A non-magnetic optical circulator for on-chip distributed fiber sensing systems

Abstract

A non-magnetic optical circulator for on-chip distributed fiber sensing system comprises an uplink lumped waveguide, a downlink lumped waveguide and a ring resonator; the uplink incident waveguide and the uplink exit waveguide are connected by a first straight waveguide to form the uplink lumped waveguide; the downlink incident waveguide and the downlink exit waveguide are connected by a second straight waveguide to form the downlink lumped waveguide; the ring resonator is at a predetermined distance from the uplink lumped waveguide and the downlink lumped waveguide to realize optical coupling of incident and exit; a phase change material film is arranged directly above a section of waveguide in the ring resonator, and the phase change material film controls the propagation direction of incident light in the ring resonator. The present application is aimed at the common situation that the intensity of forward probe light and back signal light is greatly different and the two beams of light are completely offset in time in the distributed fiber sensing application scene. The phase state of the phase change material is controlled by modulating pulsed light to change the transmission path and output port of incident light in different directions, without the need for an additional constant magnetic field, and the process is simpler and compatible with large-scale micro-nano processing technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of integrated optoelectronics, and in particular to a magnetic-free optical circulator for an on-chip distributed fiber sensing system. BACKGROUND

[0002] Distributed fiber sensing technology mainly uses the scattering (Rayleigh scattering, Brillouin scattering, Raman scattering, etc.) of light in the optical fiber to obtain sensing information in response to the external physical quantity to be measured, and can simultaneously realize signal sensing and transmission in the same optical fiber, has the characteristics of wide sensing range, high detection sensitivity, fast response speed, etc., and has a wide range of applications in bridge mine safety monitoring, ocean exploration, oil and gas resource exploration, etc.

[0003] With the development of integrated optoelectronic technology, miniaturization and integration of various optical information processing devices can not only reduce power consumption, volume and weight, improve device performance, but also reduce device cost through the large-scale production capacity of CMOS process, which is a trend for the future development of optoelectronic systems and the next step requirement of various application scenarios. At present, the distributed fiber sensing system and its optoelectronic module are composed of various discrete optical devices connected by optical fibers, which occupies a large space, and further optimization and improvement in power consumption, volume, weight, cost, anti-interference, etc. have gradually encountered bottlenecks. Integrating the distributed fiber sensing system on the chip is expected to be an effective way to solve the above limitations, so the development of integrated photonic devices for distributed fiber sensing systems has very important significance.

[0004] In the distributed fiber sensing system based on optical time domain reflection technology, the forward probe light and the back signal light need to be separated by an optical circulator. The optical circulator widely used in the market is a discrete device, which mainly realizes the optical loopback function by optically packaging bulk materials with Faraday magneto-optic effect. Although the device is quite mature, it has high isolation and low insertion loss, but the discrete device is large in size, which is not conducive to the development of miniaturized and integrated systems. The on-chip integrated optical circulator is one of the key devices for realizing the next generation of on-chip distributed fiber sensing systems. At present, the research on on-chip optical circulator mainly focuses on the heterogeneous integration of magneto-optic materials. Since a stable magnetic field needs to be applied for the normal operation of magneto-optic materials, and it is still not well compatible with large-scale micro-nano processing technology, the wide application of such heterogeneous integrated on-chip devices still faces great challenges. SUMMARY

[0005] To overcome the above problems, the present application provides a magnetic-free optical circulator for an on-chip distributed fiber sensing system, which uses a phase change material with excellent process compatibility, effectively solving the problems of large size, complex integration process and difficulty in large-scale micro-nano processing of optical circulators in distributed fiber sensing systems.

[0006] The technical scheme adopted by the present application is: a non-magnetic optical circulator for an on-chip distributed optical fiber sensing system, comprising an uplink incident waveguide, an uplink outgoing waveguide, a ring resonant cavity, a downlink incident waveguide, a downlink outgoing waveguide and a phase change material film;

[0007] The uplink incident waveguide and the uplink outgoing waveguide are connected through a first straight waveguide to form an uplink lumped waveguide; the downlink incident waveguide and the downlink outgoing waveguide are connected through a second straight waveguide to form a downlink lumped waveguide; the ring resonant cavity is arranged between the uplink lumped waveguide and the downlink lumped waveguide, and is at a predetermined distance from the uplink lumped waveguide and the downlink lumped waveguide, and is coupled with the uplink lumped waveguide and the downlink lumped waveguide through evanescent waves to form a coupling region I and a coupling region II, thereby realizing optical coupling incidence and coupling incidence; the phase change material film is arranged above a section of the waveguide in the ring resonant cavity, and controls the propagation direction of incident light of the ring resonant cavity.

[0008] Further, the phase change material film comprises two phase states of a crystal state and an amorphous state, and the phase state of the phase change material film is switched through a pulse light sequence;

[0009] The pulse light sequence comprises two pulse lights of a de-crystalization pulse light required for controlling the phase state of the phase change material and a forward detection light required for detection of the sensing system; in an initial state, the phase change material film is in a crystal state, the pulse light sequence is transmitted along the uplink incident waveguide into the coupling region I, and is coupled into the ring resonant cavity through evanescent waves; the de-crystalization light in the pulse light sequence first enters the ring resonant cavity, the wavelength of the de-crystalization pulse light is located in a passband of a transmission spectrum of the ring resonant cavity, and the de-crystalization light is output from the uplink outgoing waveguide after circulating in the ring resonant cavity, at this time, the phase change material film is converted into an amorphous state by being warmed up and then rapidly cooled under the action of the de-crystalization pulse light, so that the resonant wavelength of the resonant cavity is changed to the wavelength of the forward detection pulse light;

[0010] Subsequently, the forward detection pulse light in the pulse light sequence enters the ring resonant cavity, the wavelength of the forward detection pulse light is located at the resonant wavelength of the resonant cavity, and the forward detection pulse light is output from the downlink incident waveguide; the downlink incident waveguide is connected with a sensing optical fiber in the distributed optical fiber sensing system, and the forward detection pulse light enters the sensing optical fiber as a detection light; after the forward detection pulse light passes through the ring resonant cavity, the phase change material film in the amorphous state is converted into a crystal state under the action of the forward detection pulse light, so that the resonant wavelength of the ring resonant cavity deviates from the wavelength of the forward detection pulse light;

[0011] The backscattered signal light generated in the transmission process of the forward probe pulse light in the sensing fiber returns to the ring resonator from the drop-in waveguide; the backscattered signal light cannot cause phase transition of the ring resonator, and the wavelength of the backscattered signal light is located in the passband of the transmission spectrum of the resonator, and the backscattered signal light is output from the drop-out waveguide; the drop-out waveguide is connected with the photodetector receiving end in the distributed optical fiber sensing system, and the backscattered signal light enters the photodetector receiving end after being output from the drop-out waveguide.

[0012] Preferably, the optical circulator has a symmetrical shape, so that the same ring transmission effect can be achieved when the pulse light sequence is incident from any one of the ports of the uplink incident waveguide, the uplink output waveguide, the downlink incident waveguide and the downlink output waveguide.

[0013] Preferably, the operating wavelength of the optical circulator is selected by adjusting the diameter of the ring resonator.

[0014] Preferably, when the ring resonator approaches or meets the critical coupling condition, the optical circulator has the maximum isolation and the minimum insertion loss.

[0015] Preferably, the shape of the ring resonator is circular or racetrack-shaped.

[0016] Preferably, the uplink lumped waveguide, the downlink lumped waveguide and the ring resonator include but are not limited to strip-shaped silicon waveguide or ridge-shaped silicon waveguide or strip-shaped lithium niobate waveguide or ridge-shaped lithium niobate waveguide or strip-shaped silicon nitride waveguide or ridge-shaped silicon nitride waveguide.

[0017] Preferably, the phase change material film is Ge-Se-Te film or Ge-Sb-Se-Te film or Sb-S film.

[0018] Further, the pass-through output port transmittance of the pulse light sequence on the optical circulator satisfies the following relationship:

[0019]

[0020] The shunt output port transmittance of the pulse light sequence on the optical circulator satisfies the following relationship:

[0021]

[0022] where γ is the loss factor of the ring resonator, including the intrinsic loss factor γ0 and the coupling loss factor γc of the ring resonator. e l w is the frequency of the incident laser light, and w0 is the resonant frequency of the ring resonator.

[0023] An on-chip distributed optical fiber sensing system includes the above-described non-magnetic optical circulator.

[0024] ​The principle of the present application is: using the material characteristics of phase change material, such as fast phase change speed and large difference of refractive index between two phase states, controlling the phase state of phase change material by pulse light, changing the resonant wavelength of the ring resonator, thereby changing the transmission path of the input light and the output waveguide, and realizing the on-chip integrated magnetic-free optical circulator. The specific implementation is as follows:

[0025] In the distributed optical fiber sensing system, the incident continuous laser is modulated by the modulator to generate a pulse light sequence. The pulse light sequence is composed of two pulse lights, namely, the amorphous light required to control the phase state of the phase change material and the forward probe light required for the sensing system to detect, and the wavelength is set to the resonant wavelength of the ring resonator when the phase change material film is in the amorphous state. The initial phase state of the phase change material film is the crystalline state. When the pulse light sequence is incident from the upper incident waveguide, the amorphous pulse light first enters the ring resonator, and since its wavelength is located in the passband of the resonant cavity transmission spectrum, it is output from the upper incident waveguide after circulating in the ring resonator. The sensing fiber in the distributed optical fiber sensing system is connected to the lower incident waveguide, and the photoelectric detection receiving end of the system is connected to the lower incident waveguide. Therefore, the amorphous pulse light does not enter the sensing fiber and the photoelectric detection receiving end of the sensing system. The phase change material film is first heated and then rapidly cooled under the action of the amorphous pulse light, and changes from the crystalline state to the amorphous state, so that the resonant wavelength of the resonant cavity changes to the incident light wavelength. Subsequently, the forward probe pulse light enters the ring resonator, and since its wavelength is exactly located at the resonant wavelength of the resonant cavity, it is output from the lower incident waveguide and enters the sensing fiber in the system as the probe light. When the forward probe pulse light passes through the ring resonator, the amorphous phase change material film crystallizes to the crystalline state under its action, causing the resonant wavelength of the resonant cavity to deviate from the incident light wavelength. The backscattered signal light generated by the Rayleigh scattering, Brillouin scattering, Raman scattering and other effects in the process of the forward probe light transmitting in the sensing fiber returns to the ring resonator from the lower incident waveguide. The backscattered signal light has a low intensity, generally more than 50dB weaker than the forward probe light, and cannot cause the phase change of the phase change material film. Its wavelength is located in the passband of the resonant cavity transmission spectrum, so it is output from the lower incident waveguide and enters the photoelectric detection receiving end of the system, thereby realizing the on-chip integrated optical circulator for the distributed optical fiber sensing system under the condition of no magnetism. Since the forward probe light and the backscattered signal light are completely staggered in time, they will not exist simultaneously in the ring resonator and cause mutual interference.

[0026] The beneficial effects of the present application are:

[0027] (1) The present application realizes the optical circulator for the on-chip distributed optical fiber sensing system based on the on-chip micro-ring resonator, which has the advantages of small size, low cost and low power consumption compared with the fiber circulator used in the traditional distributed optical fiber sensing system.

[0028] (2) The application uses a phase change material with excellent process compatibility, utilizes the material characteristics of fast phase change speed and large difference in refractive index between two states, and realizes loop transmission of forward probe light and back signal light through a micro-ring resonant cavity on a chip, compared with a conventional on-chip optical circulator based on magneto-optical material, no constant magnetic field is needed, and the process is simpler and compatible with large-scale micro-nano processing technology. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the overall structure schematic diagram of the magnetic-free optical circulator of the on-chip distributed optical fiber sensing system of the application;

[0030] Figure 2 is the schematic diagram of the pulse light sequence of the application;

[0031] Figure 3 is the cross-sectional schematic diagram of the ring resonant cavity waveguide of the phase change material film region of embodiment one;

[0032] Figure 4 is the mode field distribution diagram of the ring resonant cavity waveguide TE base mode when the phase change material film of embodiment one is in an amorphous state;

[0033] Figure 5 is the mode field distribution diagram of the ring resonant cavity waveguide TE base mode when the phase change material film of embodiment one is in a crystalline state;

[0034] Figure 6 is the straight-through exit port and the shunt exit port of the ring resonant cavity of embodiment one, corresponding to the output transmission spectrum of the two different phase states of the phase change material;

[0035] Figure 7 is the straight-through exit port and the shunt exit port of the ring resonant cavity of embodiment two, corresponding to the output transmission spectrum of the two different phase states of the phase change material.

[0036] Explanation of reference signs: 1, silica cladding; 2, GSST film; 3, silicon strip waveguide; 11, uplink incident waveguide; 12, uplink exit waveguide; 13, ring resonant cavity; 14, downlink incident waveguide; 15, downlink exit waveguide; 16, phase change material film; 17, coupling region I; 18, coupling region II. DETAILED DESCRIPTION

[0037] The technical solutions of the application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0038] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like are based on the orientation or positional relationship shown in the drawings, 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. In addition, the terms "first", "second", "third" appear only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0039] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood in a broad sense, 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; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0040] As shown in Figure 1 The on-chip distributed fiber sensing system-oriented non-magnetic optical circulator of the present application includes an uplink incident waveguide 11, an uplink outgoing waveguide 12, a ring resonant cavity 13, a downlink incident waveguide 14 and a downlink outgoing waveguide 15. The uplink incident waveguide 11 and the uplink outgoing waveguide 12 are connected by a straight waveguide to form an uplink lumped waveguide. The downlink incident waveguide 14 and the downlink outgoing waveguide 15 are connected by a straight waveguide to form a downlink lumped waveguide. The ring resonant cavity 13 is simultaneously connected to the above-mentioned uplink lumped waveguide and downlink lumped waveguide at a certain distance, forming a coupling area through evanescent wave coupling to realize the coupling of incident and outgoing light. The phase change material film 16 is located directly above a section of waveguide in the ring resonant cavity 13, which is used to control the transmission direction of incident light in the ring resonant cavity.

[0041] The resonant wavelength of the ring resonant cavity 13 is related to the optical path of light circulating in the ring, and the refractive index difference of different phase states of the phase change material is large, so that the effective refractive index and optical path of the ring resonant cavity 13 can be changed by changing the phase state of the phase change material film 16, and then the resonant wavelength is deviated or coincides with the incident light wavelength, so that the transmission path of the incident light and the output waveguide are changed. In addition, the phase change speed of the phase change material can reach sub-nanosecond level, which fully meets the requirements of the distributed fiber sensing system.

[0042] Using the on-chip distributed fiber sensing system-oriented non-magnetic optical circulator of the present application, the incident continuous laser is modulated by the modulator in the sensing system to generate a pulse light sequence. As shown in Figure 2As shown, the pulse light sequence is composed of two pulse lights, one is the de-crystallization light needed to control the phase state of the phase change material, and the other is the forward probe light needed to be detected by the sensing system, and the wavelength is set to be the resonant wavelength of the ring resonator when the phase change material film 16 is in the amorphous state.

[0043] Initially, the phase change material film 16 is in the crystalline state, and the pulse light sequence is transmitted into the coupling area along the upper incident waveguide 11 and is coupled into the ring resonator 13 through evanescent wave. The de-crystallization pulse light in the pulse light sequence first enters the ring resonator 13, and since its wavelength is in the passband of the resonant cavity transmission spectrum, it is output from the upper exit waveguide after circulating in the ring resonator. The sensing fiber in the distributed fiber sensing system is connected to the lower incident waveguide, and the photoelectric detection receiving end of the system is connected to the lower exit waveguide. Therefore, the de-crystallization pulse light does not enter the sensing fiber and the photoelectric detection receiving end of the sensing system. Under the action of the de-crystallization pulse light, the phase change material film 16 in the crystalline state is first heated and then rapidly cooled to transform into the amorphous state, so that the resonant wavelength of the resonant cavity changes to the incident light wavelength. Subsequently, the forward probe pulse light enters the ring resonator 13, and its wavelength is at the resonant wavelength of the resonant cavity, so it is output from the lower incident waveguide 14 and enters the sensing fiber in the system as probe light. When the forward probe pulse light passes through the ring resonator 13, the amorphous phase change material film 16 crystallizes under its action, causing the resonant wavelength of the resonant cavity to deviate from the incident light wavelength. During the transmission of the forward probe light in the sensing fiber, the backscattered signal light generated by Rayleigh scattering, Brillouin scattering, Raman scattering, etc. returns to the circulator from the lower incident waveguide 14. The backscattered signal light has a low intensity, generally more than 50 dB weaker than the forward probe light, and cannot cause the phase change material film 16 to change phase. And its wavelength is in the passband of the resonant cavity transmission spectrum, so it is output from the lower exit waveguide 15 and enters the photoelectric detection receiving end of the system, thereby realizing the on-chip integrated optical circulator for the distributed fiber sensing system under the condition of no magnetism. Since the forward probe light and the backscattered signal light are completely staggered in time, they will not exist simultaneously in the circulator and cause mutual interference.

[0044] The specific embodiments of the present application are as follows:

[0045] Embodiment one:

[0046] The specific embodiments of the present application are as follows: Figure 1As shown, the upper incident waveguide 11, upper exit waveguide 12, ring resonator 13, lower incident waveguide 14, and lower exit waveguide 15 are preferably strip-shaped silicon waveguides. The strip-shaped silicon waveguide has a height of 220 nm, a width of 500 nm, and a cladding of silicon dioxide. The ring resonator is preferably circular with a radius of 5 μm, and the spacing between the upper and lower lumped waveguides and the ring resonator 13 is the same. The transmission loss of the strip-shaped silicon waveguide is assumed to be 2 dB / cm. In this embodiment, the operating wavelength of the optical circulator is set to 1567.76 nm (the operating wavelength can be arbitrarily selected by changing the diameter of the ring resonator 13). The refractive index of silicon near this wavelength is 3.47, and the refractive index of silicon dioxide is 1.44.

[0047] The phase change material thin film 16 is preferably made of Ge-Sb-Se-Te (GSST). Crystalline GSST has a refractive index of 5.24 ± 0.38i in the wavelength range around 1550 nm, while amorphous GSST has a refractive index of 3.07 in the same range. Figure 3 As shown, the phase change material thin film 2 is located directly above the ring resonant cavity waveguide 3. It is an arc-shaped structure with a radius and width completely consistent with the ring resonant cavity, with a thickness of 20 nm and a length of 1 μm. Figure 4 As shown, numerical simulations revealed that the effective refractive index of the waveguide's TE fundamental mode is 2.49 when the GSST is in an amorphous state. Figure 5 As shown, numerical simulations show that when the GSST is in a crystalline state, the effective refractive index of the waveguide TE fundamental mode is 2.65+0.05i, and the additional absorption loss introduced by the crystalline GSST is 15899dB / cm.

[0048] for Figure 1 The structure shown, consisting of lumped waveguides and a ring resonator, satisfies the following relationship for the transmittance of the incident light through the direct exit port:

[0049]

[0050] In the formula, γ is the loss factor of the ring resonator, which includes the intrinsic loss factor γ0 and the coupling loss factor γ of the ring resonator. e w l Let w be the frequency of the incident laser, and w0 be the resonant frequency of the ring resonator. The transmittance of the incident light at the split-out exit ports satisfies the following relationship:

[0051]

[0052] Ring resonator coupling loss factor γ e Set to 5×10 9 Based on the effective refractive index obtained from simulation, the intrinsic loss factor γ0 of the resonant cavity corresponding to the crystalline phase change material is calculated to be 1.28 × 10⁻⁶ Hz. 11The resonant frequency is 190.97 THz; the intrinsic loss factor γ0 of the resonant cavity corresponding to the amorphous phase change material is 6.92 × 10⁻⁶. 7 The resonant frequency is 191.36 THz. The final transmission spectra of the ring resonator corresponding to the two phase transition materials are as follows: Figure 6 As shown. (The direct output port is determined by the direction of the incident light; for forward probe light, it is the upper output waveguide; for backward signal light, it is the lower output waveguide.)

[0053] When a pulsed light sequence of the TE fundamental mode with a wavelength of 1567.76 nm is incident from the upper incident waveguide 11, the direct output port is the upper output waveguide 12, and the branched output port is the lower incident waveguide 14. The crystal-de-coated pulsed light first enters the ring resonator 13, as... Figure 6 As shown, the pulsed light is output from the upper exit waveguide 12 and does not enter the sensing fiber. The decrystalline pulsed light causes the phase change material thin film 16 to change from a crystalline state to an amorphous state. Subsequently, the forward probed pulsed light enters the ring resonant cavity 13. At this time, the phase change material thin film 16 is in an amorphous state, and the probed light is output from the lower incident waveguide 14 and enters the sensing fiber. The insertion loss is 0.12dB and the isolation is 36.83dB. Under the action of the forward probed pulsed light, the amorphous phase change material thin film 16 crystallizes into a crystalline state. When the back signal light returned in the sensing fiber due to scattering is incident from the lower incident port 14, the direct exit port is the lower exit port 15, and the branched exit port is the upper incident port 11. Figure 6 As shown, the back signal light is output from the lower output waveguide 15 and enters the receiving end of the sensing system. The insertion loss is 0.03dB and the isolation is 38.31dB.

[0054] Example 2:

[0055] A magnetless optical circulator based on lithium niobate (z-tangential) on a 400nm insulating substrate for on-chip distributed fiber optic sensing systems, such as... Figure 1 As shown, the upper incident waveguide 11, upper exit waveguide 12, ring resonator 13, lower incident waveguide 14, and lower exit waveguide 15 are preferably ridge-type lithium niobate waveguides. The ridge-type lithium niobate waveguide has a height of 400 nm, an etching depth of 200 nm, an etching tilt angle of 70°, a width of 1000 nm, and a cladding of silicon dioxide. The ring resonator is preferably circular with a radius of 50 μm, and the spacing between the upper and lower lumped waveguides and the ring resonator 13 is the same. The transmission loss of the ridge-type lithium niobate waveguide is assumed to be 2 dB / cm. In this embodiment, the operating wavelength of the optical circulator is set to 1549.88 nm (the operating wavelength can be arbitrarily selected by changing the diameter of the ring resonator 13). The ordinary refractive index of z-tangential lithium niobate near this wavelength is 2.21, and the refractive index of silicon dioxide is 1.44.

[0056] The phase change material thin film 16 is made of the same Ge-Sb-Se-Te (GSST) as in Example 1, with a thickness of 20 nm and a length of 10 μm. Numerical simulations show that when the GSST is in the amorphous state, the effective refractive index of the waveguide TE fundamental mode is 1.84. Numerical simulations also show that when the GSST is in the crystalline state, the effective refractive index of the waveguide TE fundamental mode is 1.97 + 0.05i, and the additional absorption loss introduced by the crystalline GSST is 17296 dB / cm.

[0057] Ring resonator coupling loss factor γ e Set to 8×10 9 Based on the effective refractive index obtained from simulation, the intrinsic loss factor γ0 of the resonant cavity corresponding to the crystalline phase change material is calculated to be 2.27 × 10⁻⁶ Hz. 11 The resonant frequency is 193.13 THz; the intrinsic loss factor γ0 of the resonant cavity corresponding to the amorphous phase change material is 1.19 × 10⁻⁶. 8 The resonant frequency is 193.56 THz. The transmission spectra of the ring resonant cavity corresponding to the two phase change materials were obtained using the same calculation method as in Example 1, as shown below. Figure 7 As shown.

[0058] When a pulsed light sequence of the TE fundamental mode with a wavelength of 1549.88 nm is incident from the upper incident waveguide 11, the direct output port is the upper output waveguide 12, and the branched output port is the lower incident waveguide 14. The crystal-de-coated pulsed light first enters the ring resonator 13, as... Figure 7 As shown, the pulsed light is output from the upper exit waveguide 12 and does not enter the sensing fiber. The decrystalline pulsed light causes the phase change material thin film 16 to change from a crystalline state to an amorphous state. Subsequently, the forward probed pulsed light enters the ring resonant cavity 13. At this time, the phase change material thin film 16 is in an amorphous state, and the probed light is output from the lower incident waveguide 14 and enters the sensing fiber. The insertion loss is 0.13dB and the isolation is 36.19dB. Under the action of the forward probed light, the amorphous phase change material thin film 16 crystallizes into a crystalline state. When the back signal light returned from the sensing fiber due to scattering is incident from the lower incident port 14, the direct exit port is the lower exit port 15, and the branched exit port is the upper incident port 11. Figure 7 As shown, the back signal light is output from the lower output waveguide 15 and enters the receiving end of the sensing system. The insertion loss is 0.06dB and the isolation is 35.77dB.

[0059] It can be seen that the application utilizes the characteristics of the phase change material, such as fast phase change speed and large difference in refractive index in two phase states, and realizes the optical circulator for the on-chip distributed optical fiber sensing system based on the micro-ring resonant cavity, the insertion loss of the circulator is less than 0.2 dB, and the isolation is greater than 35 dB. Compared with the optical fiber circulator used in the conventional distributed optical fiber sensing system, the application has the advantages of small size, low cost and low power consumption based on the micro-ring resonant cavity structure. The phase change material used in the application is compatible with large-scale CMOS process and is controlled by optical means. Compared with the conventional on-chip optical circulator based on magneto-optical material, the application does not need an external constant magnetic field, and the process is simpler and compatible with large-scale micro-nano processing technology. In summary, the application effectively solves the problems of large size, complex integration process and inability to large-scale micro-nano processing of the optical circulator in the distributed optical fiber sensing system.

[0060] The content described in the embodiments of the present specification is only a list of implementation forms of the inventive concept, and the protection scope of the present application should not be regarded as being limited to the specific forms stated in the embodiments, and the protection scope of the present application also extends to equivalent technical means that can be thought of by those skilled in the art according to the inventive concept.

Claims

1. A magnetless optical circulator for on-chip distributed fiber optic sensing systems, characterized in that: It includes an upper incident waveguide (11), an upper outgoing waveguide (12), a ring resonator (13), a lower incident waveguide (14), a lower outgoing waveguide (15), and a phase change material thin film (16); The upper incident waveguide (11) and the upper exit waveguide (12) are connected through a first straight waveguide to form an upper lumped waveguide; the lower incident waveguide (14) and the lower exit waveguide (15) are connected through a second straight waveguide to form a lower lumped waveguide; the ring resonator (13) is disposed between the upper lumped waveguide and the lower lumped waveguide, and the ring resonator (13) is simultaneously close to the upper lumped waveguide and the lower lumped waveguide at a predetermined distance. Through evanescent waves, it couples with the upper lumped waveguide and the lower lumped waveguide to form coupling region I (17) and coupling region II (18) respectively, realizing optical coupling incident and coupling out; the phase change material film (16) is attached to the top of a waveguide in the ring resonator (13), and the phase change material film (16) controls the propagation direction of the incident light in the ring resonator (13); The phase change material thin film (16) includes two phase states: crystalline and amorphous. The phase state of the phase change material thin film (16) is switched by a pulse light sequence. The pulsed light sequence includes two pulsed light beams: a decrystalline pulsed light required to control the phase state of the phase change material and a forward probed light required for the sensing system. In the initial state, the phase change material film (16) is crystalline. The pulsed light sequence is transmitted along the upper incident waveguide (11) into the coupling region I (17) and enters the ring resonant cavity (13) through evanescent wave coupling. The decrystalline light in the pulsed light sequence first enters the ring resonant cavity (13). The wavelength of the decrystalline pulsed light is located in the passband of the transmission spectrum of the ring resonant cavity (13). After the decrystalline light travels around in the ring resonant cavity, it is output from the upper outgoing waveguide (12). At this time, the phase change material film (16) is heated and then rapidly cooled under the action of the decrystalline pulsed light, transforming into an amorphous state, so that the resonant wavelength of the resonant cavity changes to the wavelength of the forward probed light. Subsequently, the forward probe pulse in the pulse sequence enters the ring resonant cavity (13). The wavelength of the forward probe pulse is located at the resonant wavelength of the resonant cavity. The forward probe pulse is output from the lower incident waveguide (14). The lower incident waveguide (14) is connected to the sensing fiber in the distributed optical fiber sensing system. The forward probe pulse enters the sensing fiber as the probe light. When the forward probe pulse passes through the ring resonant cavity (13), the amorphous phase change material film (16) becomes crystalline under the action of the forward probe pulse, causing the resonant wavelength of the ring resonant cavity (13) to deviate from the wavelength of the forward probe pulse. The back signal light generated during the transmission of the forward probe pulse light in the sensing fiber returns to the ring resonator (13) from the lower incident waveguide (14); the back signal light cannot cause a phase transition in the ring resonator (13), the wavelength of the back signal light is located in the passband of the resonator's transmission spectrum, and the back signal light is output from the lower exit waveguide (15); the lower exit waveguide (15) is connected to the photoelectric detection receiver in the distributed optical fiber sensing system, and the back signal light enters the photoelectric detection receiver after being output from the lower exit waveguide (15).

2. The magnetless optical circulator for on-chip distributed optical fiber sensing systems as described in claim 1, characterized in that: With a symmetrical shape, the same ring transmission effect can be achieved when the pulse light sequence is incident from any of the ports of the upper incident waveguide (11), upper exit waveguide (12), lower incident waveguide (14), and lower exit waveguide (15).

3. The magnetless optical circulator for on-chip distributed optical fiber sensing systems as described in claim 1, characterized in that: The operating wavelength is selected by adjusting the diameter of the ring resonator (13).

4. The magnetless optical circulator for on-chip distributed optical fiber sensing systems as described in claim 1, characterized in that: When the ring resonator (13) approaches or satisfies the critical coupling condition, the maximum isolation and minimum insertion loss are obtained.

5. A magnetless optical circulator for an on-chip distributed optical fiber sensing system as described in claim 1, characterized in that: The ring resonant cavity (13) is circular or racetrack shaped.

6. The magnetless optical circulator for an on-chip distributed optical fiber sensing system as described in claim 1, characterized in that: The upper lumped waveguide, lower lumped waveguide, and ring resonator (13) include, but are not limited to, strip silicon waveguides or ridge silicon waveguides or strip lithium niobate waveguides or ridge lithium niobate waveguides or strip silicon nitride waveguides or ridge silicon nitride waveguides.

7. A magnetless optical circulator for an on-chip distributed optical fiber sensing system as described in claim 1, characterized in that: The phase change material film (16) is a Ge-Se-Te film, a Ge-Sb-Se-Te film, or a Sb-S film.

8. A magnetless optical circulator for an on-chip distributed optical fiber sensing system as described in claim 1, characterized in that: The transmittance of the pulsed light sequence at the through-out port of the optical circulator satisfies the following relationship: The transmittance of the pulsed light sequence at the output port of the optical circulator satisfies the following relationship: In the formula, γ is the loss factor of the ring resonator, which includes the intrinsic loss factor γ0 and the coupling loss factor γ of the ring resonator. e ;w l ω is the frequency of the incident laser, and w0 is the resonant frequency of the ring resonant cavity.

9. A distributed fiber optic sensing system for on-chip applications, characterized in that: Including the non-magnetic optical circulator as described in any one of claims 1-8.

Images