WO2014141973A1 - Pulse laser device - Google Patents

Abstract

A pulse laser device comprises: a laser source for outputting a pulse beam; a phase modulator for changing the phase of the pulse beam output from the laser source; a beam detector for detecting a pulse beam output from the laser source and outputting a detection signal that is a time-based waveform of a change in intensity; and a phase modulator driving power source for outputting a drive signal generating a phase change in proportion to the time-based waveform of the change in intensity on the basis of the detection signal output from the beam detector, and driving the phase modulator.

Description

Pulse laser equipment

The present invention relates to a pulse laser apparatus in a usage form in which pulse light output from a laser light source is incident on a transmission optical fiber, an amplification optical fiber, or the like and output.

A laser apparatus having the pulse laser apparatus as described above is preferably used as a light source for an exposure apparatus or inspection apparatus used in a semiconductor or liquid crystal panel manufacturing process, or a light source for an observation apparatus such as a microscope or a telescope (for example, (See Patent Document 1).

In such a pulse laser device, pulsed light emitted from a laser light source is transmitted by a transmission optical fiber, and in some cases, is amplified by an amplification optical fiber of an optical fiber amplifier. Since the core of the amplification optical fiber has a small diameter, self-phase modulation (SPM: Self-Phase Modulation = SPM) is generated by nonlinear optical effect when pulse light with high peak power is transmitted or amplified (see, for example, Patent Document 2) .

Japanese Unexamined Patent Publication No. 2002-50815 Japanese Unexamined Patent Publication No. 2012-2965

In many cases, the self-phase modulation (SPM) acts so as to widen the spectral width of the laser light propagating in the optical fiber, so that the spectral width of the laser light (output light) emitted from the optical fiber is the optical fiber. Spectral broadening that is wider than the spectral width of the laser light (incident light) incident on the light beam occurs. In particular, in a single mode fiber having a small core diameter of several μm to several tens of μm, the power density of the propagating laser beam is extremely high, and therefore the spectrum spread by self-phase modulation becomes large. The wide spectral width is an obstacle when a narrow band light source with high monochromaticity is required.

For example, when transmitting pulsed light having a peak power P of 10 kW into a transmission optical fiber having a mode field diameter of 15 μm and a length L of 1 m, the pulsed light emitted from the optical fiber is φ≈γPL≈ 7 rad self-phase modulation occurs. Here, γ is a quantity representing the nonlinear optical effect, and is obtained by γ = 2πn ₂ / λA _eff . N ₂ is a nonlinear refractive index, n ₂ ≈3 × 10 ⁻²⁰ [m ² / W], and A _eff is an effective cross-sectional area in the waveguide mode of the optical fiber.

Due to the occurrence of self-phase modulation, even if the incident light incident on the optical fiber is a Fourier-limited pulse light and has a narrow-band spectrum, the spectrum of the emitted light expands to about φ times after propagation through the optical fiber. This is a major obstacle in realizing a light source that requires a narrow band.

The present invention has been made in view of such circumstances, and an object thereof is to provide a pulse laser apparatus capable of outputting narrow-band pulse light.

As one means for solving the above problems, the inventors of the present application devised a pulse laser device 9 as shown in FIG. The pulse laser device 9 includes a laser light source 110 that outputs pulsed light and a phase modulator 132 that changes the phase of the pulsed light output from the laser light source 110. The laser light source 110 includes a light source 111 that generates laser light, an intensity modulator 112 that modulates the intensity of the laser light generated by the light source 111 and outputs pulsed light, and a pulse generator 116. And a modulator driving power source 115 for driving the phase modulator 132. FIG. 4 shows a DFB semiconductor laser (DFB-LD: Distributed Laser Diode) as an example of the light source 111, and an intensity modulation type electro-optic modulator (EOM: Electro Optic 、 Modulator, hereinafter referred to as EO intensity modulation) as an example of the intensity modulator 112. As an example of the phase modulator 132, a configuration using a phase modulation type electro-optic modulator (EOM, hereinafter referred to as EO phase modulator) is illustrated.

In this configuration example, the light source 111 emits light by CW (Continuous Wave). The EO intensity modulator 112 is supplied with an intensity modulator driving signal V ₁ (t) having a waveform corresponding to the pulse pattern of the pulsed light to be output from the laser light source from the modulator driving power supply 115, and the laser output from the light source 111. A part of the light is cut out to generate pulsed light. A time axis waveform P (t), which is a temporal intensity change of the pulsed light generated by the EO intensity modulator 112, is expressed by the following equation from the relationship between the transmittance of the EO intensity modulator 112 and the applied voltage. V _π in the equation is a half-wave voltage of the EO intensity modulator 112.

Assuming that an optical fiber that transmits or amplifies the pulsed light output from the pulse laser device 9 has no distortion of the time axis waveform due to dispersion or the like, phase modulation by self-phase modulation (SPM) that occurs in the optical fiber is assumed. φ _SPM (t) is proportional to the time axis waveform P (t) and is expressed by the following equation.

Therefore, with respect to pre-pulsed light by EO phase modulator 132 by the inverse of the phase modulation and phase modulation phi _SPM (t) by SPM that occurs within the optical fiber, phase modulation by SPM that occurs within the optical fiber phi _SPM It is possible to cancel (t) and output narrow-band pulsed light from the optical fiber. Alternatively, an EO phase modulator 132 is provided in the vicinity of the output end of the optical fiber, and phase modulation opposite to the phase modulation φ _SPM (t) due to SPM occurring in the optical fiber is performed, whereby the phase due to SPM generated in the optical fiber. It is possible to cancel the modulated φ _SPM (t) and output narrow-band pulsed light. Note that the reverse phase modulation refers to phase modulation in which the modulation amount is substantially the same as that of the phase modulation by SPM occurring in the optical fiber.

In order to perform phase modulation opposite to φ _SPM (t) by the EO phase modulator 132, the phase modulator drive signal V ₂ (t) for driving the EO phase modulator 132 is expressed by the following equation.

With such a configuration, it is possible to suppress narrowing of the spectrum due to self-phase modulation that occurs in the optical fiber for transmission or amplification, and output narrow-band pulsed light. At this time, it is necessary to generate a signal such as V ₂ (t) from the pulse generator 116 of the modulator driving power source, and a relatively complicated electric circuit is required. Further, in this method, when the pulsed light P (t) is given from the outside, for example, when given from a mode-locked laser or Q-switched laser, the phase modulator drive signal V ₂ (t) is increased. It is necessary to synchronize with the incident pulse with time accuracy, and the control configuration including the electric circuit may be further complicated. Therefore, the inventors have further researched and proposed a pulse laser having the following configuration.

The pulse laser device according to the first aspect of the present invention detects a laser light source that outputs pulsed light, a phase modulator that changes the phase of the pulsed light output from the laser light source, and the pulsed light output from the laser light source. A detector that outputs a detection signal that is a time axis waveform of an intensity change, and a drive signal that causes a phase change proportional to the time axis waveform of the intensity change based on the detection signal output from the photodetector. And a phase modulator driving power source that outputs and drives the phase modulator.

The pulse laser device according to the second aspect of the present invention further includes a fiber amplifier for amplifying the pulsed light output from the laser light source in the pulse laser device according to the first aspect, and the photodetector outputs from the laser light source. It is preferable to detect the pulse light amplified by the fiber amplifier and output a detection signal that is a time-axis waveform of intensity change.

The pulse laser device according to the third aspect of the present invention is the pulse laser device according to the first or second aspect, wherein the phase modulation by the phase modulator is a pulse generated in an optical fiber on which the pulsed light output from the laser light source is incident. Preferably, the self-phase modulation of light and the amount of modulation are substantially the same and the phase modulation is opposite in phase. The pulse laser device according to a fourth aspect of the present invention is the pulse laser device according to any one of the first to third aspects, wherein the phase modulator is a phase modulation type electro-optic modulator and the drive signal is an optical signal. It is preferable that the electric signal has a time-axis waveform proportional to the detection signal output from the detector.

The pulse laser device according to the fifth aspect of the present invention is the pulse laser device according to any one of the first to fourth aspects, wherein the optical fiber to which the pulsed light output from the laser light source is incident is a single mode fiber. Is preferred.

A pulse laser device according to a sixth aspect of the present invention is the pulse laser device according to any one of the first to fifth aspects, wherein the laser light source includes a light source that generates laser light, and an intensity of the laser light generated by the light source. And an intensity modulator driving power source for generating a drive signal corresponding to the pattern of the pulsed light to be output and driving the intensity modulator.

According to the present invention, based on the detection signal output from the photodetector, that is, the time axis waveform P (t) that is the temporal intensity change of the pulse light described above, the drive signal that causes a phase change proportional thereto. Is supplied from the phase modulator driving power source to the phase modulator. Therefore, it is possible to cancel the phase modulation φ _SPM (t) due to _SPM and output narrow-band pulsed light.

In addition, since the phase modulator drive power supply does not need to artificially generate a relatively complex signal such as V ₂ (t) described above, a pulse laser that outputs narrow-band pulse light with a simple configuration is provided. can do. In addition, because this configuration detects pulsed light with a photodetector, it provides a pulse laser that outputs narrowband pulsed light with a simple configuration, regardless of whether pulsed light is applied from the outside or generated internally. can do.

It is a schematic block diagram (block diagram) of the pulse laser apparatus of a 1st structure form shown as an example of application of this invention. It is a schematic block diagram (block diagram) of the pulse laser apparatus of a 2nd structure form shown as an example of application of this invention. It is a schematic block diagram (block diagram) of the pulse laser apparatus of a 3rd structure form shown as an example of application of this invention. It is a general | schematic block diagram (block diagram) of the pulse laser apparatus of another structure form for implement | achieving a narrow band.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. As an application example of the present invention, FIG. 1 shows a schematic configuration diagram (block diagram) of a pulse laser device 1 of a first configuration form. The pulse laser device 1 includes a laser light source 10 that outputs pulsed light, an SPM compensation unit 30 that compensates for self-phase modulation, and a control unit (not shown) that controls the operation of the entire pulse laser device. .

The pulsed light output from the pulse laser device 1 enters an amplification optical fiber or a transmission optical fiber (not shown). These optical fibers can be either single mode fibers or multimode fibers, but a greater effect can be obtained in the case of a single mode fiber having a small mode diameter and being susceptible to self-phase modulation. In the pulse laser devices 1, 2, and 3 described below, single mode fibers can be used by eliminating the influence of self-phase modulation that occurs in the optical fiber.

The laser light source 10 corresponds to a light source 11 that generates CW laser light, an intensity modulator 12 that modulates the intensity of the laser light generated by the light source 11, and a pulse light pattern to be output from the pulse laser device 1. An intensity modulator driving power source 15 that generates the intensity modulator driving signal V ₁ (t) and drives the intensity modulator 12 is provided.

FIG. 1 illustrates a configuration in which a DFB semiconductor laser (DFB-LD) is used as the light source 11 and an intensity modulation type electro-optic modulator (EOM, EO intensity modulator) is used as the intensity modulator 12. The intensity modulator driving power source 15 includes a pulse generator 16 that generates a pulse signal corresponding to a pattern of pulse light to be output from the pulse laser device 1 (for example, an on time of 1 nsec, a repetition frequency of 1 MHz, and the like), and the pulse generator 16 And an amplifier (not shown) for amplifying and outputting the pulse signal generated by the above to an amplitude level necessary for driving the EO intensity modulator 12.

That is, the intensity modulator drive power supply 15 outputs an intensity modulator drive signal V ₁ (t) corresponding to the pattern of pulsed light to be output from the pulse laser device 1 to the EO intensity modulator 12. Thereby, a part of the CW laser light generated by the light source 11 is cut out by the EO intensity modulator 12, and pulse light having a time axis waveform P (t) is output from the laser light source 10.

As described above, when a CW laser beam is output from the DFB semiconductor laser as the light source 11 and a part thereof is cut out by the EO intensity modulator 12, a chirp generated when the DFB semiconductor laser is directly pulse-modulated ( It is possible to generate pulsed light having an extremely narrow band close to the Fourier limit without frequency modulation. Although the bandwidth of the pulsed light is slightly widened, the light source 11 may be configured to output pulsed light having a sufficiently long on time and cut out a part of the pulsed light by the EO intensity modulator 12.

The SPM compensation unit 30 detects the pulsed light output from the laser light source 10 and outputs a detection signal V _PD (t) proportional to the time axis waveform P (t), and the laser light source 10. A phase modulator 32 that changes the phase of the pulsed light output from the phase modulator, and a phase modulator drive signal that causes a phase change proportional to the time axis waveform P (t) based on the detection signal output from the photodetector 31 And a phase modulator driving power source 35 that outputs V ₂ (t). The intensity modulator 12 and the phase modulator 32 are connected by an optical fiber 22 for connection, and a coupler (not shown) that branches out and extracts a part of the pulsed light (for example, about several percent) into the optical fiber 22. Provided. Then, the pulsed light extracted through the coupler is guided to the photodetector 31 and detected.

FIG. 1 illustrates a configuration in which a photodiode (PD) is used as the photodetector 31 and a phase modulation type electro-optic modulator (EOM, EO phase modulator) is used as the phase modulator 32. The phase modulator drive power supply 35 is provided with an adjustment circuit 36 that gives a required delay to the detection signal V _PD (t) output from the photodetector (PD) 31 and adjusts the waveform as necessary. In addition, an amplifier 37 is provided for amplifying the signal output from the adjustment circuit 36 to an amplitude level necessary for driving the EO phase modulator 32.

At this time, the detection signal V _PD (t) output from the photodetector 31 is proportional to the time axis waveform P (t) of the pulsed light and is expressed by the following equation.

As described above, assuming that there is no distortion of the time axis waveform due to dispersion or the like in an optical fiber that transmits or amplifies pulsed light, the phase modulation φ _SPM (t) due to SPM generated in the optical fiber is expressed as follows. It is proportional to the time axis waveform P (t) of light (refer to the above-mentioned equation (2)). Then, the EO phase modulator 32 performs phase modulation on the pulsed light in advance opposite to the phase modulation φ _SPM (t) due to SPM generated in the optical fiber, thereby phase modulation φ _SPM due to SPM generated in the optical fiber. (t) can be offset.

That is, the detection signal V _PD (t) output from the photodetector 31 is an electric signal to be applied to the EO phase modulator 32 in order to cancel the phase modulation φ _SPM (t) due to SPM in the optical fiber. It can be seen that the waveforms are similar. The adjustment circuit 36 adjusts the waveform of the detection signal V _PD (t) output from the light detector 31 as necessary, and further converts it into pulse light P (t) in the EO phase modulator 32 as necessary. The required delay is given so that the timing with the phase modulation is exactly matched. The detection signal adjusted by the adjustment circuit 36 is amplified to an amplitude level necessary for driving the EO phase modulator 32 by the amplifier 37, and the amplified phase modulator drive signal V ₂ (t) is supplied to the EO phase modulator 32. Entered.

  The phase modulator drive signal V ₂ (t) is an electrical signal that causes the EO phase modulator 32 to generate a phase modulation opposite to the self-phase modulation of the pulsed light generated in the optical fiber. The amplitude of V ₂ at which the modulation amount is the same as the self-phase modulation φ _SPM of the pulsed light is approximately represented by the following equation.

The phase modulator drive signal V ₂ (t) is input to the EO phase modulator 32 in accordance with the transmission timing of the pulsed light, and phase modulation is performed, so that the modulation amount is the same as the phase modulation due to SPM generated in the optical fiber. Thus, the pulsed light is subjected to antiphase modulation. For this reason, phase modulation caused by SPM is canceled in the optical fiber, and narrowband pulsed light having a narrow spectral width is output from the output end of the optical fiber.

In the above embodiment, the EO phase modulator 32 is configured to give a required delay to the detection signal (electric signal) output from the photodetector 31 in order to match the timing of the pulse light P (t) with the phase modulation. Was illustrated. However, the pulse laser device may be other means as long as the pulse light P (t) and the phase modulation timing are matched in the EO phase modulator 32. For example, the length of the optical fiber 22 for connection between the EO intensity modulator 12 and the EO phase modulator 32, or the length of the optical fiber branched from the optical fiber 22 and connected to the photodetector 31. The pulse laser device may be configured to adjust the length, or to adjust by a light delay circuit (delay line). An electrical delay circuit and an optical delay circuit can be combined as appropriate. The adjustment circuit 36 may be configured to correct the nonlinear response of the input / output that the amplifier 37 has.

According to the pulse laser device 1 described above, it is possible to cancel the phase modulation due to SPM generated in the optical fiber and output narrow-band pulse light. Further, as described with reference to FIG. 4, it is not necessary to independently generate a complex signal as the phase modulator drive signal V ₂ (t) for driving the EO phase modulator 32, and thus a simple configuration Thus, it is possible to provide a pulse laser device that outputs narrow-band pulse light.

Next, the pulse laser device 2 of the second configuration form will be described with reference to FIG. The pulse laser device 2 includes a laser light source 10 that outputs pulsed light, a fiber amplifier 20 that amplifies the pulsed light output from the laser light source 10, an SPM compensation unit 30 that compensates for self-phase modulation, and an overall pulse laser device. And a control unit (not shown) for controlling the operation.

The pulse laser apparatus 2 of this configuration form detects the pulsed light amplified by the fiber amplifier 20 with the photodetector 31, and compensates for the self-phase modulation generated in the amplification fiber 25 of the fiber amplifier 20 based on the detection signal. Configured as follows. In other words, the pulse laser apparatus 2 of this configuration form compensates the phase modulation by SPM based on the pulse light actually transmitted through the optical fiber, and performs phase modulation by SPM based on the pulse light before passing through the optical fiber. This is different from the pulse laser device 1 of the first configuration form that compensates for the above. The basic configurations of the laser light source 10 that outputs pulsed light and the SPM compensation unit 30 that compensates for self-phase modulation are the same as those of the laser light source 10 and the SPM compensation unit 30 of the pulse laser device 1 described above. Therefore, in FIG. 2, the same components are assigned the same numbers to simplify the description, and different portions will be mainly described.

The laser light source 10 corresponds to a light source 11 that generates CW laser light, an intensity modulator 12 that modulates the intensity of the laser light generated by the light source 11, and a pulse light pattern to be output from the pulse laser device 2. An intensity modulator driving power source 15 that generates the intensity modulator driving signal V ₁ (t) and drives the intensity modulator 12 is provided. A configuration using a DFB semiconductor laser (DFB-LD) as the light source 11 and an EO intensity modulator (EOM) as the intensity modulator 12 is illustrated. The intensity modulator driving power source 15 includes a pulse generator 16 and an amplifier (not shown). With this configuration, a part of the CW laser light generated by the light source 11 is cut out by the EO intensity modulator 12, and pulse light having a time axis waveform P (t) is output from the laser light source 10.

The fiber amplifier 20 includes an amplification optical fiber (amplification fiber) 25 having a core doped with a laser medium, an excitation light source (not shown) that excites the amplification fiber 25, and an operation (not shown) that controls the operation of the excitation light source. And a control unit. FIG. 2 illustrates a configuration using an erbium-doped fiber amplifier (EDFA) in which the core of the amplification fiber 25 is doped with erbium (Er). The amplification fiber 25 is a single mode fiber having a mode field diameter of about 1 to 15 μm or less. The laser light source 10 and the fiber amplifier 20 can be appropriately selected according to the wavelength of the pulsed light output from the pulse laser device. For example, as the fiber amplifier 20, an ytterbium-doped fiber amplifier (YDFA), a thulium-doped fiber amplifier (TDFA), or the like can be used.

The SPM compensation unit 30 detects the phase modulator 32 that changes the phase of the pulsed light output from the laser light source 10 and the amplified pulsed light (hereinafter referred to as amplified pulsed light) output from the fiber amplifier 20. _A photodetector 31 that outputs a detection signal proportional to the time axis waveform P _A (t), and a phase change proportional to the time axis waveform P _A (t) based on the detection signal output from the photodetector 31 And a phase modulator driving power source 35 that outputs a phase modulator driving signal V ₂ (t) that generates the above. The phase modulator 32 is provided between the laser light source 10 and the fiber amplifier 20.

In the vicinity of the output end of the amplification fiber 25, a coupler (not shown) for branching out and extracting a part of the amplified pulse light (for example, about 1%) is provided, and the amplified pulse light extracted via this coupler is It is guided to the light detector 31 and detected. FIG. 2 illustrates a configuration using a photodiode (PD) as the photodetector 31 and an EO phase modulator (EOM) as the phase modulator 32.

The phase modulator drive power supply 35 is provided with an adjustment circuit 36 that gives a required delay to the detection signal V _PD (t) output from the photodetector 31 and adjusts the waveform as necessary, and its output signal. Is provided to an amplitude level necessary for driving the EO phase modulator 32. The pulsed light detected by the photodetector 31 is pulsed light that has passed through the EO phase modulator 32. Therefore, the phase modulation by the EO phase modulator 32 is performed on an optical pulse that is about one pulse to several pulses after the optical pulse detected by the photodetector 31 among the optical pulses incident at a predetermined repetition period. Done. In the EO phase modulator 32, the adjustment circuit 36 gives a required delay to the detection signal of the photodetector 31 so that the timings of the pulsed light P (t) and the phase modulation recording drive signal V ₂ (t) match. give.

When the pulse energy of the pulse light amplified by the fiber amplifier 20 is sufficiently smaller than the saturation energy of the amplification fiber 25, the time axis waveform P of the amplified pulse light emitted from the amplification fiber 25 is shown. _A (t) has a waveform similar to the time axis waveform P (t) of the pulsed light incident on the amplification fiber 25. That is, in this case, P _A (t) ∝P (t), and the detection signal V _PD (t) output from the photodetector 31 is V _PD (t) ∝P _A (t) ∝P (t ). Therefore, the effect in this case cancels out the phase modulation φ _SPM (t) due to SPM generated in the amplification fiber 25 as in the case of the pulse laser device 1 described above.

On the other hand, when the pulse energy of the pulse light amplified by the fiber amplifier 20 becomes a non-negligible magnitude as compared with the saturation energy of the amplification fiber 25, the time axis waveform of the amplified pulse light emitted from the amplification fiber 25 P _A (t) is considerably different from the time axis waveform P (t) of the pulsed light incident on the amplification fiber 25. Even if the time axis waveform of the pulsed light incident on the amplification fiber 25, that is, the pulse waveform P (t) is a beautiful rectangular wave, the pulse waveform P _A (t) of the amplified pulsed light emitted from the amplification fiber 25 is For example, the waveform may be a distorted waveform that gradually decreases after rising sharply at the top. The degree of self-phase modulation (SPM) increases as the peak power of pulsed light increases. Therefore, it becomes the largest near the exit end of the amplification fiber 25.

In such a case, the pulse waveform P _A (t) of the amplified pulsed light is not similar to the pulse waveform P (t) of the pulsed light before amplification, and the phase modulator drive signal is based on the pulse waveform P (t). In the configuration for generating V ₂ (t), self-phase modulation by SPM cannot be compensated. Thus, the pulse laser apparatus to output an amplified pulse light having a saturation energy equal to or higher pulse energy, the amplifying fiber 25, the pulse waveform P _A of the amplified pulse light output from the amplifying fiber 25 It is desirable to generate the phase modulator drive signal V ₂ (t) based on (t). In the pulse laser device 2 of this configuration, the photodetector 31 that is branched from the vicinity of the output end of the amplification fiber 25 detects the amplified pulse light, and generates a pulse waveform P _A (t) of the amplified pulse light. Based on this, a phase modulator drive signal V ₂ (t) is generated. Then, the EO phase modulator 32 is driven by the generated phase modulator drive signal V ₂ (t), and the pulse light is subjected to phase modulation opposite to phase modulation φ _SPM (t) by _SPM .

According to the pulse laser device 2 of this configuration, even when pulse light having a relatively large pulse energy that does not necessarily resemble the pulse waveform before and after amplification is output, phase modulation due to SPM that occurs in the amplification fiber is canceled out. be able to. Further, it is not necessary to independently generate a relatively complicated signal such as V ₂ (t), and therefore a pulse laser device that outputs a narrow-band amplified pulse light with a narrow spectrum width with a simple configuration is provided. Can do.

Next, the pulse laser apparatus 3 of the third configuration form will be described with reference to FIG. The pulse laser device 3 includes a laser light source (pulse laser) 17 that outputs pulsed light, an SPM compensation unit 30 that compensates for self-phase modulation, and a control unit (not shown) that controls the operation of the entire pulse laser device. Configured.

The pulse laser device 3 of this configuration form is a modification of the pulse laser device 1 of the first configuration form, and the configuration of a laser light source 17 that outputs pulsed light is different from the laser light source 10 of the pulse laser device 1. On the other hand, the basic configuration of the SPM compensation unit 30 that compensates for self-phase modulation is the same as that of the SPM compensation unit 30 of the pulse laser device 1. Therefore, in FIG. 3, the same components are assigned the same numbers to simplify the description, and different portions will be mainly described.

The laser light source (pulse laser) 17 is a light source that autonomously outputs pulsed light. The pulse laser device 3 is a configuration example in the case where pulsed light having a time axis waveform P (t) is given from the outside. It is a simple configuration.

The pulse light of the time axis waveform P (t) output from the laser light source 17 enters the phase modulator 32 through the connection optical fiber 23. The optical fiber 23 is provided with a coupler (not shown) that branches out and extracts a part (for example, about 1 to several percent) of the pulsed light output from the laser light source 17, and the pulsed light extracted through this coupler. Is guided to the photodetector 31 and detected. FIG. 3 illustrates a configuration using a photodiode (PD) as the photodetector 31 and an EO phase modulator (EOM) as the phase modulator 32.

The detection signal V _PD (t) output from the photodetector 31 is proportional to the time axis waveform P (t) of the pulsed light and is expressed by the above-described equation (4). Assuming that there is no distortion of the time-axis waveform due to dispersion or the like for an optical fiber that transmits pulsed light or an optical fiber that amplifies, phase modulation φ _SPM (t) caused by SPM generated in the optical fiber is the pulsed light. Is proportional to the time axis waveform P (t) (see the above-mentioned equation (2)). Therefore, with respect to pre-pulsed light by EO phase modulator 32, by the reverse of the phase modulation and phase modulation phi _SPM (t) by SPM that occurs within the optical fiber, phase modulation by SPM that occurs within the optical fiber phi _SPM (t) can be offset.

According to the pulse laser device 3 described above, it is possible to cancel the phase modulation due to SPM generated in the optical fiber and output narrow-band pulse light. Further, since it is not necessary to artificially generate a complex signal as the phase modulator drive signal V ₂ (t) for driving the EO phase modulator 32, a pulse laser that outputs narrow-band pulse light with a simple configuration. An apparatus can be provided.

As described above, according to the pulse laser devices 1, 2, and 3, the phase modulation driving signal that causes a phase change proportional to the pulse light detected by the photodetector is supplied to the phase modulator. Is done. For this reason, it is possible to cancel the phase modulation caused by the SPM generated in the optical fiber and to output narrow-band pulsed light. In addition, since the phase modulator drive power supply does not need to artificially generate a complex signal, a pulse laser that outputs narrow-band pulse light with a simple configuration can be provided. It is also possible to provide a pulse laser that outputs narrow-band pulse light with a simple configuration regardless of whether the pulse light is supplied from outside the device or generated inside the device. it can.

In the above, before the pulsed light output from the laser light sources 10 and 17 is subjected to phase modulation opposite to the phase modulation by SPM generated in the transmission or amplification optical fiber before entering these optical fibers. In the above, the configuration performed in advance by the EO phase modulator 32 has been described. However, the EO phase modulator 32 may be provided in the vicinity of the emission end of the transmission optical fiber or the amplification optical fiber so as to cancel after phase modulation occurs due to SPM in these optical fibers. In addition, when the amount of modulation is insufficient with one phase modulator, it is possible to secure a sufficient amount of phase modulation by connecting two or more phase modulators in series.

The disclosure of the following priority application is hereby incorporated by reference.
Japanese Patent Application 2013 No. 50235 (filed on March 13, 2013)

DESCRIPTION OF SYMBOLS 1 Pulse laser apparatus 2 of 1st structure form Pulse laser apparatus 3 of 2nd structure form 3 Pulse laser apparatus 9 of 3rd structure form Pulse laser apparatus 10 of another structure form Laser light source 11 Light source 12 Intensity modulator (EO intensity modulator) )
DESCRIPTION OF SYMBOLS 15 Intensity modulator drive power supply 16 Pulse generator 17 Laser light source 20 Fiber amplifier 22 Optical fiber for connection 23 Optical fiber for connection 25 Optical fiber for amplification 30 SPM compensation part 31 Photo detector 32 Phase modulator (EO phase modulation) vessel)
35 Phase modulator drive power supply P (t) Time axis waveform P _A (t) of pulsed light Time axis waveform V ₁ (t) of amplified pulse light Intensity modulator drive signal V ₂ (t) Phase modulator drive signal V _PD (t) Detection signal

Claims (6)

A laser light source that outputs pulsed light;
A phase modulator that changes the phase of the pulsed light output from the laser light source;
A photodetector that detects the pulsed light output from the laser light source and outputs a detection signal that is a time-axis waveform of intensity change;
Based on the detection signal output from the photodetector, a drive signal for generating a phase change proportional to the time axis waveform of the intensity change is output, and a phase modulator driving power source for driving the phase modulator A pulse laser device provided. The pulse laser device according to claim 1,
A fiber amplifier that amplifies the pulsed light output from the laser light source;
The light detector is a pulse laser device that detects pulsed light output from the laser light source and amplified by the fiber amplifier, and outputs a detection signal that is a time-axis waveform of intensity change. In the pulse laser device according to claim 1 or 2,
The phase modulation by the phase modulator is a pulse laser device in which the modulation amount is substantially the same as the self-phase modulation of the pulsed light generated in the optical fiber on which the pulsed light output from the laser light source is incident, and the phase modulation is opposite in phase. The pulse laser device according to any one of claims 1 to 3,
The pulse laser device, wherein the phase modulator is a phase modulation type electro-optic modulator, and the driving signal is an electric signal having a time axis waveform proportional to the detection signal output from the photodetector. In the pulse laser device according to any one of claims 1 to 4,
An optical fiber on which pulsed light output from the laser light source is incident is a pulsed laser device that is a single mode fiber. The pulse laser device according to any one of claims 1 to 5,
The laser light source generates a drive signal corresponding to a pattern of pulse light to be output by generating a light source that generates laser light, an intensity modulator that modulates the intensity of the laser light generated by the light source, and the intensity modulation A pulse laser device comprising: an intensity modulator driving power source for driving the detector.

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