically shown.

[0034] As Figure 2As shown, the present disclosure provides a vertical cavity surface emitting laser based on a coupled cavity, comprising: a central cavity and N coupled cavity groups.

[0035] The central cavity is used to generate a first light beam.

[0036] N coupling cavity groups, each coupling cavity group includes two coupling cavities, the two coupling cavities are symmetrically distributed on both sides of the central cavity and coupled to the central cavity. Each coupling cavity is configured to receive a first light beam, and output a second light beam to the central cavity after multiple reflections of the first light beam.

[0037] By controlling the phase of the second light beam corresponding to each coupling cavity, the phases of the 2N second light beams are adjusted to match the phase of the first light beam, so that the 2N second light beams and the first light beam produce a photon-photon resonance effect.

[0038] In the embodiments of the present disclosure, although the mode bandwidth of VCSELs can be improved by providing external feedback through a single transverse coupling cavity. However, as the power supply current increases, the stability of the laser will decrease, resulting in a relatively large "kink" in the electro-optical characteristic curve (IL curve). That is, when approaching the threshold current, the output power of the laser is very sensitive to changes in current. When the current increases to a certain extent, the nonlinear effects and mode competition in the gain medium will cause an obvious "kink" in the output power, that is, the growth of the output power is no longer smooth but abrupt or fluctuating. And under high current conditions, the laser may experience a mode jump, that is, a sudden switch from one stable mode to another. This mode jump will cause a sharp fluctuation in the output power and appear as an obvious kink in the IL curve. This instability is not conducive to achieving single-mode operation and limits its scope of application. For example, loss peaks are easily formed during high-frequency modulation.

[0039] In addition, although the kink defect of the above-mentioned PPR effect can be avoided by setting a shorter coupled cavity length to induce a carrier-photon resonance effect, strong coupling is required to achieve the same bandwidth enhancement as a long cavity, which is difficult to achieve for a single coupled cavity.

[0040] Based on this, in this embodiment, by setting N coupling cavity groups, each coupling cavity group includes two short coupling cavities, and the two coupling cavities are symmetrically distributed on both sides of the central cavity and coupled with the central cavity, strong coupling with large bandwidth increase can be achieved while avoiding the PPR effect defect. Each coupling cavity can directly realize slow light feedback to the central cavity, and this slow light feedback is moderate, and the light field density will be redistributed through the slow light mode converged into the central cavity. It can effectively allow sufficient feedback to expand the transient laser bandwidth. At the same time, it can provide stronger and more uniform feedback, which can effectively improve the mode bandwidth of VCSELs. It also avoids the generation of loss peaks and reduces signal transmission efficiency during high-frequency modulation.

[0041] The N coupled cavity groups not only provide more slow light coupling, but also ensure a greater feedback required for enhanced modulation bandwidth through the slow light feedback accumulated by the round trips in multiple TCCs. Moreover, in a laser, a higher modulation frequency can be achieved with lower optical coupling. And an even number of strongly coupled cavities has strong robustness, maximizing the bandwidth while ensuring the reliability of the transmitted signal, which helps to increase the intensity modulation response above the carrier-photon frequency.

[0042] In an embodiment of the present disclosure, each coupled cavity is further configured to: regulate the phase of the corresponding second light beam by controlling the slow light delay time of each coupled cavity.

[0043] The corresponding slow light delay time can be determined according to the cavity length of each coupled cavity and the group refractive index of the corresponding coupled cavity.

[0044] By utilizing the slow light effect of each coupled cavity, the cumulative phase of the corresponding first light beam reflected back and forth in the corresponding coupled cavity can be precisely and efficiently controlled. When the cumulative phase of the second light beam matches the phase of the first light beam, an effective photon-photon resonance effect can be achieved. For example, the phase difference between the first light beam and the second light beam is a preset phase difference.

[0045] Based on the above embodiment, controlling the slow light delay time corresponding to each coupled cavity includes: controlling the injection current corresponding to each coupled cavity to regulate the corresponding slow light delay time.

[0046] Controlling the injection current corresponding to each coupled cavity to regulate the corresponding slow light delay time includes: controlling the carrier concentration in the active region corresponding to each coupled cavity by controlling the injection current corresponding to each coupled cavity; determining the corresponding slow light delay time according to the carrier concentration in the active region.

[0047] In an embodiment of the present disclosure, by utilizing the relationship between the carrier concentration and the refractive index, the refractive index is changed by adjusting the injection current, thereby regulating the slow light delay time. The slow light delay time can be precisely controlled, the cumulative phase can be optimized, and the phase matching between the light fed back from each coupled cavity to the central cavity and the original light beam in the central cavity can be ensured.

[0048] Based on the above embodiment, each coupled cavity includes: an oxidation confinement hole, configured to regulate the phase of the corresponding second light beam by controlling the aperture size of the oxidation confinement hole to generate a vernier effect. Through the vernier effect, by finely adjusting the oxidation confinement hole corresponding to each coupled cavity, the mode of the light beam can be significantly changed.

[0049] According to an embodiment of the present disclosure, the N coupled cavity groups are symmetrically distributed around the central cavity.

[0050] In an embodiment of the present disclosure, N coupling cavity groups are symmetrically distributed around the central cavity, ensuring that the distances and optical properties between the coupling cavities are the same, providing a uniform feedback path and intensity. This enables photons to reflect multiple times within the cavity and accumulate phase, enhancing the gain at a specific frequency.

[0051] According to an embodiment of the present disclosure, it further includes: a radio frequency electrode connected to the central cavity. The back electrode semi-wraps around the radio frequency electrode.

[0052] At least two DC electrodes serve as the front electrodes of the coupling cavities. One DC electrode is connected to one coupling cavity; wherein, the radio frequency electrode and the at least two DC electrodes are coplanar.

[0053] There are also at least two ground electrodes, and one ground electrode is connected to one coupling cavity.

[0054] By independently setting the electrodes in the coupling cavities, the slow light delay time of each coupling cavity can be independently controlled, which is beneficial for precisely regulating the slow light time in each coupling cavity.

[0055] According to an embodiment of the present disclosure, it further includes: an epitaxial structure, on which the central cavity and N coupling cavity groups are disposed.

[0056] In some possible embodiments, the size of the central cavity can be 4μm×4μm.

[0057] When the number of N is 6, the cavity length of the coupling cavity is 12.5μm. This can meet the requirements of slow light feedback. Among them, the number of N can be determined according to the electrode arrangement and electrode size, ensuring that the number of coupling cavities is an even number, ensuring the symmetry between the coupling cavities and the consistency of the resonance effect, which is beneficial for achieving a more stable slow light feedback effect. But it is not limited thereto. As Figure 2 shown, N can be 2, that is, the number of coupling cavities is 4. The central cavity is connected to the 4 coupling cavities through oxidation confinement holes. In the direction of each coupling cavity, a leaky traveling wave (with a length of Lc) is introduced by this kind of coupled waveguide structure. In the transverse coupled waveguide, light propagates vertically and its speed slows down. In each coupling cavity, the slow light propagates back and forth multiple times between the end of the coupling cavity and the central cavity at the group velocity of n g . The slow light is completely reflected back at the corresponding oxidation confinement hole and is coupled into the central cavity with a coupling ratio. The round-trip period between the central cavity and the distal end of the mth coupling cavity satisfies the relational expression , where, n g = fn, fn is the group refractive index, n and f are the average material refractive index and the slow light factor respectively, and c is the speed of light.

[0058] The principle of enhancing the modulation bandwidth with a single coupled cavity is to control the delay of the slow light feedback of the PPR. When the optical feedback of each of the multiple laterally coupled cavities is moderate, the entire system will redistribute the optical field distribution, and the optical feedback of each coupled cavity will enter the central cavity in a funnel-like shape. In this embodiment, by introducing the vernier effect, a large change in the central cavity graduation is caused by the change of each small value of the coupled cavity in the oxidation confinement hole design, enhancing the optical power output, and realizing single-mode characteristics while obtaining a high modulation bandwidth.

[0059] Therefore, the vertical cavity surface emitting laser based on a coupled cavity in this embodiment breaks the limitation of the 3dB modulation bandwidth of traditional structure VCSELs affected by carrier-photon resonance effect, thermal effect, parasitic resistance, capacitance, and nonlinear gain effect (such as relaxation oscillation). The new coupled cavity structure VCSELs introduce the slow light feedback effect, reduce the laser speed, and achieve fine control of the laser feedback, so as to increase the modulation bandwidth by adding a new degree of freedom to the laser design. The vernier effect is usually applied in high-precision and short-distance ranging. In optics, the vernier effect is used to obtain a comb-like spectrum, and it is applied to tunable semiconductor lasers to expand the wavelength tuning range. In this embodiment, the oxidation aperture of VCSELs is enhanced through the vernier effect to achieve a large optical power output and realize single-mode output under a high modulation bandwidth.

[0060] The second aspect of the present disclosure provides a method for manufacturing a vertical cavity surface emitting laser based on a coupled cavity, including: epitaxial growth to prepare an epitaxial structure.

[0061] Etching treatment is performed on the epitaxial structure to prepare a central cavity and N groups of coupled cavities. Among them, the central cavity is used to generate a first light beam; for the N groups of coupled cavities, each group of coupled cavities includes two coupled cavities, and the two coupled cavities are symmetrically distributed on both sides of the central cavity and are coupled to the central cavity. Each coupled cavity is configured to receive the first light beam, and after multiple reflections of the first light beam, a second light beam is output to the central cavity. Among them, by controlling the phase of the second light beam corresponding to each coupled cavity, the phases of the 2N second light beams are adjusted to match the phase of the first light beam, so that the 2N second light beams and the first light beam generate a photon-photon resonance effect.

[0062] Figure 3 The flowchart of the method according to the embodiment of the present disclosure is schematically shown.

[0063] As Figure 3 shown, S1: Prepare an epitaxial wafer;

[0064] S2: Etch the central cavity and 4 coupled cavities on the upper part of the epitaxy;

[0065] S3: Evaporate the front electrode, thin the substrate, and evaporate the back electrode.

[0066] Among them, the shape of the coupling cavity is not limited to a rectangle, and the width of the oxidation confinement hole at the connection between the coupling cavity and the central cavity is smaller than the width of the side of the coupling cavity away from the oxidation confinement hole. The raw materials of the epitaxial wafer in S1 are shown in Table 1.

[0067] Table 1-1

[0068]

[0069]

[0070] Table 1-2

[0071]

[0072] Table 1-3

[0073]

[0074] Table 1-4

[0075]

[0076] In the embodiments of the present disclosure, the preparation method is simple and the cost is low. In addition to the above-mentioned epitaxial structure of the quantum well, the present disclosure also covers an epitaxial structure with quantum dots as the active region. At the same time, based on the above-mentioned epitaxial structure, it is not limited to meeting the gain of 850 nm lasers.

[0077] Those skilled in the art can understand that the features recited in the various embodiments and / or claims of the present disclosure can be combined and / or 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.

[0078] The above describes the embodiments of the present disclosure. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the various embodiments are described separately above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A vertical cavity surface emitting laser based on a coupled cavity, characterized in that: include: a central cavity for generating a first light beam; N coupling cavity groups, each coupling cavity group includes two coupling cavities, the two coupling cavities are symmetrically distributed on both sides of the central cavity and coupled to the central cavity; each coupling cavity is configured to receive the first light beam, reflect the first light beam multiple times, and output a second light beam to the central cavity; By controlling the phase of the second light beam corresponding to each coupling cavity, the phases of the 2N second light beams are adjusted to match the phase of the first light beam, so that the 2N second light beams and the first light beam produce a photon-photon resonance effect.

2. The coupled cavity vertical cavity surface emitting laser according to claim 1, characterized in that: Each coupling cavity is further configured as: The phase of the corresponding second light beam is regulated by controlling the slow light delay time of each coupling cavity.

3. The coupled cavity vertical cavity surface emitting laser according to claim 2, characterized in that: The controlling of the slow light delay time corresponding to each coupling cavity comprises: The injection current corresponding to each coupling cavity is controlled to adjust the corresponding slow light delay time.

4. The coupled cavity vertical cavity surface emitting laser according to claim 3, characterized in that: The controlling the injection current corresponding to each coupling cavity to adjust the corresponding slow light delay time comprises: Controlling the carrier concentration of the active region corresponding to each coupling cavity by controlling the injection current corresponding to each coupling cavity; The corresponding slow light delay time is determined according to the carrier concentration of the active region.

5. The coupled cavity vertical cavity surface emitting laser according to claim 1, characterized in that: Each coupling cavity comprises: The oxidation limiting hole is configured to adjust the phase of the second light beam corresponding to each coupling cavity by controlling the aperture size of the oxidation limiting hole.

6. The coupled cavity vertical cavity surface emitting laser according to claim 1, characterized in that: The N coupling cavity groups are symmetrically distributed around the central cavity.

7. The coupled-cavity straight-cavity surface-emitting laser according to claim 1, characterized in that: Also includes: A radio frequency electrode connected to the central cavity; at least two DC electrodes, one DC electrode being connected to the one coupling cavity; Wherein, the radio frequency electrode and the at least two direct current electrodes are coplanar.

8. The coupled cavity vertical cavity surface emitting laser according to claim 1, characterized in that: Also includes: At least two ground electrodes, one ground electrode is connected to the one coupling cavity.

9. The coupled cavity vertical cavity surface emitting laser according to claim 1, characterized in that: Also includes: The epitaxial structure, the central cavity and the N coupling cavity groups are arranged on the epitaxial structure.

10. A method for preparing a vertical cavity surface emitting laser based on a coupled cavity, characterized in that: include: Epitaxial growth to prepare epitaxial structures; Etching the epitaxial structure to prepare a central cavity and N coupling cavity groups, wherein the central cavity is used to generate a first light beam; The N coupling cavity groups, each coupling cavity group includes two coupling cavities, the two coupling cavities are symmetrically distributed on both sides of the central cavity and coupled to the central cavity; each coupling cavity is configured to receive the first light beam, reflect the first light beam multiple times, and output a second light beam to the central cavity; By controlling the phase of the second light beam corresponding to each coupling cavity, the phases of the 2N second light beams are adjusted to match the phase of the first light beam, so that the 2N second light beams and the first light beam produce a photon-photon resonance effect.

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