JP2001274483A - Modulation control method and calibration method for laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the frequency and the phase of a frequency modulation signal equal in synchronization with the frequency modulation signal of an (iodine stabilized He-Ne) laser device, and to measure and calibrate the frequency difference between lasers highly accurately when the frequency of the laser device is calibrated or the like. SOLUTION: A plurality, e.g. two, of laser devices 1, 2 in which a laser oscillation frequency is modulated by a modulation signal so as to generate a modulation laser beam are provided. A reference clock signal and a synchronizing signal which are generated by the first laser device 1 are supplied as the modulation-operation reference signal of the second laser device 2, and a modulation signal whose frequency and phase are identical is obtained. The first laser device 1 is set as the master side, and the second laser device 2 is set as the slave side. The modulation signal of the laser device on the slave side is used as a modulation signal whose frequency and phase are identical to those of the modulation signal on the master side, and a specific frequency on the slave side is calibrated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a modulation control method and a calibration method for a laser device, and more particularly to a laser device useful for an iodine stabilized laser device for synchronizing a modulation frequency of an iodine stabilized laser with an external reference signal. The present invention relates to a modulation control method and a calibration method.

[0002]

2. Description of the Related Art An iodine-stabilized He--Ne laser is one in which the oscillation frequency of a He--Ne laser is locked to an absorption line of iodine so that the oscillation frequency is high. Iodine has a large number of saturated absorption lines. In order to lock to the desired saturated absorption line, the oscillation frequency of the He-Ne laser light is modulated with an AC signal, and the harmonic of the modulated wave is detected. Is used to specify the saturated absorption line of iodine. The specified absorption line is locked using the third harmonic signal of the modulated wave.

At present, the light source of a laser interferometer, He-
An iodine-stabilized He-Ne laser in which the laser oscillation frequency is locked to a saturated absorption line of iodine molecules is used as a reference laser when the frequency calibration of the Ne laser is performed.

In calibrating the oscillation frequency of this iodine stabilized He—Ne laser, two iodine stabilized He—N lasers are used.
The oscillation frequency of the e-laser is compared.

As a method for calibrating the frequency of an iodine-stabilized He—Ne laser, usually, the oscillation frequency of a calibration / test laser is fixed to each of different saturated absorption lines adjacent to each other of iodine molecules, and two lasers are used. Measure the difference in oscillation frequency.

The oscillation frequency of an iodine-stabilized He—Ne laser is usually frequency-modulated with a width of 6 MHz, and this value is は of the interval between saturated absorption lines of adjacent iodine molecules.
, Which is a size that cannot be ignored. For this reason, there is a problem in obtaining the frequency difference with high accuracy.

Now, the light wave of the first laser and the light wave of the second laser are expressed by focusing only on the time term as follows. cos [ω1 + (1/2) △ ωsin (Ω1 · t + θ1)] t (1) cos [ω2 + (1/2) △ ωsin (Ω2 · t + θ2)] t (2) where t is time and ω1 and ω2 are Each is the oscillation frequency of the laser. Ω1 and Ω2 are each about 3kHz at the modulation frequency of the laser
It is. θ1 and θ2 are the phases of the modulation frequency of the laser, respectively. △ ω is a frequency modulation width, which is usually 6 MHz.

When the difference between the equations (1) and (2) is obtained, the beat, which is the difference between the oscillation frequencies of the two iodine-stabilized He-Ne lasers, is obtained according to the equation (3). (ω1−ω2) + (1/2) △ ω [sin (Ω1 · t + θ1) −sin (Ω2 · t + θ2)] (3) Here, the second term represents the fluctuation of the beat. (3)
In the equation, if Ω1 = Ω2 and θ1 = θ2, ie,
If the laser oscillation frequency is modulated at the same frequency and in phase, no beat variation will occur.

Conventionally, the difference between the oscillation frequencies is averaged by making the measurement time of the oscillation frequency difference sufficiently longer than the beat period caused by the difference between the oscillation frequencies between the two lasers, thereby averaging the difference between the oscillation frequencies. The effect was reduced.

[0010]

As described above, in the conventional iodine-stabilized He-Ne laser, when the two laser beams are mixed and the laser oscillation frequency difference is measured, the laser beam between the two A method of averaging the difference between the oscillation frequencies by taking a sufficiently large measurement time of the oscillation frequency difference as compared with the change in the beat has been used for the influence of the fluctuation component of the beat caused by the modulation frequency difference.

However, even if the measurement time of the beat, which is the oscillation frequency difference between the lasers, is sufficiently long compared to the fluctuation of the beat, and the average is taken, it is difficult to reduce the error to a certain degree or less. there were.

A frequency counter that performs a rounding process when measuring a frequency difference to increase the number of significant digits increases the frequency of a frequency-modulated signal such as the difference in the oscillation frequency of an iodine stabilized He—Ne laser. Then, there was a problem that an error occurred.

In view of the above problems, it is an object of the present invention to synchronize the frequency modulation signal of the (iodine-stabilized He-Ne) laser device so that the frequency and the phase of the frequency modulation signal can be equalized. (Iodine-stabilized He-N
e) An object of the present invention is to provide a modulation control method and a calibration method for a laser device that enable high-accuracy measurement and calibration of a frequency difference between lasers in frequency calibration and the like of the laser device.

[0014]

In order to solve the above-mentioned problems, a modulation control method and a calibration method for a laser device according to the present invention employ the following characteristic configurations.

(1) A plurality of laser devices for generating a modulated laser beam by modulating a laser oscillation frequency with a modulation signal are provided. The reference clock signal and the synchronization signal generated by the first laser device are converted into at least one other signal. A modulation control method for a laser device that supplies a modulation operation reference signal for a second laser device.

(2) Two laser devices for generating a modulated laser beam by modulating a laser oscillation frequency with a modulation signal are provided, and a reference clock signal and a synchronization signal generated by the first laser device are transmitted to a second laser device. A modulation control method for a laser device that supplies a modulation operation reference signal for the device.

(3) Two laser devices for generating a modulated laser beam by modulating the laser oscillation frequency with a modulation signal are provided. Each of the two laser devices has an internal reference clock source and an internal reference clock source. A modulation signal generator for outputting a synchronization signal based on an internal clock from a clock source; and transmitting a reference clock and a synchronization signal generated by the first laser device as a modulation operation reference signal of the second laser device. Modulation control method for a laser device.

(4) Two laser devices for generating a modulated laser beam by modulating the laser oscillation frequency with a modulation signal are provided, and the second laser device is provided with a first modulation device generated by the first laser device. A modulation control method for a laser device, which receives a signal and generates a modulation signal having the same frequency and the same phase as the first modulation signal by a PLL operation based on the input first modulation signal.

(5) The first laser device is set as a master device, and the second laser device is set as a slave device.
The modulation control method for a laser device according to any one of (1) to (4) above, wherein the modulation signal has the same frequency and the same phase as the modulation signal on the master side.

(6) The modulation control method for the laser device according to any one of (1) to (5), wherein the first laser device and the second laser device are iodine stabilized laser devices.

(7) The laser device according to any one of (1) to (6) above, wherein the first laser device is set as a master side, the second laser device is set as a slave side, A calibration method for a laser device, comprising: calibrating a specific frequency on a slave side as a modulation signal having the same frequency and the same phase as a modulation signal on a master side using a modulation signal from a laser device on a slave side.

(8) The method for calibrating a laser device according to (7), wherein the first laser device and the second laser device are iodine-stabilized laser devices.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a modulation control method for a laser device according to the present invention will be described.
The e-laser synchronization control will be described with reference to the drawings.

FIG. 1 is a block diagram for explaining an embodiment of a method for synchronizing and calibrating an iodine stabilized He—Ne laser according to the present invention. As described above, the main object of the present invention is to equalize the frequency modulation signals of a plurality of (for example, two) (iodine-stabilized He-Ne) laser devices. A method used as a synchronization signal will be described.

In the embodiment shown in FIG. 1, a reference clock is used as a synchronization signal, and the laser is operated in a master-slave system in which the reference laser 1 is used as a master and the laser 2 to be calibrated is used as a slave.

The reference laser 1 and the laser 2 to be calibrated are mixed via mirrors 3 and 4, and beat light having a difference between these frequencies is generated. The beat light is converted into an electric signal by the detector 5, and the difference between the frequencies of the two laser lights is counted by the counter 6.

Controllers 7 and 8 are connected to the reference lasers 1 and 2, respectively. The input and output terminals of the reference clock signal 9 and the synchronization signal 10 are connected to the controllers 7 and 8.

FIG. 2 shows the internal structure of the reference laser 1 and the laser 2 to be calibrated.
It comprises an iodine cell 102, mirrors 103 and 105, a piezo 104 for frequency control, and a piezo 106 for modulation. The DC voltage applied to the frequency control piezo 104 is changed to change the oscillation frequency of the laser. The laser is modulated by giving a low-frequency signal to the modulation piezo.

FIG. 3 shows the detailed configuration of the controllers 7 and 8 shown in FIG. The controllers 7 and 8 operate in a master-slave system, and operate the reference laser 1 as a master and the calibration target laser 2 as a slave. That is, the controller 7 is set to the master state and the controller 8 is set to the slave state, and the reference clock signal input / output terminals of the two iodine stabilized He-Ne lasers and the synchronization signal input / output terminals are connected.

In FIG. 3, the reference clock signal input / output terminal 201 and the synchronization signal input / output terminal 210 are provided when the master / slave selector switches 203 and 209 are set to the master side.
A reference clock and a synchronization signal are output from the reference clock input / output terminal 201 and the synchronization signal input / output terminal 210, respectively.

The reference clock input / output terminal 201 has bidirectionality. When the master / slave changeover switch 203 is set to the master side, a clock signal generated by the reference clock (4 MHz) of 202 is output from this terminal to the device on the slave side. On the other hand, when the master / slave switch 203 is set to the slave side, the reference clock is supplied from the master side device to the slave side device.

With respect to the modulation signal, when the master / slave switch 203 is set to the master side, the 4 MHz reference clock 202 is supplied to the modulation signal generator 2.
04. This reference clock is frequency-divided and a 3.472 kHz signal is output as a synchronous output 207.
This synchronization output is sent from the synchronization signal input / output terminal 210 to the slave device via the changeover switch 209.

As a result, a clock signal is sent from the reference clock input / output terminal 201 from the master controller 8.
A synchronization signal synchronized with the clock signal is sent from the synchronization signal input / output terminal 210 to the device on the slave side.

As described above, since the master side reference clock signal and the synchronization signal are supplied to the slave side calibration target laser 2, the frequency modulation is performed under the same conditions as the master side reference laser 1. The variation of the beat, which is an error factor when measuring the frequency difference between the lasers, is eliminated, and highly accurate measurement can be performed.

FIG. 4 shows two iodine-stabilized H of the present invention.
14 shows another embodiment for equalizing the frequency modulation signal of the e-Ne laser. In this embodiment, a modulation signal generator of the PLL system is provided in the controller, the modulation signal of the master is injected into the synchronization input of the modulation signal generator on the slave side, and the modulation signal of the slave is transmitted by the PLL operation to the master. Synchronized with the modulation signal. This is realized by connecting the synchronization signal input / output terminal on the master side and the synchronization signal input / output terminal on the slave side of the controller.

By connecting in this manner, the iodine stabilized He—Ne laser on the slave side does not use the signal of its own reference clock 303, but transmits the modulation signal on the master side via its own synchronization signal input / output terminal 301. Since it is received as a reference signal, the PLL modulation signal generator 307 generates a modulation signal (1f) having the same frequency and the same phase as the master side. In addition, a third harmonic demodulation signal (3f) of the lock modulation signal is similarly generated.

As a result, since the modulation signals on the master side and the slave side become the same, there is no beat variation which is an error factor when measuring the frequency difference between the two lasers.
Highly accurate measurement is possible.

In FIG. 4, reference numeral 301 denotes a synchronization signal input / output terminal. This terminal is a master / slave switch 30
2 are connected.

If this controller is the master side, the switch is connected to "M" and the modulation signal generator 304 outputs the fundamental wave (1f) of the modulation signal to the slave side.

On the other hand, if the controller is on the slave side, the switch is connected to "S", and a modulation signal is applied from the master side to the PLL modulation signal generator 307 via the synchronization signal input / output terminal 301. As a result, on the slave side, the fundamental wave (1f) and the third harmonic (3f) of the modulation signal synchronized with the master side from the PLL modulation signal generator 307.
f) is obtained. These signals 1f and 3f are output from a fundamental wave output terminal (1f) 306 and a third harmonic output terminal (3f) 309 via master / slave changeover switches 305 and 308.

The modulation signal generator 304 receives the reference clock 3
03 is divided to generate a modulation signal (1f) and a third harmonic (3f) of the modulation signal. When the controller is set as a master (set to the “M” side), the master-slave changeover switches 305 and 308 apply the fundamental wave (1f) and the third harmonic (3f) synchronized with its own reference clock 303 to the 1f terminal 306. , 3f terminal 309.

On the other hand, the master / slave changeover switch 30
5 and 308, when the controller is set as a slave (set on the “S” side), the master-side modulation signal connected to the synchronization signal input / output terminal 201 is added to the PLL modulation signal generator 307 as a reference signal, and As a result, a fundamental wave (1f) and a third harmonic (3f) synchronized with the reference clock 303 on the master side are obtained from the 1f terminal 306 and the 3f terminal 309.

The preferred embodiments of the modulation control method and the calibration method of the laser device according to the present invention have been described above. However, this is merely an example, and it is needless to say that various modifications can be made in accordance with a specific application. It is.

[0044]

As described above, according to the modulation control method and the calibration method of the laser device of the present invention, not only the frequency modulation signal of the laser device is synchronized but the frequency and the phase of the frequency modulation signal are made equal. In addition, high-precision measurement and calibration of a frequency difference between lasers can be performed in frequency calibration of a laser device or the like. That is, in the present invention, the modulation signal of the laser oscillation frequency is synchronized with the external reference signal. Specifically, synchronization is achieved by a master-slave method in which a reference laser is a master and a calibration target laser is a slave.

In the first embodiment, the slave laser does not use its own clock signal, but generates the same frequency modulation signal as the master using the master clock signal and the synchronization signal.

As a second embodiment, a PLL type modulation signal generator is provided inside a controller, and a modulation signal of a reference laser (master) is supplied to a modulation signal of a laser to be calibrated (slave) to provide two devices. Are made to have the same frequency and phase.

Thus, when measuring the difference between the oscillation frequencies of the lasers, there is an advantage that the beat due to the difference in the frequency modulation signal of each laser is eliminated, and the difference between the oscillation frequencies of the modulated lasers can be measured accurately. is there.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram for explaining a modulation control method and a calibration method of a laser device according to the present invention.

FIG. 2 is a diagram showing an internal structure of an iodine stabilized He—Ne laser.

FIG. 3 is a configuration block diagram of a controller shown in FIG. 1;

FIG. 4 is a block diagram showing a configuration employing a PLL method as the controller shown in FIG. 1;

[Explanation of symbols]

1 Reference laser 2 Laser to be calibrated 3, 4, 103, 105 Mirror 5 Detector 6 Counter 7, 8 Controller 101 Laser tube 102 Iodine cell 104 Piezo for frequency control 106 Piezo for modulation 202 Reference clock 203, 209, 302, 305, 308 Master / slave selector switch 204, 304 Modulation signal generator

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshiaki Tohsaka 6-3-20 Tsunashima Higashi, Kohoku-ku, Yokohama Inside NF Circuit Design Block (72) Inventor Hiroaki Iwao 6-3-20, Tsunashima Higashi, Kohoku-ku, Yokohama F term in NF circuit design block (reference) 5F072 AA01 JJ05 JJ20 KK06 MM06 QQ02 YY20

Claims (8)

[Claims] A plurality of laser devices for generating a modulated laser beam by modulating a laser oscillation frequency with a modulation signal;
A modulation control method for a laser device, comprising: supplying a reference clock signal and a synchronization signal generated by a first laser device as a modulation operation reference signal of at least one other second laser device. 2. A laser device comprising: two laser devices for generating a modulated laser beam by modulating a laser oscillation frequency with a modulation signal, wherein a reference clock signal and a synchronization signal generated by a first laser device are transmitted to a second laser device. A modulation control method for a laser device, wherein the modulation control signal is supplied as a modulation operation reference signal. 3. Two laser devices for generating a modulated laser beam by modulating a laser oscillation frequency with a modulation signal, wherein each of the two laser devices has an internal reference clock source and an internal reference clock. A modulation signal generator that outputs a synchronization signal based on an internal clock from a source,
A modulation control method for a laser device, comprising: transmitting a reference clock and a synchronization signal generated by a first laser device as a modulation operation reference signal of a second laser device. 4. A laser apparatus comprising: two laser devices for generating a modulated laser beam by modulating a laser oscillation frequency with a modulation signal; and a second laser device comprising a first laser device generated by the first laser device.
A modulation signal having the same frequency and the same phase as the first modulation signal is generated by a PLL operation based on the input first modulation signal. Method. 5. The first laser device is set as a master side, and the second laser device is set as a slave side. The modulation signal of the slave side laser device has the same frequency as that of the master side modulation signal. 5. The modulation control method for a laser device according to claim 1, wherein the modulation signals have the same phase. 6. The modulation control method for a laser device according to claim 1, wherein said first laser device and said second laser device are iodine-stabilized laser devices. 7. The laser device according to claim 1, wherein the first laser device is set as a master device, the second laser device is set as a slave device, and the slave device is set as a slave device. A calibration signal of the slave device as a modulation signal having the same frequency and the same phase as the modulation signal of the master device. 8. The method according to claim 7, wherein the first laser device and the second laser device are iodine-stabilized laser devices.