JPS636890A - Semiconductor laser optical system - Google Patents

Abstract

PURPOSE:To reduce the effect of spontaneous radiation and extend a laser-beam dependent output region to a low luminescent region by providing an interference filter for selectively transmitting only light in a wavelength range including the laser beam wavelength. CONSTITUTION:A semiconductor laser 1 emits light with a quantity corresponding to an applied current and the light is incident on a collimator lens 2 provided in a light path. The light converted to parallel beams by the collimator lens 2 is incident on an interference filter 3. The interference filter 3 selectively transmits light in a wavelength range including the laser beam wavelength. Thus, the effect of spontaneous radiation is reduced and the large output region of the laser beam can be enlarged into a low luminescent region. Further, since the spontaneous radiation used by the interference filter is quasi-monochromatic, the effect of chromatic aberration can be removed. Accordingly, the laser beams can be focused to a small spot over a wide output range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a semiconductor laser light source device equipped with a semiconductor laser, and more particularly to a semiconductor laser light source device that is capable of focusing oscillated light into a small spot diameter over a wide output range. This invention relates to a semiconductor laser optical system.

(Technical Past and Prior Art of the Invention) Semiconductor lasers having semiconductor chips have conventionally been used as scanning light generating means in various scanning recording devices and scanning reading devices. This semiconductor laser has various advantages compared to gas lasers, etc., such as being smaller, cheaper, and consumes less power, as well as being capable of so-called analog direct modulation, which changes the output by controlling the drive current. . In particular, when this semiconductor laser is used in the scanning recording device, the above-mentioned direct modulation can be performed using a signal emitted according to image information.
Extremely convenient.

By the way, it is known that there are two types of light emitted from the semiconductor laser: laser oscillation light and spontaneous light emission in the fi range. The relationship between the current applied to the semiconductor laser, the laser oscillation light, and the light from the spontaneous light emitting region will be described below with reference to FIG.

In the graph shown, line a shows the relationship between the drive current and the output of light in the spontaneous emission #A region (hereinafter referred to as spontaneous emission light), and line a shows the relationship between the drive current and the output of laser oscillation light. It is something. As shown in the graph, when a current is applied to the semiconductor laser, no laser oscillation light is output until the current exceeds the threshold current IO, and only spontaneous luminescence light is output. The output of naturally emitted light increases little by little as the driving current increases, but when the current reaches the threshold I. When the output of the laser oscillation light exceeds 1, and the output of the laser oscillation light increases, its proportion to the total emitted light becomes small, and substantially only the laser oscillation light is output. A curve C represents the relationship between the total amount of light emitted from the semiconductor laser, which is a combination of naturally emitted light and laser oscillation light, and the amount of current.

By the way, the present applicant has already proposed a radiation image information recording and reproducing system for recording, reading, and reproducing radiation image information using a stimulable phosphor sheet (Japanese Patent Application Laid-open No. 12429/1983, 55- No. 116340, same 5
No. 5-163472, No. 56-11395, No. 56
-104645, etc.), the density of the image information to be reproduced varies widely, so the recording light for reproducing this image information onto the recording material must be modulated over a wide dynamic range of i:100 to 1000. be.

Therefore, when directly modulating a semiconductor laser and using it as a light source for the recording light of a recording device that reproduces the radiographic image, it is necessary to also use light in a low-output region that is greatly affected by naturally emitted light. . However, compared to laser oscillation light, the naturally emitted light has problems such as a mixture of various angular components, so when focused by a focusing lens, laser oscillation light cannot be focused to a small spot diameter. There is this inconvenience. For this reason, when using light in a low power range where naturally emitted light is dominant as well as light in a high power range where laser oscillation light is dominant, problems arise such as the spatial resolution of scanning being impaired. .

Further, a semiconductor laser light l provided with the above-mentioned semiconductor laser may be used.
I! The device is usually equipped with lenses such as collimator lenses and focusing lenses. Emitted light is approximately 4Q
Because it has spectral components spanning nm, it is easily affected by the chromatic aberration of the lens mentioned above, and it is more difficult to focus it into a small spot diameter unless an expensive lens with highly accurate chromatic aberration correction is used. There is also the problem of becoming.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and is an object of the present invention to reduce the influence of naturally emitted light in an optical system equipped with a semiconductor laser, and to reduce the influence of naturally emitted light to reduce the influence of laser oscillation light. Semiconductor laser oscillation light iI! can expand the light output range, avoid the effects of chromatic aberration of the lens, and reduce the spot diameter of the focused light even in the low output range! The purpose is to provide purchasing equipment.

(Structure of the Invention) The semiconductor laser light source device of the present invention includes a semiconductor laser that emits laser oscillation light and spontaneous emission light, a focusing lens provided on the optical path of the light emitted from the semiconductor laser, and a condenser lens that emits the laser oscillation light. It is characterized by comprising an interference filter that selectively transmits only light having wavelengths in the vicinity of the wavelength range including the wavelength range.

That is, by providing an interference filter having the above characteristics on the optical path of the light emitted from the semiconductor laser, almost all of the laser oscillation light is transmitted, but most of the spontaneously emitted light is cut off.

Therefore, when both the laser oscillation light and the naturally emitted light enter the interference filter, most of the naturally emitted light is cut off by passing through the interference filter, and the relative proportion of the laser oscillation light increases. Therefore, laser oscillation light becomes dominant even in a light output region lower than that of the conventional method, and the spot diameter can be made sufficiently small even when using light in a low power region.

Furthermore, the spontaneously emitted light that passes through the interference filter is only light whose wavelength is near the wavelength range of the laser oscillation light.
It is almost unaffected by the chromatic aberration of the focusing lens, and the spot diameter at the focusing position can be made sufficiently small even if a relatively inexpensive lens without special chromatic aberration correction is used.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a side view showing a semiconductor laser optical system according to one embodiment of the present invention.

When a current is applied to the semiconductor laser 1, the semiconductor laser 1 emits light with an amount of light corresponding to the amount of current, and the light oscillated from the semiconductor laser 1 passes through a collimator lens 2 provided on the optical path.
After being made into parallel light, the light enters an interference filter 3 that selectively transmits only light of a specific wavelength.

The semiconductor laser 1 emits two types of light, the above-mentioned laser oscillation light and spontaneous light emission, depending on the applied current, and the emission spectra of these lights are as shown in FIG. In other words, the laser oscillation light has an emission spectrum of about 20 r around 785 nll as shown by line d.
However, the emission spectrum of the spontaneously emitted light extends over a range of about 40 nm, as shown by the curve e. The spectral transmittance characteristics of the interference filter 3, into which the laser oscillation light having the above-mentioned wavelength characteristics and the naturally emitted light are incident, are as shown by the dashed line in FIG. That is, the interference filter 3 selectively transmits light in the vicinity of the wavelength range including the wavelength range of the laser oscillation light, and almost 100% of the laser oscillation light passes through the interference filter 3. -On the spontaneously emitted light, only light in a wavelength range close to the wavelength of the laser oscillation light passes through the interference filter 3, but light of other wavelengths is cut by the interference filter 3.

Therefore, the amount of light PO before entering the interference filter 3 is
The relationship between the amount of light P after passing through the interference filter is Pa
>P. Amount of current applied to the semiconductor laser and light m
The relationship between P a and optical IP is as shown in the graph of FIG.

The solid line in the figure shows the amount of light Pa, and the dashed line in the figure shows the change in the amount of light P according to the current value. Since the interference filter 3 acts to selectively cut off naturally emitted light as described above, the value of P is significantly lower than Pa while the drive current is below the threshold current 1o for excavating laser oscillation light. Also, the current value is Io
The period from when the laser oscillation light starts outputting beyond 100 mA to when the light emission becomes positive where the influence of the spontaneous emission light is almost gone (within the range surrounded by the circle in the middle of Figure 3) is the relative ratio of the laser oscillation light to the natural emission light. increases. Therefore, when using light that has passed through an interference filter, the light emitting region where laser oscillation light is dominant extends to a lower light emitting region than when using light that has not passed through the interference filter. Interference filter 3
The light that has passed through the lens enters the focusing lens 4 and is focused at a focusing position P, as shown in FIG. In the light source device of this embodiment, as described above, the interference filter 3
By reducing the influence of naturally emitted light, it is possible to sufficiently focus light in a low luminescence region at the convergence position A, even though conventionally it was not possible to obtain a sufficiently focused beam spot at the convergence position P.

Incidentally, the above optical system uses lenses such as the collimator lens 2 and the condensing lens 4, and it is known that these lenses generally have chromatic aberration. For this reason, when light in a wide wavelength range is incident on these lenses, there will be a problem that the beam spot will become large at the convergence position. By extracting only light, it is possible to avoid the effects of chromatic aberration of the lens. Therefore, according to this apparatus, the spot diameter at the focusing position can be further reduced without using an expensive lens system that is specially corrected for chromatic aberration.

As mentioned above, by cutting a part of the naturally emitted light, the influence of the laser oscillation light is increased and the output range is expanded, and by cutting a part of the naturally emitted light in this way, the wavelength #4 region used is Using the limited device of this embodiment, we investigated the relationship between the spot diameter of the focused light obtained at the focusing position P and the light emission 2 after passing through the interference filter, and the results shown by the solid line in FIG. 4 were 1q. . Moreover, the dashed-dotted line in FIG. 4 shows the case where the interference filter is removed from the light source device as a comparative example.

The spot diameter shown in the graph of Figure 4 is a relative focused spot with the spot diameter in the output range where the laser oscillation light output is sufficiently large and the spot diameter is focused sufficiently small, regardless of the presence or absence of an interference filter, as 1.0. It has been found that when the interference filter is provided, the focused spot diameter in the low light emission region can be kept smaller than when no interference filter is provided.

The results shown in Fig. 4 are obtained when an interference filter with a half-width of about 5 ns is used as shown in Fig. 2, and the smaller the half-width centered around the wavelength of the laser oscillation light, The spot diameter of the low light emission region can be made small. Therefore, the half-width of the interference filter may be adjusted as appropriate depending on the manufacturing cost of the interference filter, the light emitting region used, the tolerance range of the spot diameter of the light used, and the like.

In the embodiment described above, the interference filter is provided between the collimator lens and the focusing lens, but it goes without saying that the interference filter may be provided between the semiconductor laser and the collimating lens or after the focusing lens.

(Effects of the Invention) As explained above, according to the semiconductor laser light source device of the present invention, by providing an interference filter, the influence of naturally emitted light is reduced, and the output region where the influence of laser oscillation light is large is reduced. It can be spread within the light emitting area. Furthermore, the interference filter makes the naturally emitted light used quasi-monochromatic, so that it is hardly affected by the chromatic aberration of the lens in the device. Therefore, according to the semiconductor laser light source device of the present invention, it is possible to focus the light emitted over a wider output range than before into a sufficiently small spot, modulate the light in a wide dynamic range, and achieve high precision. It can also be suitably used as a scanning light oscillation means in a scanning recording device that requires scanning.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a semiconductor laser light source device according to an embodiment of the present invention, FIG. 2 is a graph showing the emission spectra of laser oscillation light and spontaneous emission light, and the spectral transmittance characteristics of an interference filter. A graph showing the relationship between the amount of light after passing through the interference filter and the driving current of the semiconductor laser compared to before passing through the interference filter. Figure 4 shows the relationship between the amount of light emitted when an interference filter is provided and the focused spot diameter when the interference filter is provided. FIG. 5 is a graph showing the relationship between the driving current of a semiconductor laser and the output of spontaneously emitted light and laser oscillation light. 1...Semiconductor 2...Collimator lens 3...Interference filter 4...Focusing lens 1st
Figure 2 Temporary reading χ, 785 nm Figure 3 Electricity ratio (mA) -4-'' Figure 4 Cuff 7 (mW) Figure 5 Electricity ratio (mA) -4-

Claims (1)

[Claims] A semiconductor laser that emits light in a spontaneous emission region and laser oscillation light in response to an applied current; a focusing lens provided on the optical path of the light emitted from the semiconductor laser; A semiconductor laser optical system consisting of an interference filter that selectively transmits only light with wavelengths near the wavelength range.