Automated UV recoat inspection system and method

A camera system and automated translation system allows automatic image capture of a recoat of a fiber which has undergone a number of processes. These images may be used to automatically inspect the recoat of the fiber in accordance with objective criteria. A stability index may be determined based on the thickness of the recoat on the fiber, a uniformity of the recoat on the fiber, a depth of any surface cracks on the recoat, and a depth of any bubbles in the recoat. A desired stability index may be determined in accordance with a desired lifetime of the fiber and an intended use of the fiber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to inspecting a fiber which has under gone a series of processing steps, including UV recoating. More particularly, the present invention is directed to an automatic inspection of a fiber at the end of the processing thereof.

2. Description of Related Art

Optical fibers are very light, very fragile, and have very small dimensions. During their initial manufacture, there are practical limitations on the lengths of optical fibers that can be drawn. Therefore, the connections between the fibers to create longer designated lengths of fiber are accomplished by splicing. In addition, optical fibers or optical devices must be connected to pieces of terminal equipment, such as optical transmitters and optical receivers, to create functioning optical systems.

Direct fiber-to-fiber splicing can be accomplished using mechanical splicing devices or by fusing the glass fiber ends together by means of a flame or electric arc. The nature of the fibers themselves, both in the material used in their fabrication and in the minute physical dimensions involved, as well as submicron alignment requirements, make fiber splicing more difficult than conventional metallic conductor splicing. Problems with efficient transfer of energy, minimized optical reflections, and mechanical integrity must be addressed when splicing optical fibers. The complexities of interconnecting the fibers demands careful attention to connector design and a high level of precision in fiber splices.

For example, present day optical fiber splicing operations require numerous steps, including stripping, cleaning, cleaving, aligning, splicing, recoating and pull-testing. While each of the individual steps can be performed somewhat quickly, the set-up, preparation and transfer time between the steps of the splicing process consumes a significant amount of time. For instance, the total time for the fusion splicing process is approximately one-half of the total for an optical transmission equipment manufacturing process.

These processes may be performed manually, or may be automated, as described in commonly assigned, co-pending U.S. patent application Ser. No. 09/048,331 filed Mar. 26, 1998 entitled “Apparatus for Integrating Steps of a Process for Interconnecting Optical Fibers”, which is hereby incorporated by reference in its entirety for all purposes.

The ultraviolet (UV) RECOAT is typically the last step of the interconnecting processes. Thus, it is after this step that it is most desirable to verify the quality of the fiber. The fiber quality becomes more important as many applications are trying to pack fibers into smaller spaces. The tighter bend radius required places greater stresses on the fiber. Currently, a user evaluates the interconnected fiber by viewing the fiber, typically through a microscope, rotating the fiber, and making a decision as to the quality of the fiber in accordance with the visual inspection.

SUMMARY OF THE INVENTION

The present invention is therefore directed to system and method of inspecting a fiber after recoat which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.

It is an object of the present invention to provide an index for determining the stability of an interconnected fiber. It is further an object of the present invention to automate such determination. It is yet another object of the present invention to provide a system for quick, controlled data gathering for use in inspecting a fiber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail through preferred embodiments with reference to accompanying drawings. However, the present invention is not limited to the following embodiments but may be implemented in various types. The preferred embodiments are only provided to make the disclosure of the invention complete and make one having an ordinary skill in the art know the scope of the invention. The thicknesses of various layers and regions are emphasized for clarity in accompanying drawings. Throughout the drawings, the same reference numerals denote the same elements.

A block diagram of the inspection system of the present invention is shown inFIG. 1. An image capture unit100takes an image of the fiber to be inspected. This image is sent to an image processor200, e.g., a microprocessor or central processing unit. The image processor200extracts any imperfections from the images, analyzes the features of these imperfections, and compares these features to established pass/fail criteria. The supervisory controller300, discussed above, controls the movement of the fiber to be inspected in and out of the inspection station. The supervisory controller300also controls the motion controller400which moves the cameras and fiber to be inspected relative to one another at controlled intervals. The motion controller400moves the fiber to be inspected to a starting point to establish a homing position and then moves the fiber relative to the cameras along the length thereof to a finish point.

Vision System

The vision system for inspecting the UV recoat generally includes a camera and an autofocus unit. In the particular configuration shown inFIG. 2a, the vision system has two cameras, a top camera102mounted above a fiber112to be inspected and a bottom camera104mounted below the fiber112to be inspected. The fiber112is held by a metrology frame, the details of which are set forth in commonly assigned, co-pending U.S. patent application Ser. No. 09/048,331 filed Mar. 26, 1998 entitled “Apparatus for Integrating Steps for a Process for Interconnecting Optical Fibers”, which issued as U.S. Pat. No. 6,122,936 on Sep. 26, 2000, which is hereby incorporated by reference in its entirety for all purposes. An autofocus unit108automatically adjusts the focus of each camera after the fiber has been translated. The top camera102is preferably mounted horizontally and a prism106or other redirecting element provides the image from the top of the fiber112to be inspected to the top camera102. The bottom camera104is preferably mounted vertically and captures the image of the bottom of the fiber to be inspected. There is preferably a hole110in a base plate114which receives the metrology unit holding the fiber to be inspected for allowing the image of the bottom of the fiber112to be inspected to pass to the bottom camera104.

The images of the fiber captured by the respective cameras are shown inFIG. 2b, in which a cross-section of the fiber112is shown. The top camera102captures an image of a top semicircle103of the fiber112and the bottom camera104captures an image of a bottom semicircle105of the fiber112. Any configuration of cameras which allows the entire image of the fiber to be captured in an automated fashion may be used, including a single camera with the fiber rotating, which would no longer require a hole in the base plate, or a single camera receiving alternate images of the top semicircle and the bottom semicircle.

Mechanical Automation Features

In addition to the elements shown inFIG. 2a, a top of the base plate114also includes a base frame404, as shown inFIG. 3a, The base frame404holds the metrology frame housing the fiber in a static position parallel to a work surface without any vibration as the base frame404moves the fiber for inspection from start to end. As can be seen inFIG. 3a, the base frame also includes alignment pins402for receiving the metrology frame housing the fiber.

As can be seen from the elevational perspective view inFIG. 3b, a bottom of the base plate114includes a system for moving the base frame, and thus the fiber, relative to the camera(s). The base frame404extends through a slot406in the base plate114and is attached to a linear slide410on a linear motor412. The linear motor412is preferably magnetically controlled for efficient small linear movements. The actual size of the movement of the linear motor412is determined in accordance with a desired level of detail of the inspection. The alignment pins402on the base frame404and the slot406in the base plate114ensure that the same starting point for inspection is used for each fiber. For extra quality control, an encoder slide414may be used with an encoder416to optically compare slide movements generated by the linear slide410with location marks on the encoder416.

All the components on the bottom of the base plate114are preferably provided on an interface plate408. The interface plate408preferably very rigid to prevent the force from the loaded metrology frame from transferring to the encoder416. Force on the encoder will cause the encoder416to fail.

Objective Inspection Criteria

Once the data has been gathered for a fiber being tested, the image processor or microprocessor200analyzes the images to determine the size and type of any flaws on the coating. These flaws are generally either crack on the surface of the recoat, shown inFIG. 4aor imperfections in the recoat itself, called a bubble, shown inFIG. 4b. As can be seen in both these figures, the size of each imperfections is characterized by two dimensions, a width Aa@ and a depth Ab@. Generally, the maximum stress which can be withstood by the fiber is given by σ0(1+2*(b/a)). The deeper the crack, the higher the stress acting on the tip of the crack. The speed of the growth of the crack increases with increasing depth.

The surface defects are more critical than the internal defects. Wherever the fiber is unprotected, small surface defects easily occur and grow rapidly. This growth may be accelerated by exposure to water, which react chemically with the fiber. The thickness and the uniformity of the recoat also effect the lifetime of the fiber. Presence of a bubble and/or surface defect will decrease the apparent thickness and/or uniformity of the recoat. The overall stability of the fiber may be determined by the following:
si=w1exp(n1t)+w2exp(n2s)+w3exp[−n3s]+w4exp[−n4B](1)
where t is the thickness of the recoat, u is the uniformity of the recoat, s are the depth of the surface discontinuities, and B is the size of the bubbles, n1–n4are experimentally determined parameters based on fiber type and its intended use, and w1–w4are weights assigned to each factor in accordance with a desired end use. The weights w1–W4are related by:
w1+w2+w3+w4=1  (2)
The larger the stability index (si), the longer the fiber lifetime.

The desired stability index may be objectively set based on the desired end use and required lifetime. The bend diameter to which the fiber is to be subjected typically establishes the maximum stress of the fiber. The microprocessor performs an automated pass/fail comparison of bubbles and cracks in the UV recoat to the established criteria based on the required lifetime and intended use. If the fiber fails, it may then be returned to the UV recoat stage to be recoated again and then reinspected.

Thus, in accordance with the present invention, images of the UV recoat may be automatically captured, and, from these images, the fiber may be inspected to determine its stability index. This stability index may then be compared to a desired stability index, and the fiber will pass if its stability index is greater than or equal to the desired stability index and fail if its stability index is less than the desired stability index.

While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the present invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility without undue experimentation. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.