Tunable filter structure, manufacturing method and wavelength tunable light source system

Abstract

The present application discloses a tunable filter structure, a manufacturing method and a wavelength tunable light source system, which relate to the technical field of semiconductors. The tunable filter structure includes a first resonant cavity, a heating component, a spacer layer and a second resonant cavity. The first resonant cavity includes a first surface and a second surface relative to each other; the heating component is provided on the first surface, and is used to change the free spectrum range of the first resonant cavity; the spacer layer is provided on the second surface; the second resonant cavity is cascaded with the first resonant cavity through the spacer layer, and the free spectrum range of the first resonant cavity is different from the free spectrum range of the second resonant cavity; the spacer layer is annular to form an air cavity between the first resonant cavity and the second resonant cavity; the thermo-optic coefficient of the second resonant cavity is smaller than the thermo-optic coefficient of the first resonant cavity; the heating component is used to change the refractive index of the first resonant cavity to adjust the transmission wavelength of the tunable filter structure. Therefore, the present application has the advantages of a large tuning range, a simple structure, a high degree of integration and convenient batch processing.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductors, and in particular to a tunable filter structure, a manufacturing method, and a wavelength tunable light source system. Background Art

[0002] In existing technology, external-cavity tunable lasers consist of a semiconductor diode and an external feedback cavity. The semiconductor diode generally serves as the gain medium, and the external feedback cavity acts as a frequency-selective or wavelength-selective structure. The external feedback cavity selects the light output by the semiconductor laser, allowing only light of a specific wavelength to return to the gain region, thereby narrowing the linewidth, suppressing side modes, and outputting light of a specific wavelength. However, these lasers are large and expensive, making them uncompetitive in the communications and sensing fields.

[0003] To address the above issues, the current method to reduce costs is to use micro-electromechanical (MEMS) structures to make external wavelength selection structures to reduce costs. More compact integrated tunable lasers often change the resonant wavelength of the filter by adjusting the waveguide refractive index of its filter. The main methods for adjusting the refractive index of the waveguide are: electrical tuning through carrier injection (carrier dispersion effect), and thermal tuning by heating the waveguide (thermo-optical effect). Due to the limitations of actual physical properties, the refractive index adjustment range of the material is small. When tuning is performed by tuning only a single filter, the wavelength tuning range is often only a few nanometers. However, in some current application scenarios such as communications and sensing, a single laser is required to achieve broadband wavelength tuning of tens or even hundreds of nanometers. Summary of the Invention

[0004] The purpose of this application is to provide a tunable filter structure, a manufacturing method and a wavelength tunable light source system, which can be combined and tuned based on the vernier effect and achieve a wider range of wavelength tuning by improving the filter structure.

[0005] The embodiment of the present application is implemented as follows:

[0006] In a first aspect, the present application provides a tunable filter structure, comprising: a first resonant cavity, a heating component, a spacer layer, and a second resonant cavity. The first resonant cavity comprises a first surface and a second surface facing each other; the heating component is disposed on the first surface; the spacer layer is disposed on the second surface of the first resonant cavity; the second resonant cavity is cascaded with the first resonant cavity via the spacer layer, and the free spectral range of the first resonant cavity is different from the free spectral range of the second resonant cavity; the spacer layer is annular to form an air cavity between the first resonant cavity and the second resonant cavity; the thermo-optic coefficient of the second resonant cavity is smaller than the thermo-optic coefficient of the first resonant cavity; and the heating component is used to change the refractive index of the first resonant cavity to adjust the transmission wavelength of the tunable filter structure.

[0007] In an embodiment, the tunable filter structure further comprises a reflective layer, and the reflective layer comprises a first reflective layer disposed at the center of the first surface.

[0008] In an embodiment, the heating assembly comprises a heating element disposed on the first surface and surrounding the first reflective layer.

[0009] In an embodiment, the heating element is a non-temperature-sensitive resistor.

[0010] In an embodiment, the heating assembly further comprises a temperature-sensing element disposed on the first surface and surrounding the heating element.

[0011] In an embodiment, the temperature-sensing element is a temperature-sensitive resistor.

[0012] The second aspect of the present application provides a method for manufacturing a tunable filter structure, comprising: providing a first resonant cavity having opposite first and second surfaces; forming a heating assembly on the first surface for changing the free spectral range of the first resonant cavity; forming a spacer layer on the second surface of the first resonant cavity, the spacer layer being annular; forming a second resonant cavity on the spacer layer so that the second resonant cavity is cascaded with the first resonant cavity through the spacer layer, and an air cavity is formed between the first resonant cavity and the second resonant cavity.

[0013] In an embodiment, before forming the heating assembly on the first surface, the method further comprises: forming a first reflective layer on the first surface by magnetron sputtering or evaporation deposition.

[0014] In an embodiment, forming the heating assembly on the first surface comprises: forming a heating element on the first surface by magnetron sputtering, and the heating element surrounds the first reflective layer; and forming a temperature-sensing element on the first surface by magnetron sputtering, and the temperature-sensing element surrounds the heating element.

[0015] The third aspect of the present application provides a wavelength-tunable light source system, comprising: the tunable filter structure, the gain chip, the collimating lens, and the mirror provided in any of the embodiments of the first aspect of the present application. The collimating lens is disposed on one side of the gain chip for collimating the light emitted by the gain chip; the tunable filter structure and the gain chip are respectively disposed on two sides of the collimating lens, and the tunable filter structure is used for adjusting the transmission wavelength to filter the light of a specific wavelength; and the mirror is disposed on one side of the tunable filter structure so that the light guided out of the tunable filter structure is reflected and re-introduced into the tunable filter structure.

[0016] Compared with the prior art, the beneficial effects of the present application are that the present application forms the tunable filter structure based on the vernier effect, overcomes the problem of limited refractive index variation range of the existing filter, and further realizes the output and tuning of a larger range of transmission wavelengths. In addition, the wavelength tunable light source system provided by the present application does not need to be provided with movable components, and only needs to change the heating temperature of the tunable filter structure to realize the change of the transmission wavelength thereof, and the working reliability is high. Therefore, the tunable filter structure and the wavelength tunable light source system provided by the present application are simple, compact, high in integration, low in cost, and conducive to mass production. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced below, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 a structure schematic view of the wavelength tunable light source system shown in an embodiment of the present application;

[0019] Figure 2 a structure schematic view of the tunable filter structure shown in an embodiment of the present application;

[0020] Figure 3 a top view schematic view of the tunable filter structure shown in an embodiment of the present application;

[0021] Figure 4 a vernier effect schematic view of the multi-filter cascade shown in an embodiment of the present application;

[0022] Figure 5 a manufacturing method flowchart of the tunable filter structure shown in an embodiment of the present application.

[0023] Figure legend: 1-wavelength tunable light source system; 10-gain chip; 20-collimating lens; 30-tunable filter structure; 301-first surface; 302-second surface; 303-third surface; 304-fourth surface; 31-first resonant cavity; 32-separation layer; 33-second resonant cavity; 34-heating assembly; 341-heating element; 342-temperature measuring element; 35-reflective layer; 351-first reflective layer; 352-second reflective layer; 353-third reflective layer; 354-fourth reflective layer; 40-mirror. DETAILED DESCRIPTION

[0024] The terms "first", "second", "third", etc. are only used for differentiation and description, and do not represent the arrangement number, and cannot be understood as indicating or implying relative importance.

[0025] In addition, the terms "horizontal", "vertical", "overhanging", etc. do not mean that the components must be absolutely horizontal or overhanging, but can be slightly inclined. For example, "horizontal" only means that it is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0026] In the description of the present application, it should be noted that the terms "inner", "outer", "left", "right", "upper", "lower", etc. indicate the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present application is used, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0027] In the description of the present application, unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements.

[0028] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings.

[0029] Please refer to Figure 1 , Figure 1 The structure schematic diagram of the wavelength tunable light source system 1 shown in an embodiment of the present application. As shown in Figure 1 , the wavelength tunable light source system 1 comprises: an adjustable filter structure 30, a gain chip 10, a collimating lens 20 and a mirror 40.

[0030] Among them, the collimating lens 20 is arranged on one side of the gain chip 10, used for collimating the light emitted by the gain chip 10; the adjustable filter structure 30 and the gain chip 10 are arranged on the two sides of the collimating lens 20 respectively, used for adjusting the transmission wavelength to screen the light of a specific wavelength; the mirror 40 is arranged on one side of the adjustable filter structure 30, so that the light led out by the adjustable filter structure 30 is reflected and re-led into the adjustable filter structure 30.

[0031] In an embodiment, an antireflection film, also known as an anti-reflection film (AR, Antireflecting Film), is also arranged on the gain chip 10. The main function of the antireflection film is to reduce or eliminate the reflected light of the optical surface, thereby increasing the light transmission of the element, to further reduce or eliminate the stray light of the related system.

[0032] In an application process, the wavelength tunable light source system 1 can propagate in the manner as shown in the figure during use. Figure 1 The light beam emitted from the gain chip 10 is collimated by the collimating lens 20 and then is incident on the tunable filter structure 30. Part of the light is transmitted through the tunable filter structure 30 to the mirror 40 and then is reflected by the mirror 40 back to the tunable filter structure 30, is refracted by the tunable filter structure 30 and then is returned to the gain region to continue oscillation, so as to narrow the linewidth, suppress the side mode and finally output light of a specific wavelength. The other part of the light is directly guided out after being reflected by the tunable filter structure 30.

[0033] The tunable filter structure 30 in the present application can also be called a MEMS tunable filter. The tunable filter structure 30 is a cascaded F-P resonant cavity, which mainly realizes a larger wavelength tuning range based on the vernier effect. During use of the wavelength tunable light source system 1, the transmission wavelength of the tunable filter structure 30 can be adjusted by changing the refractive index of one of the FP cavities.

[0034] Please refer to Figure 2 , Figure 2 for the structure diagram of the tunable filter structure 30 shown in an embodiment of the present application. As shown in the figure, Figure 2 the tunable filter structure 30 comprises a first resonant cavity 31, a heating component 34, a spacing layer 32 and a second resonant cavity 33.

[0035] The first resonant cavity 31 comprises opposite first and second surfaces 301 and 302. The second resonant cavity 33 comprises opposite third and fourth surfaces 303 and 304. The spacing layer 32 is arranged on the second surface 302 of the first resonant cavity 31, and the second resonant cavity 33 is cascaded with the first resonant cavity 31 through the spacing layer 32. The spacing layer 32 is annular to form an air cavity between the first resonant cavity 31 and the second resonant cavity 33 after the tunable filter structure 30 is processed.

[0036] The heating component 34 is arranged on the first surface 301 and is used to change the refractive index of the first resonant cavity 31 to adjust the transmission wavelength of the tunable filter structure 30. The materials of the first resonant cavity 31 and the spacing layer 32 are both silicon, and the material of the second resonant cavity 33 is glass. Because the thermal-optic coefficient of glass is much smaller than that of silicon, the temperature change has little effect on the bottom glass. Therefore, when the tunable filter structure 30 is heated by the heating component 34, the refractive index of the first resonant cavity 31 changes with the temperature, the refractive index of the second resonant cavity 33 is basically unchanged, and then the transmission wavelength of the tunable filter structure 30 also changes with the temperature.

[0037] For a single resonant cavity, its transmission spectrum is comb-shaped, and the free spectral range (FSR) is about 100 nm. The FSR of the tunable filter structure 30 is about 200 nm, which is twice that of a single resonant cavity. m) can be calculated according to the following formula:

[0038] FSR m = λ m 2 / (2nhcosθ).

[0039] wherein λ m is the central wavelength, n is the refractive index, h is the cavity length, and θ is the incident angle.

[0040] The tunable filter structure 30 further comprises a reflective layer 35, which comprises a first reflective layer 351, a second reflective layer 352, a third reflective layer 353, and a fourth reflective layer 354. The first reflective layer 351 is arranged on the first surface 301, the second reflective layer 352 is arranged on the second surface 302, the second resonant cavity 33 further has a third surface 303 and a fourth surface 304, the third reflective layer 353 is arranged on the third surface 303, and the fourth reflective layer 354 is arranged on the fourth surface 304. Each reflective layer 35 is arranged at the center of each surface to reflect light of non-specific wavelength.

[0041] The reflectivity of the reflective film is used to control the half-wave width of the longitudinal mode, and the calculation formula is:

[0042]

[0043] wherein R is the reflectivity, λ m is the central wavelength, and n is the refractive index. Generally, the higher the reflectivity, the narrower the half-wave width, and the better the coherence of the transmission wavelength, so the narrower the wavelength half-peak width of the coherent light module light in optical communication is better. The reflective layer 35 can use a multilayer dielectric film to increase the reflectivity to reduce the half-wave width, and the reflective layer 35 can be made by magnetron sputtering or evaporation.

[0044] Please refer to Figure 3 , Figure 3 is a top view schematic diagram of the tunable filter structure 30 according to an embodiment of the present application. As shown in Figure 3 , the heating assembly 34 comprises a heating element 341 and a temperature measuring element 342. The heating element 341 is arranged on the first surface 301 and surrounds the first reflective layer 351. Preferably, the heating electrode uses Al, Au, Ti, or other non-temperature-sensitive resistors. The temperature measuring element 342 is arranged on the first surface 301 and surrounds the heating element 341. Preferably, the temperature measuring electrode uses Pt or other temperature-sensitive resistors.

[0045] Please refer to Figure 4 , Figure 4 is a vernier effect schematic diagram of the multi-filter cascade according to an embodiment of the present application. As shown in Figure 4As shown, the present application utilizes the Vernier effect to design a multi-cavity cascade tunable filter structure 30. By combining tuning, the problem of limited refractive index variation is overcome, and a wide range of wavelength tuning is achieved. The specific principles are described as follows:

[0046] Vernier effect Figure 4 , which can usually be obtained by cascading two comb filters (FP resonant cavities) with slightly different free spectral ranges (FSR) (FSR1≠FSR2). Figure 4 The spectrum shown at the bottom. When the peak wavelengths of the two free spectral ranges are just aligned and the adjacent wavelengths are staggered, the cascaded adjustable filter structure 30 has the corresponding highest peak at the point where the highest peaks of the free spectral ranges of the multiple filters are aligned, and its corresponding peak will be reduced accordingly at other misaligned points. In addition, to ensure the single-mode output of the laser, the wavelength tuning range of the adjustable filter structure 30 must be between the two highest peaks, that is, the wavelength tuning range is FSRbeat; in addition, the side mode suppression ratio (SMSR) of the adjustable filter structure 30 must be large enough. At the same time, the cost of the adjustable filter structure 30 constructed in a cascade manner is lower than that of a single filter with a larger wavelength tuning range, which is convenient for mass production.

[0047] Please refer to Figure 5 , Figure 5 This is a flow chart of a manufacturing method of an adjustable filter structure 30 according to an embodiment of the present application. Figures 3-5 As shown, the manufacturing method of the tunable filter structure 30 includes:

[0048] S410: Providing a first resonant cavity 31, wherein the first resonant cavity 31 has a first surface 301 and a second surface 302 opposite to each other;

[0049] S420 : forming a heating assembly 34 on the first surface 301 .

[0050] This step creates heating electrodes and temperature-measuring electrodes on the surface of the silicon wafer. The heating electrodes are used to heat the first resonant cavity 31 (also known as the silicon FP cavity) to produce a thermo-optical effect, thereby changing the refractive index of silicon and, in turn, the free spectral range (FSR) of the first resonant cavity 31, causing its output wavelength after series connection to change with temperature. The heating electrodes are made on the silicon film. Since the silicon film, as a thin film structure, has a small thermal mass, it has a faster response speed. This step includes:

[0051] First, the heating element 341 is formed on the first surface 301 by magnetron sputtering, and the heating element 341 is arranged around the center of the first surface 301. Then, the temperature measuring element 342 is formed again on the first surface 301 by magnetron sputtering, and the temperature measuring element 342 is arranged around the heating element 341.

[0052] S430: Forming a spacer layer 32 on the second surface 302 of the first resonant cavity 31, and the spacer layer 32 is annular.

[0053] The top layer of the tunable filter structure 30 is made of silicon to form the first resonant cavity 31 and the spacer layer 32. The spacer layer 32 is initially a closed silicon whole, which needs to be processed by deep silicon etching or wet etching in the bulk silicon process to form a spacer gap in the center of the spacer layer 32, and then form an annular spacer layer 32, so as to form an air cavity between the two resonant cavities after the first resonant cavity 31 and the second resonant cavity 33 are cascaded.

[0054] S440: Forming a second resonant cavity 33 on the spacer layer 32, so that the second resonant cavity 33 is cascaded with the first resonant cavity 31 through the spacer layer 32.

[0055] In this step, the second resonant cavity 33 is made of glass, and the model is usually BF33. Because the thermal-optical coefficient of glass is much smaller than that of silicon (the thermal-optical coefficient of silicon is usually 1.84e-4 1 / K, and the thermal-optical coefficient of glass is 0.1e-4 1 / K), the temperature change has little effect on the bottom glass F-P cavity.

[0056] The second resonant cavity 33 has opposite third and fourth surfaces 303 and 304. The spacer layer 32 and the second resonant cavity 33 are bonded by an anodic bonding technique, and the spacer layer 32 is bonded to the third surface 303. The spacer height of the spacer layer 32 should be as large as possible to minimize the influence between the two resonant cavities. In an embodiment, the height of the spacer layer 32 needs to be several hundred microns to form a spacer gap with sufficient height, thereby minimizing the degree of narrowing of the wave width of the output waveform of the first resonant cavity 31 and the second resonant cavity 33 with the increase of reflectivity.

[0057] In an embodiment, the manufacturing method of the tunable filter structure 30 further comprises: through magnetron sputtering or evaporation manufacturing, layer by layer depositing dielectric films respectively on the center positions of the first surface 301 and the second surface 302 of the first resonant cavity 31, and the third surface 303 and the fourth surface 304 of the second resonant cavity 33, to finally form the respective reflection layers 35, the dielectric films usually adopt different material combinations such as Si3N4 / SiO2 or TiO2 / SiO2 or Ta2O5 / SiO2. After forming the reflection layers 35, the following manufacturing steps are performed: forming the heating component 34 on the first surface 301 through magnetron sputtering, forming the spacing layer 32, and cascading the first resonant cavity 31 and the second resonant cavity 33. Among them, forming the heating component 34 on the first surface 301 through magnetron sputtering comprises: forming the heating element 341 on the first surface 301 through magnetron sputtering, and the heating element 341 surrounds the first reflection layer 351; forming the temperature measuring element 342 on the first surface 301 through magnetron sputtering, and the temperature measuring element 342 surrounds the heating element 341.

[0058] In other embodiments of the present application, there is no strict sequence requirement for the manufacturing of the heating component 34 and the first reflection layer 351, the second reflection layer 352 and the third reflection layer 353 need to be formed before the first resonant cavity 31 and the second resonant cavity 33 are cascaded, and the first reflection layer 351 and the fourth reflection layer 354 can be adjusted to other processing sequences according to the needs of on-site processing.

[0059] The above structure and process are all processed by micro-electro-mechanical system (MEMS, Micro-Electro-Mechanical System), and the consistency of the finished product is high, which is suitable for mass production.

[0060] The tunable filter structure 30 of the present application is based on the vernier effect, which overcomes the problem of limited refractive index range of the existing filter, and further realizes the output and tuning of a larger range of transmitted wavelengths. In addition, the wavelength tunable light source system 1 provided by the present application does not need to set movable parts, and only needs to change the heating temperature of the tunable filter structure 30 to realize the change of the transmitted wavelength, and the working reliability is high. Therefore, the tunable filter structure 30 and the wavelength tunable light source system 1 provided by the present application have the advantages of simple structure, compactness, high integration, low cost, and are beneficial to mass production.

[0061] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A tunable filter structure, characterized in that: include: A first resonant cavity comprising a first surface and a second surface opposite to each other; a heating component, the heating component being disposed on the first surface; a spacer layer, the spacer layer being provided on the second surface of the first resonant cavity; a second resonant cavity, cascaded with the first resonant cavity via the spacer layer, wherein the free spectral range of the first resonant cavity is different from the free spectral range of the second resonant cavity; The spacer layer is annular to form an air cavity between the first resonant cavity and the second resonant cavity; The thermo-optic coefficient of the second resonant cavity is smaller than the thermo-optic coefficient of the first resonant cavity; the heating component is used to change the refractive index of the first resonant cavity to adjust the transmission wavelength of the tunable filter structure; The tunable filter structure further includes a reflective layer, wherein the reflective layer includes a first reflective layer, and the first reflective layer is disposed at the center of the first surface.

2. The tunable filter structure according to claim 1, characterized in that: The heating assembly comprises: A heating element is disposed on the first surface and surrounds the first reflective layer.

3. The tunable filter structure according to claim 2, characterized in that: The heating element is a non-temperature sensitive resistor.

4. The tunable filter structure according to claim 2, characterized in that: The heating assembly further comprises: A temperature measuring element is disposed on the first surface and surrounds the heating element.

5. The tunable filter structure according to claim 4, characterized in that: The temperature measuring element is a temperature sensitive resistor.

6. A method for manufacturing a tunable filter structure, characterized in that: include: Providing a first resonant cavity, the first resonant cavity having a first surface and a second surface opposite to each other; forming a heating assembly on the first surface; forming a spacer layer on the second surface of the first resonant cavity, wherein the spacer layer is annular; A second resonant cavity is formed on the spacer layer, so that the second resonant cavity is cascaded with the first resonant cavity through the spacer layer, and an air cavity is formed between the first resonant cavity and the second resonant cavity.

7. The manufacturing method according to claim 6, characterized in that Before forming the heating assembly on the first surface, the method further includes: A first reflective layer is formed by stacking multiple dielectric films on the first surface through magnetron sputtering or evaporation.

8. The manufacturing method according to claim 7, characterized in that The step of forming a heating assembly on the first surface includes: forming a heating element on the first surface by magnetron sputtering, wherein the heating element is disposed around the first reflective layer; A temperature measuring element is formed on the first surface by magnetron sputtering, and the temperature measuring element is arranged around the heating element.

9. A wavelength tunable light source system, characterized in that: include: Gain chip; a collimating lens, the collimating lens being disposed on one side of the gain chip and being used to collimate the light emitted by the gain chip; The tunable filter structure according to any one of claims 1 to 5, wherein the tunable filter structure and the gain chip are respectively arranged on both sides of the collimating lens, and the tunable filter structure is used to adjust the transmission wavelength to filter light of a specific wavelength; A reflector is provided on one side of the tunable filter structure so as to reflect the light guided out by the tunable filter structure and reintroduce it into the tunable filter structure.

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