CN1688069A - Phase locking multi-light beam coherent superimposed optical fiber laser - Google Patents

Abstract

The invention belongs to the technical field of fiber lasers, and in particular relates to a phase-locked multi-beam coherent superposition fiber laser. The laser is composed of a fiber laser that outputs polarized light, a fiber phase modulator, a fiber amplifier, a fusion-tapered polarization-maintaining fiber coupler, and a feedback control circuit. It is a phase-locked multi-beam coherent superposition fiber laser with high output power and high beam quality. It is widely used in many fields such as industrial laser processing, medical treatment, optical communication, image recording and printing, computer and microelectronics manufacturing, and military affairs.

Description

Phase-locked multi-beam coherent superposition fiber laser

Technical field:

The invention relates to a fiber laser, in particular to a fiber laser with coherent superposition output of phase-locked multi-laser beams.

technical background:

Fiber lasers have been around almost as long as the lasers themselves. Not long after the advent of lasers, Znitzer and Koestor of American Optical Corporation first proposed the idea of fiber lasers and amplifiers in 1963. Fiber laser has the characteristics of high efficiency, low threshold, narrow line width, tunable, compact, high cost performance, easy to manufacture, rich wavelength, etc. It is widely used in optical communication, industrial processing, medicine, scientific research, image recording and printing, computer and Microelectronics manufacturing, spectroscopy and other fields have a very wide range of uses. By superimposing multiple laser beams, if the multiple laser beams meet the complete coherence condition, high-power and near-diffraction-limited laser light can be obtained. The incoherent superposition of N laser beams with the same power will increase the light intensity by N times, while if the coherent superposition is performed, the amplitude will increase by N times and the light intensity will increase by ^N2 times. Considering benefits and costs, the coherent superposition scheme is more ideal. However, in order to achieve coherent superposition between multiple laser beams, the conditions of the same frequency, consistent polarization, and phase matching must be met. The phase of conventional laser output lasers has random drift, and each laser beam passes through different optical paths. There is a phase difference between them; for the polarization state of each laser beam, even if the laser output from the light source is linearly polarized, after a certain distance of optical fiber transmission, the polarization state will change due to the mode birefringence of the optical fiber; for each laser beam The frequency of the beam, the nonlinear effect in the fiber may cause frequency differences between the laser beams, so in order to achieve multi-beam coherence, it is necessary to control the same frequency, uniform polarization and phase matching of each laser beam to achieve complete coherence conditions.

At present, the method to achieve multi-beam fiber laser superposition is mostly through the incoherent superposition method, which bundles multiple output fibers of the fiber laser into one bundle, which can realize a high-power fiber laser, but the output is multi-mode light, and the beam quality factor is A few mm*mrad or even a dozen mm*mrad, the beam quality is very poor, which limits the application of this fiber laser to industrial fields that do not require high beam quality. The research on the coherent superposition of fiber lasers is still in the laboratory stage. S.J.Augst et al. conducted experimental research on the coherent combination of two fiber lasers, and realized the coherent superposition of two fiber lasers through phase locking. However, due to the introduction of deformation in the structure Non-fiber optic components such as prism pairs and beam splitters do not have an all-fiber structure. The introduction of non-fiber optic components also limits the maximum power that the system can obtain, and only realizes the coherent superposition of two fiber lasers.

Invention content:

In order to solve the problem that the superimposed beam energy in the incoherent superposition of multiple laser beams is just a simple addition of the energy of each laser beam, and the beam quality of the multi-mode output after superimposition is not good, the invention realizes the phase locking of multiple laser beams, and provides a A fully coherent and single-mode laser is output to obtain a fiber laser with higher power and better beam quality than ordinary multi-laser beams without phase locking.

The present invention includes a fiber laser 1 that outputs polarized light, a polarization-maintaining fiber isolator 2, a 1×N+1 fusion-tapered polarization-maintaining fiber coupler 3, a fiber phase modulator 4, a fiber amplifier 5, and a 90:10 polarization-maintaining fiber coupling 6, 1×N fusion-tapered polarization-maintaining fiber coupler 7, 1×2 fusion-tapered polarization-maintaining fiber coupler 8, feedback control circuit 9, lens 10, avalanche photodiode or PIN photodiode 11, high-frequency amplifier 12 . The entire system uses polarization-maintaining fiber, and ensures that the optical paths of the N-beam lasers from the 90:10 polarization-maintaining fiber coupler 6 to the 1×2 fusion-tapered polarization-maintaining fiber coupler 8 are equal, ensuring that the N-beam lasers The optical paths of the N fusion-tapered polarization-maintaining fiber coupler 7 to the 1×2 fusion-tapered polarization-maintaining fiber coupler 8 are equal.

The function of fiber laser 1 is to provide linearly polarized laser light.

The function of the polarization-maintaining fiber isolator 2 is to ensure the unidirectional transmission of the polarized laser beam output from the fiber laser 1 that outputs polarized light, to prevent the possible harm to the fiber laser 1 caused by the reflected light that may appear in the optical path, and to improve the system reliability. Stability, reduce the impact of noise.

The function of 1×N+1 fusion-tapered polarization-maintaining fiber coupler 3 is to divide a beam of polarized laser into N+1 beams while keeping the same polarization state of N+1 beams of lasers. Among the N+1 beams of lasers, there is a laser beam As a reference laser beam, it is divided into N beams in the secondary optical path B; the other N beams of polarized laser are modulated and amplified in the main optical path A. After complete coherence, the laser intensity increases by ^N2 , which can obtain high power and high beam quality laser output.

The function of the fiber phase modulator 4 is to compensate the phase difference between N bundles of fiber lasers to achieve ideal precise phase modulation. The fiber phase modulator 4 receives the feedback signal given by the feedback control circuit 9 to make the N bundles of fiber lasers on the main optical path A The phases of the optical fiber phase modulators are consistent to achieve phase locking, and the use of the optical fiber phase modulator 4 fundamentally reduces the insertion loss and echo reflection of the device.

The function of fiber amplifier 5 is to amplify the power of N beams of fiber lasers. Although the intensity of N beams of fiber lasers is completely coherent, the intensity is N2 ^times that of a single beam of laser light. However, in order to achieve high-power laser output, it is necessary to control the power of the main optical path A. The power of each fiber laser is amplified, so the fiber amplifier 5 is used to amplify the N beams of fiber lasers on the main optical path A with the same power, so that the coherently superimposed laser has a higher power, and a 10W fiber amplifier can be used. 10W The power will not significantly excite the nonlinear effect in the fiber and cause the laser frequency to shift, which ensures that the N beams of fiber lasers have the same frequency and meet the conditions of complete coherence, and the power of each fiber laser of 10W is right to obtain high-power coherent laser That's enough.

The function of the 90:10 polarization-maintaining fiber coupler 6 is to split the fiber laser amplified by the fiber amplifier 5, 90% of the fiber laser is output from the end face of the fiber, and after being focused by the lens 10, it is coherently superimposed in free space to obtain high power and coherent laser with high beam quality; 10% of the fiber laser passes through the same optical path from the 90:10 polarization-maintaining fiber coupler 6 to the 1×2 fusion-tapered polarization-maintaining fiber The polarization-maintaining fiber coupler 8 is superimposed with the reference laser beam. The intensity of the superimposed laser reflects the respective phase differences between the N beams of fiber lasers on the main optical path A and the reference laser. The superimposed laser intensity is detected by the avalanche photodiode or PIN photodiode 11 to detect and convert the phase difference into a control electrical signal. The signal is amplified by the feedback control circuit 9, and then acts on the optical fiber phase modulator 4, so that the phases of the N bundles of fiber lasers on the main optical path A tend to be consistent with the phases of the reference laser, and realize the phase adjustment of the N bundles of fiber lasers on the main optical path A. locking.

The function of the 1×N fusion-tapered polarization-maintaining fiber coupler 7 is to divide the reference laser light obtained from the 1×N+1 fusion-tapered polarization-maintaining fiber coupler 3 into N beams, which are respectively coupled with the 90:10 polarization-maintaining fiber The N beams of laser light on the main optical path A split by 10% in the device 6 are superimposed in the 1×2 fusion-tapered polarization-maintaining fiber coupler 8, and the superimposed light is transmitted to the avalanche in the feedback control circuit 9 through the secondary optical path B. photodiode or PIN photodiode 11.

The function of the 1×2 fusion-tapered polarization-maintaining fiber coupler 8 is to make the reference laser obtained from the 1×N fusion-tapered polarization-maintaining fiber coupler 7 separate from the 90:10 polarization-maintaining fiber coupler on the main optical path A by 6 minutes. The beams out of the fiber laser are superimposed. Due to the phase difference between the N bundles of fiber lasers on the main optical path A, the N bundles of fiber lasers containing 10% of the energy in the main optical path A and the reference laser obtained from the 1×N fusion-tapered polarization-maintaining fiber coupler 7 are at 1× 2 The superimposed light intensity in the fusion-tapered polarization-maintaining fiber coupler 8 is different, and this difference reflects the phase difference between the N beams of fiber lasers on the main optical path A. The reasons for the phase difference of the laser beams on the main optical path A include the influence of the amplifier, the influence of the optical fiber phase modulator, temperature fluctuations, and the difference in the optical path of each optical path.

The function of the feedback control circuit 9 is to detect the strength of the light from the 1×2 fusion-tapered polarization-maintaining fiber coupler 8, and convert it into an electrical signal to act on the optical fiber phase modulator 4 to modulate the N beams on the main optical path A The fiber laser phase tends to be consistent. The feedback control circuit 9 is composed of an avalanche photodiode or PIN photodiode 11 and a high frequency amplifier 12 . The function of the avalanche photodiode or PIN photodiode 11 is to detect the light intensity transmitted from the 1×2 fused-taper polarization-maintaining fiber coupler 8 and convert it into an electrical signal through the avalanche photodiode or PIN photodiode 11 . The electrical signal is amplified by the high-frequency amplifier 12 and then acts on the optical fiber phase modulator 4 to implement phase regulation on the N bundles of fiber lasers on the main optical path A. As long as the response time of the feedback control circuit 9 is sufficiently small compared with the coherence time of the laser light, good tracking and control of the phases of the N beams of fiber lasers on the main optical path A can be achieved. In this way, the phases of the N beams of fiber lasers on the main optical path A tend to be consistent with the phases of the reference lasers obtained from the 1×N+1 fusion-tapered polarization-maintaining fiber coupler, realizing the realization of the N beams of fiber lasers on the main optical path A Phase locking means that the coherent superposition of N beams of fiber lasers on the main optical path A in free space is realized, thereby obtaining a phase-locked multi-beam coherent superposition fiber laser.

The invention realizes the complete coherent superposition of multiple beams of fiber lasers, and the superimposed laser beams have high power and beam quality close to the diffraction limit. The feedback control circuit 9 is used to ensure that the phases of N bundles of fiber lasers on the main optical path A are constantly detected and modulated, and the phase locking quality (coherence) can reach a uniform and stable high level, thereby satisfying the condition of complete coherence of N bundles of fiber lasers. Achieve complete coherence; use 1×N+1 fusion-tapered polarization-maintaining fiber coupler 3, so the number of coherently superimposed fiber laser beams is almost unlimited; use polarization-maintaining fiber isolator 2 to ensure the polarization state of light while reducing The influence of noise is reduced, and the stability of the system is increased; the insertion loss and echo reflection of the device are fundamentally reduced by using the optical fiber phase modulator 4; It is beneficial to the miniaturization and practicability of the system, and is easier for commercial application. Since the present invention realizes a phase-locked multi-beam superposition output fiber laser with high output power and high beam quality, it solves the disadvantage that high power and high beam quality cannot be balanced in existing fiber laser beam synthesis methods. This high-power, high-beam-quality fiber laser can be used to convert ordinary fiber lasers or gas, solid, and semiconductor lasers with pigtails into laser sources that output high-power, high-beam quality light, as well as industrial laser processing, military and many other fields. The invention is suitable for continuous or pulse output fiber lasers, and also for fiber lasers doped with Tm ³⁺ , Pr ³⁺ , Ho ³⁺ , Er ³⁺ , Sm ³⁺ , Nd ³⁺ , and Yb ³⁺ ions. The laser device of the invention has a simple and compact structure, is easy to process and manufacture, and is easy to industrial production.

Description of drawings:

Figure 1. Schematic diagram of the structure of a multi-beam coherent superposition output fiber laser using a feedback loop to achieve phase locking. Fig. 1 is also the accompanying drawing of the abstract of the description.

FIG. 2 is a schematic structural diagram of the feedback control circuit 9 .

Detailed ways:

Example 1:

Specific Implementation A phase-locked multi-beam coherent superposition fiber laser is manufactured. As shown in Figure 1, it comprises the fiber laser 1 of output polarized light, the polarization maintaining fiber isolator 2, 1 * N+1 fusion taper type polarization maintaining fiber coupler 3, fiber phase modulator 4, fiber amplifier 5,90: 10 Polarization-maintaining fiber coupler 6, 1×N fusion-tapered polarization-maintaining fiber coupler 7, 1×2 fusion-tapered polarization-maintaining fiber coupler 8, feedback control circuit 9, lens 10. As shown in FIG. 2 , the feedback control circuit 9 includes an avalanche photodiode or a PIN photodiode 11 and a high frequency amplifier 12 . The polarized light output from the fiber laser 1 is split into N+1 beams of polarized laser beams with equal energy through a 1×N+1 fusion-tapered polarization-maintaining fiber coupler 3, one of which is used as a reference laser beam, which is again The 1×N fusion-tapered polarization-maintaining fiber coupler 7 splits into N beams of polarized laser light with equal energy so as to interfere with the 10% split fiber laser on the main optical path A. The other N beams of polarized fiber lasers split by the 1×N+1 fused-taper polarization-maintaining fiber coupler 3 pass through the fiber phase modulator 4 and are then amplified by the fiber amplifier 5 . The amplified N beams of polarized laser beams on the main optical path A are split by 90:10 polarization-maintaining fiber coupler 6, and 90% of the fiber laser beams are coherently superimposed in free space after being focused by the lens 10, outputting laser beams with high power and high beam quality . 10% of the polarized laser light enters the sub-optical path B, where it interferes with the beam-split reference laser in the 1×2 fusion-tapered polarization-maintaining fiber coupler 8 . The light after interference enters the feedback control circuit 9, the voltage control connector of the optical fiber phase modulator 4 is connected to the feedback control circuit 9 (as shown in Figure 2), and the avalanche photodiode or PIN photodiode 11 is used to detect the 1×2 fusion cone The light intensity in the polarization-maintaining fiber coupler 8 is output in the form of an electrical signal, which is amplified by the high-frequency amplifier 12 and used to control the optical fiber phase modulator 4 to achieve phase locking.

Claims (2)

1. A phase-locked multi-beam coherently stacked fiber laser, characterized in that it includes a fiber laser (1) outputting polarized light, a polarization-maintaining fiber isolator (2), and a 1 × N+1 fusion-tapered polarization-maintaining fiber coupler (3), fiber phase modulator (4), fiber amplifier (5), 90:10 polarization-maintaining fiber coupler (6), 1×N fusion-taper type polarization-maintaining fiber coupler (7), 1×2 fusion-taper Type polarization maintaining fiber coupler (8), feedback control circuit (9), lens (10); One end of the polarization-maintaining fiber isolator (2) is connected to the fiber laser (1) and the other end is connected to the 1×N+1 fusion-tapered polarization-maintaining fiber coupler (3); the fiber phase modulator (4) is connected to the 1×N+ 1 The fusion-tapered polarization-maintaining fiber coupler (3) is connected and also connected with the fiber amplifier (5) and the feedback control circuit (9); the 90:10 polarization-maintaining fiber coupler (6) is connected with the fiber amplifier (5) and connected with the fiber amplifier (5) 1×2 fusion-tapered polarization-maintaining fiber coupler (8) and lens (10) connected; 1×N fusion-tapered polarization-maintaining fiber coupler (7) and 1×2 fusion-tapered polarization-maintaining fiber coupler (8) connected to the feedback control circuit (9), and also connected to the 1×N fusion-tapered polarization-maintaining optical fiber coupler (3). 2. A kind of phase-locked multi-beam coherent superposition fiber laser according to claim 1, characterized in that said feedback control circuit (9) is composed of an avalanche photodiode or a PIN photodiode (11) and a high-frequency amplifier (12 )constitute.

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