Thermally tunable ring resonator filter based on topological valley photonic crystal

Abstract

The present invention relates to the field of topological photonic crystals and integrated photonic chips, and discloses a thermally tunable ring resonant filter based on topological valley photonic crystals, which can realize thermally tunable filtering in the optical communication band. The present invention comprises a silicon substrate; the silicon substrate is divided into a first region, a second region and a third region by a straight dividing line and a ring dividing line; the straight dividing line is located on the straight line where the light incident direction is located; the first region and the third region are respectively arranged with a row of first circular air holes on one side close to the straight dividing line to form a straight waveguide, and the second region and the third region are respectively arranged with a row of first circular air holes on one side close to the ring dividing line to form a ring waveguide. The device of the present invention has a small size and a simple structure, and is suitable for photonic chip integration.

Description

Technical Field

[0001] The invention relates to the field of topological photonics and optical communication systems, and in particular to a thermally tunable ring resonant filter based on valley photonic crystals. Background Art

[0002] In recent years, silicon photonics has been considered one of the most promising photonic integration platforms because it combines very high refractive index contrast (silicon to air) and the ability to directly use CMOS technology to manufacture photonic chips. Silicon photonic devices show unprecedented compactness, especially wavelength selective devices. Ring resonators play an important role in silicon photonic devices because the high refractive index of silicon makes the size of ring resonators unprecedentedly small.

[0003] Typically, a ring resonator consists of a set of waveguides, in which at least one closed loop is coupled to the input waveguide and the output waveguide. The working principle of the ring resonator is based on the interference of light at the resonant wavelength, and the intensity gradually increases after multiple round trips. Since resonance only occurs when the optical path length of the resonator is exactly an integer of a wavelength, the ring resonator can be used as a filter. In addition, two or more ring resonators and waveguides can be coupled to each other to form an add / subtract filter or an all-pass filter. In addition, ring resonators can be applied to wavelength division multiplexing devices, logic gates, optical modulators, tunable lasers, optoelectronic devices, etc. Tunable ring resonators have also been widely studied. In 2019, Su et al. (Record Purcell factors in ultracompact hybrid plasmonic ring resonators [J]. Science Advances, 2019, 5 (8): eaav1790) designed a tunable ring resonator coupled with a traditional straight waveguide and a circular ring, with a quality factor Q of 320, which can be adjusted by changing the temperature, and the modulation efficiency reaches 0.052nm / ℃. In 2008, Shen et al. (Thermally tunable microring resonator for self-collimated beams in photonic crystals [C] International Workshop on Metamaterials. IEEE, 2008) designed a tunable ring resonator based on photonic crystal straight waveguide and square ring coupling in the optical communication band. The quality factor Q is 363, which can be adjusted by changing the temperature, and the modulation efficiency is 0.08nm / ℃.

[0004] A ring resonator exhibits a series of equally spaced resonance peaks, and the spacing between these resonance peaks is defined as the free spectral range (FSR). In many applications, there will be a relatively large FSR (a few nanometers), which requires the size of the ring to be small. Although the high refractive index contrast between silicon and air imposes strong constraints on waveguides, including traditional silicon waveguides and waveguide-based photonic crystal (PC) structures, structural defects during the manufacturing process still introduce strong optical losses, reducing the performance of microring resonators. In contrast, topological photonic crystals (TPCs) have unique anti-scattering unidirectional transmission properties. In recent years, with the development of valley photonic crystal (VPC) structures, efficient ring resonators with small size, low loss and integrability can be realized. In 2021, Gu et al. (A topological photonic ring-resonator for on-chip channel filters [J]. Journal of Lightwave Technology, 2021, PP (99): 1-1) designed a topological valley photonic crystal ring resonator filter in the optical communication band. Furthermore, the resonant wavelength can be changed by simply increasing or decreasing the effective optical path length of each ring, so the effective optical path length of the structure can be tuned by controlling the effective refractive index of the structure without changing the geometry, which is important in the application of silicon photonic devices.

[0005] However, in the prior art, there is no tunable filter device based on topological valley photonic crystals in the optical communication band. Summary of the invention

[0006] The present invention overcomes the deficiencies of the prior art and aims to solve the technical problem of providing a thermally tunable ring resonant filter based on a topological valley photonic crystal to realize an adjustable filter device in an optical communication band based on a photonic crystal structure.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a thermally tunable ring resonator filter based on a topological valley photonic crystal, characterized in that it includes a silicon substrate; the silicon substrate is divided into a first region, a second region and a third region by a straight dividing line and a ring dividing line; the straight dividing line is located on the straight line where the light incident direction is located; the first region is located on one side of the straight dividing line, the second region and the third region are located on the other side of the straight dividing line, and the second region is located in the third region;

[0008] In the first region and the second region, the first circular air holes and the second circular air holes are respectively arranged in a triangular lattice and staggered to form a first energy valley type photonic crystal, and in the third region, the second circular air holes and the first circular air holes are respectively arranged in a triangular lattice and staggered to form a second energy valley type photonic crystal;

[0009] A row of first circular air holes is arranged on one side of the first area and the third area close to the straight dividing line to form a straight waveguide, and a row of first circular air holes is arranged on one side of the second area and the third area close to the circular dividing line to form a circular waveguide, and the circular waveguide is connected to the straight waveguide; the radii of the first circular air hole and the second circular air hole are R1 and R2 respectively, which satisfy the condition: R1>R2.

[0010] The lattice constant of the triangular lattice formed by the first circular air hole and the second circular air hole is both a=482 nm.

[0011] The radii of the first circular air hole and the second circular air hole are respectively: R1=129nm, and the radius of the small circular air hole is R2=43nm.

[0012] The annular waveguide is an equilateral triangle with one side being parallel to the straight waveguide, and the vertex of the annular waveguide intersects with the straight waveguide.

[0013] The thickness of the silicon substrate is 220 nm, and the first circular air hole and the second circular air hole penetrate the silicon substrate.

[0014] The thermally tunable ring resonant filter based on topological valley photonic crystals changes the refractive index of the silicon substrate by changing the temperature of the silicon substrate, thereby achieving an adjustable filtering function.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides a thermally tunable ring resonator filter based on topological valley photonic crystals. The anti-scattering and unidirectional transmission properties of topological photonic crystals are used to construct a filter that couples a thermally tunable topological ring resonator with a topological straight waveguide to achieve a high quality factor Q value and a wide free spectrum range (FSR). The position of the resonance peak formed by the coupled resonator is adjusted by changing the temperature. Due to the characteristics of silicon, the increase (decrease) in temperature increases (decreases) its refractive index, causing the resonance peak to move to a long (short) wavelength. Within the temperature variation range of 100K–750K, the modulation phase reaches 7.73π, and the adjustment efficiency is 0.064nm / K. The entire reversible adjustment process provides great convenience for optoelectronic integration. The design is small in size and simple in structure, and is suitable for on-chip integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the structure of a thermally tunable ring resonator filter based on a topological valley photonic crystal provided by an embodiment of the present invention;

[0018] Figure 2 This is the energy band diagram of the topological structure of the first valley photonic crystal (VPC1) in an embodiment of the present invention;

[0019] Figure 3 Schematic diagram of the change of the central wavelength of the energy band of the first valley photonic crystal (VPC1) topological structure with temperature in an embodiment of the present invention;

[0020] Figure 4 The edge state energy band structure diagram of the topological straight waveguide at different temperatures in the embodiment of the present invention (the display temperature is 100K, 450K, and 750K);

[0021] Figure 5 This is a diagram showing the electric field intensity distribution of the TE mode light wave transmission at a wavelength of 1531.12 nm of the ring resonator filter in an embodiment of the present invention;

[0022] Figure 6 This is a distribution diagram of the electric field intensity of the TE mode light wave transmission at a wavelength of 1538.13nm of the ring resonator filter in an embodiment of the present invention;

[0023] Figure 7 1 is the wavelength transmittance spectrum of the ring resonator filter at a temperature of 100K in an embodiment of the present invention;

[0024] Figure 8 The wavelength transmittance spectra of the ring resonator filter at different temperatures in an embodiment of the present invention;

[0025] Fig. 9 A linear fitting diagram showing the change of the resonance wavelength of the ring resonator filter at different temperatures with temperature in an embodiment of the present invention;

[0026] Figure 1 In the figure, 1 is a straight waveguide, 2 is a ring waveguide, 3 is a first region, 4 is a second region, 5 is a third region, 6 is a first energy valley type photonic crystal, 7 is a second energy valley type photonic crystal, 8 is a straight line boundary, 9 is a ring boundary, 10 is a first circular air hole, and 11 is a second circular air hole. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] like Figure 1As shown, an embodiment of the present invention provides a thermally tunable annular resonant filter based on a topological valley photonic crystal, comprising a silicon substrate; the silicon substrate is divided into a first region 3, a second region 4 and a third region 5 by a straight dividing line 8 and a ring dividing line 9; the straight dividing line 8 is located on a straight line where the light incident direction is located; the first region 3 is located on one side of the straight dividing line 8, the second region 4 and the third region 5 are located on the other side of the straight dividing line 8, and the second region 4 is located in the third region 5, that is, the second region 4 is surrounded by the third region 5.

[0029] In the first region 3 and the second region 4, the first circular air holes 10 and the second circular air holes 11 are respectively arranged in a triangular lattice staggered to form a first energy valley type photonic crystal (VPC1) 6, and in the third region 5, the second circular air holes 11 and the first circular air holes 10 are respectively arranged in a triangular lattice staggered to form a second energy valley type photonic crystal (VPC2) 7. Specifically, in this embodiment, the first energy valley type photonic crystal and the second energy valley type photonic crystal are mirror structures, that is: in the first energy valley type photonic crystal, in the minimum hexagonal honeycomb structure formed with the center of the first circular air hole as the vertex, the second circular air hole forms an inverted equilateral triangle, on the contrary, in the second energy valley type photonic crystal, in the minimum hexagonal honeycomb structure formed with the center of the first circular air hole as the vertex, the second circular air hole forms an upright equilateral triangle.

[0030] A row of first circular air holes 10 are arranged on one side of the first area 3 and the third area 5 close to the straight dividing line 8 to form a straight waveguide 1, and a row of first circular air holes 10 are arranged on one side of the second area 4 and the third area 5 close to the annular dividing line 9 to form an annular waveguide 2, and the annular waveguide 2 is connected to the straight waveguide 2, and the radii of the first circular air hole 10 and the second circular air hole 11 are R1 and R2 respectively, which satisfy the condition: R1>R2.

[0031] Specifically, in this embodiment, the lattice constants of the triangular lattices formed by the first circular air holes 10 and the second circular air holes 11 are both a=482 nm.

[0032] Specifically, in this embodiment, the radii of the first circular air hole 10 and the second circular air hole 11 are respectively: R1 = 129 nm, and the radius of the small circular air hole is R2 = 43 nm.

[0033] Specifically, in this embodiment, the annular waveguide 2 is an equilateral triangle with one side being parallel to the straight waveguide 1 , and the vertex of the annular waveguide 2 intersects with the straight waveguide 1 .

[0034] Specifically, in this embodiment, the thickness of the silicon substrate is 220 nm, and the first circular air hole 10 and the second circular air hole 11 penetrate the silicon substrate.

[0035] Preferably, in this embodiment, the centers of the circular air holes (including the first circular air hole 10 and the second circular air hole 11) in all regions (including the first region 3, the second region 4, and the third region 5) on the silicon substrate 1 follow a uniform hexagonal honeycomb structure arrangement, and the side length of the hexagonal honeycomb is Wherein a represents the lattice constant of the triangular lattice formed by the first circular air holes 10 or the second circular air holes 11 .

[0036] Specifically, in this embodiment, the refractive index of the silicon substrate is changed by changing the temperature, thereby achieving an adjustable filtering function.

[0037] A thermally tunable ring resonator filter based on a topological valley photonic crystal provided by an embodiment of the present invention can be processed based on CMOS technology, and its processing method is: first select a standard SOI wafer with a 220nm thick top silicon and a 3μm thick silicon dioxide layer, the first step is to coat a photoresist (ZEP520A) on the silicon surface, then use electron beam lithography to expose the photoresist, and then use the photoresist as a mask layer for reactive ion etching. In this step, it is important to obtain a vertically etched side wall to maintain the mirror symmetry of the photonic crystal structure relative to the xy plane located in the middle of the photonic crystal plate. Then on this basis, a photoresist is coated on the fabricated structure, and a pattern to be etched is made on the photoresist at the same time, and then the photoresist is used as a mask, and diluted hydrofluoric acid is used to etch for 15 minutes to remove the silicon dioxide substrate. This can obtain a free-standing ring resonator structure.

[0038] like Figure 2 As shown in FIG. 1 , it is an energy band diagram of the first energy valley photonic crystal (VPC1) in an embodiment of the present invention. The dotted shaded area is the air light cone. It can be seen that there is a TE mode band gap in the range of 1455.31nm–1776.72nm, which is marked by the vertical shaded area. The second energy valley photonic crystal (VPC2) has the same energy band structure as the first energy valley photonic crystal (VPC1). Figure 3 In the figure, the central wavelength of the energy band of the first valley photonic crystal (VPC1) changes at different temperatures, where the temperature changes from 100K to 750K (the temperature interval is 50K, except for the temperature interval of 250K to 293K, which is 43K, and the temperature interval of 293K to 350K, which is 57K). It can be seen that as the temperature increases, the central wavelength of the energy band of the first valley photonic crystal (VPC1) moves toward a longer wavelength because the refractive index of silicon increases.

[0039] like Figure 4As shown, it is the edge state energy band diagram of the topological straight waveguide 1 in the embodiment of the present invention, in which the horizontal line shadow area is the body band, and the dotted line shadow area is the air light cone. It can be seen from the figure that the topological waveguide is in different working bands at different temperatures.

[0040] like Figure 5 The distribution diagram of the electric field intensity of the TE mode light wave transmission at a wavelength of 1531.12nm at a temperature of 100K in the ring resonant filter. Since the resonance condition is met at 1531.12nm, it can be seen that in the resonance mode, the light wave is well confined in the ring and plays a filtering role. Figure 6 This is the distribution diagram of the electric field intensity of TE mode light wave transmission in the ring resonator filter at a wavelength of 1538.13nm at a temperature of 100K. It can be seen that at 1538.13nm, the light wave is almost transmitted in the straight waveguide.

[0041] like Figure 7 As shown in the figure, it is the transmittance curve of the ring resonator filter at a temperature of 100K. It can be seen from the figure that the working band is in the range of 1492.57nm-1632.50nm. In this working range, there are resonance peaks with equal intervals, and the free spectrum region (FSR) is 10.54nm. At the resonance wavelength of 1531.12nm, the half-height width is 1.2nm and the quality factor is 1275.93. At 1538.13nm, the transmittance reaches more than 0.78. Figure 8 As shown in Figure 1, taking the specific peak of 1531.12nm at 100K as the reference, it can be seen that the peak position moves toward longer wavelengths as the temperature increases. Fig. 9 As shown, the shift of a specific resonance peak at different temperatures is based on 1531.12nm at 100K. The shift of the resonance peak and the change in temperature satisfy a linear relationship, and the modulation efficiency is 0.064nm / K. The output end of the resonant ring continues to maintain a low transmittance, so it can be said that this structure realizes the function of adjustable filtering. In this embodiment, the silicon substrate adopts a dispersive refractive index; the refractive index of the white air hole is 1.

[0042] The present invention provides a thermally tunable annular resonant filter based on topological valley photonic crystals. The filter is obtained by forming a straight waveguide and an annular waveguide at the boundary of two photonic crystals. Due to the joint action of the valley edge states at the edges of the first photonic crystal VPC1 and the second photonic crystal VPC2, unidirectional transmission of photons in the straight waveguide and the annular waveguide can be achieved. The high quality factor Q value and wide free spectrum range (FSR) can be achieved. Due to the characteristics of silicon, the increase (decrease) of temperature increases (decreases) its refractive index, causing the resonance peak to move to a long (short) wavelength. Within the temperature variation range of 100K–750K, the modulation phase reaches 7.73π, and the regulation efficiency is 0.064nm / K. The entire reversible regulation process provides great convenience for optoelectronic integration. At the same time, the device is small in size and simple in structure, and is suitable for photonic chip integration. Therefore, within the band near 1550nm, the present invention can change the refractive index of silicon by changing the temperature, and further change the relative refractive index of silicon and air, which can be used to realize the tunable filtering function of the valley photonic crystal device.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thermally tunable ring resonator filter based on topological valley photonic crystals, characterized in that: The invention comprises a silicon substrate, wherein the silicon substrate is divided into a first region (3), a second region (4) and a third region (5) by a straight dividing line (8) and a circular dividing line (9); the straight dividing line (8) is located on a straight line where the light incident direction is located; the first region (3) is located on one side of the straight dividing line (8), the second region (4) and the third region (5) are located on the other side of the straight dividing line (8), and the second region (4) is located within the third region (5); In the first region (3) and the second region (4), the first circular air holes (10) and the second circular air holes (11) are arranged in a triangular lattice to form a first energy valley type photonic crystal, and in the third region (5), the second circular air holes (11) and the first circular air holes (10) are arranged in a triangular lattice to form a second energy valley type photonic crystal; A row of first circular air holes (10) is arranged on one side of the first region (3) and the third region (5) close to the straight dividing line (8) to form a straight waveguide (1); a row of first circular air holes (10) is arranged on one side of the second region (4) and the third region (5) close to the circular dividing line (9) to form a circular waveguide (2); the circular waveguide (2) is connected to the straight waveguide (1); the radii of the first circular air holes (10) and the second circular air holes (11) are R1 and R2 respectively, which satisfy the condition: R1>R2; The annular waveguide (2) is an equilateral triangle, one side of which is parallel to the straight waveguide (1), and the vertex of which intersects with the straight waveguide (1).

2. The thermally tunable ring resonator filter based on topological valley photonic crystal according to claim 1 is characterized in that: The lattice constant of the triangular lattice formed by the first circular air hole (10) and the second circular air hole (11) is both a=482nm.

3. The thermally tunable ring resonator filter based on topological valley photonic crystal according to claim 1, characterized in that: The radii of the first circular air hole (10) and the second circular air hole (11) are respectively: R1=129 nm, and R2=43 nm.

4. The thermally tunable ring resonator filter based on topological valley photonic crystal according to claim 1, characterized in that: The thickness of the silicon substrate is 220 nm, and the first circular air hole (10) and the second circular air hole (11) penetrate the silicon substrate.

5. The thermally tunable ring resonator filter based on topological valley photonic crystal according to claim 1, characterized in that: The refractive index of the silicon substrate is changed by changing the temperature of the silicon substrate, thereby achieving an adjustable filtering function.

Images