Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
2001-03-13
2003-07-29
Nasri, Javaid H. (Department: 2839)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
C385S091000, C385S081000
Reexamination Certificate
active
06599029
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ferrule assembly for connection with an optical part incorporating an optical fiber, and particularly to a receptacle-type optical transmission module using a ferrule assembly.
2. Description of the Related Art
In recent information communication field, increase of information amount is followed by a need to transmit a large quantity of information at high speed, and high-speed large-capacity optical communication networks such as optical subscriber systems are now spreading. For popularization of the optical subscriber systems, cost-down of optical modules is an unavoidable task. The cost of optical modules consists of parts cost, assembly cost, and test and adjustment cost; among others, the assembly cost and adjustment cost constitute a major part of the total cost. As a means of reducing the assembly cost, receptacle-type optical modules have come to be spotlighted in recent years.
Parts mounted on a printed wiring board to be incorporated in a communication device are generally classified into surface mounting type and through-hole mounting type. A representative example of the surface mounting type parts is LSI, which is so-called flat package type in shape. This type of parts are soldered by a technique called reflow soldering. Namely, a pasty solder is printed on a printed wiring board, a surface mounting type part is adhered to the pasty solder, and soldering is carried out in a conveyor furnace in which the solder surface temperature is brought to 220° C. or higher.
Representative examples of the through-hole mounting type parts are high-capacity capacitors and LSIs with a large number of terminals (200 terminals or more). The LSIs with a large number of terminals have a terminal form called PGA (Pin Grid Array). These through-hole mounting type parts are soldered by a technique called flow soldering. Namely, terminals of the through-hole mounting type part are inserted in through-holes of a printed wiring board, and soldering is carried out by placing the opposite side of the part mounting surface of the printed wiring board in a solder bath at a temperature of about 260° C.
For a technique of mounting optical modules on a printed wiring board by soldering just like the surface mounting type parts and the through-hole mounting type parts, the so-called pig-tail type optical modules with an optical fiber cord are unsuitable. Normally, an optical fiber cord has a nylon covering, which has a heat resistance of only about 80° C. and, therefore, will melt in a soldering step. In addition, the optical fiber cord itself causes troubles or difficulties in containing and handling at production sites, thereby conspicuously lowering the efficiency of mounting on printed wiring boards.
Therefore, in order to enable soldering of optical modules and contrive a reduction in production cost, it is essentially required to provide a so-called receptacle-type optical module which does not comprise an optical fiber cord. The receptacle-type optical module is an optical module having a connector portion so that an optical fiber cord having a covering with low heat resistance can be fitted to and detached from the module. The receptacle-type optical module allows application of a solder reflow step at high temperature and, therefore, can be mounted on a printed wiring board simultaneously with surface mounting type electronic parts.
By simultaneously mounting optical parts and electronic parts on a print wiring board, a plurality of mounting steps using solders having different melting points required in the prior art can be simplified, which promises a large reduction of cost. As a means of reducing adjustment cost, a self-alignment technique has been investigated. In the technique, guide portions specified in positional relationship with optical parts at high precision are formed on the optical part mounting substrate, and optical wave guide parts (optical fiber, ferrule, etc.) are mounted along the guides, thereby accomplishing optical coupling. The self-alignment technique makes it possible to omit alignment steps which require a large number of steps and high cost.
Japanese Patent Laid-open No. 11-264926 (1999) discloses a structure of an interface portion between a PLC (Planar Lightwave Circuit) and an optical fiber. The optical module described in the publication has a structure such that a ferrule incorporating an optical fiber is mounted along a groove formed in an optical device mounting substrate. This structure is characterized in that optical coupling can be achieved automatically (self-alignment) by precisely designing the relative positions of the groove and the optical part.
An optical module disclosed in Japanese Patent Laid-open No. 7-318764 (1995) proposes another mode of self-alignment in which a bare optical fiber is protruded from an end of a ferrule and the optical fiber is inserted and fixed in a guide groove formed in an optical device mounting substrate. This structure is characterized in that positioning of the optical fiber can be carried out directly by the guide groove and, therefore, a high mounting precision can be obtained.
As a further example of the prior art, Japanese Patent Laid-open No. 2000-171668 may be mentioned. An optical module described in this publication proposes a further mode of self-alignment in which a bare optical fiber is semi-exposed by cutting away a part of a ferrule and is mounted and fixed in a guide groove formed in an optical device mounting substrate. The optical module of this structure is characterized in that since a part of the ferrule is used for retaining the bare optical fiber, a retaining part can be omitted and adhesion area can be made small.
There are four characteristics required of an inexpensive and highly reliable receptacle-type optical module: (1) easy mounting, (2) high strength, (3) capability of end face polishing and measure against reflection, and (4) high positioning precision. Particularly, the end face polishing is expected much as a means of coping with reflection. Reduction of reflected-back light has become a major task in recent years, and in order to reduce reflected-back light from a value of about 25 dB at present to a value of not less than 40 dB required in future, a slant polishing structure in which a fiber end face is slanted against optical axis is effective. For realizing this structure, it is required that the fiber end can be polished.
The optical module described in the above-mentioned Japanese Patent Laid-open No. 11-264926 (1999) has the following problems. It is required to form a guide groove having a depth corresponding to the radius of the ferrule (about 650 &mgr;m in the case of an MU-type ferrule of standard specifications), so that etching time is increased and it is difficult to provide a protective film. In addition, a large sized optical part mounting substrate is required. The large guide groove leads to low controllability of width at the time of formation thereof, and long-time etching may easily produce an abnormal etched surface at a slant surface. Further, since positioning is carried out using the outer shape of the ferrule, a loss in optical coupling will be generated due to eccentricity of the inside diameter of the ferrule and eccentricity at the time of insertion of optical fiber.
The optical module disclosed in the Japanese Patent Laid-open No. 7-318764 (1995) has the following problems. It is impossible to polish end faces of the optical fiber. In addition, since the optical fiber is entirely exposed from the ferrule, there is a high danger of breaking of the optical fiber at the time of handling. Further, since an optical fiber fixing portion and a ferrule fixing portion are independent in the optical module, a stress may be generated at the boundary portion between the optical fiber and the ferrule, possibly producing bad effects on reliability.
The optical module disclosed in the Japanese Patent Laid-open No. 2000-171668 has the following problems. End face polishing is
Nakagawa Goji
Nobuhara Hiroyuki
Yamazaki Yousuke
Fujitsu Limited
Nasri Javaid H.
Staas & Halsey , LLP
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