JPH0821930A - Light beam interface device for hybrid circuit - Google Patents

Abstract

PURPOSE: To increase a bake-out temperature and to increase device production by providing a cover body with a limited area featured by transparency to the light energy of a predetermined band with on an electrooptic element. CONSTITUTION: A window 16 is provided on the upper cover body 18 of a casing 14, the entrance of the light energy is allowed and the energy is connected to an optical signal receiver provided inside a hybrid package, a photodetector 12 for instance. The window 16 is constituted of a material selected to be transparent to the light energy of a specified band width and is matched on one line with the photodetector 12. The end part 36 of a fiber 10 is cut so as to form a 45-dergree surface 36 for forming a flat elliptic plane in the case of being viewed from the front. The inclined flat end part 36 of the fiber 10 is turned to a reflection surface for changing the direction of the light energy and thus, the light energy propagated inside a clad 34 is made incident to the upper photodetection area of the photodetector 12 in a perpendicular downward direction 38 through the window 16.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a device for coupling light energy from a fiber into a hybrid circuit of the type containing at least one electrooptic element. In particular, the invention relates to an optical interface arrangement that facilitates assembly and testing of such a hybrid package prior to mounting the pigtails of the fiber optic conductor.

[0002]

Optical networks may include hybrids. A hybrid integrated circuit is composed of two or more integrated circuit types or a combination of one integrated circuit type and separate elements. Optoelectronic hybrid circuits may include photodetectors that convert an optical signal carried in a fiber optic network into a corresponding electrical signal. Photodetector devices consist of various components including silicon, indium, gallium arsenide, gallium arsenide with cadmium sulfide. In many precision applications, hybrid circuit elements need to be enclosed or encapsulated. Fabrication of the circuit generally involves a bake-out step of cleaning the sealed environment within the container by removing contaminants such as hydrocarbons, epoxy resin and solder flux prior to sealing.

In conventional optical networks including electro-optical hybrids, fiber optic conductors are connected to the hybrid package through ferrules on the sides of the hybrid container. Fiber optic connections to the hybrid are made prior to device testing and bakeout. Bakeout specifications can be demanding, especially for military applications. Removal of significant amounts of contaminants can significantly lengthen the manufacturing process.

Optical fibers are typically coated with a jacket of acrylic plastic material with limited temperature tolerances. In general, the material should not be exposed to temperatures above 105 ° C as the most common fiber jacket. This significantly affects (decreases the temperature) the bakeout temperature in conventional arrangements where the fiber is affixed to the hybrid container. As a result, the time required to clean the environment is affected (longer). Nowadays, bakeout of hybrids with fiber pigtails typically requires an 8 hour process. In addition, circuit testing is prevented in advance until the bakeout is complete, further limiting the production of the device.

[0005]

SUMMARY OF THE INVENTION The present invention addresses the aforementioned problems of the prior art by placing light energy propagating in an optical fiber covered with a fiber jacket in a container having a substantially flat lid. Overcoming by providing a device for coupling to an electro-optic device that has been created. In the present invention, the lid includes a limited area overlying the electro-optic element and characterized by transparency to light energy of a predetermined bandwidth. In connection with the end of the fiber, means are provided for directing light energy of a predetermined bandwidth in a direction substantially perpendicular to the direction of propagation of the light energy in the fiber. Finally,
Means are provided for placing the fiber in contact with the lid so that a predetermined bandwidth of light energy is directed to the electro-optic element through the confined area.

[0006]

The foregoing and other features of the present invention will become more apparent from the detailed description below. The detailed description is accompanied by a set of drawings. The numbers in the drawings correspond to the numbers in the description and show the features of the present invention. Like numbers refer to like features throughout the description and drawings. Referring to the drawings, FIG. 1 is a side sectional view of the present invention. As shown,
The fiber 10 transmits light energy to a hybrid circuit that includes a photodetector 12 disposed within a casing 14. As previously mentioned, in the prior art it was common to have ferrules on the sides of the casing 14 so that the fiber 10 could be accessed internally for delivering light energy to the hybrid circuit. The required ferrules make the design of the hybrid package rather cumbersome and eventually increase the bakeout time and significantly reduce the production of the device.

In the present invention, the problems associated with the above arrangement are avoided by an optical interface arrangement that allows bakeout to occur before the optical fiber is connected to the casing 14. In the prior art, the fiber 10 was necessarily attached to the hybrid container via the ferrule on bakeout to ensure a seal of the casing 14 containing the sidewall ferrule for internal access as described above. In the present invention, the fiber 10 is never inserted into the hybrid casing 14. Rather, a window 16 is provided in the upper lid 18 of the casing 14 to allow entry of light energy and couple it to an optical signal receiver, such as the photodetector 12, in the hybrid package. This window 16 may be flat or may consist of a focusing lens as shown. The design choice is Photo Detector 12
Is determined by factors including the size of the photoactive surface, the intensity of light energy propagating in the fiber, and the like. In some applications, the window 16 may be constructed of a material selected to be transparent to a particular bandwidth of light energy, thereby providing a filtering function.

The fiber 10 is never inserted into the casing 14 as described above and thus does not break the casing 14. Rather, the cradle 20 has the casing 14
It is provided on top of the upper lid 18 for positioning and fitting the fiber 10 to the outer surface of the. This cradle 20
2A and 2B is more clearly shown, it is preferably a molded structure that includes a central recessed region 22 for receiving the end of the optical fiber 10 and forms a groove-like shape. If the cradle 20 and lid 18 are formed as one unitary member, they should preferably be constructed of a suitable ceramic or corrosion resistant metal. It is, for example,
It can be made of a metal marketed under the trademark KOVAR. The ceramic base 24 to which the photodetector 12 is soldered or bonded with a suitable epoxy resin is
It should have a coefficient of thermal expansion that closely matches the coefficient of thermal expansion of the casing 14. Structural epoxy can be used to bond the fiber 10 to the cradle 20 and the base 24 to the bottom 30 of the hybrid casing 14 with the adhesive layers 26 and 28 shown, respectively.

The fiber 10 is a hybrid casing 1.
Since there is no direct access to 4, the means for directing light energy from the fiber 10 to the photodetector 12 must be provided. Therefore, the window 16 described above is aligned with the photodetector 12. The acrylic plastic jacket 32 of the fiber 10 is a fiber cladding or central core 34 that carries most of the light energy.
The area near the end is stripped to expose the. The ends of the fibers 34 are cut to form a 45 degree surface 36 that forms a flat elliptical plane when viewed from the front. The cut end of the fiber is coated with a reflective coating, such as silver, or a dielectric coating designed to produce a 100 percent reflection coefficient at the cut end 36 of the fiber. You may coat.

The sloping flat end 36 of the fiber 36 provides a reflective surface that redirects the light energy so that the light energy propagated (longitudinally) within the cladding 34 is directed downward through the window 16 at a right angle. The light is incident on the upper photodetection region of the photodetector 12 in the direction 38. The flat end 36 is silver plated or comprises a dichroic mirror and is capable of reflecting incident light energy of a predetermined bandwidth. The type of reflective surface of the flat end 36, as well as the choice of metal forming the window 16, will depend on the intended application. Said selections, which depend in part on requirements such as critical bandwidth, signal noise tolerance, and the evaluation of the selections that can be made, are well known in the art.

The end of fiber 10 is encapsulated in a UV curable, index-matched epoxy resin capsule 40. The resin 40 acts to reduce the strain that would otherwise be caused by the cylindrical shape of the cladding 34. Therefore, the optical signal incident on the upper detection surface of the photodetector 12 is exactly the same as the optical signal propagating in the fiber 10.

Of course, it is especially important that the photodetector 12, the flat end 36 and the window 16 are exactly in line. After bakeout of the hybrid circuit, a two-step process can be used to position the fiber 10. A coarse adjustment can be made by first positioning the surface 36 on the cradle 20 and rotating the fiber 10 until the maximum response of the photodetector 12 is observed. The position of movement can then be determined by sliding the fiber 10 along the cradle 20 until the photodetector 12 indicates a reduction in optical signal. The other axes can be controlled by some movement and rotation using the same technique. Lens 16
Is about 25% of the mold area to reduce the saturation and the effect of scratches.
Designed to focus over a percentage. The cut end of the fiber is held in place after alignment by the optical epoxy encapsulation 40 of the fiber end. The refractive index of the epoxy matches that of the fiber and lens. Epoxy, which is optically transparent in the frequency band of interest, eliminates or depletes the light loss and reflection from the optical window that occurs at the curved outer surface of the fiber.

FIG. 3 shows another embodiment of some of the present inventions.
It redirects the light and directs it through the fiber 10 to the optoelectronic network within the casing. As shown in the previous figure, the redirected light energy passes through a window 16 provided in an upper surface (ie, lid) 18 of the casing 14. This alternative device consists of a prism element 42 which is secured to the cladding (after the acrylic jacket has been stripped from the end 32) by a suitable optical epoxy. The prism element 42 includes a reflective flat surface 44 inclined with respect to the optical axis of the fiber 10.
including. The surface 44 functionally corresponds to the flat end 36 of the cladding of the embodiment shown in FIGS. 1, 2A and 2B.
As before, surface 44 may be wholly or selectively reflective in nature. Further, the prism element 42 can be designed to have the dimensions described above and to eliminate the encapsulation of the resin 40 required in the embodiment of the previous figure. In the above case, the element 42
A thin layer of optical epoxy may be provided on the bottom of the window 16 to secure it to the top surface of the window 16 (not shown in FIG. 3), and an optical layer between the element and the end of the fiber 45. It is also possible to provide a thin layer of selective epoxy.

Accordingly, it can be seen that the present invention provides an improved optical interface for hybrid circuits. By using the teachings of the present invention, which features a non-intrusive attachment of a fiber optic pigtail to a hybrid casing, the bakeout temperature can be increased, resulting in increased device production. Although the present invention has been described with respect to a presently preferred embodiment, it is not so limited. Rather, the invention is limited only insofar as defined in the appended claims and includes within its scope all equivalents thereof.

[Brief description of drawings]

FIG. 1 is a side sectional view of an arrangement according to the invention for interfacing a hybrid circuit with an optical fiber.

FIG. 2A is a plan view of a fiber accommodating portion provided on an upper portion of a lid of a hybrid container according to the present invention.

FIG. 2B is a side view of the fiber container provided on the top of the lid of the hybrid container according to the present invention.

FIG. 3 is a side view of another embodiment of the reflector used in the present invention.

[Explanation of symbols]

 Fiber 10 Cradle 20 Casing bottom 30 Resin 40

Claims (11)

[Claims] 1. An apparatus for coupling light energy propagating in an optical fiber covered with a fiber jacket to an electrooptic element disposed in a case having a substantially flat lid, comprising: a). The lid includes a confined region above the element and characterized by a transparency to the light energy of a predetermined bandwidth, b) a predetermined band in relation to the end of the fiber. Means for directing the light energy of width in a direction substantially perpendicular to the direction of propagation of the light energy in the fiber; and c) a predetermined bandwidth of the light energy through the confined region. Means for locating the fiber in contact with the lid so that it is directed toward the element. 2. The device according to claim 1, wherein the positioning means comprises a concave groove formed in an upper portion of the lid to accommodate the fiber. 3. The device according to claim 2, wherein the groove is integral with the lid. 4. The device of claim 1, wherein the limited area comprises a window characterized by a predetermined bandwidth. 5. The device of claim 4, wherein the window is flat. 6. The apparatus according to claim 4, wherein the window comprises an optical lens. 7. The apparatus of claim 1, wherein the means associated with the end of the fiber comprises a flat surface having a predetermined reflective characteristic. 8. The apparatus of claim 7, further comprising: a) the flat surface formed at the distal end of the fiber; and b) the flat surface is 45 with respect to the optical axis of the fiber.
A device characterized by being inclined at an angle of degrees. 9. The device of claim 8, wherein the area between the flat surface and the confined area is encapsulated with an optical resin. 10. The apparatus of claim 7, wherein the flat surface is further characterized by: a) the surface formed in a prism element, and b) the prism element attached to the distal end of the fiber. apparatus. 11. The device according to claim 10, wherein a bottom portion of the prism element is fixed to the limited area by an optical resin.