JPH0980269A - Optical coupling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the optical coupling device which does not deteriorate in the polarized wave extinction ratio of projection light of a laser diode and obtains a high polarized wave extinction ratio after light passes through a polarization plane maintaining type optical fiber by reducing birefringence caused by optical components by constituting a structure wherein stress resulting from mechanical fixation is hardly applied to optical components such as a lens and an optical fiber. SOLUTION: This device is provided with a lens holder 15 which connects an inside cylinder 15a, where the lens 3 is fixed, and an outside cylinder 15b, mechanically connected to a package 11 holding a laser diode 1 provided at the outer periphery of the inside cylinder and a ferrule holder 9 holding the optical fiber 5 at a weld zone 13 and a weld zone 14, at the center part 15 between the inside cylinder 15a and outside cylinder 15b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling device for coupling the light emitted from a laser diode to a polarization maintaining optical fiber.

[0002]

2. Description of the Related Art FIG. 17 shows, for example, a laser diode hermetically sealed by a package, a lens holding portion in which a lens is held by a lens holder by adhesion, and an optical fiber by an ferrule in which a ferrule chip is press-fitted. FIG. 6 is a configuration explanatory view of a conventional optical coupling device further including a fiber terminal in which a ferrule is held by a ferrule holder with a screw. In the figure, 1 is a laser diode,
Reference numeral 2 denotes the light emitted from the laser diode 1, 3 is a lens, 4 is a lens holder for holding the lens 3, 5 is a polarization-preserving optical fiber, 6 is a core of the optical fiber 5 with the coating removed, and 7
Is a ferrule chip holding the core wire 5, 8 is a ferrule holding the optical fiber 5 into which the ferrule chip 7 is press-fitted, 9 is a ferrule holder holding the ferrule 8, 1
0 is a screw for fixing the ferrule 8 to the ferrule holder 9, 11 is a package, and 12 is outgoing light 2 in the package 1
1 is a window that is taken out of the package 1 to keep the inside of the package 11 airtight, 13 is a welded portion that fixes the package 11 and the lens holder 4, 14 is the lens holder 4 and the ferrule holder 9
It is a welded portion that fixes and.

Next, the operation will be described. The emitted light 2 of the laser diode 1 passes through the lens 3 and the optical fiber 5
Is connected to the core wire 6. As a result, the laser diode 1
The emitted light can be extracted from the optical fiber 5 to the outside.

[0004]

Since the conventional laser diode module is constructed as described above, it has a function of coupling the light emitted from the laser diode to the optical fiber and extracting it to the outside. However, since optical components such as lenses and optical fibers undergo birefringence due to stress due to mechanical fixation, the polarization extinction ratio of the emitted light of the laser diode deteriorates, and high polarization after passing through the polarization-preserving type optical fiber. There was a problem that the wave extinction ratio could not be obtained and the characteristics of the polarization-maintaining optical fiber could not be utilized.

The present invention has been made in order to solve the above problems. In order to reduce birefringence that occurs in optical components such as lenses and optical fibers, stress due to mechanical fixation is applied to the optical components. It is an object to obtain a high polarization extinction ratio after passing through a polarization-maintaining optical fiber without deteriorating the polarization extinction ratio of the light emitted from the laser diode.

[0006]

An optical coupling device according to the present invention comprises an inner tube for fixing a lens, an outer tube for mechanically connecting a lens diode or an optical fiber, an inner tube and an outer tube. And a connecting portion for connecting to each other.

Further, there is provided a cylinder in which the wall thickness of the portion mechanically connected to the laser diode or the optical fiber is thinner than the wall thickness of the portion for fixing the lens.

Further, it is provided with a lens having a disk-shaped flange on the side surface, and a tube for connecting the lens with the flat surface of the flange.

Further, a cylinder for fixing the lens having a coefficient of thermal expansion substantially equal to that of the lens is provided.

Further, the ferrule for fixing the optical fiber and the tube for fixing the ferrule are fixed by removing the position of the circumferential surface of the portion where the coating of the optical fiber is removed.

The ferrule for fixing the optical fiber and the tube for fixing the ferrule are temporarily fixed and then fixed by adhesion.

Further, a ferrule having a thermal expansion coefficient substantially equal to that of the optical fiber is provided.

Further, a polarizer is provided between the lens and the optical fiber.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 to 3 and 5 to 14 are exactly the same as the above-mentioned conventional ones. Reference numeral 15 denotes an inner cylinder 15a for fixing the lens 3 and a laser diode 1 provided on the outer circumference thereof.
And the ferrule holder 9 holding the optical fiber 5 and the outer tube 15b mechanically connected to each other by the welds 13 and 14, and the inner tube 15a and the outer tube 15b. The lens holder is connected at the central portion 15c. A sectional view of the lens holder 15 is shown in FIG.
It was shown to.

The material of the lens holder 15 is selected from, for example, Kovar or SF20T, which have a similar coefficient of thermal expansion when the material of the lens is TaF3. For your reference,
Table 1 shows the coefficient of thermal expansion of the examined materials.

[0016]

[Table 1]

In the optical coupling device constructed as described above, since the lens holder 15 has a double cylinder structure, the welding portion 13 for fixing the package 11 and the ferrule holder 9 are fixed. The mechanical stress from the welded portion 14 is hard to be applied to the inner cylinder 15a, and the birefringence of the lens 3 is reduced. Therefore, since the polarization extinction ratio of the outgoing light 2 is coupled to the optical fiber 5 without deterioration, a high polarization extinction ratio can be obtained after passing through the polarization-maintaining optical fiber 5.

Further, in the above-mentioned conventional method, the fluctuation amount of the polarization extinction ratio before and after welding is about 5 dB deterioration in average value and about 7 dB in standard deviation, whereas in the first embodiment, it is before and after welding. It was confirmed by experiments that the fluctuation amount of the polarization extinction ratio was about 0 dB in average and about 2 dB in standard deviation.

Furthermore, since the coefficients of thermal expansion of the lens 3 and the lens holder 15 are close to each other, both parts expand and contract in an almost equivalent manner even if the ambient temperature fluctuates, and the lens 3 is not distorted. Therefore, a high polarization extinction ratio can be obtained after passing through the polarization-maintaining fiber regardless of the ambient temperature.

In FIG. 3, the material of the lens 3 is TaF3,
The experimental results of the temperature characteristics of the polarization extinction ratio when the lens holder 15 is made of SUS303 having a thermal expansion coefficient of about 3 times that of TaF3 and when it is made of Kovar having substantially the same thermal expansion coefficient are shown. From this, it can be seen that when the lens holder 15 is Kovar, it has better temperature characteristics.

Embodiment 2 FIG. In the first embodiment described above, the lens holder 15 is provided, but a tube 16b having a wall thickness smaller than that of the tube 16a and an outer diameter equal to that of the tube 16a is provided on both bottom surfaces of the tube 16a for fixing the lens 3 shown in FIG. Also in the method of providing the lens holder 16 connected to the package 1,
The mechanical stress from the weld 13 for fixing the lens 1 and the weld 14 for fixing the ferrule holder 9 is less likely to be applied to the lens, and the birefringence of the lens 3 is reduced.
Further, by providing the lens holder 16 with a material having a coefficient of thermal expansion substantially equal to that of the lens 3, temperature characteristics are also improved. Therefore, the same effect as that of the first embodiment can be expected.

Embodiment 3 FIG. Also, the lens 3 shown in FIG.
The inner cylinder 17a for fixing the inner cylinder 17a and the outer cylinder 17a longer than the inner cylinder 17a with one bottom surface aligned,
You may provide the lens holder 17 which connected the other bottom face of a and the outer side cylinder 17 by the connection part 17c.

Embodiment 4 Also, the lens 3 shown in FIG.
An inner cylinder 18a for fixing the inner cylinder 18a and an outer cylinder 18b having the same length as the inner cylinder 18a, and one bottom surface is connected to the connecting portion 18c.
It is also possible to provide the lens holder 18 which is connected to the outer cylinder 18b and is connected to the bottom surface connected to the cylinder 18b, which is thinner than the outer cylinder 18b and has the same outer diameter as the cylinder 18b, by the connecting portion 18c.

Embodiment 5 In addition, the lens 3 shown in FIG.
The inner cylinder 19a for fixing the inner cylinder 19a and the outer cylinder 19b having the same length as the inner cylinder 19a are connected at one bottom surface to the connecting portion 19c.
Connected to the lens holder 19 and a cylindrical second outside of the lens holder 19.
The holder 20 of the lens holder 1 is provided as shown in FIG.
9 and the second holder 20 may be fixed to each other by the welded portion 21, and the second holder 20 may be fixed to the package 11 and the ferrule holder 9.

Embodiment 6 FIG. In addition, in the fifth embodiment, the lens holder 22 in which the tube 22a for fixing the lens 3 shown in FIG. Good.

Embodiment 7 Further, as shown in FIG. 10, a lens 2 provided with a disk-shaped flange on the side surface of which the material is the same as that of the body.
3 and the lens holder 24 for connecting the lens 23 by adhesion with the flat surface of the collar, the lens 23
The birefringence of is reduced. In addition, the temperature characteristics are also improved by using a material whose coefficient of thermal expansion is substantially the same as that of the lens 23 for the lens holder 24. Therefore, the same effect as that of the first embodiment can be expected.

FIG. 11 is a perspective view of the lens 23, and FIG. 12 is a sectional view of the lens holder 24.

The lens holder 17 of the third embodiment, the lens holder 18 of the fourth embodiment, the lens holder 19 of the fifth embodiment, the lens holder 22 of the sixth embodiment and the lens holder 24 of the seventh embodiment are You may insert in the direction of the emitted light 2.

Embodiment 8 As shown in FIG. 13, the ferrule 8 is provided with a ferrule holder 25 having a screw hole so that the ferrule 8 can be fixed by removing the position of the core wire 6 of the optical fiber 5, that is, the position of the ferrule tip 7, and the screw 1
In the method of fixing with 0, the axial force of screw fixing is hard to be applied to the core wire 6, and birefringence is reduced. Therefore, the outgoing light 2 coupled to the optical fiber 5 maintains a high polarization extinction ratio, and after passing through the optical fiber 5, a high polarization extinction ratio can be obtained.

FIG. 14 shows a configuration including an optical fiber 5 having a core wire 6 with a diameter of 125 μm, a ferrule tip 7 having an outer diameter of 1.4 mm and a length of 2.5 mm, and a ferrule 8 having an outer diameter of 3 mm. , When fixing the axial direction rotated 45 degrees from the axis (generally called the slow axis) of the stress imparting portion of the polarization-preserving type optical fiber 5 with the M1.6 screw with the screw tightening torque of 400 gf · m. Ferrule chip 7
The relationship between the distance from the end face to the screw and the polarization extinction ratio is shown. From this, it is understood that it is necessary to remove the position of the ferrule chip 7 and fix it in order to set the polarization extinction ratio to 20 dB or more.

Further, for example, when the material of the optical fiber is quartz glass, the ferrule tip 7 and the ferrule 8
If the material is selected from quartz glass and super invar, which have similar thermal expansion coefficients, the temperature characteristics of the polarization extinction ratio can be improved. For reference, Table 2 shows the thermal expansion coefficients of the examined materials.

[0032]

[Table 2]

In the eighth embodiment, the ferrule 8
The ferrule holder 25 and the ferrule holder 25 may be fixed by welding.

Embodiment 9 Further, in the conventional optical coupling device shown in FIG. 17, even after temporarily fixing with the screw 10 and then fixing the core wire 6 by adhesion or the like so that mechanical stress is not applied, the same effect as that of the eighth embodiment is obtained. Can be expected.

FIG. 15 shows a structure including an optical fiber 5 having a core wire 6 having a diameter of 125 μm, a ferrule tip 7 having an outer diameter of 1.4 mm, and a ferrule 8 having an outer diameter of 3 mm.
The relationship between the tightening torque of the screw and the polarization extinction ratio when an arbitrary position is fixed with the M1.6 screw 10 is shown. From this, it is understood that the temporary fixing needs to have a tightening torque of 50 gf · cm or less in order to set the polarization extinction ratio to 20 dB or more.

In the eighth and ninth embodiments, the case where the ferrule chip 7 and the ferrule 8 are provided has been described. However, the same effect is expected even when the ferrule chip and the ferrule are integrated. it can.

Embodiment 10 FIG. In addition, as shown in FIG. 16, by providing a polarizer 26 between the lens 3 and the optical fiber 5 in the first embodiment, which allows only the light vibrating in a specific direction to pass, the outgoing light 2 that has passed through the lens 3 is transmitted. Since it has a high polarization extinction ratio after passing through the polarizer 26 and is coupled to the optical fiber 5 regardless of the state of polarization, it is possible to obtain a high polarization extinction ratio after passing through the polarization-maintaining optical fiber 5. it can.

By the way, in the above description, the case of the optical system using one lens is shown, but the same effect can be expected in the optical system using two lenses.

In the above description, the case where the laser diode is used as the optical semiconductor element has been described.
It can be diverted to the case where other semiconductor elements are used.

Further, in the above description, the transmission system for transmitting the output light of the laser diode through the lens and the optical fiber is shown as an example, but this may be applied to the receiving system (optical fiber, lens, light receiving element). .

Further, in the optical coupling devices of the eighth and ninth embodiments, the lens holders of the first, second, third, fourth, fifth and fifth embodiments are used.
It was experimentally obtained that the polarization extinction ratio is higher than that of the optical coupling devices of the first to sixth embodiments by using the lens holder of No. 6.

[0042]

Since the present invention is configured as described above, it has the following effects.

Since the stress due to the mechanical fixing to the lens holder or the ferrule holder is less likely to be applied to the lens, the birefringence of the lens is reduced, and the light emitted from the light emitting element (or the light incident on the light receiving element) is polarized. It can be coupled to an optical fiber (or a light receiving element) without deteriorating the wave extinction ratio, and a high polarization extinction ratio can be obtained after passing through a polarization-preserving optical fiber.

Further, since the stress due to the mechanical fixing of the ferrule to the ferrule holder is less likely to be applied to the core of the optical fiber, the birefringence of the optical fiber is reduced and the optical semiconductor element coupled to the optical fiber is reduced. The outgoing light or the incident light maintains a high polarization extinction ratio, and a high polarization extinction ratio can be obtained after passing through the polarization-preserving optical fiber.

Further, the temperature characteristics of the polarization extinction ratio can be improved by making the coefficients of thermal expansion of the lens and the lens holder, the core of the optical fiber, and the ferrule chip uniform.

Further, since the polarizer is inserted between the lens and the optical fiber, the light emitted from the optical semiconductor element passes through the polarizer and has a high polarization extinction ratio. Therefore, after passing through the polarization-preserving type optical fiber. A high polarization extinction ratio can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens holder 15.

FIG. 3 is a diagram showing a temperature characteristic of a polarization extinction ratio.

FIG. 4 is a sectional view of a lens holder 16 showing Embodiment 2 of the present invention.

FIG. 5 is a sectional view of a lens holder 17 showing Embodiment 3 of the present invention.

FIG. 6 is a sectional view of a lens holder 18 showing a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a lens holder 19 showing a fifth embodiment of the present invention.

FIG. 8 is a configuration diagram of a fifth embodiment of the present invention.

FIG. 9 is a sectional view of a lens holder 22 showing a sixth embodiment of the present invention.

FIG. 10 is a configuration diagram of a seventh embodiment of the present invention.

FIG. 11 is a perspective view showing a lens 23 according to Embodiment 7 of the present invention.

FIG. 12 is a lens holder 2 according to a seventh embodiment of the present invention.
FIG.

FIG. 13 is a configuration diagram of an eighth embodiment of the present invention.

FIG. 14 is a diagram showing the relationship between the distance from the end face of the ferrule chip 7 and the polarization extinction ratio.

FIG. 15 is a diagram showing the relationship between the tightening torque of the screw 10 and the polarization extinction ratio.

FIG. 16 is a configuration diagram of a tenth embodiment of the present invention.

FIG. 17 is a configuration diagram of a conventional laser diode module.

[Explanation of symbols]

1 laser diode, 2 emitted light, 3 lens, 5
Optical fiber, 6-core wire, 7 ferrule tip, 8 ferrule, 10 screw, 15 lens holder, 16 lens holder, 17 lens holder, 18 lens holder, 19 lens holder, 20 second holder, 22
Lens holder, 23 lens, 24 lens holder, 2
5 ferrule holders, 26 polarizers.

Claims (10)

[Claims] 1. An optical semiconductor element, a polarization-maintaining optical fiber, a lens for optically coupling the optical semiconductor element and the optical fiber, and an inner tube for fixing the lens,
An optical coupling device comprising: an outer cylinder for mechanically connecting the optical semiconductor element and the optical fiber; and a lens holder having a connecting portion for connecting the inner cylinder and the outer cylinder. 2. An optical semiconductor device, a polarization-maintaining optical fiber, a lens for optically coupling the optical semiconductor device and the optical fiber, and the semiconductor device and the optical fiber are mechanically connected. An optical coupling device, comprising: a lens holder having a cylinder whose thickness is smaller than that of a portion for fixing the lens. 3. An optical semiconductor element, a polarization-maintaining optical fiber, a lens provided with a collar on a side surface for optically coupling the optical semiconductor element and the optical fiber, and a flat surface of the collar for the lens. And an optical coupling device having a lens holder having a tube to be connected with. 4. The optical coupling device according to claim 1, wherein the thermal expansion coefficient of the cylinder for fixing the lens is substantially equal to the thermal expansion coefficient of the lens. 5. An optical semiconductor device, a polarization-maintaining optical fiber, a lens for optically coupling the optical semiconductor device and the optical fiber, a ferrule for fixing the optical fiber, and a machine for the ferrule. The optical coupling device comprises: a cylindrical tube that is fixedly fixed; and a fixing unit that fixes the ferrule and the cylindrical tube at a position where the circumferential surface of the portion where the coating of the optical fiber is removed is removed. 6. An optical semiconductor device, a polarization-maintaining optical fiber, a lens for optically coupling the optical semiconductor device and the optical fiber, a ferrule for fixing the optical fiber, and a machine for the ferrule. The optical coupling device comprises: a tube for mechanically fixing the ferrule; and a fixing means for temporarily fixing the ferrule and the tube and then fixing by adhesion. 7. The optical coupling device according to claim 5, wherein the coefficient of thermal expansion of the ferrule is substantially equal to the coefficient of thermal expansion of the optical fiber. 8. The optical coupling device according to claim 1, further comprising a polarizer inserted between the lens and the optical fiber. 9. A lens comprising an inner tube for fixing the lens, an outer tube for mechanically connecting the optical semiconductor element and the optical fiber, and a connecting portion for connecting the inner tube and the outer tube. The optical coupling device according to claim 5, further comprising a holder. 10. A lens holder having an outer cylinder for mechanically connecting the optical semiconductor element and the optical fiber, and an inner cylinder having a thickness larger than that of the outer cylinder and for fixing the lens. The optical coupling device according to claim 5 or 6.