Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
1998-01-15
2001-02-27
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Accessories
External retainer/clamp
C385S065000, C385S071000, C385S083000, C385S089000
Reexamination Certificate
active
06195495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing an optical transmitting member-holding structure in which one or more optical transmitting members such as optical fibers are held at a given location. The invention also relates to such an optical transmitting member-holding structure itself.
2. Related Art Statement
Various substrates for fixing plural optical fibers each having a diameter of for example, about 125 &mgr;m are known. Ordinarily, a holding substrate is provided with fixing grooves, such as V-shaped grooves, for fling the optical fibers at given locations. After plural optical fibers, for example, sixteen optical fibers are fixed to the holding substrate, this substrate itself is fixed to another optical part. At that time, each optical fiber is coupled to, for example, a light-emitting diode or a light-receiving element, or optically coupled to another optical fiber or rod lens.
As a material for the holding substrate, silicon, optical glass, ceramics, etc. are known. Further, the above fixing grooves are formed by etching for the holding substrate made of silicon or by grinding for the glass or ceramic substrate.
In any type of the substrate, if the optical axis of the optical fiber fixed to the substrate is deviated from its given location, a transmission loss increases between the optical fiber and the other optical transmitting means. Therefore, an extremely high working precision, for example, not more than 0.5 &mgr;m, is required as that in working the fixing groove on the optical fiber-holding substrate. The optical fibers are usually fixed in the V-shaped grooves with a resinous adhesive.
However, it is feared that if each optical fiber of such an optical transmitting member-holding structure is coupled to the light-emitting diode or the light-receiving element, an organic gas is generated from the resinous adhesive, is adhered to a light-emitting interface of the light-emitting diode, and deteriorates its light-emitting performance.
In order to avoid the occurrence of the above problem, the present inventors examined a technique for fixing each optical fiber into the corresponding V-shaped groove with solder. However, since the present optical fiber ordinarily has a diameter of about 125 &mgr;m and a gap between the surface of the V-shaped groove and the optical fiber is very small, it turned to be difficult to flow the solder into the V-groove from a terminal end face of the holding substrate and fill it in the V-shaped groove with no void. Therefore, a void in which no solder flows is likely to be formed between the surface of the V-shaped groove and the optical fiber.
The behavior of such a void in the solder within the groove is not clear. The optical fiber-holding structure as referred above is often placed in a principal position in such a state that the holding structure is received in a gas-tight casing or package. Into the receiving casing or package is often charged an inert gas such as nitrogen gas so as to prevent degradation of the optical element such as laser. However, if the package is sealed with such an optical fiber-holding structure itself it was made clear that if the groove is not fully filled with the solder as mentioned above, a void is retained and such a void propagates along the groove over a large distance, the inert gas may leak out along the propagated void inside the groove.
The package as mentioned above in which the optical fiber-holding structure is received is often placed under severe outside environment, so that it may be exposed to a high temperature of 60° C. to a low temperature of −40° C. or may be exposed to desert environment to highly humid environment. Therefore, the package in which the optical fiber-holding structure is placed must operate stably under the above severe surrounding environment for a long time. However, if a void is retained in the solder within the groove as mentioned above, air remaining in the void is repeatedly expanded and shrunk or moisture may enter the void. This sometimes makes the fixing location of the optical fiber slightly change. If the fixing location of the optical fiber changes, its optical axis deviates even in the case that such a change is slight. Consequently, the coupling loss increases or changes.
SUMMARY OF THE INVENTION
In a holding structure in which an optical transmitting member such as an optical fiber is fixed at a given location, it is an object of a first aspect of the present invention to assuredly fix an optical transmitting member into a fixing groove with use of solder while making it difficult for a gap to be formed between the optical transmitting member and the surface of the groove.
The first aspect of the present invention relates to a method for producing an optical transmitting member-holding structure in which an optical transmitting member is held and fixed at its given location on a holding substrate, said process comprising the steps of: (1) preparing the holding substrate provided with a groove for receiving and fixing the optical transmitting member onto the holding substrate, (2) placing the optical transmitting member within the groove, (3) placing a sheet of solder over the groove and the optical transmitting member, (4) heating the resulting assembly under application of pressure upon the solder sheet in a direction toward the groove, (5) flowing the solder into a gap between a surface of the groove and the optical transmitting member and charging the solder there; and (6) thereby fixing the optical transmitting member at the given location. In the above, “an optical transmitting member” means at least one optical transmitting member according to the first aspect of the present invention.
The present inventors contrived the technical idea that if the optical transmitting member is placed in the groove, then a sheet of solder is placed over and/or on the groove and the optical transmitting member, and the solder is flown into and changed into the gap between the surface of the groove and the optical transmitting member by heating the resulting assembly under application of pressure upon the solder sheet in a direction toward the groove. During the heating/pressurizing step, the solder sheet is crushed to flow preferentially into the groove and fill the gap between the optical transmitting member and the surface of the groove while the optical transmitting member itself is strongly pressed against the surface of the groove, and fixed at its given location. Thereby, the inventors succeeded in minimizing the deviation of the optical transmitting member from the given location and also in minimizing the gap between the surface of the groove and the optical transmitting member. By so doing, the inventors succeeded in putting into practical use the optical transmitting member-holding structure in which the optical transmitting member is fixed in the groove with the solder.
During the examination of the fixing the optical transmission member into the V-shaped groove of the holding substrate, the present inventors further noted the following problem from another point of view. As mentioned above, the optical fiber-holding structure is often placed in a principal position in such a state that the holding structure is received in a gas-tight casing or package. Into the receiving casing or package is often charged an inert gas such as nitrogen gas so as to prevent degradation of the optical element such as laser.
However, when the package is sealed with the optical fiber-holding structure itself and nitrogen is sealingly charged into the package, a very small amount of oxygen is contained in it. Therefore, the solder layer may be oxidized as viewed from a long-term standpoint. Once the solder layer begins to be oxidized, an oxidized portion grows so that an oxidized film is formed at an end face of the optical fiber-holding structure or an array. This oxidized film unfavorably makes transmission loss larger and the amount of light transmitted smaller.
Further, it cannot be basically sa
Fukuyama Masashi
Kurimoto Hironori
Ota Takashi
Burr & Brown
NGK Insulators Ltd.
Sanghavi Hemang
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