JP3334819B2 - Laser light observation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light observation device for observing laser light.

[0002]

2. Description of the Related Art A laser beam observation apparatus for evaluating a laser beam shape in order to examine the oscillation characteristics and stability of various lasers is commercially available. These laser light observation devices are
It is generally called a laser beam profiler or a laser beam shape measuring device. Such a laser light observation device includes a laser light photodetector, and a photodiode, a line sensor, and a CCD image sensor are used as the photodetector.

A laser beam observation apparatus using a photodiode is known as a standard measuring method for measuring a beam intensity distribution by mechanically scanning a photodiode. Although this method is capable of accurate measurement, the measurement is performed by mechanical scanning of a photodiode, so that a large amount of measurement time is required, and there is a problem that laser fluctuation during the measurement time is not traced. Further, in this method, since only one point of data can be measured by one oscillation, the measurement time becomes extremely long especially for a pulse laser having a low repetition rate.

Therefore, there is known an apparatus which uses a line sensor (a line sensor having a MOS structure) to increase the area measured by a photodetector and shorten the measurement time. Since this line sensor has no wiring on the element,
Although accurate measurement can be performed, only the cross-sectional shape on one line of the beam can be obtained. Therefore, at present, a laser beam observation device adopting a camera system for two-dimensionally capturing the entire shape of the laser beam has become mainstream, and a CCD camera has been used.

[0005]

However, in a normal CCD camera, various filters are inserted in front of a light receiving area in which the light receiving elements are arranged, and these glass end faces, electric wiring portions of the light receiving elements (normally, polysilicon) are used. Is used), the incident light is reflected and diffracted by the element protection film and the light receiving element itself, and the incident light to be measured and the reflected light from each part are complicatedly combined on the light receiving surface. Such reflected light and diffracted light do not pose a major problem when imaging ordinary incoherent light. However, when imaging coherent light (light with high coherency), such as laser light, it appears on the output screen. A relatively large size interference fringe may be generated. In particular, in the laser beam shape measuring device, the intensity distribution of the beam is deformed by the interference fringes, and a problem arises that a true beam shape cannot be measured.

As a method for dealing with such a problem of the interference fringes, the following method can be considered.

(A) An anti-reflection film in a wavelength range to be used is applied to a protective glass disposed in front of a CCD element to reduce reflection.

(B) Remove the protective glass placed on the front of the CCD.

However, according to the above method (a), the interference fringes generated by the protective glass can be reduced, but the protective glass such as the wiring portion of the light receiving element and the element protective film, which is a major factor of the interference fringes, is reduced. Subsequent interference can occur. When lasers having different wavelengths are used, it is necessary to use an element provided with another reflection film. According to the method (b), it is possible to reduce interference, but there remains a problem in the reliability of the device. In addition, these interferences also occur due to the element protection film and wiring, but this is because
From the standpoint of device reliability and operation, it is impossible to remove these device protective films and wirings.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a laser light observation device capable of observing a laser beam having high coherency without generating large interference fringes. .

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. In a laser light observation apparatus for observing laser light, (A) an incident surface irradiated with laser light and And an emission surface from which the laser light is emitted. The incidence surface and the emission surface are formed by both end surfaces of the bundled optical fibers, and the phases of the laser light emitted from the emission surface are made different. A fiber plate having a plurality of optical fibers, and (B) a solid-state imaging device having a light-receiving surface for converting incident light into electricity, the light-receiving surface being opposed to an emission surface of the fiber plate. I decided that.

[0012]

According to the present invention, first, laser light is input to the fiber plate. This fiber plate is different in the optical path from the incident surface to the emission surface and the propagating mode in each optical fiber, and the phase of the laser light emitted from the output surface is different. When the output surface of each optical fiber is considered as a point light source, large interference fringes do not appear on the light receiving surface of the solid-state imaging device arranged opposite to the output surface because the phases of the laser beams are different. . That is, the present fiber plate functions as a mode scrambler. Then, on the light receiving surface of the solid-state imaging device,
Since the incident laser light is converted into electricity, when a laser beam is incident, the intensity distribution of the laser light can be extracted as an electric signal.

However, simply installing this fiber plate on a solid-state image sensor has a certain effect on imaging, but does not provide good imaging. If the distance between the fiber plate and the solid-state imaging device is too close, the fluctuation of the signal caused by the structure of the fiber plate (pitch of the fiber plate) becomes dominant, and the shape of the obtained laser beam becomes rough. This is because the focus deviates significantly and the resolution is reduced. The present inventor carefully studied such an interval, and as a result, by providing a gap of about 10 μm between the fiber plate and the solid-state imaging device, the fiber plate was arranged close to the solid-state imaging device. It has been found that it is possible to reduce the resulting interference noise.

In the laser beam observation apparatus of the present invention, the incident surface of the fiber plate is inclined such that the optical axis of the laser beam incident on the fiber plate does not coincide with the optical axis of the beam reflected by the fiber plate. That is, it is possible to prevent the laser beam from returning to the laser light source to change the oscillation characteristics. Note that if the incident surface of the fiber plate is arranged so that the exit surface is parallel to the light receiving surface of the solid-state image sensor, and the incident surface is inclined with respect to the exit surface (for example, 2 °), from the exit surface to the solid-state image sensor. Can be kept constant, so that the focus can be kept constant.

If the fiber plate is a tapered fiber plate in which each fiber has a tapered shape, the laser beam image is enlarged and reduced without using an extra optical system that may cause interference fringes. be able to.

However, although the above-described fiber plate has an effect of suppressing interference fringes, high frequency noise appears in a video signal by providing the fiber plate. Therefore, the laser light observation device of the present invention is further provided with an electric filter for removing high frequency noise of a video signal output from the solid-state imaging device. Since the spectrum of the obtained laser light is smoothed by the electric filter, a precise beam shape can be measured when observing a laser beam.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laser beam observation apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.

FIG. 1 is a configuration diagram showing the overall configuration of a laser beam device according to a first embodiment of the present invention. Laser light emitted from the laser light source 100 is reflected by the beam splitter 500a, passes through the ND filter 500b, and enters the CCD camera 200. A CCD image sensor (solid-state imaging device) is installed in the CCD camera 200, and captures a laser beam incident on the CCD camera 200, and inputs this video signal to the image processing device 300. The image processing device 300 processes the video signal and
The shape of the laser beam imaged by the CCD camera 200 is output on an RT (display).

FIG. 2 shows a laser beam observation apparatus using a fiber plate 200c formed by bundling a plurality of optical fibers. In the figure, the output surface of the fiber plate 200c is arranged to face the light receiving surface of the CCD image sensor 200a. And this fiber plate 20
Reference numeral 0c denotes a special fiber plate, which is a CCD from a laser beam side incident surface on which each optical fiber is incident.
The optical path of the laser beam passing through to the emission surface on the image sensor 200a side is designed to be different. The cores of the respective optical fibers are indicated by reference numerals 2a to 2f in the figure, and the laser beams passing through these cores 2a to 2f are schematically drawn by alternate long and short dash lines. Each of the cores 2a to 2f has a diameter and an interval of about 5 μm, a thickness of 4 mm, and several million optical fibers. In addition, 3a-3g
Is a clad formed with a lower refractive index than the core.

Hereinafter, the fiber plate 200c will be described in detail. The core 2c is larger in diameter than the core 2b, and allows the passing laser beam to take many modes. The core 2f is smaller in diameter than the core 2b, and can only take a mode in which the number of laser beams passing therethrough is small. Although the core 2a has the same diameter as the core 2b, disturbance due to external stress and internal fluctuation are introduced, and the laser beam passing through the core 2a and the laser beam passing through the core 2b Have different phases at the exit surface. In this way, by making the phases at the emission surfaces of the optical fibers different (mode scrambling), it is possible to suppress the occurrence of interference fringes due to the beam applied to the CCD image sensor 200a. When a single-mode optical fiber is bundled and a fiber plate formed so that the phase of the laser beam on the emission surface is the same, the emission surface of the optical fiber becomes a point light source and interference fringes are generated by the interference of the beam. Is not preferred.

The CCD image sensor 200a is
a p-type epitaxial layer 30a on the p-type semiconductor substrate 10,
The light receiving surface is formed by sequentially laminating the n-type buried layer 30b and the oxide film 40, and the transfer electrodes 50a and 50b are buried in the oxide film 40. And this C
The CD image sensor 200a transfers a signal charge generated in response to the incidence of a beam by applying a drive voltage to the transfer electrodes 50a and 50b. As described above, the laser beam observation device according to the present embodiment includes the CCD image sensor 20.
Laser beam (1a-1g) incident on the light receiving surface of 0a
Of the fiber plate 20 so that the phases of
0c, the CCD image sensor 2
No large interference fringes appear on the light receiving surface of 00a. In the CCD image sensor 200a of the present invention, since the p-type epitaxial layer 30a is introduced, the influence of impurities distributed unevenly in the substrate 10 is suppressed, and the p-type epitaxial layer 30a is formed on the p-type epitaxial layer 30a. The crystallinity of the formed layer can be kept good. Therefore, if this CCD image sensor 200a is used,
Further, a highly accurate laser beam can be observed.

FIG. 3 shows the fiber plate 2 shown in FIG.
FIG. 2 is a configuration diagram of a laser light observation device in which a read / drive circuit 200e of the CCD image sensor 200a is provided in the CCD image sensor 200a and the CCD image sensor 200a. As is clear from the figure, a fiber plate obtained by cutting an optical fiber cable along a plane perpendicular to the optical axis is fixed to the light receiving element in the CCD image sensor 200a. In this embodiment, the fixing is performed by applying an adhesive around the CCD image sensor 200a and the fiber plate 200c.
The package may be bonded and fixed to the CD image sensor 200a, or may be fixed by inserting matching oil between the fiber plate 200c and the CCD image sensor 200a. In this embodiment, the thickness of the fiber plate 200c is set to about 4 mm in consideration of the protection of the CCD image sensor 200a and the distortion of the fiber plate 200c itself. The thickness may be about 1 mm.

Next, FIG. 7A shows the two-dimensional shape of the laser beam measured by the laser light observation apparatus shown in FIG. 1 having the CCD camera shown in FIG. In addition, FIG.
FIG. 3 is a diagram when a two-dimensional shape of a laser beam is measured without using the fiber plate 200c in FIG. 2, and a semiconductor laser having a wavelength of 850 nm is used as a laser light source. That is, FIG. 2 shows the result of photoelectrically converting the laser beam applied to the light receiving surface of the CCD image sensor 200a and displaying the electric signal on the CRT 400. In FIG. 2, the beam of the laser beam on the CRT 400 is shown. The spectrum obtained by decomposing the shape (beam intensity distribution) in the horizontal direction and the vertical direction is also shown. As is clear from these figures (photographs), a large interference fringe is observed in the figure (b), while this interference fringe is removed in the figure (a) using the fiber plate 200c.

However, as in the first embodiment,
Fiber plate 20 with mode scramble effect
0c is installed in close contact with the CCD image sensor 200a, despite the interference fringe removing action,
As is apparent from FIG.
The fluctuation of the laser light imaged by the CCD image sensor 200a due to the structure of Oc (particularly the pitch of the fiber plate) becomes dominant, and the beam image observed by the CRT 400 becomes rough. Therefore, the second embodiment according to the laser light observation apparatus of the present invention is configured to remove such roughness of the beam image. Hereinafter, a second embodiment will be described with reference to FIG.

FIG. 4 shows a laser observation apparatus shown in FIG. 3 in which a space of about 10 μm (5 to 15 μm) is provided between the fiber plate 200c and the CCD image sensor 200a. The present inventors have proposed that the CCD image sensor 200a and the fiber plate 20
The image of the laser beam obtained by variously adjusting the interval from 0c was observed. As a result, when this interval is gradually increased, laser light emitted from a specific optical fiber constituting the fiber plate 200c interferes with laser light emitted from an optical fiber close to the specific optical fiber. (Synthesized) and found that the speckle pattern changes to a size smaller than the pitch of the optical fiber. When the interval is about 10 μm, when the CCD image sensor 200a having the pixel pitch of 10 to 17 μm is used, the interference noise of laser light can be reduced most, and an image with smoothing can be obtained. At the same time, the amount of light from the adjacent optical fiber does not increase, so that a high-resolution image can be obtained.

FIG. 7C is a diagram showing the shape of the laser beam observed by the laser light observation device of FIG. The figure is a far-field image of a semiconductor laser having a wavelength of 850 nm.
As is clear from this figure, the roughness of the beam image observed is reduced as compared with FIG. 7A. As described above, in the present embodiment, a gap of about 10 μm is provided between the CCD image sensor 200a and the fiber plate 200c to reduce interference noise caused by disposing the fiber plate 200c close to the CCD image sensor 200a. Therefore, it is possible to obtain a high-resolution and smooth image without roughness.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 5 shows that the optical axis of the laser beam incident on the fiber plate 200c and the optical axis of the beam reflected by the fiber plate 200c do not coincide with each other in the laser light observation device of FIG.
0c is inclined.
In this embodiment, the incident surface of the fiber plate 200c has a configuration in which the exit surface is arranged parallel to the light receiving surface of the CCD image sensor 200a, and the incident surface is inclined by 2 ° with respect to the exit surface. With this configuration, it is possible to prevent the laser beam from returning to the laser light source to change the oscillation characteristics of the laser light source, and to keep the distance from the emission surface to the light receiving surface of the CCD image sensor 200a constant. Since it can be held, the focus can be kept constant. In the present embodiment, the fiber plate 200c is brought into close contact with the light receiving surface of the CCD image sensor 200a. However, as shown in FIG. 4, the fiber plate 200c may be brought close with a gap of about 10 μm. .

Next, a fourth embodiment of the present invention will be described.

FIG. 6 shows a laser beam observation apparatus of FIG. 3 in which the fiber plate 200c is a tapered fiber plate in which each optical fiber has a tapered shape. And with such a configuration,
The laser beam image can be enlarged and reduced without using an extra optical system that may cause interference fringes.

Next, a fifth embodiment of the present invention will be described.

The first to fourth fiber plates 200c have the effect of suppressing interference fringes.
As described in the second embodiment, this fiber plate 2
By providing 00c, high frequency noise appears in the video signal. Therefore, in the fifth embodiment of the laser light observation device of the present invention, the CCD image sensor 200a is provided with an electric filter for removing high frequency noise of the video signal output from the CCD image sensor 200a. That is, in the fifth embodiment, high frequency noise is removed by providing such an electric filter in the image processing apparatus 300 of FIG.

As a configuration of such an electric filter (low-pass filter) for removing high-frequency noise, a method of performing smoothing on the original image by a mask operation such as 3 × 3, 5 × 5, or the like.

A method of obtaining an average value of a plurality of scanning lines along the X or Y axis.

A method of obtaining a moving average of neighboring data.

A method of performing a fitting process on an XY profile.

Are listed.

Such a method can be appropriately selected by the processing software in the image processing apparatus 300. In this embodiment, the image output from the CCD camera 200 is
A profile display is performed using an average value of the intensities of five lines in the image, and a moving average is further performed to remove high-frequency noise. FIG. 8 shows the intensity distribution of the laser beam obtained by this method. As the original image, a far-field image of a semiconductor laser having a wavelength of 780 nm captured by the CCD camera 200 of the first embodiment is used. Although large interference fringes are removed from the original image without smoothing as in the first embodiment, fine irregularities due to high-frequency noise are observed in the profile (FIG. 7A). Therefore, when the number of points of the moving average (the number of smoothing points) is increased, the high-frequency noise seen in the line profile decreases ((b) to (d) in the same figure), and the profile is smoothed. .

As described above, in this embodiment, the CCD image sensor 200a is
Since an electric filter for removing high-frequency noise of the video signal output from a is provided, a smoothed image can be obtained, and the precise beam shape of the laser beam can be measured. it can.

The laser beam observation apparatus of the present invention has been described with reference to the first to fifth embodiments. The packaging and the like of the CCD image sensor 200a of the present invention are described in Japanese Utility Model Application Laid-Open No. 63-0.
68602).

[0040]

As described above, according to the present invention, large interference fringes do not appear on the light receiving surface of the solid-state imaging device, so that highly accurate laser light can be observed. Further, since it is possible to reduce interference noise caused by disposing the fiber plate close to the solid-state imaging device,
The laser beam can be observed with higher accuracy.

If the incident surface of the fiber plate is inclined, it is possible to prevent the laser beam from returning to the laser light source and changing the oscillation characteristics, so that the true characteristics of the laser beam can be measured. can do. In addition, when a tapered fiber plate is used, the laser beam image can be enlarged and reduced without using an extra optical system that may cause interference fringes. This is convenient when it is desired to increase the intensity of the laser light. Further, by providing an electric filter, a precise beam shape can be measured when observing a laser beam.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a configuration of a first embodiment of a laser light observation device according to the present invention.

FIG. 2 is a sectional configuration diagram illustrating details of a CCD camera 200 shown in FIG.

FIG. 3 is a configuration diagram in which a read / drive circuit is mounted in details of the CCD camera 200 shown in FIG. 2;

FIG. 4 is a configuration diagram illustrating a configuration of a second embodiment of the laser light observation device according to the present invention.

FIG. 5 is a configuration diagram illustrating the configuration of a third embodiment of the laser light observation device according to the present invention.

FIG. 6 is a configuration diagram illustrating the configuration of a fourth embodiment of the laser light observation device according to the present invention.

FIG. 7A is a photograph showing the shape (intensity distribution) of a laser beam obtained by the laser light observation device of the first embodiment, and FIG. 7B is a photograph showing the shape of the laser beam obtained by the laser light observation device without using a fiber plate. (B) is a photograph (c) showing the shape of a laser beam obtained by the laser light observation device of the second embodiment.

FIG. 8 is a diagram showing a shape (line profile) of a laser beam obtained by the laser light observation device of the fifth embodiment. FIG. 11A shows the case where the smoothing is not performed, FIG. 10B shows the case where the number of the smoothing points is 5, FIG. 9C shows the case where the number of the smoothing points is 11, and FIG. Shows the case.

[Description of Signs] 100 laser light source 200 CCD camera 300
Image processing device, 400 ... CRT.

Continuation of the front page (56) References JP-A-3-252533 (JP, A) JP-A-62-129745 (JP, A) JP-A-3-202704 (JP, A) JP-A-2-108006 (JP) JP-A-3-242603 (JP, A) JP-A-6-160032 (JP, A) JP-A-5-225933 (JP, A) JP-A-7-244086 (JP, A) 3-80335 (JP, U) Hira 2-77686 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30

Claims (5)

(57) [Claims] 1. A laser light observation device that observes laser light, comprising: an incident surface on which the laser light is irradiated; and an emission surface from which the laser light is emitted, wherein the incident surface and the emission surface are different from each other. A fiber plate having a plurality of optical fibers formed by both end faces of a plurality of bundled optical fibers and having different phases of laser light emitted from the emission surface; and converting incident light into electricity. A solid-state imaging device having a light receiving surface that faces the light emitting surface of the fiber plate. 2. A gap between the fiber plate and the solid-state imaging device having a gap of about 10 μm for reducing interference noise caused by disposing the fiber plate close to the solid-state imaging device. The laser light observation device according to claim 1. 3. The fiber plate according to claim 1, wherein the incident surface of the fiber plate is inclined such that the optical axis of the laser beam incident on the fiber plate does not coincide with the optical axis of the beam reflected by the fiber plate. The laser light observation device according to the above. 4. The laser light observation device according to claim 1, wherein the fiber plate is a tapered fiber plate in which the optical fiber has a tapered shape. 5. The laser light observation device according to claim 1, further comprising an electric filter for removing high frequency noise of a video signal output from the solid-state imaging device.