Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-07-21
2002-08-20
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S088000
Reexamination Certificate
active
06435736
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical device such as a laser diode module used for optical transmissions, and a method for manufacturing the same.
BACKGROUND OF THE INVENTION
Conventionally, a laser diode module has been used for optical transmissions. The laser diode module is such that a laser diode (LD) element for transmitting light and optical fibers for propagating light from the laser diode element are optically coupled in advance, and these are composed as a module. FIG.
4
A and
FIG. 4B
show one example of a laser diode module in a sectional view.
The laser diode module shown in the same drawings has a metal-made package
9
. A laser diode element
1
is disposed and fixed at the fixing portion of a base
10
fixed in the package
9
via a heat sink
11
. Also, the tip end side of a lensed fiber
2
having a lens
3
formed at the tip end side of the optical fiber is inserted from an insertion portion
20
secured at the sidewall of the package
9
into the package
9
. The tip end side (the attached portion of the lens
3
) of the lensed fiber
2
is aligned with the light emitting portion of the laser diode element
1
and is opposed thereto. That is, the laser diode element
1
and lensed fiber
2
are opposed to each other and disposed so that the excitation efficiency (optical coupling efficiency) between the laser diode element
1
and the lensed fiber
2
is maximized.
Also, the package
9
is such that, for example, the bottom plate
22
thereof is made of CuW, and the other portions thereof are made of an Fe—Ni—Co based alloy represented by KOVAL (Trade name).
The first ferrule
5
is fixed on the base
10
via ferrule retaining portion
16
and
17
, and the tip end side of the lensed fiber
2
is inserted into and fixed at the first ferrule
5
, and the second ferrule
6
is provided at the rear end side of the first ferrule
5
with a spacing, wherein the intermediate portion of the lensed fiber
2
is inserted into and fixed at the second ferrule
6
. The second ferrule
6
is inserted into the insertion portion
20
of the package
9
. The second ferrule
6
is fixed at the sidewall of the package
9
via a ferrule fitting portion
15
provided at the package
9
.
Metal is plated on the surface of the lensed fiber
2
between the first ferrule
5
and the second ferrule
6
. One end side of the metal plated portion
4
is fixed at the second ferrule
6
by soldering
8
, and the second ferrule
6
is fixed at the ferrule fitting portion
15
by soldering
7
. By the metal plate portion
4
of the lensed fiber
2
being fixed at the second ferrule
6
by soldering and the second ferrule
6
being fixed at the ferrule fitting portion
15
by soldering, the package
9
can be kept hermetic.
The first ferrule
5
is fixed at the ferrule retaining portions
16
and
17
by, for example, YAG laser welding, etc. Also, a monitor photo diode
13
is fixed on the base
10
, and a Peltier element module
12
is fixed at the lower side of the base
10
. The Peltier module
12
is provided with a Peltier element to keep the temperature of the laser diode element
1
at a fixed level.
As described above, if the laser diode module is constructed by using such a lensed fiber
2
, there is an advantage in that the composition of parts can be simplified to reduce production costs. Also, by optimizing the shape of the lens
3
of the lensed fiber
2
, the laser diode module having the abovementioned lensed fiber
2
can increase the optical coupling efficiency between the lensed fiber
2
and the laser diode element
2
remarkably. Thus, a laser diode module having very high optical coupling efficiency, which is provided with a lensed fiber
2
, is an excellent laser diode module.
Further, in a prior art laser diode module thus constructed, as shown in
FIG. 4A
, the laser diode module is formed so that no deflection arises in the lensed fiber
2
between the first ferrule
5
and the second ferrule
6
at a temperature (for example, 25° C.) for producing the laser diode module.
OBJECTS AND SUMMARY OF THE INVENTION
In order to secure reliability of a laser diode module, at an environmental temperature where the laser diode module is used, it is desirable that no breakage, etc., of the lensed fiber
2
occurs. At present, the temperature at which the laser diode module is used is generally from 0° C. through 75° C. Also, taking various climatic conditions into consideration, the environmental temperature at which the laser diode module is kept in custody will become −40° C. through 85° C. Therefore, the environmental temperature at which the laser diode module is used will be from −40° C. through 85° C. In this temperature range, a laser diode module having no breakage or interruption of the lensed fiber
2
is requested.
However, since a metal-made package
9
has a larger thermal expansion coefficient than a lensed fiber
2
made of a glass-based material, it is liable to expand due to heat. Accordingly, as the environmental temperature for use rises, the distance between the first ferrule
5
and the second ferrule
6
varies and increases. And, as the environmental temperature where the laser diode module is used becomes higher than the production temperature, the distance between the first ferrule
5
and the second ferrule
6
becomes large as shown in FIG.
4
B. On the other hand, the thermal expansion coefficient of the lensed fiber
2
is very slight in comparison with that of the package
9
, and it hardly changes due to changes in the abovementioned environmental temperature for use. Therefore, a tensile stress is applied to the lensed fiber
2
fixed between the first ferrule
5
and the second ferrule
6
.
Further, as described above, since an optical fiber such as a lensed fiber
2
is made of a glass-based material, and is very weak to tensile stress, in prior art laser diode modules, a problem such as breakage arises in the lensed fiber
2
due to a tensile stress applied onto the lensed fiber
2
in high temperatures. Further, instead of breakage of the lensed fiber
2
, such trouble occurs, in which the lensed fiber
2
is separated from the first ferrule
5
or the second ferrule
6
at the fixing portion. Such breakage of the lensed fiber
2
or the problem of separation at the fixing portion may damage the reliability of a laser diode module, and these were critical problems.
The present invention was developed in order to solve such problems in the prior arts, and it is therefore an object of the invention to provide an optical device such as a laser diode module, having high reliability, in which no break occurs in an optical fiber at an environmental temperature for use, and optical fibers are not separated from the ferrules at the fixing portion, and a method for producing the same.
In order to achieve the abovementioned object, the present invention employs the following construction as the means for solving the problems. That is, an optical device according to the first aspect of the invention is featured in that the first ferrule in which an optical fiber is inserted and fixed is fixed in a package formed of a material having a larger thermal expansion coefficient than that of the optical fiber, the second ferrule in which the optical fiber is inserted and fixed is fixed in the package at a position spaced from the first ferrule in the lengthwise direction of the optical fiber, and the distance between the first ferrule and the second ferrule varies and increases as the environmental temperature for use of the optical device rises, wherein the optical device is provided with a tensile stress suppressing means which can prevent a tensile stress exceeding a specified allowable range from being applied to an optical fiber between the first ferrule and the second ferrule at the upper limit of the environmental temperature for use.
An optical device according to the second aspect of the invention is featured in that, in addition to the first aspect, a means for preventing the above tensile stress from being
Irie Yuichiro
Miyokawa Jun
Shimizu Takeo
Knauss Scott A
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sanghavi Hemang
The Furukawa Electric Co. Ltd.
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