JPH0361927B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor laser coupling device in which a semiconductor laser and an optical fiber are stably coupled using a ball lens.

(Prior Art) In the optical fiber communication system, it is necessary to develop a semiconductor laser coupling device that efficiently couples the light of a semiconductor laser to an optical fiber. In particular, when considering the introduction of such devices into subscriber systems, it is necessary to develop an LD coupling device that can simplify the manufacturing process and reduce costs.

In conventional devices of this kind, when coupling a semiconductor laser, such as a laser diode (hereinafter also abbreviated as LD), to an optical fiber, the core diameter of the optical fiber is as small as 50 μm or less, so a fine movement table or the like is required. It is necessary to perform fine positioning by using the machine, and after the positioning is completed, each part must be fixed with adhesive, etc., which takes a long time to assemble and reduces manufacturability and yield. This made it difficult to reduce costs.

This type of conventional device is shown in Figures 1, 2 and 3.
As shown in the figure.

In the LD coupling device shown in FIG. 1, an LD, that is, a laser chip 1, is fixed onto a protrusion 2A of an LD package stem 2, and power is supplied to the laser chip 1 from an electrode 3. A ball lens holding member 4 is fixed to the projection 2A, and the ball lens 5 is adjusted and fixed to a predetermined position on the holding member 4. A cap 6 with a glass window is placed over the stem 2 so as to cover the laser chip 1 and the ball lens 5, and its edges 6A and 6B are fixed to the stem 2 by welding, thereby airtightly sealing the inside of the cap 6. 7 is a window glass for airtight sealing fixed to a window 6C made in the cap 6.

Furthermore, the self-cleaning lens holding member 8 is placed over the cap 6 so as to cover the same. The holding member 8 has a hole 8C that runs through the hole 8C facing the window 6C, and a self-cleaning lens 9 is inserted into the hole 8C and fixed with an adhesive. End portion 8A of holding member 8
and 8B are fixed to the stem 2 with adhesive after adjusting the package stem 2 with respect to the holding member 8 so that the optical axes of the ball lens 5 and the self-occurring lens 9 are aligned.

The ferrule 10 is fixed to the through hole 11A of the ferrule support member 11. The ferrule 10 is fitted with a fiber coating 13 from which the fiber cord 12 of the optical fiber is removed. The tip of the fiber coating 13 is removed to expose the optical fiber strand 14. The ferrule support member 1 is placed so that the tip of the optical fiber 14 faces the self-occurring lens 9, and the end surface of the optical fiber 14 is located at the optical axis of both and at the convergence position of the light emitted from the self-occurring lens 9.
1 with respect to the self-cleaning lens support member 8, and then both members 8 and 11 are fixed with adhesive. 15 is an optical fiber support member.

In this example, a ball lens 5 is mounted inside the package stem 2 to take out the laser beam from the LD 1 as a parallel beam, and a self-occurring lens 9 as a second lens converges it into the optical fiber 14. This is an LD coupling device developed for optical fiber.

When assembling this LD coupling device, first,
The ball lens 5 is adjusted and fixed at a predetermined position on the package stem 2, and then the LD package stem 2 is combined with the holding member 8 to which the self-occurring lens 9 of the second lens is attached and the support member 11 to which the ferrule 10 is inserted. The optical axes of each component are adjusted in the X, Y, and Z directions using a fine movement table as shown by the arrows in the figure to achieve an optimal bonding state, and then each component is mounted and fixed.

As is clear from FIG. 1, this device has many parts, so there are many adjustment points, making it difficult to simplify the assembly process. Furthermore, since each component is fixed with adhesive, the optical axis is likely to be misaligned during assembly, and furthermore, it takes time to manufacture.

FIG. 2 shows a second conventional example, in which a first holding member 22 is welded and fixed to a package stem 21 to which a laser chip 1 is fixed to a protrusion 21A. A second holding member 23 is attached to this first holding member 22 through indium 24 in an airtight manner. Second
The holding member 23 has a window 25 facing the laser chip 1.
A hermetic sealing window glass 26 is fixed to this window 25. The ball lens 5 is fixed onto this window glass 26 with an adhesive. A ferrule 27 is fixed to cover the window 25 with adhesive. This ferrule 2
7, the optical fiber wire 14 from which the fiber coating 13 has been stripped is inserted. The optical fiber sheath 13 is supported on an optical fiber support member 28 and the support member 28 is fixed to the first holding member 22 .

In this example, two holding members 22 and 23 constitute a ball lens holding member in order to adjust the position of the ball lens 5 attached to the window glass 26 in the optical axis direction.
Therefore, while monitoring the optical output, the relative positions of the LD package stem 21 and the ball lens holding members 22 and 23 are optimally adjusted in the X, Y, and Z directions, and the second holding member 23 is attached to the first holding member 22. . The whole is then fixed to the package stem 21. In this example, there is no self-cleanse, so
Adjustment for making the output light of the ball lens 5 enter the optical fiber 14 is difficult, and the number of parts and adjustment points are large, resulting in poor assembly work efficiency and manufacturing yield. Furthermore, since the distance between the LD 1 and the microball lens 5 is narrow, mounting accuracy is difficult, and there is a risk that the LD chip 1 may be damaged due to contact with the microball lens 5.

FIG. 3 shows a third conventional example. In this example, a laser chip 1 is placed on a protrusion 31A of an LD package stem 31, and an electrode 3 is mounted on this laser chip 1.
Power is supplied from 2. The ball lens 5 is fixed with adhesive to the tip of a ball lens holding member 33 made of a glass tube, and this holding member 33 is attached to an optical fiber support member 34.
The optical fiber support member 34 is inserted into the through hole 34A drilled in the stem 31, and the optical fiber support member 34 is adjusted as shown by the arrow with respect to the stem 31 so that the ball lens 5 faces the laser chip 1. stick.
The optical fiber 14 is inserted into the glass tube serving as the ball lens holding member 33, and the optical fiber 14 is adjusted with respect to the holding member 33 as shown by the arrow to remove the ball lens 5.
so that the output light from the optical fiber 14 is focused onto the opposite end face of the optical fiber 14.

Here, the microsphere lens 5 and the optical fiber 14 are integrated with a holding member 33 made of a glass tube, and by setting the ball lens 5 to be slightly larger than the inner diameter of the glass tube 3, the optical axis of both can be adjusted. It can be fixed automatically in a matching state. However, since the ball lens 5 is close to the end face of the LD chip 1,
Mounting accuracy is difficult. Further, since adhesive is used to secure the ball lens 5 and the holding member 33, and the stem 31 and the support member 34, the LD chip 1 is not completely hermetically sealed. In addition,
Since the ball lens holding member 33, which also functions as a guide for the optical fiber 14, becomes long, there are drawbacks such as the fiber supporting member 34 becoming large in size.

(Objective) Therefore, in order to eliminate the above-mentioned drawbacks, an object of the present invention is to reduce the number of parts and adjustment points by using a spherical lens with relatively large external dimensions that also serves as an airtight sealing window. An object of the present invention is to provide a semiconductor laser coupling device that can shorten manufacturing time and reduce the cost of the device.

(Structure of the Invention) In order to achieve the above object, the present invention has a package stem in which a semiconductor laser element is disposed, and a lens in the form of a cylindrical cap is provided on the package stem to cover the semiconductor laser element. A holding member is fixed, thereby hermetically sealing the semiconductor laser element within the lens holding member, a hole is formed in the center of the upper surface of the lens holding member, and a ball lens is seated and fixed in the hole. The ball lens is arranged to face the semiconductor laser element so that its optical axis coincides with the optical axis of the laser beam from the semiconductor laser element, and the ferrule with the optical fiber attached thereto is inserted into the ferrule support member. and attaching the ferrule support member to the package stem so that the end face of the optical fiber faces the ball lens, and the ferrule support member covers the lens holding member,
The ferrule support member is moved and adjusted relative to the package stem so that the optical axis of the optical fiber coincides with the optical axis of the spherical lens, and the output light from the spherical lens is focused on the end face of the optical fiber. After adjusting the movement of the ferrule with respect to the ferrule support member, the ferrule support member is fixed to the package stem, and the laser beam from the semiconductor laser element is directed to the optical fiber through the ball lens. Configure to guide.

Here, it is preferable that the outer circumferential surface of the ball lens is metallized into a band shape, and the band-shaped metallized portion is seated in the hole of the lens holding member and brazed.

Further, the lens holding member may be fixed to the package stem by welding.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 4 shows one embodiment of the invention, where 4
1 is a package stem, 41A is a protrusion thereof, and the laser chip 1 is placed and fixed on this protrusion 41A. 42 is the base of the stem 41;
A stem 41 is fixed to this base 42. 43 is a ball lens holding member in the form of a cylindrical cap fixed to the package stem 41 so as to cover the laser chip 1, and a coupling ball lens 44 is seated in a window 43A formed on the central axis of this holding member 43. The ball lens 44 receives the laser output light from the laser chip 1, and the window 43A is hermetically sealed. Further, a ferrule support member 45 in the form of a cylindrical cap is attached to the base 42 so as to cover the ball lens holding member 43.
sticks to. The ferrule support member 45 is provided with a protruding tube portion 45A through which the cylindrical ferrule 46 passes. The ferrule 46 is fixed to the protruding tube portion 45A of the support member 45 with an adhesive, and the optical fiber coating 13 and the optical fiber wire 14 are attached to the ferrule 46.

As the diameter of the ball lens 44 increases, the coupling efficiency generally deteriorates, but the mounting accuracy of the ball lens 44 becomes looser. More specifically, the diameter of the spherical lens 44 is determined by considering both the coupling efficiency to the optical fiber 14 and the C/N (carrier-to-noise ratio) characteristics of the LD chip 1 when there is reflection from the surface of the spherical lens 44. It is necessary to decide together.

FIG. 5 shows the distance d [μ
m] and C/N [dB] using the signal frequency
Using light modulated with an analog signal of 100 MHz, frequency bandwidth 4 MHz, and modulation depth 0.1, the ball lens 44
A case is shown in which a ball lens 44 with a diameter of 2 mm and a reflectance of 0.077 is used. From this C/N characteristic,
It can be seen that the distance d is required to be approximately 500 μm or more.

Figure 6 shows the above distance d [μm] and coupling efficiency [dB].
This shows the relationship with the diameter of the ball lens 44 as a parameter, and the measurement results when the diameter of the ball lens 44 is 1.0, 2.0, 3.2 and 4.8 [mm] are shown by ×, ●, ○, and △ marks. . Note that when the distance d was changed, the position of the end face of the optical fiber 14 was shifted to the position where the efficiency was highest, and measurements were taken. Considering this result and the result in Fig. 5, the interval d is
It can be seen that it is preferable to set the diameter to about 500 to 600 μm, and to set the diameter of the ball lens 44 to about 2 mm.

Here, we will discuss mounting accuracy using a 2 mm diameter Sapphire spherical lens as an example. In this case, the optical fiber 14 is a multimode optical fiber (with a core diameter of
50 μm), a maximum coupling efficiency of approximately −4 dB was obtained. According to coupling experiments, the permissible amount of axis misalignment for which this value deteriorates by 0.5 dB is ±100 μ in the direction perpendicular to the optical axis.
m, ±0.5 mm in the optical axis direction. Furthermore, the fixing accuracy of the optical fiber was relatively strict at ±10 μm in the direction perpendicular to the optical axis, and ±100 μm in the direction of the optical axis. When actually developing an LD coupling device,
It is necessary to have a structure that allows the coupling system to be manufactured easily and in a short time with the above-mentioned precision, and to fix each part.

In the present invention, in order to satisfy such requirements, the configuration is as described above, but here, the coupling ball lens 44
The outer periphery of the lens can be preliminarily metallized into a band-like shape, and then fixed to the hole 43A formed in the center of the cylindrical ball lens holding member 43 by brazing.
This holding member 43 is made of the same shape and material as a normal LD package cap, and can be hermetically sealed to the stem 41 of the LD package by resistance welding. Therefore, the lens 44 attached to the holding member 43 functions both as a package window and as a lens.

Here, the inner diameter of the holding member 43 is equal to the outer diameter of the convex stepped portion 41B provided on the package stem 41.
By processing the holding member 43 so that it can be fitted with a clearance of 0.05 mm or less, the eccentricity of the holding member 43 with respect to the package stem 41 can be set to 25 μm or less and fixed. Therefore, the misalignment between the ball lens 44 and the LD 1 in the direction perpendicular to the optical axis is caused by the eccentricity of the LD chip 1 with respect to the package stem 41 and the holding member 4 of the ball lens 44.
It is almost determined by the eccentricity relative to 3. The eccentricity of the LD chip 1 is generally about ±100 μm, and the eccentricity of the ball lens 44 is within ±60 μm.
When the holding member 43 is fitted into the LD package stem 41 and resistance welding is performed, the worst value of the axis deviation of the ball lens 44 is estimated to be about 180 μm. This value is
If we allow about 1 dB of coupling efficiency deterioration, we can be satisfied. In order to reduce this eccentricity to less than the eccentricity of the chip, it is sufficient to simply rotate the ball lens holding member 43 with respect to the stem 41. On the other hand, the tolerance for the distance between the LD chip 1 and the ball lens 44 is ±
It is large enough at 0.5mm, so it is suitable for package stem 4.
1 and the machining accuracy of the ball lens holding member 43, the deterioration can be suppressed to almost no level.

Next, fixing of the optical fiber 14 will be explained. The optical fiber 14 is inserted into a ferrule 46 whose outer and inner diameters are finished with an accuracy of within a few μm, and is fixed with an adhesive. The ferrule support member 45 has a cap-like structure similar to the ball lens holding member 43, and has an outer diameter of the ferrule 46.
An insertion hole having a clearance of 0.01 mm or less is provided by the tube portion 45A. When adjusting the position of the ferrule 46, the vertical direction of the optical axis is adjusted by moving the ferrule support member 45 into which the ferrule 46 is inserted in close contact with the base 42 as shown by the arrow within its contact surface. At the same time, by sliding the ferrule 46 within the tube portion 45A of the holding member 45, the optical axis direction is also adjusted to set the optimum coupling state. The support member 45 is then temporarily fixed to the base 42 using instant adhesive or the like.
As a result, the support member 45 can be easily resistance welded to the stem base 42 similarly to the can seal. According to the measured data, the axis misalignment due to resistance welding in that case is within ±10 μm, so it can be seen that there is almost no deterioration in the coupling efficiency. Finally, the ferrule 46 is completely fixed to the tube portion 45A using a strong adhesive. With this configuration, it is only necessary to adjust the position of the ferrule holding member 45, so the number of manufacturing steps is small and the manufacturing time is also extremely short. As described above, the support member 45 is attached to the base 4.
By temporarily fixing them to 2, there is an advantage that it is not necessary to provide a jig for holding both in a predetermined position.

Note that the fixing in the present invention is not limited to fixing by resistance welding as shown in the above example,
Fusion fixation method using YAG laser, CO ₂ laser,
Metal solder fixation using high frequency heating equipment can also be used. Furthermore, the means for ensuring the airtightness of the ball lens 44 is not limited to the brazing method;
Glass soldering or other methods may also be used. In addition, in the present invention, a ball lens 44 that can provide a large distance d from the LD chip 1 is used as the window instead of an airtight window used in a normal package, so this problem has not been solved in the past for analog optical transmission. The noise characteristics of the LD itself will not deteriorate due to reflection from the airtight window. Therefore, it is also effective as a semiconductor laser coupling device for analog transmission.

(Effects) As explained above, the present invention has a small number of parts, requires only one position adjustment, and can be assembled using a commercially available resistance welding machine. It is extremely easy to manufacture. Therefore, it is expected that the manufacturing yield will be improved and the cost will be significantly reduced, so that it is effective for wide use as an optical subscriber system or a transmission device for consumer use.

[Brief explanation of drawings]

1 to 3 are cross-sectional views showing three examples of conventional devices, FIG. 4 is a cross-sectional view showing one embodiment of the present invention, FIG. 5 is a graph showing measurement results of C/N characteristics, and FIG.
The figure is a graph showing the measurement results of coupling efficiency. (Fig. 1), 1... laser chip (LD), 2...
... Package stem, 2A ... Protrusion, 3 ... Electrode, 4 ... Ball lens holding member, 5 ... Ball lens,
6... Cap with glass window, 6A, 6B... Edge of cap, 6C... Window, 7... Window glass for airtight sealing, 8... Self-cleaning lens holding member, 8
A, 8B... Edge, 8C... Window, 9... Self-cleaning lens, 10... Ferrule, 11... Ferrule support member, 11A... Through hole, 12... Optical fiber cord, 13... Optical fiber coating, 14
... Optical fiber wire, 15 ... Optical fiber support member, (Fig. 2), 21 ... Package stem, 21
A... Protrusion, 22... First holding member, 23... Second holding member, 24... Indium, 25... Window,
26... Hermetic sealing window, 27... Ferrule, 2
8... Optical fiber support member, (Fig. 3), 31...
Package stem, 31A...Protrusion, 32...Electrode, 33...Ball lens holding member, 34...Optical fiber support member, (Fig. 4), 41...Package stem, 41A...Protrusion, 41B...Step Section, 42
... Base, 43 ... Ball lens holding member, 43A
... window, 44 ... ball lens, 45 ... ferrule support member, 46 ... ferrule.

Claims (1)

[Claims] 1. A package stem having a semiconductor laser element arranged thereon, the package stem having an inner diameter such that it fits into a convex step part provided on the package stem so as to cover the semiconductor laser element. A lens holding member in the form of a cylindrical cap machined to a size with a slight clearance from the outer diameter is fixed by welding, thereby hermetically sealing the semiconductor laser element within the lens holding member,
A hole is made in the center of the upper surface of the lens holding member,
A ball lens with a large external dimension whose outer peripheral surface is metallized in a band shape is seated in the hole, the metallized portion is brazed, and the optical axis of the ball lens is aligned with the optical axis of the laser beam from the semiconductor laser element. A ferrule with an optical fiber attached thereto faces the semiconductor laser element and is inserted into the ferrule support member, and the end face of the optical fiber faces the ball lens, and the ferrule supports the ferrule. is attached to the package stem so that the ferrule support member covers the lens holding member, and the ferrule support member is attached to the package stem so that the optical axis of the optical fiber coincides with the optical axis of the spherical lens. The ferrule is adjusted to move relative to the stem, and the ferrule is adjusted to move relative to the ferrule support member so that the output light from the spherical lens is focused on the end face of the optical fiber, and then the ferrule support member is moved to the ferrule support member. 1. A semiconductor laser coupling device, characterized in that the device is fixed to a package stem and guides laser light from the semiconductor laser element to the optical fiber via the ball lens.