JPH0587638A - Light wavelength meter - Google Patents

Abstract

PURPOSE:To obtain a very accurate small-sized light wavelength meter by arranging a plurality of line sensors in parallel to each other so that one element of one line sensor and one corresponding element of the other line sensor are mutually shifted by definite quantity. CONSTITUTION:The interference fringes 5 appearing through a Fabry-Perot etalon 3 and a lens 4 are projected on the line sensors 6a, 6b parallelly arranged on the border of the center of the concentric circles thereof and the position thereof is detected. The line sensor 6b is arranged in parallel to the line sensor 6a in close vicinity thereto so that the positions of the elements of the line sensor 6b in the arrangement direction thereof are shifted by the width (12.5mum) 1/2 each of the elements, for example, having a width of 25mum from the end surface of the line sensor 6a. Therefore, when the p-th interference fringe 5p from the center of the concentric circles of the interference fringes 5 is present on the (n+1)-th element of the line sensor 6a and the n-th element of the line sensor 6b, it can be detected that the interference fringe position is present between (25n)mum and (25n+12.5)mum. Twice resolving power is obtained as compared with a case using only one line sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength meter for measuring the wavelength of a coherent light source used for high precision interferometry.

[0002]

2. Description of the Related Art As a conventional optical wavelength meter of this kind, one using a Fabry-Perot etalon (hereinafter referred to as an etalon) shown in FIG. 5 is known (A. Fisher, R. Kull).
mer and W. Demtoder: Opt.Commun. 39, 1981, 277.). This is because the incident light beam 1 is incident on the etalon 3 with a slight divergence angle by the lens system 2, and concentric interference fringes 5 appearing due to the multiple interference action of the etalon are projected on the line sensor 6 through the lens 4. It is configured as follows. With such a configuration, the diameter of the interference fringe that appears when the light to be measured and the reference light having a known wavelength λs are respectively incident, and the wavelength λx of the light to be measured is determined by comparing these. ing.

That is, the diameter Dp of the p-th ring-shaped interference fringe from the center of the concentric circle of the interference fringe 5 projected on the line sensor 6, the wavelength of the incident light 1 is λ, the resonator length of the etalon 3 is d, If the focal length of the lens 4 is f, Given in. Here, n is the refractive index of the medium forming the etalon, and n ₀ is the refractive index of air. Further, ε is a fractional part of the interference order. As is clear from the equation (1), the difference between the diameter Dp of the p-th interference fringe and the diameter Dq of the q-th interference fringe from the center of the concentric circle of the interference fringe 5 is the wavelength λ of the incident light and the resonator of the etalon. It depends on the length d. Therefore,
To obtain the interference order even if the wavelength λ of the incident light is unknown by using a plurality of etalons having different resonator lengths d and measuring the diameters Dp and Dq of some interference fringes on the concentric circles. You can Therefore, assuming that the interference order when the measured light is incident is (mx + εx) and the interference order of the reference light having the wavelength λs is (ms + εs), the wavelength λx of the measured light is Can be determined at. However, mx and ms are integer parts of the order, and εx and εs are fractions.

[0004]

In the prior art, the measurement accuracy of the wavelength .lambda.x is determined by the accuracy of the fraction of the interference order, that is, the accuracy of .epsilon.x and .epsilon.s, as is clear from the equation (2). For example, when the diameter of the interference fringes is measured using a semiconductor laser beam having a wavelength λs of 780 nm as a reference beam and an etalon having a cavity length d of 30 mm, the interference order (ms + ε
s) is about 10 ⁵ and the wavelength λx of the measured light is 10 ^−7.
In order to obtain it with a degree of accuracy, it is necessary to measure εx and εs accurately to the order of 10 ^-2 . However, since the accuracy of the fractions εx and εs depends on the measurement accuracy of the diameter of the interference fringes, and the measurement accuracy of the diameter of the interference fringes is limited by the resolution of the line sensor, the measurement accuracy is limited. In the current manufacturing technology of the detection element, the width of one element of the line sensor is about 25 μm, and making it smaller than this causes a problem such as a significant cost increase. Therefore, it was not possible to measure finer than the width of one element of this line sensor. On the other hand, the focal length f of the lens 4 is set to 1000
Although it is possible to improve the measurement accuracy by configuring it to be set to a length of about mm or more, there is a problem that the device becomes large.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a highly accurate and compact optical wavelength meter.

[0006]

In order to achieve the above object, a reference light having a known wavelength and a measured light having an unknown wavelength are incident on a Fabry-Perot etalon and projected onto a line sensor. The optical wavelength meter of the present invention for measuring the wavelength of the light to be measured from the position of the interference fringe includes a plurality of line sensors, the line sensors are parallel to each other, and one element of one line sensor and another line sensor. Are arranged so as to be lined up with a certain amount of offset.

[0007]

When the interference fringes are present on a plurality of corresponding elements between the line sensors, the accurate position or diameter of the interference fringes is determined from the number of line sensors that have detected the interference fringes and the shift amount between the line sensors. Can be done. The (n + 1) th element of the reference line sensor detects the interference fringes, and at the same time, in the other line sensor that is installed with a shift of 1/2 the width of the element, the nth element detects the interference fringes. If the interference fringes are present, it can be seen that the interference fringe is located between the nth element and the (n + 1) th element of the reference line sensor. Therefore, the measured value is not limited to the resolution of the element, and the accuracy of the measured value can be improved without increasing the size of the device.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the drawings using the same reference numerals for the same members as in the conventional example. Figure 1
Shows the optical system of the first embodiment. In the figure, the interference fringes 5 appearing after passing through the etalon 3 and the lens 4 are line sensors 6 arranged in parallel with the center of the concentric circles of the interference fringes.
It is projected on a and 6b, and its position is detected. FIG. 2 shows the installation state of the line sensors 6a and 6b together with the distance from the end face of the line sensor, and the numbers written in the line sensors 6a and 6b show the array element numbers from the end face. As is clear from FIG. 2, the line sensor 6b is displaced from the end surface of the line sensor 6a by half the width (12.5 μm) of an element having a width of 25 μm in the arrangement direction of the elements,
They are installed close to each other in parallel. Therefore, the p-th interference fringe 5p from the center of the concentric circle of the interference fringe 5 is the (n + 1) th element of the line sensor 6a and the n-th line of the line sensor 6b.
If it is on the second element, the position of the interference fringe is (25n)
It can be detected that it is between μm and (25n + 12.5) μm. As a result, compared to the conventional example using only one line sensor, it is possible to obtain a measurement value with twice the resolution, and it is possible to improve the accuracy of the measurement value without increasing the size of the device.

FIG. 3 shows the optical system of the second embodiment. In the figure, the interference light transmitted through the etalon 3 and lens 4 is vertically converged by the cylindrical lens 7 and then diffracted by the grating 8. Then, the light is incident on the line sensors 6a and 6b arranged on the diffracted light path.
Similar to the first embodiment, the line sensors 6a and 6b are arranged parallel to each other with the positions of the corresponding elements displaced by a half width of the elements in the arrangement direction of the elements. Therefore, it is possible to obtain twice the resolution as compared with the conventional example, and it is possible to improve the accuracy of the measured value without increasing the size of the device. Further, in the present embodiment, it is not necessary to bring the line sensor close to each other, which is advantageous in terms of the structure and space of the apparatus. Further, since the interference light is focused on the line sensor, there is an advantage that the light amount is not wasted. Have

As a method of disposing the plurality of line sensors by shifting their positions, for example, as shown in FIG.
The position of the line sensor may be adjusted by projecting the linear interference fringe 9 having a known interference fringe interval on the line sensors 6a and 6b. Further, in the above-described embodiment, the configuration using the two line sensors has been described, but the present invention is not limited to this, and the measurement accuracy can be further improved by using a plurality of line sensors. Furthermore, the present invention is applicable not only to the plane Fabry-Perot etalon but also to the spherical Fabry-Perot etalon.

[0011]

As described above, according to the present invention, the measurement accuracy is not limited to the resolution of the element, and the accuracy of the measurement value can be increased without increasing the size of the device, and the high accuracy of the measurement value can be obtained. It is extremely effective for downsizing and downsizing of the device.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system of a first embodiment of an optical wavelength meter according to the present invention.

FIG. 2 is a diagram for explaining an installation state of a line sensor in the first embodiment.

FIG. 3 is a diagram showing an optical system of a second embodiment of the optical wavelength meter according to the present invention.

FIG. 4 is a diagram for explaining a case where the position of a line sensor is adjusted using linear interference fringes.

FIG. 5 is a diagram showing an optical system of a conventional optical wavelength meter.

[Explanation of symbols]

 1 Incident light flux 2 Lens system 3 Fabry-Perot etalon 4 Lens 5 Interference fringe 6 Line sensor 7 Cylindrical lens 8 Grating 9 Linear interference fringe

Claims (1)

[Claims] 1. A reference light having a known wavelength and a measured light having an unknown wavelength are incident on a Fabry-Perot etalon, and the wavelength of the measured light is measured from the position of an interference fringe projected on a line sensor. The optical wavelength meter is equipped with a plurality of line sensors, and the line sensors are installed in parallel with each other, and one element of one line sensor and one element of the other line sensor are displaced by a certain amount. An optical wavelength meter characterized by being used.