Optical sensor, optical device and method for determining real-time fluid properties of particles in turbid media

Abstract

The embodiment of the specification provides an optical sensor. The optical sensor includes a single optical fiber including a modified fiber tip and a distal end opposite the modified fiber tip. The distal end may be configured to optically communicate with an external light source and an external detector. The improved optical fiber tip may be configured to be located within a turbid medium to pass light from an external light source to particles in the turbid medium, to at least minimize retroreflection of the light at the improved optical fiber tip, and to receive backscattered light from the particles to determine real-time fluid characteristics of the particles in the turbid medium by an external detector. The embodiment of the specification also provides an optical instrument, an optical device and a method for determining real-time fluid characteristics of particles.

Description

Cross-references

[0001] This application claims priority to Singapore application No. 10202202241V filed on March 7, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0002] Some embodiments of the present specification relate to an optical sensor, an optical instrument, and an optical device, each of which includes the above-mentioned optical sensor) and a method for determining real-time fluid properties of particles in a turbid medium. Background Art

[0003] In order to measure the fluid properties (e.g., flow rate and molecular concentration) in a tube (e.g., a blood vessel, a pipeline, a catheter), a guidewire-based sensing probe is usually used. For example, Doppler guidewires have been widely used in clinical intravascular flow velocity measurements. For fluid properties, such as flow rate and molecular concentration in a pipeline (e.g., a blood vessel, a pipeline, a catheter), a guidewire-based sensing probe is usually used. For example, Doppler guidewires have been widely used in clinical intravascular flow velocity measurements. However, due to the limitation of the size of the ultrasonic element, the minimum diameter that a Doppler guidewire can reach is 0.014 inches (about 360 microns). This diameter may be good enough for larger blood vessels, but it is not suitable for smaller arteries or veins. Therefore, a smaller sensing probe is needed.

[0004] The measurement of low turbidity scattering liquid media requires high sensitivity. The fiber Bragg grating (FBG) method uses a predetermined length of optical fiber for sensing, where longer gratings have higher sensitivity. However, since the FBG sensing method relies on the vibration of the optical fiber itself, it still faces the problem of low sensitivity in many applications, which may not be ideal for the application.

[0005] Fiber optic technology is a dynamic and customizable technology that offers absolute measurement readings, electromagnetic interference stability, excellent resolution and range, portability, multiplexing possibilities, and economic value. Therefore, fiber optic sensors have proven to be a promising technology for remote and continuous monitoring of the concentration and size of scattering particles in flowing media.

[0006] However, there is still a need for a method and / or system that can achieve high measurement sensitivity with very small probe size while at least solving the above-mentioned problems. Summary of the invention

[0007] One aspect of the embodiments of the present specification provides an optical sensor. The optical sensor comprises: a single optical fiber, comprising a modified optical fiber tip and a distal end, the distal end being opposite to the modified optical fiber tip, characterized in that the distal end is configured to perform optical communication with an external light source and an external detector; and the modified optical fiber tip is configured to be located in a turbid medium to transmit light from the external light source to particles in the turbid medium, at least to minimize back reflection of the light at the modified optical fiber tip, and to receive backscattered light from the particles, so as to determine real-time fluid properties of the particles in the turbid medium through the external detector.

[0008] Another aspect of the embodiments of the present specification provides an optical instrument, which includes: an optical sensor as shown in the embodiments of the present specification; and an optical circulator, including: a first port configured to be optically coupled to an external light source, a second port configured to be optically coupled to the optical sensor, and a third port configured to be optically coupled to an external detector.

[0009] Another aspect of the embodiments of the present specification provides an optical device. The optical device includes: an optical sensor as shown in the embodiments of the present specification; a light source configured to emit light to particles in a turbid medium through the optical sensor; a detector configured to receive backscattered light from the particles through the optical sensor to determine the real-time fluid properties of the particles in the turbid medium; and an optical circulator, including: a first port configured to be optically coupled to the light source to receive the light emitted by the light source; a second port configured to be optically coupled to the optical sensor to direct the received light to the particles and receive the backscattered light from the particles; and a third port configured to be optically coupled to the detector to direct the received backscattered light to the detector.

[0010] Another aspect of the embodiments of the present specification provides a method for determining the real-time fluid properties of particles in a turbid medium. The method includes: providing a single optical fiber, the single optical fiber including a modified optical fiber end and a distal end opposite to the modified optical fiber end, the modified optical fiber end being located in the turbid medium, the distal end being in optical communication with a light source and a detector; transmitting light emitted by the light source to particles in the turbid medium through the single optical fiber; receiving backscattered light of the particles through the detector through the single optical fiber, while at least minimizing the back reflection of the light at the modified optical fiber end; and processing the received backscattered light to determine the real-time fluid properties of the particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the drawings, the same reference numerals generally represent the same components in different views. The drawings are not necessarily drawn to scale, and emphasis is generally placed on illustrating the principles of one or more embodiments of the present specification. In the following description, one or more embodiments of the present specification will be described with reference to the following drawings, in which:

[0012] Figure 1A is an exemplary schematic diagram of an optical sensor according to some embodiments of the present specification;

[0013] Figure 1B is an exemplary schematic diagram of an optical instrument according to some embodiments of the present specification;

[0014] Figure 1C is an exemplary schematic diagram of an optical device according to some embodiments of the present specification;

[0015] Figure 1D is an exemplary flow chart of a method for determining real-time fluid properties of particles in a turbid medium according to some embodiments of the present specification;

[0016] Figure 2A is an exemplary side cross-sectional view of an improved optical fiber tip with a symmetrical needle shape according to some embodiments of the present specification;

[0017] Figure 2B is an exemplary side cross-sectional view of an improved optical fiber tip with an asymmetric needle shape according to some embodiments of the present specification;

[0018] Figure 3 is an exemplary schematic diagram of a distributed optical sensor and its arrangement in a scattering fluid medium or scattering liquid according to some embodiments of the present specification;

[0019] Figure 4A is an exemplary side cross-sectional view of a flat fiber tip of a fiber optic probe according to some embodiments of the present specification, showing back reflection of light from the flat fiber tip;

[0020] Figure 4B is an exemplary side cross-sectional view of an angle-polished flat optical fiber tip according to some embodiments of the present specification, wherein the reverse reflected light of the angle-polished flat optical fiber tip leaves the optical fiber probe through the side wall of the optical fiber;

[0021] Figure 5 According to some embodiments of this specification Figure 4B An exemplary side cross-sectional view of an angle-polished flat optical fiber tip in a scattering medium to detect scattered light caused by suspended particles in the medium. DETAILED DESCRIPTION

[0022] The following detailed description refers to the accompanying drawings, which show the specific details and specific embodiments of some embodiments of this specification by way of example. The detailed description of these embodiments is sufficient to enable those skilled in the art to implement some embodiments of this specification. Other embodiments may also be used and structural, logical and electrical changes may be made without departing from the scope of some embodiments of this specification. Some embodiments are not necessarily mutually exclusive, as certain embodiments may be combined with one or more other embodiments to form new embodiments.

[0023] Embodiments described in the context of one method or apparatus are equally valid for the other method or apparatus. Similarly, embodiments described in the context of a method are equally valid for the apparatus, and vice versa.

[0024] Features described in the context of one embodiment may be applicable to the same or similar features in other embodiments accordingly. Features described in the context of one embodiment may be applicable to other embodiments accordingly, even if not explicitly described in these other embodiments. In addition, additions and / or combinations and / or alternatives described for a feature in the context of one embodiment may be applicable to the same or similar features in other embodiments accordingly.

[0025] In the context of some embodiments, the articles “a,” “an,” “an,” and / or “the” used for features or elements include reference to one or more features or elements.

[0026] In the context of some embodiments, the phrase "at least substantially" may include "completely" and reasonable deviations.

[0027] In the context of some embodiments, the term "about" as applied to numerical values ​​includes the exact value and a reasonable deviation.

[0028] In the present application, the term "and / or" may include any one or more of the relevant listed items or combinations thereof.

[0029] As used herein, a phrase of the form “at least one of A or B” may include A or B or A and B. Accordingly, a phrase of the form “at least one of A or B or C”, or including further listed items, may include any and all combinations of one or more of the associated listed items.

[0030] As used herein, "configured to" may mean "built to" or "arranged to."

[0031] Some embodiments of the present specification provide methods for performing multifunctional measurements in a scattering fluid medium using a single optical fiber. More specifically, a method for multifunctional sensing using only a single optical fiber (which can be as small as about 100 microns in diameter) can be provided. The method can utilize the interaction between photons and scattered particles, rather than the fiber vibrations used in FBG sensing methods, to achieve high sensitivity to the flow of scattering particles such as red blood cells. In order to maintain high measurement sensitivity within an extremely small probe size, a unique design is used that allows special processing of the fiber end of a single optical fiber and the use of special signal processing methods.

[0032] Figure 1A is an exemplary schematic diagram of an optical sensor according to some embodiments of this specification. Figure 1A As shown, the optical sensor 100 includes a single optical fiber 102, wherein the single optical fiber 102 includes a modified optical fiber tip 104 and a distal end 106, and the distal end 106 is opposite to the modified optical fiber tip 104. The distal end 106 can be configured to communicate with an external light source (e.g., Figure 1C 125) and external detectors (e.g. Figure 1C 127) for optical communication. The improved optical fiber tip 104 can be configured to be located in a turbid medium ( Figure 1A 104) to transmit light from an external light source to particles in the turbid medium, at least minimize back reflection of the light at the modified optical fiber end 104, and receive backscattered light from the particles so as to determine real-time fluid properties of the particles in the turbid medium by an external detector.

[0033] In the context of some embodiments, "single optical fiber" refers to only one optical fiber. The term "modified" in relation to an optical fiber end refers to an optical fiber end that has been pre-processed or engineered to have structural differences compared to a smooth, straight optical fiber end face. A smooth, straight optical fiber end face means that when the optical fiber is laid in a straight line, the core and cladding are substantially flush with each other along the same plane that is substantially perpendicular to the central axis of the optical fiber.

[0034] In other words, a single optical fiber can be used as a probe to perform optical measurements in turbid fluids (single-phase fluids, such as suspensions containing scattering particles, etc.). Turbid media can also be referred to as scattering media or liquid media. A single optical fiber can be used to both emit light to the particles and receive light scattered or reflected by the particles. A method for measuring the real-time flow rate and concentration of scattering particles by an optical fiber component including an optical fiber cable and a remote optical circulator in an optical fiber sensor system can also be provided. The optical fiber probe tip (or optical fiber tip) can be designed to reduce or even eliminate the direct backscattering / reflection of the transmitted light, thereby improving the sensitivity of the measurement and increasing the signal-to-noise ratio of the measurement. The direct backscattering / reflection of the transmitted light occurs at the optical fiber tip, more precisely, at the optical fiber end face or optical fiber interface. This technology is particularly useful for characterizing scattering and flowing fluid media, and can be applied to a variety of fields, such as intravascular blood flow and oxygenation sensors (biomedicine), in-pipe water turbidity sensors (environment), and cell growth monitoring (biotechnology).

[0035] In some embodiments, the modified fiber tip 104 can taper at an angle relative to a vertical axis 109 of the single optical fiber 102, which is outside the acceptance angle of the single optical fiber 102, and the vertical axis 109 is perpendicular to the central axis 108 of the single optical fiber 102. The acceptance angle of an optical fiber (in this case, the single optical fiber 102) is defined as the maximum angle of incidence at the interface between the medium and the fiber core where light enters and propagates along the optical fiber. For example, the angle of the modified fiber tip 104 can be greater than 15°. In other words, the tilt of the modified fiber tip 104 can be less than or equal to 75° when measured from the vertical axis 109.

[0036] In some embodiments, the improved optical fiber tip 104 may include an anti-reflection coating. The anti-reflection coating may include a dielectric thin film coating. In some embodiments, the anti-reflection coating may be a single anti-reflection coating, a double anti-reflection coating, or a broadband anti-reflection coating.

[0037] In some embodiments, the improved optical fiber tip 104 may be needle-shaped, having a partial core (e.g., 211) of a single optical fiber 102, but not having an outer cladding (e.g., 213) of the single optical fiber 102. Figure 2A As shown in the exemplary side cross-sectional view of an example 204a in FIG. 1 , the improved optical fiber tip 104 can be a substantially symmetrical needle shape. Each side of the substantially symmetrical needle shape can be inclined Φ1 from the core 211 outward toward the cladding 213, and Φ1 is between 10° and 75° relative to the central axis 208. For example, Φ1 can be about 45°. Figure 2BAs shown in another exemplary side cross-sectional view of another example 204b, the improved optical fiber tip 104 can be an asymmetric needle. The asymmetric needle can be tilted by Φ2 and Φ3 on each side, and Φ2 and Φ3 can be the same or different, each between 10° and 75° relative to the central axis 208.

[0038] In some embodiments, the sensing platform may be based on a single optical fiber 102. The single optical fiber 102 may have a core refractive index and a cladding refractive index, wherein the core refractive index is higher than the cladding refractive index. For example, the core refractive index may range from 1.4 to 1.7, and the cladding refractive index may range from 1.2 to 1.4 (excluding 1.4).

[0039] The single optical fiber 102 may be a single mode optical fiber or a multimode optical fiber.

[0040] Figure 1B is an exemplary schematic diagram of an optical instrument according to some embodiments of this specification. Figure 1B As shown, the optical instrument 120 includes the optical sensor 100 as shown in the embodiment of this specification; and an optical circulator 121. The optical circulator 121 includes a first port 123a, which is configured to communicate with an external light source ( Figure 1B a second port 123b configured to be optically coupled to the optical sensor 100; and a third port 123c configured to be optically coupled to an external detector ( Figure 1B In this case, the optical circulator 121 is a three-port device designed so that light from an external light source enters from the first port 123a and is emitted from the second port 123b to send the light to the optical sensor 100, and the backscattered light received by the optical sensor 100 enters the second port 123b and is emitted from the third port 123c to send the backscattered light to the external detector.

[0041] The optical instrument 120 may include Figure 1A The same or similar elements or components of the optical sensor 100 are therefore assigned the same numerical designations, and similar elements may be referred to as Figure 1A The related description of the components in the optical sensor 100 is not repeated here.

[0042] Figure 1C is an exemplary schematic diagram of an optical device according to some embodiments of this specification. Figure 1C As shown, the optical device 140 includes the optical sensor 100 as shown in the embodiment of this specification; the light source 125 is configured to transmit light to the turbid medium ( Figure 1C100); a detector 127 configured to receive backscattered light from particles in a turbid medium through the optical sensor 100 to determine real-time fluid properties of particles in a turbid medium; and an optical circulator 121. The optical circulator 121 may include a first port 123a configured to be optically coupled to the light source 125 to receive light emitted by the light source 125; a second port 123b configured to be optically coupled to the optical sensor 100 to guide the received light to the particles and receive backscattered light from the particles; and a third port 123c configured to be optically coupled to the detector 127 to guide the received backscattered light to the detector 127.

[0043] The optical device 140 may include Figure 1A The optical sensor 100 or Figure 1B The same or similar elements or components of the optical instrument 120 are therefore assigned the same numerical designations, and similar elements may be referred to as Figure 1A The optical sensor 100 of the element or Figure 1B The relevant description of the components of the optical instrument 120 will not be repeated here.

[0044] In some embodiments, the light source 125 may include a coherent light source. For example, the light source 125 may be a laser. For example, the laser may have a power of 0.01 mW to 5 mW and a wavelength of 400 nm to 1200 nm.

[0045] The detector 127 may include a pixel camera, such as a charged-coupled device (CCD) camera or a complementary metal-oxide-semiconductor (CMOS) camera.

[0046] Figure 1D is an exemplary flow chart of a method for determining real-time fluid properties of particles in a turbid medium according to some embodiments of the present specification. In step 162, a single optical fiber (e.g., Figure 1A 102), including improved optical fiber ends (e.g., Figure 1A 104) and a distal end opposite to the modified optical fiber tip (e.g., Figure 1A 106), the improved optical fiber tip is located in the turbid medium, and the distal end is connected to the light source (e.g., Figure 1C 125) and detectors (e.g., Figure 1CIn step 164, the light emitted by the light source can be transmitted to the particles in the turbid medium through a single optical fiber. In step 166, the detector can receive the backscattered light of the particles through a single optical fiber, while at least minimizing the back-reflected light of the modified optical fiber end. In step 168, the received backscattered light can be processed to determine the real-time fluid properties of the particles.

[0047] In other words, method 160 can be an optical method that uses backscattered photons in a scattering fluid medium for multifunctional detection (rather than using backreflected photons in existing systems). More specifically, a single optical fiber can be used for multifunctional sensing, i.e., by using an optical circulator (e.g., Figure 1B and 1C 121 in the figure) for light transmission and light collection. Currently, a single optical fiber is the smallest sensor probe (about 100 microns in diameter) that can be used for intravascular blood flow measurement or other intravascular / extravascular monitoring. Method 160 may involve Figure 1A The optical sensor 100 or Figure 1B Optical instruments 120 or Figure 1C The optical device 140 in FIG. 1 is identical or similar to the elements or components in FIG. 1 , and therefore, the corresponding description is omitted here.

[0048] In some embodiments, the improved optical fiber tip may include at least one of the following: relative to the vertical axis of the single optical fiber (e.g., Figure 1A 109) gradually tapering at an angle that is outside the acceptance angle of a single optical fiber, for example, the angle of the improved optical fiber end is greater than 15°; an anti-reflection coating; or a needle shape, having a partial core of a single optical fiber but not having the outer cladding of a single optical fiber.

[0049] The real-time fluid properties of the particles include the concentration of the particles in the turbid medium, or the flow rate of the particles in the turbid medium, or the viscosity of the particles in the turbid medium, or the average size of the particles in the turbid medium, or the Brownian motion rate of the particles in the turbid medium. The absorption spectrum of the turbid medium or the light scattering spectrum of the turbid medium can also be determined.

[0050] In some embodiments, in step 164, the step of transmitting the light emitted by the light source may include: transmitting the light emitted by the light source through an optical circulator (e.g., Figure 1C 121) of the first port (for example, Figure 1C 123a) in the optical circulator and passes the light through the second port of the optical circulator (e.g., Figure 1C 123b) in the optical fiber directs light to particles in the turbid medium, and the second port is optically coupled to the distal end of the single optical fiber.

[0051] In step 166, the step of receiving the backscattered light of the particle may include: receiving the backscattered light of the particle through the second port and transmitting the backscattered light of the particle through the third port (eg, Figure 1C 123c) in the figure guides the received backscattered light to the detector.

[0052] Although the above method is illustrated and described as a series of steps or events, it should be understood that any order of these steps or events should not be interpreted as having a restrictive meaning. For example, some steps can be carried out in different orders and / or simultaneously with other steps or events other than those described and / or described in this specification. In addition, to realize one or more aspects or embodiments described herein, all the steps of the description may not be required. In addition, one or more steps described herein can be carried out in one or more separate actions and / or stages.

[0053] The following is an example of a multifunctional method for measuring scattering fluid media, such as measuring the flow rate of scattering liquid, the concentration of scattering particles and the viscosity through a fiber optic circulator system with a specially designed end.

[0054] Versatile measurement methods can be used with Figure 1D The method 160 is described in a similar context, and the fiber circulator system and the specially designed end can include the Figure 1C The optical device 140 and Figure 1A 104 in the improved optical fiber tip 104, and therefore, the same numerical designations are assigned, and similar elements may be referred to as Figure 1C The optical device 140 and Figure 1A Related description of the improved optical fiber end 104 in.

[0055] Figure 3 3 is an exemplary schematic diagram of a distributed optical sensor 300 and its arrangement 340 in a scattering fluid medium or scattering liquid 315 (involving a fiber optic circulator system) according to some embodiments of the present specification. The description of the distributed optical sensor 300 and the fiber optic circulator system can be respectively described in Figure 1A The optical sensor 100 and Figure 1C The optical device 140 is similar to the optical device 140.

[0056] The arrangement 340 includes a multimode fiber circulator 321. A light source 325 is optically coupled to a first port 323a. As indicated by a directional arrow 317, light enters a second port 323b from the first port 323a, and then reaches a third port 323c from the second port 323b as indicated by another directional arrow 319. Light cannot directly reach the third port 323c from the first port 323a through the second port 323b. In other words, the light source 325 sends an optical signal through the first port 323a and then directs it to the second port 323b. The optical signal is scattered by particles in the scattering liquid 315 as backscattered light, sent through the second port 323b, and then directed to the third port 323c. The second port 323b of the multimode fiber circulator 321 is connected to a single optical fiber 300, and the third port 323c is connected or optically coupled to a detector 327.

[0057] The light source 325 may be a coherent light source. For example, a laser for illumination through the first port 323a. On the detector side, the grinding pattern (also called speckle pattern) may be captured by the detector 327, which may include a pixelated detector such as a CCD camera or a CMOS camera. By analyzing the image captured by the detector 327, information such as flow rate, molecular concentration, and viscosity may be extracted.

[0058] The working principle between the exemplary flat fiber tip (i.e., having a flat, straight fiber end face) and the specially designed tip will be referred to Figure 4A , Figure 4B and Figure 5 The principle is similar to that shown in some embodiments of this specification. Figure 1A Context of the improved optical fiber tip 104 in.

[0059] Figure 4A FIG. 4 is an exemplary side cross-sectional view of a flat fiber tip 404a of a fiber optic probe 402 according to some embodiments of the present specification, showing back reflection of light 455a from the flat fiber tip 404a. The flat fiber tip 404a is substantially located in a plane substantially perpendicular to the central axis 408 of the fiber optic probe 402.

[0060] like Figure 4AAs shown, the optical fiber probe 402 in contact with the medium 457 includes a core 403 and an outer cladding 401. The core 403 is the optical transmission element of the optical fiber probe 402, and an exemplary refractive index is 1.51 (n1, i.e., the core refractive index); while the outer cladding 408 has a relatively low refractive index, and an exemplary refractive index is 1.33 (n2, i.e., the cladding refractive index). This refractive index difference can ensure that the light passes through the core 408 by total internal reflection. Other refractive index differences can also be used to promote total internal reflection. In other words, at the flat optical fiber end 404a as the optical fiber interface, a portion of the light 453 of the light 451 sent through the core 408 is transmitted into the medium 457, and another portion of the light 455a is reflected back into the core 403. At the flat optical fiber end 404a, part of the light propagating inside the optical fiber probe 402 is reflected back from the flat optical fiber end 404a, reducing the signal-to-noise ratio of the measurement. Some existing systems can use this working principle to measure the medium.

[0061] In contrast, Figure 4B 4 is an exemplary side cross-sectional view 452 of a specially designed tip, an angle-polished flat fiber tip 404b, according to some embodiments of the present specification, wherein the reverse reflected light 455b of the angle-polished flat fiber tip 404b leaves the fiber probe 402 through the fiber sidewall, which may include the outer cladding 401. The angle-polished flat fiber tip 404b, which may also be referred to as an angle fiber tip or a beveled fiber end face, may be used in conjunction with Figure 1A and is substantially located in a plane that is at an angle θ to the vertical axis 409 of the fiber optic probe 402 (which may be in a plane similar to Figure 1A The vertical axis 409 is perpendicular to the central axis 408 of the fiber optic probe 402.

[0062] By polishing the fiber end face at a specific angle θ greater than 15° to obtain the angle-polished flat fiber tip 404b, the incident angle of the angle-polished flat fiber tip 404b is changed so that the reverse reflected light 455b can leave the fiber probe 402 through the fiber side wall including the outer cladding 401. In practice, the inclination of the angle-polished flat fiber tip 404b is less than or equal to 75° (e.g., Figure 4B As shown, by providing 90°-θ), the reverse reflection is redirected to an angle outside the optical fiber receiving angle, ensuring that the reverse reflection will not be transmitted along the fiber core 403 (with Figure 4A This is desirable because back reflections may degrade the signal by a significant percentage and, at high powers, may overheat the fiber around sharp bends or damage the source.

[0063] Figure 5 According to some embodiments of this specification Figure 4BAn exemplary side cross-sectional view 550 of an angle-polished flat optical fiber tip 404b in a scattering medium 555 detecting scattered light 551 caused by suspended particles 553 in the medium 555.

[0064] When the fiber optic probe 402 is located in a scattering fluid medium 555 (also referred to as a turbid medium or a turbid medium), light 453 passes through the fiber core 403 and is transmitted outward from the angle-polished flat fiber tip 404b to particles 553 in the scattering fluid medium 555. Scattered (or backscattered) light 551 from the particles 553 in the medium 555 provides a signal for determining the fluid properties of the medium 555 (e.g., the concentration of the particles 553) without being affected by Figure 4B The reverse reflected light at the angle-polished flat optical fiber tip 404b ( Figure 5 (not shown) and thus cause interference.

[0065] Other methods of eliminating or at least reducing direct back reflections may include: a) specially designed fiber tips with anti-reflection coatings on the surface of the fiber tip, and / or b) polishing the fiber tip into a needle shape to expose the unclad fiber core for a short distance. Essentially, the anti-reflection coating prevents any back reflections from occurring at the fiber tip, and the needle-shaped fiber tip works in the same way as the Figure 4B The angle-polished flat optical fiber tip 404b is similar.

[0066] As will be appreciated, the specially designed tip provides a special fiber tip engineering pattern to reduce / eliminate back reflections.

[0067] Most existing fiber optic sensors use Fabry-Perot (FP) configuration or fiber Bragg grating (FBG) method. If the pressure / flow / temperature around the fiber end changes, an interference pattern or Bragg wavelength shift will be generated. Existing fiber optic sensors do not use the direct interaction between photons and scatterers in the medium. Their sensing function is based on the stress / pressure / bending of the fiber end itself. Some embodiments of this specification do not rely on the physical state of the optical fiber itself, but use a single optical fiber as a medium to both send photons to the scattering liquid (medium) and receive backscattered photons. Then, the flow / concentration / viscosity information is calculated based on the interaction between the photons and the scatterers / absorbers in the liquid. It should be understood and recognized that the concepts of some embodiments of the present invention are very different from most existing fiber optic sensing methods.

[0068] As described above, to achieve the transmission and reception of light through a single optical fiber, a fiber circulator (e.g., Figure 3 However, from the second port 323b (such as Figure 3The reverse reflected light 455a (as shown) Figure 4A The back-reflected photons (shown) may be a significant source of noise because these photons do not enter the liquid medium 457, but are directly reflected back at the fiber boundary (e.g., the fiber core 408). Therefore, these back-reflected photons do not carry information of the liquid medium 457. Due to the size limitation of a single optical fiber, the collection efficiency of back-scattered photons from scatterers (scattering particles) is very low. The back-reflected noise makes it essentially impossible to extract useful information. To address this problem, as described above, several engineering methods have been proposed, namely, polishing at an angle greater than 15° relative to the vertical axis of the monolithic optical fiber at the end (e.g., 404b) of the second port 323b, designing a needle shape at the second port 323b, or applying an anti-reflection coating at the end (e.g., 404a or 404b) of the second port 323b. At present, among the above three methods, polishing at an angle greater than 15° relative to the vertical axis of the monolithic optical fiber at the end (e.g., 404b) of the second port 323b may be the simplest and cheapest processing method. It is possible to combine two of these methods (e.g., polishing the tip at the second port 323b at an angle greater than 15° relative to the vertical axis of the monolithic optical fiber and coating the angled tip). However, this increases the cost and the efficiency may be about the same as using only one method.

[0069] In fiber optic communications, although angle polishing of optical fiber ends to reduce back reflections has been disclosed, such disclosures are limited to polishing the optical fiber ends at angles of 5° to 15°, with the most common angle probably being about 8° relative to the vertical axis. This is because in fiber optic communications, angles exceeding 15° relative to the vertical axis can result in significant signal loss through the fiber cladding, resulting in low sensitivity. Typically, such smaller angles of optical fiber ends are suitable for air, but not for liquids (scattering or turbid media).

[0070] In contrast, some embodiments of the present specification show that a polishing angle greater than 15° relative to the vertical axis must be used to detect backscattered light. This large angle can reduce or even eliminate reflected light at the fiber interface. This allows more light to enter the liquid medium to interact with the particles and then scatter back into the fiber. It is believed that experts in the field related to fiber optic communications do not have enough understanding of light scattering theory in scattering media or laser coherence analysis, while diffuse optics experts do not have enough understanding of fiber end engineering or fiber optic circulators. To provide various embodiments of the present invention, it is necessary to have deep knowledge and rich experimental experience in optical fibers, fiber end engineering, fiber optic circulators, diffuse reflection optics and laser coherence analysis, so the present invention is not insignificant.

[0071] Although this specification has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes may be made to the form and details of this specification without departing from the spirit and scope of this specification as defined by the appended claims. Therefore, the scope of this specification is indicated by the appended claims, and therefore, all changes within the meaning and equivalent range of the claims should be included.

Claims

1. An optical sensor, include: A single optical fiber, comprising a modified optical fiber end and a distal end, wherein the distal end is opposite to the modified optical fiber end, characterized in that: The distal end is configured to be in optical communication with an external light source and an external detector; and The modified optical fiber tip is configured to be located in a turbid medium to transmit light from the external light source to particles in the turbid medium, at least minimize back reflection of the light at the modified optical fiber tip, and receive backscattered light from the particles so as to determine real-time fluid properties of the particles in the turbid medium through the external detector.

2. The optical sensor according to claim 1, It is characterized in that The improved optical fiber tip tapers at an angle relative to a vertical axis of the single optical fiber, the angle being outside an acceptance angle of the single optical fiber, and the vertical axis being perpendicular to a central axis of the single optical fiber.

3. The optical sensor according to claim 2, It is characterized in that The angle of the improved optical fiber tip is greater than 15°.

4. The optical sensor according to claim 1, It is characterized in that The improved optical fiber tip includes an anti-reflective coating.

5. The optical sensor according to claim 4, It is characterized in that The anti-reflective coating includes a dielectric thin film coating.

6. The optical sensor according to claim 4 or 5, It is characterized in that The anti-reflection coating includes a single anti-reflection coating, a double anti-reflection coating or a broadband anti-reflection coating.

7. The optical sensor according to claim 1, It is characterized in that The improved optical fiber tip is needle-shaped, has a partial core of the single optical fiber, and does not have the outer cladding of the single optical fiber.

8. The optical sensor according to claim 7, It is characterized in that The improved optical fiber end is in a symmetrical needle shape.

9. The optical sensor according to claim 7, It is characterized in that The improved optical fiber end is in an asymmetric needle shape.

10. The optical sensor according to any one of claims 1 to 9, It is characterized in that The single optical fiber has a core refractive index and a cladding refractive index, and the core refractive index is higher than the cladding refractive index.

11. An optical instrument, include: The optical sensor according to any one of claims 1 to 10; as well as Optical circulator, comprising: a first port configured to optically couple with an external light source, a second port configured to be optically coupled to the optical sensor, and The third port is configured to be optically coupled to an external detector.

12. An optical device, include: The optical sensor according to any one of claims 1 to 10; a light source configured to emit light toward particles in the turbid medium through the optical sensor; a detector configured to receive backscattered light from the particles via the optical sensor to determine real-time fluid properties of the particles in the turbid medium; as well as Optical circulator, comprising: A first port is configured to be optically coupled to the light source to receive the light emitted by the light source; a second port configured to be optically coupled to the optical sensor to direct the received light toward the particle and receive the backscattered light from the particle; and The third port is configured to be optically coupled to the detector to guide the received backscattered light to the detector.

13. The optical device according to claim 12, It is characterized in that The light source comprises a coherent light source.

14. An optical device according to claim 12 or 13, It is characterized in that The light source is a laser.

15. An optical device as claimed in any one of claims 12 to 14, It is characterized in that The detector includes a pixel camera.

16. An optical device according to any one of claims 12 to 15, It is characterized in that The detector comprises a charge coupled device camera or a complementary metal oxide semiconductor camera.

17. A method for determining real-time fluid properties of particles in a turbid medium, the method include: Providing a single optical fiber, the single optical fiber comprising a modified optical fiber tip and a distal end opposite the modified optical fiber tip, the modified optical fiber tip being located in the turbid medium, the distal end being in optical communication with a light source and a detector; transmitting the light emitted by the light source to the particles in the turbid medium through the single optical fiber; receiving, by said detector, backscattered light from said particles through said single optical fiber while at least minimizing back reflection of said light at said modified optical fiber tip; as well as The received backscattered light is processed to determine the real-time fluid properties of the particles.

18. The method of claim 17, It is characterized in that The improved optical fiber terminal includes at least one of the following: tapering at an angle relative to a vertical axis of the single optical fiber, the angle being outside an acceptance angle of the single optical fiber, and the vertical axis being perpendicular to a central axis of the single optical fiber; Anti-reflective coating; or The optical fiber is needle-shaped and has a partial core of the single optical fiber but does not have the outer cladding of the single optical fiber.

19. The method of claim 18, It is characterized in that The angle of the improved optical fiber end is greater than 15°.

20. The method according to any one of claims 17 to 19, It is characterized in that The real-time fluid properties of the particles include the concentration of the particles in the turbid medium, the flow rate of the particles in the turbid medium, the viscosity of the particles in the turbid medium, the average size of the particles in the turbid medium, or the Brownian motion rate of the particles in the turbid medium.

21. The method according to any one of claims 17 to 20, It is characterized in that The step of transmitting the light emitted by the light source comprises: transmitting the light through a first port of an optical circulator and directing the light toward the particles in the turbid medium through a second port of the optical circulator, the second port being optically coupled to the distal end of the single optical fiber; and The step of receiving the backscattered light of the particle includes: receiving the backscattered light from the particle through the second port, and guiding the received backscattered light to the detector through the third port of the optical circulator.

Images