JPS63263438A - Optical inspection device - Google Patents

Abstract

PURPOSE:To detect whether or not an optical fiber is normal with high accuracy by detecting far field images at two points of laser light emitted by a microlens on the tip of the optical fiber and finding the divergence angle of the laser light, and finding the optical radius of curvature of the lens by applying the propagation rule of a Gaussian beam. CONSTITUTION:A core 1 made of quartz to which B, F, P, Ge, etc., are added is covered with a clad 3 of pure quartz to form the optical fiber 1, which is provided with a microlens structure 5 of 10-30mum in radius a the tip on a laser light projection side. Then this fiber 1 is mounted on a control table 32 movably in an X-, a Y-, and a Z-axial direction, a light emitting device 31 is connected to the incidence side, and the projection side is set opposite an infrared camera 40 on a support table 33, so that an image from it is displayed on a CRT 43 through a video controller 42. Thus, the widths WA and WB of the half-value total angles of Gaussian type far field images 50 and 51 obtained by image processing and the beam divergence angle theta are calculated and used to decide whether or not the radius of curvature of the lens 5 is within a reference range.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is effective when applied to an optical inspection device, for example, a technique for detecting the optical radius of curvature of the tip lens portion of an optical fiber having a microlens at the tip. Regarding technology.

[Conventional technology]

Semiconductor lasers (semiconductor laser elements: laser diode chips) are widely used as light sources for optical communications and information processing.
May issue, published May 10, 1986, P73-P? 9
It is described in. This document states that when a semiconductor laser is used for optical communication, efficient coupling of laser light to an optical fiber (hereinafter also simply referred to as fiber) is important. This document also describes a structure in which a spherical lens or a cylindrical lens is interposed between the laser diode chip and the optical fiber, or a structure in which a spherical lens or a cylindrical lens is interposed between the laser diode chip and the optical fiber, or the lens A structure in which a lens system combined with a focusing rod lens is interposed, and a structure in which the tip of the optical fiber is made conical, or the center portion is partially protruded, and the tip is made semispherical to provide a microlens. is listed.

[Problem that the invention seeks to solve]

Optical fibers are used as optical transmission media for optical communications or as transmission media for optical information in sensors. Optical fibers consist of a central core with a high refractive index and a cladding with a low refractive index surrounding this core.
Optical fibers used for optical communications have a core diameter of 7.
Extremely thin single mode fiber (SMF)
) are beginning to be used. As the core diameter becomes smaller in this way, the optical coupling technology between the semiconductor laser element, which is the source of optical communication, and the optical fiber becomes even more important.

The present applicant has proposed that in order to improve the optical coupling efficiency between the laser diode chip and the optical fiber, in the case of an optical fiber whose tip faces the laser diode chip,
The tip of the optical fiber is processed into a conical shape, and the tip surface is made into a spherical surface (miniature lens). In this case, the quality of the microlens at the tip of the optical fiber is determined by enlarging the optical fiber using an optical system such as a microscope and comparing it with a reference radius of curvature.

However, in this method of sorting out the quality of optical fibers, the radius of the microlens is determined by external observation, and the quality of the microlens is determined by comparing it with a preset radius reference area. The present inventors have clarified that it is not necessarily appropriate to determine the quality of microlenses based on the radius, as the optical radius may not match in some cases.

An object of the present invention is to provide an optical inspection device that can detect the quality of this microlens with high precision.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the optical inspection device of the present invention sends a laser beam to the rear end of an optical fiber, detects a far-field image at two points of the laser beam emitted from a microlens at the tip of the optical fiber, and detects the far-field image at each point. Find the half-width of the far-field image, find the divergence angle of the laser beam from this half-width and the distance between two points, and calculate the optical radius of curvature of the microlens using the Gaussian beam propagation agent using this divergence angle. However, the optical fiber is determined to be good only when the radius of curvature obtained by this calculation is within a preset reference range.

[Function] According to the above-described means, the optical inspection device of the present invention detects the far-field image at two points of the laser beam emitted from the microlens at the tip of the optical fiber, and determines the laser beam from this detection information. The divergence angle is determined, and this divergence angle is used to determine the optical radius of curvature of the microlens using the propagation agent of the Gaussian beam.The optical radius of curvature is then determined and selected to determine the quality of the optical fiber with high precision. can be detected.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

Fig. 1 is a schematic diagram showing the principle of the optical inspection device of the present invention, Fig. 2 is a front view similarly showing the optical inspection device, Fig. 3 is a block diagram, and Fig. 4 is a schematic diagram showing the principle of the optical inspection device of the present invention. FIG. 5 is a perspective view showing the external appearance of a semiconductor laser device into which the optical fiber determined to be incorporated is the same (a sectional view showing the inside of the semiconductor laser device, and FIG. 6 is an enlarged view showing the laser diode chip and the optical fiber) The cross-sectional view and FIG. 7 are the same (a graph based on theoretical values showing the correlation between the beam divergence angle and the radius of curvature of the microlens).

In this embodiment, an example in which the present invention is applied to a single mode fiber will be described.

The optical fiber 1 has a diameter of 7 μm, as shown in FIG.
It consists of a core 2 and a cladding 3 with a diameter of 125 μm covering this core 2. Further, although not shown, the optical fiber 1 is covered with a jacket or the like and treated as an optical cable. The core 2 is doped with B, F, P, Ge, etc., and has a different refractive index from the cladding 3 made of pure quartz. Further, the tip of the optical fiber 1 is a conical tapered portion 4, and the exposed surface of the core 2 at the tip is a hemispherical surface (microlens) 5 with a radius of about 1θ to 30 μm. When this microlens 5 is incorporated into a semiconductor laser device as shown in FIG. 4, it is integrated into a laser diode chip 6 as shown in FIG.
The laser beam 8 emitted from the end of the resonator 7 is taken into the tip of the optical fiber 1.

Before explaining the quality selection of the microlenses of the optical fiber, an example of a semiconductor laser device into which the optical fiber 1 determined to be good is incorporated will be described. The semiconductor laser device 9 shown in FIG. 4 has a structure in which an optical cable 11 is connected to one end of a package 10 having a flat structure. Furthermore, two monitoring light receiving element glues 12 are attached to the other end of the package 10, and
The structure is such that two laser diode chip glues 13 are attached to the side surface of the package 10. Further, the package 10 includes a stem 14 and a cap 15 that closes the stem 14. Further, the stem 14 is provided with a mounting hole 16, and the semiconductor laser device 9 is installed at a predetermined location using the mounting hole 16.

On the other hand, the inside of the package 10 has a structure as shown in FIG. That is, a pedestal 17 is provided at the center of the main surface of the stem 14 constituting the pan cage 10, and a submount 18 is provided on the pedestal 17.
A laser diode chip 6 is fixed via the .

The laser diode chip 6 is fixed to the submount 18 via a solder 19, and then fixed to the stem 14 by fixing the submount 18 to the base 17 with the solder 20. Further, the optical fiber 1 extending inside the package 10 is guided by a fiber guide 21 and is fixed to the fiber guide 21 by a fixing member 22 attached so as to close the inner end of the fiber guide 21. . Then, the inner end of the optical fiber 1, that is, the microlens 5 is made to face the end of the resonator 7 of the laser diode chip 6, and the laser light 8 emitted from the resonator 7 of the laser diode chip 6 is taken in. There is.

On the other hand, the optical fiber 1 is connected across the laser diode chip 6.
A block 23 made of ceramic is fixed to the main surface 2 of the stem 14 on the opposite side with a solder 24. On the main surface of this block 23, that is, the surface facing the laser diode chip 6, the inner ends of the two leads 12 of the monitor light-receiving element whose outer ends protrude outside the package 10 are respectively fixed. There is. A light receiving element 25 for receiving laser light 8 emitted from the laser diode chip 6 is fixed to the inner end of the one board 12 by a solder 26 . Further, an electrode (not shown) of the light receiving element 25 and an inner end of the other lead 12 are electrically connected by a wire (not shown). Further, the electrode of the laser diode chip 6 is
They are electrically connected to leads 13, which are not shown in FIG. 5, by wires or the like.

Such a semiconductor laser device 9 monitors the output of the laser beam 8 using the light receiving element 25, and performs optical communication using the optical cable 11 while adjusting the voltage applied to the laser diode chimney based on this monitoring information. .

Here, the quality selection of the microlens 5 of the optical fiber 1 will be explained. The microlens 5 is judged to be good or bad by an optical inspection device as shown in FIG. Further, this optical inspection apparatus has a mechanism as shown in the block diagram of FIG. This optical inspection device has a base 30
It has a light emitting device 31, a control table 32, and a support table 33 on top. The control table 32 is
As shown in FIG.
4, the movement can be controlled in the plane XY direction and the vertical Z direction. Further, on this control table 32, a fiber center stand 35 for holding the optical fiber 1 is arranged. This fiber set stand 35
Hold the tip of the

On the other hand, the rear end of the optical fiber 1 is attached to the light emitting device 31. As shown in FIG. A laser beam 37 is sent to the rear end of the optical fiber 1. Further, the laser light 37 emitted from the semiconductor laser 36 is received and monitored by the light receiving element 3B, and is controlled to always have a constant intensity by an automatic output control circuit (APC) 39.

On the other hand, the tip of the optical fiber 1 held on the control table 32, that is, the first
As shown in the figure, light 3 emitted from a microlens 5
7, that is, the laser beam 37 is detected by an infrared camera (infrared vidicon) 40 which is a detection section. This infrared camera 40 is operated by a video controller 42 incorporating a video A/D converter 41, and is capable of detecting, for example, a near-field image and a far-field image of the laser beam 37. Also, these images can be viewed on a monitor TV (
It is also projected on a CRT (CRT) 43 screen.

Although not shown in FIG. 2, this optical inspection apparatus is also provided with a central processing bag W (CPU) 44 and an image processing device 45. The CPU 44 controls the mechanical controller 34, APC 39, image processing device 45, and the like.

Further, the video controller 42 is controlled by the CPU 44 via the ■0 interface 46. In addition, the CP
The keyboard interface 48 and printer interface 49 are connected to the U44 via the ■0 driver 47.
is connected.

In such an optical inspection device, as shown in FIG. 1, far-field images 50 and 51 of two points of the laser beam 37 emitted from the microlens 5 at the tip of the optical fiber 1 are detected. At the same time, the divergence angle (beam divergence angle) θ of the laser light is determined from this detection information. The far field image 50,5
1 is point A.

The brightness distribution of the laser beam 37 at point B is measured by the infrared camera 4.
A far-field image 50° 51 obtained by the 0 image processing is obtained by detecting the 0 and performing image processing with the video A/D converter 41, which approximates a Gaussian beam. Therefore, the CPU 44 calculates the full width at half maximum in the far-field images 50 and 51, that is, 1/a''c?
Width wA, w.

is calculated by calculation. When the distance between two measurement points is L, the beam divergence angle θ is given by the following equation from the geometrical relationship.

L Here, θ: Divergence angle WA: l/e'' width at measurement point A; Width WI: 1/e! width at measurement point B; L: distance between measurement points.

Next, the optical radius of curvature R of the microlens 5 of the optical fiber is determined from the propagation agent of the Gaussian beam as shown in equation (2) below.

] ×□... (2) λ Here, Wf: Spot size of the propagation mode in the optical fiber λ: Wavelength n: Optical fiber refractive index.

In this optical inspection device, the determination unit of the CPU 44 determines whether or not the radius of curvature R obtained in this way is within a preset reference range, and if the radius of curvature R is within the reference range, Only the optical fiber 1 is determined to be good and selected.

In addition, the graph of FIG. 7 shows the divergence angle θ (d e g),
It is a graph showing a theoretical correlation with the radius of curvature R (μm). The solid line in the same graph indicates the fiber spot size of 5.5 μm, and the broken line indicates the fiber spot size of 5.5 μm.
．． 0 μm is shown.

Note that this graph is a graph when the wavelength of the laser beam is 1.3 μm and the fiber refractive index is 1.45. As can be seen from the graph, as the divergence angle θ becomes smaller, the radius of curvature R suddenly becomes thicker.
As shown in this graph, the assumed target accuracy is that the radius of curvature of the microlens of the optical fiber is 15±2 μm.

Further, in this optical inspection device, the maximum coupling distance can also be determined using the radius of curvature R using the following theoretical formulas (3) to (5).

dan=□... (3) 1 +(-) ” f=□... (4) t12 p=□... (5) λ Here, r: focal length p: coefficient R: radius of curvature 6: Refractive index Wf: Spot size of propagation mode in the optical fiber λ: Wavelength This maximum coupling distance is determined by It can be used as a guideline.

According to such an embodiment, the following effects can be obtained.

(1) The optical inspection device of the present invention actually detects the laser beam emitted from a microlens of an optical fiber, calculates the beam divergence angle based on the data obtained from this detection, and performs arithmetic processing to Since the optical radius of curvature of the microlens is determined and whether or not the optical radius of curvature is within the reference range is determined as to whether or not the microlens is good or bad, it is possible to perform highly accurate determination and selection.

(2) According to the above (1), according to the present invention, it is possible to automatically select the quality of optical fibers having microlenses.

(3) According to the above (1), according to the present invention, it is possible to accurately select non-defective microlenses, so when an optical fiber is assembled and inserted into a semiconductor laser device, the laser diode chip and the optical fiber can be separated with high efficiency. The effect is that it is possible to perform coupling and provide a semiconductor laser device of excellent quality.

(4) Through (1) to (3) above, it is possible to judge and select the quality of microlenses automatically and with high precision, thereby providing a high-quality optoelectronic device incorporating an optical fiber having microlenses at a low cost. A synergistic effect can be obtained.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. For example, as shown in FIG. 8, the optical inspection MW of the present invention has a protrusion 52 at the center of the flat end surface of the optical fiber 1, and the tip of the protrusion 52 has a hemispherical shape. The present invention can also be used in the same manner for structures constituting the microlenses 53 serving as surfaces, and the same effects as those of the previous embodiment can be obtained.

The above explanation mainly describes the invention made by the present inventor in the single-mode
Although we have described the case in which the present invention is applied to a technology for selecting the curvature radius of a microlens in a fiber, the present invention is not limited thereto. Applicable to

The present invention can be applied at least to technology for selecting the quality of microlenses in optical bodies such as optical fibers.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

The optical inspection device of the present invention detects opportunities for farsightedness at two points of laser light emitted from a microlens at the tip of an optical fiber,
The laser beam spreads from this detection information.

This divergence angle is used to determine the optical radius of curvature of the microlens according to the Gaussian beam propagation law, and the quality of this optical radius of curvature is judged and sorted, making it possible to detect the quality of the optical fiber with high precision. can.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the principle of the optical inspection device of the present invention, Fig. 2 is a front view similarly showing the optical inspection device, Fig. 3 is a block diagram, and Fig. 4 is a schematic diagram showing the principle of the optical inspection device of the present invention. FIG. 5 is a cross-sectional view showing the inside of the semiconductor laser device, and FIG. 6 is an enlarged cross-sectional view showing the laser diode chip and optical fiber. 7 is a graph based on theoretical values showing the correlation between the beam divergence angle and the radius of curvature of a microlens, and FIG. 8 is a schematic diagram showing an optical fiber having another structure to be inspected by the present invention. ■... Optical fiber, 2... Core, 3... Clad, 4... Taper part, 5... Microlens, 6... Laser diode chip, 7... Resonator, 8... ... Laser light, 9... Semiconductor laser device, 10... Pan cage, 11... Optical cable, 12.13... Lead,
14... Stem, 15... Camp, 16... Mounting hole, 17... Pedestal, 18... Submount, 19
゜20...Solder, 21...Fiber guide,
22... Fixing material, 23... Block, 24... Solder, 25... Light receiving element, 26... Solder, 3
0... Base, 31... Light emitting device, 32... Control table, 33... Support table, 34... Mechanical controller, 35... Fiber set stand, 36
... Semiconductor laser, 37... Laser light, 38...
Light receiving element, 39...APC, 40...Infrared camera, 41...Video A/D converter, 42...Video controller, 43...Monitor television, 44...
cpυ, 45...Image processing device, 46...■0 interface, 47...IO driver, 48...Keyboard interface, 49...Printer interface, 50.51...Far-field image , 52...
・Protrusion, 53...Minute lens. Fig. 2 Fig. 3 Fig. J6 - Turn 4 - T゛ Fig. 7 Angle θ (Lel) Fig. 8

Claims (1)

[Claims] 1. A stage that holds the tip of an optical fiber having a lens, a light emitting source that sends coherent light to the rear end of the optical fiber, and light emitted from the lens at the tip of the optical fiber. a detection unit that detects a far-field image at two points; and a detection unit that determines a divergence angle of the light from the half-width of the far-field image, and calculates the optical radius of curvature and maximum coupling distance of the lens from this divergence angle. 1. An optical inspection device comprising: a calculation unit for calculating the calculation unit; and a determination unit for determining an optical fiber as being non-defective only when the radius of curvature calculated by the calculation unit is within a reference range. 2. The optical inspection apparatus according to claim 1, wherein the radius of curvature of the lens at the tip of the optical fiber is determined by the Gaussian beam propagation law using the value of the divergence angle.