JPH0331090Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention relates to a stabilized light source whose output light has a stable wavelength and can measure the refractive index of air, and is particularly suitable for use in measuring instruments that use light. The present invention relates to a stabilized light source having a function of measuring the refractive index of air.

<Prior Art> Semiconductor lasers are easy to handle and compact, so they are widely used in communications and measuring instruments that use light. However, since semiconductor lasers have a large half-value width of the wavelength spectrum of output light and the wavelength changes depending on the surrounding environment such as temperature, it is necessary to stabilize the wavelength or frequency when used for precise measurements. FIG. 4 shows the configuration of a light source that stabilizes the frequency. In FIG. 4, output light from a semiconductor laser 1 is incident on a half mirror 2, and the transmitted light is taken out as output light. The light reflected by half mirror 2 is reflected by mirror 3, and then reflected by half mirror 4.
The light intensity of the light reflected by the half mirror 4 is converted into an electrical signal by the photodetector 5 and is input to the control means 8. On the other hand, the light transmitted through the half mirror 4 is incident on the Fabry-Perot interferometer 6. This Fabry-Perot interferometer 6 has a vacuum inside. The light transmitted through the Fabry-Perot interferometer 6 is incident on a photodetector 7, and its light intensity is converted into an electrical signal. The output of the photodetector 7 is input to the control means 8. Control means 8 controls semiconductor laser 1 .

In such a configuration, the Fabry-Perot interferometer 6 transmits only light of a specific wavelength associated with its reference space, as shown in FIG. Therefore, a change in wavelength can be converted into a change in light intensity in the vicinity of a wavelength λ ₁ that deviates from the peak wavelength λ ₀ . Therefore, if the control means 8 controls the injection current of the semiconductor laser 1 and the ambient temperature so that the output of the photodetector 7 is constant, the frequency of the output light of the semiconductor laser 1 can be stabilized to a constant value. Note that if the intensity of the output light of the semiconductor laser changes as it is, an error will occur, so a part of the output light is incident on the photodetector 5 using the half mirror 4, and the intensity is measured and corrected. . The wavelength in vacuum is λ _v ,
If the refractive index of air is n and the wavelength in air is λ, then there is the relationship λ _v /n=λ...(1), and if the wavelength and frequency in air are λ, then λ=C ₀ / n...(2) C ₀ : There is a relationship between the speed of light in a vacuum. The stabilized light source in Figure 4 operates so that the wavelength λ _v in vacuum is constant, so from equations (1) and (2), = C ₀ / (nλ) = C ₀ / λ _v = constant, The frequency can be kept constant.

FIG. 5 shows an example of another stabilized light source. Note that the same elements as in FIG. 4 are given the same reference numerals, and their explanations will be omitted. In this example, the Fabry-Perot interferometer 9 is provided with a through hole 10 that communicates the inside and outside of the interferometer 9, so that outside air can enter the inside. Since the operation itself is the same as that shown in FIG. 4, the explanation will be omitted. This stabilized light source is controlled by a Fabry-Perot interferometer 9 so that the wavelength in the air is constant.

<Problems to be solved by the invention> However, such a stabilized light source has the following problems. In the stabilized light source of FIG. 4, the frequency of the output light remains constant even if the refractive index of the air changes, but the wavelength changes in accordance with the change in the refractive index. Furthermore, in the case of the stabilized light source shown in Fig. 5, the wavelength of the output light is stabilized even if the refractive index in the air changes.
The frequency varies with variations in the refractive index. Measuring instruments that use light may be based on the frequency of the light or wavelength, and the stabilized light source shown in Figures 4 and 5 can handle one of these, but not both. Can not. Therefore, for accurate measurements, a separate means of measuring the refractive index of air must be provided.
Although this correction was attempted, it had the disadvantage of complicating the configuration.

<Purpose of the invention> The purpose of this invention is to provide a stabilized light source having a function of measuring the refractive index of air, which can obtain light with a stabilized wavelength and at the same time measure changes in the refractive index of the air.

<Means for solving the problem> In order to solve the above problem, in the present invention, a part of the output light of the light source is incident on the first wavelength discrimination element, and the transmitted light of the first wavelength discrimination element is The light intensity of the light source is detected by a first photodetector, and the control means controls the light source based on the output of the first photodetector. Further, a part of the output light of the light source is made incident on a second wavelength discriminating element, and the transmitted light intensity of the second wavelength discriminating element is detected by a second photodetector, and the first wavelength One of the discrimination element and the second wavelength discrimination element is exposed to air, the other is made of a member having a constant refractive index, and the refractive index of the air is determined based on the output of the second photodetector. This is what I did.

<Example> FIG. 1 shows an example of a stabilized light source having a function of measuring the refractive index of air according to the present invention. In addition, the fourth
Elements that are the same as those in the figures are given the same reference numerals, and their explanations will be omitted. In FIG. 1, 20 is a half mirror, into which light reflected by the half mirror 2 is incident. The light reflected by the half mirror 20 is split into two by the half mirror 4, and the reflected light is incident on the photodetector 5, where the light intensity is converted into an electrical signal.
21 is a Fabry-Perot interferometer, which forms first and second wavelength discrimination elements. The Fabry-Perot interferometers 21 are arranged opposite to each other,
and a transmission plate 2 coated with a suitable reflective film.
11 and a cylindrical spacer 212 fixed to the transparent plate 211. Spacer 21
The inside of 2 is evacuated to vacuum, and the outside is exposed to air. The light transmitted through the half mirror 4 passes through the optical path of the Fabry-Perot interferometer 21 exposed to the air, and the transmitted light passes through the photodetector 7.
The light intensity is converted into an electrical signal. The outputs of the photodetectors 5 and 7 are input to a control means 8, and the semiconductor laser 1 is controlled by this control means 8. That is, the Fabry-Perot interferometer 21
The optical path of the semiconductor laser 1 is exposed in the air, so its configuration is the same as that shown in
The wavelength of the output light remains constant regardless of changes in the refractive index of the air. On the other hand, the light transmitted through the half mirror 20 is reflected by the mirror 22 and enters the half mirror 23. The half mirror 23 divides the incident light into 2
The intensity of the reflected light is converted into an electrical signal by a photodetector 24, and the transmitted light is input into the vacuum section of the Fabry-Perot interferometer 21. Further, the transmitted light is incident on a photodetector 25, and its light intensity is converted into an electrical signal. The outputs of the photodetectors 24 and 25 are input to a calculation means 26.

Next, the operation of this embodiment will be explained. Note that the control part of the semiconductor laser 1 is the fifth one as described above.
Since it is the same as the figure, the explanation will be omitted. The wavelength of the output light of the semiconductor laser 1 is stabilized by including the change in the refractive index of the air, and if the wavelength in vacuum is λ _v and the refractive index of air is n, then λ _v /n=C (constant )...(3) becomes. That is, the wavelength λ _v in vacuum changes in proportion to the refractive index. Therefore, half mirror 2
The transmitted light intensity of the light that has passed through 3 and entered the vacuum portion of the Fabry-Perot interferometer 21 changes in accordance with the change in the refractive index of the air. This situation is shown in FIG.
In FIG. 2, 27 is the Fabry-Perot interferometer 2
1 represents a curve showing the intensity characteristics of transmitted light incident on the vacuum portion of No. 1. If the refractive index of air in the initial state and after a predetermined period of time is n ₀ , n ₁ , and the wavelength in vacuum at that time is λ _v0 , λ _v1 , then (3)
From the formula, λ _v0 = Cn ₀ λ _v1 = Cn ₁ (4), and the transmitted light intensities are D ₀ and D ₁ , respectively.
By measuring the curve 27 showing the transmitted light intensity characteristics in advance using light whose wavelength is known, the wavelength in vacuum can be determined from the intensity of the transmitted light, and the refractive index of air can be calculated from equation (4) above. You can ask for. These calculations are performed by the calculation means 26. Note that if the refractive index is determined only from the output of the photodetector 25, an error will occur if the output light intensity of the semiconductor laser 1 changes, so the output light intensity of the semiconductor laser 1 is monitored by the photodetector 24 and corrected. Make it.

FIG. 3 shows another embodiment of the present invention. Note that the same elements as in FIG. 1 are given the same reference numerals and their explanations will be omitted. In this embodiment, light for obtaining a signal to control the semiconductor laser 1 is passed through a vacuum section of the Fabry-Perot interferometer 21, and light for obtaining a signal for determining the refractive index is passed through a section of the Fabry-Perot interferometer 21 exposed to air. This is what I did. As explained in FIG. 4, if the semiconductor laser 1 is controlled by light transmitted through a Fabry-Perot interferometer having a vacuum section, light having a constant frequency can be obtained regardless of changes in the refractive index of air. By making a part of this light incident on a Fabry-Perot interferometer exposed to air and measuring the intensity of the transmitted light, it is possible to determine the change in the refractive index of air using the same method as explained in Figure 2. can.
In the embodiments shown in FIGS. 1 and 3, the first and second wavelength discriminating elements are constructed from one Fabry-Perot interferometer 21, so the interval between the transmission plates 211 changes due to changes in ambient temperature, etc. also affects these wavelength discrimination elements in the same way, so the error can be reduced.

In these embodiments, only the outputs of the photodetectors 24 and 25 are input to the calculation means 26, but the control means 8 calculates the ratio of the outputs of the photodetectors 7 and 5, and this value is also calculated. The refractive index of air may be determined from these values by inputting them into the means 26. When the distance between the transmission plates 211 changes, the reference space length of the Fabry-Perot interferometer 21 changes, causing a change in the peak wavelength of the transmitted light and an error, but this change in wavelength occurs in the same way in both the air region and the vacuum region. By doing this, the error can be corrected.

In addition, in these examples, one semiconductor laser is used.
However, a plurality of them may be used.

Furthermore, the absolute value of the refractive index can be determined by measuring the refractive index of air by other means and correcting the distance between the planes of the transmission plate 211 of the Fabry-Perot interferometer 21, which is a wavelength discriminating element.

In addition, in this embodiment, the optical path is made into a vacuum as a wavelength discriminating element with a constant refractive index.
It may be configured using a member having a constant refractive index. The light source is not limited to a semiconductor laser, but may be a laser light source of other configurations such as a gas laser.

Further, in this embodiment, a Fabry-Perot interferometer is used as the wavelength discrimination element, but a light absorption cell filled with a substance that absorbs only light of a specific wavelength may also be used.

Further, the structure of the Fabry-Perot interferometer 21 is not limited to that shown in FIG. 1 or 3, but may be an interferometer that utilizes polygonal reflection such as a triangle.

<Effects of the invention> As explained in detail based on the embodiments above, this invention uses a wavelength discriminating element made of a material with a constant refractive index and a wavelength discriminating element exposed to the air. The light source is controlled by the light intensity, and the refractive index of the air is determined from the intensity of the transmitted light of the other wavelength discrimination element. Therefore, since both the wavelength or frequency stabilized light and the refractive index of air can be determined at the same time, accurate values can be obtained by correcting frequency fluctuations or wavelength fluctuations based on the refractive index fluctuations of air. Highly accurate measurement becomes possible.

Furthermore, since fluctuations in the refractive index of air can be monitored, it is possible to easily determine whether the measurement environment is suitable or not.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a stabilized light source having a function of measuring the refractive index of air according to the present invention;
Fig. 2 is a characteristic curve diagram for explaining the refractive index measurement method, Fig. 3 is a block diagram showing another embodiment of the present invention, and Figs. 4 and 5 are block diagrams of a conventional stabilized light source. , FIG. 6 is an intensity curve of transmitted light of the Fabry-Perot interferometer. 1... Semiconductor laser, 2, 4, 20, 23...
... Half mirror, 5, 7, 24, 25 ... Photodetector, 8 ... Control means, 21 ... Fabry-Perot interferometer, 22 ... Mirror, 26 ... Calculation means, 21
1...Transmission plate, 212...Spacer.

Claims (1)

[Scope of utility model registration request] A light source, a first wavelength discriminator that receives a portion of the output light of the light source and transmits or absorbs light of a specific wavelength, and a first light that receives the transmitted light of the first wavelength discriminator. a detector, a control means into which the output of the first photodetector is input and which controls the light source based on this input; a part of the output light of the light source is incident and transmits or absorbs light of a specific wavelength; Second to do
a wavelength discriminating element, and a second photodetector into which the transmitted light of the second wavelength discriminating element is incident, one of the first wavelength discriminating element and the second wavelength discriminating element is placed in air A stabilized light source having an air refractive index measuring function, characterized in that the other is made of a member having a constant refractive index, and the refractive index of the air is determined based on the output of the second photodetector. .