Optical despeckler, optical system and device incorporating same, and method for despeckling an optical signal

Abstract

An optical fiber subassembly for reducing optical speckle in an optical system includes an optical fiber, a vibrating element such as a piezoelectric element, and a controller. The optical fiber has a first end adapted to receive light from a light source associated with the optical system and a second end for transmitting light from the light source to a surface where a speckle pattern may occur. The optical fiber extends through the vibrating element such that the vibrating element at least partially surrounds a portion of the optical fiber intermediate the first and second ends. The controller is operably coupled to the vibrating element to vibrate the vibrating element at a frequency faster than a threshold frequency sufficient to reduce speckle on the surface.

Description

[Technical Field]

[0001] (Related Applications) This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 440,109, filed January 20, 2023, which is incorporated by reference in its entirety. [Background technology]

[0002] The present disclosure relates to reducing optical speckle, and more particularly to optical systems and devices in which optical signals propagating along optical fibers are subject to optical speckle.

[0003] Speckle can result from the self-interference of light on a surface, such as a screen or target, causing intensity variations visible to an observer or instrument and can be an undesirable side effect when using narrow-bandwidth light sources such as lasers. Speckle can also appear when light is transmitted through a material, because the surface structure of the material can randomly change the phase and polarization of the light. The resulting speckle pattern can cause noticeable, undesirable intensity variations across the surface, which often appear as a sparkling or granular structure.

[0004] For example, but not by way of limitation, laser-based projection displays often suffer from speckle. Such speckle can reduce image clarity and distract viewers. Several approaches have been proposed to reduce speckle contrast based on spatial and temporal decorrelation of speckle patterns. For example, U.S. Patent Application Publication No. 2018 / 0252863 discloses a system having a light source configured to output illumination light and a display system receiving the illumination light. The display system may be a projector for displaying moving images or images. An optical fiber is configured to direct the illumination light from the light source to the display system, and a vibrating device is attached to the optical fiber. The vibrating device communicates with a controller that senses speckle and activates the vibrating device in response. The vibrating device is operable to vibrate at a frequency higher than a threshold frequency to reduce speckle. The refractive index profile of the optical fiber can be designed to remove speckle from the output illumination light without significant light loss.

[0005] Similarly, Japanese Patent Laid-Open No. 63-082336 (Optical Fiber Exciter) shows a system in which pressing members are placed on both sides of an optical fiber and the optical fiber is pressed by a piezoelectric element driven by voltage from a control unit. The control unit supplies a periodic wave to the piezoelectric element to eliminate the effects of polarization in single-mode fibers and the effects of speckle from multi-mode fibers, thereby achieving stable and highly accurate photometry. Summary of the Invention [Means for solving the problem]

[0006] In one aspect, an optical fiber subassembly for reducing optical speckle occurring in an optical system is presented herein. The optical fiber subassembly includes an optical fiber, a vibrating element, and a controller. The optical fiber has a first end adapted to receive light from a light source associated with the optical system and a second end for transmitting light from the light source to a surface where a speckle pattern may occur. The optical fiber extends through the vibrating element such that the vibrating element at least partially surrounds a portion of the optical fiber intermediate the first end and the second end. The controller is operably coupled to the vibrating element to vibrate the vibrating element at a frequency faster than a threshold frequency sufficient to reduce speckle occurring on the surface.

[0007] In one implementation, the vibrating element is a piezoelectric element.

[0008] In another implementation, the vibrating element circumferentially surrounds the optical fiber.

[0009] In another implementation, the vibrating element is cylindrical and the optical fiber passes through the central axis of the vibrating element.

[0010] In another implementation, the fiber optic subassembly further includes at least one material disposed between the vibrating element and the portion of the optical fiber at least partially surrounded by the vibrating element.

[0011] In another implementation, the material includes an adhesive for securing the vibrating element to the optical fiber.

[0012] In another implementation, the fiber optic subassembly further includes a fiber optic connector in which the first end of the optical fiber is located, and the vibrating element is located within the fiber optic connector.

[0013] In another implementation, the fiber optic connector is of a type selected from the group consisting of LC, SC, FC, ST, SMA, and MTP / MPO connectors.

[0014] In another implementation, the fiber optic subassembly further includes a wire electrically coupleable to the vibrating element and the controller for supplying electrical energy to the vibrating element.

[0015] In another implementation, the wire extends through one end of the fiber optic connector.

[0016] In another implementation, the wire is releasably connectable to the vibrating element through a sidewall of the fiber optic connector.

[0017] In another aspect, a speckle reducer is incorporated within an optical fiber connector. The optical fiber connector includes an optical fiber connector housing, an optical fiber having a ferrule therein, and a vibrating element. The optical fiber extends within the optical fiber connector housing and has a first end that passes through the ferrule. The vibrating element is disposed within the housing and attached to the first end of the optical fiber, the vibrating element operable to vibrate at a frequency that reduces optical speckle.

[0018] This Summary is provided to introduce various concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a light source that provides light via an optical fiber to an optical system that may cause speckle. [Figure 2] 2 illustrates an example of the optical fiber and vibrating element shown in FIG. 1, where the vibrating element circumferentially surrounds a portion of the optical fiber. [Figure 3] 1 is a cross-sectional view of an example of an optical fiber connector. [Figure 4]FIG. 4 is an isometric view of the assembled fiber optic connector shown in FIG. 3. [Figure 5] FIG. 2 is a simplified schematic diagram of one non-limiting example optical arrangement in which the optical speckle despeckler described herein may be used. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present disclosure recognizes the problem of speckle in existing optical systems and discloses an optical despeckler that is easy to set up, small in size, and power efficient.

[0021] 1 is a schematic diagram illustrating an example of a light source 110 that provides light via an optical fiber 120 to an optical system 112, such as a projector, a display device, or more generally, any other arrangement that may produce speckle. The optical system 112 may be a system used in any of a variety of applications, including, for example, laser-based displays (heads-up, cinema, pico, etc.), laser beam homogenizers, laser-based metrology, microscopy, spectroscopy, interferometry, lithography, and any of various types of laser-based communication systems, probes, sensors, monitors, illuminators, etc. The light source 110 will often be a laser light source, but generally the light source may be any narrowband light source that may produce speckle.

[0022] The optical fiber 120 may be a coated, uncoated, jacketed, or unjacketed, single-mode or multimode optical fiber, glass fiber, plastic fiber, step-index fiber, graded-index fiber, or any other type of optical fiber. Such optical fibers may have diameters ranging, for example, from a few microns to about 1 mm or more.

[0023] The vibration element 140 circumferentially surrounds a portion of the optical fiber 120. In some embodiments, the vibration element 140 may only partially surround the portion of the optical fiber 120. The vibration element 140 may be any suitable element capable of imparting vibrational energy to the optical fiber 120 at a frequency and amplitude capable of reducing or eliminating speckle from the optical system 112. In some embodiments, multiple vibration elements 140 may be provided along the optical fiber 120. In one embodiment, the vibration element is a piezoelectric element. Examples of suitable piezoelectric materials include, but are not limited to, crystals, ceramics and lead-free piezoelectric ceramics, III-V and II-VI semiconductors, and polymers. In other embodiments, a suitable vibration element may be, but is not limited to, a speaker, exciter, vibrator, motor, transducer, vibration motor, shaker, buzzer, or other device. Also shown in FIG. 1 is a controller 125 that provides power to the vibration element 140 via a wired connection.

[0024] FIG. 2 illustrates one specific example of an optical fiber 120 and a vibration element 140 circumferentially surrounding a portion of the optical fiber 120. In this example, the vibration element 140 is provided in the form of a cylindrical piezoelectric element positioned along a portion of the optical fiber 120, with the optical fiber extending through the central axis of the cylindrical piezoelectric element. The piezoelectric element is designed to contract circumferentially when subjected to an electrical potential. A layer 150 of filler, adhesive, epoxy, or other suitable material may be provided between the optical fiber 120 and the piezoelectric element 140 to aid in uniform transfer of mechanical energy from the piezoelectric element to the optical fiber. The filler 150 also provides electrical insulation between the piezoelectric element 140 and the optical fiber 120. The piezoelectric element 140 may be provided anywhere along the length of the optical fiber, including at the end of the optical fiber.

[0025] 2 shows a cylindrical vibrating element 140, more generally, the piezoelectric element may have any desired shape and configuration, including configurations that cause the piezoelectric element to circumferentially surround the optical fiber asymmetrically and symmetrically. The vibrating element 140 may be left exposed or may be covered by a protective cover disposed over only the vibrating element 140 or along the entire optical fiber 120.

[0026] As described above, the vibration element may be located anywhere along the length of the optical fiber. In some embodiments of the subject matter described herein, the vibration element may be located around a portion of the optical fiber located within the optical fiber connector. Optical fiber connectors are components used to terminate the ends of fiber optic cables and generally allow for faster connection and disconnection than fiber splicing. Optical fiber connectors can be used in a wide variety of different applications, including, for example, joining segments of optical fiber to longer lengths, connecting optical fibers to active devices such as transceivers, detectors, and repeaters, or connecting optical fibers to passive devices such as switches or attenuators. The central function of an optical fiber connector is to maintain or position the ends of two optical fibers so that the core of one optical fiber is axially aligned with the core of the other optical fiber. Another function of an optical fiber connector is to align light emitted from a light source with the optical fibers so that light from one fiber can be coupled to or transmitted between the other fiber as efficiently as possible. Yet another function of an optical fiber connector is to provide mechanical stability and protection to the optical junction in its operating environment. In general, stability and joint protection are important features of connector design (eg, minimizing differential thermal expansion and mechanical motion effects).

[0027] Fiber optic connectors can be classified into different types based on a number of different classification methods. For example, such connectors can be classified according to the connector's pin endface (they can be classified as PC, UPC, and APC) or according to the type of transmission medium (single-mode and multimode fiber optic connectors). Common standard types of fiber optic connectors include, by way of example, LC, SC, FC, ST, SMA, and MTP / MPO connectors.

[0028] In general, most fiber optic connectors typically include multiple components, including, for example, a ferrule, a connector body, and a connector coupling mechanism. The ferrule is a thin, typically cylindrical structure that holds the fiber in place. It is often made from ceramic, metal, or plastic. The fiber is precisely aligned and secured within the ferrule to ensure optimal light transmission. The connector body is the outer housing that surrounds the ferrule and provides mechanical support and protection. The connector coupling mechanism allows the connector to be easily attached and detached. Common coupling mechanisms include threaded connectors, push-pull connectors, and bayonet-style connectors.

[0029] According to the subject matter described herein, a vibrating element, such as a piezoelectric element, can surround a portion of an optical fiber located within any type of fiber optic connector, including connectors conforming to one or more established standards, such as those described above, or essentially proprietary connectors. In this manner, the fiber optic connector effectively functions as an optical speckle eliminator. In non-limiting specific examples, vibrating elements according to the present disclosure can be integrated into: 1) high-power assemblies using high-power SMA and high-power industrial FD-80 connectors to provide a fiber optic link between a laser source and a target; 2) high-temperature assemblies for optical sensing in sealed, high-temperature environments; 3) single-fiber assemblies for a wide range of applications, including spectroscopy, industrial sensing, and low-power laser light delivery; and 4) bundle assemblies for a wide variety of photonics systems for optical sensing and laser power delivery for industrial, medical, military, and research applications.

[0030] FIG. 3 is a cross-sectional view of an example fiber optic connector 200, and FIG. 4 is an isometric view of the same assembled fiber optic connector 200. The connector 200 includes a connector body 210, a connector coupling mechanism 220, and a ferrule 230. FIG. 3 also shows an optical fiber 240 extending within the connector body 210. A piezoelectric element 250 (or other vibrating element) is located within the connector body 210 and circumferentially surrounds the optical fiber 240. The piezoelectric element 250 may be located in any suitable position within the connector body 210 that allows it to circumferentially surround the optical fiber 240. Generally, the piezoelectric element 250 is longitudinally aligned with the optical fiber 240 and the connector body 210 and is positioned such that the optical fiber 240 can pass completely through the piezoelectric element. As previously mentioned, a layer of filler, adhesive, epoxy, and / or other suitable material may be provided between the optical fiber 240 and the piezoelectric element 250 to secure the piezoelectric element 250 in place and to aid in the uniform transfer of mechanical energy from the piezoelectric element 250 to the optical fiber. The dimensions of the piezoelectric element 250 may be selected to be small enough to be accommodated within the connector body 210, yet capable of imparting sufficient vibrational energy to the optical fiber 240. By way of example, in some embodiments, the piezoelectric element 250 may have an overall length of 4 to 50 mm, an inner diameter of 0.2 to 40 mm, and an outer diameter of 0.5 to 50 mm.

[0031] In a non-limiting embodiment, a controller (e.g., controller 125 shown in FIG. 1 ) or other suitable device is used to apply a voltage to the piezoelectric element. The voltage is used to control the aforementioned contraction of the piezoelectric element and the application of pressure to the optical fiber. The pressure on the optical fiber can be cycled periodically or applied on a random, pseudo-random, or other complex basis to change the polarization state of the optical signal propagating along the optical fiber. For example, a periodic form of mains power, 50 / 60 Hz, in the form of a sine wave can be used. For a compound / compound cycle form, the electrical signal can be generated by superimposing different waveforms and frequencies using a signal generator or the like. In other embodiments, the voltage applied to the piezoelectric element can be in the range of 300 Hz to 70 KHz.

[0032] The voltage may be supplied to the piezoelectric element 250 within the connector body 210 in any of a variety of ways. For example, wires may extend from the interior of the connector body 210 and exit at a distal end of the connector body 210, away from the connector coupling mechanism 220. In other embodiments, the wires may exit at a proximal end of the connector coupling mechanism 220. In still other embodiments, the wires may exit from the side of the connector body 210, for example, using a removable plug, thereby providing a releasable connection.

[0033] In some embodiments, the controller or equivalent device is operable to sense speckle in the optical fiber and, in response, apply appropriate control signals to the piezoelectric elements to reduce the speckle. For example, in the exemplary system shown in FIG. 1 , the controller 125 may be used to sense speckle occurring in the optical system 112. The vibrating element 140 may be in communication with the controller 125, which senses speckle occurring in the optical system 112 and, in response, activates the vibrating element 140. In another embodiment, the vibrating element 140 may be in a constantly on state.

[0034] FIG. 5 is a simplified schematic diagram of one non-limiting example of an optical arrangement in which the optical speckle despeckler described herein may be used. The optical system in this example is a fluorescence microscope for performing fluorescence microscopy. As shown, the arrangement includes a laser source 310 in which the optical speckle despeckler described herein may be used. The optical speckle despeckler may use an optical fiber assembly 350 having a vibrating element circumferentially surrounding all or a portion of an optical fiber 320 through which light is emitted by the laser source 310. The vibrating element may be located along any suitable portion of the optical fiber 320, including a portion located within the optical fiber connector that connects to the laser source 310. Light from the optical fiber 320 is directed to a beam splitter 325, which directs the light to a fluorescence microscope 330 to excite fluorescent molecules. The resulting fluorescence is returned to the beam splitter 325 and, after necessary filtering by a filter 345, is directed to a detector 340. The detector 340 may be associated with a display or a camera. Optical speckle in the resulting image is reduced by using the optical despeckler described herein.

[0035] It should be noted that the applications of the optical despeckler disclosed herein are not limited to the applications described above, and it will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments disclosed herein without departing from the spirit or scope of the present disclosure.

Claims

1. 1. An optical fiber subassembly for reducing optical speckle occurring in an optical system, comprising: an optical fiber having a first end adapted to receive light from a light source associated with the optical system and a second end for transmitting light from the light source to a surface on which a speckle pattern may occur; a vibrating element through which the optical fiber extends, the vibrating element at least partially surrounding a portion of the optical fiber intermediate the first end and the second end; a controller operably coupled to the vibrating element and configured to vibrate the vibrating element at a frequency greater than a threshold frequency sufficient to reduce speckle on the surface.

2. The fiber optic subassembly of claim 1 , wherein the vibrating element is a piezoelectric element.

3. The optical fiber subassembly of claim 1 , wherein the vibrating element circumferentially surrounds the optical fiber.

4. 2. The fiber optic subassembly of claim 1, wherein the vibrating element is cylindrical and the optical fiber passes through a central axis of the vibrating element.

5. The fiber optic subassembly of claim 1 , further comprising at least one material disposed between the vibrating element and a portion of the optical fiber at least partially surrounded by the vibrating element.

6. The fiber optic subassembly of claim 5 , wherein the at least one material comprises an adhesive for securing the vibrating element to the optical fiber.

7. The fiber optic subassembly of claim 1 , further comprising a fiber optic connector in which the first end of the optical fiber is located, the vibrating element being located within the fiber optic connector.

8. 10. The fiber optic subassembly of claim 1, wherein the fiber optic connector is of a type selected from the group consisting of LC, SC, FC, ST, SMA, and MTP / MPO connectors.

9. The fiber optic subassembly of claim 1 , further comprising a wire electrically couplable to the vibrating element and the controller for providing electrical energy to the vibrating element.

10. The fiber optic subassembly of claim 9 , wherein the wire extends through one end of the fiber optic connector.

11. The fiber optic subassembly of claim 9 , wherein the wire is releasably connectable to the vibrating element through a sidewall of the fiber optic connector.

12. An optical fiber connector incorporating a speckle reducer therein, an optical fiber connector housing having a ferrule therein; an optical fiber extending into the optical fiber connector housing and having a first end passing through the ferrule; a vibrating element disposed within the housing and attached to a first end of the optical fiber, the vibrating element operable to vibrate at a frequency that reduces optical speckle.

13. The fiber optic connector of claim 12 , wherein the vibration element at least partially surrounds the first end of the optical fiber.

14. The fiber optic connector of claim 13 , wherein the vibrating element comprises a piezoelectric element.

15. 13. The fiber optic connector of claim 12, wherein the vibrating element is located within the fiber optic connector housing but outside the ferrule.

16. The fiber optic connector of claim 12 , wherein the vibrating element is located within the ferrule.

17. 13. The fiber optic connector of claim 12, wherein the vibration element is cylindrical and the optical fiber passes through a central axis of the vibration element.

18. 20. The fiber optic connector of claim 17, further comprising at least one material disposed between the vibration element and a portion of the optical fiber at least partially surrounded by the vibration element.

19. 20. The fiber optic connector of claim 18, wherein the at least one material comprises an adhesive for securing the vibrating element to the optical fiber.

20. the fiber optic connector is of a type selected from the group consisting of LC, SC, FC, ST, SMA, and MTP / MPO connectors; The fiber optic connector of claim 12 , wherein the vibration element circumferentially surrounds the first end of the optical fiber.

21. The fiber optic connector of claim 12 , wherein the vibration element circumferentially surrounds the first end of the optical fiber.

Images