JPH05136514A - Output light stabilizer for semiconductor laser - Google Patents

Abstract

PURPOSE:To eliminate multiple reflection, to prevent generation of interference between multiple reflection light and monitoring light, and the accurately compensate the wavelength dependency of the sensitivity of a photosensitive body by a method wherein the light passing surface is used as a light diffusion surface and it is used as the optical filter inserted into the light path of the light made incident as a light detector. CONSTITUTION:The light beam 31 made to radiate from a semiconductor laser 30 in a divergent light state is formed into a parallel beam by a collimater lens 32, and it is made incident on a beam splitter 33. The light beam reflected by the beam splitter 33 is condensed by a condensing lens 35 as a monitoring light 31B, and then it is received by a light detector 36 used to control optical output stabilization. The monitoring light 31B is led to a light detector 36 passing through an optical filter 37. The surface 37, where the monitoring light 31B passes through, of the optical filter 37 is used as a light diffusion surface by conducting a surface reflecting work and the like, for example. As no multiple reflection is generated, the amount of received light of the light detector 36 is not changed by the variation of interference state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser light output stabilizing device, and more particularly, to a light output for a semiconductor laser which irradiates a photosensitive member whose sensitivity changes with the wavelength of the irradiation light. It relates to a stabilizing device.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser has been widely used as one of light sources for generating a light beam in an optical scanning recording device, an optical communication device and the like. This semiconductor laser has a number of advantages such as smaller size, lower cost, lower power consumption, and direct modulation by changing the drive current, as compared with a gas laser.

In a light source device using this semiconductor laser, a so-called APC (Automatic Power) is provided so that a predetermined light amount indicated by a constant light amount command signal or a light amount command signal which can be changed stepwise or continuously is accurately obtained.
A control circuit is often provided to control the optical output stabilization. This APC circuit splits a rear emission light of a semiconductor laser (a light beam emitted in a direction opposite to a front emission light used for image recording or the like) or a part of the front emission light by a beam splitter or the like. The amount of monitor light is detected by a photodetector, and the drive current of the semiconductor laser is feedback-controlled so that the detected amount of light is maintained at a predetermined value.

The semiconductor laser, which has been subjected to the light output stabilization control as described above, is often used as a light source for emitting light for irradiating various photoconductors. In addition, most of the photoconductors have a sensitivity that varies depending on the wavelength of the irradiation light. As such photoconductors, for example, silver salt photographic film and the storage disclosed in JP-A-55-116340 are disclosed. Fluorescent phosphor sheet and the like.

Here, the stimulable phosphor sheet will be briefly described. Radiation (X-rays,
When irradiated with α rays, β rays, γ rays, electron rays, ultraviolet rays, etc.,
It is known that a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated emission depending on the accumulated energy. A phosphor having such a property is called a stimulable phosphor (stimulable phosphor).

Using this stimulable phosphor, radiation image information of the human body or the like is once recorded on a sheet having a layer of the stimulable phosphor, and the stimulable phosphor sheet is two-dimensionally excited by excitation light such as laser light. Scanning produces stimulated emission light, and the obtained stimulated emission light is photoelectrically read to obtain an image signal. Based on this image signal, a recording material such as a photographic light-sensitive material or a display device including a CRT or the like is irradiated with radiation. A radiation image information recording / reproducing system for outputting an image as a visible image has already been proposed by the present applicant (Japanese Patent Laid-Open Nos. 55-12492 and 56-11395).

By the way, in a semiconductor laser, a phenomenon called so-called mode hopping in which the oscillation wavelength fluctuates due to changes in ambient temperature or the like can occur. When the light emitted from the semiconductor laser is applied to the photoconductor having the sensitivity characteristic having wavelength dependence as described above, this oscillation wavelength variation causes an unfavorable situation. That is, when the photoconductor is a recording material, the density of the recorded image is changed due to the fluctuation of the oscillation wavelength, and when the photoconductor is the above-mentioned storage phosphor sheet, it is stimulated by the fluctuation of the oscillation wavelength. The amount of emitted light, that is, the density of the read image changes.

Japanese Examined Patent Publication No. 63-60385 discloses a device for stabilizing the optical output of a semiconductor laser capable of compensating for the wavelength dependence of the sensitivity of the photoconductor as described above. This optical output stabilization device for semiconductor lasers has an optical filter having a spectral transmittance characteristic corresponding to the spectral sensitivity characteristic of a photoconductor in the optical path of monitor light detected by a photodetector for optical output stabilization control. It is inserted. With this configuration, for example, when the oscillation wavelength of the semiconductor laser changes to the side where the sensitivity of the photoconductor is lowered, the light output is increased because the amount of light detected by the photodetector is also decreased, and the sensitivity of the photoconductor is reduced. It is compensated by the increase of the light quantity. The opposite is true when the oscillation wavelength changes to the side of increasing the sensitivity of the photoconductor.

[0009]

However, in the conventional apparatus, even if the optical filter having the spectral transmittance characteristic that exactly corresponds to the spectral sensitivity characteristic of the photoconductor is used as the above optical filter, There was a case where the wavelength dependency of sensitivity of could not be compensated accurately.

The present invention has been made in view of the above circumstances, and can accurately compensate for the wavelength dependence of the sensitivity of a photoconductor when the oscillation wavelength of a semiconductor laser changes due to mode hopping or the like. It is an object of the present invention to provide a semiconductor laser light output stabilizing device that can be used.

[0011]

SUMMARY OF THE INVENTION A light output stabilizing device for a semiconductor laser according to the present invention comprises a semiconductor laser for irradiating a photosensitive member whose sensitivity changes according to the wavelength of the irradiation light, as described above, and this semiconductor laser. A photodetector for detecting the light amount of the light emitted from the photodetector, a feedback control circuit for receiving the light amount signal output from the photodetector, and controlling the semiconductor laser drive current so as to keep the light amount signal at a predetermined value, Having a spectral transmittance characteristic corresponding to the spectral sensitivity characteristic of the body, in the optical output stabilizing device of a semiconductor laser comprising an optical filter inserted in the optical path of light incident on the photodetector, as the optical filter, It is characterized in that a surface through which light passes is used as a light diffusing surface.

[0012]

According to the research conducted by the present inventors,
As mentioned above, the problem that the wavelength dependence of the sensitivity of the photoconductor cannot be accurately compensated is that the monitor light is multiply reflected between both surfaces of the optical filter, and this multiple reflected light is directly detected without multiple reflection. Interference with the monitor light going to the vessel,
It was found that the interference state was changed due to the wavelength variation, and the amount of light received by the photodetector was changed.

Therefore, if the surface of the optical filter is made to be a light diffusing surface as in the device of the present invention, the above-mentioned multiple reflection does not occur, and therefore, the multiple reflected light and the monitor light directly directed to the photodetector without multiple reflection. Also, the wavelength dependency of the sensitivity of the photoconductor is accurately compensated for.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows an optical output stabilizing device for a semiconductor laser according to an embodiment of the present invention. The semiconductor laser 30 whose light output is stabilized by the device of this embodiment is used as a light source of the excitation light with which the above-mentioned stimulable phosphor sheet is irradiated, for example. As shown in the figure, a light beam (laser beam) 31 emitted from the semiconductor laser 30 in a divergent state is collimated by a collimator lens 32 and enters a beam splitter 33. A part of the light beam 31 passes through the beam splitter 33 and is incident on a light deflector 34 such as a galvanometer mirror as excitation light 31A. On the other hand, the light beam reflected by the beam splitter 33 is collected as a monitor light 31B by a condenser lens 35 and then received by a photodetector 36 for controlling the light output stabilization. The monitor light 31B is guided to the photodetector 36 through the optical filter 37 described later.

The stimulable phosphor sheet 1 in which the radiation image information of the subject is accumulated and recorded by irradiating the radiation transmitted through the subject is a sub-scanning means such as an endless belt.
It is moved in the direction of arrow Y by 11 and, at the same time, the excitation light 31A is deflected by the optical deflector 34 to move X on the sheet 1.
Main scan in the direction. From the portion of the stimulable phosphor sheet 1 that has been scanned with this excitation light, stimulated emission light 13 having a light amount corresponding to the radiation image information stored and recorded is diverged. The stimulated emission light 13 enters the inside of the light guide 14 from one end face 14a of the light guide 14 formed by molding a transparent acrylic plate, and travels through the light guide 14 while repeating total reflection to form a circular shape. The light is emitted from the end face 14 b rounded into the light and is received by the photomultiplier (photomultiplier tube) 15. This photomultiplier 15 corresponds to the amount of stimulated emission light 13,
That is, the image signal S indicating the radiation image information is output.

The image signal S is logarithmically amplified by a logarithmic amplifier 16 and then passed through an A / D converter 17 to be converted into a digital image signal D. This digital image signal D
Next, after undergoing image processing such as gradation processing in the image processing circuit 20, it is sent to the image reproducing device 21 and is used for reproduction of the radiation image. The image reproducing device 21 may be a display device such as a CRT or a recording device for performing optical scanning recording on a photosensitive film.

Next, the light output stabilization control of the semiconductor laser 30 will be described. The photodetector 36 is a monitor light 31B.
And outputs a light amount signal S1 indicating the light amount of
Is input to the feedback control circuit 38. In this embodiment, the feedback control circuit 38 causes
Light output stabilization control is performed so that the light amount of 31 A becomes constant. That is, the feedback control circuit 38 compares the light amount signal S1 with the reference signal, and when the former exceeds the latter, lowers the drive current I injected into the semiconductor laser 30,
In the opposite case, control for increasing the drive current I is performed. As a result, the light amount of the monitor light 31B, that is, the light amount of the corresponding excitation light 31A is stabilized at a constant value. As the feedback control circuit 38, a generally known conventional one may be used.

The operation of the above-mentioned optical filter 37 will be described below. Excitation light 31 of the stimulable phosphor sheet 1
The sensitivity to A has wavelength dependence as shown in FIG. The optical filter 37 has a spectral transmittance characteristic corresponding to the spectral sensitivity characteristic of the stimulable phosphor sheet 1, as indicated by the curve a in FIG. When such an optical filter 37 is inserted in the optical path of the monitor light 31B, when the wavelength of the light beam 31 changes due to mode hopping of the semiconductor laser 30, the monitor light reception of the photodetector 36 according to the wavelength. The amount changes. That is, as the wavelength of the light beam 31 shifts to the long wavelength side, the amount of this monitor light received decreases. Then, the feedback control circuit 38 controls the optical output of the semiconductor laser 30 in the increasing direction according to the decrease in the received light amount. When the wavelength of the light beam 31 is shifted to the short wavelength side, the opposite is true.

Therefore, the light quantity of the light beam 31, that is, the excitation light
The light amount of 31 A is the inverse characteristic of the spectral sensitivity characteristic of the stimulable phosphor sheet 1 as shown by the curve b in FIG. 3, and changes according to the wavelength change. As described above, if the wavelength dependence of the sensitivity of the stimulable phosphor sheet 1 is compensated by the increase or decrease of the excitation light irradiation amount, the density of the radiation image reproduced by the image reproducing device 21 changes due to the change of the excitation light wavelength. Disappears,
A high quality radiographic image is reproduced.

Also, monitor light 31B of the optical filter 37
Both surfaces 37a, 37b through which the light passes are made light diffusion surfaces by, for example, roughening. If these surfaces 37a,
If 37b is processed to be flat, a part of the monitor light 31B can be multiply reflected between these two surfaces 37a, 37b. The light thus multi-reflected can directly interfere with the monitor light 31B directed to the photodetector 36 without being multi-reflected. This interference state changes depending on the wavelength of the monitor light 31B, and if the interference state changes, the monitor light reception amount of the photodetector 36 changes. Therefore, if this wavelength changes as described above, the excitation light 31A is changed due to the change in the interference state.
It is possible that the light intensity of the light changes with a characteristic different from that of the curve b in FIG.

However, here, the surface 37 of the optical filter 37 is
If a and 37b are used as light diffusing surfaces, the above-mentioned multiple reflection does not occur, so that the amount of light received by the photodetector 36 does not change due to changes in the interference state. Therefore, in this apparatus, the light amount of the excitation light 31A always changes due to the inverse characteristic of the spectral sensitivity characteristic of the stimulable phosphor sheet 1, and a high quality radiation image is always reproduced.

Although the embodiment formed so as to stabilize the light amount of the excitation light 31A as the used light to a constant value has been described above, the present invention is continuous or stepwise in directly modulating the semiconductor laser. It is also applicable to the case where the light output stabilization control is performed so that the used light quantity becomes a predetermined value with respect to the light quantity command signal that can be changed to.

Further, the present invention is not limited to a semiconductor laser that emits excitation light for irradiating a stimulable phosphor sheet, but other semiconductors, for example, for irradiating a photosensitive member whose sensitivity changes according to the wavelength of irradiation light with recording light. The same can be applied to a device for stabilizing the laser light output. Further, the present invention can be similarly applied to an apparatus in which the front emission light of the semiconductor laser is used as the used light and the rear emission light is detected as the monitor light.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a radiation image information reading apparatus to which an apparatus according to an embodiment of the present invention is applied.

FIG. 2 is a graph showing spectral sensitivity characteristics of a stimulable phosphor sheet handled by the radiation image information reading apparatus of FIG.

3 is a graph showing spectral transmittance characteristics of the optical filter in the apparatus of FIG. 1 and wavelength characteristics of the excitation light versus irradiation amount characteristics.

[Explanation of symbols]

 1 Storage phosphor sheet 11 Sub-scanning means 15 Photomultiplier 30 Semiconductor laser 31 Light beam 31A Excitation light 31B Monitor light 33 Beam splitter 34 Optical deflector 36 Photodetector 37 Optical filter 38 Feedback control circuit

Claims (2)

[Claims] 1. A semiconductor laser for irradiating light on a photoconductor whose sensitivity changes according to the wavelength of irradiation light, a photodetector for detecting the amount of light emitted from this semiconductor laser, and an output for this photodetector. A feedback control circuit that receives a light amount signal and controls a semiconductor laser drive current so as to maintain the light amount signal at a predetermined value; and a spectral transmittance characteristic corresponding to the spectral sensitivity characteristic of the photoconductor, In a light output stabilizing device for a semiconductor laser, which comprises an optical filter inserted in an optical path of incident light, the optical filter is characterized in that a surface through which light passes is a light diffusing surface. Optical output stabilizer for semiconductor lasers. 2. The photoconductor is a stimulable phosphor sheet, and the semiconductor laser is used as a light source for emitting excitation light that stimulates the stimulable phosphor sheet to emit light. 1. A semiconductor laser light output stabilizing device according to 1.