EP4652487A1 - Optical despecklers, optical systems and devices incorporating the same, and methods for despeckling optical signals - Google Patents

Abstract

An optical fiber subassembly for reducing optical speckle arising in an optical system includes an optical fiber, a vibration element such asa piezoelectric element and a controller. The optical fiber has a first end portion adapted to receive light from a light source associated with the optical system and a second end portion for communicating light from the light source to a surface on which a speckle pattern may arise. The optical fiber extends through the vibration element such that the vibration element at least partially surrounds a portion of the optical fiber intermediate to the first and second end portions. The controller is operably couplable to the vibration element for causing the vibration element to vibrate at a frequency faster than a threshold frequency sufficient to reduce speckle that arises on the surface.

Description

Docket No. MX-2020-PAT-0270-WO-PCT OPTICAL DESPECKLERS, OPTICAL SYSTEMS AND DEVICES INCORPORATING THE SAME, AND METHODS FOR DESPECKLING OPTICAL SIGNALS RELATED APPLICATION [0001] This patent application claims the benefit of United States Provisional Patent Application No.63/440,109, filed January 20, 2023, which is incorporated by reference in its entirety. BACKGROUND [0002] The present disclosure relates to the reduction of optical speckling and, more particularly, to optical systems and optical devices where an optical signal propagating along an optical fiber is subject to optical speckling. [0003] Speckle may result from the self-interference of light on a surface such as a screen or target which causes variations in intensity that can be seen by the observer or instrument and may be an undesirable side effect of using narrow bandwidth sources such as lasers. Speckle may also appear when light is transmitted through a material since the surface structures of the material can randomly change the phase and polarization of the light. The resulting speckle pattern may create noticeable undesirable intensity variations across the surface that often manifest as a sparkly or granular structure. [0004] For example, and not by way of limitation, laser-based projection displays often suffer from speckling, Such speckling can reduce image sharpness and be distracting to a viewer. Several approaches for reducing speckle contrast have been proposed based on spatial and temporal decorrelation of speckle patterns. For example, US Patent Appl. No. 2018/0252863 shows a system with a light source that is configured to output illuminating light and a display system that receives the illuminating light. The display system could be a projector for displaying movies or images. An optical fiber is configured to direct the illuminating light from the light source to the display system and a vibration device is attached to the optical fiber. The vibration device is in communication with a controller that senses speckle and, in response, activates the vibration device. The vibration device is operable to vibrate at a frequency greater Docket No. MX-2020-PAT-0270-WO-PCT than a threshold frequency to reduce speckle. The index profile of the optical fiber may be designed to despeckle the output illumination light without losing too much light. [0005] Similarly, Japanese Patent Publ. No.63-082336 (Optical Fiber Exciter) shows a system that arranges a pressing member on both sides of an optical fiber to apply pressure to the optical fiber with a piezo-electric element that is driven by a voltage from a control section. The control section supplies a periodic wave to the piezo-electric element that enables the removal of effect of a polarized light in a single mode fiber and removal of speckle effect from the multi- mode fiber thereby achieving stable and accurate photometry. SUMMARY [0006] In one aspect, an optical fiber subassembly for reducing optical speckle arising in an optical system is presented herein. The optical fiber subassembly includes an optical fiber, a vibration element and a controller. The optical fiber has a first end portion adapted to receive light from a light source associated with the optical system and a second end portion for communicating light from the light source to a surface on which a speckle pattern may arise. The optical fiber extends through the vibration element such that the vibration element at least partially surrounds a portion of the optical fiber intermediate to the first and second end portions. The controller is operably couplable to the vibration element for causing the vibration element to vibrate at a frequency faster than a threshold frequency sufficient to reduce speckle that arises on the surface. [0007] In one implementation, the vibration element is a piezoelectric element. [0008] In another implementation, the vibration element circumferentially surrounds the optical fiber. [0009] In another implementation, the vibration element is cylindrical in shape and the optical fiber traverses a central axis of the vibration element. [0010] In another implementation, the optical fiber subassembly further includes at least one material disposed between the vibration element and the portion of the optical fiber that is at least partially surrounded by the vibration element. [0011] In another implementation, the material includes an adhesive for securing the vibration element to the optical fiber. Docket No. MX-2020-PAT-0270-WO-PCT [0012] In another implementation, the optical fiber subassembly further includes an optical fiber connector in which the first end portion of the optical fiber is located, the vibration element being located within the optical fiber connector. [0013] In another implementation, the optical fiber 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 optical fiber subassembly further includes wires that are electrically couplable to the vibration element and the controller for supplying electrical energy to the vibration element. [0015] In another implementation, the wires extend through one end of the optical fiber connector. [0016] In another implementation, the wires are releasably connectable to the vibration element through a sidewall of the optical fiber connector. [0017] In another aspect, an optical fiber connector has a despeckler integrated therein, The optical fiber connector includes an optical fiber connector housing, an optical fiber having a ferrule therein, and a vibration element. The optical fiber has a first end portion extending into the optical fiber connector housing and through the ferrule. The vibration element is disposed within the housing and attached to the first end portion of the optical fiber, the vibration element being operable to vibrate at a frequency that reduces optical speckle. [0018] This summary is provided to introduce a selection of 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 DESCRIPTION OF THE DRAWINGS [0019] FIG.1 is a schematic diagram showing one example of a light source that provides light via an optical fiber to an optical system that may give rise to speckle. [0020] FIG.2 shows one example of the optical fiber and the vibration element shown in FIG. 1, where the vibration element circumferentially surrounds a portion of the optical fiber. [0021] FIG.3 is a cross-sectional view of one example of an optical fiber connector. [0022] FIG.4 is an isometric view of the assembled optical fiber connector shown in FIG.3. Docket No. MX-2020-PAT-0270-WO-PCT [0023] FIG.5 is a simplified schematic illustration of one non-limiting example of an optical arrangement in which the optical despeckler described herein may be employed. DETAILED DESCRIPTION [0024] The present disclosure recognizes the problem of speckling in existing optical systems and discloses an optical despeckler that is easy to setup, small in size, and power efficient. [0025] FIG.1 is a schematic diagram showing one example of a light source 110 that provides light via an optical fiber 120 to an optical system 112 such as a projector, display device or, more generally, any other arrangement that may give rise to speckle. The optical system 112 may be a system that is 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 a variety of types of laser- based communication systems, probes, sensors, monitors, illuminators and the like. While light source 110 may often be a laser light source, in general the light source may be any narrow-band light source that can give rise to speckle. [0026] The optical fiber 120 may be a coated, uncoated, jacketed, or unjacketed, single-mode or multi-mode optical fiber, a glass-fiber, a plastic-fiber, step-index fibers, graded-index fibers 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. [0027] A vibration element 140 circumferentially surrounds a portion of the optical fiber 120. In some embodiments the vibration element 140 may only partially surround a portion of the optical fiber 120. The vibration element 140 may be any suitable element that can impart vibrational energy to the optical fiber 120 at a frequency and amplitude that is able to reduce or eliminate the speckle that arises from the optical system 112. In some embodiments, a plurality of 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, without limitation, crystalline, ceramic and lead free piezoceramics, III-V and II-VI semiconductors, and polymers. In other embodiments suitable vibration elements may be, without limitation, devices such as speakers, exciters, vibrators, motors, transducers, vibrating motors, shakers, buzzers. Also shown in FIG.1 is a controller 125 that supplies electrical power to the vibration element 140 through a wired connection. Docket No. MX-2020-PAT-0270-WO-PCT [0028] FIG.2 shows one particular example of the optical fiber 120 and the 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 that is positioned along a portion of an optical fiber 120, with the optical fiber extending through the central axis of the cylindrical piezoelectric element. The piezoelectric element is designed to constrict 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 help transfer mechanical energy from the piezoelectric element to the optical fiber in a uniform manner. The filler 150 also provides electrical isolation 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 ends of the optical fiber. [0029] While FIG.2 shows the vibration element 140 being cylindrical in shape, 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 in a circumferentially asymmetric manner as well as a symmetric manner. The vibration element 140 may remain exposed or may be covered by a protective covering that is placed over only the vibration device 140 or along the entire optical fiber 120. [0030] As noted above, the vibration element may be provided 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 an optical fiber that is located within an optical fiber connector. An optical fiber connector is a component that is used to terminate the end of an optical fiber cable and generally enables quicker connection and disconnection than fiber splicing. Optical fiber connectors can be used in a wide variety of different applications including, for example, to join segments of optical fibers into longer lengths, to connect optical fibers to active devices such as transceivers, detectors and repeaters, or to connect optical fibers to passive devices such as switches or attenuators. A central function of an optical fiber connector is to maintain or position two optical fiber ends such that the core of one optical fiber is axially aligned with the core of the other optical fiber. Another function of the optical fiber connector is to align the light emitted from a light source with an optical fiber. Consequently, the light from one fiber can be coupled to the other fiber or transferred between the fibers as efficiently as possible. Yet another function of the optical fiber connector is to Docket No. MX-2020-PAT-0270-WO-PCT provide mechanical stability and protection for the optical junction in its working environment. Generally, stability and junction protection are key functions of connector design (e.g., minimization of the different thermal expansion and mechanical movement effects). [0031] Optical fiber connectors can be divided into different types based on a number of different classification methods. For instance, such connectors can be divided according to the pin end surface of the connector (they can be divided into PC, UPC, and APC) or according to the type of transmission media (single mode and multimode fiber optic connectors). Common standard types of optical fiber connectors include, by way of illustration, LC, SC, FC, ST, SMA and MTP/MPO connectors. [0032] In general, most optical fiber connectors include a number of components in common, 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 of 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 is the mechanism that allows the connector to be easily attached and detached. Common coupling mechanisms include threaded connectors, push-pull connectors, and bayonet-style connectors. [0033] In accordance with the subject matter described herein, a vibration element such as a piezoelectric element may surround a portion of an optical fiber that is located within any type of optical fiber connector, including connectors that conform to one or more established standards such as those mentioned above, or connectors that are proprietary in nature. In this way the optical fiber connector effectively serves as an optical despeckler. In non-limiting particular examples, the vibration element according to the present disclosure may be integrated into 1) High Power Assemblies that use High Power SMA and High Power Industrial FD-80 connectors to provide a fiber optic link between the laser source and the 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) Bundled Assemblies for a wide variety of photonics systems for performing optical sensing and laser power delivery for industrial, medical, military, and research applications. Docket No. MX-2020-PAT-0270-WO-PCT [0034] FIG.3 is a cross-sectional view of one example of an optical fiber connector 200 and FIG.4 is an isometric view of the same assembled optical fiber connector 200. The connector 200 includes a connector body 210, connector coupling mechanism 220 and ferrule 230. Also shown in FIG.3 is optical fiber 240 extending into the connector body 210. Piezoelectric element 250 (or other vibration element) is located within the connector body 210 and circumferentially surrounds the optical fiber 240. The piezoelectric element 250 may be provided at any suitable location within the connector body 210 that allows it to circumferentially surround the optical fiber 240. In general, the piezoelectric element 250 will be longitudinally aligned with the optical fiber 240 and the connector body 210 and positioned so that the optical fiber 240 can pass completely through it. 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 help transfer mechanical energy from the piezoelectric element 250 to the optical fiber in a uniform manner. The dimensions of the piezoelectric element 250 may be selected so that it is able to impart sufficient vibrational energy to the optical fiber 240 while being sufficiently small to be accommodated within the connector body 210. By way of example, in some embodiments the piezoelectric element 250 may have an overall length of between 4 and 50 mm, an inner diameter of between 0.2 and 40mm and an outer diameter of 0.5 to 50 mm. [0035] In a non-limiting embodiment, a controller (e.g., controller 125 shown in FIG.1) or other suitable device is used for applying electrical voltage to the piezoelectric element. The electrical voltage is used to control the aforementioned constriction of the piezoelectric element and the application of pressure on the optical fiber. The pressure on the optical fiber may be cycled periodically or applied on a random, pseudo-random, or other complex basis to alter the polarization state of an optical signal propagating along the optical fiber. For example, the periodic form 50/60 Hz of a commercial power supply in the form of a SIN wave may be used. For a composite/complex cycle form, an electrical signal may be generated by overlapping different waveforms and frequencies with a signal generator or the like. In other embodiments the voltage that is applied to the piezoelectric element may be in the range of 300 Hz - 70 KHz. [0036] The electrical 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 the distal end of the connector body 210 remote from the Docket No. MX-2020-PAT-0270-WO-PCT connector coupling mechanism 220. In other embodiments the wires may exit from the proximal end of the connector coupling mechanism 220. In yet other embodiments the wires may exit from the side of the connector body 210 using, for example, a removable plug to thereby provide a releasable connection. [0037] In some embodiments, the controller or an equivalent device is operable to sense speckle in the optical fiber, and in response, apply a suitable control signal to the piezoelectric element to reduce speckling. For example, in the illustrative system shown in FIG.1 the controller 125 may be used to sense speckle arising in the optical system 112. The vibration element 140 may be in communication with the controller 125 that senses speckle arising in optical system 112 and in response, activates the vibration element 140. In another embodiment, the vibration element 140 may be in an always-on state. [0038] FIG.5 is a simplified schematic illustration of one non-limiting example of optical arrangement in which the optical despeckler described herein may be employed. The optical system in this example is fluorescence microscope for performing fluorescence microscopy. As shown, the arrangement includes a laser source 310 in which the optical despeckler described herein is employed. The optical despeckler may employ an optical fiber assembly 350 having a vibration element that circumferentially surrounds all or part of the optical fiber 320 in which light is launched by the laser source 310. The vibration element may be located along any suitable portion of the optical fiber 320, including a portion that is located within the optical fiber connector that connects to the laser source 310. The light from the optical fiber 320 is directed to a beam splitter 325 that directs the light to the fluorescence microscope 330 in order to excite fluorescent molecules. The resulting fluorescent light is directed back to the beam splitter 325 and is directed to a detector 340 after undergoing any necessary filtering by filter 345. The detector 340 may be associated with a display or camera. Optical speckle in the resulting image is reduced by use of the optical despeckler described herein. [0039] It should be noted that applications of the optical despeckler disclosed herein are not limited to the above-discussed applications. It should also 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

Docket No. MX-2020-PAT-0270-WO-PCT What is claimed is: 1. An optical fiber subassembly for reducing optical speckle arising in an optical system, comprising: an optical fiber having a first end portion adapted to receive light from a light source associated with the optical system and a second end portion for communicating light from the light source to a surface on which a speckle pattern may arise; a vibration element through which the optical fiber extends such that the vibration element at least partially surrounds a portion of the optical fiber intermediate to the first and second end portions; and a controller operably couplable to the vibration element for causing the vibration element to vibrate at a frequency faster than a threshold frequency sufficient to reduce speckle that arises on the surface. 2. The optical fiber subassembly of claim 1 wherein the vibration element is a piezoelectric element. 3. The optical fiber subassembly of claim 1 wherein the vibration element circumferentially surrounds the optical fiber. 4. The optical fiber subassembly of claim 1 wherein the vibration element is cylindrical in shape and the optical fiber traverses a central axis of the vibration element. 5. The optical fiber subassembly of claim 1 further comprising at least one material disposed between the vibration element and the portion of the optical fiber that is at least partially surrounded by the vibration element. 6. The optical fiber subassembly of claim 5 wherein the at least one material includes an adhesive for securing the vibration element to the optical fiber. Docket No. MX-2020-PAT-0270-WO-PCT 7. The optical fiber subassembly of claim 1 further comprising an optical fiber connector in which the first end portion of the optical fiber is located, the vibration element being located within the optical fiber connector. 8. The optical fiber subassembly of claim 1 wherein the optical fiber connector is of a type selected from the group consisting of LC, SC, FC, ST, SMA and MTP/MPO connectors. 9. The optical fiber subassembly of claim 1 further comprising wires that are electrically couplable to the vibration element and the controller for supplying electrical energy to the vibration element. 10. The optical fiber subassembly of claim 9 wherein the wires extend through one end of the optical fiber connector. 11. The optical fiber subassembly of claim 9 wherein the wires are releasably connectable to the vibration element through a sidewall of the optical fiber connector. 12. An optical fiber connector having a despeckler integrated therein, comprising: an optical fiber connector housing having a ferrule therein; an optical fiber having a first end portion extending into the optical fiber connector housing and through the ferrule; and a vibration element disposed within the housing and attached to the first end portion of the optical fiber, the vibration element being operable to vibrate at a frequency that reduces optical speckle. 13. The optical fiber connector of claim 12 wherein the vibration element at least partially surrounds the first end portion of the optical fiber. 14. The optical fiber connector of claim 13 wherein the vibration element includes a piezoelectric element. Docket No. MX-2020-PAT-0270-WO-PCT 15. The optical fiber connector of claim 12 wherein the vibration element is located within the optical fiber connector housing but outside the ferrule. 16. The optical fiber connector of claim 12 wherein the vibration element is located within the ferrule. 17. The optical fiber connector of claim 12 wherein the vibration element is cylindrical in shape and the optical fiber traverses a central axis of the vibration element. 18. The optical fiber connector of claim 17 further comprising at least one material disposed between the vibration element and the portion of the optical fiber that is at least partially surrounded by the vibration element. 19. The optical fiber connector of claim 18 wherein the at least one material includes an adhesive for securing the vibration element to the optical fiber. 20. The optical fiber connector of claim 12 wherein the optical fiber connector is of a type selected from the group consisting of LC, SC, FC, ST, SMA and MTP/MPO connectors. wherein the vibration element circumferentially surrounds the first end portion of the optical fiber. 21. The optical fiber connector of claim 12 wherein the vibration element circumferentially surrounds the first end portion of the optical fiber.