JPH0515316B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light source for optical communication, and in particular to a light source for efficiently coupling a semiconductor laser (LD) and an optical fiber.
Regarding the integrated LD module.

[Conventional technology]

As optical fibers for optical communications, single mode fibers are preferred over multimode fibers for branch lines and subscriber lines due to lower prices due to mass demand in trunk lines and greater flexibility for future increases in capacity. is becoming mainly used.

By the way, unlike the trunk line, branch lines and subscriber lines do not normally carry out relaying and are located at the end of the network, so the transmission distance is relatively short and the deviation is large. In addition, since the multiplicity of the line is low, there is a strong demand for a low price. Therefore, the branch line system and subscriber system transmission systems are separated into two systems, long-range and short-range, and designed to be optimal in terms of cost.
LDs are becoming mainstream as light sources for short-range systems because they are fast, have good coupling characteristics to single-mode fibers, and are expected to be low-cost in the future.

The optical output of the LD module for the short-range method may be 10 dB or more lower than that for the long-range method, and therefore,
In the future, in this type of LD module, a ball lens 5, which does not provide high coupling efficiency but is inexpensive, will be used to couple the LD pellet 1 and the optical fiber 3, as shown in FIG.

[Problem to be solved by the invention]

By the way, LD pellets are usually mounted in a hermetically sealed can case, but currently the mounting position error is in the x, y, and z directions (x, y are perpendicular to the optical axis, z
is approximately ±100 μm (in the optical axis direction), which is an order of magnitude larger than the mounting position error of the ball lens and optical fiber. For this reason, in a long-distance high-coupling LD module, x,
Optical axis adjustment is required in a total of six y- and z-axis directions. On the other hand, even with a short-range low-coupling LD module, which has a coupling efficiency about 10 dB lower than that of a long-range model, x,
It is necessary to adjust the optical axis in three axes, y and z.

For short-range LD modules, there are strict requirements for low cost and high output. However, as described above, the conventional configuration has the problem that the optical axis adjustment cannot be simplified and the cost cannot be sufficiently reduced.

[Means to solve the problem]

The LD module of the present invention is characterized in that a transparent plate having a different refractive index and thickness at the center and periphery is inserted between the LD and the lens system so that its central axis coincides with the optical axis.

〔Example〕

First, the principle of the present invention will be explained.

Referring to FIG. 1, in a coupling system in which emitted light from LD pellet 1 is focused by lens 2 and coupled to optical fiber 3, LD pellet 1 and lens 2
A transparent plate 4 is inserted between them. This transparent plate 4
As shown in the figure, the optical thickness is different between the center and the periphery. That is, in this example, the optical thickness of the central portion of the transparent plate 4 is thicker than the optical thickness of the peripheral portion. Therefore, the imaging position of the lens 2 is shifted in the axial direction between the light that has passed through the center of the transparent plate 4 and the light that has passed through the periphery.

FIG. 2 shows the transparent plate in detail.

Referring also to Fig. 2, the LD caused by the light passing through the center of the transparent plate 4 and the light passing through the peripheral part.
The optical length deviation Δa between the pellet 1 and the lens 2 can be expressed by the following equation.

Δa= _d1 − _d1 / _n1− ( _d2 − _d2 / _n2 ) where, _d1 : Thickness at the center, _d2 : Thickness at the periphery, _n1 : Refractive index at the center, n ₂ : Refractive index of the peripheral area The deviation in the imaging position caused by the light passing through the center of the transparent plate 4 and the light passing through the peripheral area in FIG. Corresponds to the length deviation Δa.

FIG. 3 shows the relationship between the coupling loss L between the LD pellet 1 and the optical fiber 3 and the distance Z between the LD pellet 1 and the lens 2.

L ₁ is the L curve when the transparent plate 4 is not inserted,
L ₂ is the L curve when the transparent plate 4 is inserted.
The tolerance range ΔZ in the Z direction until the coupling loss increases by ΔL from the minimum value becomes larger (ΔZ ₂ >ΔZ ₁ ) when a transparent plate is inserted. In other words, the LD generated by the light passing through the center of the transparent plate and the light passing through the periphery.
The L curve shifts as shown in the curves L 21 _{and L 22 according to the optical length shift Δa between the pellet 1 and the lens 2, so when these curves L 21 and L 22} are added, the minimum value is reached as shown in Fig. 3. becomes large, but the curve has a flat bottom. Therefore, ΔZ ₂ >ΔZ ₁ .

The above-mentioned characteristics are suitable as a coupling system for short-range LD modules that do not require high output and have strict requirements for low cost. That is, since the sensitivity in the Z direction is relaxed, the optical axis can be adjusted only in the x and y directions, which simplifies the adjustment and, as a result, also simplifies the components.
Therefore, it is possible to significantly reduce the price.

Here, one embodiment of the present invention will be specifically described with reference to FIG.

The transparent plate 4 is, for example, a glass disk with a circular hole formed in the center, thereby making the optical thickness of the center portion different from the optical thickness of the peripheral portion. The LD pellet 1 is hermetically sealed in the LD package 6, and by inserting the optical fiber core wire 7 into the ferrule 8 and bonding and polishing it, the end face of the optical fiber is positioned on the end face of the ferrule 8. ing. The ferrule 8 is mechanically fixed in the through hole of the holder 9 with a screw 10, and the transparent plate 4 and the ball lens 5 are fixed in the holder without adjustment by soldering, press fitting, or the like.

When adjusting the optical axis, the collar of the LD package 6 is brought into contact with the end face of the holder 9, and then the optical axis is adjusted only in the x and y directions. Then, the collar of the LD package 6 is fixed to the end face of the holder 9 by YAG laser spot welding, etc., and the assembly is completed.

In addition, as a result of experiments using an LD with a wavelength of 1.31 μm and a single mode fiber with a core diameter of 10 μm, the minimum coupling loss for 10 samples was 19 dB and the error margin was 3 dB, which is sufficient for a short-range LD module. was confirmed.

In addition, in the above embodiment, one ball lens 5 is used.
Although the case where the LD pellet 1 and the optical fiber are optically coupled has been described, the present invention can be similarly applied to the case where the LD pellet 1 and the optical fiber are optically coupled using a plurality of lenses.

〔Effect of the invention〕

As explained above, in the LD module of the present invention, since a transparent plate with different optical thicknesses at the center and periphery is inserted between the LD and the lens, adjustment of the optical axis direction of the LD pellet can be eliminated. It is also possible to create LD modules with less manufacturing variation. Therefore,
Since the optical axis adjustment is simplified and the components are simplified, there is an effect of significantly lower costs than in the past. As a result, the present invention can be used for short sections of branch lines and subscriber lines that do not require high output and have low cost requirements.
If applied to LD modules, the cost will be reduced, and this will have the effect of creating mass demand for LD modules and, by extension, optical communication equipment.

[Brief explanation of drawings]

Figure 1 is a block diagram of the present invention, Figure 2 is a diagram for explaining the principle of the invention, Figure 3 is a diagram showing the relationship of coupling loss L with respect to the distance Z between the LD pellet and the lens, and Figure 4. 5 is a configuration diagram of a conventional example, and FIG. 5 is a basic configuration diagram of an embodiment of the present invention. 1...LD pellet, 2...lens, 3...optical fiber, 4...transparent plate, 5...ball lens, 6...
...LD package, 7...Optical fiber core wire, 8...
...Ferrule, 9...Holder, 10...Screw.

Claims (1)

[Claims] 1. A semiconductor laser module including a semiconductor laser and an optical fiber, and a lens system for coupling the semiconductor laser and the optical fiber, wherein the central axis of the semiconductor laser and the lens system coincides with the optical axis. 1. A semiconductor laser module comprising a transparent plate inserted in such a manner that the transparent plate has different optical thicknesses at its center and at its periphery.