Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2003-06-19
2004-09-21
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S053000, C385S088000, C361S600000
Reexamination Certificate
active
06793411
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical fibers and, more particularly, to methods and apparatus for communicating optical signals between an optical fiber and a receiver or transmitter, such as a semiconductor receiver or transmitter mounted in a package.
BACKGROUND ART
Integrated circuit devices (ICs), such as microprocessors, micro controllers, and signal processors, are operating at higher and higher frequencies. For example, computer processors are currently being clocked at speeds in excess of 1 Gigahertz (GHz). At least two technological developments have contributed to this increase in operating speeds. Switching transistors, which are the building blocks of computers, now operate at lower voltages. For example, IC operating voltages have systematically dropped from 5.0 Volts to 2.2 Volts and below. Because switching power losses in transistors are proportional to the square of the operating voltage, the lower voltages reduce power dissipation, allowing higher frequency switching on the same substrate for the same total power dissipation. The second development is the use of sophisticated “radio frequency” modeling techniques for designing the layouts of conductive leads. The leads can be modeled as high frequency transmission lines, and coupling between adjacent leads as well as discontinuities, such as bends, taken into account. Such modeling has allowed the design of high-performance, multi-layered PC boards.
Unfortunately, there are disadvantages associated with such advances, such as increased sensitivity to electromagnetic interference (EMI), to voltage transients, and to common-mode noise. Desired signals can be degraded. Creative engineering and sophisticated board layouts can help reduce the deleterious effects described above. However, limits still remain. It is understood that conductive leads to high speed, low voltage ICs simply create certain problems with signal integrity and limit the speed at which signals can be propagated. For example, designers of high-speed microprocessor boards restrict communication buses emanating from the microprocessor IC to approximately 300 MHz. Multiple, parallel 300 MHz buses are used to communicate with the IC at the full bandwidth of which the IC is capable, such as 1 GHz. Each bus carries only a part of the communication with the IC. Each bus, of course, has sensitivity to EMI and other influences that reduce the integrity of the transmitted signal.
Optical fibers are known to be highly desirable for the transmission of data and other signals. Optical fibers are low cost, flexible, have a large bandwidth, and are not sensitive to EMI. However, optical fibers are not widely adopted for the communication data to and from an IC, such as the microprocessor in a personal computer.
Basically, problems associated with launching signals onto the fiber or retrieving signals off of the fiber, or, in other words, communicating with the optical fiber, limit the use of optical fibers in environments such as a personal computer, despite the advantages of fiber in terms of bandwidth, flexibility and reduced sensitivity to EMI. Many of the known techniques for communicating with an optical fiber are simply too expensive compared to other technologies, such as the use of multiple conductive 300 MHz buses.
For example, in communicating an optical signal using a fiber, optical alignment of the fiber with the transmitter or receiver with which the fiber communicates is very important, especially in higher power and/or long haul applications, to ensure that light is efficiently transferred between the receiver or transmitter and the fiber. Optical fibers have very small dimensions, and often very tight tolerances must be achieved and maintained over a range of operating parameters, such as temperature, vibration, and humidity, to provide proper optical alignment.
One approach is to terminate optical fibers in precision connectors and to mate the connectors. However, an optical connector, such as a plug connector, is typically complex and includes multiple parts, some of which can be spring loaded. The connector maintains contact between the mated fiber faces when the plug is connected with a similarly highly engineered discrete socket, or jack. Plug and jack optical connectors can also require meticulous cleaning and are subject to all manner of degradation of the face of the fiber, including degradation due to micro-cracking, and due to foreign object damage caused by triboelectric charge forces attracting and holding small particles on the end face of the fiber prior to connection. The lowest cost multimode product known today, although injection molded and known for its lowest selling price, cannot be field terminated. It must be prepared in advance to a predetermined length, and in addition, is restricted to duplex applications.
Furthermore, fibers are typically too fragile without a protective coating, or buffering, to survive in real world applications. For example, an optical fiber is coated to prevent water ingression, which can lead to catastrophic failure due to water induced microcrack propagation. Typically, the fiber is coated with a polymer or polymers. In some cases the coating is applied in eight or more individual steps to protect the fiber from such failure. The most common protective coating is an ultra violet (UV) cured acrylate. Other coatings including fluoroacrylates, polyimides, Teflon fluoropolymers, and a number of other organic compounds.
Unfortunately, problems are associated with these protective coatings. The core of the fiber is often unpredictably located with respect to the outer circumference of the coating, hindering proper optical alignment for communication of light with the fiber.
Accordingly, the protective coating is often stripped away from a short length of the optical fiber prior to assembly of the length of fiber into a connector or optical package. The fiber is often mechanically stripped, which can damage the surface of the fiber and render the fiber more likely to fail in service. The fiber can also be stripped using hot sulfuric acid. However, the acid can degrade the fiber, including any remaining coatings, due to the wicking of the acid underneath one or more of the coatings. Stripping the fiber introduces a discontinuity in the protective coating where the coating suddenly ends and the stripped portion of the fiber begins. This discontinuity can concentrate stresses on the fiber at the discontinuity, also tending to promote failure of the fiber. The amount of stress concentrated can depend on the nature of the coating that is stripped.
It is also known to metallize, typically via electroplating, electroless plating, or vapor deposition, the cladding layer that is exposed upon stripping the fiber. The metallized cladding can be soldered into a ferrule, which ferrule is in turn soldered into a passage in an active or passive component package. “Glues,” such as epoxy resins, and RTV silicone compounds are used to fill in gaps and to avoid microbend induced stresses that cause unacceptable optical performance degradation. To enhance the mechanical integrity of the optical assembly, a part of the fiber in the ferrule may retain the polymer layer, such that the core of the optical fiber may be displaced relative to and/or disposed at an angle to the longitudinal axis of the ferrule. Often the length of the passage is longer than the length of the ferrule, and because of the high variability in fiber thickness due to unpredictable thickness and/or location of the protective coating, as noted above, the passage includes a large diameter. This creates the larger gap to fill with the “glue” and also increases the risk of angular misalignment of the fiber.
After all of the foregoing—stripping, plating, and soldering a ferrule onto the fiber and into a package—it is typically still necessary for a technician to optically align the fiber and the device, that is, the receiver or transmitter in the package, with which the fiber communicates. Typically, the location of the packaged device
Doan Jennifer
Nufern
Palmer Phan T. H.
Rainville Peter J.
LandOfFree
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