JPH081975B2 - Semiconductor laser device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device.

2. Description of the Related Art In a semiconductor laser device having a built-in photodiode, the photodiode detects emitted light from behind the semiconductor laser and is used as a monitor of the emitted light. For example, a change in output due to a change in temperature is detected, and a negative feedback is applied to make the optical output constant.

In a device using a conventional GaAlAs-based semiconductor laser and a Si pin photodiode, the oscillation wavelength of the semiconductor laser is
It exists in the same wavelength region as the wavelength where the sensitivity of the Si pin photodiode becomes maximum.

However, in a device using such a GaAlAs semiconductor laser and a pin photodiode, when the temperature changes,
Since the oscillation wavelength of the semiconductor laser and the sensitivity of the photodiode change, the output (photocurrent) of the photodiode with respect to a constant light output changes.

The conventional semiconductor laser device as described above will be described below with reference to the drawings.

For example, the operating temperature range of the semiconductor laser device is −10 ° C.
Set to + 60 ℃. At room temperature (25 ℃), the oscillation wavelength is 830 nm,
It is assumed that the peak of the spectral sensitivity of the pin photodiode is 830 nm. The temperature dependence of the oscillation wavelength of a semiconductor laser is about 0.3n
Since it is m / ° C, as shown in Fig. 3 (b), -10 ° C to +60
The change is 819.5 nm to 840.5 nm at ℃.

On the other hand, the spectral sensitivity curve of the pin photodiode is as shown in FIG. 3 (a), and its temperature dependence hardly changes on the short wavelength side of the peak and slightly increases with temperature on the long wavelength side. The dotted line in Fig. 3 (a) is -10 ° C,
The solid line is the sensitivity curve at + 60 ° C. And from -10 ℃ to +60
It takes an intermediate value up to ° C.

Therefore, when the temperature changes from −10 ° C. to + 60 ° C., assuming that the laser output is constant, the output of the pin photodiode has a peak as shown in FIG. 4 and does not change monotonously. Therefore, correction based on this curve is necessary to perform accurate output stabilization using the output of the pin photodiode. This correction becomes very complicated when there is such a peak with respect to temperature.

Problems to be Solved by the Invention In the device using the GaAlAs semiconductor laser and the Si pin photodiode as described above, when the temperature changes, the output (photocurrent) of the photodiode with respect to a constant light output changes. In view of the above-mentioned drawbacks, the present invention provides a semiconductor laser device in which the output of the built-in photodiode for monitoring is monotonously changed with respect to the temperature change in the operating temperature range.

Means for Solving the Problems In order to solve the above problems, the semiconductor laser device of the present invention has a spectral sensitivity curve of the photodiode, that is, the wavelength dependence of the sensitivity has a single peak and is convex upward. It has a chevron shape, and its maximum wavelength is longer than the oscillation wavelength of the semiconductor laser at the maximum temperature used. The photodiode is made of silicon PI.
When the N structure is used, the peak wavelength of the spectral sensitivity curve of this photodiode can be shifted to the long wavelength side by thickening the I layer.

Operation With this configuration, even if the oscillation wavelength of the semiconductor laser changes due to a change in temperature, the output of the built-in monitor photodiode can monotonically increase or decrease with respect to temperature, and the change is small. Not only can it be done, but even when correction is performed by an external circuit,
It will be easy to do.

Examples Hereinafter, one example of the present invention will be described with reference to the drawings.

FIG. 1 shows the spectral sensitivity curve (FIG. 1 (a)) of the PIN photodiode at −10 ° C. to 60 ° C. of the semiconductor laser device with a built-in PIN photodiode and the oscillation wavelength of the semiconductor laser ( FIG. 1 (b)) is shown. GaAlAs is used as the semiconductor laser, and the oscillation wavelength is set to 845 nm or less. The photodiode has a Si PIN structure and an I layer thickness of 40
The wavelength at which the sensitivity is maximized by setting the thickness above μm is 850n.
It can be more than m. In a Fabry Bellow oscillator type GaAlAs semiconductor laser, the oscillation wavelength becomes longer as the temperature rises, and the coefficient is about 0.3 nm / ° C. Therefore, the oscillation wavelength changes by about 21 nm in the above temperature range. On the other hand, the temperature change of the sensitivity of the PIN photodiode is very small on the shorter wavelength side than the peak. Furthermore, when the spectral sensitivity peak is on the side of a wavelength slightly longer than the longest oscillation wavelength, the change in spectral sensitivity is small, so the change in sensitivity due to temperature change is small. FIG. 2 shows changes in the photodiode output with respect to changes in temperature in this embodiment. Here, the optical output of the laser is made constant. As shown in the figure, the change is small and increases monotonically, and correction by an external circuit is easy.

EFFECTS OF THE INVENTION As a result, in the temperature range used, the output of the built-in photodiode for monitoring becomes monotonous with respect to the temperature change, and it can be easily corrected by the external circuit, and its practical effect is great. .

[Brief description of drawings]

FIG. 1 (a) is a spectral sensitivity curve diagram of a PIN photodiode of a semiconductor laser device according to an embodiment of the present invention, FIG. 1 (b) is a temperature characteristic diagram of an oscillation wavelength of a semiconductor laser, and FIG. 2 is an embodiment. Temperature characteristic diagram of photodiode output in
3 (a) and 3 (b) are respectively a spectral sensitivity curve diagram of a photodiode of a conventional semiconductor laser device, a temperature characteristic diagram of an oscillation wavelength of a semiconductor laser, and FIG. 4 is a photodiode output with respect to a temperature change in a conventional example. It is a temperature characteristic diagram.

Claims (1)

[Claims] 1. In a semiconductor laser device having a semiconductor laser element and a photodiode for detecting light emitted backward from the semiconductor laser element, the wavelength at which the wavelength dependence of the sensitivity of the photodiode is maximum is within the operating temperature range of the semiconductor laser element. I of the PIN photodiode is set so that the wavelength becomes longer than the oscillation wavelength of the semiconductor laser device at the maximum temperature.
A semiconductor laser device, wherein a layer thickness is set.