JPH04343035A - Method and device for inspecting optical module - Google Patents

Abstract

PURPOSE:To achieve a required inspection and a proper positioning by allowing a light source which outputs a coherent light to be coupled to an optical module and then observing interference fringes of the coherent light which is projected on a surface of a photodetector. CONSTITUTION:A coherent light P2 which is generated by operating a visible laser light source 27 is introduced into a package 21 through a light synthesizer 25 and optical fibers F2 and F1 and is emitted from a tip portion of the fiber F1 toward a light-reception surface of a photodetector 22. Since the light P2 is a visible light with a wavelength of lambda2 so that a color development image which is determined by a wavelength, namely the color-development image with interference fringes in concentric shape appears and it can be visually confirmed. Then, when vivid interference fringes are observed, it is judged that an optical system is normal. Further, a proper positioning can be made by allowing a central point of the interference fringes to be matched to a center of the photodetector 22.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting optical modules, particularly light receiving/emitting element modules for optical communications. Generally, an optical module for optical communication is assembled by incorporating an optical element into a package and then coupling an optical fiber to the optical element, but great care is taken to align the optical fiber and the optical element. This is because unless the optical axis of the optical fiber is accurately aligned with the light-receiving surface (in the case of a light-receiving element), a large coupling loss will occur.

0002

2. Description of the Related Art FIG. 6 is a diagram illustrating a conventional inspection method. In FIG. 6, 10 is a package, 11 is a stage, 12 is, for example, a light receiving element, and 13 is an optical fiber. For assembly, the stage 11 on which the light-receiving element 12 was mounted was attached to the package 10, the tip of the optical fiber 13 was taken into the package 10 through the receptacle 10a, and the positional relationship between the optical fiber tip 13a and the light-receiving surface 12a was adjusted appropriately. After that, it is fixed to ensure that it does not shift.

[0003] Since such alignment is performed in an extremely small range, sufficient inspection accuracy cannot be obtained by visual confirmation alone. Therefore, a laser beam Pa having a predetermined wavelength λa is introduced through the optical fiber 13, and the light receiving element 12
The adjustment work is carried out while monitoring the electric signal Sa from. Specifically, (1) moving the optical fiber tip 13a while comparing the electric signal Sa and a predetermined reference value R to find a position where Sa>R; (2) or moving the optical fiber tip 13a in a planar manner. While moving, the two-dimensional light-receiving characteristics of the light-receiving surface are measured by synchronizing the movement with the electric signal Sa, and the two-dimensional light-receiving characteristics of the light-receiving surface are adjusted to match the light-receiving peak position.

Note that the wavelength λa mentioned above is a predetermined wavelength at which the light receiving element 12 shows an electrical response, and corresponds to, for example, the wavelength of an infrared laser (eg, 1.55 μm or 1.3 μm). Generally, optical communication uses light with a longer wavelength than visible light. This is because the longer the wavelength, the lower the transmission loss of the optical fiber and the longer the communication distance.

[0005]

[Problems to be Solved by the Invention] However, in such conventional inspection methods, the adjustment work was based on the electrical responsiveness of the optical element. ), accurate positioning is difficult, and a method for reproducing the two-dimensional distribution of photoresponse (2
), each of which has its own problems, such as the need for complex signal processing.

Accordingly, an object of the present invention is to realize proper alignment by visual observation or image processing by observing coherent light on the surface of an optical element.

[0007]

[Means for Solving the Problems] The inspection method of the present invention applies to an optical module in which an optical element and an optical component are integrated.
a step of inputting coherent light from the optical component side;
and a step of inspecting the optical component, and preferably, the optical element is a light receiving element, and the coherent light is used also as optical axis alignment light, and The optical element is a light receiving element, and the coherent light and the optical axis alignment light having different wavelengths from the coherent light are incident on the optical component, and the optical element is a light emitting element. , the wavelength of the coherent light is selected to be different from the emission wavelength of the light emitting element, and the optical component is inspected at the same time as the optical axis is aligned by the light emission of the light emitting element.

[0008]Furthermore, the device integrates a light source that outputs coherent light, an optical element and an optical component to be inspected, by observing the state of interference fringes of the coherent light projected onto the optical element. The present invention is characterized by comprising a coupling means for optically coupling the optical module and the light source, and a recognition means for recognizing interference fringes of the coherent light projected onto the surface of the optical element of the optical module.

[0009]

[Operation] In the present invention, a coherent light image is formed on the surface of an optical element by coherent light. Then, by observing this imaging state, necessary inspections are performed. Here, when the optical system is normal, clear concentric interference fringes are observed in the image formation. These interference fringes are caused by repeated reflections of coherent light in the gap between the tip of the optical fiber and the surface of the optical element.

[0010] Therefore, if clear interference fringes are observed, it is determined that the optical system is normal. Further, by aligning the center point of the interference fringes with the center of the optical element, proper positioning can be easily performed.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. 1 to 5 are diagrams showing an embodiment of an inspection apparatus to which an optical module inspection method according to the present invention is applied. First, the system configuration will be explained. In FIG. 1, 20 is an optical module, which here is assumed to be a module including a light receiving element. The module 20 includes a stage 23 in which a light receiving element 22 as an optical semiconductor is mounted inside a package 21.
Attach the receptacle 21 integrated with the package 21.
Insert one end of the optical fiber F1 into a and assemble. The inner diameter of the receptacle 21a is slightly larger than the outer diameter of the optical fiber F1, and the positional relationship between the tip of the optical fiber F1 and the light-receiving surface of the light-receiving element 22 (or the active layer in the case of an edge-emitting type, the same applies hereinafter) is finely adjusted. After the adjustment, one end of the optical fiber F1 is fixed to the package 21 or the receptacle 21a.

[0012] The optical fiber F1 is cut into a length of several tens of centimeters to several meters, and the other end is
It is attached to the V-shaped groove 24a (so-called butting groove) of the inspection connection jig 24, and is detachably coupled to one end of the inspection optical fiber F2 similarly attached. The other end of the optical fiber F2 is connected to a light combiner 25 such as an optical coupler, into which the infrared laser light P1 and visible laser light P2 from an infrared laser light source 26 and a visible laser light source 27 are introduced. . The above-mentioned inspection connection jig 24 and optical combiner 25 are integrally connected to an optical module 20 in which an optical element to be inspected (in this case, the light receiving element 22) and optical components are integrated, and a light source (in this case, an infrared light source). It functions as a coupling means for optically coupling the laser light source 26 and the visible laser light source 27).

[0013] Here, the infrared laser light P1 is light with a longer wavelength (for example, 1.55 μm) than light in the visible region, and has a single wavelength λ1 and coherent light (hereinafter referred to as laser light with the same phase). 1 coherent light). Further, the visible laser light P2 is light whose wavelength is at least included in the visible region, and is coherent light (hereinafter referred to as second coherent light) having a single predetermined wavelength λ2 and the same phase. Examples of P2 include semiconductor laser light (660 nm to 850 nm) such as a laser diode or gas laser light (632.8 nm) such as a helium neon laser.

In such a configuration, when only the visible laser light source 27 is operated, this visible laser light source 27
The second coherent light P2 generated in the light combiner 25
and package 21 via optical fibers F2, F1
be introduced inside. FIG. 2 is a diagram showing the inside of the
The introduced second coherent light P2 is irradiated from the tip of the optical fiber F1 toward the light receiving surface 22a of the light receiving element 22.

Note that a microlens is formed at the tip of the optical fiber F1, forming a so-called spherical fiber. This microlens is for expanding the apparent angle of irradiation (the angle of incidence if the optical semiconductor is a light emitting element), thereby making the light receiving range of the light receiving surface 22a larger than the core cross-sectional area of the optical fiber. can do.

Here, since the second coherent light P2 is "visible light" with a wavelength λ2, a colored image determined by the wavelength (for example, λ2 is 660 nm) is placed on or near the light-receiving surface 22a.
m, a red image) appears and can be visually confirmed. Note that if the light-receiving element to be inspected has sensitivity to light in the visible light band, coherent light can be used for both inspection and optical axis alignment.

FIGS. 3A to 3E are diagrams showing typical observation results on the light-receiving surface 22a. FIG. 3(a) is a clearly colored image with concentric interference fringes. Such interference fringes occur in the gap between the tip of the optical fiber F1 and the light receiving surface 22a (generally a distance on the order of microns exceeding 0).
This is a phenomenon caused by the second coherent light P2 repeating multiple reflections and the light intensity being strengthened or weakened. The interval between the interference fringes depends on the distance between the tip of the optical fiber F1 and the light receiving surface 22a, and the brightness thereof depends on the amount of light (light power) of the second coherent light P2.

Therefore, by observing such clear interference fringes, it is possible to determine whether the optical system including the optical fibers F1 and F2, the light combiner 25, and the visible laser light source 27 is operating normally. FIG. 3(b) Although the image has sufficient brightness, it is a blurred colored image without clear interference fringes as shown in FIG. 3(a). Such a blurred image is observed, for example, when the optical fibers F1 and F2 are broken and the broken portions are in a butting state (a state in which the broken surfaces are in contact with each other). Therefore, by observing such a blurred image, an abnormality in the optical system can be determined. FIG. 3(c) is a colored image that is darker and smaller than the image in FIG. 3(b). Such a small image is observed, for example, when the optical fibers F1 and F2 are sharply bent. Generally, the bending limit of an optical fiber is determined by the diameter of the optical fiber, and bending the optical fiber beyond the allowable value increases the skin loss of the optical fiber. That is, the image becomes darker due to the increased loss,
Furthermore, since the above-mentioned reflection phenomenon is less likely to occur, interference fringes are no longer observed. Therefore, by observing such a dark and small image, abnormalities in the optical system can be determined. Figure 3(d) is a moderately bright (but darker than Figure 3(a)) colored image with a strange flickering effect. If you look closely at the magnified image, you may notice extremely fine interference fringes. Such a flickering image is caused by, for example, the optical fiber F1.
, F2 is broken and reflection occurs at the broken part. Therefore, by observing such a flickering image, an abnormality in the optical system can be determined. FIG. 3(e) shows a state in which there is no colored image at all. For example, this is the case when the optical fibers F1 and F2 are broken and the broken parts are completely separated. Therefore, in this case as well, it is possible to determine whether there is an abnormality in the optical system.

As described above, in this embodiment, the light receiving surface 22
From the observation results of the colored image in a, it is possible to determine whether the optical system is normal or abnormal, and in the case of an abnormality, the cause thereof can be determined. Therefore, the inspection system can always be maintained in the best condition, and inspection accuracy can be improved. In this example, when the optical system is normal, that is, when clear interference fringes as shown in FIG. 3(a) are observed, the center of the interference fringes (the optical axis of the second coherent light P2 The positional relationship between the light-receiving surface 22a and the optical fiber F1 can be adjusted by simply aligning the light-receiving surface 22a with the center of the light-receiving surface 22a. This positioning work is simple and effective as it is all done visually, and is effective over a wide range including the light receiving surface 22a.Moreover, since the center of the interference fringes corresponds correctly to the core of the optical fiber F1, accurate positioning can be achieved. It is possible to make adjustments.

Note that the infrared laser light source 26 is operated at the same time, and the combined light P1, 2 of the first coherent light P1 and the second coherent light P2 from this light source is sent to the light receiving surface 2.
The alignment work may be performed while irradiating the area 2a. In this case, the first coherent light P1 is emitted from the light receiving element 22.
An electrical signal corresponding to is extracted. Therefore, by using the evaluation results of this electric signal in combination, more precise positioning can be achieved.

Note that the interference fringes can be observed not only visually, but also by using a television camera or the like. FIG. 4 shows an example of the system configuration, in which coherent light projected onto a light receiving element 40 is captured by a television camera 41,
Interference fringes are displayed on the screen of the monitor 42. If such a configuration is adopted, not only can light other than visible light be used as inspection light due to the imaging characteristics of the television camera 41, but it also eliminates the need to directly view the coherent light itself, which is preferable in terms of protecting the eyesight of the worker. It can be done. Furthermore, the system of FIG.
The image signal from 1 is taken into the signal processing device 43, and the signal processing device 43 compares the image with, for example, a reference pattern that has been registered as a non-defective product in advance, thereby making it possible to automate the inspection and improve the accuracy and reproducibility of the inspection. properties, stability, etc. can be improved. Signal processing device 43 in this case
functions as a recognition means for recognizing interference fringes of coherent light projected onto the surface of the optical element (here, the light receiving element 40).

Further, in the above embodiment, a light-receiving element is assumed, but it goes without saying that a light-emitting element may also be used. Furthermore, the optical fiber is not limited to a bulbous fiber, and as shown in FIG. Alternatively, the optical lens 32 may be placed in the center.

[0023]

According to the present invention, since coherent light on the surface of the optical element is observed, proper positioning can be achieved by visual observation or image processing.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an inspection system according to an embodiment.

FIG. 2 is a configuration diagram of main parts of an embodiment.

FIG. 3 is an image diagram of one embodiment.

FIG. 4 is a system configuration diagram of an embodiment using a television camera.

FIG. 5 is another main part configuration diagram of an embodiment.

FIG. 6 is a sectional view of a conventional optical semiconductor module.

[Explanation of symbols]

22: Photodetector (optical semiconductor) F1: Optical fiber P1: first coherent light P2: second coherent light

Claims (5)

[Claims] 1. A step of injecting coherent light into an optical module in which an optical element and an optical component are integrated from the optical component side, and determining the state of interference fringes of the coherent light projected onto the optical element. A method for inspecting an optical module, comprising the step of inspecting the optical component by observing it. 2. The method according to claim 1, wherein the optical element is a light receiving element, and the coherent light is used also as optical axis alignment light. 3. The optical element according to claim 1, wherein the optical element is a light receiving element, and the coherent light and the optical axis alignment light having different wavelengths are incident on the optical component. Method. 4. The optical element is a light emitting element, the wavelength of the coherent light is selected to be different from the emission wavelength of the light emitting element, and the optical element is aligned simultaneously with the optical axis by light emission of the light emitting element. 2. A method according to claim 1, characterized in that a test is carried out. 5. A light source that outputs coherent light; coupling means for optically coupling the light source to an optical module in which an optical element and optical component to be inspected are integrated; An inspection apparatus for an optical module, comprising: recognition means for recognizing interference fringes of the projected coherent light.