JPH09178567A - Wavemeter for light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavemeter for light in which fluctuation of interference frequency due to a heat mass generated in an interference path can be suppressed while enhancing the accuracy of measurement. SOLUTION: A reference light and a measuring light from a reference light source 1 and a measuring light source 16 are split, reflected and multiplexed, respectively, by means of a beam splitter 2, a fixed mirror 3 and a moving mirror 4 to generate a reference interference light and a measuring interference light which are then subjected to photoelectric conversion and the interference wave numbers N, K are counted at wave number counting sections 11, 12. The air is fed to the interference optical path using a fan 15 and, while stirring a tot mass generated in the interference optical path, a moving mirror 4 is moved in the direction of optical axis through a linear motion mechanism 5 and then the moving mirror 4 is located by means of three positional sensors 6, 7, 8. Wave numbers N, K, a positional signal, and a reference light wavelength λ1 are inputted to an arithmetic section 13 where the wavelength λ2 of measuring light is calculated for each moving section of moving mirror 4 and averaged and then the operation results are presented at a display section 14.

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, and more particularly to an optical wavelength meter for measuring the wavelength of measuring light by utilizing the interference with reference light.

[0002]

2. Description of the Related Art FIG. 3 shows the configuration of a conventional optical wavelength meter.
This will be described with reference to FIG. Incidentally, FIG. 3 is a block diagram of an optical wavelength meter according to the prior art. FIG. 4 is a diagram comparing the heat mass generated in the optical path of the moving mirror in FIG. 3 with the waveform diagram of the signal output from the optical receiver when the moving mirror is swept. Indicates the distance (time). Further, the reference numerals in FIG. 4 correspond to the same reference numerals in FIG.

In FIG. 3, a reference light source 1 outputs a reference light L1 having a known wavelength. The reference light L1 is split by the beam splitter 2 into a reflected light L1a and a passing light L1b. The reflected light L1a is reflected by the fixed mirror 3 and is incident on the beam splitter 2 again. The passing light L1b is reflected by the moving mirror 4 and is combined with the reflected light L1a from the fixed mirror 3 in the beam splitter 2. As a result, the reference interference light L1 'on which the reference interference fringes are formed is formed. This reference interference light L1 'is received by the light receiver 9 as the reference interference signal S.
It is photoelectrically converted into 1 and is input to the wave number counting unit 11.

Similarly, the measuring light source 16 outputs measuring light L2 having an unknown wavelength in parallel with the reference light L1. The measuring light L2 is split into two by the beam splitter 2 into a reflected light L2a and a passing light L2b. The reflected light L2a is reflected by the fixed mirror 3 and enters the beam splitter 2. Passing light L
2b is reflected by the moving mirror 4 and is combined with the reflected light L2a from the fixed mirror 3 in the beam splitter 2. As a result, the measurement interference light L2 'on which the measurement interference fringes are formed is formed. The measurement interference light L2 ′ is photoelectrically converted into a measurement interference signal S2 by the light receiver 10 and input to the wave number counting unit 12.

The movable mirror 4 is fixed to the movable stage 51 of the linear movement mechanism 5 composed of the movable stage 51 and the guide rail 52, and the movable stage 51 moves on the guide rail 52 in the direction of arrow A (beam). When moving in a direction parallel to the light beams L1b and L2b passing through the splitter 2), the reference interference signal S1 and the measurement interference signal S2 become analog signals corresponding to light intensity changes which are periodically repeated due to interference.

When the moving speed of the moving stage 51 is V, the frequencies F of the reference interference signal S1 and the measurement interference signal S2 can be obtained by the equation (1). The frequency ratio between the reference interference signal S1 and the measurement interference signal S2 is the reference light L1.
And the optical frequency ratio of the measurement light L2.

F = 2 × V / (λ ₀ / n ₀ ) ... (1) where λ ₀ is the optical wavelength of the reference light L1 or the measurement light L2 in vacuum, and n ₀ is the reference light L1 or It represents the refractive index of the measurement light L2 in the atmosphere.

The wave number counting units 11 and 12 count the wave number N of the reference interference signal S1 and the wave number K of the measurement interference signal S2.
Since the frequency ratio between the reference interference signal S1 and the measurement interference signal S2 corresponds to the optical frequency ratio between the reference light L1 and the measurement light L2, the calculation unit 13 calculates from the wave numbers N and K input from the wave number counting units 11 and 12 ( Equation (2) is calculated to obtain the wavelength λ ₂ of the measurement light L2 in vacuum. The wavelength λ ₂ of the measurement light L2 obtained by this calculation is appropriately displayed on the display unit 14.

Λ ₂ = (N / K) × (n ₂ / n ₁ ) × λ ₁ (2) where λ ₁ is the wavelength of the reference light L ₁ in vacuum, and n ₁ is the atmosphere of the reference light L 1. The refractive index, n ₂ is the atmospheric refractive index of the measurement light L2.

[0010]

By the way, generally, the atmosphere exists as a mass of temperature, and the mass of temperature is called a heat mass. Further, since the optical refractive index in the atmosphere changes depending on the temperature, atmospheric pressure, and humidity, the optical wavelength meter with the configuration shown in FIG.
As shown in FIG. 4, when the heat mass C1 is generated only in the optical path of the passing light L1b of the reference light L1, an air refractive index difference is generated inside and outside the heat mass C1, and the reference interference signal S1 represented by the equation (1) The frequency changes temporarily.

This is equivalent to an error in the wave number N of the reference interference signal S1. Therefore, the accuracy of the measurement light wavelength λ ₂ obtained by the equation (2) deteriorates. In particular, if the diameter of the heat mass C1 is large, the improvement due to the averaging process cannot be expected.

An object of the present invention is to provide an optical wavelength meter capable of eliminating an error due to a heat mass existing in the path of the reference light and further improving the measurement accuracy.

[0013]

In order to achieve the above object, an optical wavelength meter according to the present invention comprises a reference light source 1 for outputting reference light having a known wavelength, a light from the reference light source 1 and a measurement light. Beam splitter 2 that splits each of the light beams into two directions and multiplexes the reflected light beams from the respective branching directions, and one of the reference light beam and the measurement light beam split by this beam splitter 2 is reflected and re-entered into the beam splitter 2. Fixed mirror 3 and moving mirror 4 for reflecting the other reference light and measurement light split by the beam splitter 2 and re-inputting them into the beam splitter 2.
And a linear movement mechanism 5 for moving the movable mirror 4 in the optical axis direction, and a position detection means 6 for dividing the moving range of the movable mirror 4 and detecting that the movable mirror 4 has reached the positions at both ends of the division. 7, 8 and light receiving means 9 and 10 for photoelectrically converting the reference interference light and the measurement interference light obtained by the combination of the beam splitter 2, and the light receiving means 9 and 10.
Wave number counting means 11, 12 for counting the wave numbers of the reference interference signal and the measurement interference signal from the position detecting means 6,
An arithmetic unit that calculates the wavelength of the measurement light for each section from the wave number of the reference interference signal corresponding to each section, the wave number of the measurement interference signal, and the wavelength of the reference light based on the position detection signals from 7 and 8 and performs averaging processing. 13, a display unit 14 for displaying a calculation result from the calculation unit 13, a space between the beam splitter 2 and the fixed mirror 3, the beam splitter 2 and the movable mirror 4.
And an air blowing unit 15 for blowing air toward at least one of the optical paths.

Further, the moving mirror 4 is swept a plurality of times to obtain the measuring light from the wave number of the reference interference signal, the wave number of the measuring interference signal and the reference light wavelength generated in each section obtained by the position detecting means 6, 7 and 8. Was calculated a plurality of times and the respective calculation results were averaged.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. However, in FIGS. 1 and 2, the same parts as those of FIGS. 3 and 4 are denoted by the same reference numerals, and the duplicated description is omitted here.

FIG. 1 is a diagram showing the configuration of an optical wavelength meter as an embodiment of the present invention. Further, FIG. 2 is a waveform diagram of a signal output from the light receiver at the time of sweeping the moving mirror in FIG. 1, in which the vertical axis represents current and the horizontal axis represents distance (time). Further, the reference numerals in FIG. 2 correspond to the same reference numerals in FIG.

A feature of the optical wavelength meter of this embodiment is that a fan 15 for sending wind is provided between the beam splitter 2 and the movable mirror 4, and it is further detected that the movable mirror 4 has reached an arbitrary position. At least three or more position sensors 6,
7 and 8 are provided along the moving direction of the movable mirror 4.

The wind direction of the fan 15 is adjusted so as to be perpendicular to the optical axis of the movable mirror 4. Reference light source 1 and measurement light source 16
The process of the light output from the light receiving unit 9 and the light receiving unit 10 is the same as in the prior art.

That is, in the above configuration, by driving the fan 15 installed so that the wind direction is perpendicular to the optical axis of the movable mirror 4, the air in the incident / reflected optical path of the movable mirror 4 is agitated to obtain the reference. The large heat mass C1 distributed on the light side and affecting the frequency is separated into a uniform heat mass C2 distribution with a small diameter.

Here, the moving stage 5 of the linear moving mechanism 5
When 1 moves in the direction of arrow A on the guide rail 52 where the heat mass C2 is distributed, the reference interference signal S1 and the measurement interference signal are emitted from the reference light receiving unit 9 and the measurement light receiving unit 10 as in the conventional technique. S2 is output and the wave number counting unit 1 is output.
1, 12 are input.

The wave number counting units 11 and 12 count the wave number N of the reference interference signal S1 and the wave number K of the measurement interference signal S2. On the other hand, the calculation unit 13 reads the wave numbers N and K between the position sensors 6 and 7 and between the position sensors 7 and 8 from the counting units 11 and 12 from the moving mirror position detection signals from the position sensors 6, 7, and 8.

Next, the calculation unit 13 is arranged between the position sensors 6 and 7,
From the wave number N and the wave number K generated between the position sensors 7 and 8, the measurement light wavelength λ ₂ is separately calculated by the above equation (2). Furthermore, in order to reduce the wavelength measurement error due to the difference in air refractive index between the inside and outside of the small-diameter heat mass C2, the measurement light wavelength λ ₂ calculated separately is reduced.
Is calculated, and the calculation result is displayed on the display unit 14.

Therefore, the optical wavemeter having the above-mentioned configuration is
By driving the fan 15, the air in the incident / reflection optical path of the movable mirror 4 is agitated, and the heat mass C1 distributed on the reference light side is agitated.
Is separated into a uniform distribution of heat lumps C2 having a small diameter, the influence on the frequency of the reference interference signal S1 can be suppressed.

Further, in the arithmetic unit 13, the moving range of the moving mirror 4 is divided based on the moving mirror position detection signals from the position sensors 6 to 8, and the measurement light wavelength λ obtained in each division.
_{Since 2} is averaged, the wavelength measurement error can be improved by (number of position sensors-1) ^1/2 ,
This can improve the measurement accuracy.

In the above embodiment, the fan 15 stirs the air in the incident / reflected optical path of the movable mirror 4, but the wind direction is perpendicular to the optical axis with respect to the incident / reflected optical path of the fixed mirror 3. The same effect can be obtained by disposing the fan 15 so that the air in the optical path is agitated. Of course, it is better to do both.

Further, the calculation unit 13 includes position sensors 6, 7,
After calculating the wavelength λ _{2 of the} measurement light from the wave number N and wave number K generated between 8 and the reference light wavelength λ ₁ by the formula (2), the wave number N and wave number generated between the position sensors 6, 7 and 8 are further repeated. The wavelength λ _{2 of the} measurement light is calculated from K and the reference light wavelength λ ₁ by the equation (2). Then, the average value of the measurement light wavelength λ ₂ measured a plurality of times may be calculated, and the calculation result may be displayed on the display unit 14. By doing so, it is possible to further reduce the wavelength measurement error due to the difference in air refractive index between the inside and outside of the heat lump C2 having a small diameter.

[0027]

As described above, according to the present invention, the heat lump in the optical path of the movable mirror is agitated by the wind of the fan to separate the heat lump into a distribution of the heat lump having a small diameter and a uniform measurement light wavelength. By measuring and averaging, the optical wavelength meter in which the wavelength measurement error due to the difference in air refractive index between the inside and outside of the small-diameter heat mass is improved by (position sensor number-1) ^1/2 can be made.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing, in association with each other, a state of stirring a heat mass in an optical path of a movable mirror and a state of frequency change of a reference interference signal and a measurement interference signal in the same embodiment.

FIG. 3 is a diagram showing a configuration of an optical wavelength meter according to a conventional technique.

FIG. 4 is a diagram showing a conventional optical wavelength meter when a heat mass is generated in the optical path of a movable mirror and a frequency change of a reference interference signal and a measurement interference signal.

[Explanation of symbols]

 1 Reference Light Source 2 Beam Splitter 3 Fixed Mirror 4 Moving Mirror 5 Linear Moving Mechanism 51 Moving Stage 52 Guide Rails 6, 7, 8 Position Sensor 9 Reference Light Receiver 10 Measuring Light Receiver 11, 12 Wavenumber Counting Unit 13 Computing Unit 14 display section 15 fan 16 measurement light source L1 reference light L1 'reference interference light S1 reference interference signal L2 measurement light L2' measurement interference light S2 measurement interference signal N reference interference wave number K measurement interference wave number

Claims (2)

[Claims] 1. A reference light source for outputting reference light having a known wavelength.
(1), a beam splitter (2) that splits the light from the reference light source (1) and the measurement light into two directions, respectively, and multiplexes the reflected light from each split direction, and this beam splitter (2) A fixed mirror (3) that reflects one of the split reference light and measurement light and re-enters the beam splitter (2), and reflects the other split reference light and measurement light by the beam splitter (2). Moving mirror (4) that re-enters the beam splitter (2) and a linear moving mechanism that moves the moving mirror (4) in the optical axis direction.
(5) and the position detection means (6, 6) that divides the movement range of the movable mirror (4) and detects that the movable mirror (4) has reached the positions at both ends of the division.
7,8), a light receiving means (9,10) for photoelectrically converting each of the reference interference light and the measurement interference light obtained by the combination of the beam splitter (2), and this light receiving means device (9,10) From the reference interference signal corresponding to each section by the wave number counting means (11, 12) for counting the wave number of the reference interference signal and the measurement interference signal from the position detection signal from the position detection means (6, 7, 8). A calculation unit (13) that calculates the wavelength of the measurement light for each category from the wave number, the wave number of the measurement interference signal, and the wavelength of the reference light, and displays the calculation result from this calculation unit (13). Display (14)
And a blowing means (1) for blowing air toward at least one optical path between the beam splitter (2) and the fixed mirror (3) and between the beam splitter (2) and the movable mirror (4).
5) An optical interferometer comprising: 2. The wave number of a reference interference signal, the wave number of a measurement interference signal, and the reference light generated for each section by the position detecting means (6, 7, 8) obtained by sweeping the movable mirror (4) a plurality of times. An optical interferometer characterized by calculating the wavelength of measurement light a plurality of times from the wavelength and averaging the respective calculation results.