JPS6131931A - Measuring method of oscillation wavelength of semiconductor laser - Google Patents

Abstract

PURPOSE:To measure laser oscillation wavelength by shaping light from a semiconductor laser into a parallel beam and comparing the position where an image is formed through a diffraction grating with the position where the light from the LD is image-formed by the same means. CONSTITUTION:The pitch P of a modulating signal is set to an optional value between 1/10-1sec according to the specifications of a data logger 13 and an XY recorder 16 in use. The laser light emitted by the LD is modulated with the modulating signal 9 and a constant electric current is flowed to a Peltier element 5 during said period to raise the ambient temperature of the LD from, for example, 25 deg.C to 40 deg.C; and the ambient temperature is detected by a thermistor 6 and the wavelength is detected by a position sensor 3, so that outputs of the both are drawn on the data logger 13 or XY recorder 16. Consequently, temperature characteristics of the oscillation frequency and wavelength stepping of an LD to the inspected and the influence of image frequency on them are measured.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for measuring the wavelength of light emitted from a semiconductor laser used in a laser printer or the like.

Conventional technology In laser printers and the like, the surface of a photoconductor is scanned with a laser beam for image information reproduction, which is emitted from a semiconductor laser after being modulated by an acousto-optic modulator according to the image information signal, thereby creating an image corresponding to the image information signal. When forming an image, main scanning is performed by deflecting the reproduction light in an angular range corresponding to the image width. As one of the deflection means for that purpose,
Recently, holographic scanners (usually called holoscanners) have come into use, which consist of multiple facets of hologram diffraction gratings arranged circumferentially on a disk with lattice spacing varying stepwise in the circumferential direction. became. When reproducing image information with a hologram scanner, when the hologram scanner is rotated at a constant angular velocity and the reproduced beam t is incident on the 7 assets of the hologram diffraction grating at a constant angle of incidence and a constant position, the interval between the diffraction gratings The diffracted light is emitted at the corresponding diffraction angle, and as the diffraction grating interval changes sequentially as the Boro scanner rotates, the emitting direction of the diffracted light changes sequentially, and the diffracted light is deflected within a certain angular range for each facet. However, the f-theta characteristic is corrected by an f-theta lens provided in the optical path, and the imaging point moves linearly on the surface of the photoreceptor at a constant speed, so that main scanning of a predetermined image width is performed.

By the way, semiconductor laser (1aser diode,
(hereinafter abbreviated as LD) has variations in oscillation wavelength for each individual product. For example, visible light J and D range from 780 nm to 80 nm.
It is distributed between about 0 nm. When the wavelength changes, the diffraction angle by the diffraction grating changes, and the scanning width changes. Therefore, the image may protrude from a predetermined image width or be shrunk, resulting in an error equivalent to the magnification error in a normal copying machine. In order to correct this, the frequency of the clock (interval of the signal with respect to the dots) at which the image information signal is injected into the laser beam by the acousto-optic modulator is changed according to the oscillation wavelength of the LD, and the image information signal is written on the photoreceptor. The interval between the inserted dots is always constant so that the scanning width matches a predetermined image width. Therefore, in order to perform this correction control, L
It is essential to detect the oscillation wavelength of D.

Further, it is known from literature that the oscillation wavelength of an LD changes not only due to variations among individual products but also due to changes in the temperature of the LD. In reality, the temperature of the LD itself cannot be detected, so the temperature of its surroundings is detected. The relationship between the change in ambient temperature and the oscillation wavelength of the LD is shown in FIG. 1, where the wavelength shifts stepwise with respect to the change in ambient temperature.

In other words, at a certain ambient temperature, the wavelength changes discontinuously even if the temperature changes very slightly. This development is called wavelength skipping (wavelength mode jump). For example, the wavelength shift range is 0.3 for a 1°C change in ambient temperature.
Although the dots are very narrow, on the order of nm, the intervals between dots written on the photoreceptor may become irregular, or in severe cases, dots may fall out.

Therefore, it is necessary to consider the wavelength mode jump and use the LD in a stable temperature range between the temperature at which the wavelength jump occurs.

However, it is known that the curve of the LD ambient temperature and wavelength mode jump shown in FIG. 1 changes depending on the image frequency of image information that modulates the laser beam. Images produced by a laser printer are created as a series of black and white dots.

In the black solid area, all dots are black, and in the ground area, all dots are mortar and the LD does not blink, so it is DC (direct current) and the frequency is low. If black and white repeats every other dot, the frequency is the highest. , this is called the fundamental frequency. Actual image information contains a mixture of various frequencies. In the case of DC with a low image frequency, the current is left flowing through the LD, so even if the ambient temperature of the LD is low, the temperature inside the LD rises, as shown by A in the wavelength jump part of the curve in Figure 2. Thus, the point at which the wavelength jump occurs will shift toward the lower ambient temperature.

On the other hand, when the image frequency is high, the LD repeats blinking and the current flows on and off frequently, so the temperature of the LD does not rise very much. Wavelength skipping occurs. Therefore, it is very dangerous to use an LD in the hatched area between A and B, and it must be used in a stable region between two adjacent wavelength jump ranges.

The criteria for determining the set temperature of the LD are as follows.

(a) The stability region width is wide. (Because temperature control is easy.) (b) If the width of the stable region is the same, the temperature is low.

(The lower the ambient temperature, the longer the life of the LD.) Purpose: In view of the above-mentioned situation of fluctuations in the oscillation wavelength of the LD of a laser printer that performs scanning using a holo scanner, the present invention aims to improve accuracy with a simple device. The present invention aims to provide a method for measuring the oscillation wavelength of an LD and a method for measuring the oscillation wavelength by changing the ambient temperature in order to obtain the temperature characteristics of the mode jump of the LD's oscillation wavelength.

Structure In order to achieve the above object, the present invention uses a coupling lens to capture light emitted from a semiconductor laser! Shaping the beam into a parallel beam, making this beam incident on a diffraction grating, and deflecting the imaging position of the obtained diffracted beam from the imaging position of the diffracted beam by the same means as that of light from a semiconductor laser with a known oscillation wavelength. It is characterized by measuring the oscillation wavelength of a semiconductor laser by detecting the amount.

By performing the above measurements while changing the ambient temperature of the semiconductor laser, the temperature characteristics of the wavelength jump of the oscillation wavelength of the semiconductor laser can be obtained.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 3 is a diagram explaining the theory of the method of the present invention. When the laser light emitted from the LD1 is incident on the diffraction grating 2 with the grating spacing d at an incident angle α, the diffracted light is emitted at a diffraction angle β. Suppose we did. In that case, assuming that the wavelength of the laser beam is λ, the position sensor (or C0D) 3 is placed at a position far away from the diffraction position by the diffraction grating 2 on the optical path of the diffracted light. death,
The incident points of the diffracted light by the diffraction grating 2 of two laser beams whose oscillation wavelengths measured by the above equation (1) have two values, for example, 780 nm and 800 nm, respectively, are defined as P and Q, and the points between them are equally divided. If you have a linear wavelength scale, you can measure the oscillation wavelength by reading the scale at the point where the diffraction beam of the laser beam emitted from the LD enters the position sensor 3. The oscillation wavelength of the LD is immediately measured.

Since the angles of the line segments P and Q with respect to the 20 diffraction points of the diffraction grating are very small, it is safe to say that there is practically no error in the above method.

In order to obtain the temperature characteristics of the wavelength jump of the LD's oscillation wavelength, the temperature may be varied and measured using the method described above.

Furthermore, in order to examine the influence of the image frequency on the temperature characteristics of wavelength skipping, a device that provides a modulation signal corresponding to the image information is added to the LD, and the temperature is measured for the case of unmodulated DC and the case of modulation. All you have to do is change it and measure it.

FIG. 4 schematically shows an example of an apparatus for measuring the LD oscillation wavelength and its temperature characteristics based on the above theory.

The LD1 constitutes an LD unit 20 together with a coupling lens 4, a Peltier element 5 that controls the ambient temperature of the LD, a thermistor 6 that measures the ambient temperature of the LD, a casing 7 that houses these, and a radiator 8. Furthermore, L.D.L.
A modulation signal generation board 9 for providing a modulation signal corresponding to an image information signal is connected via an LD drive board 10 to.

Divergent than LDl, with coupling lens 4! A neutral density filter 11 for adjusting the amount of light and a diffraction grating 2 are provided in the optical path of the laser beam that has been shaped into a parallel beam. An f-theta lens 12 is provided on the optical path of the diffracted light diffracted by the diffraction grating 2, and a position sensor 6 is provided at the imaging position thereof. The output of the thermistor 6 and the position sensor 3 provided in the LD unit are input to the data logger 13, and the output is sent to the output section 1.
4, it is displayed on the display 15 and printed out.

The modulation signal generated by the modulation signal generation board 9 is a signal that repeats, for example, IM-Hz and DC at a constant pitch P, and can represent normal image information.

Note that instead of the display device below the data logger 13, an XY recorder 16 is used as shown by the broken line in the figure, and the output of the mister 6 is transferred to the XY recorder 16 via the thermistor voltage conversion board 17.
It is also possible to input the output of the position sensor 3 to the X axis of the Y recorder 1B and input the output of the position sensor 3 to the Y axis of the XY recorder 16 to display the relationship of the LD oscillation wavelength to the LD ambient temperature. The pitch P of the modulation signal depends on the specifications of the data logger or X-Y recorder used, for example, 1 second when using a data logger, and 1 second from the ring when using an X-Y recorder.
It may be selected as appropriate, such as setting it to an arbitrary value between seconds.

This modulation signal modulates the laser light emitted from the LD, and during this period a certain current is passed through the Peltier element 5, and the LD
By gradually increasing the ambient temperature of the LD from 25°C to 40°C, for example, detecting the ambient temperature with the thermistor 6 and the wavelength with the position sensor 3, and recording the outputs of both on the data logger 16 or the XY recorder 16, It is possible to measure the temperature characteristics of the oscillation frequency and wavelength jump, and the influence of the image frequency on them.

Effects As described above, according to the present invention, the oscillation wavelength of a semiconductor laser used in a laser printer or the like and the temperature characteristics of the wavelength jump can be measured with high accuracy by simple operations.

[Brief explanation of drawings]

Figure 1 is a curve diagram qualitatively showing the relationship between changes in the ambient temperature of a semiconductor laser and changes in the oscillation wavelength of the semiconductor laser.
The figure is a curve diagram showing the influence of the image frequency on the wavelength jump of the oscillation wavelength of the semiconductor laser, Figure 3 is a schematic diagram for explaining the theory of the method of the present invention, and Figure 4 is a diagram showing the method of the present invention being implemented. 1 is a schematic diagram showing an example of the configuration of a measuring device for 1... Semiconductor laser 2... Diffraction grating 6...
Position sensor (diffraction light imaging position detection means) 4...
Coupling lens 9...Laser beam modulation means 13...Data logger 16...XY recorder Figure 1 Ambient temperature Figure 3 Semiconductor laser Figure 2 Ambient temperature

Claims (3)

[Claims] (1) The light emitted from the semiconductor laser is shaped into a nearly parallel beam using a coupling lens, and this beam is made incident on a diffraction grating. 1. A method for measuring an oscillation wavelength of a semiconductor laser, characterized in that the oscillation wavelength of the semiconductor laser is measured by detecting the amount of deviation of the diffracted beam from the imaging position of the light from the laser by the same means. (2) Shape the light diverging from the semiconductor laser into a nearly parallel beam using a coupling lens, make this beam incident on a diffraction grating, and place the image of the resulting diffracted beam on a semiconductor whose oscillation wavelength is known. The oscillation wavelength of the semiconductor laser is measured by detecting the amount of deviation of the light from the laser from the imaging position by the same means.This measurement is performed while changing the ambient temperature of the semiconductor laser, and the oscillation wavelength of the semiconductor laser is determined by A method for measuring the oscillation wavelength of a semiconductor laser, characterized in that the temperature characteristics of the wavelength jump are obtained. (3) The method according to claim 2, characterized in that the semiconductor laser is modulated by changing the image frequency to oscillate laser light, and the temperature characteristics of the mode jump of the oscillation wavelength of the semiconductor laser are obtained. Method.