JPH03272404A - Phase measuring apparatus for heterodyne interferometer - Google Patents

Abstract

PURPOSE:To achieve an accurate detection of a phase by calculating a phase difference between a sine wave signal and a cosine wave signal based on a reference light with respect to a clock signal based on a measuring light to detect a phase difference between a clock signal and the clock signal based on the measuring light by counting them. CONSTITUTION:A reference light (a) undergoes a square-law detection with a photodiode 1 to be converted into an electric signal, further converted into a voltage signal with a voltage-current converter 5 and by removing a noise component therefrom with a bandpass filter 8, the signal is sent out to an A/D converter 12 and a comparator 10 as reference signal (c) of a sine wave. Then, the reference light (a) is compared with an interfering light thereof by a 1/4 wavelength plate to be converted to a reference light a' which generates an interfering light of a cosine wave delayed by 1/4 phase and likewise, the light is converted into an electric signal after the square-law detection and by removing a noise component contained therein therefrom, the signal is sent to a converter 12 as reference signal c' of the cosine wave. On the other hand, a measuring light (b) also undergoes conversions to be sent to a incremental/ decremental counter 14 as measuring signal (d) and a phase difference within one cycle between the signals c, c' and d to be sent to a addition processing section 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a phase measuring device for a Herodyne interferometer that reads phase differences.

[Prior Art] A conventional phase measuring device for a heterodyne interferometer measures the phase difference of light by measuring the phase of measurement interference light from the phase of the frequency of reference interference light.

Then, the reference interference light and the measurement interference light are each converted into electrical signals, and the phase difference between these electrical signals is detected by
As shown in FIG. 3, this is performed by detecting the time difference between the seven-point cross positions of the reference signal a1 converted into each electric signal and the measurement signal d1. That is, in order to detect this time difference, a triangular wave signal S as shown in Fig. 3(b) is created based on the reference signal al shown in Fig. 3(a). Based on the measured signal d, a rectangular wave signal C as shown in (c) is created. Then, by comparing these signals, the phase difference between the reference signal a1 and the measurement signal dl is detected.

That is, if a triangular wave signal S is created from the reference signal a1, the voltage of this signal b1 is proportional to the time from the zero-crossing point of the reference signal a1. Then, if the voltage value of this triangular wave signal S is read at the zero cross point of the measurement signal d1, that is, at the rising edge of the rectangular wave signal c1,
The time difference, that is, the phase difference, between the reference signal a1 and the measurement signal d1 can be detected.

Further, since the reference signal a1 may overtake the measurement signal d1 by one cycle or may be overtaken by the measurement signal d1 by one cycle, an up/down counter is provided to count the number of times the reference signal a1 overtakes the measurement signal d1. These counted values are displayed, for example, in the upper digits on a display section (not shown), and the display of the phase difference in the lower digits, that is, the display of the phase difference within one cycle, is the display of the phase difference between the triangular wave signal b1 and the rectangular wave signal c1. The time difference within one cycle between the two is detected and displayed.

[Problem to be Solved by the Invention 1] Such a conventional phase measuring device for a heterodyne interferometer detects a phase difference by converting the reference signal a1 into a triangular wave signal, so linear calculations can be performed at high speed. The phase difference detection process corresponding to the lower digits, that is, the phase difference detection process within one cycle, can be performed at high speed.

However, since this type of interferometer generally requires a signal of 1M82 or more, it is difficult to create a highly accurate triangular wave signal h1 from this LM) 12 or more reference signal a1, and therefore, the phase detection cannot be performed accurately. There was a problem of not being able to do well.

``Means for Solving the Problems'' In order to solve such distance problems, the phase detection device for a heterodyne interferometer according to the present invention has a first phase detection device that converts reference interference light into an electrical signal and outputs a sine wave signal. photoelectric conversion means,
a second photoelectric conversion means that converts the interference light obtained by shifting the phase of one of the reference interference lights by 1/'4 wavelength into an electrical signal and outputs a cosine wave signal; a third photoelectric conversion means for outputting; and a calculation means for capturing a sine wave signal and a cosine wave signal based on a clock signal, calculating a phase difference between the sine wave signal and a cosine wave signal with respect to the clock signal from the amplitude value, and outputting the result. , an up/down counter that inputs a clock signal based on a sine wave signal and a clock signal output from the third photoelectric conversion means to the A/Tsub terminal and the DOWN terminal for counting, and a count output from the arithmetic means. It is provided with addition processing means for inputting and adding the phase difference signal and the count value output from the up/down counter.

Effect: The phase difference between the sine wave signal and cosine wave signal based on the reference interference light is calculated with respect to the clock signal based on the measurement interference light, and the phase difference between the clock signal based on the sine wave signal and cosine wave signal and the measurement interference light is calculated. The base clock signal is input and counted.Then, this count value and the phase difference value calculated above are added, and as a result, the phase difference between the reference interference light and the measurement interference light is calculated. Detected.

[Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a phase measuring device for a heterodyne interferometer according to the present invention. In the figure, 1-3 is a photodiode that square-law detects an optical signal and converts it into an electrical signal, 4 is a 1774 wavelength plate that delays the input optical signal by 1-74 wavelengths and outputs it, and 5-7 are current converters. 8.9 is a bandpass filter 10; 1 is a comparator; and 12 is an A/D converter that converts an analog electrical signal into a digital signal. In addition, 13 is a high-speed calculation unit composed of a DSP (digital signal processor), etc., which inputs the measurement signal and the reference signal converted into digital signals and performs high-speed calculation of the phase difference within one period of these signals; 14 is an up/down counter that counts the number of times the phase difference between the reference signal and the measurement signal is overtaken or overtaken in one cycle; 15 is input with the phase difference signal within one cycle and the count value from the up/down counter 14; 16 is a display section that displays the added value. Note that a and a' are reference lights (reference interference lights), b is measurement light, c and c'' are reference signals, d is measurement signal, and e and f are clock signals.

The operation of the interference phase detection device configured as above will be explained.

The reference light a is square-law detected by the photodiode 1 and converted into a current signal, further converted into a voltage signal by the current-voltage conversion circuit 5, and noise components are removed by the bandpass filter 8, resulting in the signal shown in FIG. 2(a). As shown in the figure, it is sent to the A/D converter 12 and the comparator 10 as a sine wave reference signal C.

Further, this reference light a is converted by a 1/4 wavelength plate into reference light a' which generates a cosine wave interference light whose phase is delayed by 1/4 compared to the interference light of the reference light a, and the reference light a' is converted by a photodiode 2. In the same way as described above, it is converted into a current signal after square law detection, further converted into a voltage signal by the current-voltage conversion circuit 6, and the noise component is removed by the band-pass filter 9, as shown in FIG. 2(b). , the reference signal C is sent to the A 7' D converter 12 as a cosine wave reference signal C'' whose phase is shifted by 1/4 wavelength.

On the other hand, the measurement light beam is converted into a current signal by the photodiode 3, and further converted into a voltage signal by the current-voltage conversion circuit 7 to generate a measurement signal d as shown in FIG. 2(d). . This measurement signal d is transmitted to comparator 1
1, the clock signal e is generated as a clock signal e as shown in FIG.

The A/D converter 12 inputs this clock signal e and sends it to the high-speed arithmetic unit 13, and also converts the reference signals c and c' into digital signals based on this clock signal e to the high-speed arithmetic unit 13. 13, high-speed arithmetic unit 13
Then, each of these signals is input and high-speed arithmetic processing is performed.

That is, the reference signal C is As1nΦ, and the reference signal C' is A
When cos Φ, the phase difference Φ becomes A cos Φ. Further, the amplitude value A is as follows.

Then, in the A/D converter 12, the clock signal e
As1nΦ A c of the reference signal c, c" at the rising edge of
The value of osΦ is converted into a digital signal and the high-speed arithmetic unit 13
The high-speed arithmetic unit 13 inputs this to the above equation! 11. ! 21 is obtained, and the phase difference Φ and amplitude value A are processed at high speed from the digitized values of As1nΦ and AcosΦ.

In this way, at the rising edge of the clock signal e generated from the measurement signal d, that is, at the point where the phase difference is "0", the reference signal c
, c' is read. Therefore, the phase difference within one cycle between the reference signals c, c' and the measurement signal d can be detected, and this detection result is sent to the addition processing section 15.

Further, the comparator 10 receives the reference signal C, generates a clock signal f, and sends it to the down terminal of the up/down counter 14. And up/down counter 14
inputs the clock signal f based on the reference signal C and the clock signal e based on the measurement signal d, counts the number of times the phase difference between these signals is overtaken or overtaken by one cycle or more, and The count value is sent to the addition processing section 15.

In this way, the addition processing unit 15 inputs the value of the phase difference of one cycle or more and the value of the phase difference of less than one cycle between the reference signal C and the measurement signal d, and adds these values to obtain the total phase difference. is calculated, and the calculation result is sent to the display unit 16 for display.

As explained above, the phase detection device for a heterodyne interferometer of the present invention uses a cosine wave interference whose phase is optically shifted by 1/4 wavelength from the measurement light a which generates interference light which is a sine wave as a signal to be read. Since the measurement beam that generates light is easily generated with high precision, it is possible to perform phase detection with high precision, unlike conventional triangular wave signals.

[Effects of the Invention] As explained above, the phase detection device for an interferometer according to the present invention calculates the phase difference between a sine wave signal and a cosine wave signal based on a reference destination with respect to a clock signal based on a measurement light, In addition, a clock signal based on a sine wave signal and a cosine wave signal and a tarokk signal based on measurement light are input and counted.
This count value and the phase difference value calculated above are added together to detect the phase difference between the measurement light and the reference light, so the signal that is read and referenced is generated using conventional equipment. Unlike the triangular wave signal that is generated, a highly accurate cosine wave signal can be generated, which has the effect that phase detection can be performed accurately.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the phase detection device for a heterodyne interferometer of the present invention, Fig. 2 is a timing chart of each part of this device, and Fig. 3 is a timing diagram of a conventional phase detection device for an interferometer. It is a chart. 1-3...Photodiode, 4...1/4 wavelength plate, 5-7...Current-voltage conversion circuit, 8, 9...
・Band pass filter, 10° 11...Comparator, 12...A, /D converter, 13...High speed arithmetic unit, 14.Up/down counter, 15...Addition processing unit, 16...Display section, a, a'...Reference light, b-...Measurement light, c, c'...Reference signal, d...Measurement signal, e, f... -...Clock signal.

Claims (1)

[Claims] In a phase measuring device for a heterodyne interferometer that measures a value according to a phase difference of a measurement signal with respect to a reference signal, a first photoelectronic device that converts reference interference light into an electrical signal and outputs a sine wave signal is provided. a conversion means; a second photoelectric conversion means for converting light obtained by shifting the phase of the reference interference light by a quarter wavelength into an electrical signal and outputting a cosine wave signal; and a second photoelectric conversion means for converting the measurement interference light into an electrical signal and outputting a clock signal. a third photoelectric conversion means that captures the sine wave signal and the cosine wave signal based on the clock signal, calculates and outputs a phase difference between the sine wave signal and the cosine wave signal with respect to the clock signal from the amplitude value; a calculation means for transmitting a clock signal based on the sine wave signal and a clock signal output from the third photoelectric conversion means to an up terminal;
It has an up/down counter that inputs each input to a down terminal and counts, and an addition processing means that inputs and performs addition processing on the phase difference signal output from the calculation means and the count value output from the up/down counter. A phase measuring device for a heterodyne interferometer.