温度调控Er掺杂随机光纤激光器模式选择

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"Temperature-controlled mode selection of Er-doped random fiber laser with disordered Bragg gratings" 本文介绍了一种利用掺铒随机光纤激光器（RFL）与无序光纤布拉格光栅（FBG）阵列来实现温度控制的激光模式选择的方法。在该系统中，无序的FBG阵列同时充当增益介质和随机分布的反射器，与可调谐的点反射器共同构成了RFL。通过加热无序FBG阵列的特定位置，可以有效地控制激光器的发射模式。掺铒光纤激光器（Er-doped fiber laser，简称Erbium laser）是一种常见的激光设备，其核心是掺杂了铒离子的光纤，这些离子在特定的能级间跃迁时能够实现激光振荡。在本文提出的RFL中，无序FBG阵列的独特设计使得激光器能够在多模随机激光状态下发射。这种多模随机激光的阈值功率在7.5到10毫瓦之间，当点反射器的反射率从4%变化到50%时，功率效率在23%至27%的范围内。温度控制是通过改变特定FBG区域的温度来调整激光模式的关键。FBG的反射特性会随着温度的变化而变化，因此，通过对特定FBG加热，可以改变其反射率，进而影响整个激光腔的反馈特性，从而实现对激光模式的选择性激发。这种控制方法为精细调控激光输出提供了新的可能性，对于激光技术的应用，如光通信、光谱分析、精密测量等领域具有重要意义。此外，文章指出，通过这种温度控制方式，可以精确地选择和控制随机发射的激光模式。这对于理解和优化随机激光器的性能，以及探索新型激光器设计有着重要的理论价值和实践意义。这项工作不仅展示了掺铒光纤激光器在模式控制方面的创新，还进一步推动了对随机激光现象的理解。总结来说，这篇文章提出了一个新颖的温度控制技术，用于掺铒随机光纤激光器的模式选择。通过利用无序FBG阵列的特性，结合可调谐点反射器，实现了对激光模式的高效控制，为未来激光技术的发展开辟了新的研究方向。

Temperature-controlled mode selection of Er-doped

random fiber laser with disordered Bragg gratings

W. L. Zhang,* Y. B. Song, X. P. Zeng, R. Ma, Z. J. Yang, and Y. J. Rao

Key Laboratory of Optical Fiber Sensing & Communications (Education Ministry of China),

University of Electronic Science & Technology of China, Chengdu 611731, China

*Corresponding author: wl_zhang@aliyun.com

Received November 17, 2015; revised January 24, 2016; accepted March 16, 2016;

posted March 18, 2016 (Doc. ID 254132); published April 22, 2016

In this paper, we proposed a way to realize an Er-doped random fiber laser (RFL) with a disordered fiber Bragg

grating (FBG) array, as well as to control the lasing mode of the RFL by heating specific locations of the disordered

FBG array. The disordered FBG array performs as both the gain medium and random distributed reflectors, which

together with a tunable point reflector form the RFL. Coherent multi-mode random lasing is obtained with a

threshold of between 7.5 and 10 mW and a power efficiency between 23% and 27% when the reflectivity of the

point reflector changes from 4% to 50%. To control the lasing mode of random emission, a specific point of the

disordered FBG array is heated so as to shift the wavelength of the FBG(s) at this point away from the other FBGs.

Thus, different resonance cavities are formed, and the lasing mode can be controlled by changing the location of

OCIS codes: (060.3510) Lasers, fiber; (140.3500) Lasers, erbium.

http://dx.doi.org/10.1364/PRJ.4.000102

1. INTRODUCTION

Random lasers (RLs) are disordered optical structures of

stimulated emission in which light waves are both multiply

scattered and amplified. Fabrication of RLs is simple and cost

effective (i.e., no fine mirrors or a well-defined cavity are

needed), especially for nanoscale structures. RLs have the

characteristics of low spacial coherence and wide emission

angle, while keeping a high Q-factor and high photon density

of state that is comparable to those of ordinary lasers [1–3].

Thus, RLs are attractive for both fundamental theoretical and

technological research and have great potential applications

in wide areas such as photonic information, imaging, and

display.

One of the main challenges in developing RLs is a lack of

ways to regulate their output (e.g., laser mode selection and

modulation), because the randomly formed feedback loops of

light are difficult to specify or access. A few groups have

attempted to tune and control RLs in different ways, such

as temperature tuning, resonance driving, variation of effec-

tive lifetime of the cavity, and choice of different pump beam

profiles [4–6]. Recent achievements of random fiber lasers

(RFLs) in low dimensional waveguides also provide fine ways

to tailor their output [7–12]. Some inherent characteristics of

fiber waveguides (e.g., slow light, tight transverse mode con-

finement, and rich interaction of inner fields) offer efficient

ways to control laser output.

As one of the three typical types of RFLs [13], an active fiber

with random mirrors of distributed or phase-shifted Bragg gra-

tings [14–17] emits coherent light with a low lasing threshold

compared with the other two types. However, such RFLs

exhibit several coherent random lasing modes, and the output

is less stable because of mode competition or cavity thermal

effect. Hence, it is important to stabilize or even to select the

emission mode of these RFLs, which is of great significance to

realize high-efficiency, mode/wavelength controllable, and

dynamically tunable RFLs.

In RFLs, passive methods such as introducing wavelength

tunable components and mixing different types of fibers

have been proposed to optimize the output characteristics.

However, these methods have less flexibility of light control.

Temperature tuning, spatial phase modulation [4–6], and so

forth have been demonstrated for actively controlling random

lasing in bulk structures. However, these active methods of

RL control have been studied less in RFLs. In one of our

recent works, an optical control method (i.e., introducing con-

trol light laterally as spatial gain perturbation) of an Er-doped

RFL was proposed to select individual modes of random emis-

sion [13]. We propose a new way to control lasing modes of

an Er-doped RFL by heating different positions of the disor-

dered fiber Bragg grating (FBG) array. Besides, a tunable point

reflector is introduced to optimize output characteristics of the

RFLs. The experimental results show that several stable lasing

modes can be selected by heating different positions of the dis-

ordered FBG array. Compared with the method of light control,

the thermal control is simpler, more cost efficient, and has a

relatively wider heating range (e.g., a large area and high power

density light beam is difficult to obtain). The proposed method

provides a dynamic and flexible means of laser mode control

in RFLs. The location dependent mode selection mechanism

could also be a potential means for laser mode switching in

applications for information optics.

2. PRINCIPLE OF OPERATION

A schematic diagram of the experimental setup is shown in

Fig. 1. A 1480 nm laser is used as the pump laser, whose output

is coupled into the gain fiber through a 1480/1550 nm wave-

length division multiplexer (WDM). The gain fiber is com-

posed of a 7 m length erbium-doped fiber (EDF), with an

102 Photon. Res. / Vol. 4, No. 3 / June 2016 Zhang et al.

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