JPH0511291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a temperature control device for a semiconductor laser in an optical scanning device.

(Prior Art) Optical scanning devices are known that record and read images by scanning with a laser beam.

As one type of such an optical scanning device, a device using a semiconductor laser as a light source and a holoscanner as a means for deflecting the light has been proposed (for example, Japanese Patent Application No. 59-28066). An optical scanning device that uses a semiconductor laser and a holo scanner in this manner will hereinafter be referred to as a holographic optical scanning device.

In a hologram type optical scanning device, a laser beam from a semiconductor laser is diffracted to obtain a diffracted beam, and this diffracted beam is deflected to perform optical scanning.

On the other hand, as is well known, the emission wavelength of a semiconductor laser changes depending on the temperature of the semiconductor laser. When the emission wavelength of a semiconductor laser changes, in a holographic optical scanning device, the diffraction angle of a diffracted beam used for optical scanning changes, which adversely affects optical scanning. The temperature of the semiconductor laser changes depending on the ambient temperature inside the optical scanning device and the Joule heat caused by the drive current passed through the semiconductor laser, so in order to perform optical scanning properly, the temperature of the semiconductor laser must be kept constant. need to be controlled. Note that semiconductor lasers are extremely small, and it is difficult to directly control their temperature. Therefore, by controlling the temperature of the holder that holds the semiconductor laser, the temperature of the semiconductor laser can be adjusted to a predetermined set temperature. It is decided that the control will be carried out in the vicinity.

By the way, the characteristic line showing how the emission wavelength of a semiconductor laser changes with temperature is not constant but changes over time. Therefore, a temperature control method that controls the temperature of a semiconductor laser to be around a certain set temperature is not sufficient in the long term.

In other words, when a semiconductor laser is used for a long period of time, the characteristic line changes over time, so even if the temperature of the semiconductor laser is controlled to the set temperature,
This is because the emission wavelength itself may deviate significantly from the initially set wavelength.

(Purpose) Therefore, an object of the present invention is to provide a novel temperature control method for a semiconductor laser in a hologram-based optical scanning device, which also takes into account changes over time in the characteristic line.

(composition) The present invention will be explained below.

The temperature control device of the present invention also indirectly controls the temperature of the semiconductor laser by controlling the temperature of the holder that holds the semiconductor laser.

Now, the temperature control device of the present invention includes a temperature sensing element,
It has a Peltier element, a control means, a beam position detection element, and a temperature reset means. Of these, the beam position detection element is integrally configured with a synchronization detection element for synchronizing main scanning of optical scanning.

The temperature sensing element detects the temperature of the holder that holds the semiconductor laser.

The Peltier element heats and cools the holding body.

The control means controls the temperature of the holder to be close to the set temperature by controlling energization to the Peltier element in accordance with the holder temperature detected by the temperature sensing element.

The beam position detection element detects the beam position of the deflected laser beam.

The temperature resetting means resets the set temperature for temperature control in the control means based on the output of the beam position detection element. There are two methods for resetting the set temperature, as described below.

The operation of the temperature control device of the present invention is as follows.

That is, during main scanning, that is, when optical scanning is performed for image recording or image reading, the temperature sensing element, Peltier element, and control means work to control the temperature of the holder to a temperature near the set temperature. and indirectly controls the temperature of the semiconductor laser.

During non-main scanning, that is, when the semiconductor laser is emitting light, the holoscanner is operating, and optical scanning for image recording or image reading is not being performed, the temperature sensing element, Peltier element, Together with the control means, a beam position detection element and temperature resetting means work.

Information about the characteristic line of the semiconductor laser at any given time is obtained from the output of the beam position detection element, and based on this output, the temperature resetting means sets a new set temperature for temperature control as necessary. Reset.

By updating the set temperature for temperature control based on information about the characteristic line of the semiconductor laser at any given time, changes in the characteristic line over time can be incorporated into temperature control.

The following description will be made with reference to the drawings.

FIG. 1 shows the temperature control device of the present invention implemented.
Main parts of an image recording device using a holographic optical scanning device are schematically illustrated.

In FIG. 1(), 10 is a semiconductor laser, 12 is a collimating lens, 14 is a cylindrical lens, 16, 18, and 22 are plane mirrors, 20 is a holo scanner, 24 is a θ lens, and 26, 28 are plane mirrors. A plane mirror, 30 is a cylindrical lens, 32 is a photoconductive photoreceptor, 34 is a beam position detection element, 38
40 is a holder for holding the semiconductor laser 10, and 42 is a thermistor as a temperature sensing element.
indicates a Peltier device, and 44 indicates a microcomputer, respectively.

In FIG. 1(), the semiconductor laser 10 and the holder 38 that holds it are shown separately for ease of understanding, but the semiconductor laser 10 is, of course, held integrally by the holder 38.

The holo scanner 20 is composed of a holo disk 20A and a motor 20B. The holodisk 20A is disc-shaped and has a motor 20B.
It is fixed to the shaft of motor 2 in the direction of the arrow.
It is designed to be rotationally driven by 0B.

A plurality of diffraction gratings 200 having the same shape are arranged in a ring shape on one side of the transparent circular substrate of the holodisk 20A. The diffraction gratings 200 are linear diffraction gratings, are optically equivalent to each other, and are formed as holograms.

The outline of image recording by this image recording apparatus will be briefly explained below.

The laser beam emitted from the semiconductor laser 10 is collimated by the collimating lens 12, and is then collimated by the cylindrical lens 14 and the plane mirrors 16, 1.
8 from a predetermined direction.
The light is incident on the diffraction grating 200 of A. Then, a diffracted beam is generated by the diffraction grating 200. When the holodisk 20A rotates, the diffracted beam is deflected. This is because the relative positional relationship between the laser beam incident on the diffraction grating 200 and the grating direction changes. The diffracted beam deflected in this way is called a deflected laser beam.

The diffracted beam passes through a plane mirror 22, a θ lens 24, plane mirrors 26 and 28, and a cylindrical lens 30. It reaches the belt-shaped photoreceptor 32, and the θ lens 2
4. The light is focused into a spot on the surface of the photoreceptor 32 by the imaging action of the cylindrical lenses 14 and 30. As the holodisk 20A rotates, the spot of the deflected laser beam is linearly displaced on the photoreceptor 32, and each time the diffraction grating on which the laser beam is incident is switched, the same displacement, ie, optical scanning, is repeated. In FIG. 1, a straight line 36 indicates the locus of the spot in optical scanning, and this straight line 36
6 is called a main scanning line. Further, on the photoconductor 32, a direction perpendicular to the main scanning direction is referred to as a sub-scanning direction.

The circumferential surface of the photoreceptor 32 is uniformly charged, and when the charged portion reaches the optical scanning section by rotation, it is optically scanned by a deflected laser beam. At this time,
By modulating the emission intensity of the semiconductor laser 10 with an image signal corresponding to the image to be recorded, an electrostatic latent image corresponding to the image is formed on the photoreceptor 32. Therefore, by developing this electrostatic latent image and transferring and fixing the resulting visible image onto a recording sheet such as paper, a desired recorded image can be obtained.

Note that during optical scanning for image recording, the beam position detection element 34 receives a polarized laser beam just before each optical scanning, and sends its pulsed output to the microcomputer 44 as the synchronization detection signal 100. The microcomputer 44 synchronizes each optical scan using the above output, and controls the starting point of the main scan to be at the same position.

The above is an overview of optical scanning.

When the temperature of the semiconductor laser changes and the emission wavelength changes, the diffraction angle of the polarized laser beam changes, which causes the position of the main scanning line to change in the sub-scanning direction, making it impossible to perform proper optical scanning. .

Now, semiconductor lasers are generally used in optical scanning devices in a temperature range of about 20 to 50 degrees Celsius, but in this temperature range, the characteristic line showing the relationship between temperature and emission wave maximum is generally , it becomes step-like as shown in FIG. Although the shape of the characteristic line itself is determined as a characteristic for each individual semiconductor laser, it is common for the characteristic line to have a step-like shape. In FIG. 2, areas A, B, and C of the characteristic line
A region where the emission wavelength changes gradually in response to temperature changes is called a shelf, and a region between the shelves where the emission wavelength jumps is called a step. In reality, there are some unevenness on the shelf, but they are
In practice, this problem is ignored in FIG. 2 because it does not pose a problem that would interfere with optical scanning.

The width of the shelf-shaped portion, that is, the temperature range between one stepped portion and an adjacent stepped portion is usually about several degrees. Therefore, if the temperature width of the shelf B, that is, the temperature difference (T _U − T _L ) is 5 degrees, the temperature T ₀ in the middle is set as the set temperature, and the temperature of the holder that holds the semiconductor laser is set. ,Preset temperature
If the wavelength of the laser light from the semiconductor laser is controlled to be near T ₀ , for example within the range of T ₀ ±1° C., the wavelength of the laser light from the semiconductor laser can actually be controlled to be constant. This is the basic concept of semiconductor laser temperature control.

In addition, in FIG. 2, even if the temperature of the semiconductor laser changes from T _L to T _U , the wavelength change at this time is λ _U −λ _L , and this change is small. Therefore, as long as the temperature of the semiconductor laser varies on the same shelf, the above-mentioned variation in the main scanning line does not pose a practical problem.

However, if the temperature of the semiconductor laser is T _U or T _L
If the laser beam wavelength exceeds , the wavelength of the laser light changes discontinuously by (λ ₂ - λ _U ) or (λ _L - λ ₁ ), and when such a large wavelength change occurs, proper optical scanning becomes difficult. Become.

Now, there are two patterns in the change over time in the characteristic line of a semiconductor laser. Figure 3 (), ()
In this, the solid characteristic line 3-1 is the same as the characteristic line shown in FIG. 2, and is the characteristic line when fatigue has not yet occurred in the semiconductor laser.

In the first pattern of change over time of the characteristic line, the entire characteristic line shifts toward the lower temperature side as if sliding on a shelf, and in the second one, conversely, it shifts toward the higher temperature side. Broken characteristic line 3- in Figure 3 ()
2 is the characteristic line 3-1 shifted to the lower temperature side over time, and the broken line characteristic line 3-3 in Fig. 3()
, the characteristic line 3-1 shifts toward the higher temperature side over time.

The change in the characteristic line over time differs for each individual semiconductor laser, and in some cases the characteristic line shifts unilaterally toward the higher or lower temperature side, and in other cases the direction in which the characteristic line shifts changes over time. Strictly speaking, the shape itself of the characteristic line also changes over time, but this change in the shape itself over time can be ignored in the temperature control of the present invention.

Now, returning to FIG. 1 again, in the image recording apparatus shown in FIG. 1, the temperature control device includes a beam position detection element 34 and a thermistor 4 as a temperature sensing element.
0, a Peltier device 42, and a microcomputer 44.

The microcomputer 44 serves both as a control means and a temperature reset means.

As the beam position detection element, what is conventionally known as a semiconductor position detection element can be used. Various types of semiconductor position detection elements are known. For example, as shown in FIG. 4(), there is one having a single light-receiving surface 5-1, and as shown in FIG. Light receiving surfaces 5-2, 5-3
Some have four light-receiving surfaces 5-4, 5-5, 5-6, and 5-7 as shown in FIG. 5().

The detection of the beam position will be explained using an example having a single light-receiving surface 5-1 as shown in FIG. 4(). In FIG. 5, if the spot of the polarized laser beam received by the light-receiving surface 5-1 of the beam position detection element 34 is a spot Sp, the light intensity of this spot Sp is changed as shown on the left side of FIG. It has a bell-shaped distribution. Now, if this spot Sp crosses the light receiving surface 5-1 in the X direction, the output of the beam position detection element 34 is
It depends on the position where the center of Sp crosses the Y axis,
Therefore, by the output of the beam position detecting element 34, the position on the Y axis where the spot Sp crosses can be detected. One of the features of the present invention is that the beam position detection element and the synchronization detection element are integrally configured. That is, as shown in FIG. 1(), the beam position detection element 34 has two light receiving surfaces 341 and 342.
has. The light receiving surface 341 is for synchronization detection,
From this light receiving surface, the above-mentioned synchronization detection signal 10
0 is obtained. On the other hand, the light receiving surface 342 is for beam position detection, and the beam position detection signal 101 is obtained from this light receiving surface. Note that, of course, the light receiving surface for detecting the beam position may be divided into a plurality of parts.

Now, as described above, when the emission wavelength of the semiconductor laser changes, the diffraction angle in the holodisk changes, and as a result, the deflected laser beam fluctuates in the direction corresponding to the sub-scanning direction. Therefore, if the left-right direction (corresponding to the X direction in FIG. 5) of the light-receiving surface 342 of the beam position detection element 34 corresponds to the main scanning direction of the deflected laser beam, the vertical direction of the light-receiving surface 342 The variation in the beam detection signal 101 of the beam position detection element 34 corresponds to the variation in the emission wavelength of the semiconductor laser.

Two specific examples of temperature control methods using the temperature control device of the present invention will be given below.

The characteristic line of a semiconductor laser whose temperature should be controlled is the characteristic line 3-1 shown in Fig. 3 () and () in a state without fatigue, and in this characteristic line 3-1, the emission wavelength when the temperature is T ₀ is Let be λ ₀ .

Now, the first temperature control method is as follows.

First, in the microcomputer 44, which is a control means for temperature control, the set temperature for temperature control is set to _T0 , the position of the beam position detection element 34 is adjusted, and the spot Sp of the deflected laser beam is set to the receiving point. 0 point in the vertical direction of surface 342 (Fig. 1 ()) (corresponds to 0 point in the Y-axis direction in Fig. 5)
so that it crosses the

Hereinafter, 1/2 (T _U - T _L ) will be written as ΔT, and it is assumed that T ₀ = T _L + ΔT. In addition, the beam position detection element 3
The light receiving surface 342 of 4 is the light receiving surface 5- in FIG.
The explanation will be given assuming that it is shown as 1.

For the emission wavelength, λ ₀ + (λ ₂ − λ _U ) = λ _A , λ ₀ − (
λ _L
−λ ₁ )=λ _B.

and of a polarized laser beam of wavelength λ _A ,
The beam position is detected on the light-receiving surface 5-1 (Fig. 5), and this is designated as Y _1. The beam position when the wavelength λ _B is detected on the light-receiving surface 5-1, and is designated as Y ₂ . The beam positions Y ₁ and Y ₂ are set in the microcomputer 44 as comparison values.

Now, the microcomputer 44 as a control means for temperature control functions as follows.

That is, the output of the thermistor 40 is taken in and compared with the set temperature, and based on the result, the energization to the Peltier element 42 is controlled so that the temperature of the holder 38 becomes the set temperature.

Since the set temperature is T ₀ when the semiconductor laser 10 is not fatigued, the temperature of the holder 38 is controlled to a temperature near T ₀ at this time.

On the other hand, the microcomputer 44 as temperature resetting means works as follows.

That is, as shown in FIG. 6, the detection result of the beam position Y by the beam position detection element 34, that is, the beam position detection signal 10 from the light receiving surface 342
1 is taken in and compared with the comparison values Y ₁ and Y ₂ described above. When Y≧Y ₁ and Y≦Y ₂ , that is, Y ₁ >
When Y>Y ₂ , the set temperature T ₀ is the characteristic line 3-1.
Regardless of the presence or absence of fatigue, the temperature is on the shelf B of the same characteristic line, so in this case, the set temperature T ₀ is set as the set temperature of the control means.

When the detected beam position Y is Y≧Y ₁ , the characteristic line of the semiconductor laser is as shown in Fig. 3 ().
The characteristic line 3-2 is as follows. Therefore, at this time, the set temperature is shifted by ΔT lower than the previous set temperature T ₀ and the new set temperature T ₁ (Figure 3 ()) is reset as the set temperature of the control means. . In this way, the central part of the shelf B in the characteristic line 3-2 that has become fatigued can be used again.

Conversely, when the detected beam position Y is Y≦Y ₂ , the characteristic line is characteristic line 3 in Fig. 3 ().
-3. Therefore, in this case, T ₂ = shifted by ΔT to the higher temperature side than T ₀
(T ₀ +ΔT) is reset to the control means as a new set temperature.

The second temperature control method is as follows.

In this case, beam position changes ΔY ₁ and ΔY ₂ corresponding to (λ ₂ −λ _U ) and (λ _L −λ ₁ ) are stored in the microcomputer 44 together with Y ₁ and Y ₂ .

Microcomputer 44 as control means
The function is the same as in the previous example.

The microcomputer 44 as temperature resetting means works as follows. Please refer to FIG.

First, the set temperature of the control means is set to T ₀ ,
In this state, the beam position Y is detected. It is determined whether the detected beam position Y is larger than Y ₁ or smaller than Y ₂ . When Y ₁ > Y > Y ₂ , the set temperature T ₀ is on the shelf B of the characteristic line, regardless of the fatigue of the characteristic line. At this time,
Slowly raise the set temperature T in the control means by a minute temperature dT, for example 0.1 degrees, on the stairs,
Each time, the temperature of the holding body 38 is 0.1
The beam position Y is detected each time the temperature rises, and the temperature difference is
The beam position shift Z corresponding to dT is compared with ΔY ₁ . When Z＞ΔY ₁ , the temperature T ₂ is
Since the step part on the high temperature side of the shelf upper part B is provided, the temperature
T ₂ −ΔT is reset in the control means as the set temperature for temperature control.

Furthermore, when the detected beam position Y in the state of T=T ₀ is larger than Y ₁ , the characteristic line becomes, for example, the characteristic line 3-2 in Fig. 3(), and the temperature T ₀ is on shelf C. Therefore, at this time, the temperature is lowered stepwise by minute temperatures dT,
At each stage of temperature reduction, the beam position Y is detected, the beam position change Z at each step of reduction is compared with ΔY ₁ , and the temperature T ₂ (on the high temperature side of shelf B) when Z > ΔY ₁ is determined. The temperature (T ₂ - ΔT), which is shifted by ΔT to the lower temperature side from the temperature (which gives the stepped portion), is set in the control means as the set temperature for temperature control.

Further, when the beam position Y detected in the state of T=T ₀ is smaller than Y ₂ , the temperature T ₀ is on the shelf A of the characteristic line (FIG. 3()). So, in this case, raise the temperature by dT steps,
The beam position Y is detected every time the temperature changes slightly, and the beam position change Z corresponding to each temperature rise is compared with ΔY ₂ , and the temperature T ₁ when Z>ΔY ₂ is satisfied.
A temperature (T ₁ +ΔT) shifted by ΔT from (which provides a stepped portion on the low temperature side of the shelf portion B) to the high temperature side is reset as the set temperature for temperature control in the control means.

(Effects) As described above, according to the present invention, a novel temperature control device for a semiconductor laser in an optical scanning device can be provided.

This temperature control device performs temperature control in consideration of changes over time in the characteristic line of the semiconductor laser, so it is possible to perform stable temperature control over a long period of time. In addition, since the beam position detection element is integrated with the synchronization detection element, these detection elements,
There is no need to separately provide a sensing element, and the device can be simplified. Further, since the synchronization detection signal and the beam position detection signal are obtained separately from the beam position detection element, handling of the signals is easy.

Note that temperature control is performed during non-main scanning, that is, when the semiconductor laser emits light and the holodisk rotates.
And when optical scanning for image recording or image reading is not performed, specifically,
This is performed between consecutive image recordings, between consecutive image readings, or during a standby period after starting the optical scanning device. Of course, this may be performed at each non-main scan, or may be performed periodically.

[Brief explanation of the drawing]

FIG. 1 is an explanatory perspective view showing an image recording apparatus having an optical scanning device embodying the present invention, and FIG. 2 is a diagram illustrating a characteristic line representing the relationship between emission wavelength and temperature in a semiconductor laser. Figure, 3rd
4 and 5 are diagrams for explaining the beam position detecting element. FIGS. 6 and 7 are diagrams for explaining the temperature control device of the present invention. It is a figure for explaining two examples of the temperature control method by. DESCRIPTION OF SYMBOLS 10... Semiconductor laser, 20... Holoscanner, 38... Holder, 34... Beam position detection element, 40... Thermistor as a temperature sensing element, 4
2...Peltier element, 44...Microcomputer (also serves as control means and temperature reset means)

Claims (1)

[Scope of Claims] 1. An optical scanning device in which light from a semiconductor laser is deflected by a holoscanner, comprising: a temperature-sensitive element that detects the temperature of a holder that holds the semiconductor laser; and a Peltier device that heats and cools the holder. and controlling the energization to the Peltier element according to the output of the temperature sensing element, and setting the set temperature T of the holding body.
a control means for controlling the temperature to be in the vicinity of the initial setting temperature T ₀ ; a beam position detection element for detecting the beam position of the deflected laser beam; and a beam position detected by the beam position detection element within a preset appropriate area. When one of the limit values is exceeded, the set temperature T of the above-mentioned holder is T=T ₀ +ΔT where, ΔT=(T _U − T _L )/2 T _U : The emission wavelength of the semiconductor laser changes depending on the temperature. In the characteristic line that represents the state, the temperature that is closest to T _{0 among the temperatures at the step part that are higher than T 0 T L} : In the above characteristic line, the temperature that is closest to T ₀ among the temperatures at the step part that are lower than T ₀ and temperature resetting means for resetting the set temperature T of the holding body to T=T ₀ −ΔT when the beam position exceeds the other limit value of the appropriate range. , when the beam position detection element is used in optical scanning,
A temperature control device for a semiconductor laser, characterized in that it is integrally configured with a synchronization detection element for synchronizing main scanning. 2. An optical scanning device that uses a holoscanner to deflect light from a semiconductor laser, which includes: a temperature-sensitive element that detects the temperature of a holder that holds the semiconductor laser; a Peltier element that heats and cools the holder; Control the energization to the Peltier element according to the output of the element, and set the set temperature T of the holder.
a control means for controlling the temperature to be in the vicinity of the initial setting temperature T ₀ ; a beam position detection element for detecting the beam position of the deflected laser beam; and a beam position detected by the beam position detection element within a preset appropriate area. Detects the temperature T ₁ when it exceeds one limit value or the temperature T ₂ when it exceeds the other limit, and when the above temperature T ₁ is detected, the set temperature T of the above holding body is T = T ₁ + ΔT Here, ΔT=(T _U − T _L )/2 T _U : In the characteristic line that shows how the emission wavelength of a semiconductor laser changes with temperature, the temperature at the step part higher than T ₀ is the highest at T ₀ . Nearest temperature T _L : In the above characteristic line, reset the temperature to the temperature closest to T ₀ among the temperatures of the stepped portion lower than T ₀ , and when the beam position detects the above temperature T ₂ , the above holder temperature resetting means for resetting the set temperature T to T=T ₂ −ΔT, and the beam position detection element
A temperature control device for a semiconductor laser, characterized in that it is integrally configured with a synchronization detection element for synchronizing main scanning.