JPS5812385A - Emitting light wave length sweep system of wave length variable laser - Google Patents

Abstract

PURPOSE:To make a wave length variable laser to enable to cope with secular change of the laser characteristic, and moreover to make the laser to enable to sweep the broad range of wave length in a short time by a method wherein a laser driving current is made to vary being made to vibrate, while the temperature of a heat sink equipped with a laser element is made to vary monotonously. CONSTITUTION:Ejected light from the semiconductor laser assembled in the refrigerator 1 is injected in a spectroscope 10 to be condensed by a concave mirror 2 inside of the spectroscope 10, and enters in a grating 3 to be diffracted by the grating 3. Light having the desired wave length out of diffracted light is injected in a concave mirror 4, and light condensed by the concave mirror thereof is made to be ejected outside of the spectroscope 10 to constitute the spectroscope. By sweeping the driving current and the cooling temperature of the element, and by rotating the angle of grating following after wave length of emitting light of the laser, light corresponding to the angle of grating can be selected to be ejected outside of the spectroscope although it is discrete (owing to mode hop).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an emission wavelength sweeping method for sweeping the emission wavelength of a wavelength tunable semiconductor laser used in an infrared gas analyzer over a wide range.

Harmful gases that cause air pollution, such as sulfur dioxide (S
A method of analyzing carbon oxide (Os), -carbon oxide (CO), etc. by infrared absorption is already well known. Conventionally, a wavelength tunable semiconductor laser has been used as an infrared light source for such analysis, that is, infrared spectroscopic analysis. As a means of changing the emission wavelength of this semiconductor laser, we used a method of changing the operating current of the laser element or the cooling temperature of the laser element. The wavelength change range when the conventional wavelength sweeping method is used will be described below with reference to FIG. In FIG. 1, the vertical axis shows the emission wavelength λ, and the horizontal axis shows the driving current of the laser. Region (I), α) indicates a non-emission region of the laser.

Curves A1 and B respectively show the change in the emission wavelength when the current is changed when the laser element is cooled at the same temperature. Curve A shows the cooling temperature of the element constant at 200 (Con
st) The light emitting characteristics of the device are shown when K is maintained and the device drive current is changed from Em to Step 1. In addition, the curve - shows the light emitting characteristics of the device when the cooling temperature of the device is kept constant at 86' and the driving current of the device is changed from A to T.
Similarly, curve C shows the emission wavelength characteristics of the device when the driving current of the cable is changed from 1 to 1 when the device cooling temperature is 60°. Note that the cooling temperature of the element is 'RO'
Taking curve A in the case of K as an example, the gap between wavelengths λa and l'b and the gap between wavelengths 11) and λC are in the non-emission wavelength region, and are in the hop region where the device does not have an emission mode. be. Generally, the wavelength range in which this mode hop occurs is about several angstroms (6), which poses no problem for spectroscopic analysis using infrared absorption.

Regarding the example shown in Fig. 1 above, when it becomes necessary to perform spectroscopic analysis by sweeping the emission wavelength of the device from While only vibrating the work, from M to the work IIt
, and sweeps from wavelength A to λ1. Thereafter, the cooling temperature of the device was raised to 60'K, and the device drive current was changed from 10G to 200% while oscillating by .DELTA., thereby sweeping the emission wavelength from λ1 to λ1t. When using such a wavelength sweeping method for a moxibustion laser, it takes several minutes to change the cooling temperature of the element from 20@K to 50@Kt, making it difficult to sweep the emission wavelength at a high speed. Met. Another disadvantage is that the sweep width of the laser emission wavelength is narrow when the device cooling temperature is kept constant and the drive current is varied, and when the drive current is kept constant and the cooling temperature is varied.

The present invention aims to eliminate the above-mentioned drawbacks, and focuses on the fast response speed to the laser drive current and the slow response speed of element cooling temperature control, and changes the laser drive current while oscillating. The present invention provides an emission wavelength sweeping method for a tunable laser that can respond to changes in laser characteristics over time by monotonically changing the temperature of the heat sink on which the device is attached, and that can sweep a wide wavelength range in a short time. , the gist of which is to monotonically increase or decrease the cooling temperature by the refrigerator in an emission wavelength sweeping method for a wavelength tunable laser having a current source that drives the wavelength tunable semiconductor laser and a refrigerator that cools the semiconductor laser. At the same time, the semiconductor laser driving current is monotonically increased or decreased while being oscillated, thereby sweeping the emission wavelength of the semiconductor v-laser over a wide range.

Embodiments of the present invention will be described below with reference to FIGS. 2 and 8.

Figure 1@2 shows lead/tin/tefi as a wavelength tunable semiconductor laser.
/N (PbSnT*), lead/sulfur/selenium (PbS8
e) etc. is used as a light source, and if the optimum values of operating temperature and drive current are selected,
It is possible to obtain light emission having a wavelength of 8 μm.

Now, when detecting methane (OH4), which has an infrared absorption peak wavelength of 7.9μm, and nitrogen dioxide (NOx), which has an absorption peak wavelength of around 7μm, generally the infrared absorption peak wavelength is 7.9μm to 8μm.
Even if you change the driving current with one element cooled to the same temperature over the wavelength range of 3.35 nm, it is not possible to obtain the same amount of wavelength change. 2-) had to be used. Therefore, in the present invention, the cooling temperature T of the laser element is set to around 20 DEG, and the driving current Em is set to an operating condition that allows an emission wavelength of 8 microns tuning around 200 to 800 Mk to be obtained. Next, gradually increase the cooling temperature of the laser element (Kl/-), and at the same time gradually increase the drive current, superimpose several mA of oscillating current Δ on this current, and lower the cooling temperature T of the laser element to about By increasing the drive current to around 500mA and increasing the drive current to 500-600mA, light emission with a wavelength of 7μ can be obtained.If you drive the device in this way, a single V-the device can cover a wide wavelength range. luminescence can be obtained easily and simply.

Next, an embodiment of a gas analyzer using the emission wavelength sweeping method of a wide wavelength tunable laser according to the present invention will be briefly described with reference to FIG.

A semiconductor laser is built into the refrigerator 1, and the emitted light from the laser enters the spectroscope 10, is focused by the concave mirror 2 inside the spectrometer 10, enters the grating 8, and is diffracted by the grating 8. Among the diffracted lights, light with a desired wavelength enters the concave mirror 4, and the light collected by the concave mirror is sent to the spectroscope 1.
It is configured to emit light outside of zero. The grating V-ting can be set in advance so that a desired wavelength can be extracted from the spectrometer external pressure, but a stepping motor (not shown) is used as the angle setting means for this grating 8, and the resolution of the grating 8 is higher than that of a semiconductor laser. It is necessary to set it so that it is less than the mode hop. Note that in this apparatus, although a power source for driving the semiconductor laser element is not shown, it may be provided within the refrigeration tsl or may be provided externally.

Using the apparatus shown in Fig. 8, the laser element driving method explained in Fig. 2 is used, that is, the driving current and element cooling temperature are swept, and the grating angle is rotated to follow the laser emission wavelength. Although the light may be discrete (due to the 4-dimensional structure), it is possible to select light corresponding to the angle of the grating and emit it to the outside of the spectrometer.

If the driving method of the laser element explained above is used, the light emission at point A where the cooling temperature of the V laser element is low as shown in Fig.
It is possible to sweep a wide wavelength range from the wavelength range to the short wavelength interval of the emission from the high-temperature F point with a single temperature change of the refrigerator.The sweep speed is faster than conventional models, and it is also possible to sweep a wide wavelength range from the wavelength range to the short wavelength interval of the emission from the high-temperature F point. Even if a conventional refrigerator is used, it is possible to easily sweep the emission wavelength over a wide range, which is the object of the present invention.

Contrary to the above explanation, even if the cooling temperature of the laser element is changed from a high temperature side to a low temperature side, and the driving current is also controlled to decrease from a large side to a small side, it is possible to sweep a wide range of emission wavelengths in the same way. It can be realized.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the driving current and the emission wavelength when the cooling temperature of the semiconductor laser element is used as a parameter. Figure 2 shows the relationship between the driving current and the emission wavelength when the cooling temperature of the semiconductor laser element is gradually changed and the driving current is changed to the cooling temperature. The emission wavelength characteristics according to the present invention K are shown when changing according to the following. FIG. 8 shows an embodiment of an emission wavelength sweeping device used in a gas analyzer using the V-za driving method of the present invention. 1: Freezer, 2: Concave mirror, 8: Grating. 4: concave mirror, 10: spectrometer, ゛λ: emission wavelength, f: drive current, Δf: vibration component of drive current, T: cooling temperature of the laser element. Figure 3

Claims (1)

[Claims] In a wavelength tunable laser O emission wavelength sweeping method having a current source that drives a wavelength tunable semiconductor laser and a refrigerator that cools the wrinkled semiconductor laser, the semiconductor laser is driven while the cooling temperature by the refrigerator is monotonically increased or decreased. A variable wave V-laser characterized in that the semiconductor laser drive current is monotonically increased or decreased while being oscillated by changing a current source, thereby sweeping the emission wavelength of the semiconductor laser over a wide range. emission wavelength sweep method.