JPH0156549B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser device that corrects the temperature dependence of the wavelength of an emitted beam from a semiconductor laser device using a photodetector and a heat-sensitive element.

When a semiconductor laser device is used for image recording or the like, the wavelength dependence of the sensitivity of the photoreceptor used in the device poses a major problem. With a short wavelength laser such as a normal He--Ne laser, the sensitivity of the photoreceptor is often flat with respect to the laser wavelength, making it very easy to use.

On the other hand, the wavelength of the semiconductor laser emitted from the semiconductor laser element is around 8000 Å, which is longer than that of the He-Ne laser, so the sensitivity of the photoreceptor normally used is not very high. When this semiconductor laser is used in such an image recording device, the photoreceptor is often sensitized. However, even if sensitized, the sensitivity will have a gradient with respect to the wavelength at around 8000 Å where it is practical, taking into consideration the stability of image quality and the durability of the photoreceptor.

Therefore, the amount of light required varies depending on the wavelength of the semiconductor laser used, so if wavelength fluctuations occur during operation,
Good images cannot be obtained using the APC (AUTO POWER CONTROL) method.

To give an example, a semiconductor laser has a temperature coefficient at a wavelength of 2.5 to 3.0 Å, and if there is a temperature change of 30°C,
A wavelength change of up to 90 Å occurs. Therefore, the higher the wavelength dependence of the sensitivity of the photoreceptor, the worse the obtained image becomes.

On the other hand, there is a method of using a semiconductor laser element at a constant temperature using a cooling element, but this method requires a large number of components and increases costs.

The present invention eliminates the above-mentioned drawbacks and provides a semiconductor laser device that can always maintain the amount of laser light at an optimum value.

In other words, a heat-sensitive element such as a thermistor whose resistance changes depending on the temperature is installed in a place that more faithfully transmits the temperature of the light source, and the heat-sensitive element is connected to a circuit that extracts the output from a photodetector that receives light from the light source. By feeding back information so that when a wavelength fluctuation occurs due to a wavelength change, the necessary light amount corresponding to that wavelength can be obtained, the optimum light amount can always be maintained.

As a result, even if the sensitivity of the photoreceptor has wavelength dependence, by appropriately selecting the temperature coefficient of the resistance value of the heat-sensitive element, it is possible to always record an image with the optimum amount of light.

1 and 2 show embodiments of the present invention. In FIG. 1, 1 is a semiconductor laser element that emits a front beam L ₁ and a back beam L ₂ ;
3 is a laser mount (support member) made of metal and supports the semiconductor laser element; 3 is a heat-sensitive element, such as a thermistor, which shows a resistance change according to the temperature change of the semiconductor laser element; Although it is firmly fixed with the heat conductive adhesive 4, it may also be fixed on the semiconductor laser element 1. 5 is the laser beam on the side not used for recording of the semiconductor laser element, that is, the back beam
The photodetector 5 is a photodetector for receiving the back beam _L2 , and the light receiving surface of the photodetector ₅ is fixedly provided on the support member 2 with the light receiving surface tilted so as not to be perpendicular to the back beam L2.

As shown in FIG. 2, a resistor 6 (resistance value Rs) is connected in series to the photodetector 5, and a heat sensitive element 3 (resistance value R _TH ) is connected in parallel to the photodetector 5 and the resistor 6. Ru.

The input IN1 of the error amplifier is connected to the terminal T1 of this photodetector 5, and the input IN1 of the error amplifier IN2 and the terminal T2 are connected to the terminal T1 of the photodetector 5.
A reference potential source 8 is connected between them.

When the back beam L2 from the laser element 1 hits the photodetector 5, a current I1 flows. Then, the terminal voltage V ₁ across the thermistor 3 becomes I ₁ R _TH and is compared with the reference voltage V ₀ , and a signal is fed back to the laser drive circuit 9 which drives the laser element 1 to emit light so that V ₁ becomes V ₀ . Controls the current supplied to the

In the semiconductor laser device of the present invention, even if the wavelength changes and the required light amount changes due to an increase in the temperature of the semiconductor laser element 1, the laser output is always corrected to the optimum value based on the amount of temperature change of the temperature sensing element 3.

To explain in more detail, first, the sensitivity of a photoreceptor (not shown) to which the front beam is irradiated is measured, and the laser wavelength λ versus the required light amount P is determined. An example is shown in FIG.

Next, the temperature coefficient of the wavelength of the semiconductor laser △λ/△T
seek. From these results, it is possible to determine the amount of change in wavelength within the operating temperature range, as well as the amount of change in the required amount of light. Therefore, it is only necessary to correct the required light amount by the change in wavelength.

This correction is as follows.

Since the circuit operates so that the relationship I ₁ R _TH =V ₀ is always maintained, the resistance value R _TH of the thermistor only needs to change depending on the temperature so as to correct the sensitivity curve of the photoreceptor shown in FIG. For this purpose, the temperature coefficient (B constant) of the resistance of the thermistor may be determined within the operating temperature range of the device, for example, 10 to 40°C.

Now, if R _TH 10℃/R _TH 40℃=2.0 Find B from 2000K.

In other words, if a thermistor with a B constant of 2000K is installed in the laser mount, an appropriate amount of light can be obtained.

Although it is not possible to obtain an arbitrary value for the B constant of a thermistor, it is possible to obtain various B constants by combining a thermistor and a fixed resistor. Even if the drum has different coefficients and drum sensitivities are different, it can be sufficiently handled. Also, although the temperature change in the thermistor's resistance is not linear, there is virtually no problem with temperature fluctuations of about 30°C.

As explained above, according to the present invention, even if the required amount of light changes due to changes in the wavelength of the semiconductor laser element, the laser output can always be shifted to an appropriate value using the photodetector and the thermosensitive element.

As a result, good images can always be obtained even if the temperature of the semiconductor laser element changes due to environmental changes or self-heating of the semiconductor laser element.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a semiconductor laser device, FIG. 2 is a circuit diagram of the semiconductor laser device, and FIG. 3 is a diagram of laser output versus wavelength characteristics. Here, 1 is a semiconductor laser element, 2 is a support member,
4 is a heat conductive adhesive, 5 is a photodetector, and 6 is a resistor.

Claims (1)

[Claims] 1. A semiconductor laser element whose sensitivity is wavelength-dependent for exposing a photoreceptor; a heat-sensitive element provided near the semiconductor laser element for detecting fluctuations in the output wavelength of the semiconductor laser element due to temperature changes; A semiconductor laser device comprising: a control means for changing the beam output of the semiconductor laser element according to the output of the heat-sensitive element so as to compensate for changes in the amount of light necessary for exposing the photoreceptor due to wavelength fluctuations.