A semiconductor laser with dual-wavelength output and its preparation method
By combining the grating structure of the side-coupled grating and the ridge grating and etching grooves to reduce mode competition, the process difficulty and high cost problems of dual-wavelength output are solved, and stable and efficient dual-wavelength laser output is achieved.
Patent Information
- Application Number
- CN202311721711.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-14
- Publication Date
- 2025-09-26
- Estimated Expiration
- 2043-12-14
AI Technical Summary
The existing technology for achieving dual-wavelength output has high preparation costs and is difficult, and there are problems such as low coupling coefficient and low reflection peak due to mode competition.
A grating structure combining side-coupled gratings and ridge gratings is adopted. By etching grooves, mode competition is reduced, the coupling coefficient is enhanced, and the stability of dual-wavelength output is ensured.
The stability of dual-wavelength output and the improvement of coupling coefficient are achieved, and the process difficulty and cost are reduced.
Smart Images
Figure CN117913650B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of semiconductor laser technology, and in particular to a semiconductor laser with dual-wavelength output and a preparation method thereof. Background Art
[0002] Raman spectroscopy has become a well-established and widely used analytical tool in laboratories and practical applications. However, Raman spectrometers are subject to interference from background signals during operation, such as fluorescence from the sample being tested, sunlight, blackbody radiation, incandescent lamps, fluorescent lamps, or energy-saving lamps. This interference can severely affect the identification of characteristic peaks in the Raman spectrum. Shifted differential Raman spectroscopy (SERDS) can overcome this problem. The position of the characteristic peaks in the Raman spectrum is fixedly related to the position of the spectrum of the excitation light source. When the excitation light frequency shifts, the Raman peaks shift accordingly, while the spectra of sunlight, artificial light sources, and fluorescence remain unchanged. By recording Raman spectra at two slightly shifted wavelengths and performing a differential process on the two spectra, the stimulated emission spectrum and background noise are completely offset in the resulting differential spectrum, leaving a difference image between the Raman spectrum and its own shifted spectrum. The Raman spectrum is then restored using a denoising convolution algorithm.
[0003] However, achieving dual wavelengths is difficult with existing technologies. Due to strong mode competition between two Bragg structures with different periods, the lasing wavelength corresponding to one grating group experiences significant loss and a low coupling coefficient, resulting in high and low peaks in the output dual wavelengths. The low intensity of the low peak spectrum further affects the detection results. Furthermore, mode competition can cause the overall reflection peak to be low, meaning the output reflection peak remains relatively low.
[0004] The currently more mature Y-branch structure achieves dual-wavelength output by coupling two distributed Bragg reflectors (DBRs). However, due to the presence of large-angle branches, the process preparation cost is high and difficult. Summary of the Invention
[0005] The embodiments of the present application provide a semiconductor laser with dual-wavelength output to solve the problem of high cost and difficulty in the process of achieving dual-wavelength output in the prior art.
[0006] Correspondingly, an embodiment of the present application also provides a method for preparing a semiconductor laser with dual-wavelength output, to ensure the implementation and application of the above method.
[0007] In order to solve the above technical problems, an embodiment of the present application discloses a dual-wavelength output semiconductor laser, including a grating structure, the grating structure including a side-coupling grating and a ridge grating; the side-coupling grating includes two groups of side gratings with the same period and duty cycle, and a connecting waveguide arranged between the two groups of side gratings; the ridge grating is etched on the connecting waveguide; a groove is etched between the side grating and the ridge grating.
[0008] In the embodiments of the present application, a ridge grating and a side-coupling grating are combined to ensure that the grating reflection spectrum has two reflection peaks. By varying the width of the side-coupling grating, the coupling coefficient of the corresponding grating can be enhanced, making the coupling strength of the side-coupling grating and the ridge grating substantially the same, thereby achieving dual-peak lasing with substantially consistent intensity. Etching a groove between the side-coupling grating and the ridge grating can reduce mode competition between the side-coupling grating and the ridge grating. Therefore, using this grating structure, the laser can achieve stable dual-wavelength output, effectively reducing the mode competition caused by the dual Bragg grating structure and improving the coupling coefficient.
[0009] Preferably, the etching depths of the side coupling grating and the ridge grating are the same, which can reduce the difficulty of the process.
[0010] Preferably, the grating structure is a uniform grating structure with an order of 5-20 and a duty cycle of 0.3-0.7, which can determine a longitudinal mode with a narrow line width and a high side mode suppression ratio.
[0011] Preferably, the period interval between the side-coupling grating and the ridge grating is 1-3 nm, which can precisely control the spacing between two reflection peaks in the grating reflection spectrum to achieve wavelength control.
[0012] Preferably, an electrode window is opened in the middle of the ridge grating.
[0013] Preferably, the grating structure is formed by etching a stacked structure; the stacked structure comprises, from bottom to top, a substrate layer, a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding layer, and a cap layer.
[0014] The present application also discloses a method for preparing the dual-wavelength output semiconductor laser. The method comprises:
[0015] Using a preset photolithography pattern, the pre-generated epitaxial structure is etched to generate ridge waveguides and grooves;
[0016] The epitaxial structure with ridge waveguide and groove is etched using the preset second-plate photolithography pattern to generate a side-coupled grating and a ridge grating;
[0017] The lateral coupling grating includes two groups of lateral gratings with the same period and duty cycle, and a connecting waveguide arranged between the two groups of lateral gratings; the ridge grating is etched on the connecting waveguide; and the groove is arranged between the lateral grating and the ridge grating.
[0018] Preferably, after etching the epitaxial structure having the ridge waveguide and the groove using the preset second-plate photolithography pattern to generate the side-coupled grating and the ridge grating, the preparation method further comprises:
[0019] A SiO2 passivation layer was grown on the ridge grating using plasma enhanced chemical vapor deposition.
[0020] Using three-plate photolithography patterns, the area outside the electrode window is covered with photoresist, and the SiO2 passivation layer is corroded with buffered oxide etching solution to form an electrode window.
[0021] Preferably, before etching the pre-generated epitaxial structure using a preset photolithography pattern to generate the ridge waveguide and the groove, the preparation method further comprises:
[0022] The material is grown on the substrate layer by adopting metal organic chemical vapor deposition method, and the lower cladding layer, the lower waveguide layer, the active layer, the upper waveguide layer, the upper cladding layer and the cap layer are sequentially epitaxially grown.
[0023] Additional aspects and advantages of the embodiments of the present application will be given in the following description, which will become apparent from the following description or be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:
[0025] Figure 1 A top view of a semiconductor laser with dual wavelength output provided in an embodiment of the present application;
[0026] Figure 2 A schematic structural diagram of a semiconductor laser with dual-wavelength output provided in an embodiment of the present application;
[0027] Figure 3 A schematic cross-sectional view of a semiconductor laser with dual-wavelength output provided in an embodiment of the present application;
[0028] Figure 4 A schematic diagram of the reflection spectrum of the grating structure provided in an embodiment of the present application;
[0029] Figure 5 A schematic structural diagram of a laminated structure provided in an embodiment of the present application;
[0030] Figure 6A flow chart of a method for preparing a dual-wavelength output semiconductor laser provided in an embodiment of the present application;
[0031] Figure 7 This is an overall flow chart for preparing a semiconductor laser with dual-wavelength output provided in an embodiment of the present application.
[0032] Among them, 1-lateral coupling grating; 1-1-lateral grating; 1-2-connecting waveguide; 2-groove; 3-ridge grating. DETAILED DESCRIPTION
[0033] The following describes embodiments of the present application in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application.
[0034] It will be understood by those skilled in the art that, unless expressly stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of this application refers to the presence of features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, "connected" or "coupled" as used herein may include wireless connections or wireless couplings. The term "and / or" used herein includes all or any units and all combinations of one or more associated listed items.
[0035] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention pertains. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless specifically defined as herein, will not be interpreted in an idealized or overly formal sense.
[0036] With regard to the technical problems existing in the prior art, the dual-wavelength output semiconductor laser and the preparation method thereof provided in this application are intended to solve at least one of the technical problems in the prior art.
[0037] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.
[0038] The present application embodiment provides a possible implementation method, such as Figure 1 As shown, a top view of a semiconductor laser with dual wavelength output is provided.
[0039] like Figure 1 As shown, the semiconductor laser includes a grating structure, which includes a side coupling grating 1 and a ridge grating 3; the side coupling grating 1 includes two groups of side gratings 1-1 with the same period and duty cycle, and a connecting waveguide 1-2 arranged between the two columns of side gratings 1-1; the ridge grating 3 is etched on the connecting waveguide 1-2; a groove 2 is etched between the side grating 1-1 and the ridge grating 3.
[0040] Figure 2 FIG. 1 shows a schematic diagram of the structure of a semiconductor laser with dual wavelength output in an embodiment of the present application. Figure 1 and Figure 2 As shown, the grating structure of the semiconductor laser in the embodiment of the present application adopts a surface high-order grating. Compared with the buried grating, the surface grating generally has a larger etching depth to increase the overlap between the grating area and the lateral light field, thereby obtaining sufficient coupling strength. The grating structure in the embodiment of the present application includes two parts: a side coupling grating 1 and an intermediate ridge grating 3. The side coupling grating 1 is composed of two groups of gratings with the same period and duty cycle on both sides and a connecting waveguide 1-2 in the middle. The ridge grating 3 is etched on the intermediate connecting waveguide 1-2, and the width of the ridge grating 3 is smaller than the width of the connecting waveguide 1-2. The above design can well ensure that the grating reflection spectrum has two reflection peaks. Since there is severe mode competition between the two Bragg grating structures (lateral coupling grating 1 and ridge grating 3), even if a single peak intensity is fine-tuned, the peak intensity is still low. Therefore, in the embodiment of the present application, a groove 2 is etched in the rectangular waveguide area between the ridge grating 3 and the lateral coupling grating 1 to reduce the mode competition between the lateral coupling grating 1 and the ridge grating 3. From the simulation data, it can be seen that the coupling coefficient is improved by 12.84 cm -1 , the percentage is about 57.7%.
[0041] In the embodiment of the present application, the combination of the ridge grating 3 and the side-coupling grating 1 can effectively ensure that the grating reflection spectrum has two reflection peaks. By changing the width of the side-coupling grating 1, the coupling coefficient of the corresponding grating can be enhanced, so that the coupling strength of the side-coupling grating 1 and the ridge grating 3 is substantially the same, and dual-peak lasing with substantially consistent intensity can be achieved. Etching a groove 2 between the side-coupling grating 1 and the ridge grating 3 can reduce the mode competition between the side-coupling grating 1 and the ridge grating 3. Therefore, using the above-mentioned grating structure, the laser can achieve stable dual-wavelength output, effectively reducing the mode competition caused by the dual Bragg grating structure and improving the coupling coefficient.
[0042] Figure 3 A schematic cross-sectional view of a semiconductor laser with dual wavelength output according to an embodiment of the present application is shown. In an optional embodiment, as shown in FIG. Figure 3 As shown, the etching depths h of the side coupling grating 1 and the ridge grating 3 are the same, which can reduce the difficulty of the process.
[0043] The two groups of lateral gratings 1 - 1 of the lateral coupling grating 1 are Bragg gratings with the same period, the same duty cycle and the same etching depth.
[0044] In an optional embodiment, the grating structure is a uniform grating structure with an order of 5-20 and a duty cycle of 0.3-0.7.
[0045] By designing the above-mentioned grating order and duty cycle, a longitudinal mode with narrow line width and high side mode suppression ratio can be determined.
[0046] In an optional embodiment, the period interval between the side coupling grating 1 and the ridge grating 3 is 1-3 nm.
[0047] By designing the above periodic interval, the distance between the two reflection peaks in the grating reflection spectrum can be precisely controlled to achieve wavelength control.
[0048] Figure 4 The reflection spectrum of the grating structure is shown in Figure 2, where the horizontal axis is the wavelength (nm) and the vertical axis is the reflectivity. eff Λ=mλ (m=1, 2,...), where n eff is the effective refractive index of the grating, Λ is the grating period, m is the grating order, and λ is the wavelength corresponding to the reflection peak of the Bragg grating. Since the grating structure contains two layers of gratings with different periods, there will be two Bragg reflection peaks in the reflection spectrum. The spacing between the two Bragg reflection peaks can be expressed by Δλ = 2n eff |Λ1-Λ2| calculation,
[0049] For example, the side coupling grating 1 and the ridge grating 3 adopt 11-order gratings. According to the above formula 2n effΛ=mλ(m=1, 2, . . . ), and finally the period of the side coupling grating 1 is 1.264 um, and the period of the ridge grating 3 is 1.262 um.
[0050] Furthermore, the difference between the two excitation wavelengths for solid and liquid measurements can be 3-10 cm -1 (When the wavelength of the emitted laser is 785 nm, it is 0.2-0.6 nm.) Therefore, the difference between the three periods of the ridge grating and the one period of the side coupling grating in the embodiment of the present application is 2 nm, achieving a wavelength interval of less than 1 nm.
[0051] In an optional embodiment, an electrode window is opened in the middle of the ridge grating 3 .
[0052] In an optional embodiment, if Figure 5 As shown, the grating structure is etched from a stacked structure; the stacked structure includes a substrate layer, a lower cladding layer, a lower waveguide layer, an active layer (QW), an upper waveguide layer, an upper cladding layer, and a cap layer from bottom to top.
[0053] Optionally, the material of the substrate layer and the cap layer is GaAs, the material of the lower cladding layer, the lower waveguide layer, the upper waveguide layer and the upper cladding layer is AlGaAs, and the material of the active layer is GaAsP.
[0054] After carrier injection, the active layer will generate photons of various frequencies through spontaneous radiation within its gain spectrum bandwidth. All photons that meet the phase conditions will continuously resonate in the laser, and will be amplified every time they pass through the active layer. Eventually, through mode competition, those photons with the lowest threshold will be the first to achieve lasing and clamp the gain. For a Bragg feedback laser, the wavelength where the Bragg grating reflection peak is located will obtain maximum feedback and minimize loss, becoming the lasing wavelength. In an embodiment of the present application, the grating structure selects two reflection peaks, and the wavelengths where these two reflection peaks are located will eventually become the lasing wavelengths at the same time because they have the lowest loss at the same time, or the loss is very close.
[0055] The embodiment of the present application is a monolithically integrated dual-wavelength semiconductor laser, in which the grating structure shares the same cavity length to achieve dual-wavelength output.
[0056] The present application also provides a method for preparing the dual-wavelength output semiconductor laser. Figure 6 As shown, the preparation method includes:
[0057] Step 601 : etching the pre-generated epitaxial structure using a preset photolithography pattern to generate a ridge waveguide and a groove 2 .
[0058] Reference Figure 7In the embodiment of the present application, a photoresist is used as a buried layer on the pre-generated epitaxial structure, an image of a photolithography pattern is photoetched, and then the ridge waveguide and the groove 2 are etched using an inductively coupled plasma (ICP) etching process.
[0059] Step 602 : etching the epitaxial structure having the ridge waveguide and the groove 2 using a preset second-plate photolithography pattern to generate the side-coupling grating 1 and the ridge grating 3 .
[0060] After etching the ridge waveguide and the groove 2, a second photolithography pattern is photoetched on the epitaxial structure, and then the side coupling grating 1 and the ridge grating 3 are etched using an ICP process.
[0061] Among them, the lateral coupling grating 1 includes two groups of lateral gratings 1-1 with the same period and duty cycle, and a connecting waveguide 1-2 arranged between the two groups of lateral gratings 1-1; the ridge grating 3 is etched on the connecting waveguide 1-2; and the groove 2 is arranged between the lateral grating 1-1 and the ridge grating 3.
[0062] In addition, the grating structure manufactured according to the above method in the embodiment of the present application is compact and easy to integrate. It can be prepared by traditional photolithography or holographic exposure methods. The etching depth of the ridge waveguide and the groove 2 uses the same value, the process is simple, and the cost is low.
[0063] The semiconductor laser generated by etching according to the above-mentioned etching steps uses a combination of a ridge grating 3 and a side-coupling grating 1 to effectively ensure that the grating reflection spectrum has two reflection peaks. By varying the width of the side-coupling grating 1, the coupling coefficient of the corresponding grating can be enhanced, so that the coupling strength of the side-coupling grating 1 and the ridge grating 3 is substantially the same, thereby achieving dual-peak lasing with substantially consistent intensity. Etching a groove 2 between the side-coupling grating 1 and the ridge grating 3 can reduce mode competition between the side-coupling grating 1 and the ridge grating 3. Therefore, using the above-mentioned grating structure, the laser can achieve stable dual-wavelength output, effectively reducing the mode competition caused by the dual Bragg grating structure and improving the coupling coefficient.
[0064] In an optional embodiment, before etching the pre-generated epitaxial structure using a preset photolithography pattern to generate the ridge waveguide and the groove 2, the method further includes:
[0065] The material is grown on the substrate layer by adopting metal organic chemical vapor deposition method, and the lower cladding layer, the lower waveguide layer, the active layer, the upper waveguide layer, the upper cladding layer and the cap layer are sequentially epitaxially grown.
[0066] Optionally, the material of the substrate layer and the cap layer is GaAs, the material of the lower cladding layer, the lower waveguide layer, the upper waveguide layer and the upper cladding layer is AlGaAs, and the material of the active layer is GaAsP.
[0067] In an optional embodiment, if Figure 7 As shown, after etching the epitaxial structure having the ridge waveguide and the groove 2 using the preset second-plate photolithography pattern to generate the side-coupling grating 1 and the ridge grating 3, the preparation method further includes:
[0068] A SiO2 passivation layer was grown on the ridge grating using plasma enhanced chemical vapor deposition.
[0069] Using three-plate photolithography patterns, the area outside the electrode window is covered with photoresist, and the SiO2 passivation layer is corroded with buffered oxide etching solution to form an electrode window.
[0070] After etching to form the side-coupling grating 1 and ridge grating 3, the photoresist is removed. The ridge grating 3 region is then filled and covered with a dielectric material (such as silicon oxide, silicon nitride, or styrene-propylcyclobutene). A SiO2 passivation layer is grown on the cross-section using plasma-enhanced chemical vapor deposition (PECVD). The areas of the SiO2 passivation layer not covered by the photoresist are etched using a buffered oxide etchant (BOE), creating a window for the P-side electrode. The dielectric filling and covering of the ridge grating 3 region prevents the metal electrode from sputtering into the grooves of the ridge grating 3.
[0071] In an optional embodiment, if Figure 7 As shown, a SiO2 passivation layer is grown on the ridge grating using a plasma enhanced chemical vapor deposition method; a three-plate photolithography pattern is used to cover the area outside the electrode window with photoresist, and the SiO2 passivation layer is etched using a buffered oxide etchant to form the electrode window. The preparation method further includes:
[0072] Ti, Pt, and Au electrode metals are plated on the P-side (the upper surface of the grating structure) by magnetron sputtering to form a P-side electrode layer with a thickness of 250-400 nm, and then annealed;
[0073] The substrate layer is thinned, polished, and the N-side (upper surface of the grating structure) is pretreated. An N-side electrode layer is sputtered on the substrate. The thickness of the N-side electrode layer is 500-700 nm, and annealed.
[0074] Cleavage, coating.
[0075] The preparation method of the embodiment of the present application can prepare the above Figures 1 to 5 For a detailed functional description of the dual-wavelength output semiconductor laser, please refer to the description of the corresponding dual-wavelength output semiconductor laser shown in the previous text, which will not be repeated here.
[0076] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the above-mentioned disclosed concepts. For example, a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.
Claims
1. A dual-wavelength output semiconductor laser comprising a grating structure, characterized in that: The grating structure includes a side-coupling grating and a ridge grating, wherein the side-coupling grating and the ridge grating have different periods; The lateral coupling grating includes two groups of lateral gratings with the same period and duty cycle, and a connecting waveguide arranged between the two groups of lateral gratings; The ridge grating is generated by etching on the connecting waveguide; A groove is etched between the side grating and the ridge grating.
2. The dual-wavelength output semiconductor laser according to claim 1, characterized in that: The etch depths of the side coupling grating and the ridge grating are the same.
3. The dual-wavelength output semiconductor laser according to claim 1, characterized in that: The grating structure is a uniform grating structure with an order of 5-20 and a duty cycle of 0.3-0.
7.
4. The dual-wavelength output semiconductor laser according to claim 1, characterized in that: The period interval between the side coupling grating and the ridge grating is 1-3 nm.
5. The dual-wavelength output semiconductor laser according to claim 1, characterized in that: An electrode window is provided in the middle of the ridge grating.
6. The dual-wavelength output semiconductor laser according to claim 1, characterized in that: The grating structure is formed by etching a stacked structure; The stacked structure comprises, from bottom to top, a substrate layer, a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding layer, and a cap layer.
7. A method for preparing a dual-wavelength output semiconductor laser according to any one of claims 1 to 6, characterized in that: The preparation method comprises: Using a preset photolithography pattern, the pre-generated epitaxial structure is etched to generate ridge waveguides and grooves; Etching the epitaxial structure having the ridge waveguide and the groove using a preset second-plate photolithography pattern to generate a side-coupled grating and a ridge grating; The lateral coupling grating includes two groups of lateral gratings with the same period and duty cycle, and a connecting waveguide arranged between the two groups of lateral gratings; the ridge grating is etched on the connecting waveguide; and the groove is arranged between the lateral grating and the ridge grating.
8. The preparation method according to claim 7, characterized in that After etching the epitaxial structure having the ridge waveguide and the groove using the preset second photolithography pattern to generate the side-coupled grating and the ridge grating, the preparation method further includes: growing a SiO2 passivation layer on the ridge grating by using a plasma enhanced chemical vapor deposition method; The electrode window is formed by using three photolithography patterns, covering the area outside the electrode window with photoresist, and etching the SiO2 passivation layer with a buffered oxide etching solution.
9. The preparation method according to claim 7, characterized in that Before etching the pre-generated epitaxial structure using a preset photolithography pattern to generate the ridge waveguide and the groove, the preparation method further includes: The material is grown on the substrate layer by adopting metal organic chemical vapor deposition method, and the lower cladding layer, the lower waveguide layer, the active layer, the upper waveguide layer, the upper cladding layer and the cap layer are sequentially epitaxially grown.