AM / FM seed for nonlinear spectral compression fiber amplifiers

Abstract

To provide a fiber amplifier system with high power and narrow linewidth.SOLUTION: A fiber amplifier system 10 includes an optical source providing an optical seed beam, and an FM electro-optic modulator (EOM) 20 that frequency modulates the seed beam to broaden its spectral linewidth. The system also includes an AM EOM 24 that amplitude-modulates the seed beam to provide an amplitude modulated seed beam that is synchronous with the frequency modulated seed beam. The system also includes a nonlinear fiber amplifier 28 that receives the seed beam that is AM-modulated and FM-modulated, the amplitude modulated seed beam causes self-phase modulation in the fiber amplifier that phase-modulates the seed beam as it is being amplified by the fiber amplifier that acts to cancel the spectral linewidth broadening caused by the frequency modulation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Government clause

[0001] This invention is based on Contract No. FA granted by Air Force Research Laboratory This was done with government support under document number 9451-18-C-0101. The government issued this document. They possess certain rights under the Ming dynasty.

[0002] background field

[0002] The present disclosure generally relates to fiber laser amplifiers having high power output and narrow linewidth. This relates to, and more specifically, to fiber optic modulators (EOMs) This concerns the amplifier system, and EOM uses frequency modulation (FM) to send a seed beam. The signal is applied to widen the line width, and the amplitude is then modulated to a seed beam synchronized with the FM signal. (AM) A signal is applied, and the modulated seed beam is amplified by a nonlinear fiber amplifier. The seed beam is amplified by the amplifier, and as the seed beam propagates through the amplifier, the seed • Self-phase modulation, which phase-modulates the beam, cancels out the frequency modulation of the beam, thus canceling out the original frequency modulation. Restore the spectrum of the beam. [Background technology]

[0003] Consider

[0003] High-power laser amplifiers have many applications, including industrial, commercial, and military applications. For these and other applications, laser amplifier designers increase the power of the laser amplifier. We are continuously researching methods to achieve this. One known type of laser amplifier is doped-fa This is a fiber laser amplifier using IBA, where the doped fiber is used for the seed beam and It receives a pump beam that amplifies the seed beam and generates a high-power laser beam. This fiber is approximately 10-20 μm or larger in diameter, and is an active fiber. It has a core diameter.

[0004]

[0004] Improvements in the design of fiber laser amplifiers have made their practical power and beam The output power of the fiber was increased to approach the quality limit. To further increase power, some fiber laser systems use multiple fibers • Using laser amplifiers, they combine multiple amplified beams in a certain manner. This generates high power. This is a design for this type of fiber laser amplifier system. The challenge in this calculation is to take multiple beams from multiple fiber amplifiers and combine those multiple beams into one. The beams are coupled in a way that provides a beam output, and that beam can be focused to a small focal point. The goal is to achieve this by combining with small spots over long distances (far field). Focusing the beam limits the quality of the beam.

[0005]

[0005] In one known multi-fiber amplifier design, the master oscillator (MO) is seeded. A beam is generated, and that seed beam is split into multiple fiber seed beams. Each of these beams has a common wavelength, and each fiber beam is amplified. The amplified fiber seed beam is then collimated and diffractive with a diffractive optical element (D It is sent to the OE (Output Emissions), which combines multiple coherent fiber beams into a single output beam. They bond. DOE has a periodic structure formed within the element, so each one is slightly different. When individual fiber beams with different angular directions are reoriented by a periodic structure All of those beams diffract from the DOE in the same direction. Each fiber beam has a phase shift. Provided to the tuner, the phase modulator controls the phase of the beam, and the position of all fiber beams Ensure that the phases are maintained coherently. However, there are limitations on bandwidth and phase alignment. This error limits the number of fiber beams that can be combined coherently. Therefore, the output power of the laser is limited.

[0006]

[0006] In another known multi-fiber amplifier design, multiple master oscillators (MOs) Multiple fiber seed beams are generated at the same wavelength, and each fiber seed beam is amplified. The amplified fiber seed beam is then collimated and used with a diffraction grating. The beam is then sent to another wavelength-selective element, which allows multiple fiber beams of different wavelengths to be combined into one. It couples to the output beam. The diffraction grating has a periodic structure formed within the element, so Individual fiber beams, each with slightly different wavelengths and angular directions, form a periodic structure. When the direction is changed, all of those beams diffract from the diffraction grating in the same direction. However, due to bandwidth limitations, the number of fiber beams that can be wavelength-coupled is limited, This limits the laser's output power.

[0007]

[0007] In order to overcome these limitations and further increase the power of the laser beam, It can provide multiple master oscillators to generate multiple seed beams of various wavelengths. In that case, each of the seed beams of individual wavelengths is a multiple fiber seed The beam is split into two, and each group of fiber seed beams has the same wavelength and phase They are mutually coherent. Multiple coherent fiber seeds of each wavelength in each group · The beams are first coherently combined by a DOE and then the coherently combined beams in each group are sent to a spectral beam combining (SBC) grating at slightly different angles, which diffracts those beams in the same direction to form one combined beam of multiple wavelengths . The SBC grating also includes a periodic structure for combining multiple beams of different wavelengths

[0008]

[0008] To improve the quality of the beam, it is often desirable for the output beam from the fiber amplifier to have a narrow line width, i.e., to have a narrow frequency range. However, since a wide beam line width is required for high output, typically, it is difficult to achieve both high output and narrow line width simultaneously. Conventionally, providing both high output and narrow line width has been a challenge in the art . More specifically, stimulated Brillouin scattering (SBS), i.e., the non - linear backward scattering of the beam as it propagates along the fiber amplifier, increases with a narrow line width in a small frequency range, which acts to reduce the power of the beam. However, the wider the beam line width, the more difficult it is to coherently combine or spectrally combine multiple beams from multiple fibers into one beam through known beam combining techniques. In particular, the dispersion effects from the SBC grating require a narrow line width of the amplified beam, where spectral dispersion diffracts the spectral components of the beam at various angles. In other words, for SBC, the spectral brightness of the seed beam directly limits the theoretical brightness of the combined beam output

[0009] ​​​​​​​​​​​​​

[0009] Since the group delay and variance between amplifiers are not perfectly matched, coherent B Regarding com-beam coupling (CBC), the spectral brightness of the seed beam limits the coupling efficiency. Typically, the source spectral brightness is limited by SBS, and the peak SBS value... To reduce input and achieve the desired output power, seed beams are introduced into the fiber amplifier. The source must be frequency modulated. Frequency modulation spectral widening is one f The spectral brightness achievable from the fiber amplifier is limited, and therefore the system output is limited. do.

[0010]

[0010] To overcome these limitations, fiber amplifier designers typically use a circumferential connection. To reduce the linewidth through wavenumber modulation, one or more phase shifts are introduced before the amplification stage of the fiber amplifier. A tuner is used. However, before the beam is amplified by the fiber amplifier, the frequency of the beam is changed. When modulation is applied, the broadening of the spectral components of the beam is preserved through the amplifier, As a result, the beam becomes amplified with low spectral brightness.

[0011]

[0011] "Nonlinea" issued on May 19, 2015 to Goodno and others U.S. Patent No. 9036252, titled "Spectrally Narrowed Fiber Amplifier," Fiber lasers with high power output and narrow linewidth to improve spectral brightness. An amplifier system is disclosed, and this document is incorporated herein by reference. This '25 The fiber amplifier system disclosed in the two patents provides an optical seed beam. It includes a seed beam source and a harmonic phase modulator, the harmonic phase modulator is a seed beam and RF drive It receives a motion signal and uses the drive signal to frequency modulate the seed beam, and the seed beam The optical power from the main band or 0th order frequency of the signal is removed, and that power is converted to the frequency of the drive signal. The signal is placed into the sideband frequencies delimited by the dispersive element, which is the frequency-modulated seed beam. It receives and provides temporal amplitude modulation of its seed beam. The nonlinear fiber amplifier The frequency and amplitude modulated seed beam is received from the dispersive element, and the seed beam... This amplifies the beam and is caused by frequency modulation and the nonlinearity of the fiber amplifier. Self-phase modulation (SPM) couples and removes optical power from the sideband frequencies, which then becomes the zeroth-order frequency. Return to wavenumber.

[0012]

[0012] As generally explained above, the '252 fiber amplifier system is The seed beam is frequency modulated, and then the frequency-modulated seed beam is shaken using dispersion. Width modulation occurs, while amplitude modulation is caused by the self-phase change resulting from the nonlinearity of the fiber amplifier. Drive the adjustment so that the beam spectrum is reduced when the beam is amplified. This technology generates a high-power output beam with a narrow linewidth. While it can effectively provide a powerful and narrow-linewidth beam, amplitude modulation is more precise than frequency modulation. Since it is inconsistent, relying on dispersion to provide amplitude modulation of the seed beam is not feasible. This is limited, and this affects the efficiency of nonlinear spectral compression in fiber amplifiers at high modulation levels. It imposes limitations. More specifically, with respect to fiber amplifiers with low modulation and high nonlinearity, Spectral compression is effective in fiber amplifiers. However, the nonlinearity in fiber amplifiers When the amplitude modulation is low, more dispersion is required to increase the amplitude modulation of the beam. However, when the dispersion is large, the shape during amplitude modulation is the same as the shape during frequency modulation linewidth widening. It does not exactly match, that is, the waveform of amplitude modulation is not a perfect sine wave, so the nonlinear spectrum Torr compression is inefficient, leaving a lot of power in the sidebands, which reduces the linewidth that could otherwise be reduced. The quantity is limited. Therefore, there is a trade-off between the efficiency of spectral compression and the suppression of high SBS. There are days off. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic block diagram of the input section of a fiber laser amplifier system, including separate EOMs for providing frequency and amplitude modulation of the seed beam. [Figure 2] Figure 2 is a schematic block diagram of the input section of a fiber laser amplifier system that includes one EOM to provide both frequency and amplitude modulation of the seed beam. [Figure 3] Figure 3 is a schematic block diagram of the input section of a fiber laser amplifier system that includes one EOM to provide both frequency and amplitude modulation of the seed beam and uses a CBC with matched B integrals between multiple fiber amplifiers. [Figure 4] Figure 4 is a schematic block diagram of the input section of a fiber laser amplifier system using a CBC with unmatched B integrals between multiple fiber amplifiers, which includes one EOM to provide both frequency and amplitude modulation of the seed beam. [Figure 5] Figure 5 is a schematic block diagram of a fiber laser amplifier system with multiple channels, each channel containing one EOM to provide both frequency and amplitude modulation of the seed beam, and using an SBC. [Modes for carrying out the invention]

[0014]

[0018] Seed beam frequency to increase beam power and reduce beam width Embodiments of this disclosure relating to a fiber laser amplifier that provides number modulation and amplitude modulation The following description is essentially illustrative and is not intended to limit this disclosure or its applications or use. Not illustrated.

[0015]

[0019] As mentioned above, fiber laser amplifiers cannot achieve both high power and narrow linewidth. Because it does not happen, the spectral brightness is limited. To overcome this incompatibility... This disclosure describes how to use both frequency modulation and amplitude modulation to control the linewidth of the seed beam. Then, widening the signal, and using the self-phase modulation caused by the nonlinearity of the high-power fiber amplifier, The amplified beam's linewidth is brought close to the original, unwidened seed beam's linewidth in the spectrum. I suggest compressing it.

[0016]

[0020] Figure 1 is a schematic block diagram of a part of the fiber laser amplifier system 10. Yes, this system generates a seed beam with a specific wavelength in line 14. Includes oscillator 12. The seed beam is supplied to auxiliary RF electro-optic modulator (EOM) 16. This EOM is controlled by an auxiliary RF driver 18 to provide frequency modulation. The frequency modulation provided by 16 is either white noise or a pseudo-random bit sequence. This exhibits conventional techniques for providing frequency modulation widening, such as PRBS. Yes, and in some amplifier systems, it may not be necessary or desired. EO The M16 can be placed at any suitable position before the seed beam of system 10 is amplified. Please note the following. The laser field E1(t) following the auxiliary EOM16 is as follows: It takes the shape of...

[0017]

number

[0018]

[0021] As can be seen from equation (1), the amplification of the laser field over time It is constant, and its phase changes over time by a function φ(t) imposed by EOM16. .

[0019]

[0022] The modulated seed beam from EOM16 is then sent to FM EOM20. The FM EOM20 also receives an RF drive signal f(t) from the RF driver 22. The EOM20 applies an RF drive signal to the phase of the optical seed beam, thereby controlling the seed in time. Frequency modulation is provided by changing the frequency of the beam. Frequency modulation from EOM20 The field output is in the following format:

[0020]

number

[0021] In the above, the drive signal f(t) is zero-averaged (time-averaged) and normalized to 1. Assume that β is the frequency modulation in radians.

[0022]

[0023] Frequency modulation provides a time-dependent change in the phase of the seed beam, This widens the beam linewidth, and a wider linewidth provides SPS suppression. In one non-limiting example for clarity, the RF drive signal provided by driver 22 is , single-tone sine wave signal f(t) = sin(ω m t) And here, ω m t / 2π This is the modulation frequency, which can be set to 32 GHz, and this is the S in fused silica fibers. It is twice the Stokes frequency shift caused by BS. However, in various applications, other It should be noted that it is also possible to use high-frequency sinusoidal drive signals. More generally, The drive signal f(t) does not necessarily have to be a sine wave; in fact, for example, PRBS f Any function form is acceptable, including formatting and shaped noise spectra.

[0023]

[0024] The frequency modulation provided by EOM20 generates an optical seed beam, This is the widened spectrum determined by the function form f(t) of the drive signal and the modulation degree β. This includes the beam width. In the non-limiting example described here, the contents of the seed beam spectrum are: Includes frequency sidebands separated at 32 GHz. Modulation degree of the RF drive signal from driver 22. β is selected according to the desired spectral width; signals with high modulation have a wide spectrum. This creates a range. For example, in the non-limiting example described here, the modulation degree β of the drive signal is E In OM20, select to remove all power from the 0th order frequency of the seed beam. It can be selected. Alternatively, the modulation degree β of the drive signal is the seed beam in EOM20. Select to produce equal amplitude power at the 0th and + / -1st order sideband frequencies. It is possible. Alternatively, the modulation degree β of the drive signal is the number of seed beams in EOM20. A number of sidebands can be selected to create a certain number of sidebands.

[0024]

[0025] The frequency-modulated seed beam is then sent to AM EOM24, and this The RF driver 26 receives an RF drive signal, and the RF drive signal is used for the seed beam. A device that provides amplitude modulation, that is, a device that changes the power of the seed beam over time. Therefore, EOM2 provides amplitude modulation by applying a drive signal to the amplitude of the optical seed beam. The RF driver 26 is connected to the RF driver 22 via a common underlying drive signal f(t). In sync with this, the EOM24 will provide AM / FM field output in the following format. It can be done.

[0025]

number

[0026] In the above, parameter B is the fiber seeding by the AM / FM source. This is a nonlinear phase shift (in radians) caused by self-phase modulation associated with the width sensor 28. In other words, the amplified high-power beam emitted from the fiber amplifier 28 is parametrically controlled. We experience a nonlinear phase shift in -B.

[0027]

[0026] In the absence of frequency modulation, the amplitude modulation of the seed beam (1-(β / B)f(t)) 1 / 2 This will provide a slight widening of the seed beam line width. This is evident from the examination of equation (3). Thus, amplitude modulation is synchronized with frequency modulation, and the amplitude peaks are aligned with the phase troughs. It is made to do so. EOM24 directly provides beam amplitude modulation, and '252 special Since it does not depend on variance to provide amplitude modulation as in the case of X, the amplitude modulation term (1-(β / B)f(t)) 1 / 2 and the section on frequency modulation e iβf(t) Even with a high modulation depth β and / or low amplifier nonlinearity B, the matching is precise. It can be done.

[0028]

[0027] Also, if the order of EOM20 and EOM24 can be changed, • It is not necessary to perform beam frequency modulation before seed beam amplitude modulation. However, this is clear from equation (3). Furthermore, FM EOM20 and AM EOM24 are combined into one It can be combined as a device. An embodiment of this is the fiber amplifier system shown in Figure 2. As illustrated by Tem 40, in its embodiment, components similar to those in System 10 are the same They are indicated by the same reference number. In system 40, EOM20 and EOM24 are not combined. It is set up as one AM / FM EOM41, which is driven synchronously from the RF driver 44. The EOM42 receives a signal and simultaneously applies amplitude modulation and frequency modulation to the seed beam. This can be any device suitable for the purpose described here, and it is EOspac Commercially available broadband low-loss LiNbO3 from e (trademark) Electro-optic dual-drive Mach-Zehnder interferometer Examples include tric intensity modulators.

[0029]

[0028] The amplitude and frequency modulated seed beam is then subjected to nonlinear fiber amplification. The signal is sent to instrument 28, which can be configured as multiple fiber amplification stages, each stage being a pump-bike A fiber doped with ytterbium (Yb) and having a core of 10-20 μm. This includes a doped fiber of a certain length, and the amplified output beam is fiber Provided to B30. Amplitude modulation and frequency modulation are synchronized by equation (3), As a result, with respect to the given nonlinear parameter B of the fiber amplifier 28, high power and It can provide optimal spectral compression of the amplified beam for very narrow linewidths. The seed beam, which is created by combining amplitude modulation and frequency modulation, is a fiber amplifier. Since it is designed to match the nonlinearity of 28, when the seed beam is sent to amplifier 28... The spectral linewidth is widened. This is because the fiber amplifier 28 exhibits a nonlinear Kerr effect. The power-dependent refractive index of the fiber causes a large phase shift in the optical beam at high power. This is because it causes interference with amplitude-modulated power fluctuations in the seed beam. This causes a synchronization phase shift of the beam in the fiber amplifier 28. The time-dependent, nonlinear phase caused by phase modulation is as follows:

[0030]

number

[0031]

[0029] Therefore, the amplified field output from the fiber amplifier 28 is as follows: It will become.

[0032]

number

[0033]

[0030] Equation (5) is the phase shift SPM(t) that occurs due to nonlinear self-phase modulation. However, this shows that it cancels out the frequency modulation βf(t) previously provided by EOM20. The remaining phase term is a constant global phase shift (constant g) that does not affect the optical spectrum. (global phase shift) B. The seed beam propagates through the fiber amplifier 28. When amplified, the nonlinear Kerr effect causes self-phase modulation in amplifier 28, and therefore The beam power is then shifted back to the original linewidth associated with field E1(t). This provides a high-power beam with a narrow linewidth at the output of the fiber amplifier.

[0034]

[0031] By canceling out the frequency modulation of the optical signal through this effect, the original beam E1 The spectrum of (t) is the output of amplifier 28, with a residual amplitude modulation term. (1-(β / B)f(t)) 1 / 2 Although it involves only a small amount of linewidth widening resulting from this, it is almost completely restored. The input and output of amplifier 28 The change in the spectrum between forces (fields E3(t) and E4(t), respectively) is: Spectrum of backscattered SBS from various positions in a fiber amplifier 28 of a certain length Reduces the overlap of the torrent. This is because, compared to the unmodulated seed spectrum, the SBS Increase the threshold. In other words, when the seed beam is frequency modulated, The spectral linewidth of the seed beam, represented by field E3(t), is widened. As a result, the linewidth and spectrum of the amplified beam, represented by field E4(t) The beam overlaps, reducing backscattering of light. The beam propagates through the fiber amplifier 28. When the light power is spectrally compressed by the accumulated self-phase modulation, the SBS It increases, but this is limited by the decrease in spectral brightness during the initial stages of beam propagation.

[0035]

[0032] As mentioned above, the seed beam first broadens its spectral linewidth. When modulated, and the seed beam is amplified and a nonlinear phase accumulates, the power becomes The spectrum is compressed to the original linewidth associated with field E1(t). Fiber amplifier 28 Backscattered SBS Stokes light from any point in that region is local to that point. Represents a vector. The beam propagating forward through most of the fiber amplifier 28 is the fiber The spectral overlap with the backscattered waves near the output terminal of amplifier 28 is very small. Therefore, the SBS gain is considerably lower than when there is no AM / FM modulation. This increases the threshold for frequency modulation without self-phase modulation compression. This enables higher spectral brightness output than conventional technologies. Furthermore, it provides unlimited sine wave modulation. In this case, the modulation frequency is set to twice the SBS Stokes shift, i.e., 32G. The wise choice of Hz is to reduce the threshold of SBS, thus reducing self-seeding Many of the self-seeding effects can be eliminated.

[0036]

[0033] Maximum compression efficiency to the original spectral linewidth associated with the input field E1(t) To ensure this, the magnitude of the amplitude modulation is the optimal value described by equation (3). (1-(β / B)f(t)) 1 / 2 It can be adjusted to follow this. This adjustment changes the modulation degree of the drive voltage for amplitude modulation. What is the difference between doing so, or adding a passive delivery fiber behind amplifier 28? This can be done by either method, which increases the B integral, or by amplifier 28 This can be done by changing the power of, which proportionally changes the B integral. That is the case.

[0037]

[0034] An example of a set of modulation parameters useful for illustrating the suppression of SBS is described below. The fiber amplifier 28 can be a 2 kW fiber amplifier, and the typical B integral associated with this is B = 10 radians. The modulated RF drive signal is selected to be f(t)=sin(ω t), where ω m / 2π = 32 GHz. By selecting a frequency modulation degree of β = 2.4 radians, the spectral line width of the FM field E2(t) is broadened to ~2βω / 2π = 150 GHz. The EOM 24 imposes the synchronous amplitude modulation described by Equation (3), whereby the AM / FM field becomes as follows. m m / 2π = 150 GHz. The EOM 24 imposes the synchronous amplitude modulation described by Equation (3), whereby the AM / FM field becomes as follows. The resulting power variation is a sine wave with a peak-to-peak modulation degree of ~48% with respect to the unmodulated continuous wave power level. When amplification occurs in the non-linear fiber amplifier 28, the accumulated SPM cancels out the imposed frequency modulation, and the output field simply becomes as follows.

[0038]

Equation

[0039]

[0035] The resulting power variation is a sine wave with a peak-to-peak modulation degree of ~48% with respect to the unmodulated continuous wave power level. When amplification occurs in the non-linear fiber amplifier 28, the accumulated SPM cancels out the imposed frequency modulation, and the output field simply becomes as follows.

[0040]

Equation

[0042]

[0037] The fiber laser amplifier systems 10 and 40 described above can be used with any suitable fiber It can be part of an IBA amplifier system, and those skilled in the art will be able to construct various configurations in accordance with the description herein. You will understand the method of arranging the components. For example, fiber amplifier system 10 or 4 0 is a coherence containing multiple parallel fiber amplifiers 28 that have the same (matched) B integral. When considered as part of a CBC (Central-Beam Coupling) fiber amplifier system, frequency modulation is performed. The seed beam is then split into multiple channels after EOM24 or 42. The channel also includes a phase actuator. Each channel has a fiber amplifier 28, B If they do not match in terms of integration, the seed beams are EOM16 and EOM20 or 4 The signal is split between two channels, and the downstream components of EOM16 are duplicated for each channel. Fiber amplifier system 10 or 40 is spectral-beam coupled (CBC) fiber amplification. When considered as part of a system, there are several fiber amplifier systems 10 or 40. As a result, each operates at a different wavelength and has no common components. The fiber amplifier system will be explained further below.

[0043]

[0038] Figure 3 is a schematic block diagram of the fiber laser amplifier system 50, The fiber laser amplifier system 50 has a seed beam frequency similar to that of system 40. It includes one EOM to provide both modulation and amplitude modulation, and here, similar configurations The elements are identified by the same reference number, and also have a matched B integral between the fiber amplifiers 28. It uses CBC. System 50 includes a beam splitter 52 behind EOM42. The beam demultiplexer 52 splits the modulated seed beam into multiple channels 54. The modulated seed beams from each channel 54 are sent to the phase actuator 56. Then, the phase actuator 56 controls the modulated seed beam of each channel 54 The phase is controlled, so that they are in phase with each other. Phase-controlled and modulated seed The beam is then amplified by the amplifier 28 for each channel 54, and multiple amplified beams are then generated. The beams are coupled by a beam coupling optical system 58, which has a common wavelength. This includes appropriate optics and gratings for the CBC of the beam, and coupling The beam is then emitted from there.

[0044]

[0039] Figure 4 is a schematic block diagram of the fiber laser amplifier system 60, The fiber laser amplifier system 60 is similar to the seed beams of systems 40 and 50. It includes one EOM to provide both frequency modulation and amplitude modulation of the m, and here, The components are identified by the same reference number, and are matched among the fiber amplifiers 28. It uses a CBC with no B integral. System 60 includes a beam demultiplexer 52, and B The demultiplexer 52 splits the seed beam before it is modulated by the EOM42. The split seed beam is sent to multiple channels 62. The split beam is sent to EOM42 on channel 62, where the modulated seed... The beam is sent to the phase actuator 56, and the phase actuator 56 controls each channel The Nell 54 modulated seed beams are controlled in phase with each other. The phase-controlled and modulated seed beam is then passed through amplifier 2 of each channel 54. The beams are amplified by 8, and then the multiple amplified beams are coupled by the beam coupling optical system 58. It is then output from there as a combined beam.

[0045]

[0040] Figure 5 shows a fiber laser amplifier system 70 including multiple channels 72. This is a schematic block diagram, where each channel 72 corresponds to the laser amplifier systems 40 and 50 It has one of these, and here similar components are identified by the same reference number, and also, Each MO12 in each channel 72 operates at a separate wavelength suitable for SBC. The amplified beam from amplifier 28 is coupled by beam coupling optical system 74, The beam-coupled optical system 74 provides appropriate grating for SBCs of beams with various wavelengths. A combined beam is generated using a rapping and optics system.

[0046]

[0041] The above description merely discloses and describes an example embodiment of the present disclosure. Those skilled in the art will understand from this description and from the attached drawings and claims the following requests Without deviating from the spirit and scope of this disclosure as defined in the scope of the request, various changes, modifications, and It will be easy to recognize that deformation can occur.

Claims

1. A fiber amplifier system, An optical source that provides an optical seed beam, A frequency-modulated (FM) electro-optic modulator (EOM) that responds to the seed beam and a first drive signal, the FM EOM frequency modulates the seed beam using the first drive signal to widen the spectral linewidth of the seed beam, An amplitude-modulated (AM) EOM that responds to the seed beam and a second drive signal, wherein the seed beam is amplitude-modulated using the second drive signal to provide an amplitude-modulated seed beam synchronized with the frequency-modulated seed beam, and the first drive signal and the second drive signal are synchronized with each other so that the amplitude peaks of the frequency-modulated and amplitude-modulated seed beam align with the phase troughs of the frequency-modulated and amplitude-modulated seed beam, and the first drive signal and the second drive signal are single-tone sinusoidal signals, A nonlinear fiber amplifier that receives the AM-modulated and FM-modulated seed beam and amplifies the seed beam, wherein the amplitude-modulated seed beam causes self-phase modulation in the fiber amplifier, and when the seed beam is amplified by the fiber amplifier, the seed beam is phase-modulated to cancel out the spectral linewidth widening caused by FM EOM, Before the seed beam is amplified, an auxiliary EOM is used to frequency modulate the seed beam to provide frequency modulation broadening. A fiber amplifier system including a fiber optic amplifier.

2. The system according to claim 1, wherein the FM EOM and the AM EOM are separate modulation devices.

3. A system according to claim 1, wherein the FM EOM and the AM EOM are a single combined modulation device.

4. The system according to claim 1, wherein the amplitude of the first drive signal is selected such that the FM EOM removes most of the power from the zeroth frequency of the seed beam.

5. The system according to claim 1, wherein the amplitude of the first drive signal is selected such that the FM EOM generates power of equal amplitude at the 0th and + / -1st order frequencies of the seed beam.

6. The system according to claim 1, wherein the first drive signal has a frequency of 32 GHz.

7. The system according to claim 1, wherein the optical source is a master oscillator.

8. A system according to claim 1, wherein the fiber amplifier system is part of a coherent beam-coupled (CBC) fiber amplifier system or a spectral beam-coupled (SBC) fiber amplifier system.

9. A method for amplifying an optical seed beam, The steps include frequency modulating the seed beam using a first drive signal to broaden its spectral linewidth, To provide an amplitude-modulated seed beam synchronized with the frequency-modulated seed beam, the seed beam is amplitude-modulated using a second drive signal, and the first drive signal and the second drive signal are synchronized with each other so that the amplitude peaks of the frequency-modulated and amplitude-modulated seed beam align with the phase troughs of the frequency-modulated and amplitude-modulated seed beam, and the first drive signal and the second drive signal are single-tone sinusoidal signals, step, The steps include amplifying the frequency-modulated and amplitude-modulated seed beam in a nonlinear fiber amplifier so that the amplitude-modulated seed beam generates self-phase modulation in the fiber amplifier, modulating the seed beam when it is amplified by the fiber amplifier, and working to cancel out the spectral linewidth affected by the frequency modulation, A step of frequency modulating the seed beam to provide frequency modulation broadening before the seed beam is amplified, which is different from the step of frequency modulating the seed beam using the first drive signal. A method that includes this.

10. A method according to claim 9, wherein the amplitude of the first drive signal is selected to remove most of the power from the zeroth frequency of the seed beam during the frequency modulation.

11. The method according to claim 9, The amplitude of the first drive signal is selected in such a way as to generate power of equal amplitude at the 0th and + / -1st order frequencies of the seed beam during the frequency modulation.

12. A method according to claim 9, wherein the first drive signal has a frequency of 32 GHz.

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