JPH03192208A - Optical module - Google Patents

Abstract

PURPOSE:To reduce the optical coupling loss, and to improve productivity and reliability by providing a parallel plane plate which is made of a material with high optical transmissivity between a coupling lens and the end surface of an optical fiber on the side of the coupling lens and setting the end surface of the optical fiber almost in level with the joined surface between a fitting ring and a package. CONSTITUTION:The parallel plane plate 11 which is made of the material with high optical transmissivity is provided between the coupling lens 4 and optical fiber 7 and the end surface of the optical fiber 7 is almost in level with the joined surface between the coupling ring 9 and package 2. Therefore, the geometric length between the coupling lens 4 and optical fiber end surface increases and even if a lens has variance in optical constant, member size, etc., the end surface can be matched with the joined surface of a fiber input end module package. Consequently, the optical coupling loss is small, the cost is low, and the reliability is improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a transmitting/receiving optical module for optical communication.

(Prior Art) With the demand for higher speed and larger capacity of optical communications, there is a desire for higher performance and higher reliability of various optical modules such as light emitting and light receiving components, which are the components thereof. FIGS. 2(a) and 2(b) show an example of a normal semiconductor laser (LD) module. Figure 2 (a
) shows a top view, and FIG. 2(b) shows a cross section cut along BB'. The box-shaped package 2 is composed of a plurality of inline metal lead rods 3. metal rod 3
In the notch in the center, there is an LD mounted on a heat sink 5, a lens is located in the hollow part, and a light beam coated with metal (ferrule) is placed at the tip via a ring-shaped connecting member (slide ring) 9. It holds fiber 7. Here, the emitted light from the LD 6 is magnified and imaged through the lens 4, and is efficiently coupled to an optical fiber whose end face is located at the image formation position. The optical fiber is first aligned in the optical axis direction (Z) and fixed to the slide ring 9, then aligned in the xy force direction, and then fixed to the slide ring 9 and the package 2 to be held in the package. has been done. For fixing, spot welding using a YAG laser or soldering, which is considered to be highly reliable, is generally used.

(Problems to be Solved by the Invention) As described above, the slide ring 9 and the optical fiber 7, and the slide ring 9 and the package 2 are bonded together by YAG laser welding or solder bonding. In the case of YAG laser welding, spot welding is performed at 3 or 6 points, but optical axis deviation (lateral deviation) within the joint surface due to power imbalance between multiple laser beams, surface accuracy and parallelism of the joint surface may occur. The optical axis of the fiber may be tilted due to a problem with the optical fiber angle, and the optical coupling efficiency may deteriorate.

FIG. 3 (aXb) shows the lateral deviation (Δy) and inclination (Δe) of the fiber optical axis at the joint, and shows an enlarged cross-section of the joint. The amount of axis deviation Δγ due to the optical axis inclination Δθ is proportional to the distance d between the joint 10 and the fiber tip. A similar problem occurs in solder joints due to non-uniformity in the amount of solder. In addition, changes over time and external forces may cause displacement in the bonded portion, deteriorating the optical coupling efficiency.

There are countermeasures to reduce this deviation, such as controlling component accuracy, carefully assembling, and using the module in an environment with small temperature changes, but considering manufacturing costs and user usage conditions, it is not necessary to take drastic measures. It's not a solution. If the optical fiber input end is arranged on the same plane as the joint surface between the slide ring 9 and the package 2, d#0 will be obtained, so the lateral deviation of the fiber optical axis caused by the inclination Δθ can be reduced, but dimensional errors of the members, such as the lens 4 Due to variations in the focal length, dimensional errors in the package 2, slight errors in the distance between the laser 6 and the lens 4, etc., it is difficult to focus the image on the end face of the fiber. Although it would be possible to strictly manage this, the cost would be extremely high.

An object of the present invention is to solve the above-mentioned problems and provide a module with low optical coupling loss, low cost, and high reliability.

(Means for Solving the Problem) An optical module comprising a light emitting or light receiving element installed in a package, a coupling lens, and an optical fiber protected by a ferrule fixed to the package via a fitted ring, A parallel flat plate made of a material with high light transmittance is provided between the coupling lens and the optical fiber, so that the end surface of the optical fiber is substantially flush with the joining surface of the fitting ring and the package. It is characterized by the following.

(Function) The geometric length of a ray transmitted through a parallel flat plate having a thickness t and a refractive index n becomes longer by about t(1-1/n) than in air.

Therefore, before installing the parallel plate, the image formation position should be placed on the lens side to some extent with respect to the end face of the optical fiber, and then a parallel plate having the desired thickness and refractive index is provided between the coupling lens and the optical fiber. . Then, the geometric length between the coupling lens and the end face of the optical fiber becomes longer, and even if there are variations in the optical constants of the lens, variations in component dimensions, etc., it will coincide with the joint surface of the fiber input end module package. The deviation of the optical axis relative to the fiber inclination is approximately proportional to the distance between the joint surface of the fiber and the package and the fiber input end. However, in the present invention, since the joint surface and the fiber input end surface are made to be approximately on the same plane, the fiber tilt The optical axis shift due to this can be almost ignored.

In this manner, by providing a parallel plate having a desired thickness and refractive index, the fiber input end can be made to coincide with the bonding surface of the module package even if there is a dimensional error in the member.

For this reason, it is possible to eliminate one of the two main causes of optical axis deviation, fiber lateral deviation and fiber inclination, and to significantly suppress the deterioration of coupling efficiency, without having to manage component precision or carefully assemble. becomes possible. This reduces assembly man-hours and improves productivity and reliability. still,
Optical loss in the parallel plates can be reduced to a negligible level by using a material with high light transmittance as the material for the parallel plates.

(Example) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view of a module illustrating the present invention. The components are the same as those of the conventional example shown in FIG. 2, and the package 2 is composed of a plurality of in-line leads and a metal rod 3. In the metal rod 3, a notch in the center has a semiconductor (LD) 6 mounted on a heat sink 5, a lens 4 is located in the hollow part, and the tip is covered with metal (ferrule) via a slide ring 9. It holds an optical fiber 7. The emitted light from the LD 6 is condensed by a lens 4, transmitted through a parallel flat plate 11 made of ordinary optical glass having a thickness of about 3 mm and a refractive index of 1.5, and is coupled to an optical fiber 7.

Here, the light focused by the lens 4 is transmitted to the package 2.
The parallel plate 11 connects the lens 4 and the optical fiber 7 so that the image is formed in approximately the same plane as the joint surface of the slide ring 9 and the slide ring 9.
The geometric length between the input ends of is lengthened by 1 mm. what if,
Even if the package 2 has a dimensional error due to manufacturing defects, the geometric length can be corrected by adjusting the thickness of the parallel plate 11, and the fiber input end can be made to coincide with the bonding surface of the package 2.

The parallel plate 11 is made by applying a gold coat to the periphery of the parallel plate 11, and fixing the gold coat to the inside of the package 2 with solder.
Fixed. Note that the method of fixing the parallel plate 11 is not limited to the above-mentioned method, and may simply be fixed using an adhesive or the like. The procedure for fixing the position of the optical fiber 7, etc. is as follows. First, the image formation position is set to be closer to the lens 4 than the end surface of the optical fiber without the parallel plate 11. Next, several types of parallel flat plates with different thicknesses are replaced to align the imaging position with the end face of the optical fiber. The optical fiber 7 and the slide ring 9 are fixed, and after alignment in the x and y directions, the slide ring 9 and the package 2 are fixed. Fixation is performed by spot welding using a YAG laser or by soldering.

The input end of the fiber 7 is positioned approximately within the joining plane with the package. As mentioned above, the optical axis deviation is proportional to the distance between the fiber end face and the bonding surface of the package and the fiber, so even if the fiber optical axis is tilted due to external pressure or changes over time, the optical axis deviation can be almost ignored in this configuration. Therefore, compared to the conventional configuration, it is possible to not only reduce coupling loss but also significantly reduce adjustment man-hours and improve productivity and reliability.

In this embodiment, an LD is shown as a light emitting element, but an LED or a light receiving element such as a photodiode (PD) may also be used. In addition, although the imaging system was constructed with one lens,
An imaging system with two or more lenses may also be used.

Further, in the above embodiment, glass is used as the material of the parallel plate having high light transmittance, but the material is not limited to this, and any material having high light transmittance may be used, for example, plastic or the like may be used. Furthermore, in order to improve the light transmittance of the parallel plate, an anti-reflection coating may be applied to the end face of the parallel plate.

(Effects of the Invention) As described above, according to the present invention, an optical module with low optical coupling loss, high productivity, and high reliability can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 (aXb
) is a configuration diagram of a conventional optical module, and FIG. 3 (aXb) is a diagram showing optical axis deviation of a fiber. In the figure, 1...Lead, 2...Package, 3
°°°Metal side, 4...Lens, 5...Heat sink,
6... Semiconductor laser, 7... Optical fiber, 9...
Slide ring, 1o...joint surface, 11...parallel flat plate.

Claims (1)

[Claims] In an optical module comprising a light emitting or light receiving element installed in a package, a coupling lens, and an optical fiber protected by a ferrule fixed to the package via a fitted ring, the coupling lens and the optical fiber A parallel flat plate made of a material with high light transmittance is provided between the end face on the coupling lens side and the end face of the optical fiber so that the end face of the optical fiber is substantially flush with the joining face of the fitting ring and the package. An optical module characterized by: