JP6232334B2 - Laser phase noise reduction device - Google Patents

Description

  The present invention relates to a laser phase noise reduction apparatus used for reducing phase noise of laser light.

  Generally, laser light used for optical communication, measurement, and the like includes phase noise, and various techniques have been proposed to reduce this phase noise. For example, Non-Patent Document 1 describes an apparatus that uses an optical modulator, a frequency discriminator, and a voltage controlled oscillator, and uses a Mach-Zehnder interferometer and a photodetector as the frequency discriminator.

  In the apparatus described in Non-Patent Document 1, a beam emitted from a laser light source is bifurcated, and one is incident on an optical modulator and the other is incident on a frequency discriminator. The frequency discriminator is composed of a Mach-Zehnder interferometer and a photodetector, and measures the amount of change in phase noise of the laser beam. Then, by driving the voltage controlled oscillator with the measured phase noise variation, a modulation signal including the phase noise of the laser beam is generated, and the laser beam input to the optical modulator is fed forward by the modulation signal. By controlling, light with reduced phase noise is obtained.

F. Aflatouni and H. Hashemi, "Wideband tunable laser phase noise reduction using single side-band modulation in an electro-optical feed-forward scheme," Optics Letters, vol. 37, no. 2, 2012.

  However, in the technique described in Non-Patent Document 1, in order to accurately measure the change amount of the phase noise of the laser, the delay provided in one arm of the Mach-Zehnder interference system is smaller than the coherence time of the laser beam. And ντ = n + 1/4 (ν: frequency of laser, τ: delay provided on one arm of Mach-Zehnder interferometer, n: integer) must be satisfied. However, in order to satisfy this condition, for example, in the case of a laser beam having a frequency of 200 THz, it is necessary to adjust the delay τ with accuracy of fs order, which is not easy. In the technique described in Non-Patent Document 1, the above condition is satisfied by feedback controlling the delay τ. However, another problem arises in that the bandwidth of the laser light phase noise reduction device is limited by the bandwidth of the feedback control.

  The present invention has been made paying attention to the above circumstances, and the object of the present invention is to accurately measure the amount of change in the phase noise of the laser light without satisfying the delay condition set in the Mach-Zehnder interferometer. Thus, an object of the present invention is to provide a laser phase noise reduction device capable of reducing the phase noise of laser light without being band-limited.

To achieve the above object, according to a first aspect of the present invention, there is provided an optical branching device for bifurcating a laser beam outputted from a laser light source into a first laser beam and a second laser beam; Measuring a change in phase noise of the laser beam 2 using a Mach-Zehnder interferometer and a photodetector and outputting an electric signal thereof, and based on the electric signal output from the measuring instrument, A control signal generation circuit that generates a feedforward control signal in which the change is converted into a voltage change, and is driven by the feedforward control signal generated by the control signal generation circuit, and corresponds to a change in the voltage value of the feedforward control signal A modulation signal generation circuit that generates a modulation signal having a frequency and a modulation signal generated by the modulation signal generation circuit change the branched first laser beam. Comprising an optical modulator. The control signal generation circuit includes an in-phase component and a quadrature component time average calculation unit for calculating a time average for each of the in-phase component and the quadrature component of the electrical signal output from the measuring device , and the quadrature component Sign inversion means for inverting the time average value of the quadrature component calculated by the time average calculation means, quadrature component of the electrical signal output from the measuring device , and time average calculation means for the in-phase component. A first multiplying unit that multiplies the time-average value of the in-phase component, a multi-phase component of the electrical signal output from the measuring device, and a time-average value of the quadrature component whose sign is inverted. and second multiplying means, adding hand the mutually adding the respective multiplied values obtained by the first and second multiplication means, and outputs the signal after the addition as the feedforward control signal It is those with a door.

The first aspect of the present invention is characterized by comprising the following several aspects.
In the first aspect, a modulation signal generated by a feedforward control system composed of the measuring device, a control signal generation circuit, and a modulation signal generation circuit based on the second laser beam branched by the optical branching unit is Timing for adjusting the timing to be input to the optical modulator and the timing at which the first laser beam branched simultaneously with the second laser beam by the optical splitter is incident on the optical modulator. Adjustment means is further provided.

  In the second aspect, a −1st-order sideband modulator is used as the optical modulator, and the −1st-order sideband light of the first laser light is modulated by a modulation signal generated by the modulation signal generation circuit. It is.

  In the third aspect, the optical modulator is driven by a modulation signal generated by the modulation signal generation circuit, and modulates the first laser light by intensity modulation or phase modulation, and is modulated by the modulator. And an optical filter that extracts and outputs the −1st-order sideband light from the first laser light.

  In a fourth aspect, as the modulation signal generation circuit, an integrator that integrates a voltage value of a feedforward control signal generated by the control signal generation circuit and outputs an electric signal representing the phase noise, and the integration The first laser beam by the sign-inverted electrical signal output from the sign inverter as the optical modulator. Is provided with a phase modulator for phase-modulating the signal.

  According to the first aspect of the present invention, it is possible to reduce the phase noise included in the laser light only by the feedforward control system without using the feedback control system. For this reason, it is possible to relax the condition for delay set in the Mach-Zehnder interferometer, further reduce the influence of the band limitation of the feedback control, and obtain a high phase noise reduction effect.

  According to the first aspect, by providing the timing adjustment means, the timing at which the modulation signal generated by the feedforward control system is input to the optical modulator and the timing at which the laser light enters the optical modulator are as follows. Can be adjusted to match. For this reason, even when the processing delay in the feedforward control system is large, it is possible to match the input timing of the laser light and the modulation signal to the optical modulator, thereby realizing highly accurate phase noise reduction processing. it can.

  According to the second aspect, the phase noise component of the laser beam can be obtained by using the −1st-order sideband modulator as the optical modulator and supplying the modulation signal generated by the feedforward control system to the optical modulator as it is. Can be reduced.

  According to the third aspect, as the optical modulator, comparison is made by using a modulator that modulates the intensity or phase of the laser light and an optical filter that extracts the −1st-order sideband light from the modulated laser light. The present invention can be implemented with inexpensive optical components.

  According to the fourth aspect, as the modulation signal generation circuit, an integrator that integrates the voltage value of the feedforward control signal and outputs an electrical signal representing phase noise, and an electrical circuit that represents the phase noise output from the integrator. By using a sign inverter that reverses the sign of the signal, it can be realized without using a voltage controlled oscillator.

  That is, according to each aspect of the present invention, it is possible to accurately measure the amount of change in phase noise of a laser beam without satisfying the delay condition provided in one arm of the Mach-Zehnder interference system, thereby limiting the bandwidth. It is possible to provide a laser phase noise reduction device capable of reducing the phase noise of the laser light without receiving it.

1 is a block diagram showing a configuration of a laser phase noise reduction device according to a first embodiment of the present invention. The figure which shows the constellation map used for operation | movement description of the apparatus shown in FIG. The block diagram which shows the structure of the laser phase noise reduction apparatus which concerns on 2nd Embodiment of this invention. The block diagram which shows the structure of the laser phase noise reduction apparatus which concerns on 3rd Embodiment of this invention.

Several embodiments according to the present invention will be described below with reference to the drawings.
[First Embodiment]
(Constitution)
FIG. 1 is a block diagram showing a configuration of a laser phase noise reduction apparatus according to a first embodiment of the present invention. 1 is a laser light source that generates laser light, and 100A is a laser phase noise reduction apparatus. .

  The laser phase noise reduction apparatus 100A includes optical branching devices 2-1, 2-2, a delay applying unit 3, an optical 90-degree hybrid unit 4, and balanced light receivers 5-1, 5- as optical circuit devices. 2, an optical path length adjustment unit 11, and a minus first-order sideband modulation unit 13. Of these, the delay applying unit 3 and the 90-degree optical hybrid unit 4 constitute a Mach-Zehnder interferometer.

  The laser phase noise reduction apparatus 100A includes electrical signal branching units 6-1 and 6-2, time average calculation units 7-1 and 7-2, a sign inversion unit 8, and a multiplier 9 as electrical circuit devices. -1, 9-2, an adder 10, and a voltage controlled oscillator 12. These circuits constitute a feedforward control circuit.

  The optical branching device 2-1 bifurcates the laser light emitted from the laser light source 1, and passes one of the first laser light to the optical path length adjusting unit 11 and the other second laser light to the optical branching device 2. -2 respectively. The optical splitter 2-2 further splits the second laser beam into two, and outputs one of them to the delay applying unit 3 and the other to the optical 90-degree hybrid unit 4.

  The delay applying unit 3 of the Mach-Zehnder interferometer gives a delay amount τ to the input laser beam. The light 90-degree hybrid unit 4 generates interference between the laser beam given the delay amount τ by the delay applying unit 3 and the laser beam not given the delay amount τ, and outputs the interference wave. The balanced light receivers 5-1 and 5-2 receive the interference wave output from the optical 90-degree hybrid unit 4 and output the quadrature component Q (t) and the in-phase component I (t) of the received light signal. .

  The electric signal branching units 6-1 and 6-2 bifurcate the quadrature component Q (t) and the in-phase component I (t) of the received light signals output from the balanced light receivers 5-1 and 5-2, respectively. . The time average calculation units 7-1 and 7-2 calculate time average values for a predetermined period for the quadrature component Q (t) and the in-phase component I (t) of the bifurcated received light signal. The sign inversion unit 8 inverts the sign of the time average value of the orthogonal component Q (t) calculated by the time average calculation unit 7-1.

  The multiplier 9-1 includes the quadrature component Q (t) of the received light signal bifurcated by the electric signal branching unit 6-1 and the in-phase component I (t) calculated by the time average calculating unit 7-2. Multiply by time average. The multiplier 9-2 takes the time of the in-phase component I (t) of the received light signal bifurcated by the electric signal branching unit 6-2 and the quadrature component Q (t) whose sign is inverted by the sign inverting unit 8. Multiply by the average value. The adder 10 adds the multiplication values output from the multipliers 9-1 and 9-2 to each other, and supplies the added signal to the voltage controlled oscillator 12 as a feedforward control signal.

  The voltage controlled oscillator 12 oscillates a signal including a frequency corresponding to the voltage value of the feedforward control signal supplied from the adder 10, that is, a frequency corresponding to the frequency fluctuation included in the laser beam. Then, this oscillated signal is supplied to the −1st-order sideband modulator 13 as a modulation signal.

  The −1st-order sideband modulator 13 optically modulates the first laser light emitted from the optical splitter 2-1 with the modulation signal supplied from the voltage-controlled oscillator 12, and the modulated −1st-order sideband Outputs band light.

  The optical path length adjusting unit 11 includes the timing at which the first laser beam emitted from the optical branching unit 2-1 enters the negative primary sideband modulating unit 13, and the optical branching unit 2-1 to the first So that the modulation signal generated by the feedforward control circuit based on the second laser beam emitted simultaneously with the laser beam coincides with the timing at which the −1st-order sideband modulation unit 13 is input. The optical path length of the first laser light is adjusted.

ここで、Ａはレーザ光源１から出射されるレーザ光の振幅、νはレーザ光源１から出射されるレーザ光の周波数、θ(t) はレーザ光源１から出射される光の位相雑音を表す。 (Operation)
Next, the operation of the laser phase noise reduction apparatus configured as described above will be described using mathematical expressions.
The complex electric field amplitude E (t) of the light emitted from the laser light source 1 is expressed by the following equation.

Here, A represents the amplitude of the laser light emitted from the laser light source 1, ν represents the frequency of the laser light emitted from the laser light source 1, and θ (t) represents the phase noise of the light emitted from the laser light source 1.

  The laser beam represented by the expression (1) is bifurcated by the optical branching element 2-1, and one is input to the −1st-order sideband modulator 13. The other is input to the Mach-Zehnder interferometer via the optical splitter 2-2. In the Mach-Zehnder interferometer, the light incident on the 90-degree hybrid unit 4 through the delay applying unit 3 and the light directly incident on the 90-degree hybrid unit 4 without passing through the delay applying unit 3 Interference occurs in part 4.

のように表される。ここで、Δθ(t) は遅延量τに対する位相雑音の変化量を示す。 At this time, if the delay amount given by the delay applying unit 3 is τ, the interference S (t) is

It is expressed as Here, Δθ (t) represents a change amount of the phase noise with respect to the delay amount τ.

のように表される。Δθ(t) は遅延量τに依存する量であり、遅延量τをレーザ光源１のコヒーレンス時間よりも短く調整することで、

を満たす。 The amount of change Δθ (t) of the phase noise with respect to the delay amount τ is

It is expressed as Δθ (t) is an amount that depends on the delay amount τ, and by adjusting the delay amount τ to be shorter than the coherence time of the laser light source 1,

Meet.

のように表される。 The in-phase component and the quadrature component of the interference expressed by the equation (2) are detected and output by the balanced light receivers 5-1 and 5-2. Assuming that the in-phase component of the output signal is I (t) and the quadrature component is Q (t), these can be calculated using the above equation (2).

It is expressed as

のように表せる。 Equations (5) and (6) above use a matrix

It can be expressed as

が得られる。 From the equation (7), the in-phase component I (t) and the quadrature component Q (t) rotate (cosΔθ (t), sinΔθ (t)) by an angle 2πντ in the constellation map, for example, as shown in FIG. It can be seen that the rotation matrix is multiplied.
(7) Multiplying both sides of Eq.

Is obtained.

のように表される。 Then, from equation (4), if sinΔθ (t) ≈ Δθ (t) is approximated, sinΔθ (t) in equation (8) is calculated using I (t) and Q (t)

It is expressed as

ここで、Δθ(t)はランダムな波形であり、かつ(4) 式を満たす。
このため、

なる近似式が成り立つ。 Next, the time average of equation (5) is obtained as follows.

Here, Δθ (t) is a random waveform and satisfies the equation (4).
For this reason,

The following approximate expression holds.

なる近似が成り立つ。 And from equations (10)-(12)

The following approximation holds.

そして、(11) 、(12) 、(14) 式より、

なる近似式が成り立つ。 Similarly, the time average of equation (6) is obtained as follows.

And from the equations (11), (12), (14),

The following approximate expression holds.

のように表される。 From the equations (9), (13), and (15), Δθ (t) is calculated using I (t) and Q (t).

It is expressed as

  The electric signal represented by the equation (16) is used as a feedforward control signal, and includes electric signal branching units 6-1 and 6-2, time average calculating units 7-1 and 7-2, and a sign inverting unit 8. , Multipliers 9-1 and 9-2, and an adder 10.

ここで、ｖ_mは電圧制御発振器１２の発振周波数を表す。 Next, the voltage controlled oscillator 12 is driven by the feedforward control signal expressed by the equation (16). As a result, a signal having an instantaneous frequency v _osc (t) expressed by the following equation is output from the voltage controlled oscillator 12.

Here, v _m represents the oscillation frequency of the voltage controlled oscillator 12.

ここで、θ_mod(t) は、電圧制御発振器１２によって得られたレーザ光の位相雑音成分を表す。 Further, the time waveform φ _m (t) of the signal having the instantaneous frequency of the equation (17) is expressed by the following equation.

Here, θ _mod (t) represents the phase noise component of the laser beam obtained by the voltage controlled oscillator 12.

のように表される。 The modulation signal represented by the equation (18) is input to the modulation signal input terminal of the −1st-order sideband modulation unit 13. As a result, the laser beam subjected to feedforward control is output from the −1st-order sideband modulation unit 13. That is, laser light with reduced phase noise can be obtained. The complex electric field amplitude E _red (t) of the laser light is

It is expressed as

  In order to reduce the phase noise of the laser beam by the feedforward control described above, the timing at which the first laser beam emitted from the optical splitter 2-1 enters the −1st-order sideband modulation unit 13; The modulation signal generated by the feedforward control circuit based on the second laser beam emitted from the optical splitter 2-1 at the same time as the first laser beam is input to the −1st-order sideband modulation unit 13. It is necessary to match the timing to be performed. Therefore, the optical path length of the first laser beam is adjusted by the optical path length adjusting unit 11. This optical path length adjustment operation is performed manually by maintenance personnel.

(effect)
As described above in detail, in the first embodiment, the laser light emitted from the laser light source 1 is incident on the Mach-Zehnder interferometer and the delay applying unit 3 gives a delay τ to generate interference. The amount of change in the phase noise with respect to the delay τ included in is detected by the balanced light receivers 5-1 and 5-2. Then, a feedforward control signal obtained by converting the detected change amount of the phase noise into a change amount of the voltage value is generated, and the feedforward control signal is input to the voltage controlled oscillator 12 and the frequency corresponding to the change of the phase noise is generated. Is generated, and this signal is given as a modulation signal to the −1st-order sideband modulator 13 to modulate the −1st-order sideband of the laser light, thereby outputting the laser light with the phase noise cancelled. I am doing so.

  Therefore, the phase noise included in the laser light can be reduced only by the feedforward control system without using the feedback control system. Therefore, it is not necessary to perform feedback control on the delay τ set in the Mach-Zehnder interferometer, the condition for the delay τ can be relaxed, and the band of the phase noise reduction device 100A is limited to the band of the feedback control. Thus, the phase noise contained in the laser light can be effectively reduced.

  Furthermore, by providing the optical path length adjustment unit 11, the timing at which the laser light enters the −1st-order sideband modulation unit 13 is adjusted, and the modulation signal generated by the feedforward control system is −1. The timing can be matched with the timing input to the next sideband modulator 13. For this reason, even when the processing delay in the feedforward control system becomes large, it becomes possible to match the input timing of the laser light and the modulation signal to the −1st-order sideband modulation unit 13. Phase noise reduction processing can be realized.

[Second Embodiment]
In the second embodiment of the present invention, a modulator that performs intensity modulation or phase modulation and an optical filter are used in place of the −1st-order sideband modulator 13 used in the first embodiment. is there.

  FIG. 3 is a block diagram showing a configuration of a laser phase noise reduction apparatus according to the second embodiment of the present invention. In the figure, the same parts as those in FIG.

  The laser phase noise reduction apparatus 100B according to the second embodiment includes an optical length adjustment unit 11, an intensity modulation or phase modulation unit 14 and an optical path on the optical path of the first laser beam branched by the optical branching unit 2-1. A filter 15 is arranged. The intensity modulation or phase modulation unit 14 modulates the intensity or phase of the laser beam incident through the optical path length adjustment unit 11 by the modulation signal generated from the voltage controlled oscillator 12. The optical filter 15 extracts and outputs only the −1st-order sideband light from the laser light whose intensity or phase is modulated by the intensity modulation or phase modulation unit 14.

  Because of such a configuration, the modulation signal represented by the equation (18) generated by the voltage controlled oscillator 12 is supplied to the intensity modulation or phase modulation unit 14, whereby the intensity modulation or phase modulation unit 14 Feed forward control is performed and an optical frequency comb is generated. Then, by passing this optical frequency comb through the optical filter 15, −1st-order sideband light shown in the equation (19) is extracted from the optical frequency comb and output.

  Therefore, also in the second embodiment, the phase noise included in the laser beam can be reduced only by the feedforward control system without using the feedback control system, as in the first embodiment described above. It becomes. For this reason, the condition for the delay τ set in the Mach-Zehnder interferometer can be relaxed, and the band of the phase noise reduction device 100B is not limited to the band of the feedback control, thereby the phase included in the laser light Noise can be effectively reduced.

  In the second embodiment, the intensity modulation or phase modulation unit 14 and the optical filter 15 are used as the light modulation unit. For this reason, compared with the case where the −1st-order sideband modulation unit 13 is used, a general-purpose optical component can be used, and thus the apparatus can be provided at low cost.

  Furthermore, also in the second embodiment, the optical path length adjustment unit 11 adjusts the timing at which the laser light enters the −1st-order sideband modulation unit 13, and the incident timing is generated by the feedforward control system. It is possible to match the timing when the modulation signal is input to the −1st-order sideband modulator 13. For this reason, even when the processing delay in the feedforward control system becomes large, it becomes possible to match the input timing of the laser light and the modulation signal to the −1st-order sideband modulation unit 13. Phase noise reduction processing can be realized.

[Third Embodiment]
In the third embodiment of the present invention, an integrator and a sign inverting unit are used instead of the voltage controlled oscillator, and a signal obtained by the integrator and the sign inverting unit is applied as a modulation signal to the phase modulating unit, and laser light is supplied. A laser beam whose phase noise is reduced by phase modulation is outputted.

  FIG. 4 is a block diagram showing a configuration of a laser phase noise reduction apparatus according to the third embodiment of the present invention. In the figure, the same parts as those in FIG.

  The laser phase noise reduction device 100 </ b> C according to the third embodiment inputs the feedforward control signal output from the adder 10 to the integrator 16. The integrator 16 integrates the feedforward control signal and inputs the integrated output signal to the sign inverting unit 17. The sign inverting unit 17 inverts the sign of the input integral output signal and provides the integrated output signal after the sign inversion to the phase modulation unit 18 as a modulation signal. The phase modulation unit 18 modulates the phase of the laser beam with the modulation signal, and outputs the phase-modulated laser beam as a laser beam with reduced phase noise.

  The operation of the apparatus configured as described above will be described using mathematical expressions. Note that, in the Mach-Zehnder interferometer and the feedforward control circuit, the processing shown in equations (1) to (16) is performed to generate a feedback control signal, which is the same as in the first embodiment.

のように表される。 When the electric signal represented by the equation (16) is integrated by the integrator 16, a signal representing the phase noise of the laser light source 1 is obtained. This signal is

It is expressed as

のように表される。なお、θ_mod(t) は、積分器１６から出力される、レーザ光の位相雑音成分を表す。 Next, when the signal obtained by the integrator 16 is input to the sign inverting unit 17 to invert the sign, and the sign-inverted signal is given to the phase modulating unit 18 as a modulation signal, the phase modulating unit 18 performs laser processing. The light is feedforward controlled, whereby laser light with reduced phase noise is output. The complex electric field amplitude E _red (t) of this laser beam is

It is expressed as Θ _mod (t) represents the phase noise component of the laser beam output from the integrator 16.

  Therefore, also in the third embodiment, similarly to the first embodiment, the phase noise included in the laser light can be reduced only by the feedforward control system without using the feedback control system. Therefore, the condition for the delay τ set in the Mach-Zehnder interferometer can be relaxed, and the band of the laser phase noise reduction device 100C is not limited to the band of the feedback control, and is thereby included in the laser light. Phase noise can be effectively reduced.

  In addition, since the modulation signal is generated using the integrator 16 and the sign inverting unit 17, the circuit configuration of the feedforward control system can be realized easily and inexpensively as compared with the case where the voltage controlled oscillator 12 is used.

  Furthermore, also in the third embodiment, the optical path length adjustment unit 11 adjusts the timing at which the first laser beam enters the −1st-order sideband modulation unit 13, and the incident timing is determined by the feedforward control system. The generated modulation signal can be made to coincide with the timing at which the −1st-order sideband modulation unit 13 is input. For this reason, even when the processing delay in the feedforward control system becomes large, it becomes possible to match the input timing of the laser light and the modulation signal to the −1st-order sideband modulation unit 13. Phase noise reduction processing can be realized.

[Other Embodiments]
In each of the embodiments described above, the optical path adjustment unit 11 is disposed in the optical path of the first laser light, and the timing at which the laser light enters the light modulation unit is adjusted. However, the present invention is not limited to this, and a delay unit that gives a predetermined fixed delay amount to the first laser beam is arranged in the optical path of the first laser beam, and in the electric circuit of the feedforward control system. A variable delay device for adjusting the output timing of the feedforward control signal is provided. Then, by variably controlling the delay amount of the variable delay device, the timing at which the first laser light enters the −1st-order sideband modulation unit 13 and the modulation signal generated by the feedforward control system are −1st The timing input to the sideband modulator 13 may be matched. If comprised in this way, it will become possible to perform timing adjustment more simply and correctly.

  In addition, the circuit configuration of the feedforward control system, the configuration of the circuit that generates the modulation signal, the type of the optical modulation unit, and the like can be variously modified and implemented without departing from the gist of the present invention.

  In short, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2-1, 2-2 ... Optical splitter, 3 ... Delay imparting part, 4 ... Light 90 degree hybrid part, 5-1, 5-2 ... Balance type light receiver, 6-1, 6 DESCRIPTION OF SYMBOLS 2 ... Electric signal branching device, 7-1, 7-2 ... Time average calculation part, 8 ... Sign inversion part, 9-1, 9-2 ... Multiplier, 10 ... Adder, 11 ... Optical path length adjustment part, 12 DESCRIPTION OF SYMBOLS ... Voltage controlled oscillator, 13 ... Negative sideband modulation part, 14 ... Intensity modulation or phase modulation part, 15 ... Optical filter, 16 ... Integrator, 17 ... Sign inversion part, 18 ... Phase modulation part.

Claims (5)

An optical branching device for bifurcating a laser beam output from a laser light source into a first laser beam and a second laser beam;
A measuring device that measures a change in phase noise of the branched second laser light using a Mach-Zehnder interferometer and a photodetector and outputs an electrical signal thereof;
A control signal generation circuit that generates a feedforward control signal obtained by converting the change in the phase noise into a voltage change based on the electrical signal output from the measuring instrument;
A modulation signal generation circuit that is driven by a feedforward control signal generated by the control signal generation circuit and generates a modulation signal having a frequency corresponding to a change in the voltage value of the feedforward control signal;
An optical modulator that modulates the branched first laser beam with a modulation signal generated by the modulation signal generation circuit;
The control signal generation circuit includes:
Time average calculating means for in-phase component and quadrature component for calculating time average for each of the in-phase component and the quadrature component of the electrical signal output from the measuring device ;
Sign inverting means for inverting the time average value of the orthogonal component calculated by the time average calculating means for the orthogonal component;
First multiplication means for multiplying the quadrature component of the electrical signal output from the measuring instrument by the time average value of the in-phase component calculated by the time average calculation means for the in-phase component;
Second multiplication means for multiplying the in-phase component of the electrical signal output from the measuring instrument by the time average value of the quadrature component with the sign inverted;
Laser phase noise reduction comprising: addition means for adding each multiplication value obtained by the first and second multiplication means to each other and outputting the signal after the addition as the feedforward control signal apparatus. Based on the second laser beam branched by the optical splitter, a modulation signal generated by a feedforward control system including the measuring device, a control signal generation circuit, and a modulation signal generation circuit is input to the optical modulator. And a timing adjusting unit that adjusts the timing so that the timing at which the first laser beam branched simultaneously with the second laser beam by the optical splitter matches the timing at which the first laser beam enters the optical modulator is further provided. lasers position phase noise reduction apparatus according to claim 1, wherein a.   The said optical modulator is comprised by the -1st order sideband modulator which modulates the -1st order sideband light of the said 1st laser beam with the modulation signal generated by the said modulation signal generation circuit. 3. The laser phase noise reduction device according to 1 or 2. The light modulator is
A modulator that is driven by the modulation signal generated by the modulation signal generation circuit and modulates the intensity or phase of the first laser beam;
The laser phase noise reduction device according to claim 1, further comprising: an optical filter that extracts −1st-order sideband light from the first laser light modulated by the modulator. The modulation signal generation circuit includes:
An integrator that integrates the voltage value of the feedforward control signal generated by the control signal generation circuit and outputs an electrical signal representing the phase noise;
A sign inverter that reverses the sign of the electrical signal representing the phase noise output from the integrator, and
3. The laser phase according to claim 1, wherein the optical modulator includes a phase modulator that phase-modulates the first laser light by an electric signal after code inversion output from the code inverter. Noise reduction device.

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