A method for measuring beam quality of few-mode fiber lasers

Abstract

The present invention discloses a method for measuring the beam quality of a few-mode fiber laser, comprising the following steps: first, installing a pigtail at the output end of the few-mode fiber laser and installing a device for detecting the input power and output power of the pigtail laser; the few-mode fiber laser has m modes; 2≤m≤6; the pigtail is a double-clad fiber; second, designing m experiments, in each of which at least one of the coiling radius and fiber length of the pigtail is changed to obtain the corresponding integrated loss #imgabs0#; and third, establishing a system of equations, solving for the proportion of each mode laser in the pigtail input laser to obtain the laser beam quality. The present invention is low-cost, has simple experimental equipment, is easy to operate, and reduces the technical threshold for testers.

Description

Technical Field

[0001] The invention belongs to the field of lasers, and in particular relates to a method for measuring the beam quality of a few-mode fiber laser. Background Art

[0002] Beam quality is a crucial parameter for lasers, a key physical quantity that determines the quality of a laser and its suitability for laser precision machining. For many single-mode lasers, high-quality lasers typically exhibit excellent beam quality. Furthermore, high-quality laser beams are more conducive to beam shaping, meeting the requirements of laser precision machining and customization.

[0003] In the existing technology, spot analyzers, beam quality analyzers and other devices are often used to measure beam quality. When using a spot analyzer, the laser cross-section data is collected at different positions, and then the beam quality M is synthesized by the built-in program of the instrument. 2 If there is an operational error or measurement error during the sampling process, it is impossible to measure and analyze M 2 For high-power measurements, however, a complex attenuation system is required to keep the laser power within a measurable range and prevent excessive power from damaging the instrument's detection surface. While beam profilers can address these issues, their complex and sophisticated structure and high price have deterred many laser manufacturers. Summary of the Invention

[0004] To address these issues, the present invention discloses a method for measuring the beam quality of a few-mode fiber laser. A few-mode fiber laser is one whose output laser contains no more than six modes. This method is low-cost, requires simple experimental equipment, and is easy to perform, lowering the technical requirements for acceptance personnel.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] A method for measuring the beam quality of a few-mode fiber laser comprises the following steps:

[0007] Step 1: Install a pigtail at the output end of the few-mode fiber laser and install a device for detecting the input power and output power of the pigtail laser; the laser output by the few-mode fiber laser has m modes; 2≤m≤6; the pigtail is a double-clad fiber with parameters a / b; where a represents the diameter of the pigtail core and b represents the diameter of the pigtail outer cladding;

[0008] Step 2: Design m experiments. In each experiment, change at least one of the pigtail's coiling radius and fiber length to obtain the corresponding comprehensive loss.

[0009] Step 3: Establish a set of equations and solve them to obtain the proportion of each mode laser in the input laser of the pigtail. The laser beam quality can be obtained by the proportion of each mode laser.

[0010] As a further improvement, the pigtail is fixed in a coiled manner, and the device for detecting the output power of the pigtail is a power meter; the laser output from the few-mode laser is transmitted through the pigtail and then enters the cladding optical power stripper CPS, the output end cap and the power meter in sequence.

[0011] Further improvement, the steps of step 2 are as follows: Assume that the power of the input laser of the pigtail is P in The input laser contains m modes of laser, which are respectively j Indicates, j = 1, ..., m, m ≤ 6, LP j The energy percentage in the output light is x j ,but The output power of the pigtail is For the core diameter a of the pigtail, in the ith experiment, the coiling radius r of the pigtail i Under certain conditions, the bending loss of lasers in different modes is is determined by the length L of the pigtail i Under certain conditions, the length loss of lasers in different modes is determined; the combined loss effect of bending loss and length loss is expressed as parameter Indicates, i=1, ..., m, m≤6;

[0012] Assuming there are m modes in the laser, m experiments are designed; in each experiment, the coiling radius and fiber length are determined, and the corresponding comprehensive loss effect is is certain; establish an equation for each experiment, and obtain m equations for m experiments:

[0013]

[0014] Solve the equations to get the proportion x of each mode in the input laser j The value of is used to obtain the beam quality of the laser input to the pigtail.

[0015] Advantages of the present invention:

[0016] 1. The present invention has low cost, simple experimental equipment, and easy experiment operation, which reduces the technical threshold of testers.

[0017] 2. No need to purchase expensive equipment, reducing the production and R&D costs of laser manufacturers.

[0018] 3. It has low requirements on the detection environment and no restrictions on the output laser power. It is a beam quality measurement method with good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the assembly structure of the method for measuring the beam quality of a few-mode fiber laser of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] like Figure 1 The pigtail structure for beam quality detection shown in the figure is to install a pigtail structure at the output end of the laser to be tested. The optical fiber in the pigtail structure is consistent with the specifications of the output optical fiber of the laser to be tested, including: a coiled optical fiber (pigtail), CPS, and an output end cap. The laser is incident on the power meter through the end cap to measure the output power of the laser after passing through the pigtail.

[0022] Here’s how:

[0023] The pigtail uses double-clad fiber. The parameters of double-clad fiber are a / b (for example, 20 / 400). Assume that the power of the input laser of the pigtail is P in , the input laser contains m modes, respectively, using LP j (j=1, ..., m, m≤6) means that their energy proportions in the output light are x j , The output power of the pigtail is For the fiber core diameter a, the fiber coiling radius r i Under certain conditions, the bending loss of lasers in different modes is is determined by the length L of the optical fiber. i Under certain conditions, the length loss of lasers in different modes The combined loss effect of bending loss and length loss is expressed as Indicates, (i=1,…,m,m≤6).

[0024] Assuming there are m modes in the laser, m experiments can be designed. In each experiment, the coil radius and fiber length are fixed, and the corresponding comprehensive loss effect is fixed. An equation is established for each experiment, and m experiments can obtain m equations. The unknown number in this equation group is the proportion x of each mode in the input laser. j By solving the equations, we can obtain the proportion x of each mode in the input laser. j , so that the beam quality of the laser input to the pigtail can be calculated.

[0025]

[0026] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for measuring the beam quality of a few-mode fiber laser, characterized in that: The steps include: Step 1: Install the pigtail at the output end of the few-mode fiber laser, and then install a device to detect the input power and output power of the pigtail laser. The laser output of the few-mode fiber laser has m modes; 2≤m≤6; the pigtail is a double-clad optical fiber with the following parameters: a / b ;in a Indicates the diameter of the pigtail core, b Indicates the outer cladding diameter of the pigtail; Step 2: Design m In each experiment, at least one of the pigtail coiling radius and fiber length is changed to obtain the corresponding comprehensive loss. ; Assume that the power of the input laser of the pigtail is , the input laser contains m The laser modes are respectively express, j =1,……, m , m ≤6, The energy proportion in the output light is ,but The output power of the pigtail is ;For the core diameter of the pigtail a , in i In the experiment, the coiling radius of the pigtail Under certain conditions, the bending loss of lasers in different modes is is determined by the length of the pigtail Under certain conditions, the length loss of lasers in different modes is determined; the combined loss effect of bending loss and length loss is expressed as parameter express, i =1,……, m , m ≤6; Assume that there is a laser m mode, then design m experiments; in each experiment, the coiling radius and fiber length are determined, and the corresponding comprehensive loss effect It is certain; Step 3: Establish a set of equations and solve them to obtain the proportion of each mode laser in the input laser of the pigtail, that is, to obtain the laser beam quality: For each experiment, create an equation. m Experiments obtained m Equations: Solve the equations to get the proportion of each mode in the input laser The value of is used to obtain the beam quality of the laser input to the pigtail.

2. The method for measuring the beam quality of a few-mode fiber laser according to claim 1, wherein: The pigtail is fixed in a coiled manner, and the device for detecting the output power of the pigtail is a power meter; the laser output from the few-mode laser is transmitted through the pigtail and then enters the cladding optical power stripper CPS, the output end cap and the power meter in sequence.

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