KR102023486B1 - High contrast long-term stabilizing system for optical pulse amplitude modulator and method thereof - Google Patents

Abstract

The present invention relates to a high contrast ratio long term stabilization system and method for an optical pulse amplitude modulator. According to the present invention, there is provided a pulse light source generator for generating a pulse light source of a frequency multiplied n times (n is an integer of 2 or more) than a target output pulse wave, a signal generator for generating a transmission pulse to be transmitted, and the pulse light source. Supplying a DC voltage for zero adjustment to the optical amplitude modulator for outputting the pulse wave by amplitude-modulating the transmission pulse using a power supply, and supplying the DC voltage based on the output value of the pulse wave. A high contrast ratio long term stabilization system for an optical pulse amplitude modulator including a zero error correction controller for controlling a level to correct a zero error caused by a phase drift.
According to the present invention, the phase variation of the optical amplitude modulator is corrected in real time to stabilize the contrast ratio of the seed laser for a long time, and the output power of the seed laser output from the optical amplitude modulator can be increased by using a pulsed light source with low heat generation as a source. have.

Description

High contrast long-term stabilizing system for optical pulse amplitude modulator and method

The present invention relates to a high contrast ratio long-term stabilization system and method for an optical pulse amplitude modulator. More particularly, the present invention relates to a high-contrast stabilization system for optical pulse amplitude modulator. The present invention relates to a long term stabilization system and a method thereof.

With the development of the electronics industry, high specifications of lasers are required. In particular, when amplifying the seed laser (Seed Laser) can be used to implement a high power laser system.

1 is a view for explaining the concept of a general laser amplification system. As shown in FIG. 1, when a seed laser is input to a pumped gain medium Amp, a high power laser may be output.

The seed laser generated by the oscillator is output at higher power through several stages of amplification medium. In this case, when the temporal shape (Temporal Shape) of the low power seed laser is generally controlled, a high power laser output may be obtained, and a high laser power may be obtained even when the power of the seed laser and the pumping source is increased.

Here, the oscillator is a means for generating a seed laser, and may be implemented in various known manners. As an example, the laser light source may include a laser light source unit for providing a laser light source, and an optical modulator for modulating and outputting a pulse wave using the laser light source. The output signal of the light modulator means a seed laser.

The laser light source unit may be implemented as a CW laser source continuously outputting a beam of a predetermined size. However, since the continuous wave laser continuously outputs a beam over time, the calorific value is very high and thus cannot be applied at high power to the optical modulator. As a result, it is difficult to obtain a high power seed laser from the optical modulator.

In addition, the optical modulator has a phase drift caused by temperature change, device deterioration (aging), etc. during a long time operation. The phase drift of the optical modulator deteriorates the signal-to-noise contrast ratio of the seed laser. It must be compensated in real time.

The background technology of the present invention is disclosed in Korea Patent Registration No. 10-1176447 (2012.08.30 announcement).

It is an object of the present invention to provide a high contrast ratio long-term stabilization system and method for an optical pulse amplitude modulator capable of stabilizing the contrast of the seed laser for a long time by correcting the phase variation of the optical amplitude modulator in real time.

The present invention provides a pulse light source generator for generating a pulse light source of a frequency multiplied n times (n is an integer of 2 or more) than a target output pulse wave, a signal generator for generating a transmission pulse to be transmitted, and the pulse light source. Supplying a DC voltage for zero adjustment to the optical amplitude modulator for outputting the pulse wave by amplitude modulating the transmission pulse using the optical pulse modulator, and supplying the DC voltage based on the output value of the pulse wave. It provides a high-contrast ratio long-term stabilization system for an optical pulse amplitude modulator including a zero error correction controller for controlling the zero error due to phase drift by controlling the control.

The zero error correction controller may be configured to supply the DC voltage using an optical sensor measuring the output pulse wave and a phase shift value calculated based on an output power of the pulse wave measured by the optical sensor. It may include a power supply to determine the level.

The zero error correction controller may calculate a phase shift value based on the currently measured output power of the pulse wave, and then determine the supply level of the DC voltage using the phase shift value.

In addition, the phase shift value Δθ may be calculated by the following equation.

Here, I _in is the input power of the pulsed light source input to the optical amplitude modulator, I _out is the output power of the pulse wave output from the optical amplitude modulator, T _mod represents the optical transmittance of the optical amplitude modulator.

In addition, the supply level New V _DC of the DC voltage may be determined by the following equation.

Here, V _{DC, 0} is the initial setting value of the DC voltage corresponding to the zero error state, Δθ is the phase shift value, V _π is the half-wave voltage (voltage required to change the phase by π) of the optical amplitude modulator Indicates.

The zero error correction controller may calculate the phase shift value from the output power of n-1 extra pulse components except for the seed pulse component for the modulation among the n pulse components of the pulse wave. Whenever one of the redundant pulse components is detected, the phase shift value can be calculated in real time from the detected output power.

In the high contrast ratio long term stabilization method using a high contrast ratio long term stabilization system for an optical pulse amplitude modulator, the present invention generates a pulsed light source having a frequency multiplied n times (n is an integer of 2 or more) than a target output pulse wave. Generating a transmit pulse to be transmitted, and amplitude modulating the transmit pulse using the pulse light source in an optical amplitude modulator in a state where a DB voltage for zero adjustment is supplied, and outputting the pulse wave; and A high contrast ratio long-term stabilization method for an optical pulse amplitude modulator is provided by controlling a supply level of the DC voltage based on an output value of the pulse wave to correct a zero error caused by a phase drift.

According to the present invention, the phase variation of the optical amplitude modulator is corrected in real time to stabilize the contrast ratio of the seed laser for a long time, and the output power of the seed laser output from the optical amplitude modulator can be increased by using a pulsed light source with low heat generation as a source. have.

In particular, the present invention is able to meet the high contrast ratio of the seed laser by real-time correction of the zero point error of the modulator by adjusting the DC offset during the output of the pulse wave from the optical amplitude modulator, effectively for optical systems that require long-term continuous operation Can be applied.

1 is a view for explaining the concept of a general laser amplification system.
2 is a view showing the configuration of a high contrast ratio long-term stabilization system for an optical pulse amplitude modulator according to an embodiment of the present invention.
3 is a diagram illustrating extinction ratio characteristics of an optical amplitude modulator.
4 is a detailed diagram corresponding to FIG. 2.
FIG. 5 is a diagram illustrating an output waveform for each component of FIG. 4.
6 is a view for explaining a method for real-time correction of the zero error of the optical amplitude modulator in the embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

2 is a view showing the configuration of a high contrast ratio long-term stabilization system for an optical pulse amplitude modulator according to an embodiment of the present invention.

As shown in FIG. 2, the high contrast ratio long-term stabilization system 100 for an optical pulse amplitude modulator according to an embodiment of the present invention includes a pulsed light source generator 110, a signal generator 120, an optical amplitude modulator 130, and a zero error. Correction controller 140.

The pulsed light source generator 110 generates a pulsed light source of a frequency multiplied by n times (n is an integer of 2 or more) than the target output pulse wave. Here, the pulsed light source means a pulsed laser source.

The pulsed laser emits a laser beam at regular intervals with a short pulse width, and has a very low heat generation rate than a CW laser continuously emitting a laser beam. Thus, a pulsed laser can be applied at a higher power for the same modulator than a continuous wave laser, resulting in a higher power seed laser from the modulator.

The signal generator 120 generates a transmission pulse to be transmitted. The signal generator 120 may be implemented as an Arbitrary Waveform Generator (AWG).

The optical amplitude modulator 130 receives a pulse light source and a transmission pulse, respectively, and receives a DC voltage for zero adjustment. The optical amplitude modulator 130 amplitude modulates a transmission pulse by using an input pulse light source and finally outputs a pulse wave. The output pulse wave corresponds to a seed laser.

The optical amplitude modulator 130 may include two signal input ports to which a pulse light source and a transmission signal are respectively input, a voltage application port to which a zero DC voltage is applied, and an output signal port to which a modulated final signal is output. .

The zero error correction controller 140 supplies the DC voltage for zero adjustment to the optical amplitude modulator 130 and supplies the DC voltage based on the result of monitoring the output value of the pulse wave output from the optical amplitude modulator 130. By controlling the level in real time, the zero error of the modulator 130 due to phase drift is corrected in real time.

The zero error correction controller 140 includes an optical sensor 141 and a power supply 142. The optical sensor 141 senses and measures a pulse wave emitted from an output port of the optical amplitude modulator 130 and may be implemented through a light sensing means, for example, a photo-detector.

The power supply 142 supplies a zeroing DC voltage to the optical amplitude modulator 130 based on the value measured by the optical sensor 141. In detail, the power supply 142 calculates a phase shift value based on the measured output power of the pulsed wave and determines a supply level of the DC voltage using the phase shift value.

Prior to the description of the specific principle, the reason for correcting the zero error of the optical amplitude modulator in real time will be described in detail.

3 is a diagram illustrating extinction ratio characteristics of an optical amplitude modulator.

3 shows the characteristics of an arbitrary optical amplitude modulator for convenience of description, and the present invention is not necessarily limited thereto.

3 is the DC voltage applied to the modulator, and the vertical axis represents the extinction ratio of the modulator. As shown in Figure 3, the optical amplitude modulator can be seen that the extinction ratio characteristics change significantly according to the magnitude of the applied DC voltage, the higher the negative value indicates that the extinction ratio is higher.

For the best modulation performance, it is desirable to use a DC voltage value corresponding to the point with the highest extinction ratio. In the case of Figure 3 corresponds to a DC voltage value (ex, -4V, 7.5V) corresponding to -30dB, it can be used as a voltage for zero adjustment of the modulator. That is, zero adjustment of the modulator is performed by applying a DC voltage having the best extinction ratio characteristic to the optical amplitude modulator.

However, the optical amplitude modulator may cause phase drift due to the effects of temperature change, temperature heterogeneity, internal degradation (aging), and electrostatic effects during long time operation, which causes extinction ratio and signal-to-noise contrast ratio. Causes performance degradation.

If the phase change of the modulator occurs, the graph characteristic of FIG. This means that the DC voltage (zero adjustment voltage) corresponding to the minimum point also fluctuates from side to side. In other words, when the DC voltage applied initially is fixed as it is for a long time, a zero error occurs due to phase variation, and the zero error should be corrected in real time.

In the exemplary embodiment of the present invention, by correcting the zero error caused by the phase variation of the optical amplitude modulator 130 in real time, the contrast ratio of the seed laser finally output from the modulator may be stabilized for a long time.

FIG. 4 is a detailed diagram corresponding to FIG. 2, and FIG. 5 is a diagram illustrating output waveforms for each component of FIG. 4.

First, as shown in FIG. 4, the system 100 of the present invention corresponds to the oscillator portion of FIG. 1, which generates a seed laser from a pulsed light source and provides it as an amplification medium.

In FIG. 4, the master clock source 10 sets and transmits clock frequency information on a signal to be generated by each of the pulsed light source generator 110 and the signal generator 120. Each generator 110, 120 then generates a pulsed light source and a transmit pulse, respectively, based on the received condition.

Here, f _source is a clock frequency of the pulse light _source , and f _seed is a clock frequency (seed clock frequency) of the transmission pulse. In an embodiment of the present invention, f _source is an integer multiple (n times; n is an integer of 2 or more) of f _seed , and can be expressed by Equation 1 below.

5 illustrates a case where the frequency of the pulsed light source is 5 times higher than the frequency of the transmission pulse, that is, n = 5. For example, if the clock frequency of the transmission pulse is 20 Hz, the frequency of the pulsed light source is set to 100 Hz. The modulated pulse wave also has the same frequency as the transmit pulse.

The optical amplitude modulator 130 receives the pulsed light source and the transmit pulse and loads the transmit pulse on the pulsed light source to output amplitude. In Fig. 4, I _in on the input side of the modulator represents the input power of the pulsed light source and I _out on the output side represents the output power of the pulse wave.

The zero error correction controller 140 calculates a DC voltage value for zero adjustment in real time based on a result of real-time measurement of the pulse wave output from the optical amplitude modulator 130. Through this, the zero error of the modulator can be compensated in real time.

Referring to the output pulse wave of FIG. 5, in the case of the pulse wave without zero adjustment, the magnitudes of n-1 pulse components (hereinafter, redundant pulse components) other than the seed pulse component are changed over time. It can be seen that the increase gradually. This can be seen as the accumulation of zero error over time.

However, when the zeroing is performed in real time, the output pulse wave shows that only the seed pulse component to be originally transmitted is output and the remaining extra pulse components are hardly detected.

Here, the embodiment of the present invention corrects the zero error in real time by calculating a new DC voltage based on the magnitude of the redundant pulse component.

 To this end, the zero error correction controller 140 calculates the phase shift value based on the output power of the pulse wave currently measured, and then determines the supply level of the DC voltage using the phase shift value. Here, the output power of the pulse wave currently measured represents the output power of the remaining n-1 extra pulse components except the seed pulse component for the actual seed radar modulation among the n pulse components of the pulse wave.

The extra pulse component is detected with a smaller size than the seed pulse component, but as the zero error accumulates with time, the magnitude gradually increases and causes a decrease in the signal-noise contrast ratio and needs to be suppressed.

At this time, the zero error correction controller 140 calculates a phase shift value from the detected output power in real time whenever one of the redundant pulse components is detected in the output pulse wave, and calculates a DC voltage based on the calculated phase shift value. Adjust in real time. The specific embodiment is as follows.

6 is a view for explaining a method for real-time correction of the zero error of the optical amplitude modulator in the embodiment of the present invention.

In FIG. 6, I _in is the power of the pulse light source input to the modulator 130, I _out is the output power of the pulse wave output from the modulator 130, θ is the phase of the modulator 130, and V _DC is the modulator 130. ) Shows the DC voltage applied.

First, referring to the left figure of FIG. 6, the zero error correction controller 140 waits for detection of a pulse wave or waits for detection of a next pulse (S610). Then, the power of the pulse wave is measured using the optical sensor (S620).

Here, it is checked whether the currently detected pulse component is a seed pulse (S630). If it is a seed pulse, it repeats step S610 again, and if it is an extra pulse component other than a seed pulse, it moves to the next step S640. Whether or not it is a seed pulse may be determined by comparing the power of the currently detected pulse with a threshold value or may be determined using the current time and clock information.

If the currently detected output wave is identified as the extra pulse component, the phase shift value (theta change amount Δθ) is calculated from the power of the detected extra pulse (S640). Then, a new V _DC value is calculated from the calculated phase shift value and supplied to the optical amplitude modulator 130 (S660). If there was little phase variation, the newly calculated V _DC value would also be close to the initial V _DC value.

Thereafter, the above-described process is repeated for the next pulse. If the above process is for the first extra pulse detected in time among the four extra pulses, the next pulse means the next second extra pulse. Of course, when n = 2, since the seed pulse and the extra pulse alternately occur, the next pulse becomes a seed pulse again.

Further, after computing the New V _DC value by the power of the first redundant pulse and one it is applied without the additional phase variation when the second extra pulse, because you do not detected, maintaining in this case as the old New V _DC value is applied to the do.

6 shows an example in which the first extra pulse is hardly detected among the four extra pulses, and the DC voltage is adjusted after the second extra pulse is detected.

In addition, the output pulse wave when the zero adjustment is not performed is detected as the magnitude of the redundant pulse component gradually increases with time. However, it is understood that the extra pulse component is hardly detected when the zero adjustment is performed. This is V _DC from the magnitude of the previous redundant pulse component. This is because the new value is calculated and applied and it is repeated in the next pulse.

The following describes how to obtain the phase shift value and DC voltage supply level during zero error correction. First, the phase shift value Δθ may be calculated through Equation 2 below.

Here, I _in represents the input power of the pulsed light source input to the optical amplitude modulator 130, and I _out represents the output power of the pulse wave output from the optical amplitude modulator 130. T _mod is the optical transmittance of the optical amplitude modulator 130, which corresponds to the equipment characteristic value of the modulator.

The supply level New V _DC of the DC voltage may be determined by Equation 3 below.

Here, V _{DC, 0} is a DC voltage value corresponding to a state in which there is no zero error, that is, an initial setting value of DC voltage, Δθ is a phase shift value, and V _π is a half wave voltage of the optical amplitude modulator 130 (phase is π). Voltage required to change by That is, the new V _DC value can be obtained by summing the voltage change amount ΔV _DC to the initial DC voltage value V _{DC, 0} .

The derivation principle of Equations 2 and 3 is as follows.

First, Equation 4 shows a transfer function (AM transfer function) of general optical amplitude modulation.

이며, V_RF는 도 4와 같이 신호 생성기(120)가 보낸 신호 전압을 나타낸다.here,

V _RF indicates a signal voltage sent by the signal generator 120 as shown in FIG. 4.

The factors included in Equation 4 are the same as described above. However, T _temp , ∇T _temp , D _aging , and C _es represent the effects of temperature, temperature heterogeneity, deterioration with time, and static electricity, respectively.

The θ (phase) property of Equation 4 may vary due to the influence of the above-described components. In particular, since the fluctuation of θ cannot be neglected during the long time operation of the modulator, the zero error caused by the fluctuation of θ should be compensated in real time by adjusting V _DC .

Assuming there is no signal input from the signal generator 120 (V _RF = 0), the AM transfer function general formula shown in equation (4) is changed to equation (5).

Here, V _{DC, 0} is an initial DC voltage value without a zero error, and θ ₀ is an initial phase value with no error. Using the condition on the right, Equation 5 is rearranged into Equation 6.

가 된다. 이를 수학식 6에 적용하여 수식을 재배치하면 수학식 7이 유도된다.Here, assuming that the offset was completely compensated in the situation before the drift occurred,

Becomes When the equation is rearranged by applying it to Equation 6, Equation 7 is derived.

When Equation 7 is arranged based on Δθ, Equation 2 is obtained. Since I _in and T _{mod in} Equation 2 are known values, it is easy to calculate the phase shift value Δθ by applying the current measured I _out .

And, New V _DC of Equation 3 is derived through the following process.

First, when the DC voltage and offset substitution into the phase term of the cosine function described in Equation 5 should be 0, which is summarized as in Equation 8 below.

에

,

를 각각 대입하여 얻어진다. 수학식 8을 재정렬하면 수학식 9와 같이 된다.This is a phase term

on

,

It is obtained by substituting for each. Rearranging Equation (8) results in Equation (9).

이므로, 이를 수학식 9에 대입하면 수학식 3 하단에 기재된 ΔV_DC 식(전압 변화량)이 얻어지며, 이로부터 New V_DC 값을 쉽게 계산할 수 있다.By the way,

Therefore, by substituting this in Equation 9, the ΔV _DC equation (voltage change amount) described in Equation 3 below is obtained, and the New V _DC value can be easily calculated from this.

According to the present invention as described above, the seed laser output from the optical amplitude modulator is used to correct the phase variation of the optical amplitude modulator in real time to stabilize the contrast ratio of the seed laser for a long time, and also use a pulsed light source having a lower heat generation than the continuous wave laser as a source. It can increase the output power of.

In particular, the present invention is able to meet the high contrast ratio of the seed laser by real-time correction of the zero point error of the modulator by adjusting the DC offset during the output of the pulse wave from the optical amplitude modulator, effectively for optical systems that require long-term continuous operation Can be applied.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

100: high contrast long-term stabilization system 110: pulse light source generator
120: signal generator 130: optical amplitude modulator
140: zero error correction controller 141: light sensor
142: power supply

Claims (12)

A pulsed light source generator for generating a pulsed light source of a frequency multiplied by n times (n is an integer of 2 or more) than the target output pulse wave;
A signal generator for generating a transmission pulse to be transmitted;
An optical amplitude modulator for amplitude modulating the transmission pulse using the pulse light source to output the pulse wave; And
A zero error correction controller which supplies a DC voltage for zero adjustment to the optical amplitude modulator, and controls a supply level of the DC voltage based on an output value of the pulse wave to correct zero error due to a phase drift. Including;
The zero error correction controller,
Calculating a phase shift value based on the currently measured output power of the pulse wave, and then determining a supply level of the DC voltage using the phase shift value,
Computing the phase shift value from the output power for the remaining n-1 extra pulse components except for the seed pulse component for modulation among the n pulse components of the pulse wave, one of the extra pulse components is detected A high contrast ratio long term stabilization system for an optical pulse amplitude modulator that calculates, in real time, the phase shift value from the detected output power. The method according to claim 1,
The zero error correction controller,
An optical sensor for measuring the output pulse wave; And
And a power supply for determining a supply level of the DC voltage using a phase shift value calculated based on the output power of the pulse wave measured by the optical sensor. delete The method according to claim 1,
The phase shift value Δθ is a high contrast ratio long-term stabilization system for an optical pulse amplitude modulator calculated by the following equation:

Here, I _in is the input power of the pulsed light source input to the optical amplitude modulator, I _out is the output power of the pulse wave output from the optical amplitude modulator, T _mod represents the optical transmittance of the optical amplitude modulator. The method according to claim 1,
The high contrast ratio long term stabilization system for an optical pulse amplitude modulator, wherein the supply level of the DC voltage (New V _DC ) is determined by the following equation:

Here, V _{DC, 0} is the initial setting value of the DC voltage corresponding to the zero error state, Δθ is the phase shift value, V _π is the half-wave voltage (voltage required to change the phase by π) of the optical amplitude modulator Indicates. delete A high contrast ratio long term stabilization method using a high contrast ratio long term stabilization system for an optical pulse amplitude modulator,
Generating a pulse light source of a frequency multiplied by n times (n is an integer of 2 or more) than a target output pulse wave, and generating a transmission pulse to be transmitted;
Outputting the pulse wave by amplitude modulating the transmission pulse using the pulse light source in an optical amplitude modulator in the state where a DC voltage for zero adjustment is supplied; And
Controlling a supply level of the DC voltage based on an output value of the pulse wave to correct a zero error due to a phase drift,
Correcting the zero error,
Calculating a phase shift value based on the currently measured output power of the pulse wave, and then determining a supply level of the DC voltage using the phase shift value,
Computing the phase shift value from the output power for the remaining n-1 extra pulse components except for the seed pulse component for modulation among the n pulse components of the pulse wave, one of the extra pulse components is detected And a high contrast ratio long term stabilization method for an optical pulse amplitude modulator that calculates in real time a phase change value from a detected output power. The method according to claim 7,
Correcting the zero error,
A high contrast ratio long-term stabilization method for an optical pulse amplitude modulator for determining a supply level of the DC voltage using a phase shift value calculated based on an output power of the pulse wave measured by an optical sensor. delete The method according to claim 7,
The phase shift value Δθ is a high contrast ratio long-term stabilization method for an optical pulse amplitude modulator calculated by the following equation:

Here, I _in is the input power of the pulsed light source input to the optical amplitude modulator, I _out is the output power of the pulse wave output from the optical amplitude modulator, T _mod represents the optical transmittance of the optical amplitude modulator. The method according to claim 7,
A high contrast ratio long term stabilization method for an optical pulse amplitude modulator, wherein the supply level (New V _DC ) of the DC voltage is determined by the following equation:

Here, V _{DC, 0} is the initial setting value of the DC voltage corresponding to the zero error state, Δθ is the phase shift value, V _π is the half-wave voltage (voltage required to change the phase by π) of the optical amplitude modulator Indicates. delete

Images