Characteristics of Collimators Based on the Large-Mode-Area CMCF for Coupling Laser Beam

Xuran Zhang,Zhaoxin Geng,Xiao Liang,Zhenxu Bai,Tianhe Yin,Shuo Liu

doi:10.3390/app112411604

Xuran Zhang, Zhaoxin Geng + Show 4 more

Open Access

https://doi.org/10.3390/app112411604

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Abstract

A new collimator based on a homemade concentric multilayer-core fiber (CMCF) is proposed and experimentally demonstrated. This collimator was fabricated using a tail fiber with large mode area and single-mode operation. By exploiting the optical transmission matrix, the propagation characteristic and coupling mechanism of this CMCF-based collimator was introduced meticulously. The coupling losses of the laser beam using this collimator in the off-axis, angular, and axial deviations were analyzed separately. In order to determine the relationship between the geometric redundancy of this collimator and the effective mode field area of the tail fiber, the corresponding mathematical model was established. Through model calculation and experiment measurement, the coupling properties of the collimator were improved effectively. Compared with the common SMF-based collimator, the declination redundancy of the CMCF-based one improved by 20%, which could make the coupling of the optical fiber collimator easier. Therefore, this collimator has potential application value in the laser diode coupling unit and high-speed optical communication system.

Highlights

With the development of high-speed optical communication, optical fiber collimators have been used for a wide variety of applications, in optical transmission systems and in coupled laser systems and other fields as important optical passive devices [1,2,3,4]
The theory and experimental measurements for the concentric multilayer-core fiber (CMCF)-based collimator are introduced, and some alignment processes are discussed and compared. This testing system was set up using an excitation laser as a light source and a pair of homemade collimators, and the coupling loss introduced by the angular deviation was calculated theoretically and measured experimentally
According to the detailed analysis of the alignment deviations, enlarging the mode field diameter of its tail fiber could reduce the coupling loss caused by angular deviation, while off-axis and axial deviation losses would become higher

Summary

Introduction

With the development of high-speed optical communication, optical fiber collimators have been used for a wide variety of applications, in optical transmission systems and in coupled laser systems and other fields as important optical passive devices [1,2,3,4]. As the numerical aperture of ordinary optical fiber is relatively small, it is difficult to achieve the direct free-space alignment of the laser beam between the two fibers Under this circumstance, the coupling loss is very high. A Gaussian beam would be expanded and collimated by optical fiber collimators to achieve high coupling efficiency It can couple the collimated light into the fiber with very small losses and is widely used in optical switching, optical signal processing, laser alignment, optical measurement, and other systems [2,12,13,14,15]. The theory and experimental measurements for the CMCF-based collimator are introduced, and some alignment processes are discussed and compared This testing system was set up using an excitation laser as a light source and a pair of homemade collimators, and the coupling loss introduced by the angular deviation was calculated theoretically and measured experimentally. Satisfactory results were obtained through calculation and experiments, which improved the coupling efficiency by 20%, and significantly increased the stability of the optics coupling system

Theoretical Analysis of the Coupling Loss Mechanism

Findings

Off-Axis Deviation

Conclusions