Optical waveguide device based on directional coupler

Abstract

Phase-change material films are embedded in two waveguides of the directional coupler to form mixed waveguides, the refractive index of the phase-change material films is larger than that of a core layer and a cladding layer in a straight waveguide, and the two mixed waveguides serve as interference arms respectively. And the phase difference of the two interference arms is realized by changing the crystal phase of the phase change material film. By optimizing the parameters of the directional coupler and the parameters of the phase-change material film, the optical waveguide device can realize the functions of an optical switch, a polarization beam splitter, a 3dB coupler or a tunable filter. According to the optical waveguide device, the size of the interference arm is reduced, and a bent waveguide connected between a directional coupler and the interference arm of a conventional MZI is omitted, so that the structure of the device is more compact, and the power consumption of dynamic switching of an optical path is lower.

Description

Technical Field

[0001] The present invention relates to an integrated optical waveguide device, and more particularly to an optical waveguide device based on a directional coupler. Background Art

[0002] With the rapid development of integrated optics, optical tunable units, such as optical switches, tunable phase shifters, and tunable couplers, make the system more flexible, and promote the widespread application of photonic integrated circuits in the fields of optical computing, optical neural networks, photonic storage, and data centers. In these application fields, the state of the optical switch does not need to be switched frequently, and the switching speed is less important than the power consumption. In general, optical tuning units usually rely on weak tuning mechanisms, such as thermo-optical effect, electro-optical effect, and free carrier effect. These weak tuning mechanisms provide small refractive index changes and require a large action length to achieve a phase shift of π. At the same time, the maintenance of the state requires continuous power consumption, which not only limits the tuning range of the optical tuning unit and the large-scale scalability of the tunable unit, but also leads to larger device size and higher energy consumption. When multiple tunable units are required in the system, high energy consumption can easily cause thermal crosstalk to the system, affecting the performance of the system. If the high performance of the system is to be maintained, a more complex tuning mechanism is required. Summary of the invention

[0003] In view of the deficiencies of the prior art, the present invention proposes an integrated optical waveguide device based on a directional coupler.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] An optical waveguide device based on a directional coupler comprises an input waveguide, a curved waveguide I, a directional coupler, a curved waveguide II, and an output waveguide connected in sequence; the directional coupler comprises two straight waveguides with a spacing of submicrometers or micrometers, a phase change material film is embedded in the core layers of the two straight waveguides, the phase change material film and the straight waveguide part in which it is embedded constitute a hybrid waveguide, and the hybrid waveguide divides the directional coupler into a waveguide coupler I and a waveguide coupler II;

[0006] By optimizing the parameters of waveguide coupler I and waveguide coupler II and the parameters of phase change material film, the functions of optical switch, polarization beam splitter, 3 dB coupler or tunable filter are realized;

[0007] The refractive index of the phase change material film is greater than the refractive index of the core layer and the cladding in the straight waveguide, and the two hybrid waveguides serve as interference arms respectively, and the phase difference between the two interference arms is achieved by changing the crystal phase of the phase change material film.

[0008] Further, the input waveguide and the output waveguide are grating couplers, inverted tapered couplers, straight waveguides, or a combination of tapered waveguides and straight waveguides;

[0009] The curved waveguide I and the curved waveguide II are cosine-type curved waveguides, sine-type curved waveguides, arc-type curved waveguides or Euler-curve-type curved waveguides;

[0010] The waveguide coupler I and the waveguide coupler II are 3 dB beam splitter structures.

[0011] Furthermore, the phase change material film is made of antimony selenide, antimony trisulfide, germanium antimony telluride, germanium antimony selenium telluride or vanadium dioxide.

[0012] Further, for all waveguides in the optical waveguide device, when the refractive index of the substrate is less than the refractive index of the core layer, from bottom to top, the waveguides include a substrate, a lower cladding layer, a core layer and an upper cladding layer, or include a substrate, a core layer and an upper cladding layer; when the refractive index of the substrate is not less than the refractive index of the core layer, from bottom to top, the waveguides include a substrate, a lower cladding layer, a core layer and an upper cladding layer;

[0013] The refractive indexes of the lower cladding layer and the upper cladding layer are both smaller than the refractive index of the core layer.

[0014] Furthermore, the upper cladding layer of the hybrid waveguide is an oxide film, and a heating electrode is placed above the upper cladding layer, and the phase change material film is heated by the heating electrode, thereby changing the phase state of the phase change material film.

[0015] Further, the phase change material film is embedded in the straight waveguide by any of the following methods:

[0016] (1) Using photolithography technology to define the directional coupler waveguide and the air slot on the directional coupler waveguide; etching the waveguide to the required depth by dry etching, thereby forming a waveguide with an air slot; using a photoresist pattern to define the air slot; depositing a layer of phase change material film so that the air slot is completely filled with the phase change material, removing the excess phase change material on the photoresist outside the air slot by a wet stripping process, obtaining a phase change material film with a length of micrometers, and spin coating or depositing a layer of oxide film on the upper surface of the waveguide as an upper cladding layer;

[0017] (2) After the waveguide is manufactured, a window is opened in the upper cladding layer of the waveguide by photolithography and etching, and an air slot with a length of micrometers is etched in the core layer of the waveguide through the window. The air slot is defined by a photoresist pattern, and a phase change material is deposited inside the air slot until the air slot is filled with the phase change material. The phase change material outside the air slot is removed by a wet stripping method, and a layer of oxide film is spin-coated or deposited on the phase change material by a deposition method as an upper cladding.

[0018] Furthermore, during the embedding process, air grooves are made in the waveguide core layer on both sides of the phase change material.

[0019] Furthermore, by optimizing the parameters of the waveguide coupler I and the waveguide coupler II and the parameters of the phase change material film, the functions of an optical switch, a polarization beam splitter, a 3 dB coupler or a tunable filter are realized, specifically:

[0020] The two phase change material films are set to different sizes, and the phase state of the phase change material is changed by applying voltage to the electrodes, so that the optical waveguide device can realize the function of tunable filtering;

[0021] By optimizing the parameters of waveguide coupler I and waveguide coupler II, the optical waveguide device can realize the function of 3 dB coupler in both TE and TM polarization modes;

[0022] By optimizing the phase change material film, when the phase change material films of the two interference arms are in different phases, when the input optical signal is in TE polarization and TM polarization, the phase differences of the corresponding two interference arms are M*π and N*π respectively. If M and N are both odd numbers, the optical waveguide device can realize the polarization-independent optical switch function; if one of M and N is an odd number and the other is an even number, the optical waveguide device can realize the polarization beam splitter function.

[0023] The function of a tunable beam splitter is achieved by tuning the ratio of crystalline to amorphous states in one of the phase change material films.

[0024] An optical waveguide device based on a directional coupler is characterized in that it includes a ring resonator and at least one straight waveguide, the straight waveguide is coupled to the ring resonator, the coupling region adopts a directional coupler structure, a phase change material film is horizontally or vertically embedded in the waveguide core layer of the directional coupler to form a hybrid waveguide, and the function of the beam splitter can be tuned by changing the crystal phase of the phase change material film, thereby realizing the functions of tunable filtering and tunable delay.

[0025] Furthermore, an electrode is provided on the annular resonator.

[0026] The technical solution provided by the embodiments of the present application may have the following beneficial effects:

[0027] In the optical waveguide device based on the directional coupler of the present invention, the phase change material film is located in the middle of the directional coupler, and the directional coupler is divided into a waveguide coupler I and a waveguide coupler II. The submicron or micron-level length portion between the phase change material film and the directional coupler constitutes a hybrid waveguide interference arm. Since the effective refractive index of the phase change material waveguide differs greatly in different phases, a phase shift of π can be achieved at a shorter action length (micron level) in different phases, which not only reduces the size of the interference arm, but also avoids the introduction of a curved waveguide connected between the interference arm and the coupler, making the device structure more compact, and the dynamic switching power consumption of the optical path is lower. After the phase change is completed, there is no need for continuous power supply to maintain the state of the phase change material, thereby maintaining the state of the switch, and achieving zero static power consumption.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0030] Figure 1 A schematic diagram of the structure of an optical waveguide device (optical switch) based on a directional coupler.

[0031] Figure 2 for Figure 1 A schematic cross-sectional view of an optical waveguide device (optical switch) based on a directional coupler is shown.

[0032] Figure 3 This is a schematic diagram of the structure of an optical waveguide device (filter) based on a directional coupler.

[0033] Figure 4 The figure is a schematic diagram of the structure of a tunable filter based on a directional coupler.

[0034] Figure 5 Schematic diagram of the structure of another tunable filter based on directional coupler.

[0035] Among them, 1 is the input waveguide; 2 is the bent waveguide I; 3 is the directional coupler; 4 is the bent waveguide II; 5 is the output waveguide; 3-1 is the substrate; 3-2 is the lower cladding; 3-3 is the core layer; 3-4 is the phase change material film; 3-5 is the upper cladding; 3-6 is the heating electrode; 6-1 is the first straight waveguide input end; 6-2 is the straight waveguide output end; 6-3 is the first coupling region; 6-4 is the first phase shifter; 7-1 is the second straight waveguide input end; 7-2 is the straight waveguide through output end; 7-3 is the straight waveguide download end; 7-4 is the second coupling region; 7-5 is the phase shifter. DETAILED DESCRIPTION

[0036] Here, exemplary embodiments are described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application.

[0037] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0038] It should be understood that although the terms first, second, third, etc. may be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0039] like Figure 1 and Figure 2 As shown, the present application provides an optical waveguide device based on a directional coupler 3, comprising an input waveguide 1, a curved waveguide I 2, a directional coupler 3, a curved waveguide II 4, and an output waveguide 5 connected in sequence; the directional coupler 3 comprises two straight waveguides with a spacing of submicron or micron order, a phase change material waveguide is embedded in the core layers of the two straight waveguides, the phase change material film 3-4 and the straight waveguide part in which it is embedded constitute a hybrid waveguide, and the hybrid waveguide divides the directional coupler 3 into a waveguide coupler I and a waveguide coupler II; wherein the refractive index of the phase change material film 3-4 is greater than the refractive index of the core layer and the cladding in the straight waveguide, the two hybrid waveguides are respectively used as interference arms, and the phase difference of the two interference arms is achieved by changing the phase state of the phase change material film 3-4.

[0040] In the optical waveguide device, the phase change material film 3-4 has three stable and reversible states: crystalline phase, amorphous phase, and partial crystalline phase. In the three states, the refractive index of the phase change material is greater than the refractive index of the waveguide, resulting in no coupling of the fundamental mode in the hybrid waveguide. The hybrid waveguide can act as an interference arm, and the optical signal in the hybrid waveguide is mainly concentrated in the phase change material; the submicron or micron-level length portion between the phase change material film 3-4 and the directional coupler 3 constitutes a hybrid waveguide. Since the effective refractive index of the phase change material waveguide differs greatly in different phases, it is possible to achieve a phase shift of π under a shorter action length (micron level) of the interference arm in different phases, which not only reduces the size of the interference arm, but also eliminates the curved waveguide connected between the directional coupler 3 and the interference arm of the conventional MZI (Mach-Zehnder interferometers), making the device structure more compact, and the dynamic switching power consumption of the optical path is lower. After the phase change is completed, there is no need for continuous power supply to maintain the state of the phase change material, thereby maintaining the state of the switch and achieving zero static power consumption.

[0041] By embedding phase change material into the core layer of the waveguide, the interaction between light and the phase change material is enhanced, and then by changing the phase state of the phase change material, the effective refractive index of the waveguide changes significantly, making the device structure more compact.

[0042] In a specific implementation, the upper cladding layer 3-5 of the hybrid waveguide part is an oxide film, which is used to protect the phase change material film 3-4. The heating electrode 3-6 is placed above the upper cladding layer 3-5, so it can also be used to separate the heating electrode 3-6 from the core layer 3-3, reducing the absorption loss of the heating electrode 3-6 to the optical signal. The heating electrode 3-6 can be a metal electrode or a graphene electrode.

[0043] Specifically, assuming that the phase states of the two hybrid waveguides are the same at the beginning, one of the interference arms is heated by the heating electrode 3-6 to change the phase state of its phase change material, thereby achieving the phase difference between the two interference arms. For the optical switch, the phase difference between the two interference arms can change the transmission direction of the optical signal in the optical switch. After the phase change is completed, the voltage applied to the electrode is removed, the phase state of the phase change material remains unchanged, the state of the optical switch remains unchanged, and the static power of the device is zero.

[0044] Specifically, the two waveguide interference arms can be a symmetrical structure or an asymmetrical structure. If it is a symmetrical interference arm structure, a low-power, compact, and non-volatile optical switch can be realized; if it is an asymmetrical interference arm structure (for example, when the sizes of the two phase change material films 3-4 are inconsistent), a non-volatile, compact waveguide filter can be realized.

[0045] Specifically, for all waveguides in the optical waveguide device, when the refractive index of the substrate 3-1 is less than the refractive index of the core layer 3-3, from bottom to top, it may include the substrate 3-1, the lower cladding layer 3-2, the core layer 3-3 and the upper cladding layer 3-5, or may include the substrate 3-1, the core layer 3-3 and the upper cladding layer 3-5; when the refractive index of the substrate 3-1 is not less than the refractive index of the core layer 3-3, from bottom to top, it may include the substrate 3-1, the lower cladding layer 3-2, the core layer 3-3 and the upper cladding layer 3-5; the refractive indexes of the lower cladding layer 3-2 and the upper cladding layer 3-5 are both less than the refractive index of the core layer 3-3, and according to Maxwell's equations and their boundary conditions, the waveguide dimensions are optimized to meet the waveguide total reflection transmission conditions.

[0046] In a specific implementation, the phase change material film 3-4 is embedded in the straight waveguide by any of the following methods:

[0047] (1) Use high-precision photolithography technology to define the directional coupler 3 waveguide and the air slot on the directional coupler 3 waveguide; use dry etching (such as inductively coupled plasma etching) to etch the waveguide to the required depth, so as to form a waveguide with an air slot; use the photoresist pattern to define the air slot again; deposit a layer of phase change material film 3-4 so that the air slot is completely filled with phase change material, and remove the excess phase change material on the photoresist outside the air slot through a wet stripping process. At this point, the micrometer-level phase change material film 3-4 is prepared. Then, a layer of oxide film is deposited or spin-coated on the upper surface of the waveguide as an upper cladding layer 3-5.

[0048] (2) After the waveguide is fabricated, a window is opened in the upper cladding layer 3-5 of the waveguide by photolithography and etching, and an air slot of micrometer length is etched in the waveguide core layer 3-3 through the window. The air slot is defined again by a photoresist pattern, and a phase change material is deposited inside the air slot until the air slot is filled with the phase change material. The phase change material outside the air slot is removed by a wet stripping method. A layer of oxide film is deposited or spin-coated on the phase change material by a deposition method to protect the phase change material film 3-4.

[0049] If the phase change material film 3-4 is horizontally embedded in the middle or bottom of the core layer 3-3, the polymer waveguide core layer 3-3 is first spin-coated on the phase change material film 3-4, and then the upper cladding layer 3-5 is spin-coated or deposited.

[0050] like Figure 2 As shown, air grooves are made on both sides of the directional coupler 3, and the thermal conductivity of air is smaller than the thermal conductivity of the waveguide material, so that the power consumption of the device can be further reduced.

[0051] It should be noted that the inclination angles of the air slot and the waveguide sidewall in the present application are determined by actual process conditions.

[0052] Specifically, if the phase change material film 3-4 is horizontally embedded on the top of the core layer 3-3 or vertically embedded in the core layer 3-3, the core layer 3-3 can adopt silicon waveguide, lithium niobate waveguide, silicon nitride waveguide, polymer waveguide or III-V waveguide.

[0053] Specifically, the phase change material film 3-4 is made of antimony selenide (Sb2Se3), antimony trisulfide (Sb2S3), germanium antimony telluride (Ge2Sb2Te5, GST), germanium antimony selenium telluride (Ge2Sb2Se4Te, GSST) or vanadium dioxide (VO2). Non-volatile materials such as Sb2Se3 and Sb2S3 have significantly different optical refractive indices between the crystalline state and the amorphous state, are stable and reversible in the two crystalline states, do not require continuous power supply once the phase change is completed, and the static power consumption is zero. These materials help to realize stable optical switches, 3 dB couplers, polarization beam splitters, and tunable beam splitters in a non-volatile state. Specifically, by setting the two phase change material films 3-4 to different sizes and applying a certain voltage on the electrodes to change the phase state of the phase change material, the function of tunable filtering can be realized; in addition, by optimizing the parameters of the waveguide coupler I and the waveguide coupler II, the function of the 3 dB coupler can be realized in both TE and TM polarization modes; by optimizing the thickness, width, and length of the phase change material film 3-4, when the phase change material film 3-4 of the two interference arms is in different phases, when the input optical signal is in TE polarization and TM polarization, the phase difference of the corresponding two interference arms is M*π and N*π respectively, if M and N are both odd numbers, a polarization-independent optical switch can be realized; if M and N are odd numbers and even numbers, a polarization beam splitter can be realized; by tuning the ratio of the crystalline state to the amorphous state in one of the phase change material films, the function of the tunable beam splitter can be realized. Therefore, by optimizing the parameters of the waveguide coupler I and the waveguide coupler II and the parameters of the phase change material film 3-4, a polarization-independent optical switch, a tunable beam splitter, and a polarization beam splitter can be realized.

[0054] Specifically, the input waveguide 1 and the output waveguide 5 can be a grating coupler, an inverted cone coupler, a straight waveguide, or a combination of a cone waveguide and a straight waveguide. In one embodiment, the input waveguide 1 and the output waveguide 5 are straight waveguides, and both the input waveguide 1 and the output waveguide 5 need to be coupled to the optical fiber array. The input channel spacing is set to 127 μm or 250 μm, and the output channel spacing is set to 127 μm or 250 μm according to actual conditions.

[0055] Specifically, the curved waveguide I 2 and the curved waveguide II 4 may be cosine-type curved waveguides, sine-type curved waveguides, circular arc-type curved waveguides or Euler curve-type curved waveguides.

[0056] Specifically, the waveguide coupler I and the waveguide coupler II may be a 3 dB beam splitter structure.

[0057] The above-mentioned optical waveguide device eliminates the curved waveguide connecting the interference arm and the coupler, reduces the device size, makes the device structure more compact, and makes the device scalable and reconfigurable. The phase change material has three stable and reversible phases: crystalline phase, amorphous phase, and partial crystalline phase. By heating or photo-photographing the phase change material, it is crystallized or amorphized. Due to the large difference in the effective refractive index of the hybrid waveguide in different phases, the hybrid waveguide at the micron-level length in the middle of the directional coupler 3 can achieve a phase change of π, thereby realizing the function of optical signal switching. Under the action length of the hybrid waveguide interference arm of the micron level, a phase shift of π can be achieved. Compared with the ordinary waveguide interference arm, the interference arm length is reduced by 3~4 orders of magnitude, and the electrode heating length is also reduced by 3~4 orders of magnitude, thereby reducing the overall size of the device and reducing the power consumption of the device. In addition, the filtering function can be achieved by setting an asymmetric interference arm in the device.

[0058] The optical waveguide device has the advantages of low power consumption, compact structure, non-volatility and scalability. It can be connected with waveguide pairs of different lengths to realize the function of a tunable delay line, making the device size more compact and avoiding thermal crosstalk caused by a large number of switches working at the same time, which affects the performance of the delay line. In addition, it also has significant advantages in optical neural networks and photon storage in scenarios where a large number of optical switches, tunable filters or tunable couplers are used and reconfigurable optical waveguide devices do not need to be frequently switched or tuned, avoiding system thermal crosstalk caused by a large number of system switches working and affecting the stability of the system.

[0059] Embodiment 1 A low-power, compact, non-fading optical switch based on directional coupler 3

[0060] The low-power, non-volatile lithium niobate thin film optical switch based on the directional coupler 3 of this embodiment is as follows Figure 1As shown, it includes an input waveguide 1, an output waveguide 5, a directional coupler 3, and a pair of phase change material films 3-4 (using Sb2Se3) of the same size. The specific manufacturing process is: the lithium niobate film waveguide core layer 3-3 and the air groove on the top of the core layer 3-3 for filling the phase change material film 3-4 are made by photolithography and etching, and the micrometer-level phase change material film 3-4 is made in the middle of the directional coupler 3 by coating and stripping. A layer of SiO2 film is sputtered on the entire waveguide to protect the phase change material film 3-4 from crystallization and volatilization. The hybrid waveguide composed of Sb2Se3 and lithium niobate film is micrometer-level in length and can act as an interference arm. Assume that the optical signal is input from the upper port of the input waveguide 1, passes through the curved waveguide I2, enters the directional coupler 3, and when it is transmitted to the hybrid waveguide in the directional coupler 3, it is assumed that the size of the phase change material film 3-4 of the two hybrid waveguides and the phase of the phase change material are consistent, and the phase difference generated by the parallel hybrid waveguide is zero, and then it continues to be transmitted in the straight waveguide part of the directional coupler 3, enters the curved waveguide II4, and is output from the lower port of the output waveguide 5. Assume that the initial state of the two hybrid waveguides is an amorphous state, and a voltage is applied to the graphene electrode on one of the hybrid waveguides, heated to a certain temperature for crystallization, while the other hybrid waveguide cannot reach the crystallization temperature, and the voltage on the graphene electrode is removed. At this time, the phase difference generated by the two interference arms is π, and the optical signal is output from the upper port of the output waveguide 5, and the optical signal has switched its path. By analogy, reversible optical signal switching can be achieved.

[0061] Embodiment 2 Low power consumption, compact structure, non-volatile filter based on directional coupler 6

[0062] Different from the first embodiment, the tunable non-volatile filter is as follows Figure 3 As shown, in the directional coupler 6, the widths of the two phase change materials are different. The two phase change materials and the waveguides embedded therein together form a hybrid waveguide, which can act as an asymmetric interference arm. The hybrid waveguide divides the directional coupler into a waveguide coupler I and a waveguide coupler II. Both the waveguide coupler I and the waveguide coupler II are 3 dB couplers. In this way, an asymmetric MZI structure is formed. By tuning the ratio of the crystalline phase and the amorphous phase of one of the phase change materials, the phase difference of the two arms is tuned, and then the central wavelength of the filter is tuned. The filter has a compact structure and non-volatile performance.

[0063] The present application also provides another optical waveguide device based on a directional coupler, comprising a ring waveguide and at least one straight waveguide, wherein the straight waveguide is coupled to the ring waveguide, and a directional coupler structure is adopted in the coupling region, and a phase change material film is horizontally or vertically embedded in the waveguide core layer of the directional coupler to form a hybrid waveguide. The function of the beam splitter can be tuned by changing the phase state of the phase change material film, thereby realizing the functions of tunable filtering, optical switching and tunable delay.

[0064] Electrodes may also be arranged on the annular waveguide to realize the function of a phase shifter, thereby realizing a tunable filtering function, an optical switch and a tunable delay function.

[0065] For a tunable optical waveguide device composed of a ring waveguide, when multiple ring waveguides are cascaded, a low-power, compact, non-volatile tunable optical delay line, optical filter, and optical switch can be further realized compared to a single ring waveguide structure.

[0066] Example 3

[0067] like Figure 4 As shown, this embodiment provides a tunable filter based on a directional coupler, including a ring waveguide (micro-ring) and a straight waveguide, the two ends of the straight waveguide are respectively the first straight waveguide input end 6-1 and the straight waveguide output end 6-2, the straight waveguide is coupled with the ring waveguide, the first coupling region 6-3 of the two adopts a directional coupler structure, the phase change material film is horizontally or vertically embedded in the waveguide core layer of the directional coupler to form a hybrid waveguide, and a metal electrode is also provided on the ring resonator as a first phase shifter 6-4, the directional coupler can be used as a tunable beam splitter, and the optical power coupling ratio is adjusted by changing the phase state of the phase change material film, thereby realizing the function of tunable filtering. When the optical signal is input from the first straight waveguide input end 6-1 of the straight waveguide, part of the light will be coupled into the ring waveguide when passing through the first coupling region 6-3. The light entering the ring waveguide will propagate along the ring waveguide for one circle and then return to the first coupling region 6-3 again. If the phase change of the light propagating in the ring waveguide for one circle and the phase change of the light in the straight waveguide meet certain conditions, interference will occur. When the optical path of light propagating in the ring waveguide is an integer multiple of the wavelength, that is, the resonance condition is met, light will interfere constructively in the micro-ring, the wavelength of light is the resonance wavelength, and the energy is enhanced in the ring waveguide, otherwise it will be destructive. This phenomenon determines the intensity distribution of the optical signal at the straight waveguide output end 6-2, thereby realizing the frequency selection function of light. By selectively suppressing or enhancing the optical signal of a specific waveguide, the functions of wavelength selection and filtering are realized. By tuning the electrodes on the first phase shifter 6-4, the resonant wavelength can be tuned, thereby realizing the function of tunable filtering. For a given wavelength, it can also be used to construct the functions of optical switches and modulators.

[0068] Example 4

[0069] like Figure 5As shown, this embodiment provides another tunable filter based on a directional coupler. Different from the third embodiment, the tunable filter includes a ring waveguide and two straight waveguides, also known as an add-drop type micro-ring structure. The two straight waveguides are respectively located on both sides of the ring waveguide to form two coupling regions, namely the second coupling region 7-4. The two coupling regions of the second coupling region 7-4 both adopt a directional coupler structure, wherein the two ends of a straight waveguide are respectively the second straight waveguide input end 7-1 and the straight waveguide direct output end 7-2, and one end of another straight waveguide is the straight waveguide download end 7-3. The phase change material film is horizontally or vertically embedded in the waveguide core layer of the directional coupler to form a hybrid waveguide. A metal electrode is also provided on the ring waveguide as a second phase shifter 7-5. The directional coupler can be used as a tunable beam splitter. The optical power coupling ratio is adjusted by changing the crystal phase of the phase change material film, thereby realizing the function of tunable filtering. When an optical signal is input into the coupling region from the second straight waveguide input end 7-1 of a straight waveguide, part of the optical signal will be coupled into the ring waveguide. After transmitting one circle in the ring waveguide, it comes to the coupling zone again. Depending on the wavelength of the light and the coupling conditions, the light may be coupled to the output of the straight waveguide download end 7-3 of another straight waveguide, or continue to be transmitted in the ring waveguide. When the wavelength of the light meets the resonance condition of the microring, the light will be reflected and interfered multiple times in the microring, so that the intensity of the light of a specific wavelength at the straight waveguide direct output end 7-2 or the straight waveguide download end 7-3 is significantly enhanced or suppressed, thereby realizing the add or drop function of the optical signal. It can be used for multiplexing and demultiplexing of the wavelength of the optical signal, and can distribute and extract optical signals of different wavelengths between two straight waveguides. It can also realize the functions of a tunable filter and an optical switch, and realize the tunable filtering characteristics and switch state by tuning the second phase shifter 7-5.

[0070] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not disclosed in the present application.

[0071] It should be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. An optical waveguide device based on a directional coupler, characterized in that: It comprises an input waveguide, a curved waveguide I, a directional coupler, a curved waveguide II, and an output waveguide connected in sequence; the directional coupler comprises two straight waveguides with a spacing of submicron or micron order, a phase change material film is embedded in the core layers of the two straight waveguides, the phase change material film and the straight waveguide part in which it is embedded constitute a hybrid waveguide, and the hybrid waveguide divides the directional coupler into a waveguide coupler I and a waveguide coupler II; By optimizing the parameters of waveguide coupler I and waveguide coupler II and the parameters of phase change material film, the functions of optical switch, polarization beam splitter, 3 dB coupler or tunable filter are realized; The refractive index of the phase change material film is greater than the refractive index of the core layer and the cladding in the straight waveguide, and the two hybrid waveguides serve as interference arms respectively, and the phase difference between the two interference arms is achieved by changing the phase state of the phase change material film.

2. The optical waveguide device based on a directional coupler according to claim 1, characterized in that: The input waveguide and the output waveguide are grating couplers, inverted tapered couplers, straight waveguides, or a combination of tapered waveguides and straight waveguides; The curved waveguide I and the curved waveguide II are cosine-type curved waveguides, sine-type curved waveguides, arc-type curved waveguides or Euler-curve-type curved waveguides; The waveguide coupler I and the waveguide coupler II are 3 dB beam splitter structures.

3. The optical waveguide device based on a directional coupler according to claim 1, characterized in that: The phase change material film is made of antimony selenide, antimony trisulfide, germanium antimony telluride, germanium antimony selenium telluride or vanadium dioxide.

4. The optical waveguide device based on a directional coupler according to claim 1, characterized in that: For all waveguides in the optical waveguide device, when the refractive index of the substrate is less than the refractive index of the core layer, from bottom to top, it includes the substrate, the lower cladding layer, the core layer and the upper cladding layer, or includes the substrate, the core layer and the upper cladding layer; when the refractive index of the substrate is not less than the refractive index of the core layer, from bottom to top, it includes the substrate, the lower cladding layer, the core layer and the upper cladding layer; The refractive indexes of the lower cladding layer and the upper cladding layer are both smaller than the refractive index of the core layer.

5. The optical waveguide device based on a directional coupler according to claim 1, characterized in that: The upper cladding layer of the hybrid waveguide is an oxide film. A heating electrode is placed above the upper cladding layer. The phase change material film is heated by the heating electrode, thereby changing the crystal phase of the phase change material film.

6. The optical waveguide device based on a directional coupler according to claim 1, characterized in that: The phase change material film is embedded in the straight waveguide by any of the following methods: (1) Using photolithography technology to define the directional coupler waveguide and the air slot on the directional coupler waveguide; etching the waveguide to the required depth by dry etching, thereby forming a waveguide with an air slot; Using a photoresist pattern to define the air slots; Depositing a layer of phase change material film so that the air slot is completely filled with the phase change material, removing the excess phase change material on the photoresist outside the air slot by a wet stripping process to obtain a phase change material film with a length of micrometer order, and spin coating or depositing a layer of oxide film on the upper surface of the waveguide as an upper cladding layer; (2) After the waveguide is manufactured, a window is opened in the upper cladding layer of the waveguide by photolithography and etching, and an air slot with a length of micrometers is etched in the core layer of the waveguide through the window. The air slot is defined by a photoresist pattern, and a phase change material is deposited inside the air slot until the air slot is filled with the phase change material. The phase change material outside the air slot is removed by a wet stripping method, and a layer of oxide film is spin-coated or deposited on the phase change material by a deposition method as an upper cladding.

7. The optical waveguide device based on a directional coupler according to claim 6, characterized in that: During the embedding process, air grooves are made in the waveguide core layer on both sides of the phase change material.

8. The optical waveguide device based on a directional coupler according to claim 1, characterized in that: By optimizing the parameters of waveguide coupler I and waveguide coupler II and the parameters of the phase change material film, the functions of optical switch, polarization beam splitter, 3 dB coupler or tunable filter are realized, specifically: The two phase change material films are set to different sizes, and the phase state of the phase change material is changed by applying voltage to the electrodes, so that the optical waveguide device can realize the function of tunable filtering; By optimizing the parameters of waveguide coupler I and waveguide coupler II, the optical waveguide device can realize the function of 3 dB coupler in both TE and TM polarization modes; By optimizing the phase change material film, when the phase change material films of the two interference arms are in different phases, when the input optical signal is in TE polarization and TM polarization, the phase differences of the corresponding two interference arms are M*π and N*π respectively. If M and N are both odd numbers, the optical waveguide device can realize the polarization-independent optical switch function; if one of M and N is an odd number and the other is an even number, the optical waveguide device can realize the polarization beam splitter function. The function of a tunable beam splitter is achieved by tuning the ratio of crystalline to amorphous states in one of the phase change material films.

9. An optical waveguide device based on a directional coupler, characterized in that: The invention comprises a ring waveguide and at least one straight waveguide, wherein the straight waveguide is coupled with the ring waveguide, and a directional coupler structure is adopted in the coupling region. A phase change material film is horizontally or vertically embedded in the waveguide core layer of the directional coupler to form a hybrid waveguide. The function of the beam splitter can be tuned by changing the crystal phase of the phase change material film, thereby realizing the functions of tunable filtering, optical switching and tunable delay.

10. The optical waveguide device based on a directional coupler according to claim 9, characterized in that: Electrodes are also arranged on the annular waveguide.

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