Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Reexamination Certificate
2000-03-28
2002-05-07
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
C385S033000
Reexamination Certificate
active
06382841
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to methods and devices for coupling and mounting optical components. More particularly, embodiments of the present invention relate to an improved device, as well as to its manufacture and use, for coupling fiber optic components in such a way as to ensure adjacent contact between the coupled components and thus facilitate high levels of thermal stability in the completed optical assembly.
2. The Prior State of the Art
Traditionally, data and signal transmission has been accomplished by sending a series of electronic pulses along one or more metallic wires or cables to a receiver, which then converts the pulses into a usable form. Within a limited range, metallic wires and cables are generally effective as a signal and data-carrying medium. However, metallic wires suffer from a variety of shortcomings which serve to limit their effectiveness as a transmission medium.
First, all metallic wires and cables are characterized by imperfections such as chemical impurities. These imperfections cause the electronic pulses to lose energy, or attenuate, as the pulse travels down the wire. As a result, signal regenerators are required at various points along the wire to electrically boost the electronic pulses and thus effect transmission of a signal and/or data.
Second, the amount of information that a metallic wire or cable is capable of carrying, i.e., the bandwidth of the wire, is constrained by limitations inherent in the wire. In particular, bandwidth is sharply limited by factors including, but not limited to, the size and composition of the transmission wire.
The bandwidth limitations inherent in metallic wire has become increasingly problematic as the existing wire networks of telephone companies are called upon to transport increasing amounts of voice and data signals—especially with the proliferation of the Internet. Moreover, wires and cables take up a great deal of space in already crowded wireways and trunks, and are difficult to work with and install. They are also susceptible to electromagnetic interference, voltage surges, and similar types of electronic noise. Thus, there has been an increasing need for alternative forms of technology to meet data and signal transmission needs.
One increasingly popular approach is to utilize fiber optic technology. Essentially, fiber optic technology employs optical waveguides made of glass, plastic or the like, as a means for transmission of data and/or signals in the form of light pulses. Typically, optical waveguides take the form of optical fibers. There are a number of advantages in using fiber optics as a data and signal transmission medium: fiber optics were relatively lighter in size and weight as compared to metallic transmission media—some experts have estimated that it would take 33 tons of copper to transmit the same amount of information handled by 4 ounces of optical fiber; optical fibers were not susceptible to electromagnetic interference and voltage surges; optical fibers were less prone to signal attenuation; and, perhaps most importantly, optical fibers possessed a tremendous bandwidth.
As a result of the numerous advantages associated with the use of fiber optic technology as a means for data and signal transmission, fiber optics are being used in an ever-increasing number of applications, including local area networks (LANs) and a variety of communications systems. Also, the ascendancy of the Internet has served to emphasize the need for a transmission medium capable of transmitting large amounts of data over great distances both rapidly and reliably. Fiber optic technology is well suited to serve this end because of its large bandwidth capabilities, high data transmission speeds—up to 1600 times faster than conventional copper wires, and relatively low signal attenuation characteristics.
Many examples of the implementation of fiber optic technology can be found in the telecommunications industry. Some examples of widely used fiber optic arrangements include wavelength division multiplexing (WDM) devices, and gain-flattening devices.
Clearly, fiber optic technology represents a significant advance in the field of data and signal transmission. However, despite the numerous advantages of fiber optic technology and the continuous advances being made, there are still a variety of problems in the field that are as yet unresolved. As indicated in the following discussion, one of the major unresolved problems in the fiber optics field is the thermal instability of many fiber optic assemblies.
In general, thermal instability refers to the inability of an optical assembly to consistently perform in accordance with a desired set of specifications when exposed to a particular range of temperatures. For example, an optical assembly that performs in accordance with the desired specifications at room temperature will often be ‘out of spec’ at elevated operating temperatures. Specifically, relatively high operating temperatures cause the various components in typical optical assemblies to change their orientation and/or position with respect to each other. Because the precise positioning and alignment of the optical components is critical to the effective performance of an optical assembly, any movement or shifting of the individual optical components compromises the performance of the optical assembly as a whole. The problem of thermal instability is particularly acute in the area of micro-optics where interference filters, for example, are generally as small as 4 mm
2
, or less, in cross-sectional area.
Though thermal instability can be thought of in terms of relative spatial movements or shifts of optical components in an optical assembly, practitioners in the art have found it convenient to express thermal instability in a more precise fashion. Specifically, it is generally acknowledged that thermal stability may be described in terms of the shift of the center wavelength (CWL) of the passband as a function of temperature; wherein the CWI shift is expressed in units of picometer/°C., or pm/°C., and ‘passband’ refers to a range of wavelengths desired to be transmitted, or passed, through a given interference filter. As an example, the CWL of a known 50 GHz filter is about 1.1 pm/°C. over an operating range of
0-80° C.
Thermal instability in optical assemblies very often stems from the manner in which the individual optical components are assembled and/or held in place. A typical optical assembly employs one or more gradient index (GRIN) lenses, one or more optical fibers, and at least one interference filter. Often, these components are attached to each other in a face-to-face configuration and retained in place by means of epoxy or other adhesives applied to the respective faces. The adhesive typically has an index of refraction substantially the same as the attached optical components. In other cases, the optical components are retained in a spaced-apart configuration by means of adhesive in combination with some type of structural mount.
In operation, transmitted light travels down the optical fiber to the GRIN lens, which then collimates the transmitted light. The collimated light is thus refocused by the GRIN lens for transmission through another optical fiber. Typically, an interference filter is attached to, or near, the GRIN lens so as to transmit and/or reflect only selected wavelengths of the collimated light leaving the GRIN lens.
Although widely used, the known assembly methods and mounting structures for optical components contribute significantly to the thermal instability of optical assemblies. One feature of known mounting methods that is particularly problematic is the application of adhesives or the like to the faces of optical components so as to fasten optical components together in a face-to-face configuration. The problems arising from such methods are cause for concern in any optical assembly, but are of particular concern where the method is used to attach a thin film interference filter to a GRIN lens—a c
Optical Coating Laboratory
Palmer Phan T. H.
Workman & Nydegger & Seeley
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