JP3350607B2 - Laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation frequency stabilizing device for stabilizing an oscillation frequency of a laser light source and a laser device.

[0002]

2. Description of the Related Art Conventionally, for example, a document "Nakagawa, Op.
Vol. 10, 1990 ", a Pound-Drever method is shown as a laser frequency stabilization technique.

FIG. 20 is a diagram showing a basic configuration of the pound-driver method. Referring to FIG. 20, laser light emitted from a single longitudinal mode oscillation laser light source 101 is transmitted through an optical isolator 102 to an electro-optic modulator 1.
03 and is frequency-modulated by the electro-optic modulator 103. This frequency modulation is performed by applying a modulation signal from the modulation signal generator 110 to the electro-optic modulator 103. The laser light frequency-modulated in this manner is supplied to the polarization beam splitter 104 and the λ / 4 plate 1.
The light enters a frequency discriminating device 106 such as a Fabry-Perot resonator through the line 05. At this time, the frequency discriminating device 106 discriminates the frequency of the laser light by resonating the laser light at the resonance frequency of the frequency discriminating device, and generates frequency noise such as phase fluctuation due to spontaneous emission of the laser light and frequency fluctuation due to disturbance. Can be removed.

On the other hand, the oscillation frequency of the laser light source 101 may fluctuate due to the influence of temperature or the like. In order to suppress such fluctuation of the oscillation frequency of the laser light source 101, the oscillation frequency of the frequency discriminator 106 is set as a reference frequency. Negative feedback control is performed on the laser light source 101. That is, a part of the light reflected by the frequency discriminator 106 is made incident on the light receiving element 107 by the polarization beam splitter 104, and the signal from the light receiving element 107 is amplified by the preamplifier 108 and given to the double balanced mixer (DBM) 109. . In the double balanced mixer 109, the signal from the preamplifier 108 is demodulated with the modulation signal (modulation frequency) from the modulation signal generator 110, and the oscillation frequency of the laser light source 101 and the resonance frequency of the frequency discriminator 106, that is, the reference frequency And an error signal is given to the servo circuit 112.
Thus, the oscillation frequency of the laser light source 101 can be feedback controlled.

In this way, the oscillation frequency of the laser light source 101 of single longitudinal mode oscillation can be locked to the resonance frequency (reference frequency) of the frequency discriminator 106, and the oscillation frequency of the laser light source can be stabilized.

[0006]

However, the above-mentioned conventional frequency stabilization technique can only stabilize the frequency of a single longitudinal mode laser light source, and can reduce the oscillation frequency of a longitudinal multimode oscillation laser light source. There was a problem that stabilization could not be achieved.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an oscillation frequency stabilizing optical device and a laser device capable of stabilizing the oscillation frequency of a longitudinal multimode oscillation laser light source.

[0008]

In order to achieve the above-mentioned object, according to the present invention,
Vertical multimode emitted from a laser light source that oscillates in multiple vertical modes
Modulating means for phase or frequency modulating the laser beam
And the laser light from the modulating means is incident, and the incident light is
Frequency valve that resonates at a predetermined resonance frequency and discriminates the frequency
Receives and receives light from another device and the frequency discriminator
A light receiving means for generating a signal, and a demodulating means for demodulating the received light signal
And an oscillation cycle of the laser light source based on the demodulated signal.
And servo means for feedback controlling the wave number.
The vertical multiplication of the laser light is performed by the demodulation means and the servo means.
Frequency discriminating at least one spectrum of modes
By locking to the resonance frequency of the device,
Stabilize the oscillation frequency of the laser light source that oscillates
In addition, inside the frequency discrimination device
A non-linear optical medium disposed therein, wherein the frequency discriminating apparatus is provided;
Is incident on the frequency discriminator together with the frequency discrimination function
The fundamental light as the fundamental wave, and the fundamental wave through the nonlinear optical medium.
It also has a wavelength conversion function for wavelength conversion. This
Stabilizes the oscillation frequency of the laser light source to achieve high efficiency
Generates a fundamental wave, thus increasing the converted wave (e.g., harmonics).
It can be obtained with efficiency.

[0009]

[0010]

[0011]

[0012]

[0013]

In particular, according to the third aspect of the present invention, since the end face of the nonlinear optical medium functions as a mirror (the function of a Fabry-Perot resonator), the present laser device can be easily assembled. And the size of the device can be reduced.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an oscillation frequency stabilizing device according to the present invention. Referring to FIG. 1, this oscillation frequency stabilizing device includes an optical isolator 2 on which laser light from a laser light source 1 is incident, and an optical phase modulator (for example, an electric phase modulator) for phase-modulating or frequency-modulating the laser light from the optical isolator 2. An optical modulator 3 and a polarizing beam splitter (PB).
S) 4, a λ / 4 plate 5, a frequency discriminator 6, a light receiving element 7, a preamplifier 8, a mixer (for example, a double balanced mixer (DBM)) 9, and a modulation signal generator (for example, a high frequency power supply) 10, phase shifter 11, and filter 12
And a servo circuit 13.

In such a configuration, the laser light emitted from the laser light source 1 enters the optical phase modulator 3 via the optical isolator 2 in the same manner as in the oscillation frequency stabilizing device shown in FIG. Phase modulation or frequency modulation is performed by the optical phase modulator 3. Note that this frequency modulation is performed by giving a modulation signal from the modulation signal generator 10 to the optical phase modulator 3. The phase-modulated or frequency-modulated laser light is supplied to the polarization beam splitter 4,
The light passes through the λ / 4 plate 5 and enters the frequency discriminator 6. At this time, the frequency discriminating apparatus 6 discriminates the frequency of the laser light by resonating the laser light at the resonance frequency of the frequency discriminating apparatus 6, and generates a frequency fluctuation such as a phase fluctuation due to spontaneous emission of the laser light and a frequency fluctuation due to disturbance. Noise can be removed.

On the other hand, the oscillation frequency of the laser light source 1 may fluctuate due to the influence of temperature or the like. In order to suppress such fluctuation of the oscillation frequency of the laser light source 1, the oscillation frequency of the frequency discriminator 6 is set as a reference frequency. Negative feedback control is performed on the laser light source 1. That is, a part of the light reflected by the frequency discriminator 6 is made incident on the light receiving element 7 by the polarization beam splitter 4 (for example, the light having about half the power of the reflected light from the frequency discriminator 6 is incident on the light receiving element 7). Then, the light receiving signal from the light receiving element 7 is amplified by the preamplifier 8 and supplied to the double balanced mixer (DBM) 9.
In the double balanced mixer 9, the signal from the preamplifier 8 is demodulated (synchronous detection) with the modulation signal (modulation frequency) from the modulation signal generator 10. In the example shown in FIG. 1, the phase of the signal from the modulation signal generator 10 is controlled by the phase shifter 11 and given to the double-balanced mixer 9.

As described above, the signal from the preamplifier 8 is demodulated (synchronous detection) by the double balanced mixer 9,
An error signal between the oscillation frequency of the laser light source 1 and the resonance frequency of the frequency discriminator 6, that is, the reference frequency is obtained by the filter 12 (that is, the filter 12 is a low-pass filter that transmits only a signal having a frequency lower than the modulation frequency). In this case, a signal having a frequency lower than the modulation frequency among the output signals of the double balanced mixer 9 is obtained as an error signal), and this error signal can be given to the servo circuit 13.

In the above-mentioned conventional oscillation frequency stabilizing apparatus, it is assumed that the laser light source is of a single longitudinal mode oscillation. Therefore, in this case, the single oscillation frequency (mode) of the laser light and the frequency An error signal is obtained by a difference from the resonance frequency (reference frequency) of the discriminator, and the single oscillation frequency (single oscillation mode) of the single longitudinal mode oscillation laser light is set to the resonance frequency (reference frequency) of the frequency discriminator. By locking, the single oscillation frequency can be stabilized.

On the other hand, in the present invention, it is assumed that the laser light source 1 is of vertical multi-mode oscillation. In this case, the oscillation frequency (multi-mode oscillation frequency) of the laser light of vertical multi-mode oscillation is assumed. For stabilization, in the present invention, one of the multiple modes is locked to the reference frequency.

More specifically, an error signal can be obtained by the reference frequency and the oscillation mode closest to the reference frequency. In this case, the other oscillation modes are demodulation (synchronous detection)
However, since the error signal level becomes "0", an error signal having the same shape as that of the single mode laser can be obtained. By giving this error signal to the servo circuit 13 and feeding it back to the laser light source 1,
The one oscillation mode among the multiple modes is locked to the reference frequency, whereby the oscillation frequency of this one oscillation mode can be stabilized. Further, by stabilizing the frequency of this one oscillation mode, the frequencies of the remaining oscillation modes of the multi-mode can be simultaneously stabilized.

In the oscillation frequency stabilizing device shown in FIG. 1, the polarizing beam splitter 4 and the λ / 4 plate 5 are used. Instead of these components, as shown in FIG. It can also be used. However, in the case of a configuration using the polarization beam splitter 4 and the λ / 4 plate 5 as shown in FIG. 1, the polarization (for example, linearly polarized light perpendicular to the paper surface) from the polarization beam splitter 4 is circled by the λ / 4 plate 5. The polarized light is made incident on the frequency discriminator 6, and the reflected light from the frequency discriminator 6 is again converted into linearly polarized light parallel to the paper surface by the λ / 4 plate 5, reflected by the polarization beam splitter 4, and incident on the light receiving element 7. Accordingly, the laser light can be used effectively, and a light receiving signal of a sufficient magnitude can be output from the light receiving element 7.

1 and 2, a Fabry-Perot resonator, a sweep-type Fabry-Perot resonator, a Fabry-Perot etalon, an atomic absorption line, and the like can be used as the frequency discriminator 6.

FIG. 3 shows a case where a Fabry-Perot resonator is used for the frequency discriminator 6. The Fabry-Perot resonator is constituted by two mirrors 23 and 24, and the space between the two mirrors 23 and 24 functions as a resonator. That is, the mirrors 23 and 2
Each of the coatings 4 is coated with a high reflection for the resonance spectrum of the resonator. When using a Fabry-Perot resonator frequency discriminator 6, when the multi-longitudinal-mode if 400MH _Z a longitudinal mode spacing of the oscillation of the laser light, Free Spectral Range of the Fabry-Perot resonator (F
If the integer portion of the first longitudinal mode spacing strictly laser light SR) (400MH _Z), thereby coinciding with the resonance mode of the Fabry-Perot resonators all longitudinal modes of the laser beam corresponding to each.

At this time, the modulation frequency (modulation frequency by the optical phase modulator 3) for the laser light from the laser light source 1 is smaller than the free spectrum interval of the Fabry-Perot resonator, and one mode of the laser light Frequency line width
(Half width). For example, one of the longitudinal mode frequency linewidth of the laser beam (half width) is 10 MHz _Z
, And the case free spectral interval of the Fabry-Perot resonator is 100GH _Z, the modulation frequency f by the optical phase modulator 3, it is necessary to set the range of the following equation.

[0026]

## EQU1 ## 10 MH _Z <f <100 GH _Z

FIG. 4 shows a case where a sweep type Fabry-Perot resonator is used for the frequency discriminator 6.
The swept Fabry-Perot resonator has two mirrors 23, 2
4 is a Fabry-Perot resonator which is configured to be movable in the direction of arrow A by a sweeping means (for example, a fine adjustment function element such as a piezoelectric element) 25,
The mirrors 2 and 3 of the Fabry-Perot resonator shown in FIG.
Coatings similar to 3, 24 are applied.

In this sweep type Fabry-Perot resonator, one mirror 24 is swept in the direction of arrow A and the resonator length is changed, so that the resonance frequency of the Fabry-Perot resonator is changed by the laser light of longitudinal multimode oscillation. It is easy to approach the largest oscillation spectrum. That is, in the configuration of the Fabry-Perot resonator shown in FIG. 3, when an error signal is obtained, it is difficult to determine which oscillation spectrum has locked in the resonance mode. On the other hand, in the configuration of the sweep type Fabry-Perot resonator shown in FIG.
While sweeping 4 to change the resonator length (changing the resonance frequency), search for a condition that maximizes the amplitude of the error signal, and stop the sweep when the condition becomes close to that condition. By giving a servo signal from the servo circuit 13 to the laser light source 1 and performing negative feedback control on the oscillation frequency of the laser light source 1, it is possible to lock the largest oscillation mode of the laser light to the reference frequency (resonance mode). Becomes

In the above configuration example, the reflected light from the frequency discriminator 6 is demodulated (synchronous detection). However, the transmitted light from the frequency discriminator 6 may be demodulated (synchronous detection). .

FIG. 5 shows a case where an etalon is used for the frequency discriminator 6. When an etalon is used, the free spectral interval of the resonance mode is changed by adjusting the angle θ of the etalon. be able to.
Thereby, the adjustment mechanism of the device can be simplified. When an etalon is used, light transmitted from the etalon is received by the light receiving element 7 and demodulated.

When the above-described Fabry-Perot resonator, sweep type Fabry-Perot resonator, etalon, or the like is used for the frequency discriminating device 6, the free spectral interval is set to an integral number of the longitudinal mode interval of the laser light as described above. , Which is done in the following manner.

[0032] That is, now, if the free spectral interval of the resonator is not an integral submultiple of the longitudinal mode spacing of the laser beam, i.e., for example, focusing on the longitudinal modes q _m of the laser beam, the resonant near the frequency of the q _m When there is a mode (resonance frequency), as far to the spectrum of the q _m, error signal to the frequency difference between the oscillation frequency and the resonance mode (resonance frequency) is obtained as shown in FIG. 6 (a). In this case, q
_{For the m + 1} mode, the error signal is as shown in FIG. The error signals shown in FIGS. 6A and 6B are signals of a frequency lower than the modulation frequency among the signals output from the mixer 9 at the time of open loop (when negative feedback control is not performed). And FIG. 6 (a), the as can be seen in comparison to (b), when the free spectral interval is not an integer fraction of the longitudinal mode spacing of the laser, the error signal q _m and q _{m + 1} mode was slightly different It will be.

On the other hand, when the free spectrum interval of the resonator is equal to an integer fraction of the longitudinal mode interval, q _m
The error signal for the mode and the error signal for the q _{m + 1} mode are as shown in FIGS. 7A and 7B, respectively. The error signal for the q _m mode and the error signal for the q _{m + 1} mode have the same shape. (If the magnitudes of q _m and q _{m + 1} are the same, the error signal also has the same value).

FIG. 8A shows an example of a longitudinal mode of the laser beam. In the example of FIG. 8A, the laser light source 1
Five longitudinal modes q _{-2 of, q -1, q 0, q} +1, and oscillates at q _+2, also in comparison with the mode q _0, mode q _-1,
The power of the spectrum of q ₊₁ is smaller by 3 dB, and the power of the spectra of modes q _-2 and q ₊₂ is smaller by 6 dB. Each of the mode spacing is 50GH _Z, the spectral line width of each mode has a 50 mH _Z. FIG. 8B shows an example of the free spectrum interval FSR of the resonator. In the example of FIG. 8 (b), the free spectral interval is 9.99GH _Z, also the resonance frequency linewidth has a 50 mH _Z.

When the longitudinal mode interval of the laser beam and the free spectrum interval FSR of the resonator are assumed to be as shown in FIGS. 8A and 8B, an error signal is calculated by numerical calculation. . FIG. 9 shows a calculation result of the error signal for each longitudinal mode. In addition, actually, the filter 1
The error signal output from 2 is processed by overlapping all the longitudinal modes of the laser light in this device.
It is the sum of the error signals for each mode. Therefore, in practice, the signal in FIG. 9 cannot be observed, and the error signal is the sum of the signals in FIG. 9 and is as shown in FIG. From this result, it can be seen that an error signal can be obtained even in the case of a laser that oscillates in longitudinal multimode, as in the case of a longitudinal single mode laser.

When the resonator is a sweep type Fabry-Perot resonator as shown in FIG. 4, for example, the resonance frequency of the resonator is changed while sweeping the mirror 24, and the free spectrum interval FSR is changed. By sweeping the resonator, an error signal as described above is obtained. Further, the oscillation wavelength (frequency) of the laser light is changed by finely adjusting the injection current and the case temperature. As described above, the free spectral interval is changed by sweeping the resonator, and the oscillation wavelength (frequency) of the laser light is further adjusted. When the free spectral interval FSR becomes an integral number of the longitudinal mode interval of the laser light, , The amplitude of the error signal is maximized. When the error signal becomes maximum, the sweep of the resonator and the frequency sweep of the laser beam are stopped, and the error signal at this time is given to the servo circuit 13 and used as a feedback signal.

As described above, since the free spectrum interval of the frequency discriminator can be adjusted so as to match an integer fraction of the longitudinal mode interval of the laser, all oscillation modes are demodulated.
(Synchronous detection) results in an error signal, so that the amplitude of the error signal can be increased, and the oscillation frequency can be more reliably stabilized. That is, all the oscillation frequencies of the longitudinal multi-mode laser light source can be locked at the resonance frequency, and the oscillation frequency of the longitudinal multi-mode laser can be stabilized. The width can be narrowed (each oscillation spectrum can be sharpened).

FIG. 11 is a diagram showing a configuration example of a laser device according to the present invention. In this laser device, in the oscillation frequency stabilizing device of FIG. 1 or FIG.
However, in addition to the frequency discrimination function, it is configured as having a wavelength conversion function. That is, this laser device has a function of stabilizing the oscillation frequency of the laser light source 1 as described above, and converting and outputting the wavelength of the laser light having the stable oscillation frequency emitted from the laser light source 1. I have. Therefore, a wavelength converter 90 is provided in the frequency discriminator 6.

FIG. 12 is a diagram showing a specific example of the laser device of FIG. In this example, the frequency discriminator 6 includes a Fabry-Perot resonator (eg, a swept Fabry-Perot resonator) defined by two mirrors 23 and 24, and a nonlinear optical medium 30 disposed in the Fabry-Perot resonator. And the Fabry-Perot cavity itself defined by the two mirrors 23 and 24 is the laser light source 1.
And a function of stabilizing the oscillation frequency of the laser beam. The laser beam incident on the resonator is used as a fundamental wave, and the spectrum of the fundamental wave is accumulated in the resonator by the resonator. Convert the wavelength of the waves
It also has a wavelength conversion function for emitting (for example, generating a high frequency).

For this reason, the two mirrors 23 and 24 of the Fabry-Perot resonator are coated with a high-reflection coating for the oscillation spectrum serving as the fundamental wave. A coating that makes waves (for example, harmonics) highly transparent is applied.

In the laser device having such a configuration, the laser light emitted from the laser light source 1 is
The light enters a frequency discriminator 6 as a fundamental wave via an optical phase modulator (for example, an electro-optic modulator) 3 and a half mirror 21. When the frequency discriminating apparatus 6 is composed of the Fabry-Perot resonator and the nonlinear optical medium 30 disposed in the Fabry-Perot resonator as in the example of FIG. When incident as a fundamental wave, the spectrum of this fundamental wave is accumulated in the Fabry-Perot resonator (the light intensity of the fundamental wave is increased by resonance and accumulated as a fundamental wave having the resonance frequency (resonance spectrum) of the resonator. ). The fundamental wave accumulated in the Fabry-Perot resonator in this manner is subjected to wavelength conversion by the nonlinear optical medium 30, and, for example, a harmonic is generated from the nonlinear optical medium 30. This harmonic passes through the other mirror 24 of the Fabry-Perot resonator and is emitted.

The fundamental wave (fundamental wave having the resonance frequency of the resonator) stored in the Fabry-Perot resonator
For example, the light slightly leaks from one mirror 23, returns to the half mirror 21 as reflected light, and enters the light receiving element 7 from the half mirror 21. The reflected light of the fundamental wave can be used to stabilize the oscillation frequency of the laser light source 1 in the same manner as in the above-described oscillation frequency stabilization device (the oscillation frequency of the laser light source 1 Can lock to the resonant frequency of the wave). As a result, the fundamental wave can be efficiently incident and accumulated in the Fabry-Perot resonator, and the harmonic can be efficiently generated.
(Can generate high power harmonics).

The laser devices shown in FIGS. 11 and 12 correspond to FIG.
It is compatible with the oscillation frequency stabilization device of
Although the half mirror 21 is used, the half mirror 2
Instead of 1, a polarizing beam splitter 4 and a λ / 4 plate 5 can be used.

FIG. 13 shows the polarization beam splitters 4 and λ / 4.
FIG. 1 is a view showing a specific example of a laser device using a plate 5, and FIG.
Of the oscillation frequency stabilizing device.
In this case, in order to cause the nonlinear optical medium 30 to function as a λ / 2 plate with respect to the fundamental wave (to function as a full-wave plate when the fundamental wave reciprocates in the nonlinear optical medium 30), the laser device of FIG. The temperature of the nonlinear optical medium 30 is controlled by the temperature controller 31. That is, in general, by the nonlinear optical medium 30 birefringent crystal is used, it is impossible to maintain the polarization state of light incident on the nonlinear optical medium 30, the polarization state of light by the nonlinear optical medium 30 It becomes elliptically polarized light. By the way, since the refractive index of a nonlinear optical crystal has temperature dependence,
By setting the nonlinear optical crystal to the optimal temperature,
The crystal can function as a desired wave plate. Therefore, if the temperature of the nonlinear optical crystal is set to a temperature at which the nonlinear optical crystal functions as a full-wave plate when the fundamental wave reciprocates through the nonlinear optical crystal, the polarization state when entering the nonlinear optical crystal is maintained. Thus, the reflected light of the fundamental wave can be returned to the λ / 4 plate 5. As a result, the reflected light of the fundamental wave is converted into a λ / 4 plate 5, a polarization beam splitter 4
When the light enters the light receiving element 7 from above, the light intensity does not decrease so much, so that the oscillation frequency can be stabilized stably using the fundamental wave having a sufficient light intensity. Can efficiently enter the resonator and accumulate, thereby efficiently generating harmonics.

Various modifications can be made to such a laser device. For example, in the device of FIG.
Coating films 35a and 35b having high reflection with respect to the fundamental wave are applied to both end surfaces of the nonlinear optical medium 30, so that the coating films 35a and 35b function as mirrors of the Fabry-Perot resonator. If necessary, both end faces of the nonlinear optical medium 30 can be polished into a curved shape. Further, a temperature adjusting device 31 for adjusting the temperature of the nonlinear optical medium 30 is controlled by a sweeping device 34,
By changing (sweeping) the temperature, the nonlinear optical medium 30 can also function as a swept Fabry-Perot resonator. However, it is not generally possible to use the polarizing beam splitter 4 and the λ / 4 plate 5 in the apparatus shown in FIG.

In each embodiment and configuration example of the oscillation frequency stabilizing device and the laser device described above, the laser light source 1 is
For example, a semiconductor laser (LD) of vertical multimode oscillation can be used. FIG. 15 shows a case where a semiconductor laser of longitudinal multimode oscillation is used as the laser light source 1. In FIG. 15, reference numeral 33 denotes an LD drive circuit. When a semiconductor laser is used for the laser light source 1, the semiconductor laser
It is possible to perform phase modulation (frequency modulation) by modulating the injection current to this. Therefore, in the example of FIG. 15, the injection current to the semiconductor laser 1 is modulated by the modulation signal from the modulation signal generator 10, and the phase modulation or the frequency modulation of the light emitted from the semiconductor laser 1 is performed. 15, the modulation function can be realized by the semiconductor laser 1 itself, and the optical phase modulation (electro-optic modulator) 3 becomes unnecessary. That is, in the example of FIG. 15, the servo signal from the servo circuit 13 is supplied to the LD drive circuit 33, and the DC component of the injection current of the semiconductor laser 1 is subjected to negative feedback control (feedback control) by the servo signal to thereby reduce the oscillation frequency. Stabilization can be achieved.

As described above, a laser light source other than a semiconductor laser can be used if the optical modulator 3 is disposed outside as described above.

Further, in each of the above-described embodiments and configuration examples, the case where a laser light source (for example, a semiconductor laser) that oscillates in vertical multi-mode is used. The present invention can be similarly applied to a case where a single mode oscillation is used, and similarly, a single mode oscillation frequency can be stabilized. However, when a laser light source (for example, a semiconductor laser) having a longitudinal multi-mode oscillation is used as in the above-described embodiments and configuration examples, the power is larger than that of a single longitudinal mode oscillation laser light source, and Since all the oscillation spectra can be locked to the resonance frequency of the corresponding external resonator, when performing wavelength conversion, wavelength conversion can be performed with high efficiency and a high-power converted wave (high frequency) can be obtained. Can be.

Further, in each of the above embodiments and configuration examples, the signal from the light receiving element 7 is amplified by the preamplifier 8, but the preamplifier 8 is not necessarily required, and may be omitted as occasion demands. Can also.

In the oscillation frequency stabilizing devices shown in FIGS. 1 to 5, there are various methods for extracting laser light from the laser light source 1 as output light as follows.

That is, when the laser light source 1 is a semiconductor laser chip, as shown in FIG. 16, the semiconductor laser chip 1 emits laser light from both end surfaces 1a and 1b, so that one of the two The laser light from the end face 1a is used for stabilizing the oscillation frequency, the laser light from the other end face 1b is output as it is, and this can be extracted and used as stabilized laser light.

When the laser light source 1 is a laser other than the semiconductor laser chip, the laser light source 1 has only one emission end face, so that it cannot be extracted as shown in FIG. Therefore, in this case, the laser light from the laser light source 1 is, for example, as shown in FIG.
Half mirror 41 arranged between optical isolator 2 and
For example, as shown in FIG. 18, the half mirror 2 in the configuration example of FIG.
1 and output as it is, which can be used as stabilized laser light.

When a Fabry-Perot etalon as shown in FIG. 5 or a Fabry-Perot resonator as shown in FIG. 3 is used for the frequency discriminator 6, the output light from the frequency discriminator 6 is extracted. It can also be used. That is, for example, the mirror 2 of the Fabry-Perot resonator
In any of the cases 3 and 24, when a coating highly reflecting the laser light is applied, if there is no loss (absorption) of the laser light inside the resonator, inside the mirror or inside the coating, the laser light oscillates. When the frequency coincides with the resonance frequency, the transmittance of the Fabry-Perot resonator becomes a value close to “1”, and the transmitted light (output light) from the Fabry-Perot resonator is stabilized as shown in FIG. It can be used as laser light.

[0054]

As described above, claims 1 to 3 are described.
According to the invention as set forth in claim 3, a laser that oscillates in longitudinal multimode.
Phase modulation of longitudinal multimode laser light emitted from light source
A frequency modulating means, and a signal from the modulating means.
Laser light is incident, and the incident light is resonated at a predetermined resonance frequency.
A frequency discriminating device for discriminating the frequency
Light receiving means for receiving light from the device and generating a light receiving signal
Demodulating means for demodulating the received light signal;
The oscillation frequency of the laser light source is feedback controlled.
Controlling the demodulating means and the servo means.
And at least one of multiple longitudinal modes of the laser light
Of the spectrum to the resonance frequency of the frequency discriminator.
The laser light source that oscillates in multiple longitudinal modes.
It is designed to stabilize the oscillation frequency,
A nonlinear optical medium is disposed inside the frequency discriminator.
The frequency discrimination device has a frequency discrimination function.
The light incident on the frequency discriminator as a fundamental wave,
A wavelength converter that converts the wavelength of a fundamental wave using a nonlinear optical medium
Function to stabilize the oscillation frequency of the laser light source
To generate a fundamental wave with high efficiency, and
(For example, harmonics) can be obtained with high efficiency.

[0055]

[0056]

[0057]

[0058]

[0059]

In particular, according to the third aspect of the present invention, a mirror function (a function of a Fabry-Perot resonator) is provided on the end face of the nonlinear optical medium, so that the laser device can be easily assembled. And the size of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an oscillation frequency stabilizing device according to the present invention.

FIG. 2 is a diagram showing a modification of the oscillation frequency stabilizing device of FIG.

FIG. 3 is a diagram showing an oscillation frequency stabilizing device using a Fabry-Perot resonator as a frequency discriminating device.

FIG. 4 is a diagram showing an oscillation frequency stabilization device using a sweep type Fabry-Perot resonator as a frequency discrimination device.

FIG. 5 is a diagram showing an oscillation frequency stabilizing device using an etalon for a frequency discriminating device.

FIG. 6 is a diagram showing an error signal.

FIG. 7 is a diagram showing an error signal.

FIG. 8 is a diagram showing a longitudinal mode of a laser beam and a free spectrum interval of a resonator.

FIG. 9 is a diagram showing a calculation result of an error signal.

FIG. 10 is a diagram showing a calculation result of an error signal.

FIG. 11 is a diagram showing a configuration example of a laser device according to the present invention.

FIG. 12 is a diagram showing a specific example of the laser device of FIG. 11;

FIG. 13 is a view showing a modification of the laser device of FIGS. 11 and 12;

FIG. 14 is a view showing a modification of the laser device.

FIG. 15 is a diagram illustrating a configuration example when a semiconductor laser is used as a laser light source.

FIG. 16 is a diagram for explaining how to extract laser light from a laser light source as output light.

FIG. 17 is a diagram for explaining how to extract laser light from a laser light source as output light.

FIG. 18 is a diagram for explaining how to extract laser light from a laser light source as output light.

FIG. 19 is a diagram for explaining how to extract laser light from a laser light source as output light.

FIG. 20 is a diagram showing a conventional oscillation frequency stabilizing device.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 optical isolator 3 optical phase modulator 4 polarizing beam splitter 5 λ / 4 plate 6 frequency discriminator 7 light receiving element 8 preamplifier 9 double balanced mixer 10 modulation signal generator 11 phase shifter 12 filter 13 servo circuit 21 half mirror 23, 24 Mirror 25 Sweep means 30 Nonlinear optical medium 33 LD drive circuit 35a, 35b High reflection coating film 90 Wavelength conversion unit

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 G02F 1/37 H01S 3/00-3/30 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A modulating means for phase-modulating or frequency-modulating a longitudinal multi-mode laser light emitted from a laser light source which oscillates in a longitudinal multi-mode. A laser light from the modulating means is incident, and the incident light is subjected to a predetermined resonance. A frequency discriminating device that resonates at a frequency to discriminate the frequency, a light receiving unit that receives light from the frequency discriminating device to generate a light receiving signal, a demodulating unit that demodulates the light receiving signal, and the laser based on the demodulated signal. Servo means for feedback-controlling the oscillation frequency of the light source, and the demodulation means and the servo means lock at least one spectrum of the longitudinal multimode of the laser light to the resonance frequency of the frequency discriminating apparatus, whereby the longitudinal The oscillation frequency of the laser light source that oscillates in multiple modes is stabilized, and furthermore, a non-linear The frequency discriminator has a wavelength discriminating function, in which light incident on the frequency discriminator is used as a fundamental wave and the fundamental wave is wavelength-converted by a non-linear optical medium. A laser device. 2. A laser apparatus according to claim 1 , wherein said frequency discriminator includes a Fabry-Perot resonator constituted by two mirrors, and a nonlinear optical medium is provided between the two mirrors constituting the Fabry-Perot resonator. A laser device characterized by being arranged. 3. A laser apparatus according to claim 1 , wherein said frequency discriminating apparatus has a structure in which a high-reflection coating is applied to both end faces of a nonlinear optical medium with respect to a fundamental wave. Laser device.