JP2019021909A - Compact optical fiber amplifier - Google Patents

Abstract

To provide an optical fiber coil supporting structure in which an amplifying fiber portion of an optical amplifier is miniaturized.SOLUTION: A fiber-based optical amplifier is assembled in a compact configuration by utilizing a flexible substrate to support an amplifying fiber as flat coils that are "spun" onto the substrate. A supporting structure for the amplifying fiber 20 is configured to define the minimal acceptable bend radius for the fiber, as well as the maximum diameter that fits within the overall dimensions of an amplifier package. Pressure-sensitive adhesive coating is applied to the flexible substrate 30 to hold the fiber in place. By using flexible material with an acceptable insulating quality (such as a polyimide), further compactness in a final assembly is achieved by locating electronic components in a space underneath a fiber enclosure.SELECTED DRAWING: Figure 2

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a U.S. patent application filed on March 16, 2016 that claims the benefit of US Provisional Application No. 62 / 135,641 filed on March 19, 2015. No. 071,296, which is a continuation-in-part application, both of which are incorporated herein by reference.

  The present invention relates to a fiber-based optical amplifier, and more particularly to a compact structure of an amplification fiber portion of an optical amplifier.

  Various types of fiber-based optical amplifiers, such as erbium-doped fiber amplifiers (EDFAs) and distributed Raman amplifiers (DRAs), are ubiquitous elements of optical communication systems and require opto-electrical regeneration when fading optical signal regeneration is required. -The need to perform optical signal conversion can be eliminated.

  In the case of an EDFA, an optical pump laser (typically operating at 980 nm) is coupled to a section of an Er-doped optical fiber and an incident optical signal propagates through the doped fiber along with pump light. The presence of excitation light due to the erbium dopant causes amplification of the optical signal propagating by the transition of the photoexcited erbium ions. A distributed Raman amplifier (DRA) operates by injecting short high-power pulses along a section of the transmission fiber that supports the propagation of optical signals. In the presence of those pulses (either co-propagating or counter-propagating with respect to the optical signal), the photon is excited to a higher energy level and produces stimulated emission upon returning to its ground state.

  The various components forming the optical amplifier module are typically made as fiber coupling elements, and in some cases integrated (or hybridized), for example, an isolator and WDM filter composite, or A complex of an isolator and a GFF filter is formed. Of course, low cost and small modules reduce the overall system cost. For this reason, the trend towards smaller components, further hybridization, and smaller modules has continued for some time. In fact, the industry continues to pressure on smaller form factors and lower costs.

  One way to meet these requirements is to continually reduce the size of the various components and possibly increase the degree of integration. However, this is not easily achieved in an environment where the cost of the amplifier module is also a concern. In fact, the size of these components has been reduced to a level that cannot be easily assembled by low-cost labor (ie, some sizes of these components are on the order of 1 mm × 1 mm × 1 mm).

  Furthermore, even if the size of the optical amplifier module is reduced, such as by increasing the level of integration within the hybrid component, different hybrids need to be coupled together via fiber splices and routing. As a result of the minimum bend radius of the optical fiber, and further thereby requiring a relatively large number of fiber splices and splice protectors, the ability to further hybridize current configurations is a technical limitation, a size limitation, and Reach economic feasibility quickly. “Bend radius” is a decisive factor associated with defining an acceptable amount of signal loss. In particular, the loss that occurs in the optical signal increases as the bend radius of the fiber that propagates the signal decreases. At very small bend radii values, the fiber itself can be physically damaged.

  Thus, in order for fiber-based optical amplifiers to continue to meet cost and size reduction expectations while maintaining performance requirements, a different approach for incorporating an amplification fiber into an optical amplifier module may be necessary.

  The need remaining in the prior art is addressed by the present invention with respect to fiber-based optical amplifiers, and more particularly to the compact structure of the amplifier fiber portion of the amplifier.

  According to one embodiment of the present invention, an exemplary optical amplifier is configured to include an optical module and a fiber module. The optical module is used to accommodate various optical devices that are utilized to process the amplified signal into an acceptable output format, and the fiber module to accommodate the actual fiber that is being amplified. Used for. The fiber module of the present invention comprises a flexible substrate of an insulating material (eg, polyimide) having a pressure sensitive adhesive top coating. The fiber itself is wound in coil form on an insulating material and held in place by an adhesive coating. A stiffer material support tray is used to provide mechanical strength to the flexible material and includes a guide to keep the coil radius below the specified minimum fiber bend radius can do.

  Certain embodiments of the present invention can be configured as rare earth doped optical fiber amplifiers that provide pumping light of a specific wavelength along with a coil of rare earth (eg, erbium) doped optical fiber simultaneously with an input optical signal. Propagate. Another embodiment of the invention takes the form of a distributed Raman amplifier (DRA) in which high power laser pulses are injected into the signal path through which the input optical signal propagates.

  Exemplary embodiments of the present invention include an optical module containing optical elements used to generate an output optical signal from an amplified version, and a fiber module optically coupled to the optical module. It takes the form of an optical fiber amplifier. The fiber module is used to accommodate the section of the amplification fiber for generating gain in the optical signal propagating in the presence of the pumping light, and the fiber module specifically supports the section of the amplification fiber in the form of a flat coil And a support structure disposed below the flexible substrate, the support structure including a termination for mechanically attaching the fiber module to the optical module.

  Selected embodiments of the present invention include a fiber encapsulation that includes a central bobbin (which defines the boundary defining the minimum diameter of the fiber coil) and an outer boundary element (which defines the boundary defining the maximum diameter of the fiber coil). It can take the form of a fiber optic coil support structure with components. A bottom support sheet is attached to the bottom surface of the fiber encapsulating component, and an outer cover is attached to the top surface of the outer boundary element structure and at least a portion of the central bobbin so that the fiber optic coil is interposed between the bottom support sheet and the outer cover. Forms a space for supporting and storing.

  Other and further aspects of the invention will become apparent during the course of the following description and by reference to the accompanying drawings.

Reference is now made to the drawings. Like reference symbols in the various drawings indicate like parts.
FIG. 1 is an isometric view of an exemplary fiber optic amplifier formed in accordance with the present invention. FIG. 2 is an exploded view of the optical fiber amplifier of FIG. FIG. 3 shows a section of an amplifying fiber provided as a flat coil for use in an amplifier fiber module. FIG. 4 shows the coil of the amplification fiber of FIG. 3 when placed on an exemplary fiber module. FIG. 5 is a view of the support structure portion of the fiber module, showing the parameters that control the bend radius experienced by the amplification fiber when the fiber is coiled. FIG. 6 shows another configuration for attaching a fiber module to the optical module of the optical amplifier of the present invention. FIG. 7 shows a compact configuration in which the electronic circuit board can be placed in close proximity to the optical amplifier due to the electrical insulation provided by the fiber module material. FIG. 8 is an exploded view of an alternative embodiment of a fiber module formed in accordance with the present invention. FIG. 9 is an isometric view of the fiber module of FIG. 10 is a cutaway side view of a portion of the fiber module of FIG. FIG. 11 illustrates an exemplary set of three fiber coils that can be housed in the fiber module of FIG. FIG. 12 shows the first fiber coil when placed in the fiber module. FIG. 13 shows the final assembly with a pair of fiber splice coils located on the outer portion of the fiber module away from the first fiber coil. 14 is an exploded view showing the outer cover placed on the module of FIG. FIG. 15 shows the exemplary fiber module of FIG. 9 with the outer cover in place. FIG. 16 illustrates an alternative geometry of the central bobbin that may be used within the fiber support structure according to the present invention. FIG. 17 illustrates an alternative geometry of the outer boundary element that may be used within a fiber support structure according to the present invention.

  FIG. 1 is an isometric view of an exemplary miniature optical amplifier 10 formed in accordance with the present invention. The optical amplifier 10 includes both an optical module 12 and an amplification fiber module 14. The optical module 12 is, for example, in conventional form and is used to generate an amplified output signal that meets defined system requirements (eg, requirements regarding noise floor, isolation, gain profile, insertion loss, etc.). Including various optical elements and hybrids. The fiber module 14 houses a (relatively long) section of amplification fiber that is used to perform the actual amplification function on the incident optical signal. There are many different configurations that can be used to provide the required optical functions within the optical module 12. Several preferred embodiments are described in co-pending US application Ser. No. 15 / 072,520 (filed Mar. 17, 2016). This application is hereby incorporated by reference.

  For clarity, a fiber module 14 that does not have an amplification fiber in place is shown in FIG. When designing a rare earth doped fiber amplifier, it should be understood that a section of doped fiber (eg, erbium doped fiber) is disposed within the fiber module 14. In the case of a distributed Raman amplifier, a conventional single mode fiber section is typically placed in the fiber module 14. An exemplary process for loading the amplification fiber into the module 14 is described below in connection with FIGS.

  FIG. 2 is another view of an exemplary miniature optical amplifier 10, in this case an exploded view, in which the optical module 12 is shown as being separated from the fiber module 14 and the fiber An exemplary set of components that form module 14 is also shown. With reference to both FIG. 1 and FIG. 2, the incident optical signal is introduced into the optical module 12 via the fiber pigtail connection 16. The incident light signal and excitation light (which may be supplied from separate external sources or sources packaged in the optical module 12) are combined in the optical module 12 and via the pigtail fiber connection 17. Are coupled into the fiber module 14. The optical signal and the pumping light propagate through the length portion of the amplification fiber 20 accommodated in the fiber module 14, and the amplified optical signal is finally emitted from the fiber module 14. The amplified signal is then coupled back to the optical module 12 at the fiber optic pigtail 18. Various post-amplification optical functions (gain flattening, power adjustment, etc. defined by specific system requirements) are performed on the signal, after which the signal is fiber optic pigtail as an amplified output signal from the optical amplifier 10. 19 exits the optical module 12.

  Referring to the particular embodiment of FIG. 2, the fiber module 14 includes a relatively circular distal portion 24 and opposite pairs of terminations 26, 28 used to attach the fiber module 14 to the optical module 12. Are shown as including a rigid support member 22 configured to have: A flexible substrate 30 made of a suitable insulating material (eg, a polyimide-based material) is placed in the support member 22 and a pressure sensitive adhesive coating 31 is applied to the flexible substrate 30. The adhesive coating is used to ensure the integrity of attachment of the amplification fiber 20 to the flexible substrate 30. As shown in FIG. 2, an upper cover plate 32 and a lower cover plate 34 are used to house the amplification fiber 20 in the fiber module 14 (as shown in the final configuration of FIG. 1).

  Variations on this particular configuration are possible, including using fewer or more terminations that mechanically attach the fiber module 14 to the optical module 12. In addition, although it is preferred to include an adhesive coating 31 on the flexible material 30, there are types of flexible materials that exhibit adhesion without the need for additional coatings.

  One aspect of the present invention is the specific structure of the amplifying fiber as a flat coil (as compared to bundling common fibers in the prior art). In FIG. 3, the amplification fiber 20 is shown wound to form a “stack” of two flat coils shown as 20-1 and 20-1. FIG. 4 shows the coil of the amplification fiber 20 placed in place within the circular portion 24 of the support structure 22. In the process of manufacturing this part of the miniature optical amplifier, the amplifying fiber is made of flexible material using sufficient pressure to allow the adhesive coating 31 to hold the coiled fiber in place. Spins literally on 30.

  In an EDFA implementation, amplification fiber 20 includes a section of rare earth doped fiber that is approximately 1 meter long (sometimes more than 1 meter may be required). The DRA may utilize a conventional signal mode optical fiber that is several meters long in forming the amplification fiber 20. When attempting to incorporate these relatively long amplification fibers in a relatively small size package, it is necessary to understand the effect of bending loss on the propagating signal. That is, if the fiber is bent into a curve with a very tight bend radius (in this case, forming a coil), the majority of the propagated signal is scattered from the core region and the loss decreases as the fiber radius decreases. Will increase. If the bend radius of the fiber is very small, the fiber itself may be broken. On the other hand, if the bend radius is maintained at a large value (i.e., only relatively “slow” bends are applied to the fiber), the size of the package required to accommodate one or two meters of amplified fiber is Too large for many CFP requirements.

  FIG. 5 is a diagram of an exemplary support structure 22 formed in accordance with those aspects of the present invention to control the curvature introduced into the coil structure of the amplification fiber 20. In particular, the circular portion 24 of the support structure 22 is shown as including a central opening 36, and the diameter d of the opening 36 is selected so that the amplification fiber 20 is not wound with a very tight bend radius. ing. The outer diameter D of the circular portion 24 is selected so that the final dimensions of the optical amplifier 10 are well within the limits imposed by the particular package design. The opening 36 can include a rim 38 to prevent the amplification fiber from entering this central region. Similarly, the outer periphery of the support structure 22 can include a rim 40 to maintain the fiber confined within specified boundaries.

  In one exemplary assembly process, the amplification fiber 20 is on the surface flexible substrate 30 of the support structure 22 using an opening 36 (with a rim 38) and an outer rim 40 as a guide for the process. To be spun on. That is, the amplifying fiber 20 is not bundled as in the prior art, but is wound in a flat form and a small splice protector is inserted in place for connection to the fiber pigtails 17 and 18. Thus, this part of the optical amplifier can be assembled in an automated manner, thereby achieving a highly repeatable process with high yield, low cost and even a small footprint.

  It should be understood that there are a variety of different configurations that can be used to mechanically attach the fiber module 14 to the optical module 12 (optical connections provided through the fiber pigtails 17, 18 as described above). The exemplary configuration shown in FIGS. 1 and 2 is best shown in FIG. 2 with the terminations 26 and 28 of the fiber module 14 and associated mounting elements 42 and 44 formed in the housing 46 of the optical module 12. A simple snap-fit friction fit.

  FIG. 6 is an isometric view showing an alternative mounting configuration, in which the set of screws 48 is used to mount the terminations 26 and 28 of the fiber module 14 to the housing 46 of the optical module 12. . The details of the rims 38 and 40 are also specifically shown from the underside of the optical amplifier 10 in the figure of the small optical amplifier module of the present invention showing the attachment of the fiber module 14 to the optical module 12. In this figure, both end portions 26, 28 are shown, and reinforcing elements 42, 42 'are arranged as shown. Mounting screws 50, 52 are shown as attaching the termination 26 to the optical module 12 along with similar mounting screws 50 ′, 52 ′ used to attach the termination 28.

  As mentioned above, another advantage of the miniature amplifier module configuration of the present invention is that the support structure 22 of the fiber module 14 is formed of an insulating material. For this reason, it is possible to arrange the related electric circuit close to the fiber module 14 without affecting its performance. FIG. 7 is an exemplary diagram of a compact optical amplifier of the present invention showing this aspect. For clarity, the coating layer over the amplification fiber 20 is not shown. In this case, the electronic circuit board 100 is shown as being disposed directly below the miniature optical amplifier 10 and extending under both the optical module 12 and the fiber module 14.

  The fiber module of the present invention for use with a fiber-based optical amplifier can be used to form a doped fiber amplifier (such as an EDFA) or a distributed Raman amplifier, the only modification of the assembly being on the flexible substrate of the module It should be understood that this is the type of fiber being wound. As such, the specific dimensions of the support structure 22 (especially the central opening 32) may vary as a function of the minimum bend radius associated with the specific amplifier design criteria.

  FIG. 8 illustrates another embodiment of a thin structure for encapsulating and supporting one or more coils of optical fiber, particularly suitable for use with an optical amplifier or any other fiber-based device. ing. The fiber support structure 80 is shown in an exploded view in FIG. 8 and in an assembled form in FIG. In this particular embodiment, the fiber support structure 80 includes an encapsulating component formed by an outer boundary element 82 and a bobbin 83, with the bobbin 83 disposed within the inner region of the outer boundary element 82. The dimensions of the bobbin 83 define the minimum bend radius allowed for the coil of fiber disposed within the fiber support structure 80 and wound around the bobbin 83. In some embodiments, the outer boundary element 82 can be formed to include fiber introductions 84, 86. Outer boundary element 82 and bobbin 83 may be formed from any suitable material, including relatively rigid plastic materials.

  According to this embodiment of the invention, a first sheet 90 of plastic material (eg, polyimide, polycarbonate, etc.) is attached around the bottom surface 82B of the outer boundary element 82 and the bottom surface 83B of the bobbin 83B. This first sheet of plastic material is hereinafter defined as the “bottom sheet 90” of the fiber support structure 80. The fiber coil 20 is disposed on the bottom sheet 90, and the diameter of the fiber coil 20 is smaller than the inner diameter of the outer boundary element 82. Thereafter, a second topsheet 92 of plastic material (formed of the same material as the bottomsheet 90 or a similar material) is disposed so as to cover the upper surface 82T of the outer boundary element 82. The sheets 90, 92 can be welded (eg, ultrasonic, thermal or chemical welds) to the outer boundary element 82, or otherwise adhered to the ring.

  In one or more configurations of this embodiment of the invention, the topsheet 92 has a preset width W that allows the topsheet 92 to slightly protrude from the inner surface 82I of the outer boundary element 82. Can be included. FIG. 10 is a cutaway side view of a portion of the configuration of FIG. 9, showing the overhang D of the topsheet 92 and the bottomsheet 90 relative to the inner surface 82I of the outer boundary element 82. FIG. The overhang D is designed to create a covered outer portion of the fiber support structure 80 that is slightly wider than at least two fiber diameters, as shown in FIG. It has spread. This arrangement makes it possible to insert a fiber junction below the overhang, as will be described later. Optionally, features such as slots or notches can be included in the overhang portion of the topsheet 92, thereby allowing the fiber to be removed from the structure in a controlled manner when desired during assembly operations. I can escape.

  When used to support a fiber coil, the diameter of the coil is typically such that it occupies only a portion of the available volume within the fiber support structure 80. In this case, an unoccupied area of the fiber support structure 80 (e.g., an area covered by an overhang of the topsheet 92 as described above) is often required when joining during installation or repair. Can be reserved for additional fiber storage. FIG. 11 shows a set of fibers housed within the fiber support structure 80. In this figure, a fiber coil 20 made in advance as described above, and a first fiber splice portion 20-1 and a second fiber splice portion 20-2 are shown. Coupled to both end portions of the fiber coil 20. FIG. 12 shows the top of the fiber support structure 80 on the bottom sheet 90 prior to placing the fiber splices 20-1, 20-2 in the outer portion of the fiber structure 80 below the overhang formed by the topsheet 92. The fiber coil 20 arrange | positioned is shown. It should be understood that the fiber coils need not be planar, but can include a plurality of planar coils disposed in a stacked configuration around the bobbin 83 of the fiber support structure 80.

  In fact, the lengths of the fiber splices 20-1 and 20-2 extending from the pre-made coil 20 are such that the splices can be securely received at preset positions in the fiber support structure 80. Controlled and its position is selected to minimize stress on the fiber, resulting in high reliability. The length is further specified when the fiber is folded into an increasingly smaller coil until it fits in the spare outer portion of the structure. Thus, the fiber achieves a minimum stress state (i.e., there is no residual stress in the fiber as would be caused by twisting when the length is uncontrolled or poorly controlled). . FIG. 13 shows the fiber splices 20-1 and 20-2 disposed in the fiber support structure 80.

  As shown in FIG. 13, the loops of bonded fibers 20-1, 20-2 naturally expand to fill the maximum diameter of the spare portion of the structure. Thus, the splice is near the maximum available diameter (close to the inner surface 82I of the outer boundary element 82) and is subjected to the lowest possible bending stress in the final deployed state, ensuring high reliability and low insertion loss. To do.

  In addition, after the splices 20-1 and 20-2 are disposed below the top sheet 92 due to the overhang D of the top sheet 92, as described above, the splices 20-1 and 20-2 are fixed along the outer portion of the bottom sheet 90 of the fiber support structure. It is also clear from FIG. 13 that it is possible to arrange the position. Also shown in this figure is a slot 94 used to control the placement of splices 20-1, 20-2 within fiber structure 80.

  In its final form, the fiber support structure 80 covers and protects the stored fiber coil 20 and splices 20-1, 20-2 (and / or any other fiber housed within the support structure 80). An outer cover can further be included. FIG. 14 is an exploded view of an exemplary configuration showing the outer cover 100 for the fiber structure 80. Note that fiber coil 20 and splices 20-1, 20-2 are not shown in this figure. FIG. 15 is a final view showing the outer cover 100 attached in place on the topsheet 92 of the fiber structure 80.

  The particular embodiment shown in FIGS. 8-15 illustrates the use of a circular outer boundary element 82 and a bobbin 83, but the bending (curving) that occurs in the optical fiber around the bobbin is not greater than the minimum allowable bend radius. As long as other geometric shapes can be employed. For example, a slightly rounded triangular bobbin shown as a bobbin 83A in FIG. 16 can be used.

  FIG. 17 is a plan view of an exemplary fiber support structure 80A, where a non-circular outer boundary element 82A (which meets the minimum bend radius constraint of a given fiber according to the invention). Is still configured). In this particular embodiment, the inner circumference 82AI of the outer boundary element 82A is heptagonal, providing sufficient space for the fiber coil 20 and also having additional space for any fiber splice that can be added. It should be noted that the outer shape of the outer boundary element 82A can be any suitable shape. In the specific configuration shown in FIG. 17, the outer boundary is rectangular. In other cases, it may be circular or it may follow a heptagonal design with an inner circumference 82AI. Of course, the heptagonal geometry of the outer boundary element 82A should be considered merely as an example and various other geometries as long as they meet the bend radius requirements for a particular application. The target shape can be used.

  Those skilled in the art will appreciate that changes can be made to the above-described embodiments without departing from the broad concepts of the present invention. Accordingly, the invention is not limited to the specific embodiments disclosed, but is intended to include modifications within the spirit and scope of the concepts of the invention as defined by the appended claims. It will be understood.

Claims (12)

An optical fiber coil support structure comprising:
A fiber encapsulating component including a central bobbin defining a boundary defining a minimum diameter of the fiber coil and an outer boundary element forming a boundary defining a maximum diameter of the fiber coil;
A bottom support sheet attached to the bottom surface of the fiber encapsulated component;
An outer cover, attached to at least a part of the upper surface of the outer boundary element structure and the central bobbin, and a space for supporting and storing the optical fiber coil between the bottom support sheet and the outer cover. An optical fiber coil support structure, comprising: an outer cover that forms The optical fiber coil support structure according to claim 1,
An optical fiber coil support structure, wherein the bottom support sheet is welded to the fiber encapsulating component. The optical fiber coil support structure according to claim 1,
The fiber support structure further comprises an upper support sheet disposed between the outer boundary element and the outer cover, the upper support sheet being attached to an upper surface of the outer boundary element, and the outer boundary element Sizing slightly beyond the width of the bottom support sheet, leaving the inner portion of the bottom support sheet and the central bobbin exposed, and adding an additional length of fiber splice to the overhang width of the top support sheet. An optical fiber coil support structure characterized in that it can be disposed below. The optical fiber coil support structure according to claim 1,
An optical fiber coil support structure, wherein the bottom support sheet and the top support sheet are welded to the outer boundary element. The optical fiber coil support structure according to claim 3,
An optical fiber coil support structure, wherein the upper support sheet is formed to include one or more slots for providing access to a fiber coil within the fiber coil support structure. The optical fiber coil support structure according to claim 1,
An optical fiber coil support structure, wherein the bottom support sheet is made of a plastic material. The optical fiber coil support structure according to claim 6,
The optical fiber coil support structure according to claim 1, wherein the plastic material is selected from the group consisting of polyimide, polycarbonate, and polyvinyl chloride. The optical fiber coil support structure according to claim 3,
An optical fiber coil support structure, wherein the upper support sheet is made of a transparent material. The optical fiber coil support structure according to claim 8,
An optical fiber coil support structure, wherein the upper support sheet is made of a transparent plastic material. The optical fiber coil support structure according to claim 1,
An optical fiber wherein the outer boundary element includes a length of an optical fiber entering the fiber coil support structure and a groove for supporting the length of the optical fiber exiting the fiber coil support structure Coil support structure. The optical fiber coil support structure according to claim 1,
An optical fiber coil support structure, wherein a central bobbin of the fiber encapsulating component has a circular outer periphery. The optical fiber coil support structure according to claim 1,
An optical fiber coil support structure, wherein an outer boundary element of the fiber encapsulating component has a circular inner periphery.

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