Laser based on bimetallic bragg grating and top hr reflective film

Abstract

The application relates to the technical field of semiconductor lasers, in particular to a laser based on a double-metal Bragg grating and a top HR reflection film, which comprises a gain chip, the left end face of the gain chip is coated with a first high-reflection HR film, and the right end face of the gain chip is coated with a first antireflection AR film. A metal Bragg grating waveguide is arranged on the right side of the gain chip, the right end face of the gain chip is aligned and attached to the left end face of the metal Bragg grating waveguide to form an external cavity structure, the left end face of the metal Bragg grating waveguide is coated with a second antireflection AR film, and the right end face of the metal Bragg grating waveguide is coated with a third antireflection AR film. Performance test is conducted on the laser provided by the application, and test results show that the line width is 0.6 kHz, the SMSR is 63 dB, and the threshold current is 22 mA, thereby verifying the effectiveness of the application.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of semiconductor lasers, in particular to a laser based on a double-metal Bragg grating and a top-surface HR reflection film. BACKGROUND

[0002] In the rapid development of optoelectronic technology, quantum key distribution, coherent optical communication, high-precision spectral analysis and photon integrated chips have extremely strict requirements for laser performance, and cost control is also a key factor. However, the traditional distributed feedback (DFB) laser and the conventional external cavity laser have many problems in practical application:

[0003] 1. The traditional external cavity laser adopts a single grating structure, and the side mode suppression ratio (SMSR) is only 45-50 dB, and the line width is about 20-50 kHz (IEEE Photonics Technology Letters, 2020), which cannot meet the strict requirements of high-precision applications on light sources. In terms of beam quality and integration, it is difficult to balance, relies on complex optical alignment process, increases the production difficulty and cost, and is not conducive to large-scale integrated manufacturing. In addition, the traditional external cavity laser cannot effectively solve the problem of upward diffraction light energy loss caused by the grating structure, which affects the light guiding property of the grating optical waveguide.

[0004] 2. Affected by the carrier density fluctuation and the typical 0.5mm lasing cavity length, the line width of the DFB laser is usually 1-10MHz (Optics Express, 2021). In the application scene of coherent detection, the wider line width will cause serious signal interference, greatly reducing the detection accuracy and system performance. The secondary epitaxy process is complex, and the yield is only 65-70% (Photonics Research, 2021), and the manufacturing cost is 2-3 times higher than that of the external cavity laser. The semiconductor grating reflectivity is only 93-95%, and additional gain compensation is required, which increases the power consumption by 15-20%, and also causes heat dissipation problems, affecting the stability and reliability of the laser. SUMMARY

[0005] The application provides a laser based on a double-metal Bragg grating and a top-surface HR reflection film to solve the problems in the background.

[0006] To achieve the above purpose, the application provides the following technical scheme: a laser based on a double-metal Bragg grating and a top-surface HR reflection film, comprising: a gain chip, a first high-reflection HR film is coated on the left end face of the gain chip, and a first anti-reflection AR film is coated on the right end face of the gain chip.

[0007] The gain chip is provided with a metal Bragg grating waveguide on the right side, the right end surface of the gain chip is aligned and attached to the left end surface of the metal Bragg grating waveguide to form an external cavity structure, the left end surface of the metal Bragg grating waveguide is coated with a second anti-reflection AR film, and the right end surface of the metal Bragg grating waveguide is coated with a third anti-reflection AR film.

[0008] The metal Bragg grating waveguide comprises a grating waveguide substrate, a back ridge waveguide is arranged on the upper end surface of the grating waveguide substrate, a first planar metal Bragg grating is arranged on the left side of the upper end surface of the back ridge waveguide, a second planar metal Bragg grating is arranged on the right side of the upper end surface of the back ridge waveguide, a phase difference is arranged between the first planar metal Bragg grating and the second planar metal Bragg grating, and a second high-reflection HR film is arranged on the top of the first planar metal Bragg grating and the second planar metal Bragg grating.

[0009] The second high-reflection HR film is prepared by using a magnetron sputtering deposition on the top of the first planar metal Bragg grating and the second planar metal Bragg grating, the material of the second high-reflection HR film is selected from TiO2 / SiO2 multi-layer dielectric combination material, the thickness of each layer is λ / 4, the thickness accuracy is ±5 nm, the reflectivity R3 is greater than 99.5%, and the surface roughness is less than 0.08 nm RMS.

[0010] As a preferred solution of the above technical scheme, the gain chip adopts an InP / InGaAsP quantum well structure, the center emission wavelength λ ranges from 1530 nm to 1610 nm, and the threshold current is lower than 22 mA at 25℃.

[0011] Further, the gain chip adopts an InP / InGaAsP quantum well structure, the center emission wavelength λ is 1550 nm, and the threshold current is lower than 22 mA at 25℃.

[0012] As a preferred solution of the above technical scheme, the first anti-reflection AR film has a thickness of λ / 4 and a reflectivity R1 less than 0.03%, and the first high-reflection HR film is a SiO2 / TiO2 multi-layer high-reflection film with a reflectivity R2 greater than 99.9%.

[0013] As a preferred solution of the above technical scheme, the planar metal Bragg grating waveguide has a length of 1-3 cm, a grating period of 225±0.3 nm, a duty cycle of 50±1%, and a Cr / Au layer thickness of 200±5 nm.

[0014] Further, the planar metal Bragg grating waveguide has a length of 2 cm, a grating period of 225±0.3 nm, and a duty cycle of 50±1%.

[0015] As the preferred technical scheme of the above, the back ridge optical waveguide is 3-5 microns wide and 2-4 microns high, and the matching degree with the mode field of the gain chip is greater than 98%.

[0016] Further, the back ridge optical waveguide is 4 microns wide and 3 microns high, and the matching degree with the mode field of the gain chip is greater than 98%.

[0017] As the preferred technical scheme of the above, the first planar metal Bragg grating and the second planar metal Bragg grating are Cr / Au structures with a thickness of 50 nm / 150 nm and a reflectivity of greater than 99.9% and a 3dB reflection bandwidth of less than 0.1 nm.

[0018] As the preferred technical scheme of the above, the phase difference Δφ = π, and the phase control accuracy is less than λ / 50 by atomic layer deposition technology.

[0019] The application provides a laser based on a double-metal Bragg grating and a top HR reflective film, which has the following advantages:

[0020] 1. The second high-reflection HR film prevents light energy loss: The top of the first planar metal Bragg grating and the second planar metal Bragg grating is provided with a second high-reflection HR film with a reflectivity greater than 99.5%. The reflective film works based on the multi-layer thin film interference effect and can efficiently reflect the upward diffraction light back into the waveguide. When the light propagates in the waveguide and encounters the top Bragg grating, part of the light will be upward diffraction, and the second high-reflection HR film effectively reduces the loss of this part of light energy. By optimizing the reflection characteristics of the grating, the reflection efficiency of the grating is further enhanced, the light field is constrained to propagate in the waveguide, and the light energy is prevented from overflowing into the free space, thereby maintaining the light guiding property of the metal Bragg grating waveguide and significantly improving the performance of the laser.

[0021] 2. Cost reduction advantage: The second high-reflection HR film replaces the traditional thick semiconductor secondary epitaxial waveguide layer, which fundamentally reduces the material cost and process complexity. At the same time, the first planar metal Bragg grating and the second planar metal Bragg grating are prepared by electroplating process, which provides high-quality filtering and reflection effect compared with the traditional semiconductor etching process. The process does not require multiple processes such as semiconductor crystal grating etching with complex crystal surface structure, crystal surface orientation restriction, high precision and crystal surface flatness, avoids the dependence on high-precision equipment and special chemical reagents, effectively reduces the equipment cost, raw material cost and process complexity, significantly reduces the production cost, and has good economic feasibility.

[0022] 3、Dual-grating synergistic enhancement mechanism: the first and second plane metal Bragg gratings with a phase difference Δφ=π are adopted, the reflected light of the two gratings is constructively interfered in the cavity, the main peak reflectivity is increased from 95% of the traditional single grating to 99.9%, the light field intensity in the cavity is enhanced, and the high-power and stable laser output is ensured. The destructive interference characteristics of the dual gratings are used to suppress the non-lasing mode, according to the formula:

[0023]

[0024] Wherein, R1 and R2 are the reflectivities of the two ends of the resonant cavity;

[0025] The theoretical side mode suppression ratio (SMSR) can reach 63dB, effectively weakening the side mode intensity, improving the purity and stability of the output light, and meeting the high-precision application requirements.

[0026] The dual-grating setting multiplies the equivalent cavity length, expands the free spectral range from 50GHz of the traditional external cavity to 100GHz, reduces the mode competition, improves the wavelength selection ability and stability of the laser, and facilitates the realization of laser output of different wavelengths in multi-wavelength application scenarios.

[0027] 4, linewidth compression technology: based on the Hakki-Paoli model, the linewidth formula is modified as:

[0028]

[0029] Wherein, hν: photon energy; P: laser output power; L: total length of the resonant cavity; L g : gain medium length; R1 and R2 are the reflectivities of the two ends of the resonant cavity; α: linewidth enhancement factor.

[0030] : It comprehensively considers the influence of cavity length and gain medium on photon lifetime.

[0031] : The loss term in the traditional linewidth formula is modified, which includes the coupling effect of phase noise and carrier fluctuation.

[0032] By adopting the first and second plane metal Bragg gratings with a 3cm external cavity length and a reflectivity of 99.92%, an ultra-narrow linewidth output of Δν=0.6kHz is realized, while the traditional DFB laser has a linewidth of about 1MHz. Ultra-narrow linewidth laser has important application value in the fields of coherent optical communication, high-precision spectral analysis and quantum key distribution. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of the present application;

[0034] Figure 2 for Figure 1 Top view;

[0035] Figure 3 This is a schematic diagram of the structure of the metal Bragg grating waveguide in this invention;

[0036] Figure 4 for Figure 3 The left view.

[0037] In the figure: 1. Gain chip; 11. First high-reflectivity HR film; 12. First anti-reflection AR film; 2. Metal Bragg grating waveguide; 21. Grating waveguide substrate; 22. Back ridge waveguide; 23. First planar metal Bragg grating; 24. Second planar metal Bragg grating; 25. Second anti-reflection AR film; 26. Third anti-reflection AR film; 27. Phase difference; 28. Second high-reflectivity HR film. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] Example 1

[0040] like Figures 1-4 As shown, in this embodiment, the laser based on a bimetallic Bragg grating and a top surface HR reflective film includes: a gain chip 1, wherein a first high reflectivity HR film 11 is deposited on the left end face of the gain chip 1, and a first antireflection AR film 12 is deposited on the right end face of the gain chip 1.

[0041] In specific implementation, the gain chip 1 adopts an InP / InGaAsP quantum well structure with a central emission wavelength λ of 1530nm. At 25℃, the threshold current is below 22mA, exhibiting excellent photoelectric conversion performance. The first antireflection AR film 12 has a thickness of λ / 4 and a reflectivity R1 < 0.03% to reduce light reflection loss. The first high-reflectivity HR film 11 is a SiO2 / TiO2 multilayer high-reflectivity film with a reflectivity R2 > 99.9%, enhancing light feedback.

[0042] A metal Bragg grating waveguide 2 is disposed on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and attached to the left end face of the metal Bragg grating waveguide 2 to form an external cavity structure. A second anti-reflection AR film 25 is deposited on the left end face of the metal Bragg grating waveguide 2, and a third anti-reflection AR film 26 is deposited on the right end face of the metal Bragg grating waveguide 2.

[0043] In a specific implementation, the planar metal Bragg grating waveguide 2 has a length of 1 cm, a grating period of 225±0.3 nm, a duty cycle of 50±1%, and a Cr / Au layer thickness of 200±5 nm (50 nm Cr / 150 nm Au), forming a high-reflectivity grating structure.

[0044] The metal Bragg grating waveguide 2 includes a grating waveguide substrate 21, an upper end surface of which is provided with a back ridge optical waveguide 22, a left side of an upper end surface of the back ridge optical waveguide 22 is provided with a first planar metal Bragg grating 23, a right side of an upper end surface of the back ridge optical waveguide 22 is provided with a second planar metal Bragg grating 24, and a phase difference 27 is arranged between the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24. The top of the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24 is provided with a second high-reflectivity HR film 28.

[0045] The second high-reflectivity HR film 28 is prepared by magnetron sputtering deposition on the top of the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24. The material of the second high-reflectivity HR film 28 is selected from TiO2 / SiO2 multilayer dielectric combination material, each layer has a thickness of λ / 4, a thickness accuracy of ±5 nm, a reflectivity R3>99.5%, and a surface roughness of less than 0.08 nm RMS, so as to achieve high reflectivity and good optical performance.

[0046] Further, the phase difference 27 Δφ=π, and the phase control accuracy is <λ / 50 by atomic layer deposition technology.

[0047] In a specific implementation, the back ridge optical waveguide 22 has a width of 3 μm and a height of 2 μm, and the mode matching degree with the gain chip 1 is >98%.

[0048] In a specific implementation, the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24 are of Cr / Au structure, with a thickness of 50 nm / 150 nm, a reflectivity >99.9%, and a 3 dB reflection bandwidth <0.1 nm.

[0049] It should be noted that the laser based on the double-metal Bragg grating and the top HR reflective film has a total length L cavity =800 μm+L wg of the external cavity, and a free spectral range FSR>100 GHz.

[0050] Example 2

[0051] As Figures 1-4As shown in the embodiment, the laser based on the bimetallic Bragg grating and the top HR reflective film comprises: a gain chip 1, a first high reflection HR film 11 is coated on the left end face of the gain chip 1, and a first anti-reflection AR film 12 is coated on the right end face of the gain chip 1.

[0052] In specific implementation, the gain chip 1 adopts InP / InGaAsP quantum well structure, the center emission wavelength λ is 1610 nm, the threshold current is less than 22 mA at 25℃ environment, and good photoelectric conversion performance is exhibited. The first anti-reflection AR film 12 has a thickness of λ / 4, and the reflectivity R1 is less than 0.03% to reduce light reflection loss; the first high reflection HR film 11 is a SiO2 / TiO2 multilayer high reflection film, and the reflectivity R2 is greater than 99.9% to enhance light feedback.

[0053] The right side of the gain chip 1 is provided with a metal Bragg grating waveguide 2, the right end face of the gain chip 1 is aligned and attached to the left end face of the metal Bragg grating waveguide 2 to form an external cavity structure, a second anti-reflection AR film 25 is coated on the left end face of the metal Bragg grating waveguide 2, and a third anti-reflection AR film 26 is coated on the right end face of the metal Bragg grating waveguide 2.

[0054] In specific implementation, the planar metal Bragg grating waveguide 2 has a length of 3 cm, a grating period of 225±0.3 nm, a duty cycle of 50±1%, and a Cr / Au layer thickness of 200±5 nm (50 nm Cr / 150 nm Au), to form a grating structure with high reflectivity.

[0055] The metal Bragg grating waveguide 2 comprises a grating waveguide substrate 21, a back ridge optical waveguide 22 is arranged on the upper end face of the grating waveguide substrate 21, a first planar metal Bragg grating 23 is arranged on the left side of the upper end face of the back ridge optical waveguide 22, a second planar metal Bragg grating 24 is arranged on the right side of the upper end face of the back ridge optical waveguide 22, a phase difference 27 is arranged between the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24, and a second high reflection HR film 28 is arranged on the top of the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24.

[0056] The preparation process of the second high reflection HR film 28 is as follows: the second high reflection HR film 28 is deposited on the top of the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24 by magnetron sputtering, the material of the second high reflection HR film 28 is selected from TiO2 / SiO2 multilayer dielectric combination material, each layer has a thickness of λ / 4, the thickness precision is ±5 nm, the reflectivity R3 is greater than 99.5%, and the surface roughness is less than 0.08 nm RMS, to realize high reflectivity and good optical performance.

[0057] Furthermore, the phase difference 27Δφ=π is controlled with a phase control accuracy of <λ / 50 through atomic layer deposition technology.

[0058] In specific implementation, the back ridge waveguide 22 is 5μm wide and 4μm high, and its mode field matching degree with the gain chip 1 is >98%.

[0059] In specific implementation, the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24 are Cr / Au structures with a thickness of 50nm / 150nm, a reflectivity of >99.9%, and a 3dB reflection bandwidth of <0.1nm.

[0060] It should be noted that the laser based on a bimetallic Bragg grating and a top-surface HR reflective film has a total external cavity length L. cavity =800μm+L wg Free spectral range FSR > 100 GHz.

[0061] Example 3

[0062] like Figures 1-4 As shown, in this embodiment, the laser based on a bimetallic Bragg grating and a top surface HR reflective film includes: a gain chip 1, wherein a first high reflectivity HR film 11 is deposited on the left end face of the gain chip 1, and a first antireflection AR film 12 is deposited on the right end face of the gain chip 1.

[0063] In specific implementation, the gain chip 1 adopts an InP / InGaAsP quantum well structure with a central emission wavelength λ of 1550nm. At 25℃, the threshold current is below 22mA, exhibiting excellent photoelectric conversion performance. The first antireflection AR film 12 has a thickness of λ / 4 and a reflectivity R1 < 0.03% to reduce light reflection loss. The first high-reflectivity HR film 11 is a SiO2 / TiO2 multilayer high-reflectivity film with a reflectivity R2 > 99.9%, enhancing light feedback.

[0064] A metal Bragg grating waveguide 2 is disposed on the right side of the gain chip 1. The right end face of the gain chip 1 is aligned and attached to the left end face of the metal Bragg grating waveguide 2 to form an external cavity structure. A second anti-reflection AR film 25 is deposited on the left end face of the metal Bragg grating waveguide 2, and a third anti-reflection AR film 26 is deposited on the right end face of the metal Bragg grating waveguide 2.

[0065] In a specific implementation, the planar metal Bragg grating waveguide 2 has a length of 2cm, a grating period of 225±0.3nm, a duty cycle of 50±1%, and a Cr / Au layer thickness of 200±5nm (50nmCr / 150nmAu), forming a grating structure with high reflectivity.

[0066] The metal Bragg grating waveguide 2 comprises a grating waveguide substrate 21, a back ridge optical waveguide 22 is arranged on the upper end face of the grating waveguide substrate 21, a first planar metal Bragg grating 23 is arranged on the left side of the upper end face of the back ridge optical waveguide 22, a second planar metal Bragg grating 24 is arranged on the right side of the upper end face of the back ridge optical waveguide 22, a phase difference 27 is arranged between the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24, and a second high-reflection HR film 28 is arranged on the top of the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24.

[0067] The preparation process of the second high-reflection HR film 28 is as follows: the second high-reflection HR film 28 is deposited on the top of the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24 by magnetron sputtering, and the material of the second high-reflection HR film 28 is selected from TiO2 / SiO2 multi-layer dielectric combined material, each layer has a thickness of λ / 4, the thickness accuracy is ±5 nm, the reflectivity R3 is greater than 99.5%, and the surface roughness is less than 0.08 nm RMS, so that high reflectivity and good optical performance are achieved.

[0068] Further, the phase difference 27 is Δφ=π, and the phase control accuracy is less than λ / 50 by atomic layer deposition technology.

[0069] In specific implementation, the back ridge optical waveguide 22 has a width of 4 μm and a height of 3 μm, and the mode matching degree with the gain chip 1 is greater than 98%.

[0070] In specific implementation, the first planar metal Bragg grating 23 and the second planar metal Bragg grating 24 have a Cr / Au structure, a thickness of 50 nm / 150 nm, a reflectivity greater than 99.9%, and a 3dB reflection bandwidth less than 0.1 nm.

[0071] It should be noted that the laser based on the double-metal Bragg grating and the top HR reflection film has a total length L cavity =800 μm+L wg of the external cavity, and a free spectral range FSR greater than 100 GHz.

[0072] Performance detection is performed on the three lasers provided in Embodiments 1, 2 and 3, and the test results show that the line width is 0.6 kHz, the SMSR is 63 dB, and the threshold current is 22 mA, which verifies the effectiveness of the present application.

[0073] Although the embodiments of the present application have been shown and described, it should be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A laser based on a bimetallic Bragg grating and a top-surface HR reflective film, comprising a gain chip (1), characterized in that: The gain chip (1) has a first high reflectance HR film (11) deposited on its left end face and a first antireflection AR film (12) deposited on its right end face. A metal Bragg grating waveguide (2) is provided on the right side of the gain chip (1). The right end face of the gain chip (1) is aligned and attached to the left end face of the metal Bragg grating waveguide (2) to form an external cavity structure. A second anti-reflection AR film (25) is deposited on the left end face of the metal Bragg grating waveguide (2), and a third anti-reflection AR film (26) is deposited on the right end face of the metal Bragg grating waveguide (2). The metal Bragg grating waveguide (2) includes a grating waveguide substrate (21), a back ridge waveguide (22) is provided on the upper surface of the grating waveguide substrate (21), a first planar metal Bragg grating (23) is provided on the left side of the upper surface of the back ridge waveguide (22), a second planar metal Bragg grating (24) is provided on the right side of the upper surface of the back ridge waveguide (22), a phase difference (27) is provided between the first planar metal Bragg grating (23) and the second planar metal Bragg grating (24), and a second high-reflection HR film (28) is provided on the top of the first planar metal Bragg grating (23) and the second planar metal Bragg grating (24).

2. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 1, characterized in that: The gain chip (1) adopts an InP / InGaAsP quantum well structure with a center emission wavelength λ of 1550nm and a threshold current of less than 22mA at 25℃.

3. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 2, characterized in that, The second high-reflectivity HR film (28) is specifically prepared by magnetron sputtering on the top of the first planar metal Bragg grating (23) and the second planar metal Bragg grating (24). The material of the second high-reflectivity HR film (28) is a TiO2 / SiO2 multilayer dielectric composite material with a thickness of λ / 4 per layer, a thickness accuracy of ±5nm, a reflectivity R3 > 99.5%, and a surface roughness of less than 0.08nm RMS.

4. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 2, characterized in that: The first antireflective AR film (12) has a thickness of λ / 4 and a reflectivity R1 < 0.03%; the first high reflectivity HR film (11) is a SiO2 / TiO2 multilayer high reflectivity film with a reflectivity R2 > 99.9%.

5. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 1, characterized in that: The planar metal Bragg grating waveguide (2) has a length of 2cm, a grating period of 225±0.3nm, and a duty cycle of 50±1%.

6. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 1, characterized in that: The back ridge waveguide (22) is 4μm wide and 3μm high, and its mode field matching degree with the gain chip (1) is >98%.

7. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 1, characterized in that: The first planar metal Bragg grating (23) and the second planar metal Bragg grating (24) are Cr / Au structures with a thickness of 50nm / 150nm, a reflectivity of >99.9%, and a 3dB reflection bandwidth of <0.1nm.

8. The laser based on a bimetallic Bragg grating and a top-surface HR reflective film according to claim 2, characterized in that: The phase difference (27) Δφ=π is achieved by atomic layer deposition technology to achieve a phase control accuracy of <λ / 50.

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