Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-12-09
2003-06-24
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06583902
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to the packaging of optoelectronic devices within a fiber optic transceiver for telecommunication and data communication applications.
BACKGROUND OF THE INVENTION
The speed of computers and the data transfer between them is ever increasing. Optical data transmission techniques have been developed to provide high capacity signal transmission without many of the physical limitations for electrical cables. Fiber-optic cables have advantageous transmission characteristics, which are utilized with optoelectronic devices such as fiber-optic transceivers (FOT) by converting electrical signals into optical signals and vice versa at the ends of the fiber-optic cables.
The light beams utilized within an optical signal transmission have continuously extending bandwidths, which allow higher data transmission rates in the optical connection. As a result, more optoelectronic and electronic circuitry is necessary within the FOT to process the signal flow.
The typical hardware architecture of computers involves circuit boards that are perpendicularly connected with a pin edge or a pin array in lengthy multi-pin connectors, which are laterally arrayed on a mother board. That way, the circuit boards are oriented parallel with their receptacle end showing towards the back end of the computer. The designated ends have mounting sites that carry the cable connectors. The cable connectors typically reach through open slots in the back face of the computer chassis such that the communication cables can be connected from outside.
The distance between the open slots is standardized in the computer industry, which leaves a predetermined gap between the parallel oriented circuit boards.
The core of a FOT is typically a planar optoelectronic semiconductor (POS) that receives and emits the light beams perpendicular to its top surface. Since the fiber cable is connected normal to the computer back face as other communication cables, the POS must have a first distinct orientation, which is perpendicular oriented to the circuit board.
To focus the light beams, lenses are placed between the end of the fiber cable and the planar semiconductor. They too must be placed according to the first distinct orientation and are therefore preferably united in a subassembly.
The signals converted in the POS have to be processed within the transceiver. A secondary electronic circuitry (SEC) buffers, amplifies and filters signals that are provided to and derived from the POS.
A typical transceiver board of a FOT carries the sub assembly, the SEC and a pin array, which provides the mechanical and electrical connection of the whole FOT to the mounting site of the circuit board, to which it is soldered.
The size of the pin array(s) defines (together with the space demands for the SEC) the physical extension of the transceiver board, which is several times longer than the POS size. The sub-assembly is placed together with the individual components of the SEC on the transceiver board in a second building orientation.
Due to the continuing miniaturization of semiconductor devices the circuitry involved becomes smaller in size. At the same time more conductive traces and leads needs to be provided between and within the POS and the SEC. The higher complexity and density thereby raises the demand for novel packaging designs.
With higher signal transmission rates, the resistance and the capacitance in the conductive traces and leads become more influential and impose a certain latency upon the FOT. Therefore, there exists a need for a packaging that keeps the length of conductive traces and leads to a minimum.
The high circuit density and high signal processing rate in FOT's result in a thermal load. FOT's need to be designed in a way that the circuitry receives sufficient cooling.
The increased signal density and high bandwidth of the light beams become sensitive to attenuation and reflectance in the optical path. This occurs mainly where fiber optics are interrupted or when the beams have to pass through a number of optical elements. Therefore, there exists a need to keep the optical transitions within the FOT to a minimum.
Cable ends are typically held in cable connectors with support panels connected directly to the computer chassis. Excessive mechanical load and torque on the cable ends bear the risk of overcoming the stiffness of these support panels and imposing a deformation onto the FOT. The FOT needs to be designed to withstand a minimal deformation and maintain the alignment of the cable end with the lens system and the POS.
To extend the application of FOT for mass-produced, low-cost computers, the individual components need to be economical to fabricate, and the assembly of the FOT needs to be simple and reliable at the same time.
A number of attempts have been made to integrate the design needs as described above into a feasible packaging.
The most conventional FOT as it is known to those skilled in the art is a duplex transceiver with two pre-fabricated conventional TO-can's that are soldered with bent leads onto the printed transceiver board. The bent leads impose resistance and capacitance onto the system, and reduce with their free lengths the achievable alignment precision.
The support panel has to be mounted on the transceiver board in indirect connection with the TO-cans, which reduces the achievable stiffness. The whole packaging consists mainly of a bulky, one directional assembly on the transceiver board.
U.S. Pat. No. 4,461,537 discloses a fiber optic connector assembly for first generation fiber optics with high signal levels and low bandwidth. The signal conversion is accomplished without secondary circuitry. An optical cable end has a cylindrical plug with shoulders that snap in circularly arranged hooks of a connector housing. A central element of the connector features a circular cavity with the embedded lens, against which the very end of the fiber optic comes to rest. The central element has solder pins for electrical and mechanical connection with a circuit board. The central element has two small interlocking hooks that snap into corresponding slots of the connector housing. The stiffness requirements of the connector housing do not allow sufficiently interlocking noses. The connector housing has therefore additional snap fingers that fit into corresponding holes of the circuit board and secure the assembly.
The reliability of the assembly depends on the accuracy of shape and position of the corresponding holes of the mounting site and create an external quality risk for the fiber-optic connector assembly.
U.S. Pat. No. 4,767,179 discloses an improvement of the patent described above. The fiber optic connector assembly is extended to the application of a duplex transceiver with an independent emitter and receiver station within one housing. The external quality risk as described above is also resolved by adding a bottom board to the assembly where the snap fingers of the connector housing engage.
U.S. Pat. No. 4,985,805 discloses a device for the cooling of optoelectronic components by the use of a flange joint. The patent discloses a massive constructed device with a multitude of three-dimensional mounted components for heavy duty applications. The constructive afford of the design with its space consuming components do not allow the utilization within regular computers.
U.S. Pat. No. 5,280,191 discloses a packaging for pairs of optical devices having thermal dissipation means. The patent discloses a design of a duplex transceiver with secondary circuitry and a heat sink for cooling.
Two optical subassemblies are placed in a receptacle. The POS is integrated together with the SEC on the transceiver board. As a result, the receiving and emitting light beams must be redirected over 90 degrees between the POS and the optical cable end. This is accomplished by an additional bent fiber optic segment, which results in unfavorable optical attenuation and sensitive assembly procedures.
The heat sink is a sheet metal part, which provi
Alvesta, Inc.
Leung Christina Y
Pascal Leslie
Townsend and Townsend / and Crew LLP
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