Patent Application
20130084042
1. Field of the Invention
The present invention relates generally to optical connectors, and particularly to an optical fiber connector construction and method of assembling same.
2. Discussion of the Known Art
Currently, most fiber optic connectors lack means for preventing ambient dirt and debris from depositing on a fiber endface that remains exposed at the tip of the connector while the connector is not in use. Such deposits will attenuate light signals transmitted through the connector when the connector is used in a fiber optic network. One known protective measure is to provide a removable end cap for the connector tip. Notwithstanding, persons forget or simply don't bother to place the cap over the connector tip while the connector is out of service. In addition, the cap is often misplaced or inadvertently discarded. As long as the connector remains disengaged from a mating connector or adaptor with the end cap removed, the exposed fiber endface is subject to damage especially while the connector is being handled or cleaned. Moreover, the risk of damaging fibers with extremely small diameters is very high since only a small amount of debris or a relatively small chip can block or damage a larger portion of the fiber.
A connector available from Diamond or Senko and known as type E-2000 has a spring-loaded cap that is attached to the body of the connector. This is a relatively expensive mechanical solution, however, and is difficult to retrofit on the existing standard fiber optic connectors such as types ST and SMA.
Other known solutions involve the formation of an airwell about the fiber endface for high power applications. See, e.g., U.S. Pat. No. 7,431,513 (Oct. 7, 2008) which is incorporated by reference. In the configuration of the '513 patent, a fiber protrudes from an epoxy/connector interface, and the endface of the fiber is either aligned with the open end of the connector's airwell, or is slightly recessed from the open end. These connectors may be of either the epoxy-polish type or the crimp and cleave type, or a combination thereof. The connectors are prefabricated, and each type has drawbacks during its assembly, for example, debris entrapment, poor finish quality, and/or difficult processing steps including polishing and cleaning.
According to the invention, a fiber optic connector includes a connector body, an elongated ferrule supported in the connector body, wherein the ferrule has a distal tip, and an axial passage that opens on a front surface of the tip so that an endface of a fiber retained in the passage is exposed at the front surface of the tip, and a sleeve fixed on the circumference of the distal tip of the ferrule. The sleeve has a leading edge that projects a determined distance axially beyond the front surface of the tip to form a recessed region in which the endface of the fiber is set back from the leading edge of the sleeve. A barrier is disposed in the recessed region for protecting the endface of the fiber from damage by surrounding objects. In the disclosed embodiments, the barrier may be in the form of a hardened epoxy layer, a lens, or a refractive index matching material optically aligned with the fiber endface.
For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawing and the appended claims.
In the drawing:
a) and 2(b) are diagrams of test measurement setups used to evaluate the performance of the connector;
The fiber 14 is retained inside the connector 10 in a conventional manner, either by bonding the fiber 14 to the periphery of the ferrule passage 16 using, e.g., a Type 353 epoxy compound at 20, or by crimping the ferrule 18 about the circumference of the fiber 14. The overall construction of the connector 10 may resemble, for example, that of a commercially available SMA 905 fiber optic connector but with certain modifications as detailed below. SMA type fiber optic connectors are generally disclosed in, e.g., U.S. Pat. No. 4,204,306 (May 27, 1980); U.S. Pat. No. 4,440,469 (Apr. 3, 1984); and U.S. Pat. No. 6,953,288 (Oct. 11, 2005), all of which are incorporated by reference.
According to the invention, a sleeve 30 is press fit or otherwise fixed on the circumference of a distal tip 32 of the connector ferrule 18, after an exposed endface 34 of the fiber 14 is polished flush with a front surface 35 on the tip 32 of the ferrule in a known manner. The sleeve 30 may be cut, for example, from a length of stock stainless steel hypodermic tubing. The sleeve 30 may also be cut from other commercially available metal tubing including aluminum, titanium, or brass; or from tubing made of a plastics material.
In the embodiment of
To assemble the connector 10 in
Before mounting the sleeve 30, the front surface 35 of the ferrule 18 is polished back toward the connector body 42 along with the fiber endface 34 exposed on the front surface 35, until the front surface 35 projects axially from the connector body 42 by 0.3792 inch (0.3862 in. −0.007 in.). Next, the sleeve 30 having an initial oversized length of about 0.250 inch is cut from, e.g., No. 304 stock stainless steel hypodermic tubing. One open end of the sleeve is press fit onto the circumference of the ferrule tip 32. The opposite open end of the sleeve 30 is filled with epoxy compound, e.g., Epotek 301-2 and the compound is allowed to cure. The sleeve 30 is then polished back toward the connector body 42 with the contained hardened epoxy until the leading edge 36 of the sleeve is at a distance L=0.3862 inch from the connector body 42. It is preferred that the front surface 35 of the ferrule tip not be polished so far as to extend into a chamfer 44 that is typically formed at the distal end of the axial passage 16 inside the ferrule 18. One reason to avoid polishing into the chamfer 44 is to minimize the physical size of the epoxy boundary that is subject to increased debris entrapment and voids, leading to a poor polish quality.
a) and 2(b) show transmission test measurement set-ups for the inventive connector 10 in
The output of a LED light source 210 (e.g., WT&T Model LE-IG-C) is coupled to one end of a launch fiber 212, the other end of which terminates in a standard “launch” SMA connector 214. In
Table 1 below shows test measurement results obtained for the CH A connector 10 in
Next, a sleeve 30 containing the hardened epoxy compound was placed on the ferrule tip 32 of each connector 10, and the leading edge 36 of each sleeve was polished until the edge was a distance L of 0.3862 inch from the body 42 of the connector. Light transmission through each of the connectors 10 at the ends of the fiber 200 was measured again, and the results appear under the column headed Transmission Post Epoxy Layer (μW).
A second test was performed on a lensed version of the inventive connector 10. In
In this Example, the single fiber 200 in
One end of the fiber 200 fiber was inserted in the ferrule passage 116 and retained in the body 142 of the inventive connector 110 (CH A). The front surface 135 at the tip of the ferrule 118 was polished back together with the exposed fiber endface 134 to a length of 0.379 inch from the connector body 142 (i.e., 178 μm shorter than the standard 0.3862 inch SMA ferrule tip length). The opposite end of the fiber 200 was terminated in a conventional manner by a regular SMA 905 connector (CH B). Light transmission through the fiber 200 with the connectors at both ends was then measured.
Using “Loctite 4014”, one end of a 0.250 inch length of stock stainless steel hypodermic tubing having an I.D. of 0.085 inch and an O.D. of 0.109 inch, was secured on the ferrule tip 132 of the shortened SMA connector CH A, in axial alignment with the ferrule to form the sleeve 130. The recessed region 138 formed by the sleeve 130 was filled with “Epotek 301-2” epoxy compound 143. A lens rod 145 made of BK7 glass measuring 4.0 mm in length with an O.D. of 2.0 mm, was polished at both ends to a 0.3 μm finish. The lens rod 145 was then advanced axially into the region 138, and a conventional fixture was provided to keep the inwardly facing end of the lens rod 145 in contact with the endface 134 of the fiber 116 on the front surface 135 of the shortened ferrule 118 until the epoxy cured. The sleeve 130 and the distal end of the lens rod 145 were polished back together to a distance L of 0.3862 inch from the connector body 142.
Optical transmission measurements were performed and appear in the last column of Table 2 below, under the heading Transmission Post Epoxy Layer (μW). Some of the measurements varied within expected limits as a function of rotational orientation of the connector under test at the splice bushing 215 in the test setup in
Table 2 shows that when the output of the light source 210 was connected directly to the shortened inventive connector (CH A) under test at one end of the fiber 200, a power level of 4.31 μW was measured by the detector 220 from the standard SMA 905 connector at the opposite end of the fiber 200. When the output of the source 210 was directly applied to the standard SMA 905 connector (CH B), a power level of 4.15 μW was measured by the detector 220 from the inventive connector CH A.
In summary, the measurement results in Table 1 indicate slightly more transmission loss than anticipated under the test conditions, but are satisfactory nonetheless. The measurement results shown in Table 2 are more encouraging, and are very satisfactory for the tested configurations.
Oscillations in the transmissions with respect to wavelength were detected at times. The oscillations are believed to be caused by the fiber/epoxy/lens interfaces, and to have arisen as a result of pressure that was applied to cure the epoxy compound. If persistent, it may be possible to normalize such oscillations by use of software in a known manner. Moreover, the epoxy compound may be cured without a need for applying external pressure. For example, the lens rod 145 may be cured to the fiber end face 135 using a temporary centering fixture, the fixture then removed, and the sleeve 130 installed as a secondary component. This may resolve various issues by providing a uniform stress free-bond between the lens rod 145 and the fiber end face 135, as well as a more uniform bond between the cylindrical surface of the lens rod 145 and the sleeve 130, i.e., no air or voids. Such would also allow for the use of a non-optical epoxy providing greater protection for the bond between the lens rod 145 and the sleeve 130.
It is desirable to minimize or completely eliminate the presence of air bubbles in the epoxy bond between the fiber 16 (or 116), the ferrule tip 32 (or 132) and the sleeve 30 (or 130), with no delamination or noticeable problems. For the most part, air bubbles in the bond between the circumference of the lens rod 145 and the inner diameter of the metal sleeve 130 may be polished through, but should preferably be eliminated entirely to obtain a fully solid epoxy region 143 between the lens rod 145 and the sleeve 130. This will also ensure that the connector 110 is resistant to damage caused by aggressive cleaning chemicals like “CIDEX” that are typically used on optical connectors and assemblies as high level disinfectants in the medical field.
Standard optical SMA connectors are generally configured to be butt-coupled with other optical SMA connectors. There are industry standard female-female couplers which, when fully connected at each end with a male SMA connector, define the spacing between butt coupled fiber end-faces. Normally, there is a small air gap in the fully seated position that allows the fiber endfaces to approach one another very closely without damaging them. The close proximity of the fibers helps to optimize optical coupling efficiency since it prevents diverging light from becoming lost from the coupling fiber.
With the inventive damage resistant SMA connector construction, the fiber endface is slightly recessed and shielded behind an epoxy or glass barrier. The optics diagram of
Curve 1—HPX2000 Xenon Light source→SMA connector of patch→Patch fiber→SMA connector of patch→Integrating sphere→usb2000+spectrometer→CPU.
Curve 2—HPX2000 Xenon Light source→SMA connector of patch→Patch fiber→DRSMA connector 10 of patch→Integrating sphere→usb2000+spectrometer→CPU.
Curve 1—HPX2000 Xenon Light source→200 um, 0.22 NA Patch cord→SMA connector of patch-SMA connector of patch→200 um, 0.22 NA patch→Integrating sphere→usb2000+spectrometer→CPU.
Curve 2—HPX2000 Xenon Light source→200 um, 0.22 NA Patch cord→DRSMA connector 10 of patch-SMA connector of patch→200 um, 0.22 NA patch→Integrating sphere→usb2000+spectrometer→CPU.
Curve 3—HPX2000 Xenon Light source→200 um, 0.22 NA Patch cord→SMA connector of patch-DRSMA connector 10 of patch→200 um, 0.22 NA patch→Integrating sphere→usb2000+spectrometer→CPU.
According to the invention, the recessed region 38 (or 138) is formed between the fiber endface 34 (or 134) and the distal edge 36 (or 136) of the sleeve 30 (or 130). In the embodiment of
In the embodiment of
While the foregoing represents preferred embodiments of the present invention, it will be understood by persons skilled in the art that various modifications and changes can be made without departing from the spirit and scope of the invention, and that the invention includes all such modifications and changes that are within the scope of the appended claims.
This application claims priority under 35 U.S.C. Section 119(e) of U.S. Provisional Patent Application No. 61/541,175 filed Sep. 30, 2011, entitled “Recessed Ferrule” which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61541175 | Sep 2011 | US |
