Patent Application
20130183030
This invention relates generally to an approach for reflecting signals of a certain wavelength, and, more specifically, to a low cost thin-film selective reflector for facilitating testing of an optical network.
Fiber-to-the-home (FTTH) is a form of fiber optic communication delivery in which the fiber extends from the central office to the subscriber's premises. Referring to
In the event a user loses a signal in the network 700, troubling shooting the problem requires isolating it to the physical layer or the active components, which are downstream of the modem 703. Isolating the problem to the physical layer is particularly important because the physical layer tends to be vast, extending for many miles—thus it is critical to narrow the geographical area in which the problem lies. Isolating the problem is also necessary to determine the type of response needed to resolve it. For example, a problem in the physical layer may require a crew in the field to repair the fiber 704, or a technician at the premises to the terminate the user's modem to a different fiber. On the other hand, a problem with the active components requires the technician to access the premises and troubleshoot the specific active components involved.
A preferable way of isolating a problem in an optical network is to provide a transmitter 702 that transmits a test signal having a certain wavelength that is different from the other signals being transmitted over the network. Specifically, the test signal is transmitted down the fiber 704 and is reflected back to the central office using wavelength selective filters 710. Because the wavelength selective filter 705 is located at each premises, it reflects a signal that is representative of the condition of the fiber leading to that premises. If the test signal is not received or is not received in the same condition in which it was transmitted, then the physical layer leading to that premises is compromised in some way. Because the test signal has a wavelength that is different from the other signal wavelengths, it does not interfere with the downstream conversion for use in CATV or PC or voiceover internet.
The currently preferred wavelength selective filter 710 is an add/drop filter. Such filters are well known. Briefly, they comprise essentially three components—a common fiber, a pass-through fiber and a reflective fiber. The fiber 704 is optically coupled to the common fiber and all signal wavelengths except for the test signal are allowed to pass through to the pass-through fiber. The selective wavelength is reflected back on the reflective fiber, which is also optically coupled to the fiber 704, such that the test signal is reflected back down fiber 704 and into the control office where a monitor (not shown) records the reflected test signal. If there is a disruption on the physical layer, the “fingerprint” of the test signal will change.
Although add/drop filters provide a reliable and efficient approach for reflecting a test signal back to the central office, these filters have a number of discrete components and tend to be costly and time consuming to install. Thus, there is a need for a less expensive, more readily installed solution. To this end, Applicants considered using a fiber grating at the modem 703. Such fiber gratings are low cost due to their high integration factor, especially in a patch cord configuration. Unfortunately, fiber gratings do not have the required bandwidth to reflect the test signal. For example, the test signal may have a wavelength of 1625 nanometers+/−20 nanometers. Fiber grating reflectors, however, tend to be capable of selectively reflecting only about 1 nanometer. Thus, the margin of error of the test signal is significantly greater than the reflective bandwidth of the fiber grating.
Therefore, a need exists for a selective reflector that is low cost, readily integrated with the network at the user's premises, and has sufficient bandwidth to reflect a test signal with normal wavelength variations. The present invention fulfills this need among others.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides a low cost selective reflector filter for use in verification of the physical layer of an optical network. Specifically, the invention introduces a thin film selective reflector that is conveniently inserted into the optical path of the physical layer. Furthermore, by disposing the thin-film selective reflector on the end face of a ferrule, the thin-film selective reflector can be integrated into traditional optical components, such as, patch cords, splices, and connectors, which, in turn, are readily installed in the optical network.
Accordingly, one aspect of the present invention is an optical network having the thin-film selective reflector optically linked to the physical layer near the user's premises. In one embodiment, the network comprises: (a) a fiber having first and second ends; (b) a transmitter connected to the first end of the fiber and configured to launch a test signal having a first wavelength down the fiber; and (c) a thin-film selective reflector configured to reflect the first wavelength, the thin-film selective reflector optically connected to the second end of the first fiber.
Another aspect of the invention is a thin-film selective reflector incorporated into an optical ferrule. In one embodiment, the thin-film selective reflector comprises: (a) a ferrule having a mating face; (b) a fiber having a first end disposed in the ferrule and having an end face presented at the mating face; and (c) a thin layer of reflective material disposed on the mating face covering at least the end face. The ferrule may be incorporated into any components that traditionally use a ferrule, including, for example, connectors, patch cords and splices.
Yet another aspect of the invention is a method of preparing thin-film selective reflectors. In one embodiment, the method comprises: (a) terminating a fiber with at least one ferrule and polishing a mating face of the ferrule to present an end face of the fiber; and (b) disposing a thin film of reflective material on at least the end face of the fiber to reflect a certain wavelength.
Referring to
The system 100 also comprises a transmitter 102 for transmitting a test signal having a first wavelength. However, unlike prior art systems having a discrete add/drop filter proximate to the modem 103, in this embodiment of the present invention, a thin-film selective reflector 110 is optically connected between the fiber 104 and the modem 103.
The thin film reflective filter is normal to the direction of light propagation and may have various embodiments. For example, referring to
When the test signal is transmitted down the fiber 104 and encounters the thin-film selective reflector 110, it is reflected back through the fiber 104 to the transmitter 102 and a monitor at the central office. Depending on the quality of the test signal received by the monitor, the condition of the physical layer can be determined. Each of these components is described in greater detail below.
It should be understood that when reference is made to the thin-film selective reflector being between the fiber 104 and the modem 103, this does not necessarily mean it is directly connected between these components. For example, there may be intermediate fibers and components between the thin-film selective reflector and the fiber 104. Likewise, there may be intermediate fibers and components between the thin-film selective reflector and the modem 103. Such variations will be obvious to one of skill in the art in light of this disclosure.
The thin-film selective reflector 110 functions to dispose a thin-film selective reflector in the optical path between the fiber 104 and the modem such that it reflects the test signal back to a monitor. The thin-film selective reflector may be configured in different ways. For example, in
The first and second connectors 320, 340 may be any known single or multi-fiber connector, including, for example, traditional SC, ST and FC-type connectors, small form factor designs, such as, MU and LC connectors, and multi-fiber connectors such as the MTRJ, MPX, and MPO-type connectors. Although a single fiber, SC-type connector is depicted in
Referring to
Referring to
Referring to
Still other embodiments using a thin film on the end face of a ferrule as a broadband filter will be obvious to those of skill in the art in light of this disclosure. For example, the ferrule 200 may be optically connected to the fiber 104 by splicing the fiber 203 to the end of the fiber 104. In this embodiment, the ferrule 200 may also be incorporated into a connector for easy connection to the modem or another fiber.
Therefore, the present invention can be practiced in any way in which the thin-film selective reflector 110 is optically coupled between the fiber 104 and the modem 103 approximate to the modem 103.
The ferrule of the present invention is readily prepared economically and with a high degree of repeatability. In one embodiment, the process involves terminating a fiber in a ferrule and polishing the mating face of the ferrule as is known in the art. Next, a thin film is deposited on the polished mating face of the ferrule such that it covers at least the end face of the fiber.
The filter may comprise any material known for reflecting desired wavelengths. Suitable materials include, for example, AlsO3, Al, CeF3, La2O3, MgF2, ZnS, and ZrO2. As in known in the art, the thickness of the material in the thin film affects the reflected wavelength. One of skill in the art will be able to determine the thickness of the film to achieve suitable results without undue experimentation.
The deposition of the material on the ferrule mating face can be accomplished in different ways, including, for example, vapor deposition or sputtering. In one embodiment, the vapor deposition of the material is used. This is a known process and facilitates large-scale manufacturing with a high degree of precision.
To protect the filter film, a protective coating may also be deposited over the film. Suitable protective layers include, for example, silicon oxide or any other transparent material.
In one embodiment, the ferrule in tested after the film is applied to determine whether it reflects the test wavelength, while allowing the other signal wavelengths to pass through. If it passes testing, it may be incorporated into a more elaborate thin-film selective reflector as described above.
Various steps can be used to enhance manufacturability. For example, in one embodiment, prior to the deposition of the thin film in the ferrule, the ferrule is secured to a metal base. This improves its handling and facilitates automation. Furthermore, to add efficiency to the manufacturing process, in one embodiment, a fiber segment is terminated at both ends with a ferrule. A film is then deposited on both ferrules as described above. Next, the fiber segment is separated between the two ferrules to define the ferrule 200 having a thin-film selective reflector 204 and an extending fiber 203 as shown in
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
