JP2876498B2 - High-precision near-infrared reference light frequency generation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-precision near-infrared reference optical frequency generation method for use in a technical field using a high-precision optical frequency as a reference, such as optical communication and optical applied measurement. .

[0002]

2. Description of the Related Art Hitherto, as a standard of an optical frequency in a near infrared region, which is in high demand in optical communication and the like, absorption spectra of molecules and atoms have been used. That is, semiconductor laser light oscillating in the near-infrared region is put into an absorption cell (in some cases, discharged inside) containing a specific molecule or atom, and the laser light after passing through the cell is monitored. By controlling the semiconductor laser so that the intensity becomes minimum or maximum, a reference optical frequency is obtained.

However, the stability of the reference light frequency when this method is applied to a semiconductor laser is about 10 ^-9 . Further, the frequency value of the semiconductor laser light stabilized by this method needs to be measured separately. Furthermore, this method assumes that an absorption spectrum exists.

[0004]

The technical problem of the invention It is an object of the present invention, without using an absorption spectrum of atoms and molecules, by utilizing a high precision stabilized laser extant, higher frequency stability than the conventional (10 ^{- A} reference light frequency having a frequency of ¹² or more) whose frequency value can be accurately determined is to be generated in the near-infrared region, and is to be generated at intervals of about 30 THz.

[0005]

Means for Solving the Problems, action] precision near infrared reference light frequency onset Namaho of the present invention for solving the above problems,
The methane stabilized laser output light as a reference laser
The output light of the carbon dioxide laser is phase-synchronized ,
First and second in the near infrared region by the output light of the laser
The rewritable phase control difference frequency of the semiconductor laser beam,
The frequency of the output light of the reference laser is multiplied, and the output light of the first semiconductor laser in the near-infrared region is phase-controlled by the multiplied light, so that the first semiconductor laser can be controlled .
It is characterized in that the shifted reference light frequency Frequency of carbon dioxide laser beam was set to make the oscillation in the second semiconductor laser and.

In the method for generating a high-precision near-infrared reference light frequency according to the present invention, a third semiconductor laser in the near-infrared region is provided.
And generating light having a difference frequency between the output light of the second semiconductor laser and the output light of the third semiconductor laser, and locating the light having the difference frequency by the output light of the carbon dioxide gas laser. By controlling the phase, the output light of the second semiconductor laser is controlled.
The output light of the third semiconductor laser is
It can be generated at intervals shifted by the frequency of the laser output light.

More specifically, referring to FIG.
In the method of the present invention, a methane-stabilized He-Ne 3.39 μm laser device having a frequency stability of 10 ⁻¹² or more and an absolute frequency value of which is known is preferably used as the reference laser device 10.

[0008] The CO ₂ laser device 20 is installed as having a frequency of about 1/3 of the reference laser.
The output of the CO ₂ laser device 20 is phase-synchronized with the reference laser device 10 by the phase comparison device 50. This allows
The CO ₂ laser device 20 is an optical frequency source whose output CO ₂ laser line has the same frequency stability as the reference laser and whose frequency value is known (about 30 THz).

[0009] Therefore, taking into nonlinear crystal 60 the output from the two semiconductor laser devices 30, 40 which oscillates in the near-infrared region at the same time, to generate light of their difference frequency, at the same CO ₂ in the phase comparator 51 The phase of the laser is compared with that of the laser, and one of the semiconductor laser devices 4
0 is phase-controlled. In the other semiconductor laser device 30, a frequency approximately twice as high as that of the methane-stabilized He-Ne 3.39 μm laser line is generated by the nonlinear crystal 70, and the phase is compared with the phase by the phase comparison device 52.

[0010] As a result, the semiconductor laser device 30, the laser device 10 and the frequency stability is comparable, exactly double that frequency, also the semiconductor laser device 40 is accurately CO ₂ to the semiconductor laser device 30 It will oscillate at a frequency shifted by the laser line frequency (about 30 THz). As the semiconductor laser device 30, a nonlinear crystal 70
May be used directly.

In a similar manner, the difference frequency between the semiconductor laser device 40 and the semiconductor laser device 50 is determined, and the phase of the semiconductor laser device 50 is controlled to a CO ₂ laser beam. It is possible to oscillate a frequency that is further deviated from 40 by the frequency of the CO ₂ laser line. Hereinafter, by repeating the same method, it is possible to obtain a frequency source by a semiconductor laser device separated by about 30 THz.

[0012]

FIG. 2 shows a specific configuration of an apparatus for carrying out the method of the present invention. Reference laser device 10 shown in the figure is a methane-stabilized He-Ne3.39μm laser device to stabilize the frequency by using the saturated absorption of methane, a laser beam oscillated by this, 10 ^-12 or more frequency Stability and frequency value fCH ₄ = 88,376,181.608kHz
Have.

[0013] Laser beam having the frequency, the laser beam from a CO ₂ laser device 20 (oscillation line R (32) or R
(30)) and the frequency f55G from the microwave generator 50
Is irradiated on the MIM point contact diode 71 together with the frequency-stabilized microwave (55 GHz) which has been measured in advance.
From the point contact diode 71, a beat frequency between those three frequencies is obtained. This is referred to as the phase comparison device 72.
, The phase is compared with the reference frequency from the reference frequency generator 80, and the CO ₂ laser device 20 is controlled by the phase control device 91 based on the output of the phase comparison device 72.

Thus, the frequency fCO of the CO ₂ laser line
_2, a constant relationship between methane stabilized He-Ne3.39μm Laser line: with _{(fCO 2 = fCH 4/3} ± f55G. Sign ± is previously known) with, frequency stability methane stabilized H
It is about the same as e-Ne 3.39 μm laser line.

As the semiconductor laser devices 30 and 40, those which oscillate around 1.7 μm, which is just half the wavelength (double frequency) of the He-Ne 3.39 μm laser line, and around 1.5 μm are used. The semiconductor laser device 30 having a wavelength of 1.7 μm controls the phase of the second harmonic of the 3.39 μm laser line generated by the nonlinear crystal 60 using the PIN photodiode 73. If a semiconductor laser device that oscillates around 1.7 μm cannot be obtained, the second harmonic of a 3.39 μm laser line generated by the nonlinear crystal 60 can be used directly.

In order to generate a difference frequency between the semiconductor laser devices 30 and 40, a nonlinear crystal 61 transparent to these wavelengths and a difference between the wavelengths (about 10 μm) is used. ₂ or the like can be used. This crystal can be used as a nonlinear crystal 62 for generating frequencies of 1.5 μm and 1.3 μm, which will be described later, and a nonlinear crystal 60 for generating a second harmonic of a 3.39 μm laser line. Since the output of the CO ₂ laser device is sufficient, the output from one CO ₂ laser device can be divided and used by a translucent mirror.

The phase comparison device 74 compares the difference frequency between the semiconductor laser devices 30 and 40 and the phase of the CO ₂ laser device 20, and outputs the output from the phase comparison device 74 to the phase control device 92. The semiconductor laser 40 is controlled by the output.

A similar method is applied to the phase difference between the CO ₂ laser device 20 and the difference frequency between the semiconductor laser device 40 and the semiconductor laser device 50 (oscillation at a wavelength of 1.3 μm). The semiconductor laser device 50 is controlled by the phase control device 93 based on the output.
An HgCdTe detector can be used for the phase comparison devices 74 and 75. As a result, in the semiconductor laser device 50,
An output of a reference frequency further 30 THz away from the output of the semiconductor laser device 40 can be generated.

[0019]

According to the method of the present invention described in detail above,
When generating the reference light frequency in the near-infrared region, the existing high-precision stabilized laser can be used to provide higher frequency stability (10 ^-12 or more) than in the past. Since the absorption spectrum of atoms / molecules is not used unlike the method described above, the frequency stability of the oscillation line can be improved without being affected by the pressure change of the absorption cell or the intensity of the laser input to the cell.

In order to construct a highly reliable system in optical communication or the like, it is essential to know the absolute value of the optical frequency of the light source. However, according to the method of the present invention, the absolute value of the oscillating semiconductor laser is required. Because you can know the frequency accurately, it can be used as a high-precision measurement standard,
That is, the frequency can be measured with an accuracy of 10 ⁻¹² . This is equivalent to controlling the oscillation frequency with this accuracy. As a result, the available frequency band can be finely divided, and the amount of information that can be transmitted can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus for implementing the present invention.

FIG. 2 is a block diagram showing a specific configuration example of an apparatus for implementing the present invention.

[Explanation of symbols]

10 Reference laser device, 20 CO ₂ laser device, 30, 40, 50 Semiconductor laser device, 5
0, 51, 52 phase comparison device,

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Ohnae 1-4-1 Umezono, Tsukuba-shi, Ibaraki Prefectural Institute of Metrology (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/35 J01S 3/18

Claims (2)

(57) [Claims] An output light of a carbon dioxide gas laser is phase-synchronized with an output light of a methane stabilized laser as a reference laser, and the first and second semiconductor laser lights in the near infrared region are output by the output light of the carbon dioxide gas laser. And the phase of the output light of the first semiconductor laser in the near-infrared region is controlled by multiplying the frequency of the output light of the reference laser by the multiplied light. A high-precision near-infrared reference light frequency generation method, wherein a second semiconductor laser oscillates a reference light frequency shifted from the laser by the frequency of the carbon dioxide laser light. 2. The high-precision near-infrared reference light frequency generation method according to claim 1, wherein the third semiconductor laser in the near-infrared region is used.
A light having a difference frequency between the output light of the second semiconductor laser and the output light of the third semiconductor laser, and the light having the difference frequency is output by the output light of the carbon dioxide gas laser. The output of the second semiconductor laser is controlled by controlling the phase.
The output light of the third semiconductor laser with respect to the light
A high-precision near-infrared reference light frequency generation method characterized in that the light is generated at intervals shifted by the frequency of the output light of the laser .