CN117277042B - Optical resonant cavity coupling structure, manufacturing method and ultrasonic detector - Google Patents
Optical resonant cavity coupling structure, manufacturing method and ultrasonic detector Download PDFInfo
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- CN117277042B CN117277042B CN202310930548.5A CN202310930548A CN117277042B CN 117277042 B CN117277042 B CN 117277042B CN 202310930548 A CN202310930548 A CN 202310930548A CN 117277042 B CN117277042 B CN 117277042B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10084—Frequency control by seeding
- H01S3/10092—Coherent seed, e.g. injection locking
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/48—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using wave or particle radiation means
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29331—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by evanescent wave coupling
- G02B6/29335—Evanescent coupling to a resonator cavity, i.e. between a waveguide mode and a resonant mode of the cavity
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
- H01S3/06745—Tapering of the fibre, core or active region
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/107—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using electro-optic devices, e.g. exhibiting Pockels or Kerr effect
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- Electromagnetism (AREA)
- Optics & Photonics (AREA)
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- Optical Couplings Of Light Guides (AREA)
Abstract
The invention provides an optical resonant cavity coupling structure, a manufacturing method and an ultrasonic detector, and relates to the technical field of ultrasonic detection. The optical resonant cavity coupling structure includes an optical fiber coupling assembly and an optical branching assembly. When the gain range of the laser contains the resonant frequency of the resonant cavity, part of the laser enters the second conical optical fiber from the resonant cavity, and enters the laser source through the optical branching component sequentially passing through the second port and the first port, so that the self-injection locking of the laser source is realized. When the gain range of the laser entering the resonant cavity through the optical branching component does not contain the resonant frequency of the resonant cavity, the gain range of the laser is adjusted to contain the resonant frequency of the resonant cavity, and then the self-injection locking of the laser source is realized. The frequency of the laser is adjusted by replacing the narrow linewidth tunable laser through self injection locking, so that the difficulty of locking a laser mode is reduced, the structure of the ultrasonic detection device is simplified, and the production cost of the ultrasonic detection device is reduced.
Description
Technical Field
The invention relates to the technical field of ultrasonic detection, in particular to an optical resonant cavity coupling structure, a manufacturing method and an ultrasonic detector.
Background
Ultrasound is widely used in scientific research, industry, medical treatment, etc., including underwater sonar detection, ultrasound imaging and therapy in biomedical science, nondestructive testing of materials, sonochemistry, environmental sensing, etc. In these fields, ultrasound plays an important role. In the technical field of optical ultrasonic sensing, the optical fiber sensor has the advantages of small volume, electromagnetic interference resistance, application to complex environments of cold and hot and biochemical corrosion and the like. The ultrasonic detection technology based on the optical fiber is always an important research field, and the working principle of the ultrasonic detection technology is that the ultrasonic and the optical fiber interact with each other in various ways, the light changes, and the detection result is judged according to the light change.
Although there are a variety of fiber-based ultrasound detection techniques, such as fiber-optic fabry-perot cavities and fiber bragg gratings, to some extent these schemes can improve the detection capability for ultrasound, but their bandwidth and sensitivity are relatively limited. The bandwidth is generally below 30MHz, and the sensitivity is above 100 Pa. Also, for example, a prism reflection type (total reflection type, surface plasmon resonance type), an interference type (Mach-Zehnder interference, michelson interference, fabry-Perot interference), a resonance type (optical resonance cavities of various whispering gallery forms), and the form of the optical resonance cavity is the best scheme for the current ultrasonic detection performance.
The scheme of ultrasonic detection by coupling the optical resonant cavity and the optical fiber has the advantages of small volume and high quality factor, and can greatly enhance the interaction between light and substances, thereby having extremely high sensitivity. But the scheme of ultrasonic detection based on the coupling of an optical resonant cavity and an optical fiber generally needs to be matched with a tunable laser to realize ultrasonic detection. Matching tunable lasers results in high cost and complex systems, and has many difficulties in popularization and application.
Disclosure of Invention
The invention provides an optical resonant cavity coupling structure, which is used for solving the defects of high cost and complex system of an ultrasonic detector caused by adjusting the laser frequency through a narrow linewidth tunable laser in the prior art, realizing the adjustment of the laser frequency through self-injection locking instead of setting the narrow linewidth tunable laser, reducing the difficulty of locking a laser mode, simplifying the structure of the ultrasonic detector and reducing the production cost of the ultrasonic detector.
The invention provides an optical resonant cavity coupling structure, comprising:
the optical fiber coupling assembly comprises a resonant cavity, a first conical optical fiber and a second conical optical fiber, wherein the middle part of the first conical optical fiber is provided with a first coupling section coupled with the resonant cavity, the middle part of the second conical optical fiber is provided with a second coupling section coupled with the resonant cavity, the outer diameter of the first coupling section is reduced along the direction away from the resonant cavity, and the outer diameter of the second coupling section is reduced along the direction away from the resonant cavity;
the optical branching component comprises a first port, a second port and a third port, wherein the first port is connected with a laser source, the second port is connected with the first end of the second conical optical fiber, the third port is connected with the first end of the first conical optical fiber, and the second end of the first conical optical fiber is used for transmitting optical signals.
According to the optical resonant cavity coupling structure provided by the embodiment of the invention, the resonant cavity is a micro-bottle cavity with whispering gallery modes, and the first conical optical fiber and the second conical optical fiber are positioned on the same side of the micro-bottle cavity.
According to the optical resonant cavity coupling structure provided by the embodiment of the invention, the resonant cavity is perpendicular to the first tapered optical fiber and the second tapered optical fiber; or the first coupling section and the second coupling section are arc-shaped, two ends of the first conical optical fiber are symmetrical about the central axis of the resonant cavity, and two ends of the second conical optical fiber are symmetrical about the central axis of the resonant cavity.
According to the optical resonant cavity coupling structure provided by the embodiment of the invention, the outer diameters of the first coupling section and the second coupling section are not more than 20 mu m, and the lengths of the first coupling section and the second coupling section are not more than 15mm.
According to an embodiment of the present invention, there is provided an optical resonant cavity coupling structure, further including:
the optical fiber coupling assembly is arranged inside the shell; the side wall of the shell is provided with an ultrasonic detection port communicated with the inside of the shell, and the thickness of the side wall of the ultrasonic detection port is not more than 1mm.
According to an embodiment of the present invention, there is provided an optical resonant cavity coupling structure, the housing including:
the base is provided with a placing groove; the optical fiber coupling assembly is arranged in the placing groove; the ultrasonic detection port is positioned on the base;
and the upper cover is covered on the base.
The invention also provides an ultrasonic detector, which comprises a laser, a photoelectric detector, a controller and the optical resonant cavity coupling structure, wherein the laser is connected with the first port; the second port of the photoelectric detector is connected with the second end of the first tapered optical fiber, and the third port of the photoelectric detector is connected with the controller.
The invention also provides a manufacturing method of the optical resonant cavity coupling structure, which is based on any one of the optical resonant cavity coupling structures and comprises the following steps:
preparing a resonant cavity;
preparing a first tapered optical fiber and a second tapered optical fiber;
coupling a first coupling section of the first tapered optical fiber and a second coupling section of the second tapered optical fiber with the resonant cavity;
the first port of the optical splitter assembly is connected to a laser source, the second port of the optical splitter assembly is connected to the first end of the second tapered optical fiber, and the third port of the optical splitter assembly is connected to the first end of the first tapered optical fiber.
According to the method for manufacturing the optical resonant cavity coupling structure provided by the embodiment of the invention, the steps for preparing the first tapered optical fiber and the second tapered optical fiber comprise the following steps:
the first tapered optical fiber and the second tapered optical fiber are prepared using a hydrogen flame fusion draw process.
According to the method for manufacturing the optical resonant cavity coupling structure provided by the embodiment of the invention, after the step of coupling the first coupling section of the first tapered optical fiber and the second coupling section of the second tapered optical fiber with the resonant cavity, the method further comprises the following steps:
fixing the first coupling section to the resonant cavity by using low refractive index glue and/or low expansion coefficient glue;
the second coupling section is fixed to the resonant cavity by means of a low refractive index glue and/or a low expansion coefficient glue.
According to the optical resonant cavity coupling structure provided by the embodiment of the invention, laser sequentially passes through the first port and the third port and enters the first conical optical fiber through the optical branching component. Since the first end of the first tapered fiber is connectively coupled with the resonant cavity, the laser light is transilluminated in the resonant cavity in the form of an evanescent wave. When the gain range of the laser contains the resonant frequency of the resonant cavity, as the first end of the second tapered optical fiber is connected and coupled with the resonant cavity, part of the laser enters the second tapered optical fiber from the resonant cavity and sequentially enters the laser source through the second port and the first port by the optical branching component, so that the self-injection locking of the laser source is realized, and the frequency of the laser is always consistent with the resonant frequency of the resonant cavity. When the gain range of the laser entering the resonant cavity through the optical branching component does not contain the resonant frequency of the resonant cavity, the gain range of the laser is adjusted to contain the resonant frequency of the resonant cavity, and then the self-injection locking of the laser source is realized. The frequency of the laser is adjusted by replacing the narrow linewidth tunable laser through self injection locking, so that the difficulty of locking a laser mode is reduced, the structure of the ultrasonic detection device is simplified, and the production cost of the ultrasonic detection device is reduced.
Drawings
In order to more clearly illustrate the invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of the connection relationship of an optical resonant cavity coupling structure according to an embodiment of the present invention;
FIG. 2 is a schematic perspective view of an optical fiber coupling assembly according to an embodiment of the present invention;
FIG. 3 is a schematic diagram showing a second perspective structure of an optical fiber coupling assembly according to an embodiment of the present invention;
fig. 4 is a schematic perspective view of a housing according to an embodiment of the present invention;
fig. 5 is a flowchart of a method for manufacturing an optical resonator coupling structure according to an embodiment of the invention.
Reference numerals:
100. an optical fiber coupling assembly; 110. a resonant cavity; 120. a first tapered optical fiber; 130. a second tapered optical fiber; 200. an optical branching component; 300. a housing; 310. a base; 320. an upper cover; 400. a laser; 500. a photodetector; 600. and a controller.
Detailed Description
Embodiments of the present invention are described in further detail below with reference to the accompanying drawings and examples. The following examples are illustrative of the invention but are not intended to limit the scope of the invention.
In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the embodiments of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In describing embodiments of the present invention, it should be noted that, unless explicitly stated and limited otherwise, the terms "coupled," "coupled," and "connected" should be construed broadly, and may be either a fixed connection, a removable connection, or an integral connection, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium. The specific meaning of the above terms in embodiments of the present invention will be understood in detail by those of ordinary skill in the art.
In embodiments of the invention, unless expressly specified and limited otherwise, a first feature "up" or "down" on a second feature may be that the first and second features are in direct contact, or that the first and second features are in indirect contact via an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the embodiments of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
An optical resonant cavity coupling structure, a method of fabrication, and an ultrasound probe in accordance with embodiments of the present invention are described below in conjunction with fig. 1-5.
Fig. 1 illustrates a schematic connection relationship of an optical resonant cavity coupling structure according to an embodiment of the present invention, and as shown in fig. 1, the optical resonant cavity coupling structure according to an embodiment of the present invention includes an optical fiber coupling assembly 100 and an optical branching assembly 200. The optical fiber coupling assembly comprises a resonant cavity, a first conical optical fiber and a second conical optical fiber, wherein the middle part of the first conical optical fiber is provided with a first coupling section coupled with the resonant cavity, and the middle part of the second conical optical fiber is provided with a second coupling section coupled with the resonant cavity. The outer diameter of the first coupling section decreases in a direction away from the resonant cavity and the outer diameter of the second coupling section decreases in a direction away from the resonant cavity. The optical splitter assembly 200 includes a first port connected to a laser source, a second port connected to a first end of a second tapered optical fiber, and a third port connected to a first end of a first tapered optical fiber, the second end of the first tapered optical fiber being configured to transmit an optical signal.
In the optical resonant cavity coupling structure provided by the embodiment of the invention, the laser sequentially passes through the first port and the third port to enter the first tapered optical fiber 120 through the optical branching component 200. Since the first end of the first tapered optical fiber 120 is connectively coupled with the resonant cavity 110, the laser light is transilluminated in the form of an evanescent wave coupled into the resonant cavity 110. When the gain range of the laser includes the resonant frequency of the resonant cavity, because the first end of the second tapered optical fiber 130 is coupled with the resonant cavity 110, part of the laser enters the second tapered optical fiber 130 from the resonant cavity 110, and sequentially passes through the second port and the first port to enter the laser source through the optical branching component 200, so as to realize self-injection locking of the laser source, and the frequency of the laser always keeps consistent with the resonant frequency of the resonant cavity 110. When the gain range of the laser entering the resonant cavity 110 through the optical branching component 200 does not contain the resonant frequency of the resonant cavity, the gain range of the laser is adjusted to contain the resonant frequency of the resonant cavity 110, so as to realize the self-injection locking of the laser source. The frequency of the laser is adjusted by replacing the narrow linewidth tunable laser through self injection locking, so that the difficulty of locking a laser mode is reduced, the structure of the ultrasonic detection device is simplified, and the production cost of the ultrasonic detection device is reduced.
In an embodiment of the present invention, the resonant cavity 110 is a whispering gallery mode micro-bottle cavity, and the first tapered optical fiber and the second tapered optical fiber are located on the same side of the micro-bottle cavity.
In an embodiment of the present invention, the resonant cavity 110 of the whispering gallery mode may be a micro-bottle cavity, a micro-disk cavity, a micro-column cavity, a micro-ring cavity, a microsphere cavity, or the like. A resonant cavity 110 of a Whispering Gallery Mode (WGM) is an optical component that utilizes total internal surface reflection of the resonant cavity 110 to achieve local enhancement of an optical field and mode selection. The quality factor is the most important parameter characterizing the resonator 110, and represents the storage capacity of the resonator 110 for photon energy. While the whispering gallery mode cavity 110 has a high quality factor. Thus, photons in the whispering gallery mode resonator 110 are confined to a wavelength scale space while having a higher photon lifetime. Photons are continually reflected in the whispering gallery mode resonator 110, both increasing the optical path and significantly enhancing the interaction of light with the substance. The performance of the optical cavity coupling structure can be enhanced by providing the cavity 110 with whispering gallery modes. The micro-bottle cavity may have multiple whispering gallery modes, i.e., the micro-bottle cavity has multiple resonant frequencies.
Because the thickness of the micro-disc cavity, the micro-column cavity, the micro-ring cavity, the microsphere cavity and the like is usually extremely low and is tens of micrometers to hundreds of micrometers, when the micro-disc cavity, the micro-column cavity, the micro-ring cavity, the microsphere cavity and the like are adopted as the resonant cavity 110, the first tapered optical fiber 120 is arranged on one side of the resonant cavity 110, the second tapered optical fiber 130 is arranged on the other side of the resonant cavity 110, and the occupied space of the optical resonant cavity coupling structure is increased. If the connection secondary coupling is carried out on the same side, the success rate is low and the difficulty is high.
In ultrasound detection applications, the quality factor requirement for the resonator 110 need not be too high, as long as the diameter of the resonator 110 is relatively small. The quality factor of the micro-bottle cavity is 10 6 -10 7 The diameter of the micro-bottle cavity ranges from 130um to 160um, which is far smaller than the diameter size of the conventional resonant cavity in the order of 110 mm. Therefore, the micro-bottle cavity completely meets the application requirements of ultrasonic detection.
When the micro-bottle cavity is used as the resonant cavity 110, the thickness of the micro-bottle cavity can be millimeter level, and the first tapered optical fiber and the second tapered optical fiber can be arranged on the same side of the micro-bottle cavity, so that the occupied space of the coupling structure of the optical resonant cavity is reduced. When the first tapered optical fiber and the second tapered optical fiber can be disposed on the same side of the micro-bottle cavity, the space required for packaging the optical fiber coupling assembly 100 is also greatly saved, and the volume of the ultrasound probe is reduced. Preferably, the micro-bottle cavity has a cavity thickness of 300 μm to 600 μm.
Fig. 2 illustrates one of three-dimensional schematic diagrams of an optical fiber coupling assembly according to an embodiment of the present invention, and fig. 3 illustrates the second three-dimensional schematic diagram of the optical fiber coupling assembly according to an embodiment of the present invention, where, as shown in fig. 2 and fig. 3, the resonant cavity is perpendicular to both the first tapered optical fiber and the second tapered optical fiber. Or the first coupling section and the second coupling section are arc-shaped, two ends of the first conical optical fiber are symmetrical about the central axis of the resonant cavity, and two ends of the second conical optical fiber are symmetrical about the central axis of the resonant cavity. Specifically, as shown in fig. 3, the first coupling section and the second coupling section may each be arc-shaped, and two ends of the first tapered optical fiber are symmetrical about a horizontal central axis of the resonant cavity, and two ends of the second tapered optical fiber are symmetrical about the horizontal central axis of the resonant cavity. When the resonant cavity is vertical to the first conical optical fiber and the second conical optical fiber, the optical fiber transmittance of the optical resonant cavity coupling structure is high. When the first coupling section and the second coupling section are arc-shaped, two ends of the first conical optical fiber are symmetrical about the central axis of the resonant cavity, and two ends of the second conical optical fiber are symmetrical about the central axis of the resonant cavity, namely, the first conical optical fiber and the second conical optical fiber are both U-shaped optical fibers, so that the horizontal length of the coupling structure of the optical resonant cavity can be reduced. The U-shaped optical fiber can be obtained by bending a tapered optical fiber. When the U-shaped first tapered optical fiber and the U-shaped second tapered optical fiber are packaged by the shell, the horizontal width of the shell can be correspondingly reduced due to the reduction of the horizontal width of the coupling structure of the optical resonant cavity.
In an embodiment of the invention, the outer diameter of the first coupling section and the second coupling section is not more than 20 μm, and the length of the first coupling section and the second coupling section is not more than 15mm.
Fig. 4 illustrates a schematic perspective structure of a housing provided in an embodiment of the present invention, as shown in fig. 4, the optical resonant cavity coupling structure further includes a housing 300, the optical fiber coupling assembly 100 is disposed inside the housing 300, an ultrasonic detection port is disposed on a side wall of the housing and is communicated with the interior of the housing, and a thickness of a side wall of the ultrasonic detection port is not greater than 1mm. The fiber optic coupling assembly 100 is environmentally demanding and must be operated in a clean room environment in a laboratory. Accordingly, by disposing the fiber coupling assembly 100 inside the housing 300, the optical cavity coupling structure can be used normally in a conventional environment. The external ultrasonic signals enter the shell through the ultrasonic detection port and are received by the micro-bottle cavity, so that the optical resonant cavity coupling structure converts the ultrasonic signals into corresponding optical signals. Through setting the thickness of lateral wall to be not more than 1mm, can reduce the outside straight line distance of micropin chamber and casing, can prevent simultaneously that the ultrasonic signal of other directions from being blocked by the casing to better receipt ultrasonic signal.
When the size of the ultrasonic detection port is larger than that of the micro-bottle cavity, the micro-bottle cavity is easily affected by the external environment and damaged; when the size of the ultrasonic detection port is smaller than that of the micro-bottle cavity, the external ultrasonic signal is easily shielded by the housing 300, and the micro-bottle cavity cannot receive enough ultrasonic signal. Thus, the size of the ultrasonic detection port can be set to be the same as the size of the micro-bottle cavity. The ultrasonic detection port can be circular, square or the like.
In an embodiment of the invention, the first tapered optical fiber and the second tapered optical fiber are positioned on one side of the micro-bottle cavity away from the ultrasonic detection port, or the first tapered optical fiber and the second tapered optical fiber are positioned on one side of the micro-bottle cavity close to the ultrasonic detection port.
In an embodiment of the present invention, the housing 300 includes a base 310 and an upper cover 320. The base 310 is provided with a placement groove, the optical fiber coupling assembly 100 is arranged in the placement groove, the ultrasonic detection port is positioned on the base, and the upper cover 320 covers the base 310. When the upper cover 320 is covered on the base 310, the housing 300 may be sealed by airtight glue, a sealing ring, or the like, so as to further ensure that the optical resonator coupling structure can be used normally in a conventional environment.
In an embodiment of the present invention, the base 310 is provided with a first placement groove and a second placement groove, and the first placement groove is perpendicular to the second placement groove. The micro-bottle cavity is placed in a first placing groove, and the first conical optical fiber and the second conical optical fiber are located in a second placing groove. The first tapered optical fiber and the second tapered optical fiber are symmetrically arranged about the micro-bottle cavity. The micro-bottle cavity is fixed to the first placing groove by UV glue or other quick-drying glue, and the first coupling section and the second coupling section are fixed to the second placing groove by glue with low refractive index and low expansion coefficient. The uncoupled sections of the first tapered optical fiber and the second tapered optical fiber are fixed in the second placing groove through UV glue or other quick-drying glue so as to further fix the first tapered optical fiber and the second tapered optical fiber and avoid the movement of the first tapered optical fiber and the second tapered optical fiber.
The ultrasonic detector provided by the embodiment of the invention comprises a laser 400, a photoelectric detector 500, a controller 600 and any one of the optical resonant cavity coupling structures, wherein the laser 400 is connected with a first port; a second port of the photodetector 500 is connected to the second end of the first tapered optical fiber such that the second end of the first tapered optical fiber transmits an optical signal, and a third port of the photodetector 500 is connected to the controller 600. The laser 400 may be a DFB (Distributed Feedback) distributed feedback laser for outputting laser light. The optical splitter assembly 200 may be a circulator through which laser light can only travel along a predetermined path. Specifically, as shown in fig. 1, when laser light is input from the second port of the circulator, it is output from the first port of the circulator; outputting from a third port of the circulator when the laser is input from the first port of the circulator; when laser light is input from the third port of the circulator, the laser light generates a huge input loss at the first port of the circulator and the second port of the circulator, and almost no input is generated.
The photodetector 500 is used for converting an optical signal and an electrical signal, and acquiring real-time optical data. The photodetector 500 is constituted by a photodiode. The photodiode operates at a reverse voltage. When no illumination exists, the reverse current is extremely weak and is called dark current; when there is illumination, the reverse current rapidly increases to tens of microamps, known as photocurrent. The greater the intensity of the light, the greater the reverse current, i.e., the change in light causes the photodiode current to change in order to effect conversion of the optical signal into an electrical signal. When designing and manufacturing the photodiode, the area of the PN junction can be increased as much as possible so as to receive incident light. The controller 600 is used for receiving the electrical signal converted from the optical signal by the photodetector 500 and performing ultrasonic signal decoding analysis on the converted electrical signal.
According to the optical resonant cavity coupling structure provided by the embodiment of the invention, the whispering gallery mode locking can be realized by only fine tuning the DFB laser 400, so that the frequency of the laser is adjusted to be consistent with the resonant frequency of the resonant cavity 110. Not only the superior ultrasonic detection performance of the resonant cavity 110 is maintained, but also the just-needed pain point of the narrow linewidth tunable laser is solved. The optical resonant cavity coupling structure provided by the embodiment of the invention is used as an independent device, is applied to the fields of ultrasonic/photoacoustic detection and imaging, photoacoustic endoscopic imaging and the like, and has wide application prospects. The ultrasonic detector provided with the optical resonant cavity coupling structure has high sensitivity (lower than 100 Pa) and high bandwidth (higher than 40MHz and even higher than 100 MHz) and has portability and high robustness.
Fig. 5 illustrates a flowchart of a method for manufacturing an optical resonant cavity coupling structure according to an embodiment of the present invention, where, as shown in fig. 5, the method for manufacturing an optical resonant cavity coupling structure according to an embodiment of the present invention is based on any one of the optical resonant cavity coupling structures, and the method for manufacturing an optical resonant cavity coupling structure includes:
s10: preparing a resonant cavity 110;
when the resonant cavity 110 is a micro-bottle cavity, the micro-bottle cavity can be prepared based on a single mode fiber and the thickness of the micro-bottle cavity can be controlled to 300-600 μm.
S20: preparing a first tapered optical fiber and a second tapered optical fiber;
s30: coupling the first coupling section of the first tapered optical fiber and the second coupling section of the second tapered optical fiber with the resonant cavity;
when in connection coupling, the positions of the first conical optical fiber and the second conical optical fiber are adjusted by utilizing the three-dimensional displacement platform, and simultaneously, the coupling state of each conical optical fiber and the micro-bottle cavity is observed through a microscope, so that the positions of the conical optical fibers are continuously adjusted to be as close to the critical coupling state as possible. Of course, the two ends of the tapered optical fiber may be connected to the laser 400 and the oscilloscope, respectively, and whether the coupling state reaches the critical coupling may be determined by observing the waveform change of the oscilloscope. Coupling means that the coupling section of each tapered optical fiber is attached and tangent to the side wall of the micro-bottle cavity.
It should be noted that, in order to further improve the coupling effect, glue with low refractive index may be dropped on the first coupling section and the second coupling section. On one hand, the two tapered optical fibers are more close after being coupled by using the surface tension of the low-refractive-index glue. On the other hand, light losses can be avoided with low refractive index glues.
S40: the first port of the optical splitter assembly is connected to the laser source, the second port of the optical splitter assembly is connected to the first end of the second tapered optical fiber, and the third port of the optical splitter assembly is connected to the first end of the first tapered optical fiber.
In an embodiment of the present invention,
a step of preparing a first tapered optical fiber and a second tapered optical fiber, comprising:
the first tapered optical fiber and the second tapered optical fiber are prepared by a hydrogen flame fusion process.
Because the first tapered optical fiber 120 and the second tapered optical fiber 130 are closer, in order to facilitate coupling, interference between the first tapered optical fiber 120 and the second tapered optical fiber 130 during coupling is avoided, and the first tapered optical fiber 120 and the second tapered optical fiber 130 can be prepared simultaneously by adopting a hydrogen flame fusion process. Specifically, two clean optical fibers with coating layers removed are clamped as close as possible, and then are simultaneously fused and drawn under hydrogen flame, so that the first tapered optical fiber 120 and the second tapered optical fiber 130 are prepared, and the first tapered optical fiber 120 and the second tapered optical fiber 130 are simultaneously coupled with the resonant cavity, so that the coupling difficulty is reduced, and interference caused by sequential coupling of the first tapered optical fiber 120 and the second tapered optical fiber 130 is avoided.
In an embodiment of the present invention,
after the step of coupling the first coupling section of the first tapered optical fiber and the second coupling section of the second tapered optical fiber with the resonant cavity, further comprising:
fixing the first coupling section to the resonant cavity by using low refractive index glue and/or low expansion coefficient glue;
the second coupling section is fixed to the resonator by means of a low refractive index glue and/or a low expansion coefficient glue.
The low refractive index glue is the glue with the refractive index smaller than that of the tapered optical fiber, and the smaller the refractive index is, the more excellent the performance is. The first coupling segment and the second coupling segment are fixed to the resonant cavity by a low refractive index glue so as to reduce the refractive losses of light at the first coupling segment and the second coupling segment. The glue with low expansion coefficient refers to the glue with small expansion coefficient, and the smaller the expansion coefficient is, the better the expansion coefficient is. The first coupling section and the second coupling section are fixed in the resonant cavity through the glue with low expansion coefficient, so that the situation that the first coupling section and the second coupling section are changed in the coupling process to influence the coupling effect is avoided.
And the capillary tube can be used for uniformly coating the glue with low refractive index and low expansion coefficient on the micro-bottle cavity, the first coupling section and the second coupling section, and the glue with low refractive index and low expansion coefficient is slowly cured in the air, so that the morphological changes of the first coupling section and the second coupling section in the curing process are greatly reduced. The above steps were repeated 3 times more so that the coupling region was stably cured.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (9)
1. An optical resonant cavity coupling structure, comprising:
the optical fiber coupling assembly comprises a resonant cavity, a first conical optical fiber and a second conical optical fiber, wherein the middle part of the first conical optical fiber is provided with a first coupling section coupled with the resonant cavity, the middle part of the second conical optical fiber is provided with a second coupling section coupled with the resonant cavity, the outer diameter of the first coupling section is reduced along the direction away from the resonant cavity, and the outer diameter of the second coupling section is reduced along the direction away from the resonant cavity;
the optical branching component comprises a first port, a second port and a third port, wherein the first port is connected with a laser source, the second port is connected with the first end of the second conical optical fiber, the third port is connected with the first end of the first conical optical fiber, and the second end of the first conical optical fiber is used for transmitting optical signals;
the outer diameter of the first coupling section and the second coupling section is not more than 20 mu m, and the length of the first coupling section and the second coupling section is not more than 15mm.
2. The optical resonant cavity coupling structure of claim 1, wherein the resonant cavity is a whispering gallery mode micro-bottle cavity, the first tapered optical fiber and the second tapered optical fiber being on the same side of the micro-bottle cavity.
3. The optical resonant cavity coupling structure of claim 2, wherein the resonant cavity is perpendicular to both the first tapered optical fiber and the second tapered optical fiber; or the first coupling section and the second coupling section are arc-shaped, two ends of the first conical optical fiber are symmetrical about the central axis of the resonant cavity, and two ends of the second conical optical fiber are symmetrical about the central axis of the resonant cavity.
4. The optical resonator coupling structure of any of claims 1-3, further comprising:
the optical fiber coupling assembly is arranged inside the shell; the side wall of the shell is provided with an ultrasonic detection port communicated with the inside of the shell, and the thickness of the side wall of the ultrasonic detection port is not more than 1mm.
5. The optical resonant cavity coupling structure of claim 4, wherein the housing comprises:
the base is provided with a placing groove; the optical fiber coupling assembly is arranged in the placing groove; the ultrasonic detection port is positioned on the base;
and the upper cover is covered on the base.
6. An ultrasound probe comprising a laser, a photodetector, a controller, and the optical resonant cavity coupling structure of any of claims 1-5, the laser being connected to a first port; the second port of the photoelectric detector is connected with the second end of the first tapered optical fiber, and the third port of the photoelectric detector is connected with the controller.
7. A method of fabricating an optical resonant cavity coupling structure, wherein the method of fabricating an optical resonant cavity coupling structure is based on the optical resonant cavity coupling structure of any of claims 1-5, comprising:
preparing a resonant cavity;
preparing a first tapered optical fiber and a second tapered optical fiber;
coupling a first coupling section of the first tapered optical fiber and a second coupling section of the second tapered optical fiber with the resonant cavity;
the first port of the optical splitter assembly is connected to a laser source, the second port of the optical splitter assembly is connected to the first end of the second tapered optical fiber, and the third port of the optical splitter assembly is connected to the first end of the first tapered optical fiber.
8. The method of fabricating an optical resonator coupling structure according to claim 7, wherein the step of preparing a first tapered optical fiber and a second tapered optical fiber comprises:
the first tapered optical fiber and the second tapered optical fiber are prepared using a hydrogen flame fusion draw process.
9. The method of claim 7, wherein after the step of coupling the first coupling section of the first tapered optical fiber and the second coupling section of the second tapered optical fiber to the resonant cavity, further comprising:
fixing the first coupling section to the resonant cavity by using low refractive index glue and/or low expansion coefficient glue;
the second coupling section is fixed to the resonant cavity by means of a low refractive index glue and/or a low expansion coefficient glue.
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| CN106785853A (en) * | 2017-03-21 | 2017-05-31 | 中国科学院长春光学精密机械与物理研究所 | A kind of optical resonator coupled system |
| CN108896512A (en) * | 2018-07-18 | 2018-11-27 | 清华-伯克利深圳学院筹备办公室 | The detection device and method of microfluid |
| CN109193325A (en) * | 2018-09-11 | 2019-01-11 | 中国科学院长春光学精密机械与物理研究所 | A kind of mode in optical resonator cleaves identifying system |
| CN115986543A (en) * | 2022-12-26 | 2023-04-18 | 北京大学长三角光电科学研究院 | Narrow linewidth laser |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106785853A (en) * | 2017-03-21 | 2017-05-31 | 中国科学院长春光学精密机械与物理研究所 | A kind of optical resonator coupled system |
| CN108896512A (en) * | 2018-07-18 | 2018-11-27 | 清华-伯克利深圳学院筹备办公室 | The detection device and method of microfluid |
| CN109193325A (en) * | 2018-09-11 | 2019-01-11 | 中国科学院长春光学精密机械与物理研究所 | A kind of mode in optical resonator cleaves identifying system |
| CN115986543A (en) * | 2022-12-26 | 2023-04-18 | 北京大学长三角光电科学研究院 | Narrow linewidth laser |
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