FIELD OF THE INVENTION

This invention relates to optical fibers and to systems comprised of fiber optic cables transmitting illumination and/or signals, and, more particularly, to devices and systems enabling distributed in-line measurements of optical power transmitted within fiber optic cables.

BACKGROUND

A wide range of optical detectors has been developed to detect visible and infrared illumination [Dereniak and Boreman, “Infrared Detectors and Systems”, Wiley 1996]. Typical detectors for near infrared (800 to 1700 nm) wavelengths include photodiodes fabricated from InGaAs, GaAs, Ge or SiGe wafers with active areas ranging from 50 microns to 5 mm in diameter or width. In single mode and multi-mode fiber optic applications, these detectors require efficient collection optics to capture and focus a small fraction of light from the optical fiber core onto a photodiode active area.

In numerous fiber optic applications there is a need to tap a small fraction (e.g. from less than 1% to 10%) of the light from within the central optical fiber core having diameters of 5 to 62.5 microns, and direct it out of the fiber and onto an adjacent photodiode. This application requires low optical insertion loss (<0.5 dB) in transmission through the monitor, resulting in moderate sensitivity (1 μW) and relatively low bandwidth (kHz). Low insertion loss enables spatially distributed optical monitoring across large scale fiber optic communication networks, such that multiple passes through cascaded monitors does not compromise digital and/or analog optical signal quality.

Prior art fiber optic tap monitors typically incorporate a semiconductor photodiode integral with a fused tap coupler or a dual fiber collimating lens with a micro-optic beam-splitter which passes a small portion of the guided light onto a photodiode. For example, U.S. Patent Application No. 2009/0016716 by Isida describes a fiber array, tap coupler and photodetector integrated with a planar lightwave circuit. U.S. Patent Application No. 2009/0213363 by Starodubov et al. and U.S. Pat. No. 6,259,842 to Giltner disclose monitors that utilize one or more tap beam splitters and photodiodes. Alternatively, Shapiro et al. in U.S. Patent Application No. 2004/0022494 describe a monitor device in which a small amount of power is tapped off onto a photodiode by selective removal of the optical fiber's cladding. The referenced teachings do not, however, confront the need for compact sensors which are configurable in dense arrays and which introduce only minimal loss.

U.S. Pat. No. 9,535,218 to Zhao discloses an in-line fiber optic tap that eliminates the need for micro-bends and/or micro-reflectors formed on the fiber. An external optical light guide is disclosed, made of transparent material with index of refraction equal to or smaller than the index of refraction of the fiber cladding. The smaller index of refraction of the guiding element relative to the cladding introduces undesirable back-reflections within the cladding and degrades overall link performance.

A transmissive optical detector based on a photo-thermal-electric mechanism has been reported in U.S. Pat. No. 7,289,197, entitled “Transmissive Optical Detector”, to A. S. Kewitsch. These detectors are slightly absorptive, passing the majority of the optical signal through without degradation, and utilize transparent conductive thin films such as indium tin oxide as the sensing element.

For next generation highly complex networks, there is a need for miniature, low loss, low cost measurements of optical power distributed across the network in order to support reliable operation of autonomous large-scale networks.

SUMMARY

The present invention is specified in the claims as well as in the below description. Preferred embodiments are particularly specified in the dependent claims and the description of various embodiments.

In general, without limitation, and according to exemplary embodiments hereof:

According to exemplary embodiments hereof, an optical power monitoring system is disclosed. The system may include low cost, miniature optical power monitoring assemblies, circuits and devices for support of fiber optic switching and interconnect systems, in which the system may controllably extract and detect a small fraction of light from within the core of an optical fiber. Extracted light samples may be confined within small volumes, including small individual photodiodes, and may be directed to photodetectors distributed throughout an organized sensor system for measurement.

In one exemplary embodiment, small fractions of light are leaked from each optical fiber at individual non-adiabatic junctions between abutting optical fiber segments along an optical path. The junctions, typically fusion splices, are configured to produce small (e.g. less than 1.0 dB) losses in the individual signals, such that the leakage signals are confined to their immediate areas and are also individually sensed by small proximate photodetectors (e.g., photodiodes). The photodetectors may convert the sensed light into electrical signals that may be used to determine or otherwise quantify the conditions of the optical signal paths in the fibers that may be monitored.

In some preferred implementations, the lossy interfaces may be encompassed by a small volume of material (e.g., a dome or cap) preferably of high index of refraction and shaped to direct the leaked light fraction onto the adjacent photodetectors. Preferably, the deliberately leaked light fraction is confined within the reflective dome or cap that may span the fiber junction to effectively reflect the leakage signal onto the photodetectors.

In accordance with exemplary embodiments hereof, the refractive indices and the geometries of the elements of the disclosed optical power monitoring system are interdependent but variable. By internally monitoring small fractions of each of the many signals being transmitted (e.g., within a network of fiber optic cables), the operating performance of the fiber optic network as a whole can be monitored. In addition, the In-line optical fiber power monitors may be varied in a number of ways. For example, in one exemplary embodiment hereof, the dome about the emitting portion of the lossy fiber junction may be augmented by an overlying reflective surface. Alternatively, the dome body immediately adjacent the lossy fiber surface may itself be covered by a low index of refraction encapsulant, such as silicone. Other configurations are also contemplated, preferably with the refractive indices of the adjacent elements selected to guide light emanating from the leakage junction in the cladding onto the active area of the photodetector substrate (of the photodiode). In addition, the signal reflecting structure can advantageously be configured with two separate but adjacent reflective dome segments for individually sensing oppositely directed signals in the same cable.

Combinations of such elemental optical fiber light monitors may be densely arrayed in relation to compact electronic processing circuits to provide multi-channel readouts and to monitor overall interconnection performance. For example, sets of monitors (preferably like sets) can be arrayed in multiplexed groups, and the sensors of each group may be scanned serially at a high rate to provide virtual immediate readouts of individual channel failures. In each multi-channel sensor group, for example, a temporal sample of the fractional signal then being extracted from each separate channel in the group may be sequentially multiplexed to an analog to digital converter circuit. The signal may then be processed and communicated to a network management system. This enables the then-current status of a changeable multiplicity of optical channels to be constantly and efficiently monitored in real, or near real, time. In addition, the specific channels monitored at any point in time may also be modified and controlled in real time as necessary.

Below is a list of optical power monitor embodiments. Those will be indicated with a letter “P”.P1. An optical power monitor comprising:at least one optical fiber with a lossy junction along its length and with a lengthwise cladding having a given index of refraction;transparent optical cement with index of refraction equal to or greater than that of the optical fiber cladding, positioned in contact with a selected side surface of said cladding, the optical cement being configured in a particular shape encompassing the lossy junction at the selected side thereof; anda photodiode body proximate the lossy junction on the side opposite the partial dome shape, whereinthe particular shape directs a significant fraction of light from the lossy junction onto said photodiode body.P2. The optical power monitor of embodiment P1, wherein the particular shape comprises a partial dome shape.P3. The optical power monitor of any one of embodiments P1 or P2, the particular shape directs a significant fraction of light from the lossy junction onto said photodiode body through internal reflection.P4. The optical power monitor of any one of embodiments P1 to P3 wherein the transparent optical cement is positioned in contact with the selected side surface of said cladding for a length of at least 0.5 mm.P5. The optical power monitor of any one of embodiments P1 to P4, wherein the optical fiber has a single cladding.P6. The optical power monitor of any one of embodiments P1 to P5, wherein the particular shape is covered with a highly reflective coating.P7. The optical power monitor of embodiment P6, wherein the highly reflective coating is a gold coating or titanium white paint.P8. The optical power monitor of any one of embodiments P1 to P7, wherein the lossy junction is fusion spliced.P9. The optical power monitor of any one of embodiments P1 to P8, wherein the lossy junction is the interface between two optical fibers having different mode field diameters.P10. The optical power monitor of any one of embodiments P1 to P9, wherein the photodiode has an active area with a length is at least 8 times the fiber cladding diameter.

Below is a list of device embodiments. Those will be indicated with a letter “D”.D11. A device to couple light out of an optical fiber cladding and onto a photodiode adjacent the optical fiber, the device comprising:a shaped optical polymer body with an index of refraction higher than that of the optical fiber cladding, the body having a surface within 10 degrees of the normal to the longitudinal optical axis of the optical fiber.D12. The device of embodiment D11, wherein the optical polymer body comprises a partial dome shape.D13. The device of any one of embodiments D11 or D12, wherein the photodiode is closely adjacent the optical fiber.D14. The device of any one of embodiments D11 to D13, further comprising a reflective coating or paint applied to a top surface of the optical polymer body.D15. The device of embodiment D14, further comprising a transparent cover to the shaped optical polymer body having an index of refraction less than or equal to 1.4.D16. A low loss power monitor device for an optical fiber light transmission system comprising:a length of optical fiber transferring an optical signal within a core and cladding geometry, said length comprising serial segments engaged end to end by a lossy junction, wherein a fraction of the signal energy is deflected laterally thereat;a dome segment of higher index of refraction material than the optical fiber core encompassing the length of optical fiber including the lossy coupling on one side thereof and having a convex reflective surface positioned to reflect light from the lossy coupling back toward the second side of the fiber length; anda photodiode body positioned on the second side of the dome segment in contact with the span of fiber including the lossy junction and responsive to the light fraction reflected from the dome segment.D17. The power monitor device of embodiment D16, wherein the segment comprises a dome segment.D18. The power monitor device as set forth in any one of embodiments D16 to D17, wherein the lossy junction is a fusion device and the reflected light fraction loss is in the range of 0.1 dB to 1.0 dB.D19. The power monitor device as set forth in any one of embodiments D16 to D18, wherein the segment has a bottom coextensive with a linear portion of the optical fiber length, and is in planar engagement with the adjacent photodiode body.D20. The power monitor device as set forth in any one of embodiments D16 to D19, wherein the segment has a substantially flat bottom.D21. The power monitor device as set forth in any one of embodiments D16 to D20, wherein the device comprises a highly reflective coating over the convex upper surface of the segment.D22. The power monitor device as set forth in any one of embodiments D16 to D21, wherein the segment comprises UV cure optical cement and has a curvature providing relatively large angles of incidence for light internally reflected toward the photodiode.

Below is a list of system embodiments. Those will be indicated with a letter “S”.S23. A multi-channel optical system for ascertaining an operative status of individual optical circuits in a given multiplicity of different optical fiber circuits arranged in separated control paths, the system comprising:separate individual signal extracting devices in each of said control paths, in separated segments of optical fibers, each fiber having a separate core junction excision laterally emitting less than above 1% of the signal conveyed along the fiber, each signal extracting device including an emission responsive photodiode body adjacent the junction on one side thereof, and photo-reflective means substantially encompassing the remainder of the junction and directing the laterally emitted signal onto the photodiode; andan optical signal multiplexer having at least one output and multiple inputs, each input separately receiving the signal input from a different one of the photodiodes, wherein absence of a signal in a control path indicates transmission failure.S24. The system of embodiment S23, wherein the control paths comprise separated parallel control paths.S25. The system of any one of embodiments S23 or S24, wherein the segments of optical fibers are laterally separated.S26. The system of any one of embodiments S23 to S25, wherein the segments of optical fibers are laterally separated substantially parallel segments.S27. The system of any one of embodiments S23 to S26, wherein the photo-reflective means comprises optical cement being configured in a particular shape.S28. The system of embodiment S27, wherein the particular shape comprises a partial dome shape.S29. The system of embodiments S27 or S28, wherein the particular shape is covered with a highly reflective coating.S30. The system of embodiment S29, wherein the highly reflective coating is a gold coating or titanium white paint.S31. The system of any one of embodiments S23 to S30, wherein the photo-reflective means comprises an optical energy reflector.S32. The system of any one of embodiments S23 to S31, wherein the signal extracting devices comprise junctions between opposed optical fiber segment ends of less than 5 mm in length.S33. The system of any one of embodiments S23 to S32, wherein the body enveloping each lateral junction is less than about 20 mm3in volume.S34. The system of embodiment S33, wherein the body enveloping each lateral junction comprises a higher refractive index on one side of the junction and a signal detecting photodiode on the other side of the junction.S35. The system of embodiment S23, wherein the optical system further comprises a scanning system responsive to the signal multiplexer for and providing de-multiplexed output signals indicating the amplitudes of the individual signals from the different photodiodes.S36. The system of embodiment S23, wherein the multiplexer has a single output.S37. The system of any one of embodiments S23 to S36, wherein the optical system further comprises a scanning system responsive to the signal multiplexer providing de-multiplexed output signals indicating amplitudes of the individual signals from the different photodiodes.S38. A circuit system for continuously monitoring power levels in individual ones of a plurality of optical fiber channels disposed in multi-channel sets, the system comprising:a variable plurality of optical signal sensors, each positioned individually in a different one of the optical fiber channels, each signal sensor comprising a core discontinuity between abutting ends of paired optical fibers, each said discontinuity introducing less than about 1.0 dB of energy leakage loss in the signal being transmitted in the fiber, the signal sensors each also including individual optical energy reflectors spanning the core discontinuity on one lateral side of the fiber, and a signal detector spanning the core discontinuity on the opposite lateral side thereof to sense optical energy leaked therefrom; the multi-channel sets being substantially alike in number;a plurality of different energy leakage signaling circuits, each coupled and responsive to the signals emanating from the separate sensors of a different one of the multi-channel sets and a scanner to serially scan the multiple sensors of the associated set to output the then-existing signal levels in the associated sets, each of the signaling circuits including a multiplexor to multiplex the sensors in the multi-channel sets; anda processor system coupled to control the scanning of the signaling circuits and to process one output from the sensing circuits.S39. The system of embodiment S38, wherein the discontinuities along the fiber lengths each further comprise volumes defined by dome-shaped optical reflectors individually spanning one side of the core discontinuity and wherein said optical reflectors have a higher index of refraction within their dome-shaped volumes than the optical fiber cores and claddings, and the signal detectors each comprise a photodiode body providing an output signal responsive to the loss at the discontinuity.

The above features along with additional details of the invention are described further in the examples herein, which are intended to further illustrate the invention but are not intended to limit its scope in any way.

