Collinear phase detection system for coherent beam combination

Abstract

The invention relates to a collinear phase detection system for coherent beam combination. In some implementations, a phase detector for implementing coherent beam combination includes a first half-wave plate that can rotate polarization of a first input beam and a second input beam to 45 degrees. The first birefringence window may divide the input beam into pairs of beamlets associated with cross-polarization, and the second birefringence window may shift the first and second beamlet pairs such that a first beamlet of the first beamlet pair and a second beamlet of the second beamlet pair form an overlapping beam after cross-polarization and are inverted by the second half-wave plate. The analyzer may then split the overlapping beam into a first output beam associated with the first intensity and a second output beam associated with the second intensity, where a difference between the first intensity and the second intensity is related to a phase difference between the first input beam and the second input beam.

Description

[0001] Cross - Reference to Related Applications

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 608,614, filed on December 11, 2023, with the title "PHASE DETECTION TECHNIQUES FOR COHERENT BEAM COMBINING". The disclosure of the prior application is hereby incorporated by reference in its entirety and made a part of this patent application. TECHNICAL FIELD

[0003] The present disclosure generally relates to coherent beam combining and collinear phase detectors that can detect phase errors within an array of co-propagating beams. BACKGROUND OF THE DISCLOSURE

[0004] Coherent beam combining (CBC) is a technique used in optics to combine multiple laser beams into a single output beam with higher power and / or desired beam quality. CBC is particularly useful in applications where the power of a single laser is insufficient and scaling the power of a single emitter is challenging due to physical and / or technological limitations. The basic principle of CBC involves superimposing individual laser beams in a way that results in constructive interference, thereby increasing the intensity of the combined beam. To achieve the increase in intensity, careful control of the phase and amplitude of each individual laser beam is required. For example, phase and / or amplitude control can be achieved through active and / or passive phase-locking mechanisms, which can include an electronic feedback system that adjusts the phase of the lasers in real time based on the observed interference pattern of the beams. The implementation of CBC can be classified into two main architectures: tiled-aperture combining and filled-aperture combining. In tiled-aperture combining, individual laser beams are arranged in a two-dimensional array, and the phase of the laser beams is controlled to occur constructive interference at a distant target to effectively produce a single high-power beam. The tiled-aperture approach is beneficial in high-power laser systems, such as those used in directed energy applications. Filled-aperture combining involves overlapping the beams in the same spatial mode of a single aperture, which is advantageous for applications that require high beam quality and brightness, such as fiber laser systems. However, CBC presents challenges, including the need for precise phase control to maintain coherence and the complexity of scaling the system with a large number of emitters. SUMMARY OF THE INVENTION

[0005] In some implementations, a phase detector includes a first half-wave plate (HWP) arranged to receive a first input beam and a second input beam co-propagating with a first polarization and rotate the first polarization to 45 degrees (°); a first birefringent window arranged after the first HWP, which is configured to divide the first input beam into a first pair of sub-beams associated with orthogonal polarizations and divide the second input beam into a second pair of sub-beams associated with orthogonal polarizations; a second HWP arranged after the first birefringent window, which is configured to reverse the orthogonal polarizations associated with the first pair of sub-beams and the second pair of sub-beams; a second birefringent window arranged after the second HWP, which is configured to refract and offset the first pair of sub-beams and the second pair of sub-beams such that a first sub-beam in the first pair of sub-beams and a second sub-beam in the second pair of sub-beams form an overlapping beam; and an analyzer arranged after the second birefringent window, which is configured to split the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, wherein the difference between the first intensity and the second intensity is related to the phase difference between the first input beam and the second input beam.

[0006] In some implementations, a method for phase detection to achieve coherent beam combination includes: receiving, by a phase detector including a plurality of optical devices arranged in a linear optical path, a first input beam and a second input beam; dividing, by the phase detector, the first input beam into a first pair of sub-beams associated with orthogonal polarizations and dividing the second input beam into a second pair of sub-beams associated with orthogonal polarizations; offsetting, by the phase detector, the first pair of sub-beams and the second pair of sub-beams such that a first sub-beam in the first pair of sub-beams and a second sub-beam in the second pair of sub-beams form an overlapping beam; and splitting, by the phase detector, the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, wherein the difference between the first intensity and the second intensity is related to the phase difference between the first input beam and the second input beam.

[0007] In some implementations, an optical system includes a laser source configured to generate a seed laser; a splitting stage including one or more optical devices configured to split the seed laser into a beam array, the beam array including a first input beam and a second input beam co-propagating with a first polarization; an amplification stage including a first amplifier for amplifying the first input beam and a second amplifier for amplifying the second input beam; a combining stage including one or more optical devices configured to combine the amplified first input beam and the amplified second input beam to generate an output beam; a phase detector disposed after the amplification stage, the phase detector including: a first HWP arranged to receive the first input beam and the second input beam and rotate the first polarization to 45°; a first birefringent window disposed after the first HWP, which is configured to split the first input beam into a first pair of sub-beams associated with orthogonal polarizations and split the second input beam into a second pair of sub-beams associated with orthogonal polarizations; a second HWP disposed after the first birefringent window, which is configured to reverse the orthogonal polarizations associated with the first pair of sub-beams and the second pair of sub-beams; a second birefringent window disposed after the second HWP, which is configured to refract and offset the first pair of sub-beams and the second pair of sub-beams such that a first sub-beam in the first pair of sub-beams and a second sub-beam in the second pair of sub-beams form an overlapping beam; and an analyzer disposed after the second birefringent window, which is configured to split the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, wherein the difference between the first intensity and the second intensity is related to the phase difference between the first input beam and the second input beam; and a feedback loop including one or more devices configured to measure the first intensity and the second intensity and generate a control signal, the control signal being used to modulate the phase of one or more of the first input beam or the second input beam according to the phase difference between the first input beam and the second input beam before the amplification stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a diagram illustrating an example of a phase detection system that can be used in a coherent beam combining system.

[0009] Figure 2 is a diagram illustrating an example implementation associated with a collinear phase detector that can be used in the coherent beam combining system described herein.

[0010] Figure 3 is a diagram illustrating an example implementation of a coherent beam combining system including the collinear phase detector described herein.

[0011] Figure 4 is a flowchart illustrating an example process performed, for example, by a collinear phase detector in a coherent beam combining system. DETAILED DESCRIPTION

[0012] The following detailed description of the examples implemented refers to the accompanying drawings. Identical reference numerals in different drawings may identify the same or similar elements.

[0013] Fiber laser technology has many properties that can be used for various light-induced applications in science, industry, and other fields. For example, fiber laser systems have characteristics that enable power scaling, excellent beam quality and stability, high quantum efficiency, wide gain bandwidth, and / or thermal management, which results in fiber laser systems being frequently used as multifunctional laser sources in continuous wave (CW) and pulsed regimes. For example, due to the ability of fiber laser systems to achieve power scaling, fiber laser systems are typically used in applications that require high power levels (e.g., in the kilowatt (kW) range), such as advanced material processing and laser particle accelerators. For example, fiber laser systems using high-brightness laser diodes and double-clad fibers can provide much higher output powers than fiber laser systems pumped through single-clad fibers, and chirped pulse amplification techniques can achieve further power scaling of ultrafast (e.g., femtosecond) pulses in a single amplification channel (e.g., a single-core amplifier).

[0014] However, due to various physical limitations, including nonlinear effects, polarization losses, mode instabilities, thermal issues, optical damage, and / or pump power limitations, ultrafast fiber laser technology is approaching the power scaling limit of single-core amplifiers. Thus, in some cases, beam combining techniques can be used to achieve further power scaling in fiber laser systems. For example, beam combining techniques can use several fibers or several cores before the amplification stage to split a seed laser beam to distribute the intensity of the beam over several fibers or several cores, and then amplify the split beams individually and combine them into a single output. Typically, the amplification can be performed using multiple amplifier channels, which can be individual fibers or multi-core fibers (MCFs), where multiple cores are embedded in a larger fiber and the beams are amplified in parallel before recombination. However, in order to combine multiple individual lasers in an efficient manner, phase control of the individual sub-beams is crucial.

[0015] Thus, coherent beam combination (CBC) techniques can be used to more efficiently (re)combine multiple beams. For example, in a CBC system, power scaling can be achieved by combining multiple laser amplifiers seeded by a common laser source into a single high-power output beam while maintaining beam quality and preserving the spatial and spectral characteristics of the lasers. For example, in a CBC system, there is a phase relationship between multiple laser amplifiers, and the parallel amplifiers effectively operate as a single laser. The general concept is that a seed beam is split into several copies (e.g., N channels), which are then amplified to the highest possible power and / or energy by the parallel amplifier sections, and then the amplified copies of the seed beam are combined into a single beam. To maximize the combination efficiency and avoid intensity fluctuations, the time delay (e.g., phase difference) between sub-beams in different cores or different optical fibers needs to be stabilized to a small fraction of the wavelength. For example, a CBC system can use active phase control, where a phase detector is used on the output side of the amplifier stage to detect the phase difference between adjacent beams, and a phase modulator (e.g., before or after the amplification stage) is used to correct the phase difference detected using the phase detector. However, the actuator schemes commonly used for phase control have various drawbacks.

[0016] For example, the actuator schemes commonly used for phase control include piezoelectric arrays and / or liquid phase masks, etc. In one phase control technique, a photodiode after the combining element can be used for phase optimization and stabilization, and a heterodyne jitter scheme operating at radio frequency is used to modulate the phase of each core at slightly different frequencies. The resulting signal on the photodiode can then be analyzed to generate the mutual phase difference. Another method using a single photodiode uses an optimization algorithm called stochastic parallel gradient descent (SPGD), which is an iterative method and is thus slower than any direct phase measurement technique (e.g., fast phase fluctuations are not correctable). Alternatively, the mutual phase difference of each pair of combined beams can be measured using a heterodyne coherent detector (HCD). In this method, the interference assigns the signal to two ports according to the mutual phase.

[0017] For example, Figure 1 FIG. is a diagram illustrating an example 100 of a phase detection system that can be used for CBC of two channels. For polarization beam combination, polarization detection is typically used to measure the phase difference between two orthogonally polarized beams. For example, as shown in Figure 1As shown by reference numeral 110 in the drawings, a small portion of the combined laser beam can be directed to the HCD 120, which includes a polarization beam splitter (PBS) 122, a quarter-wave plate (QWP) 124, and two photodiodes 126-1 and 126-2. There is a 45° difference between the axis of the QWP 124 and the axis of the PBS 122, which results in splitting into two laser beams with orthogonal polarizations. The two photodiodes 126-1 and 126-2 are located in different output ports of the PBS 122 and are used to measure the beam power and generate electrical signals representing the corresponding beam powers, which are used to calculate the detection signal 130 based on the difference between the beam powers. For example, as Figure 1 shown, the first photodiode 126-1 generates a first electrical signal I representing the beam power from the first output port of the PBS 122 s , and the second photodiode 126-2 generates a second electrical signal I representing the beam power from the second output port of the PBS 122 p . Thus, as shown by reference numeral 135, the detection signal 130I out can be calculated by determining the difference between the first electrical signal and the second electrical signal (e.g., I s -I p ), where the maximum difference between the first electrical signal and the second electrical signal I max is based on the sum of the absolute values of I s and I p . As further shown by reference numeral 135, when the value of the detection signal 130 is 0, the phase between the two beams is 0. Alternatively, when the value of the detection signal 130 is I max , the phase between the two beams is π / 2, or when the value of the detection signal 130 is negative I max , the phase between the two beams is -π / 2. Thus, using the method, the phase difference between the two optical signals is indicated by the detection signal 130, which is provided to the control system 140, which then controls the phase modulator 150 to adjust the phase of one or more of the two beams based on their phase difference.

[0018] In an ideal CBC of two orthogonally polarized beams with the same power and phase, the combined beam is fully linearly polarized and rotated by 45° compared to the initial input beams. If a sample of the combined beam is directed towards HCD 120, a QWP 124 rotated by 45° with respect to the axis of PBS122 produces a circularly polarized beam. PBS122 then divides the circularly polarized beam into two orthogonally polarized beams with the same optical power. In this state, the detection signal 130 can be zero, indicating perfect in-phase between the channels. In this way, the HCD 120 method provides a direct single-shot technique to control the phase (e.g., potentially enabling a feedback bandwidth up to the pulse repetition rate). Additionally, HCD 120 can be parallelized for multiple co-propagating beams. However, the HCD technique has various drawbacks. For example, HCD 120 requires beam splitters, wave plates, and mirrors, and precise alignment is needed for each pair of recombined sub-beams. Using beam splitters may require precise lateral alignment to ensure spatial overlap and path length matching of the pulsed lasers, thus ensuring temporal overlap. Additionally, using polarization beam splitters (e.g., PBS122) requires sending each pair of beams to each PBS at an angle of 90°, which occupies a large amount of space. Therefore, some implementations described in further detail herein involve a phase detector that uses wave plates and birefringent windows to achieve mirrorless phase detection in a collinear arrangement (e.g., in contrast to designs that use polarization beam splitters and mirrors to overlap and split beams). In this way, some implementations described herein can provide a compact and simple phase detector (e.g., occupying less space than HCD) that can directly detect phase errors within an array of co-propagating beams to correct phase differences that could otherwise result in losses in combined efficiency and / or output energy fluctuations. Design contrast).

[0019] Figure 2 FIG. is a diagram illustrating an example implementation associated with a collinear phase detector 200 that can be used in the coherent beam combining system described herein. As described herein, the collinear phase detector 200 can achieve a compact, simple, and direct detection of phase errors within a beam array 210 including multiple beams co-propagating in parallel, because phase differences between the beams in the beam array 210 could otherwise result in losses in combined efficiency and / or output energy fluctuations. For example, in some implementations, the collinear phase detector 200 provides an alignment-free optical arrangement to directly detect phase changes within the beam array 210. For example, compared to a configuration with a polarization beam splitter as Figure 1 shown, the collinear phase detector 200 includes various optical devices arranged in a linear optical path. Therefore, the collinear phase detector 200 is more compact and does not require folding mirrors to overlap individual beams, which greatly simplifies the alignment process.

[0020] For example, as Figure 2 shown, the beam array 210 includes a plurality of beams (beams B 0 , B 1 , ……, B N ) that co-propagate in parallel with a specific polarization, where each beam B i is associated with a corresponding phase Φ i . For example, as Figure 2 shown, the first beam B n is associated with the first phase Φ n , the second beam B n+1 is associated with the second phase Φ n+1 , and so on. In addition, in Figure 2 , the dashed line indicates horizontal polarization, the dotted line indicates vertical polarization, and the solid line indicates the superposition of horizontal and vertical polarizations. Thus, in some implementations (e.g., as Figure 2 shown), the parallel beams in the beam array 210 can co-propagate with horizontal polarization. Alternatively, in some implementations, the beams in the beam array 210 can co-propagate with vertical polarization or another suitable linear polarization. In addition, although Figure 2 illustrates a scenario where the collinear phase detector 200 is used to determine the phase difference between two input beams, the beam array 210 can include more than two beams, and the collinear phase detector 200 can appropriately measure the phase difference between any two adjacent beams in the beam array 210. In addition, the collinear phase detector 200 can be used to measure the phase difference between two non-adjacent beams in the beam array 210 (e.g., the phase difference between beam B n and beam B n+2 can be determined based on the first phase difference between beam B n and beam B n+1 and the second phase difference between beam B n+1 and beam B n+2 ).

[0021] As Figure 2 further shown, the collinear phase detector 200 includes a first HWP 220. In some implementations, the first input beam B n and the second input beam B n+1 are received at the first HWP 220, which can be oriented at a specific angle θ with respect to the propagation axis of the co-propagating beams in the beam array 210 such that the first HWP 220 rotates the polarization of the first input beam B n and the second input beam B n+1 to 2θ. For example, in some implementations, the first HWP 220 can be oriented at an angle of 22.5° with respect to the propagation axis of the beams in the beam array 210, whereby the first HWP 220 rotates the polarization of the first input beam B n and the second input beam B n+1 to 45°.

[0022] As Figure 2 Further shown, the collinear phase detector 200 includes a first birefringent window 230 disposed after the first HWP 220, and the first birefringent window is configured to divide or split the first input beam B n into a first pair of sub-beams associated with orthogonal polarizations, and divide or split the second input beam B n+1 into a second pair of sub-beams associated with orthogonal polarizations. For example, as Figure 2 shown, the first birefringent window 230 splits each input beam into a pair of sub-beams, and the pair of sub-beams includes a first sub-beam having horizontal polarization (shown by the dashed line) and a second sub-beam having vertical polarization (shown by the dotted line). The first birefringent window 230 can be made of any suitable birefringent material, such as an α-barium borate (α-BBO, α-BaB2O4 or α-BBO) birefringent crystal, undoped vanadate, calcite, and / or rutile. Since the first birefringent window 230 has birefringence (e.g., refractive indices depending on the polarization and propagation direction of the input light), the first birefringent window 230 can refract orthogonal polarizations (e.g., ordinary polarization and extraordinary polarization) at different angles. As Figure 2 shown, two copies of each beam (e.g., each pair of sub-beams) are offset in the transverse direction (e.g., shown by the vertical arrow) away from the first birefringent window 230. For example, the incident beam enters the first birefringent window 230, and the outgoing beam leaves the first birefringent window 230 in the same propagation direction, with the corresponding propagation axes being laterally offset. In addition, in some implementations, the first birefringent window 230 can have a thickness and / or an angle based on the spacing between the input beams. For example, the thickness and / or the angle of the first birefringent window 230 can cause the first birefringent window 230 to laterally offset the propagation axes of the two copies of each beam by half of the incident beam spacing. In addition, the angle of the first birefringent window 230 can be matched to avoid introducing additional phase.

[0023] As Figure 2 Further shown, the collinear phase detector 200 includes a second HWP 240 disposed after the first birefringent window 230, and the second HWP is configured to reverse the orthogonal polarizations associated with the first pair of sub-beams and the second pair of sub-beams (e.g., the second HWP 240 reverses the polarization of each sub-beam). For example, in Figure 2 the first birefringent window 230 divides the first input beam B n and the second input beam B n+1Split into two corresponding sub-beam pairs, each sub-beam pair including a first sub-beam with horizontal polarization (shown by the dashed line) and a second sub-beam with vertical polarization (shown by the dotted line). Thus, the second HWP 240 can be oriented at 45° to reverse the polarization of each sub-beam, such that each sub-beam entering the second HWP 240 with horizontal polarization exits the second HWP 240 with vertical polarization. Similarly, each sub-beam entering the second HWP 240 with vertical polarization exits the second HWP 240 with horizontal polarization.

[0024] As Figure 2 Further shown, the collinear phase detector 200 includes a second birefringent window 250 disposed after the second HWP 240, which is used to refract and shift the first sub-beam pair and the second sub-beam pair such that the first sub-beam in the first sub-beam pair and the second sub-beam in the second sub-beam pair form an overlapping beam. For example, in Figure 2 which, the two sub-beam pairs entering the second birefringent window 250 include a first sub-beam pair associated with the first input beam B n and a second sub-beam pair associated with the second input beam B n+1 as shown, the first sub-beam pair includes a sub-beam with horizontal polarization, and the second sub-beam pair includes a sub-beam with vertical polarization, where the refraction and lateral shift occurring in the second birefringent window 250 cause the horizontally polarized sub-beam in the first sub-beam pair and the vertically polarized sub-beam in the second sub-beam pair to form an overlapping beam when exiting the second birefringent window 250. In some implementations, the second birefringent window 250 can be made of any suitable birefringent material (e.g., α-BBO birefringent crystal, undoped vanadate, calcite, and / or rutile), which can be the same as or different from the birefringent material used for the first birefringent window 230. Additionally, the second birefringent window 250 can also have a thickness and / or an angle based on the spacing between the input beams (e.g., the second birefringent window 250 can have a thickness and / or an angle that causes the second birefringent window 250 to laterally shift each beam by half of the incident beam spacing).

[0025] As Figure 2 Further shown, the collinear phase detector 200 includes an analyzer 260 disposed after the second birefringent window 250, which is used to split the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity. For example, as Figure 2As shown, the analyzer may include a QWP 262 disposed after the second birefringent window 250 and a third birefringent window 264 disposed after the QWP 262. In some implementations, the third birefringent window 264 may be made of any suitable birefringent material, which may be the same as or different from the birefringent material used for the first birefringent window 230 and / or the second birefringent window 250. In some implementations, one or more of the first birefringent windows 230 may be coated with an anti-reflection coating (e.g., to ensure better transmission and avoid ghosting when generating additional beam copies during multiple reflections). In some implementations, the QWP 262 may transform the polarization state of the overlapping beam (which is a function of the phase difference between the two input beams) into a polarization state that can then be split by the third birefringent window 264. For example, the third birefringent window 264 may split the polarization state of the overlapping beam according to a splitting ratio that depends on the polarization ratio (e.g., removing the QWP 262 from the collinear arrangement will result in a splitting ratio of 1:1 at all times). For example, in some implementations, the QWP 262 may transform a left-handed circular input polarization into a horizontal output polarization, a right-handed circular input polarization into a vertical output polarization, and / or a linear input polarization of 45° into a linear output polarization of 45° (unchanged). Thus, depending on the input phase, the beam entering the QWP 262 is linearly polarized at 45° (corresponding to an input phase of zero), circularly polarized (e.g., left-handed or right-handed with an input phase of ±π), or elliptically polarized, and then the third birefringent window 264 splits the overlapping beam to generate a set of split beams 280. Thus, the intensity difference between the split beams 280 is related to the initial phase difference by the following formula:

[0026]

[0027] where I n，n+1，a and I n，n+1，b are the intensities of the respective beams, and the difference between the intensities is approximately equal to the sine of the phase difference between the first input beam B n and the second input beam B n+1 . Generally, the intensities are equal only when the phase difference between the first input beam B n and the second input beam B n+1 is zero. In this way, the feedback loop may include one or more devices (e.g., a camera or a photodiode array sensitive to the laser wavelength) to measure the intensity, such that the feedback loop acting on the phase control can stabilize the phase within the beam array 210. For example, the feedback loop may include one or more devices or components that can generate a control signal for modulating the first input beam B n or the second input beam B n+1 according to the phase difference between the first input beam B n and the second input beam B n+1the phase of one or more input beams, thereby enabling coherent combination of the various beams in the beam array 210. Additionally, for a two-dimensional beam array, a second instance of the collinear phase detector 200 can be rotated 90° and added to Figure 2 the collinear phase detector 200 shown.

[0028] Figure 2 is provided as an example. Other examples may be different from those described with respect to Figure 2 the device described. Figure 2 The number and arrangement of the devices shown are provided only as examples. In practice, there may be more devices, fewer devices, different devices, or differently arranged devices compared to those Figure 2 shown. Additionally, Figure 2 two or more of the devices shown can be implemented within a single device, or Figure 2 a single device shown can be implemented as multiple distributed devices. Additionally or alternatively, Figure 2 a set of devices shown can perform one or more functions described as being performed by Figure 2 another set of devices shown.

[0029] Figure 3 is a diagram illustrating an example implementation of a coherent beam combining system 300 including the collinear phase detector 200 described herein.

[0030] For example, in some implementations, the coherent beam combining system 300 can include or be coupled to a laser source configured to generate a seed laser 305. As Figure 3 shown, the coherent beam combining system 300 includes a splitting stage 310 that includes one or more optical devices configured to split the seed laser 305 into a beam array 315 that includes various input beams co-propagating in parallel with a specific polarization (e.g., horizontal or vertical). As Figure 3 further shown, the coherent beam combining system includes an amplification stage 320 that includes a plurality of amplifiers, each amplifier being arranged to amplify an individual input beam in the beam array to form a set of amplified beams 325. As further shown, the coherent beam combining system 300 includes a combining stage that includes one or more optical devices configured to combine the amplified beams 325 into a single output beam 335. Additionally, as shown, there may be a loss 340 of energy or power (e.g., due to the phase difference between the various beams in the beam array 315) after the combining stage 330. Thus, as Figure 3 shown, the collinear phase detector 200 can be disposed after the amplification stage 320 to measure the phase difference between the beams in the beam array 315, as described in more detail above with respect to Figure 2 Specifically, the collinear phase detector 200 can generate one or more signals indicative of the phase difference between the beams in the beam array 315. AsFigure 3 As shown, the signal(s) indicating the phase difference between the beams in beam array 315 can be provided to control system 345, which can actuate or otherwise control one or more phase modulators 350 to stabilize the phases of the individual beams in beam array 315 and thereby minimize loss 340.

[0031] Figure 3 is provided as an example. Other examples can be different from those described with respect to Figure 3 the device(s) shown. Figure 3 The number and arrangement of the devices shown are provided only as an example. In practice, there can be more devices, fewer devices, different devices, or differently arranged devices compared to those Figure 3 shown. Additionally, Figure 3 two or more of the devices shown can be implemented within a single device, or Figure 3 a single device shown can be implemented as multiple distributed devices. Additionally or alternatively, Figure 3 a set of devices shown can perform one or more functions described as being performed by Figure 3 another set of devices shown.

[0032] Figure 4 is a flow diagram of an example process 400 associated with phase detection in a coherent beam combining system. In some implementations, Figure 4 one or more of the process blocks of Figure 4 are performed by a phase detector (e.g., phase detector 200). In some implementations,

[0033] As Figure 4 shown, process 400 can include receiving a first input beam and a second input beam (block 410). For example, the first input beam and the second input beam can be received at phase detector 200, which includes a plurality of optical devices arranged in a linear optical path as described above.

[0034] As Figure 4 further shown, process 400 can include dividing the first input beam into a first pair of sub-beams associated with orthogonal polarizations and dividing the second input beam into a second pair of sub-beams associated with orthogonal polarizations (block 420). For example, phase detector 200 can divide the first input beam into a first pair of sub-beams associated with orthogonal polarizations and divide the second input beam into a second pair of sub-beams associated with orthogonal polarizations as described above.

[0035] As Figure 4As further shown, process 400 may include offsetting the first sub-beam pair and the second sub-beam pair such that the first sub-beam in the first sub-beam pair and the second sub-beam in the second sub-beam pair form an overlapping beam (block 430). For example, phase detector 200 may offset the first sub-beam pair and the second sub-beam pair such that the first sub-beam in the first sub-beam pair and the second sub-beam in the second sub-beam pair form an overlapping beam, as described above.

[0036] As Figure 4 As further shown, process 400 may include splitting the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, wherein the difference between the first intensity and the second intensity is related to the phase difference between the first input beam and the second input beam (block 440). For example, phase detector 200 may split the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, wherein the difference between the first intensity and the second intensity is related to the phase difference between the first input beam and the second input beam, as described above.

[0037] Process 400 may include additional implementations, such as any individual implementation or any combination of implementations described below and / or in combination with one or more other processes described elsewhere herein.

[0038] In a first implementation, process 400 includes providing a signal indicating the phase difference between the first input beam and the second input beam to a control system 345, the control system being configured to modulate one or more of a first phase of the first input beam or a second phase of the second input beam based on the phase difference.

[0039] In a second implementation, either alone or in combination with the first implementation, the first input beam and the second input beam are received at a first HWP 220 configured to rotate the polarization of the first input beam and the second input beam to 45°.

[0040] In a third implementation, either alone or in combination with one or more of the first implementation and the second implementation, the first input beam and the second input beam are divided into a first sub-beam pair and a second sub-beam pair by a first birefringent window 230 disposed after the first HWP 220.

[0041] In a fourth implementation, either alone or in combination with one or more of the first implementation through the third implementation, process 400 includes reversing the orthogonal polarizations associated with the first sub-beam pair and the second sub-beam pair by a second HWP 240 disposed after the first birefringent window 230.

[0042] In a fifth implementation, either alone or in combination with one or more of the first implementation through the fourth implementation, the first sub-beam pair and the second sub-beam pair are offset by a second birefringent window 250 disposed after the second HWP 240.

[0043] In a sixth implementation, alone or in combination with one or more of the first through fifth implementations, an overlapping beam is split by analyzer 260 into a first output beam and a second output beam, the analyzer including a QWP 262 disposed after second birefringent window 250 and a third birefringent window 264 disposed after quarter-wave plate 262.

[0044] In a seventh implementation, alone or in combination with one or more of the first through sixth implementations, the difference between the first intensity and the second intensity is approximately equal to the sine of the phase difference between the first input beam and the second input beam.

[0045] Although Figure 4 example boxes of process 400 are shown, in some implementations, process 400 includes more boxes, fewer boxes, different boxes, or boxes arranged differently than shown. Additionally or alternatively, two or more boxes of process 400 may be executed in parallel. Figure 4 The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit implementations to the precise forms disclosed. Modifications and variations may be made in light of the foregoing disclosure, or may be acquired from practice of the implementations. Additionally, any implementations described herein may be combined unless the foregoing disclosure expressly provides a reason that one or more implementations cannot be combined.

[0046] As used herein, the term "component" is intended to be broadly construed as hardware, firmware, and / or a combination of hardware and software. It is evident that the systems and / or methods described herein may be implemented in different forms of hardware, firmware, or combinations of hardware and software. The actual specific control hardware or software code used to implement these systems and / or methods does not limit these implementations. Accordingly, the operations and behaviors of the systems and / or methods are described herein without reference to specific software code - it being understood that software and hardware may be designed to implement these systems and / or methods based on the description herein.

[0047] As used herein, depending on the context, meeting a threshold may refer to a value being greater than a threshold, greater than or equal to a threshold, less than a threshold, less than or equal to a threshold, equal to a threshold, not equal to a threshold, and so on.

[0048]

[0049] ​Although specific combinations of features are recited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and / or not specifically disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes the combination of each dependent claim with every other claim in the claim set. As used herein, the phrase "at least one" in reference to a list of items means any combination of those items, including a single member. For example, "at least one of a, b, or c" is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as combinations of multiple items of the same.

[0050] When one or more components (e.g., a laser emitter or one or more laser emitters) are described or claimed (within a single claim or across multiple claims) as performing multiple operations or being configured to perform multiple operations, such language is intended to broadly cover a variety of architectures and environments. For example, unless otherwise specifically claimed (e.g., by using "a first component" and "a second component" or other language that differentiates components in the claim), such language is intended to cover a single component performing or being configured to perform all operations, a group of components jointly performing or being configured to perform all operations, a first component performing or being configured to perform a first operation and a second component performing or being configured to perform a second operation, or any combination of components performing or being configured to perform the operations. For example, when a claim is in the form "one or more components are configured to: perform X; perform Y; and perform Z," the claim should be interpreted as "one or more components are configured to perform X; one or more (possibly different) components are configured to perform Y; and one or more (also possibly different) components are configured to perform Z."

[0051] Unless expressly stated otherwise, no element, act, or instruction used herein shall be construed as critical or essential. Additionally, as used herein, the articles "a" and "an" are intended to include one or more items and may be used interchangeably with "one or more." Additionally, as used herein, the article "the" is intended to include one or more items referenced in conjunction with the article "the" and may be used interchangeably with "one or more." Additionally, the term "set" as used herein is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and may be used interchangeably with "one or more." If only one item is intended, the phrase "only one" or similar language is used. Additionally, as used herein, the terms "having," "comprising," "containing," etc. are intended to be open-ended terms. Additionally, unless expressly stated otherwise, the term "based on" is intended to mean "at least partially based on." Additionally, as used herein, the term "or" is inclusive when used in series and may be used interchangeably with "and / or" unless expressly stated otherwise (e.g., if used in conjunction with "any one of..." or "only one of..."). Additionally, for ease of description, spatial relative terms (such as "below," "lower," "above," "upper," etc.) may be used herein to describe the relationship of one element or feature to other elements or features shown in the figures. Except for the orientation shown in the figures, spatial relative terms are intended to encompass different orientations of the device, apparatus, and / or element in use or operation. The device may be oriented otherwise (rotated 90 degrees or in other orientations), and the spatial relative descriptors used herein may be interpreted accordingly.

Claims

1. A phase detector, comprising: a first half-wave plate arranged to receive a first input beam and a second input beam co-propagating in a first polarization and to rotate the first polarization to 45 degrees; a first birefringent window, arranged after the first half-wave plate, for dividing the first input beam into a first pair of sub-beams associated with orthogonal polarizations, and dividing the second input beam into a second pair of sub-beams associated with orthogonal polarizations; a second half-wave plate, arranged after the first birefringence window, for inverting orthogonal polarizations associated with the first pair of sub-beams and the second pair of sub-beams; a second birefringence window, arranged after the second half-wave plate, for refracting and shifting the first sub-beam pair and the second sub-beam pair so that a first sub-beam in the first sub-beam pair and a second sub-beam in the second sub-beam pair form overlapping beams; as well as an analyzer, arranged after the second birefringence window, for splitting the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, The difference between the first intensity and the second intensity is related to the following term: the phase difference between the first input beam and the second input beam.

2. The phase detector according to claim 1, wherein the first half-wave plate, the first birefringence window, the second half-wave plate, the second birefringence window and the analyzer are arranged in a linear optical path.

3. The phase detector of claim 1 , wherein the first birefringence window and the second birefringence window are made of a birefringent material, the birefringent material comprising one or more of: α-barium borate crystals, undoped vanadate, calcite, or rutile.

4. The phase detector of claim 1, wherein the first and second birefringent windows refract orthogonal polarizations at different angles to laterally shift the propagation axes of the first and second beamlet pairs.

5. The phase detector of claim 1, wherein thicknesses and angles of the first and second birefringence windows are based on a spacing between the first and second input beams.

6. The phase detector of claim 1 , wherein the analyzer comprises: a quarter wave plate, arranged after the second birefringence window; as well as The third birefringence window is arranged after the quarter wave plate.

7. The phase detector of claim 1, wherein the difference between the first intensity and the second intensity is approximately equal to the sine of the phase difference between the first input beam and the second input beam.

8. The phase detector of claim 1 , further comprising: A feedback loop comprises one or more devices configured to measure the first intensity and the second intensity and to generate a control signal for modulating the phase of one or more of the first input beam or the second input beam according to the phase difference between the first input beam and the second input beam.

9. A method for phase detection to achieve coherent beam combining, comprising: receiving the first input beam and the second input beam by a phase detector, the phase detector comprising a plurality of optical devices arranged in a linear optical path; splitting, by the phase detector, the first input beam into a first pair of beamlets associated with orthogonal polarizations and splitting the second input beam into a second pair of beamlets associated with orthogonal polarizations; offsetting the first pair of beamlets and the second pair of beamlets by the phase detector so that a first beamlet in the first pair of beamlets and a second beamlet in the second pair of beamlets form overlapping beams; as well as splitting, by the phase detector, the overlapping beams into a first output beam associated with a first intensity and a second output beam associated with a second intensity, Wherein a difference between the first intensity and the second intensity is related to a phase difference between the first input beam and the second input beam.

10. The method according to claim 9, further comprising: A signal indicative of the phase difference between the first input beam and the second input beam is provided to a control system configured to modulate one or more of a first phase of the first input beam or a second phase of the second input beam in accordance with the phase difference.

11. The method of claim 9, wherein the first input beam and the second input beam are received at a first half-wave plate, the first half-wave plate being configured to rotate polarization of the first input beam and the second input beam to 45 degrees. 12 . The method of claim 11 , wherein the first input beam and the second input beam are divided into the first pair of sub-beams and the second pair of sub-beams by a first birefringence window, the first birefringence window being arranged after the first half-wave plate.

13. The method according to claim 12, further comprising: The orthogonal polarizations associated with the first pair of sub-beams and the second pair of sub-beams are inverted by a second half-wave plate, which is arranged after the first birefringence window.

14. The method of claim 13, wherein the first pair of sub-beams and the second pair of sub-beams are offset by a second birefringence window, the second birefringence window being arranged after the second half-wave plate.

15. The method of claim 14, wherein the overlapping beams are split into the first output beam and the second output beam by an analyzer comprising: a quarter wave plate arranged after the second birefringence window; and The third birefringence window is arranged after the quarter wave plate.

16. The method of claim 9, wherein the difference between the first intensity and the second intensity is approximately equal to the sine of the phase difference between the first input beam and the second input beam.

17. An optical system comprising: a laser source configured to generate a seed laser; a splitting stage comprising one or more optical devices configured to split the seed laser into a beam array including a first input beam and a second input beam co-propagating at a first polarization; an amplifier stage, comprising a first amplifier and a second amplifier, wherein the first amplifier is used to amplify the first input beam, and the second amplifier is used to amplify the second input beam; a combining stage comprising one or more optical devices configured to combine the first amplified input beam and the second amplified input beam to generate an output beam; A phase detector, arranged after the amplification stage, comprises: a first half-wave plate arranged to receive the first input beam and the second input beam and to rotate the first polarization to 45 degrees; a first birefringent window, arranged after the first half-wave plate, for dividing the first input beam into a first pair of sub-beams associated with orthogonal polarizations, and dividing the second input beam into a second pair of sub-beams associated with orthogonal polarizations; a second half-wave plate, arranged after the first birefringence window, for inverting orthogonal polarizations associated with the first pair of sub-beams and the second pair of sub-beams; a second birefringence window, arranged after the second half-wave plate, for refracting and shifting the first beamlet pair and the second beamlet pair so that a first beamlet in the first beamlet pair and a second beamlet in the second beamlet pair form overlapping beams; and an analyzer, arranged after the second birefringence window, for splitting the overlapping beam into a first output beam associated with a first intensity and a second output beam associated with a second intensity, wherein a difference between the first intensity and the second intensity is related to: a phase difference between the first input beam and the second input beam; and A feedback loop comprising one or more devices configured to measure the first intensity and the second intensity and to generate a control signal for modulating the phase of one or more of the first input beam or the second input beam according to the phase difference between the first input beam and the second input beam before the amplification stage.

18. The optical system of claim 17, wherein the first half-wave plate, the first birefringent window, the second half-wave plate, the second birefringent window, and the analyzer are arranged in a linear optical path.

19. The optical system of claim 17, wherein thicknesses and angles of the first and second birefringent windows are based on a separation between the first and second input beams.

20. The optical system of claim 17, wherein the difference between the first intensity and the second intensity is approximately equal to the sine of the phase difference between the first input beam and the second input beam.

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