JPH0827213B2 - Optical wavelength measurement device - Google Patents

Description

The present invention relates to an optical wavelength measuring device for measuring the wavelength of light using, for example, a two-beam interferometer.

[Prior Art] As an apparatus for electrically measuring the wavelength of light to be measured without using a spectroscope such as a diffraction grating, an optical wavelength measuring apparatus using a Michelson interferometer 1 shown in FIG. 4 has been put into practical use. ing.
That is, the known reference wavelength λ output from the reference light source 2
_The coherent reference light r having _R is incident on the half mirror 4 in the beam splitter 3. The half mirror 4 is arranged at an angle of 45 ° with respect to the optical path of the reference light r. A part of the reference light r is reflected at a right angle by the point A of the tilted half mirror 4, and the traveling direction is 180 degrees by the fixed mirror 5.
It is inverted by an angle of?, Transmitted through point B of the same half mirror 4, and is incident on the reference light receiver 6. A part of the reference light r output from the reference light source 2 is transmitted through the point A of the half mirror 4, the traveling direction is reversed by 180 ° by the moving mirror 7, and reflected at the point B of the half mirror 4, and The light enters the reference light receiver 6.

On the other hand, the light to be measured a having an unknown wavelength λ passes through the point B of the half mirror 4 and travels 180 ° by the moving mirror 7.
Inverted, the light is reflected at the point A of the half mirror 4 and enters the light receiver 8 for the measured light. Further, a part of the measured light a is reflected at a point B of the half mirror 4 at a right angle, the traveling direction is inverted by 180 ° by the fixed mirror 5, and transmitted through the point A of the half mirror 4 for the measured light. It is incident on the light receiver 8. The movable mirror 7 is provided so as to be movable parallel to the optical path as shown in the figure.

Reference light r and light to be measured a incident on each of the light receivers 6 and 8
Cause an interference phenomenon between the light passing through the fixed mirror 5 and the light passing through the moving mirror 7. Therefore, when the moving mirror 7 is moved in the arrow direction, the light intensity signals r ₁ and a ₁ corresponding to the light intensities of the interference lights output from the light receivers 6 and 8 are
As shown in FIG. 5, a repetitive waveform caused by interference occurs. That is, in this type of device, as is clear from the above description and FIG. 5, it is possible to directly measure the repetitive waveform generated by the interference from the light intensity signal. Since the pitch length P of this repetitive waveform is a value corresponding to the wavelength of the light, the number N of repetitive waveforms when the movable mirror 7 is moved by a predetermined prescribed distance D _S.
If r and Na are counted, the wavelength λ of the measured light a to be obtained is (1)
It can be obtained by a formula.

λ = (Na / Nr) λ _R (1) However, since the numbers Nr and Na of the above repetitive waveforms are generally not integers, a specified distance is required to improve the measurement accuracy of the wavelength λ.
It is necessary to set D _S to be long to increase the number of digits of each measurement value Nr, Na, or to measure accurately to the decimal point.

[Problems to be Solved by the Invention] However, the optical wavelength measuring device using the Michelson interferometer 1 shown in FIG. 3 still has the following problems to be solved.

That is, when the wavelength λ of the measured light a is only a certain wavelength λ ₀ as shown in FIG. 6A, the light intensity obtained in the process of moving the movable mirror 7 by the specified distance D _S. The waveform of the signal a ₁ is constant, as shown in FIG. Therefore, the number Na of repetitive waveforms of the light intensity signal a ₁ can be accurately counted by using, for example, a wave number counter.

However, the measured light a is, as shown in FIG.
Not only a coherent light including only a single wavelength lambda _0, in some cases, for example, as shown in FIG. 6 (b), in addition to the specific wavelength lambda _0, before and after the specific wavelength lambda ₀ There may be many wavelengths λ ₁ , λ ₂ , ..., λ _n ,.
When such non-coherent light enters the Michelson interferometer 1 shown in FIG. 4 as the light to be measured a, the light intensity signal a from the light receiver 8 obtained in the process of moving the movable mirror 7 by the specified distance D _{S. In} the waveform of ₁ , as shown in FIG. 7 (a), a beat phenomenon occurs in which the amplitude of the waveform greatly changes. Further, as shown in FIG. 6 (c), the input measured light a may have a wide spectrum characteristic. In this case, the beat phenomenon shown in FIG. 7B occurs in the light intensity signal a ₁ from the light receiver 8.

As described above, the light intensity signal a ₁ is added to FIG.
When the bead phenomenon shown in occurs, the waveform is disturbed in the portion where the amplitude is reduced, defining the moving mirror 7 distance D _S
It becomes impossible to count the number of repetitive waveforms Na of the light intensity signal a ₁ obtained in the process of moving only by the wave number counter.

In the conventional wavelength measuring device, in order to secure high wavelength measurement accuracy, the number of repetitive waveforms Na
When it becomes impossible to count, as an error processing, for example, measurement impossible is displayed on the operation panel or the like.

However, a single wavelength λ as shown in FIG.
_In addition to the original function of the measuring device for measuring the wavelength λ of coherent light containing only ₀ with high accuracy, almost the center of non-coherent light containing many wavelength components as shown in FIGS. 6 (b) and (c). It has been earnestly desired to add a function capable of measuring the wavelength λ of a portion even if the measurement accuracy is slightly lowered. For example, even if the number of significant digits of the measurement result when measuring light of only a single wavelength is 7 to 8, the number of significant digits of the measurement result when measuring light containing a large number of wavelength components is 4 ~
In some cases, 5 digits is sufficient.

The present invention has been made in view of such circumstances, and by counting the number of repetitive waveforms only during a wave number measurement period in which the amplitude of the light intensity signal of the interference light exceeds the specified amplitude, coherent even if it includes a large number of wavelength components. An object of the present invention is to provide an optical wavelength measuring device capable of measuring the wavelength of non-natural light with a measurement accuracy according to the degree of coherence and measuring the wavelength of light having various properties.

It is another object of the present invention to provide an optical wavelength measuring device that can output the effective digit number information indicating the measurement accuracy at the same time as the measurement result, and that allows the operator to simultaneously grasp the property of the measured light.

[Means for Solving the Problems] In order to solve the above problems, the present invention divides an input measured light into two optical paths, and then recombines them to create an interference light, and one optical path length. In the optical wavelength measuring device for measuring the light intensity signal of the repetitive waveform composed of the interference light generated by changing the specified distance, and calculating the wavelength of the measured light from the number of repetitive waveforms that can be directly extracted from the light intensity signal, A period detection circuit that detects a period during which the amplitude of the repetitive waveform of the light intensity signal obtained in the process of changing one optical path length by the specified distance as the wave number measurement period, and one optical path length is changed by the specified distance The wave number counter that counts the number of repetitive waveforms of the light intensity signal obtained in the process only during the wave number measurement period, and the maximum wave number measurement period of the wave number measurement period and the count value of the corresponding wave number counter From those having a wavelength calculation means for calculating the wavelength of the light to be measured.

In another invention, in addition to the above-mentioned means, the wavelength calculation means calculates the length of the maximum wavenumber measurement period of the wavenumber measurement periods detected by the period detection circuit. The number of effective digits of the wavelength is set, and the effective number of digits control means for outputting this effective number of digits information together with the calculated wavelength is provided.

[Operation] According to the optical wavelength measuring device configured as described above, when the measured light is coherent light containing substantially only one wavelength, the interference light generated by changing one optical path length by the specified distance. Since the amplitude of the repetitive waveform included in the light intensity signal is substantially constant, the wave number measurement period detected by the period detection circuit, and further, the maximum wave number measurement period is the specified measurement period corresponding to the specified distance. Therefore, the number of repetitive waveforms counted by the wave number counter becomes a count value for the specified measurement period, so that a highly accurate wavelength measurement result can be obtained.

On the other hand, when the measured light is non-coherent light containing a plurality of wavelength components, the amplitude of the repetitive waveform included in the light intensity signal of the interference light changes in a beat shape, so that the number of waves detected by the period detection circuit is measured. The period is only the period when the amplitude exceeds the specified amplitude. Therefore, during this wave number measuring period, the number of repetitive waveforms can be accurately counted by the wave number counter. Therefore, the wavelength of the light to be measured is calculated with the value corresponding to the maximum wave number measurement period and the maximum wave number measurement period of the number of repetitive waveforms counted by the wave number counter. In this case, since the maximum wave number measurement period is shorter than the specified measurement period, the number of significant digits of the calculated wavelength is small.

Further, in another invention, since the number of significant digits corresponds to the maximum wave number measurement period as described above, the information of the number of significant digits corresponding to the detected maximum wave number measurement period is output at the same time as the measurement result. .

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of the optical wavelength measuring device of the embodiment. The same parts as those in FIG. 4 will be assigned the same reference numerals and overlapping explanations will be omitted.

The light to be measured a having the unknown wavelength λ input from the outside is incident on the Michelson interferometer 1 shown in FIG. The interference light corresponding to the light to be measured a output from the point A of the half mirror 4 in the Michelson interferometer 1 is equally branched by the half mirror of another beam splitter 9, and the long wavelength light receiver 8a and the short wavelength light receiver 8a. It is incident on the wavelength light receiver 8b. The optical intensity signals a ₁ and a ₂ output from the long-wavelength photodetector 8a and the short-wavelength photodetector 8b are amplified and removed by the amplifiers 10a and 10b, respectively. Then, the amplified light intensity signals a ₁ and a ₂ are respectively subjected to the following waveform shaping circuits 11a and 11b.
Accordingly, the waveform is shaped into a rectangular wave signal, and the rectangular wave signal is input to the timing circuit 12.

Further, each light intensity signal a ₁ , amplified by each amplifier 10a, 10b,
a ₂ is the one of the light intensity signal a ₃ either at the switching circuit 13 is inputted is selected by the period detection circuit 14. This period detection circuit
14, a full-wave rectifier circuit 14a for full-wave rectification as shown a light intensity signal a ₃ which is selected by the switching circuit 13 in FIG. 3, the full-wave rectified signal b output from the full-wave rectifying circuit 14a The smoothing circuit 14b configured by, for example, a low-pass filter for obtaining the envelope waveform of the envelope curve of the envelope signal c and the envelope voltage of the envelope signal c output from the smoothing circuit 14b are compared with the reference voltage V _RE, and the envelope curve It is composed of a comparator circuit 14c which outputs a wave number measurement period signal d which becomes H (high) level only during the period when the waveform exceeds the reference voltage V _RE . And this period detection circuit 1
The wave number measurement period signal d output from 4 is input to the timing circuit 12.

Furthermore, each light intensity signal a amplified by each amplifier 10a, 10b
_One of the light intensity signals ₁ and a ₂ is selected by another switching circuit 15 and input to the LOG conversion circuit 16 for logarithmic conversion. The level value of the light intensity signal logarithmically converted by the LOG conversion circuit 16 and displayed in dB is converted into a digital value by the next A / D converter 17, and then read by the CPU 19 via the bus line 18.

On the other hand, the reference light r having the known wavelength λ _S output from the reference light source 2 enters the Michelson interferometer 1. The interference light corresponding to the reference light r output from the Michelson interferometer 1 enters the reference light receiver 6. The light intensity signal r ₁ output from the reference light receiver 6 is amplified while the unnecessary frequency component is removed by the amplifier 10c. And
The amplified light intensity signal r ₁ is shaped into a rectangular wave signal by the next waveform shaping circuit 11c, and is input to the timing circuit 12.

The moving mirror 7 of the Michelson interferometer 1
The movement is controlled by the drive motor 20 driven by the motor drive circuit 20a. The moving mirror 7 has a position detector 21
Is attached to the position detector 21. When the moving mirror 7 enters a moving range of a predetermined specified distance D _S , H
The position detection signal e which is at the (high) level is output. This position detection signal e is input to the timing circuit 12.

Furthermore, a stopper 24 is installed in the Michelson interferometer 1.
When the moving mirror 7 exceeds the allowable movement limit position, the position detection circuit 25 operates to move the moving motor 20.
Forcibly stop.

Further, the timing circuit 12 counts the number of repetitive waveforms Na included in the light intensity signal a ₃ which is switched and selected by the switching circuit 13 out of the _two light intensity signals a ₁ and a ₂ input thereto.
26, and a wave number counter 27 for counting the number of repetitive waveforms Nr contained in the light intensity signal r ₁ of the reference light r input to the timing circuit 12 is connected.

The timing circuit 12 detects the rising / falling of the wave number measuring period signal d and the position detecting signal e output from the period detecting circuit 14 and detects the wave number counters 26 and 27.
To the third counting start signal and counting end signal
It is sent at the timing shown in the figure. That is, when the position detection signal e maintains the H level state and the wave number measurement period signal d rises, the wave number counters 26 and 27 start counting, and when the wave number measurement period signal d falls, the counting ends. Then, when the wave number measurement period signal d rises again, counting is restarted from the beginning. Then, when the wave number measurement period signal d falls or the position detection signal e falls, the counting is ended.

Each count value Na ₁ , N counted by each wave number counter 26,27
r ₁ , Na ₂ , Nr ₂ , ... are RAM 29 via bus line 18 each time
Stored in. The bus line 18 includes a CPU 19 that executes various arithmetic processes, a ROM 30 that stores a control program, the RAM 29 that stores various variable data, the A / D converter 17, the switching circuits 16 and 13, the measured wavelengths. A key input circuit 3 to which an interface 31 for transmitting λ to, for example, an external host computer, a device panel 32 for the operator to key in various commands, and a display 33 for displaying measurement results are connected.
4, the motor drive circuit 20a, and the position detection circuit 25
Etc. are connected.

As shown in the figure, the display 33 displays the measured wavelength λ of the measured light a by a numeral of, for example, 7 to 8 digits.

The CPU 19 in the optical wavelength measuring device configured in this way
The control operation executed by will be described with reference to FIG.

First, a drive signal is sent to the motor drive circuit 20a to activate the moving motor 20 to start moving the moving mirror 7 in the Michelson interferometer 1. When the moving mirror 7 starts to move at a constant speed, the interference light of the measured light a output from the Michelson interferometer 1 causes the long wavelength light receiver 8a and the short wavelength light receiver 8b.
Are converted into light intensity signals a ₁ and a ₂ each containing a repetitive waveform. Then, the light intensity signals a ₁ and a ₂ are input to the switching circuit 15 after being amplified by the amplifiers 10a and 10b.

The CPU 19 switches and controls the switching circuit 15 to select the light intensity signal a ₁ on the long wavelength side. Then, the light intensity level of the light intensity signal a ₁ is read. Next, the switching circuit 15 is switched to the opposite side to read the light intensity level of the light intensity signal a ₂ on the short wavelength side.
Then, the two light intensity levels are compared, and the light intensity signal a ₃ having the higher light intensity level is selected. Next, so that the higher light intensity signal a ₃ is output, the other switching circuit 13
To switch. Therefore, the light intensity signal a ₃
Is input to the period detection circuit 14.

The light intensity signal a ₃ input into the period detection circuit 14 is full-wave rectified by the full-wave rectification circuit 14a as shown in FIG.
This full-wave rectified signal b is envelope-detected by the smoothing circuit.
The envelope signal c is output to the wave number measurement period signal d in the next comparison circuit 14c.
Is converted to. Then, as described above, the wave number counters 26 and 27 count the number of repetitive waveforms of the selected light intensity signal a ₃ and light intensity signal r ₁ according to the signal level change of the wave number measurement period signal d. Corresponding to the maximum wave number measurement period (T _{2 in} FIG. 3) of each wave measurement period T ₁ , T ₂ , ... Of the count values Na ₁ , Nr ₁ , Na ₂ , Nr ₂ ,. The counted values (Na ₂ , Nr _{2 in} FIG. 3) are taken out, and the wavelength λ of the measured light a is calculated using the above-mentioned formula (1).

λ = (Na ₂ / Nr ₂ ) λ _R Then, the calculated wavelength λ is displayed on the display unit 33. In this case, the number of significant digits of the wavelength λ calculated by the above equation is determined by the number of significant digits of each of the count values Na ₂ and Nr ₂ . Since each of the count values Na ₂ and Nr ₂ is an integer, the number of significant digits changes corresponding to the length of the corresponding wave number measurement period (T _{2 in} FIG. 3). Therefore, the wavelength λ calculated with the number of significant digits corresponding to this wave number measurement period is displayed on the display 33.

With the optical wavelength measuring device configured in this manner, the measured light a has a substantially single wavelength λ as shown in FIG. 6 (a), for example.
If the light is coherent light having ₀ , each of the light receivers 8a, 8b
Since the beat phenomenon does not occur in the waveforms of the light intensity signals a ₁ and a ₂ output from, the waveforms of the smoothed detection signal c in FIG. 3 all exceed the reference voltage V _RE . Therefore, the wave number measurement period signal d output from the period detection circuit 14 maintains the H level during the period in which the moving mirror 7 moves the specified distance D _S , so that the count values Na obtained by the wave number counters 26 and 27 are obtained. Since the number of significant digits of Nr is large, the number of significant digits of the calculated wavelength λ is large, and the large number of significant digits is displayed on the display unit 33.

On the other hand, if the wavelength characteristic of the measured light a is non-coherent light containing a large number of wavelength components as shown in FIG. 6 (b) or light having a wide spectrum width as shown in FIG. 6 (c). A beat phenomenon occurs in the waveforms of the light intensity signals a ₁ and a ₂ output from the photodetectors 8a and 8b. Then, as shown in FIG. 3, the wave number measurement periods T ₁ , T ₂ ,
The approximate wavelength λ in the measured light a is calculated by the number Na, Nr of repetitive waveforms generated within the maximum wave number measurement period among the above. In this case, the number of significant digits is small, so
It is displayed on the display unit 33 with a small number of significant digits.

As described above, in the case of coherent light having a substantially single wavelength λ ₀ , the wavelength λ is accurately measured and displayed with a large number of effective digits. In the case of non-coherent light containing many wavelength components, the wavelength λ is measured with low accuracy and displayed with a small number of effective digits.

Therefore, conventionally, the wavelength can be measured with a certain degree of accuracy even for non-coherent light, which could not be measured by an optical wavelength measuring device having high measurement accuracy.
The application range of this measuring device can be greatly expanded.

Further, since the information of the effective digit number is also displayed at the same time as the measurement result, the operator can grasp the property of the measured light a to some extent.

[Effects of the Invention] As described above, according to the optical wavelength measuring apparatus of the present invention, the number of repetitive waves is counted only during the wave number measurement period in which the amplitude of the light intensity signal of the interference light exceeds the specified amplitude. Therefore,
Even for non-coherent light including a large number of wavelength components, its wavelength can be measured with measurement accuracy according to the degree of coherence.

That is, in an optical wavelength measurement device that directly measures repetitive waveforms from a light intensity signal, and the measured light contains a wavelength other than the specific wavelength, a beat phenomenon occurs in the light intensity signal, and the repetition occurs. Even if the waveform has a disturbed portion, the number of repetitive waveforms of the light intensity signal can be counted and the number of waves of the specific wavelength can be measured.

 Therefore, it is possible to measure the wavelength of light having various properties.

Further, since the effective digit number information indicating the measurement accuracy is also output at the same time as the measurement result, the operator can simultaneously grasp the property of the measured light.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical wavelength measuring device according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a Michelson interferometer used in the device of the same embodiment, and FIG. Example A time chart showing the operation of the apparatus, FIG. 4 is a schematic diagram showing a general Michelson interferometer, FIG. 5 is a waveform diagram showing the principle of wavelength measurement, and FIG. 6 is a wavelength characteristic of general measured light. FIG. 7 is a waveform diagram showing a general light intensity signal. 1 ... Michelson interferometer, 2 ... reference light source, 3 ... beam splitter, 5 ... fixed mirror, 7 ... moving mirror, 12 ... timing circuit, 13, 16 ... switching circuit, 14 ...
… Period detection circuit, 14a …… Full wave rectification circuit, 14b …… Smoothing circuit, 14c …… Comparison circuit, 19 …… CPU, 20 …… Mobile motor,
26,27 …… wave number counter, 33 …… display.

Claims (2)

[Claims] 1. The interference light generated by dividing the input light to be measured into two optical paths and then recombining to create interference light, and changing the one optical path length by a prescribed distance. In an optical wavelength measuring device that measures a light intensity signal of a repetitive waveform and calculates the wavelength of the measured light from the number of repetitive waveforms that can be directly extracted from the light intensity signal, the one optical path length is changed by the specified distance. A period detection circuit (14) for detecting a period during which the amplitude of the repetitive waveform of the light intensity signal obtained in the process exceeds a specified amplitude, and a period detection circuit (14) obtained in the process of changing the one optical path length by the specified distance. A wave number counter (26) for counting the number of repetitive waveforms of the light intensity signal only in the wave number measuring period, a maximum wave number measuring period of the wave number measuring period and the wave number counter corresponding thereto. An optical wavelength measuring device comprising: a wavelength calculating means (19) for calculating the wavelength of the light to be measured from the count value of. 2. The number of significant digits of the wavelength calculated by the wavelength calculating means is set in correspondence with the length of the maximum wave number measuring period of the wave number measuring periods detected by the period detecting circuit,
The optical wavelength measuring device according to claim 1, further comprising an effective digit number control means (19, 33) for outputting the effective digit number information together with the calculated wavelength.