JPH02130985A - Semiconductor laser module - Google Patents

Abstract

PURPOSE:To facilitate the optical axis adjustment for cutting down cost by a method wherein a transparent sheet comprising the central part and the peripheral part in different optical thickness is inserted between a semiconductor laser and a lens system. CONSTITUTION:Within a coupling system wherein radiation from a laser diode(LD) pellet 1 is focussed by a lens 2 to be entered into an optical fiber 3, a transparent sheet 4 is inserted between the pellet 1 and the lens 2. The transparent sheet 4 comprising the central and the peripheral part in different thickness, the image forming positions of the beams passing through the central part and those passing through the peripheral part are slipped from each other in the axial direction. Through these procedures, the couple loss is leveled off despite the changes in the intervals between the pellet 1 and the lens 2 so that the LD modules for short interval subjected to the least variability regardless of no adjustment of the LD pellet 1 in the direction of optical axis may be manufactured. Consequently, the adjustment of optical axis as well as the components can be facilitated thereby cutting down cost.

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 semiconductor laser (LD).
) and an optical fiber are efficiently combined to create an LD.
Regarding modules.

[Conventional technology]

As optical fibers for optical communications, multi-mode fibers are preferred over single-mode fibers for branch lines and subscriber lines due to lower prices due to mass demand in trunk lines and greater flexibility for future capacity increases. Fibers are increasingly being used.

By the way, in the branch line system and the subscriber line, unlike the main line system, normal relaying is not performed, and since they are located at the end of the network, the transmission distance is relatively short and the deviation is large. Furthermore, since the multiplicity of the nine lines 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.

As light sources for short-range systems, LDs are becoming mainstream because they are high-speed, 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 lower by *10 dB or more than that for the long-range method.

Conventionally, with this type of LD module, as shown in Fig. 4, high coupling efficiency cannot be obtained, but the low-cost ball rays 5 are used in the LD.
It is used for coupling the pellet 1 and the optical fiber 3.

[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 x
±1 in the yz direction (xty is perpendicular to the optical axis, 2 is the optical axis direction)
It is approximately 0.00 μm, which is one order of magnitude larger than the mounting position error of a 99-ball lens and an optical fiber. Therefore, in a long-distance high-coupling LD module, X is applied to both the LD pellet and the optical fiber.

Optical axis adjustment is required in a total of six axes, y and z. on the other hand.

Even in the case of a low-coupling LD module for short distances, which may have a coupling efficiency 1 OdB lower than that for long distances, it is necessary to adjust the optical axis in the three axes of X y yr2 for either the LD pellet or the optical fiber.

For short-distance LD modules, there are strict requirements for low cost as well as high output requirements. 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, a transparent plate 4 is inserted between the LD pellet 1 and a lens 20 in a coupling system in which emitted light from an LD pellet 1 is focused by a lens 2 and coupled to a source fiber 3. As shown in the figure, the optical thickness of the transparent plate 4 is different between the central part and the peripheral part. 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 optical length deviation Δa between the LD pellet 1 and the lens 2 caused by the light passing through the central part of the transparent plate 4, the light passing through the peripheral part, and K is calculated by the following formula % formula % where: , dl: thickness at the center, d2: thickness nl at the periphery
: refractive index of the central part, n2 : refractive index of the peripheral part The deviation of the imaging position caused by the light passing through the center of the transparent plate 4 and the light passing through the peripheral part in FIG.
This corresponds to the optical length deviation Δa between I and lens 2.

Figure 3 shows L for the distance 2 between the LD pellet 1 and the lens 2.
The relationship between the coupling loss between the D pellet 1 and the original fiber 3 is shown.

Ll is Lfttll when transparent plate 4 is not inserted +
L2 is the 5 curve when the transparent plate 4 is inserted. The tolerance range Δ2 in the Z direction until the coupling loss increases by ΔL from the minimum value is larger when a transparent plate is inserted (Δz2>Δz1)
Become. 5 curves are curves L21 r L2 according to the optical length deviation Δa between the LD pellet 1 and the lens 2 caused by the light passing through the center of the transparent plate and the light passing through the periphery.
2, so when these curves L21 t L22 are added, the minimum value increases as shown in Figure 3, but
It becomes a curve with a flat bottom. Therefore, Δz2>Δz1.

The above-mentioned characteristics are suitable as a coupling system for a short-range LD module that does not require high output power and has strict requirements for low cost. That is, since the sensitivity in two directions is relaxed, the optical axis adjustment in the x and y force directions is simplified, and as a result, the components are also simplified.

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 in the center, thereby making the optical thickness at the center different from the optical thickness at the periphery. LD pereyt 1ttLDzwy
The optical fiber core +y is hermetically sealed in the cage 6.
By inserting J7 into the ferrule 8 and bonding and polishing it, the end face of the optical fiber is located at the end face of the ferrule 8. The ferrule 8 is mechanically fixed in the through hole of the holder 9 by screws 10, and the transparent plate 4 and the ball lens 5 are fixed in the holder by soldering, press fitting, etc. without adjustment.

When adjusting the optical axis, the collar of the LD package 6 is brought into contact with the end surface of the holder 9, and then the optical axis is adjusted only in the x and y force directions. Then, 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 was 19 dB for 10 samples, and the error margin was 3 dB, which is sufficient for a short-range LD mosoule. It was confirmed that

Furthermore, in the above embodiment, a case was explained in which the W pellet 1 and the optical fiber were optically coupled using one ball lens 5, but the LD pellet 1 and the optical fiber were optically coupled using a plurality of lenses. The same applies to cases where

〔Effect of the invention〕

As explained above, in the LD module of the present invention, the LD
Since a transparent plate having different optical thicknesses at the center and periphery is inserted between the lens and the lens, it is possible to realize an LD monolayer with little manufacturing variation even if no adjustment is made in the optical axis direction of the LD pellet. 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 result9, if the present invention is applied to short-range LD modules for branch lines and subscriber lines that do not require high output and have a strict requirement for low cost, the cost can be reduced, and the mass demand for LD modules and optical communication equipment can be realized. It also has the effect of producing

[Brief explanation of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is a diagram for explaining the invention in detail, FIG. 3 is a diagram showing the relationship of coupling loss with respect to the distance 2 between the LD pellet and the lens, and FIG. 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. DESCRIPTION OF SYMBOLS 1... LD pellet, 2... Lens, 3... Optical fiber, 4... Transparent plate, s... Ball lens, 6...
L D / #kkeichino, 7... Optical fiber core wire, 8.
...Ferrule, 9...Holder, 10...Screw. 7LDIXX Let Figure 3 Otsu Z2

Claims (1)

[Claims] 1. In a semiconductor laser module having a semiconductor laser and an optical fiber, and including a lens system for coupling the semiconductor laser and the optical fiber, a central axis between the semiconductor laser and the lens system is aligned 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.