MXPA01002560A - Fiber coupler variable optical attenuator - Google Patents

Abstract

A fiber coupled variable optical attenuator includes an optical fiber coupler mounted through a low modulus material bushing (2) into a protective enclosure (4) with one end clamped and another end free (1). The free end (1) of the coupler is deflected by a motorized mechanism. The mechanism includes an electric step motor (10), a shaft (9) providing eccentric motion, and a support/deflection component connected with the coupler in a kinematic chain, which provides lateral deflection of the coupler's free end. The structural and material parameters of the kinematic chain members are established to satisfy conditions of thermal compensation for the enclosure enveloping this chain. The free end of the coupler is equipped with a sleeve having a spherical polished surface positioned in contact with the deflection component. The enclosure (4) is equipped with a thermal-compensating device (14) positioned in series between the enclosure (4) and optical fibers.

Description

VARIABLE OPTICAL ATTENUATOR FIBER COUPLER FIELD OF THE INVENTION The present invention relates to an optical attenuation device and in particular to a thermally compensated fiber optic variable fiber optic attenuator (VOA).

BACKGROUND OF THE INVENTION VOAs of various designs have been widely used in local and long distance telephone networks. Applications of these devices include, for example, light filters, switches, separators, light signal combiners / couplers, light multiplexers, etc. It is expected that fiber-compensated VOAs, thermally compensated, will become vital for the development of high performance telecommunications systems. The ability to design viable and reliable packages that can undergo various thermal and mechanical loads for 20 to 25 years of projected service life is of obvious practical importance. Various optical systems using variable taps coupled with fibers are already known (see for example Miller et al, US Patent 5,146,519 entitled "Rotary Variable Optical Tap", Keck et al, US Patent 5,353,363 entitled Optical Fiber Bendable Coupler / Switch Device ". The variable attenuation of the light signal is achieved by the flexural or rotational (twisting) load of a biconical coupler comprising a pair of optical fibers joined in a narrowed region Typically, the coupler is bent in the narrowed region Structurally, fiber-coupled variable optical attenuation packages are assemblies of multiple materials in which the material interactions, their sizes and configurations, and the thermally or mechanically induced loads are as important as the characteristics of the materials used The bad thermal shrinkage coupling of glass The fused silica used in the biconical coupler and fibers relative to cover materials (metal alloys or plastic packets), including also adhesives, results in thermally induced loads that affect the attenuation of light. To minimize the adverse effect of the thermally induced charges on the molten coupler caused by the poor thermal shrinkage coupling between the molten glass coupler and the loading mechanism and cover, the fiber can be tuned mechanically by alignment techniques. However, the tuning results in a change that depends on the temperature in the light attenuation caused by the combined action of the bad thermal coupling and the mismatches induced by the tuning. The charging devices used in these packages are not thermally compensated completely and produce additional mis-coupling loads when assembled in a protective cover. These packages are also sensitive to mechanical impacts and vibrations, and therefore the reproducibility of the coupling ratio varies with the passage of time. In addition, packages containing loading devices that provide variable bends or rotations are very costly to manufacture. It is desirable to obtain a variable optical attenuation system coupled with total thermal autocompensation fiber that can be easily tuned to wide ranges of deflection and temperature, which is relatively inexpensive, that is made of readily available and simple machine-made materials, and that have a reliable operation. In addition to this, the design of the cover must be adapted not only to mechanically protect fragile glass components, but also to compensate and minimize the possible thermally induced change in optical attenuation. An object of the present invention is to design a variable optical attenuation package coupled with fiber of the aforementioned type, so that it is simple in construction, miniaturized, uses economical materials and manufacturing technique, and that it is reliable during operation in a wide range of applications. margin of environmental conditions.

BRIEF DESCRIPTION OF THE INVENTION In one embodiment of the invention, a variable optical attenuator coupled with fiber includes a biconical fused silica glass coupler comprising a pair of fiber optic waveguides fused together in a narrowed region. The coupler is mounted on a protective cover with one fixed end and another free end. The cover is made of metal alloys or plastic for packaging. To reduce the thermal mismatch loads located in the clamped portion of the coupler, the coupler is mounted through a low module material inlet isolator, which acts as a charge reducing regulator. The free end of the coupler is deflected using a motorized mechanism. The mechanism includes an electric stepper motor, an arrow that produces eccentric motion, and a push rod that is perpendicular to the motor and to the arrow, and is connected in series. The end of the push rod is attached to the coupler through a V-groove in contact with a spherical-shaped sleeve around the free end of the coupler. The kinematic chain formed by the motor, shaft, push rod and coupler mechanically transfers the rotation movement of the motor through the axial movement of the rod towards the lateral deflection of the free end of the coupler. The dimensions and the thermo-mechanical parameters of the chain and cover elements have been established to satisfy the conditions of the almost total thermal compensation within the cover that surrounds this chain. Such thermal compensation can be defined herein as the sufficient dimensional stability of the optical device so that changes in emission due to temperature change are negligible in use. The motorized mechanism is also equipped with a rigid frame that limits the axial deflection of the coupler and protects it from excessive deviations caused by mechanical impacts associated with accidental drops in mishandling or during boarding. The free end of the coupler is equipped with the sleeve having a polished spherical surface in contact with the end of the push rod. The contact sleeve is designed to thermally compensate the axial expansion of the cover caused by the change in temperature and to transfer the vertical (axial) movement of the push rod in the lateral elastic deflection of the coupler. The displacing portion of the coupler is balanced with respect to the geometric center of the spherical surface of the contact sleeve to protect the coupler when excited by mechanical impact. To reduce the thermal loads on the fiber waveguides, the cover is also equipped with thermal compensation devices placed in series between the cover and the optical fibers emerging from the cover. The thermal compensation device is a laminated cylinder of two materials, which includes various thin washers (layers) made of a very low elastic material and high expansion material (for example, RTV silicone) and separated by metal discs and provided with a central opening coinciding with the axis of the fiber waveguide. With the proper selection of the thermoelastic properties of the materials, as well as the dimensions of the washers, the thermal compensation device added to the chain greatly reduces the thermal stress that is inevitably present in the fiber. The function of the metal disc is to limit the deviation of the elastomer under load conditions applied externally to the fiber. A single thick elastomer washer will be deflected under a greater load of two washers of half thickness if the washers are joined with materials with a high modulus of elasticity that limit the lateral deformation of the elastomer. The fiber is fixedly attached to the innermost element of the thermal compensator, which in turn is transported through the laminated layers of the elastomer and metal and finally the external element is fixedly attached to the cover. This arrangement allows a relative movement between the internal and external elements and said movement is caused by the thermal expansion / contraction of the materials so that a fixed dimensional relationship is maintained between the internal element and the optical fused coupler. In another embodiment of the invention, a device for variable attenuation, an optical signal transmitted through the device, includes a cover for the device; a fiber optic coupler having a first end section, a second end section, and a center section between the first and second end sections; a sleeve that encloses at least a portion of the first end section, means for fixedly securing the first end section of the coupler with respect to a surface for mounting the cover; a sleeve that wraps a portion of the second end section of the coupler; an engine connected to the surface for mounting the cover; an arrow mounted in rotating cooperation with the motor; means for supporting the second end section of the coupler, wherein these means are in cooperative engagement at one end with the arrow to deflect the second end section of the coupler; means for limiting a direction of travel of said support means in a given direction; and a thermal compensation component having an opening, arranged in alignment in series with an end section of the coupler, wherein a fiber of the coupler extends through the opening and is fixedly attached to the thermal compensation component near the opening, wherein the deviation of the second end section of the coupler variably experiences a loss of transmission through the coupler. In one aspect of the present embodiment, the means for fixedly securing the first end section of the coupler with respect to a surface for mounting the cover comprises a rigid fastener component cooperatively engaging the cover that wraps the first section of the cover. extreme. In another aspect, the cover wraps a portion of the second end section of the coupler and includes a polished spherical outer surface that cooperatively engages the support means.

In another aspect, the arrow has an axis outside the center of rotation so as to provide an eccentric movement to the rotation. In another aspect, the means for limiting the travel direction of said support means comprises a mechanical stop. In another aspect, the thermal compensation component comprises a laminated structure of two materials that includes a layer of material with a low elastic modulus (10.54-36.15 kg / cm2) of high expansion (150-300x106 / ° C) immediately adjacent to a material metal layer attached thereto, attached to a housing that is additionally attached to the cover. In another aspect, the coupler comprises a fiber output port for monitoring the optical power. In another aspect, the device includes a retention mechanism so that a transmit signal transmitted through the device is substantially constant when the device experiences a loss of electrical power. In another aspect, the device includes means for restricting the uncontrolled movement of the support means.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in greater detail below with reference to the accompanying drawings.

Figure 1 is a top view of one embodiment of the VOA with the cover lid removed. Figure 2 is a cross-sectional view of the embodiment of Figure 1 through section A-A. Figure 3 is a cross-sectional view of one embodiment of the thermal compensation component. Figure 4 is a perspective illustration of the VOA of the embodiment of Figure 1. Figure 5 is a perspective illustration of another embodiment of the VOA of the invention; and Figure 6 is a view with the parts separated from the VOA of Figure 5.

DETAILED DESCRIPTION OF THE MODALITIES PREFERRED OF THE INVENTION With reference to Figures 1, 2 and 4, where the reference numbers are equal represent equal parts of the device, an optical source (not shown) provides a broadband light signal to a biconical coupler at the input of the device. of fused silica glass 101, having a second free end section 1 and a first fixed end section 3 which is mounted on a holding block 2a through an input insulator 2 of low modulus material. This material is preferably an RTV silicone material that provides, among other characteristics, a charge reducing regulator. The coupler is mounted on a protective cover 4. A portion of the second end section 1 of the coupler is surrounded by a sleeve 5a including a polished spherical surface 5. An equilibrium counterweight 6 also wraps a portion of the second adjacent end section to deck 5a. A kinematic chain formed by a motor 10 (preferably a micro stepper motor provided by a holding capacity), an arrow 9, a push rod 8, and the coupler 101 mechanically transfers the rotation movement of the motor through axial movement from the bar to a lateral deviation of the free end of the coupler. The arrow 9 preferably has a circular transverse tension with an axis of longitudinal rotation off center to provide an eccentric movement to the rotation, a spring 20 between a side wall of the cover and the support of the coupler 25 provides a force to move the second end of the coupler in a substantially undifferentiated position when the push rod is not activated. The device is also equipped with the rigid frame 7 which limits the axial deflection of the coupler and protects it from excessive deviations caused by mechanical impacts associated with accidental drops during mishandling or shipping. In addition to this, a block 12 for guiding the push rod 8 has a central guide hole and two side ports (not shown). Two stitches (not shown) at each end of the hole guide the axial movement of the push rod 8 within the block 12. A spring 11 urges the rod 8 into contact with the guide points of the block 12 and also provides anti-rotation control. the push rod. The package is also equipped with thermal compensation devices 13 and 14 placed in series between the cover and the fiber input / output interconnections. The thermal compensator is a laminated cylinder of two materials shown in Figure 3, which includes various thin washers (layers) 16 made of a very low elastic modulus material (for example 10.54 to 35.15 kg / cm2) and very high expansion (150-300 106 / ° C'1), separated by discs of metal 17 adhesively bonded or vulcanized on the interconnection surfaces 20 to a housing 15 adhesively bonded to the fiber and coaxially connected to the housing 18 attached to the protective cover. As is evident from Figure 3, the load compensator is provided with a central opening which coincides with the axis of the fiber waveguide. With the proper selection of the properties and dimensions of the material of the washers based on the thermal and load analysis of this laminate, the load compensation device added to the chain can greatly reduce the stress of poor thermal coupling in the fiber and the stress caused by the location outside the center of the fiber inevitably produced before this addition. Conceptually, the dissimilar glass coupler, with the fibers, metallic or plastic cover, layers of adhesive material, and the previous kinematic mechanism incorporated form a mechanical thermostat-like system, which undergoes thermally induced "residual" loads due to the inevitable mis-coupling of the thermal contractions. In addition to this, the fiber placed with the misaligned end will experience additional bending loads. These thermally induced loads affect the variable attenuation and insertion losses in the optical system. In another embodiment of the invention illustrated with reference to Figures 5 and 6, a fiber VOA coupler includes a cover 4 on which a fused fiber coupler 101 is mounted as described below. The coupler 101 has a first end section 3, a second end section 1 and a central section between the first and second ends. A sleeve 104 surrounds the first end section 3 and is fixedly secured to the cover by a mounting bracket 106. Another sleeve 108 surrounds a portion of the second end section 1 of the coupler, and a sleeve extension 110 of a larger diameter surrounds the end section 1 of the coupler adjacent the sleeve 108. A portion of the sleeve 108 preferably has a polished spherical outer surface 112 that facilitates the movement of the curved bending path of the coupler to displacement. An engine 114 is connected to the surface for mounting the cover, and an arrow 116 is mounted in rotary operation with the engine. The motor is preferably a reversible, electrically driven retaining step motor. The arrow 116 has an axis of rotation that is misaligned with respect to the center as shown in Figure 6 to provide eccentric movement. A structure 118 supports the free end section of the coupler and acts as a force transfer mechanism for the device, similar to the push rod 8 of the first described mode. The structure 118 has an opening 120 that supports the free end of the coupler joining the spherical portion of the sleeve 112. The structure 118 also has a U-shaped opening 122 which clears the cam 116 so that the rotation movement of the cam is The center moves the structure 118 laterally and in this way deflects the free end section of the coupler. A bracket 124 attached to the cover includes a cantilevered section that prevents uncontrolled movement of the structure 118. The structure 118 also has a bolt (not shown) that exits laterally therefrom which is cooperatively coupled to a captive screw (not shown). shown) and acting as a stop for the travel of the structure 118 of the non-bypass direction of the coupler end. The device also includes a thermal compensation component 130 which is identical to the device 13, 14 of FIG. 3. The component 130 couples the slot 132 at one end of the cover. Both embodiments of the invention described above illustrate an approach to a design that uses three thermal compensation systems to achieve attenuation control almost independent of temperature. These are a "general" thermal compensation of the kinematic chain on the cover that surrounds this chain, the "local" thermal compensation by the load transfer contact sleeve device 5, 112; and the thermal load reducer 13, 14; 130, placed in series between the optical fibers and the cover. The desirable attenuation is achieved by using the described compensated thermal load mechanism. The prediction of the tolerable insertion loss change is based on the analysis of the loads in general in the structural elements of the assembly and the local mismatched loads in the joined regions comprising dissimilar materials. This offers the operating leaflet at a very low level of thermal sensitivity in the attenuation packages. Various additional advantages have been obtained by using the attenuation package of the type mentioned. The cover materials used in the present invention are not expensive. The electrical interface uses a simple four-conductor design that allows for increment, decrement and reset. The thermo-mechanical behavior of these materials is well understood and can be predictable. The attenuation packages can be machined with precision.

Claims (22)

NOVELTY OF THE INVENTION CLAIMS

1. - A device for variably attenuating an optical signal transmitted through the device comprising: a cover; a fiber optic coupler having a first end section, a second end section and an intermediate central section between the first and second ends; means for fixedly securing the first end section of the coupler with respect to a surface for mounting the cover, a sleeve that wraps a portion of the second end section of the coupler; a counterweight connected to a portion of the second end of the coupler adjacent the sleeve; an engine connected to the surface for mounting the cover; an arrow mounted in rotating cooperation with the motor; means for supporting the second end section of the coupler; means for providing a restoring force against the support means for counteracting the deflection of the second end section of the coupler; a force transfer element in cooperating coupling at one end with the arrow and an opposite end with the sleeve for exerting a lateral force against the second end section of the coupler; a component connected to the mounting surface having an opening through which the force transfer element passes and which has a size such as to provide a guide path for axial movement of the force transfer member, and a component of thermal compensation having an opening therethrough disposed in an alignment in series with an end section of the coupler, wherein a fiber of the coupler extends through the opening and is fixedly attached to the thermal compensation component near the opening, wherein the deviation of the second outer section of the coupler variably experiences a loss of transmission through the coupler.

2. The device according to claim 1, further characterized in that the means for fixedly securing the first end section of the coupler with respect to a surface for mounting the cover comprises a rigid fastening component and a non-rigid material in interconnection with the fastener and a portion of the first end section of the coupler.

3. The device according to claim 1, further characterized in that the sleeve includes a polished spherical outer surface.

4. The device according to claim 1, further characterized in that the counterweight wraps a portion of the second end section of the coupler.

5. The device according to claim 1, further characterized in that the arrow has an axis of rotation out of center such that provides an eccentric movement to the rotation.

6. - The device according to claim 3, further characterized in that the force transfer element is a push rod having a V-groove at the end in cooperating engagement with the spherical surface of the cover.

7. The device according to claim 6, further characterized in that the component connected to the mounting surface includes a guide point at the opposite axial ends in the opening to guide the axial movement of the push rod through the opening, and further comprises a spring connected to the cover and having a section cooperatively engaging the push rod to drive the push rod in contact with the guide points.

8. The device according to claim 1, further characterized in that the thermal compensation component comprises a sheet structure of two materials that includes a layer of material with a low modulus of elasticity (10.54-35.15 kg / cm2), high expansion (150-300 x 106 / ° C "1) immediately adjacent to a metal layer material bonded thereto, attached to a housing furthermore attached to the cover

9. The device according to claim 1 , further characterized in that it comprises an energy connection for the motor.

10. - The device according to claim 1, further characterized in that the coupler comprises a fiber output port for monitoring the optical power.

11. The device according to claim 1, further characterized in that it comprises a retention mechanism so that a transmission signal transmitted through the device is substantially constant when the device experiences a loss of electrical power.

12. The device according to claim 1, further characterized in that it comprises an optical sensor and associated means for controlling the degree of deviation of the coupler.

13. A device for variably attenuating an optical signal transmitted through the device comprising: a cover; a fiber optic coupler having a first end section, a second end section and an intermediate central section between the first and second ends; a sleeve that wraps the first end section; means for fixedly securing the first end section of the coupler with respect to the surface for mounting the cover; a sleeve that wraps a portion of the second end section of the coupler; an engine connected to the surface for mounting the cover; an arrow mounted in rotating cooperation with the motor; means for supporting the second end section of the coupler, said means being in cooperative engagement at one end with the arrow to deflect the second end section of the coupler; means for limiting a direction of travel of said support means in a given direction; and a thermal compensation component having an opening therethrough arranged in alignment in series with an end section of the coupler; wherein a coupler fiber extends through the opening and is fixedly attached to the thermal compensation component near the opening, wherein the deviation of the second end section of the coupler variably experiences a loss of transmission to through the coupler.

14. The device according to claim 13, further characterized in that the means for fixedly securing the first end section of the coupler with respect to a surface for mounting the cover comprises a rigid fastening component that cooperatively engages the sleeve that wraps the first end section.

15. The device according to claim 13, further characterized in that the sleeve that surrounds a portion of the second end section of the coupler includes a polished spherical outer surface cooperatively engaging the support means.

16. The device according to claim 15, further characterized in that it comprises another sleeve that wraps a portion of the second end section of the coupler adjacent the sleeve that wraps a second end portion.

17. - The device according to claim 13, further characterized in that the arrow has an axis of rotation out of center so as to provide eccentric movement to the rotation.

18. The device according to claim 13, further characterized in that the means for limiting the direction of travel of said support means comprise a mechanical stop.

19. The device according to claim 13, further characterized in that the thermal compensation component comprises a sheet structure of two materials that includes a layer of material with a low elastic modulus (10.54-35.15 kg / cm2), high expansion (150-300 x 106 / ° C "1) immediately adjacent to a metal layer material bonded thereto, attached to a housing furthermore attached to the cover

20. The device according to claim 13, further characterized in that the coupler comprises a fiber output port for monitoring the optical power

21. The device according to claim 13, further characterized in that it comprises a retention mechanism such that a broadcast signal transmitted through the device. it is substantially constant when the device experiences a loss of electrical power.

22. - The device according to claim 13, further characterized in that it comprises means for restricting the uncontrolled movement of the support means.