Dual-wavelength semiconductor laser based on active trapezoidal multimode interference coupler and preparation method thereof

Abstract

The invention provides a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler and a preparation method of the dual-wavelength semiconductor laser. The dual-wavelength semiconductor laser comprises a large-size active trapezoidal multimode interference coupler, the two input waveguides are connected to the input end of the large-size active trapezoidal multimode interference coupler; the output waveguide is connected to the output end of the large-size active trapezoidal multimode interference coupler; wherein grating structures with different periods are arranged on the two input waveguides, and the grating structures are lateral coupling gratings. Through the design of the large-size active trapezoidal multimode interference coupler, the wavelengths of the two input waveguides can be coupled into the output waveguide to realize dual-wavelength laser output, the gain area of the laser is increased, and the output power of the laser is ensured. Through the width design of the output end and the input end of the large-size active trapezoidal multimode interference coupler, the coupling efficiency of the output end is improved, and stable dual-wavelength output is realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler and its fabrication method. Background Technology

[0002] Semiconductor lasers, due to their small size, high efficiency, long lifespan, and ease of modulation, have become the core light source in modern optoelectronic technology. With the continuous expansion of application fields, single-wavelength laser output can no longer meet the ever-increasing technological demands. Against this backdrop, dual-wavelength semiconductor lasers have emerged, capable of simultaneously or alternately outputting two different wavelengths of laser light on a single device. This achieves functional integration and performance expansion, becoming an important research direction in the field of laser technology.

[0003] Currently, there are many ways to realize dual-wavelength semiconductor lasers. Researchers utilize the beam combining function of multimode interference couplers and prepare DBR gratings at both ends of the input waveguide to form a resonant cavity. By leveraging the self-image effect of the MMI (multimode interference coupler), two wavelengths are coupled to the same output waveguide, thereby achieving dual-wavelength output.

[0004] However, in existing dual-wavelength semiconductor lasers, the Microwave Interface (MMI) is typically used as a passive structure and is relatively small. To avoid photon coupling between the two input waveguides, a curved waveguide needs to be introduced at the MMI input, increasing losses. In recent years, active MMI structures have shown potential in improving laser output capability due to their increased active area. Using a large-size MMI as an active structure not only increases the gain area to ensure output power, but the width of the MMI also allows for a sufficiently large input waveguide spacing, avoiding coupling caused by smaller waveguide spacing. However, because the two input waveguides operate at different wavelengths, the self-image points of the two wavelengths within the MMI shift. For small-size MMIs, this shift is negligible, but in large-size MMIs, the shift effect of the self-image points becomes significant, severely reducing the coupling efficiency at the output. Summary of the Invention

[0005] In view of this, the present invention provides a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler and its fabrication method. The large-size active trapezoidal multimode interference coupler increases the active area of ​​the laser to ensure the output power of the dual-wavelength semiconductor laser. Furthermore, the shorter output end of the large-size active trapezoidal multimode interference coupler enhances the confinement of the optical field, reduces the self-image point shift that occurs with the increased size of the multimode interference coupler, and improves the coupling efficiency at the output end. In addition, the wider input end of the large-size active trapezoidal multimode interference coupler ensures sufficient spacing between the two input waveguides, avoiding mutual coupling between the waveguides, thus providing a new approach to achieving stable dual-wavelength laser output.

[0006] According to a first aspect of the present invention, a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler is provided, comprising: a large-size active trapezoidal multimode interference coupler; two input waveguides connected to the input ends of the large-size active trapezoidal multimode interference coupler; and an output waveguide connected to the output end of the large-size active trapezoidal multimode interference coupler; wherein the two input waveguides are provided with grating structures with different periods, and the grating structures are laterally coupled gratings.

[0007] In some embodiments, the input width of the large-size active trapezoidal multimode interference coupler is greater than the output width.

[0008] In some embodiments, the two input waveguides are used to oscillate and generate two different wavelengths of laser light, which are then input to the active trapezoidal multimode interference coupler for coupling. The output waveguide is used to output the dual-wavelength laser light obtained after coupling.

[0009] In some embodiments, the input width of the large-size active trapezoidal multimode interference coupler is 10μm~60μm, the output width is 5μm~40μm, and the length is 500μm~3000μm.

[0010] In some embodiments, the ridge width of the input waveguide and the output waveguide is 2μm to 20μm.

[0011] In some embodiments, the spacing between the two input waveguides is 5 μm to 20 μm.

[0012] In some embodiments, the length of the input waveguide is 1000μm~2000μm, and the length of the output waveguide is 500μm~1500μm.

[0013] In some embodiments, the etching depth of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide is 0.5 μm to 2 μm.

[0014] In some embodiments, the dual-wavelength semiconductor laser further includes a layer structure, wherein: the layer structure comprises, from bottom to top, a substrate, an N-type confinement layer, an N-type waveguide layer, an active gain layer, a P-type waveguide layer, and a P-type confinement layer; the input waveguide, the large-size active trapezoidal multimode interference coupler, the output waveguide, and the lateral coupling grating are formed by etching the layer structure from top to bottom.

[0015] According to a second aspect of the present invention, a method for fabricating a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler is provided, comprising: sequentially fabricating an N-type confinement layer, an N-type waveguide layer, an active gain layer, a P-type waveguide layer, and a P-type confinement layer on a substrate; forming a pattern of an input waveguide, a large-size active trapezoidal multimode interference coupler, an output waveguide, and a lateral coupling grating on the P-type confinement layer by spin-coating photoresist, photolithography, development, etching, and photoresist removal; growing an insulating layer on the surface of the pattern, and forming electrode windows on the upper part of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide; depositing a P-plane metal electrode layer on the surface of the insulating layer and the electrode window; thinning and polishing the back side of the substrate, and then depositing an N-plane metal electrode layer on the back side of the substrate to obtain a wafer with completed electrode fabrication; and cleaving and packaging the wafer with completed electrode fabrication to obtain the dual-wavelength semiconductor laser.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler provided by this invention, through the design of a large-size active trapezoidal multimode interference coupler, not only couples the wavelengths of the two input waveguides to the output waveguide to achieve dual-wavelength laser output, but also increases the laser's gain area, ensuring the laser's output power. The narrower output end of the large-size active trapezoidal multimode interference coupler enhances the confinement of the optical field and improves the coupling efficiency at the output end. The wider input end of the large-size active trapezoidal multimode interference coupler avoids unfavorable coupling caused by the two input waveguides being too close, thus achieving stable dual-wavelength output. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a schematic diagram of the overall structure of a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the layer structure of a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the fabrication process of a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler according to an embodiment of the present invention.

[0021] Figure 4 This is a comparison of the transmittance of trapezoidal MMI and rectangular MMI in a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler according to an embodiment of the present invention.

[0022] Figure 5 The output spectrum of a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler is shown in an embodiment of the present invention.

[0023] Figure 6 This is a power-current-voltage curve of a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler, according to an embodiment of the present invention.

[0024] Explanation of reference numerals in the attached figures: 1. Output waveguide; 2. Active trapezoidal multimode interference coupler; 3. Input waveguide; 4. Lateral coupling grating; 5. Substrate; 6. N-type confinement layer; 7. N-type waveguide layer; 8. Active gain layer; 9. P-type waveguide layer; 10. P-type confinement layer. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] See Figure 1 and Figure 2 This invention provides a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler, the dual-wavelength semiconductor laser comprising: An output waveguide 1 is connected to the output of a large-size active trapezoidal multimode interference coupler 2; Large-size active trapezoidal multimode interference coupler 2; Two input waveguides 3 are connected to the input end of a large-size active trapezoidal multimode interference coupler 2; Among them, the two input waveguides 3 are provided with grating structures with different periods, and the grating structure is a laterally coupled grating 4.

[0027] It should be understood that the type of grating structure can be a laterally coupled grating or a DBR. In a preferred embodiment of the present invention, a laterally coupled grating is used.

[0028] In some embodiments, the input width of the large-size active trapezoidal multimode interference coupler is greater than the output width.

[0029] It should be understood that the large-size active trapezoidal multimode interferometer coupler 2 ensures the output power of the device by increasing the gain area. The wider end of the large-size active trapezoidal multimode interferometer coupler 2 is the input end to ensure sufficient input waveguide spacing and avoid mutual coupling between waveguides. The narrower end of the large-size active trapezoidal multimode interferometer coupler 2 is the output end, which can enhance the confinement of the optical field, suppress the offset of the self-image point, and improve the coupling efficiency at the output end. In some embodiments, the two input waveguides are used to oscillate and generate two different wavelengths of laser light, which are then input to the active trapezoidal multimode interference coupler for coupling. The output waveguide is used to output the dual-wavelength laser light obtained after coupling.

[0030] In some embodiments, the input width of the large-size active trapezoidal multimode interference coupler is 10μm~60μm, the output width is 5μm~40μm, and the length is 500μm~3000μm.

[0031] Preferably, the input terminal width is 27μm, the output terminal width is 19μm, and the length is 903μm.

[0032] In some embodiments, the ridge width of the input waveguide and the output waveguide is 2μm to 20μm.

[0033] Preferably, the ridge width of the input waveguide and the output waveguide is 3μm.

[0034] In some embodiments, the spacing between the two input waveguides is 5 μm to 20 μm.

[0035] Preferably, the spacing between the two input waveguides is 12 μm.

[0036] In some embodiments, the length of the input waveguide is 1000μm~2000μm, and the length of the output waveguide is 500μm~1500μm.

[0037] Preferably, the length of the input waveguide is 1500 μm.

[0038] Preferably, the length of the output waveguide is 597 μm.

[0039] In some embodiments, the etching depth of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide is 0.5 μm to 2 μm.

[0040] It should be understood that the etching depths of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide are adjusted according to the different epitaxial structures.

[0041] Preferably, the etching depth of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide is 1 μm.

[0042] In some embodiments, see Figure 2 The dual-wavelength semiconductor laser further includes a layer structure, wherein the layer structure comprises, from bottom to top: Substrate 5; N-type confinement layer 6; N-type waveguide layer 7; Active gain layer 8; P-type waveguide layer 9; P-type confinement layer 10; The input waveguide 1, the large-size active trapezoidal multimode interference coupler 2, the output waveguide 3, and the lateral coupling grating 4 are formed by etching the layer structure from top to bottom.

[0043] See Figure 3 The present invention also provides a method for fabricating a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler, comprising: An N-type confinement layer 6, an N-type waveguide layer 7, an active gain layer 8, a P-type waveguide layer 9, and a P-type confinement layer 10 are sequentially fabricated on substrate 5. Photoresist was spin-coated onto the surface of the P-type confinement layer 10, and ultraviolet contact lithography, development, coating, post-baking, magnetron sputtering, and lift-off were performed to create alignment marks. Photoresist was spin-coated again on the surface of the P-type confinement layer 10, and photolithography, development, coating, and post-baking were performed to prepare the pattern of the input waveguide 1, the large-size active trapezoidal multimode interference coupler, the output waveguide 3, and the lateral coupling grating 4 on the photoresist. The developed pattern is hardened, and then transferred to the wafer using ICP etching, followed by resist removal.

[0044] The patterned wafer is coated with SiO2, and then the photoresist is selected again and ultraviolet lithography is performed to overlay the electrode window. A P-side metal electrode layer is deposited on the P-type confinement layer 10 and then stripped. The side of substrate 5 away from the P-side metal electrode layer is thinned and polished to reduce the thickness of substrate 5 to 100-150 μm. The N-side metal electrode layer is then deposited on the thinned and polished side to obtain a wafer with completed electrode fabrication. A dual-wavelength semiconductor laser was fabricated by cleaving and packaging the wafer.

[0045] See Figure 4 The transmittance of trapezoidal and rectangular MMIs at different sizes is shown to illustrate that trapezoidal MMIs can improve the coupling efficiency at the output end. In a 2×1 rectangular MMI structure, when W1 = 9 μm, the MMI size is small, the self-image point offset between the two wavelengths is small, and its impact on transmittance is weak, with a transmittance of 58.7%. As W1 increases, the increased MMI size amplifies the offset effect between the self-image points of the two wavelengths, leading to increased loss when the two wavelengths are coupled to the output waveguide, and the transmittance gradually decreases, dropping to 42% when W1 = 33 μm. In a 2×1 trapezoidal MMI structure, with a fixed input width W1 = 27 μm, when W1 = 9 μm, the narrower output end enhances the lateral confinement of the optical field, allowing the wavelengths to be coupled more concentrated into the output waveguide, and the transmittance increases to 59.5%, similar to that of the smaller MMI, but its gain area is larger, ensuring the output power of the laser.

[0046] See Figure 5 The dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler was demonstrated to output reflection spectra at 370mA, 390mA, 410mA, and 420mA. The laser achieved stable dual-wavelength output under different currents.

[0047] See Figure 6 The power-current-voltage curves of a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler are shown. As the current increases, the power of the laser also increases. When the current is 790mA, the power reaches 301.8mW and does not show a saturation trend.

[0048] In summary, the dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler provided by this invention, through the design of a large-size active trapezoidal multimode interference coupler, not only couples the wavelengths of the two input waveguides to the output waveguide to achieve dual-wavelength laser output, but also increases the laser's gain area, ensuring the laser's output power. The narrower output end of the large-size active trapezoidal multimode interference coupler enhances the confinement of the optical field and improves the coupling efficiency at the output end. The wider input end of the large-size active trapezoidal multimode interference coupler avoids unfavorable coupling caused by the two input waveguides being too close, thereby achieving stable dual-wavelength output.

[0049] Specific embodiments of the invention have now been described. Other embodiments are within the scope of the appended claims. In some cases, the actions described in the claims can be performed in a different order and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing can be advantageous.

[0050] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the embodiments of the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the embodiments of the present invention, and the patent protection scope of the embodiments of the present invention should be defined by the claims.

Claims

1. A dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler, characterized in that, include: Large-size active trapezoidal multimode interference coupler; Two input waveguides are connected to the input end of the large-size active trapezoidal multimode interference coupler; An output waveguide is connected to the output of the large-size active trapezoidal multimode interference coupler; The two input waveguides are provided with grating structures with different periods, and the grating structures are laterally coupled gratings.

2. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The input width of the large-size active trapezoidal multimode interference coupler is greater than the output width.

3. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The two input waveguides are used to oscillate and generate two different wavelengths of laser light, which are then input into the active trapezoidal multimode interference coupler for coupling. The output waveguide is used to output the dual-wavelength laser light obtained after coupling.

4. The dual-wavelength semiconductor laser according to claim 1 or 2, characterized in that, The large-size active trapezoidal multimode interference coupler has an input width of 10μm~60μm, an output width of 5μm~40μm, and a length of 500μm~3000μm.

5. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The ridge width of the input waveguide and the output waveguide is 2μm~20μm.

6. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The spacing between the two input waveguides is 5μm to 20μm.

7. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The length of the input waveguide is 1000μm~2000μm, and the length of the output waveguide is 500μm~1500μm.

8. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The etching depth of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide is 0.5μm~2μm.

9. The dual-wavelength semiconductor laser according to claim 1, characterized in that, The dual-wavelength semiconductor laser further includes a layer structure, wherein: The layer structure, from bottom to top, includes a substrate, an N-type confinement layer, an N-type waveguide layer, an active gain layer, a P-type waveguide layer, and a P-type confinement layer. The input waveguide, the large-size active trapezoidal multimode interference coupler, the output waveguide, and the lateral coupling grating are formed by etching the layer structure from top to bottom.

10. A method for fabricating a dual-wavelength semiconductor laser based on an active trapezoidal multimode interference coupler as described in any one of claims 1 to 9, characterized in that, include: An N-type confinement layer, an N-type waveguide layer, an active gain layer, a P-type waveguide layer, and a P-type confinement layer are sequentially fabricated on a substrate. The input waveguide, the large-size active trapezoidal multimode interference coupler, the output waveguide, and the lateral coupling grating are formed on the P-type confinement layer by spin coating photoresist, photolithography, development, etching, and photoresist removal. An insulating layer is grown on the surface of the pattern, and electrode windows are opened on the upper part of the input waveguide, the large-size active trapezoidal multimode interference coupler, and the output waveguide. A P-plane metal electrode layer is deposited on the surfaces of the insulating layer and the electrode window; The back side of the substrate is thinned and polished, and then an N-side metal electrode layer is deposited on the back side of the substrate to obtain a wafer with completed electrode fabrication. The wafer with the completed electrode fabrication is cleaved and packaged to obtain the dual-wavelength semiconductor laser.

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