JPS6061707A - Optical coupling method - Google Patents

Abstract

PURPOSE:To recuce an allowable axial shift quantity by a small number of lenses, and to raise a reliability and a productivity by stopping down a converging or diverging light emitted from the first lens, into a light incident element formed as one body with the second lens. CONSTITUTION:A spherical lens and a forcusing type rod lens are used for the first lens 4 and the second lens 9, respectively. A distance d0 between the first lens 4 and a light emitting surface 8 of an LD is made larger than a focal distance f1 of the first lens 4, and a slightly stopped-down light generated after emission from the lens 4 is stopped down, for instance, to an optical fiber 2 formed as one body with a rod lens 9 which is shorter than 1/4 pitch. A place to be adjusted is only the lens 9 + the optical fiber 2, and the productivity is raised remarkably. Also, a set shift of the lens 4 is comparatively small, therefore, the deterioration of a coupling efficiency caused by an angle shift which is left after correcting a position shift by moving the lens 9 + the optical fiber 2 in parallel is small, and when it is desired to correct, it is executed by inclining the lens 9 + the optical fiber 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical coupling method that efficiently couples light from a light output element to a light input element with good productivity.

As a coupling method to efficiently couple the light emitted from a semiconductor laser to a single mode optical fiber, it is coupled using two lenses (al Conventional confocal compound lens system, coupled using three lenses (bl tJ There is a two-lens split type confocal compound lens system. Fig. 1 and Fig. 4, which will be described later, show the respective combination systems.

FIG. 1 (At indicates the method of (a) above, in which two lenses 4.5 with different focal lengths are arranged between the semiconductor laser 1 and the single mode optical fiber 2, and the light from the semiconductor laser 1 is is incident on the incident end of the core 8 of the optical fiber 2.In addition, by attaching a glass plate 7 having a similar refractive index to the optical fiber core 8 to the incident end of the optical fiber 2, the The reflected light is reduced.

FIG. 1(B) shows the configuration of the K-scale lens system shown in FIG. 1(A). In the figure, 8 indicates the light emitting surface of the semiconductor laser, and 6 indicates the direction of the input end of the single mode optical fiber. The second lens 4 is separated from the light emitting surface 8 of the semiconductor laser by approximately the focal length f of the second lens 5, and the distance between the second lens 5 (focal length f) and the second lens 4 is the sum of their focal lengths. (f
+f2), and the position 6 of the optical fiber entrance plane is the second
Lens 5 and f.

is far away.

When such a lens system is used, the emission diameter (spot size) 2ivo of the semiconductor laser is expanded by the focal length ratio (f, /f1) of the lens system, and the spot size is increased at position 6 of the optical fiber entrance plane. The diameter of 2Wg is 2w, =:2
Form an image of woX (fB/fz). Therefore, when the diameter of the guided light beam of the optical fiber is 2wf, wf and w2
It is only necessary to choose f, /f, so that they are approximately equal.

Next, the axis deviation characteristics of the conventional confocal compound lens system will be explained. To manufacture a semiconductor laser module, first align the first lens 4, then align the second lens 5, and use these lens systems.

This allows matching with the fiber by beam conversion.

No matter what kind of lens system is used for the second lens 4 and the second lens 5, the fixing accuracy of the optical fiber will be equivalent to the connection characteristics of single mode optical fibers.

In FIG. 2, when a semiconductor laser with a spot size of 1 μm and a single mode optical fiber with a spot size of 5.5 μm are used, the amount of deviation X in the direction perpendicular to the optical axis of the optical fiber 8 is plotted on the horizontal axis. The figure shows the coupling efficiency η on the vertical axis. As can be seen from Figure 2, the optical fiber 8 is perpendicular to the optical axis by approximately ±2
．． It can be seen that a movement of 5 μm causes a coupling loss of 1 dB, and the permissible amount of axis deviation in the direction perpendicular to the optical axis is small, requiring strict fixing accuracy.

By the way, the coupling characteristics of two Gaussian beams with the same spot size are expressed as (Reference M, Saruwatari
andK, Nawata *: Sem1cond
uctor fiber coupler :Appl
,0pticB, vol, 18, All,
PP, 1847-1856.1979). Here, X is the axis deviation in the direction perpendicular to the optical axis, θ is the angular deviation between the two beams, w is the spot size of the Gaussian beam, and λ is the oscillation wavelength of the semiconductor laser. From this formula, if W is increased, then
It can be seen that the allowable axial deviation of the hoe increases, but the allowable angular deviation decreases. In the case of currently used single mode optical fibers, the values of X and θ with 1 dB degradation are about ±2.5 μm and about ±2.2 degrees, respectively. module M
In the case of misalignment, the angular misalignment can usually be suppressed to within one degree, so if this spot size is increased several times, the allowable amount of misalignment in the direction perpendicular to the optical axis of the single mode optical fiber will become considerably large. I understand.

Further, Fig. 8 shows a diagram in which the horizontal axis represents the axis deviation z in the optical axis direction of the optical fiber 2, and the vertical axis represents the coupling loss η.

A deviation in the optical axis direction of about 60 μm causes deterioration of l clB.

Here, consider a case where the second lens 5 is integrated with the optical fiber 8 in order to increase the spot size.

The spot size W of the semiconductor laser is approximately 1 μm due to the fourth lens. Assuming that the laser oscillation wavelength λ = 1.8 μm and the focal pressure #fl of the 4th lens = 456 μm, W = if
From the relational expression □/(πWo), spot size W□=1
Converted to 89 μm. Substituting this value into equation (1), the allowable axis misalignment, allowable angular misalignment amount X, and θ for the increase in ldB coupling loss are approximately ±87 μm and approximately ±8.6 μm, respectively.
It can be seen that the angle becomes extremely difficult.

Furthermore, if the fixing accuracy of the first hinge 4 and the semiconductor laser l in the optical axis direction is approximately ±10 μm, the waist position 1u of the beam passing through the m2 lens 5 is (f/f
)"X(±10)=±250#m There is a deviation of about 1 degree, so this deviation cannot be corrected by integrating the Z lens 5 and the optical fiber.

Furthermore, when a parallel beam with no angular deviation enters the second lens 5, it forms an image on its optical axis, so the optical axis of the second lens 5 and the optical axis of the optical fiber 8 need to be completely concentric and integrated. However, this is difficult with current machining accuracy.

Therefore, if the second lens 5 is directly integrated into the optical fiber 8, high coupling efficiency cannot be expected.

FIG. 4(A) is a side view of the configuration of the above-mentioned second lens split type common i point compound lens system which has been proposed to eliminate the above-mentioned drawbacks. A ball lens is used as the first lens 4, and two convergent rod lenses (
Below, using a rod lens and approximately -j"') 51.52,
0.5 pitch of the rod lens 52 with the light 7 is the length of the lens that images a point light source into a point light source). rod lens 5
2 is integrated with the optical fiber 2 using adhesive or the like,
The alignment of the optical fiber 2 is performed with the rod lens 52 and the optical fiber 2 fixed.

FIG. 4(B) shows the configuration of the lens system of FIG. Φ fA). The coupling characteristics of this lens system are as follows: A real image spot is generated when a light beam emitted from the semiconductor laser 1 and whose spot size is converted to WO by the first lens 4 passes only through the 10th lens 51. size.

It is determined by w2□ and its position, and the spot size Wfs of a virtual image created when a ray of spot size Wf from the core of the optical fiber 2 enters the rod lens 52 from the right and its position. For example, spot size W
When the spot sizes W and Wf of the light rays generated when the rays □ pass through the two rod lenses 51 and 52 match, the sizes and positions of the real image WilF and the virtual image Wfs match.

FIG. 6 shows an optical fiber 2 integrated with a rod lens 52.
A diagram in which the axis deviation amount X in the direction perpendicular to the optical axis of (hereinafter abbreviated as lens 52 + optical fiber 2) is plotted on the horizontal axis and the coupling efficiency η is plotted on the vertical axis is shown. Two rod lenses 51.52
When the pitch lengths are 0.06 pitch and 0.18 pitch, respectively, W8 = 12.9 μm, and the axis deviation This will be ±56 minutes.

Further, FIG. 6 shows the relationship between the axis misalignment h amount 2 of the lens 52 + optical fiber 2 in the optical axis direction and the coupling efficiency η. By comparing Figure 8 with Figure 6, it can be seen that the second lens division system is extremely loose regarding the allowable axis deviation in the optical axis direction.

In the Tsubaki 2-lens split system, 2, which increases the coupling loss by 1 dB, is extremely loose at approximately 400 μm.

In addition, in the second lens division system, the rod lens 5z reflects M
Since it acts as a stop plate and suppresses the reflected light from the end face 6 of the optical fiber 2, the optically polished glass plate 6 in the conventional confocal system is no longer necessary.

As mentioned above, in the conventional confocal system, not only the allowable axis deviation of the optical fiber 2 is small, but also the optically polished glass plate 7 for anti-reflection is required. The disadvantage is that the number of lenses is increased by one compared to the conventional confocal system.

Furthermore, when manufacturing a semiconductor laser module, it is necessary to adjust the mutual positions of the lens 5 and the optical fiber 2 in the conventional confocal system, and the rod lens 51 and the lens 52 + the optical fiber 2 in the second lens division system. This positioning work is difficult and has significantly reduced the productivity of previous conductor laser modules.

The present invention is characterized by narrowing down the converging or diverging light beam after exiting from the first lens to a light input element integrated with a second lens.The purpose of the present invention is to achieve extremely high manufacturability, the number of lenses is as small as two, and the permissible axis It is an object of the present invention to provide a method for coupling semiconductor laser light with gentle misalignment (and less reflected light).The present invention will be described in detail below with reference to the drawings.

Figure 7 (Al is a diagram of one embodiment of the present invention, Figure 7 (B
l is the principle diagram. Parts corresponding to those in FIGS. 1 and 4 are given the same reference numerals. A ball lens is used as the first lens 4, and a rod lens is used as the second lens 9. Note that when a spherical lens is used as the second lens 9,
It is necessary to leave a space between the lens 9 and the optical fiber 2, and it is necessary to insert an optically polished glass plate, optical adhesive, matting oil, etc. in between, or to apply an anti-reflection coating to the end face of the optical fiber 2. . Below, the second lens 9 and the optical fiber 2
The combination of these is abbreviated as lens 9 + optical fiber 2.

FIG. 7(A), (The embodiment of Bl is the 4th run and the LD
distance d from the light emitting surface 8. is made larger than the focal length f of the lens 4, and the narrow rays generated after exiting the lens 4 are narrowed down to the optical fiber 2 integrated with the rod lens 9, which is shorter than, for example, 1/4 pitch. The coupling characteristic of this lens system is the spot size W. The spot size W8□ of the real image created by g-directing the semiconductor laser light with the lens 4 and its position, and the virtual image created when a ray of spot size wf enters the lens 9 from the right from the core 8 of the optical fiber 2. is determined by the spot size Wfs and its position.

The distance k [[] between the light emitting surface 8 of the semiconductor laser and the first lens 4 is determined by the ray matrix (Reference M,
Saruwatari and K, Nawata
, :Sem1conduct, or fiber
coupler: Appl, 0ptics.

vol, 18, All, PP, 184'7~
1856, IQ19), it can be calculated as follows. .

For example, as the fourth lens, the focal length f0 is f, =456
When a μm ball lens is used and a 0.18 pitch Rondo lens is used as the lens 9, the oscillation wavelength of the semiconductor laser is λ=1.8 μm and the spot size W of the semiconductor laser light.

Spot size of 21 μm1 virtual image w1. =, 18μm
As, from equation (2), d. = 491 μm.

In the present invention, there is no need for lenses corresponding to the lens 5 in the conventional confocal system and the lens 51 in the second lens division system, and when a semiconductor laser package in which the lens 4 is enclosed is used, it is possible to use the lens 4! The only parts are the lens 5z and ten optical fibers 2, and the manufacturing efficiency of the module 0 is significantly improved. Further, since the setting deviation of the lens 4 is relatively small, the deterioration in coupling efficiency due to the angular deviation remaining after the positional deviation is corrected by moving the lens 9 + optical fiber <2 in parallel is small. In a conventional confocal system, the decrease in coupling efficiency due to angular shift is smaller than when the lens 5 and the optical core injector 2 are integrated, because the spot size of the n light after exiting the lens 4 is smaller than that in a conventional confocal system. In this case, it is 189 μm, and in the present invention, it is 12.9 μm and 1/18
This is because the size is as follows.

If you also want to correct the angular deviation mentioned above, use lens 9.
+ Just tilt the optical fiber 2. In this case as well, the spot size is about 12.9 μm, so 1. iF
Adjusting M is relatively easy.

FIG. 8 shows a diagram in which the axis deviation amount X of the lens 9 + optical fiber 2 in the direction perpendicular to the optical axis is plotted on the horizontal axis, and the coupling efficiency η is plotted on the vertical axis. A Rondo lens with a pitch of 0.18 is assumed.In this case, the axis deviation X and angular deviation θ that give a 1 dB loss increase are approximately ±
6.8 μm, approximately ±52 minutes.

Further, FIG. 9 shows the relationship between the axis misalignment z of the lens 9 and the optical fiber 2 in the optical axis direction and the coupling efficiency η. 1 dB
2, which gives an increase in loss of , is approximately 420/1m. In this way, although there is one less lens, the allowable axis misalignment in both the optical axis direction and the direction perpendicular to the optical axis is comparable to that of the second lens division system, that is, the one shown in Fig. 4, which is the same as that of the conventional system. It is much looser than the confocal system, ie, the one in FIG.

In addition, in the present invention, the beam waist w2Q after passing through the second lens, which occurs due to a fixed error in the optical axis direction of the second lens 4, is
It has been confirmed that variations in position can be easily corrected by adjusting the distance between the first lens 4 and the second lens 9.

Furthermore, in the present invention, since the second lens 9 is integrated into the optical fiber, the difference in refractive index at the incident end face of the optical core is small, and reflection is reduced.

In this way, the optically polished glass plate 7 for antireflection, which is necessary in the conventional confocal system, is no longer necessary.

In the above embodiment, the distance d between the light-emitting surface 8 of the semiconductor laser (1) and the second lens 4 is d. The case has been described in which the focal length f□ of the second lens 4 is set larger than the focal length f□, and the pitch number of the second lens 9 is shorter than 1/'4 pitch.

However, there is a difference d. Set 2 lens 9 to be smaller than fo.
It is also possible to make the number of pitches longer than the station. In this case, the spot size after emitting the 4th run is W8.
□ becomes a virtual image, and is it an optical fiber? 2nd from core B of
A spot size W8□ generated by entering the lens 9 becomes a real image. The coupling efficiency η can be calculated as a combination of these two spot sizes. d at this time. is calculated from the following formula.

In FIG. 1O, instead of the lens 90 in the embodiment of FIG. 7, a ball lens 10 similar to the lens 4 is used, and the optical fiber 2 is
It is an example diagram using a semiconductor laser 11 instead of
A direct optical amplifier can be realized.

FIG. 11 is an embodiment diagram in which an optical fiber 12 for light output is used instead of the semiconductor laser 1 in the embodiment shown in FIG. 10, and a rod lens 18 is used instead of the ball lens 4, realizing a direct optical amplifier. can.

In FIGS. 10 and 11, the ball lens 10 and the semiconductor laser 11 for light incidence are integrated using a fixing jig.

FIG. 12 shows an embodiment in which a rod lens 9 is used in place of the ball lens IO in the embodiment shown in FIG. 11, and an optical fiber 2 is used in place of the semiconductor laser 11, making it possible to realize a passive optical circuit. In addition, in FIG. 11 and the 12th time, the optical fiber 12 and the rod lens 18 may be attached. In the embodiment shown in FIG. 11, the ball lens IO and the rod lens 18 may be replaced.

LD module with built-in isolator using YIG bulb (
In the case of YIG, which has a high refractive index,
Since the focal point of the spherical lens enters the sphere, the light rays emitted from the YIG sphere 14 do not become parallel rays, but are narrowed down, as shown in FIG. 18 (Al).

For this reason, a conventional confocal lens configuration cannot be used.

In FIG. 18(A), 15 is a magnet and 16 is a polarizer.

In the present invention, even if a lens with a high refractive index is used as the first lens, a configuration is possible. The configuration in this case is shown in Fig. 18 (Bl).This allows us to improve the number of manufacturability and allowable axial deviation of the optical fiber 2 that integrates the second lens even in the case of an isolator using YIG spheres. It is possible to make it larger.

As explained above, according to the method of the present invention, with the same number of lenses in a conventional confocal system, it is possible to obtain a permissible axis shift gate as small as that of the second lens division system with a large number of t/lenses. Therefore, a highly reliable optical coupling device can be constructed, and its manufacturability is significantly improved.

Note that an antireflection plate, which is necessary in conventional confocal systems, is no longer necessary.

Furthermore, the method of the present invention can be applied to the configuration of a semiconductor laser coupling device for multimode optical fibers, and an improvement in the manufacturability can be expected.

[Brief explanation of drawings]

Ml (Incorporated) fAl, (B) is an explanatory diagram of an example of the configuration of a conventional confocal compound lens system and its principle, and Figures 2 and 8 are views of the conventional confocal system in the direction perpendicular to the light @. Figure 4 (Al) is a diagram explaining the axis deviation characteristics in the direction of the optical axis. The figure shows the middle 11 in the direction perpendicular to the optical axis and in the optical axis direction for the second lens division system.
Figures illustrating the I-shift characteristics, Ml diagram (A), (Bl is an explanatory diagram of one embodiment of the present invention and its principle, and Figures 8 and 9 are the directions perpendicular to the optical axis and the axis in the optical axis direction. The deviation characteristic is M
S? Figures 10, 11, and 12 are diagrams of other embodiments of the present invention, Figure 18 (Al is a configuration diagram of a conventional LD module, and Figure 18 (Bl is a diagram of a conventional LD module) It is a configuration diagram of the LD module in the case of the following. 1... Semiconductor laser for light emission, 2... Optical fiber for light input, 8... Core of optical fiber, No.... Runes, 5... Second lens in conventional confocal system, 51... First focusing type Rondo lens of the z-th lens division system, 52... Second convergence type Rondo lens of the second lens division system, 6... Optical fiber. The end face of...
・Anti-reflection plate, 8... Light emitting surface of semiconductor laser, 9...
・Second lens (focusing rod lens) in one embodiment of the present invention, lO...Second lens (spherical lens) in the Orin example of the present invention, 11...Semiconductor laser for light incidence (
optical amplifier), 12... optical fiber for light output, 1B...
・6 Runs, 14...YIG in the embodiment of the present invention
Sphere, 15...magnet, 16...sphere photon. Figure 1 Figure 2 Axis [χ (MegI) Figure 3 V Figure 4 Figure 7 , Figure 8 Axis f χ (/II?71) Figure 9 @I relative 2 (MegI) Figure 1O Figure 11 Figure 12

Claims (1)

[Claims] 1. A light output element, a second lun, and a light input element integrated with a second lens are arranged in this order, and the distance between the light output element and the first lun is set to be larger or smaller than the focal length of the second lens. By setting the position of the second lens so that the light beam emitted from the light output element converges or diverges after exiting from the light input element, and the image of this light beam is focused on the end surface of the light input element. . An optical coupling method, characterized in that the light beam emitted from the light output element is made incident on the input element.