Waveguide grating filter based on optical phase change material and filtering tuning method

Abstract

The invention discloses a waveguide grating filter based on an optical phase change material and a filtering tuning method, the waveguide grating filter comprises a substrate, a buffer layer and a phase change material layer, a waveguide grating structure is defined in the phase change material layer through an external energy field, and the waveguide grating structure comprises a core waveguide and periodic lateral gratings arranged on the two sides of the core waveguide. According to the invention, the reversible phase change characteristic of a phase change material is utilized, and a tuning method of writing-erasing-rewriting is adopted: laser is selectively irradiated on a phase change material layer to form a crystalline waveguide grating structure; the crystalline region is recovered to be in an amorphous state through heating or laser scanning, so that erasing is realized; and flexible regulation and control of the spectral response of the filter are realized by writing structural parameters such as the tooth width, the duty ratio and the core waveguide size of the dynamic tuning grating again through laser. The filter works in a communication wave band of 1.5-1.6 microns, and has the outstanding advantages of reconfigurable structure, non-volatile property, flexible tuning, simple manufacturing and the like.

Description

Technical Field

[0001] This invention relates to a waveguide grating filter, and more particularly to a waveguide grating filter based on optical phase change materials and a filtering tuning method. Background Technology

[0002] Waveguide grating filters are core wavelength selection devices in integrated photonics systems. Their function is based on the reflection or coupling of specific wavelengths of light by the periodic structure introduced into the waveguide. They play a crucial role in dense wavelength division multiplexing (DWDM) optical communication systems, accurately filtering the target channel from multi-wavelength composite signals, making them an indispensable key component for achieving high-speed, high-capacity optical communication. Compared to free-space or fiber gratings, they offer significant advantages such as smaller size, easier integration, and more flexible design.

[0003] Traditional waveguide grating filters rely entirely on micro- and nanofabrication techniques for fabrication. Once fabricated, their structure is permanently fixed, and their filtering characteristics are thus fixed. To impart tunability, researchers have primarily developed two technical approaches: one is based on thermo-optic or electro-optic effects, using an external electric field or current to fine-tune the refractive index of the waveguide material, thereby shifting the resonant wavelength; the other is the emerging phase change material (PCM) integration technology, which involves depositing PCM thin films on a pre-fabricated fixed waveguide structure and modulating the equivalent refractive index of the covered region by changing the crystal state of the PCM, thus achieving non-volatile functional tuning.

[0004] The aforementioned existing technologies have the following fundamental limitations: 1. Traditional fixed-structure filters lack flexibility, and device failure means disposal, resulting in high costs; 2. Tuning based on thermo-optic / electro-optic effects requires continuous power supply to maintain the state, resulting in high power consumption and a limited tuning range; 3. Existing PCM-based solutions modify material properties on a fixed physical structure, and the basic performance of the filters is limited during manufacturing, making it impossible to fundamentally reconfigure them according to requirements, which greatly limits their application potential in future adaptive and programmable optical networks. Summary of the Invention

[0005] Purpose of the invention: The first purpose of this invention is to provide a waveguide grating filter with a large tuning range, reconfigurable structure, and simple manufacturing process; another purpose of this invention is to provide a filtering and tuning method for the filter.

[0006] Technical Solution: The waveguide grating filter based on optical phase change material of the present invention includes a substrate, a buffer layer disposed on the substrate, and a phase change material layer disposed on the buffer layer, which is composed of an optical phase change material having reversible crystalline and amorphous phase transition characteristics; the phase change material layer includes an amorphous background region and a waveguide grating structure; the waveguide grating structure is composed of a crystalline phase change material and is defined in the phase change material layer by an external energy field; the waveguide grating structure includes a core waveguide and a periodic lateral grating disposed on at least one side of the core waveguide; wherein, the physical dimensions of the core waveguide and the periodic lateral grating can be erased and redefined by an external energy field acting on the phase change material layer for dynamically adjusting the filtering response.

[0007] Preferably, periodic lateral gratings are symmetrically distributed on opposite sides of the core waveguide.

[0008] Preferably, the periodic lateral grating is composed of periodically arranged grating teeth.

[0009] Preferably, the substrate is a silicon dioxide substrate.

[0010] Preferably, the buffer layer is a silicon nitride layer with a thickness of 0.3 micrometers.

[0011] Preferably, a silicon dioxide protective layer is provided on the phase change material layer.

[0012] Preferably, the optical phase change material is Sb2Se3.

[0013] Preferably, the redefinable physical dimensions include the width and length of the core waveguide, the unit width and duty cycle of the lateral grating; wherein the width of the core waveguide is adjustable from 0.7 micrometers to 1.2 micrometers, and the length is adjustable from 50 micrometers to 150 micrometers; the unit width of the lateral grating is adjustable from 0.2 micrometers to 0.5 micrometers, and the duty cycle is adjustable from 1 / 8 to 1 / 4.

[0014] The tuning method of the present invention includes the following steps:

[0015] (1) Writing process: Using laser to selectively irradiate a predetermined area of ​​the phase change material layer, the amorphous phase change material in the irradiated area is transformed into a crystalline state, thereby forming or modifying the waveguide grating structure;

[0016] (2) Erasure process: Apply external stimulation to the phase change material layer to restore the formed crystalline region to the amorphous state, so as to erase the waveguide grating structure.

[0017] Preferably, the external stimulus during the erasure process in step (2) is global heating or laser scanning.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The physical size of the grating can be dynamically changed to realize the reversible reconstruction of the filter hardware form; (2) It can realize the flexible control of various filtering responses in the communication band, providing a unified platform for different application needs; (3) Based on the characteristics of phase change materials reversibly converting between crystalline and amorphous states, the tuned state does not require external energy to maintain, which significantly reduces the system energy consumption; (4) Only simple coating and laser phase change processes are required, avoiding complex photolithography and etching processes, greatly reducing manufacturing difficulty and cost, which is conducive to industrial application. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0020] Figure 2 This is a cross-sectional view of the waveguide grating of the present invention, including the left and right grating teeth;

[0021] Figure 3 This is a cross-sectional view of the waveguide grating of the present invention excluding the left and right grating teeth;

[0022] Figure 4 It is the total transmittance spectrum of the input transverse electric fundamental mode optical signal after passing through grating filters with four different widths of grating teeth on both sides in sequence;

[0023] Figure 5 It is the total transmittance spectrum of the input transverse electric fundamental mode optical signal after passing through grating filters of four different core waveguide lengths in sequence;

[0024] Figure 6 It is the electric field evolution (passband) of the input transverse electric fundamental mode optical signal along the transmission direction of the waveguide grating filter.

[0025] Figure 7 It is the electric field evolution (stopband) of the input transverse electric fundamental mode optical signal along the transmission direction of the waveguide grating filter. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Example 1

[0028] This embodiment provides a method for fabricating a waveguide grating filter based on optical phase change materials.

[0029] First, a silicon nitride layer 104 with a thickness of 0.3 micrometers is formed on a silicon dioxide substrate 106 by chemical vapor deposition. Next, a phase change material Sb₂Se₃ thin film with a thickness of 0.05 micrometers is deposited on the silicon nitride layer 104 by magnetron sputtering. The initial state of this phase change material layer is amorphous 105. To prevent oxidation of the phase change material, a silicon dioxide protective layer 107 with a thickness of approximately 0.02 micrometers is deposited on top of the Sb₂Se₃ thin film by magnetron sputtering.

[0030] A pulsed laser is used to selectively write crystalline regions onto a phase change material layer by controlling the laser scanning path, forming the basic structure of a filter. The written structure includes: input and output waveguides, a core waveguide 101, a left grating tooth 102, and a right grating tooth 103, where 102a and 103a represent the cross-sections of the waveguide gratings containing the left and right grating teeth, respectively. The core waveguide 101 is a straight waveguide structure with a width of 0.9 μm, a length of 150 μm, and a height of 0.05 μm. The left grating tooth 102 and the right grating tooth 103 are both periodic matrix units, with the same length as the core waveguide along the light propagation direction, a width of 0.4 μm, a height of 0.05 μm, a period of 0.4 μm, and a duty cycle of 1 / 4. The unwritten region 105 remains amorphous, and the light field is constrained by the refractive index difference between the crystalline and amorphous regions.

[0031] Example 2

[0032] This embodiment verifies the method of achieving filter response tuning by changing the width of the grating teeth.

[0033] The same preparation method as in Example 1 was used, but during the laser writing process, the widths (Rw) of the left grating teeth 102 and the right grating teeth 103 were systematically changed to 0.2 μm, 0.3 μm, 0.4 μm and 0.5 μm respectively, while keeping other parameters unchanged.

[0034] As attached Figure 4 As shown, by inputting a transverse electric fundamental mode optical signal of a certain wavelength band into the input waveguide and detecting the transmittance of the optical signal in the output waveguide after passing through the waveguide grating, the transmission spectrum under different grating tooth widths can be obtained. The results show that the wavelength range of the filtering response is between 1.5 and 1.6 micrometers, which is located in the communication band. Comparing the obtained spectra, it is found that changing the width of the left grating tooth 102 and the right grating tooth 103 leads to changes in the transmittance spectral bandwidth and center wavelength. This result indicates that by adjusting the structural parameter of the grating tooth width, different filtering response requirements can be met, and the filtering characteristics can be effectively tuned.

[0035] Example 3

[0036] This embodiment verifies the method of achieving extinction ratio tuning by changing the length of the core waveguide 101.

[0037] The same fabrication method as in Example 1 was used, but during the device fabrication process, the grating tooth width was kept at 0.5 micrometers, the duty cycle at 1 / 4, and the period at 0.4 micrometers. Only the length (L) of the core waveguide 101 was changed, and set to 50 micrometers, 70 micrometers, 100 micrometers, and 150 micrometers, respectively.

[0038] As attached Figure 5 As shown, the total spectrum is obtained by inputting a transverse electric fundamental mode optical signal of a certain wavelength band into the input waveguide and detecting the transmittance of the optical signal in the output waveguide after passing through the waveguide grating. The results show that the wavelength range of the filtering response is between 1.5 and 1.6 micrometers, which is within the communication band. Comparing the obtained spectra reveals that different core waveguide lengths (101) lead to variations in the extinction ratio of the transmittance spectrum. This variation can meet different filtering response requirements, providing a simple and unified solution for various filtering response needs.

[0039] Example 4

[0040] This embodiment verifies the filtering function of the filter through electric field propagation simulation.

[0041] Based on the structural parameters in Example 1, transverse electric fundamental mode optical signals with wavelengths of 1.56 micrometers (passband) and 1.577 micrometers (stopband) were input, respectively. (See attached diagram.) Figure 6 Appendix Figure 7 As shown, at the passband wavelength, most optical signals can pass smoothly through the waveguide grating structure; however, at the stopband wavelength, most optical signals are reflected at the grating. This result confirms that the filter achieves wavelength selection based on the Bragg reflection principle.

Claims

1. A waveguide grating filter based on optical phase change materials, characterized in that, The system includes a substrate (106), a buffer layer (104) disposed on the substrate, and a phase change material layer disposed on the buffer layer (104) and composed of an optical phase change material having reversible crystalline and amorphous phase change characteristics; the phase change material layer includes an amorphous background region (105) and a waveguide grating structure; the waveguide grating structure is composed of a crystalline phase change material and is defined in the phase change material layer by an external energy field; the waveguide grating structure includes a core waveguide (101) and a periodic lateral grating disposed on at least one side of the core waveguide (101); The physical dimensions of the core waveguide (101) and the periodic lateral grating can be erased and redefined by an external energy field acting on the phase change material layer to dynamically adjust the filtering response.

2. The waveguide grating filter according to claim 1, characterized in that, The periodic lateral gratings are symmetrically distributed on opposite sides of the core waveguide.

3. The waveguide grating filter according to claim 1 or 2, characterized in that, The periodic lateral grating is composed of periodically arranged grating teeth.

4. The waveguide grating filter according to claim 1, characterized in that, The substrate (106) is a silicon dioxide substrate.

5. The waveguide grating filter according to claim 1, characterized in that, The buffer layer (104) is a silicon nitride layer with a thickness of 0.3 micrometers.

6. The waveguide grating filter according to claim 1, characterized in that, A silicon dioxide protective layer (107) is provided on the phase change material layer.

7. The waveguide grating filter according to claim 1, characterized in that, The optical phase change material is Sb2Se3.

8. The waveguide grating filter according to claim 1, characterized in that, The redefined physical dimensions include the width and length of the core waveguide (101), the unit width and duty cycle of the lateral grating; wherein the width of the core waveguide (101) is adjustable from 0.7 micrometers to 1.2 micrometers, and the length is adjustable from 50 micrometers to 150 micrometers; the unit width of the lateral grating is adjustable from 0.2 micrometers to 0.5 micrometers, and the duty cycle is adjustable from 1 / 8 to 1 / 4.

9. A tuning method for a waveguide grating filter as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Writing process: Using laser to selectively irradiate a predetermined area of ​​the phase change material layer, the amorphous phase change material in the irradiated area is transformed into a crystalline state, thereby forming or modifying the waveguide grating structure; (2) Erasure process: Apply external stimulation to the phase change material layer to restore the formed crystalline region to the amorphous state, so as to erase the waveguide grating structure.

10. The tuning method according to claim 9, characterized in that: The external stimulus during the erasure process is global heating or laser scanning.

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