MXene-based high-performance all-optical
modulators for actively Q-switched pulse
generation
QING WU,
1,2,†
YUNZHENG WANG,
1,†
WEICHUN HUANG,
1,†
CONG WANG,
1
ZHENG ZHENG,
2,3
MENG ZHANG,
2,
* AND HAN ZHANG
1
1
International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education,
College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
2
School of Electronic and Information Engineering, Beihang University, Beijing 100191, China
3
Beijing Advanced Innovation Center for Big Data-based Precision Medicine, Beihang University, Beijing 100083, China
*Corresponding author: mengzhang10@buaa.edu.cn
Received 3 March 2020; revised 13 April 2020; accepted 28 April 2020; posted 29 April 2020 (Doc. ID 391911); published 12 June 2020
Q-switched fiber lasers are integral tools in science, industry, and medicine due to their advantages of flexibility,
compactness, and reliability. All-optical strategies to generate ultrashort pulses have obtained considerable at-
tention as they can modulate the intracavity Q factors without employing costly and complex electrically driven
devices. Here, we propose a high-performance all-optical modulator for actively Q-switched pulse generation
based on a microfiber knot resonator deposited with V
2
CT
x
MXene. Experimental results show that the obtained
Q-switching pulses exhibit a wide adjustment range of repetition rate from 1 kHz to 20 kHz, a high signal-to-
background contrast ratio of ∼55 dB, and a narrow pulse width of 8.82 μs, indicating great potentials of prov id-
ing a simple and viable solution in photonic applications.
© 2020 Chinese Laser Press
https://doi.org/10.1364/PRJ.391911
1. INTRODUCTION
Q-switched pulse fiber lasers have played an important role in
various applications, such as optical communications, remote
sensing, material processing, and bioscience [1–4]. Different
from the passive Q-switching regime that generally utilizes satu-
rable absorbers to induce self-modulation of intracavity quality
factor (Q factor), the active approach requires an externally
driven device to periodically modulate the intracavity loss or
the round-trip phase change of the cavity [5,6]. Therefore,
the active Q-switching regime allows versatile pulse parameters
(e.g., controllable pulse width and repetition rate) and the exact
timing synchronization between the Q-switched pulses and ex-
ternally modulated signals. It can also avoid the potential stability
problems existing in most passive Q-switched cavities, e.g., low
damage threshold caused by material-based saturable absorbers
with a strong incident light, which promotes them for practical
applications. While there are many approaches to generate ac-
tively Q-switched pulses, including bulk electro-optical [7]or
acoustic-optical [8] Q-switches, they are not without limitations,
such as sophisticated spatial structure, high driving voltage, and
narrow operation bandwidth. In contrast, all-optical methods of-
fer intrinsic advantages in terms of broad bandwidth operation,
ease of fabrication and implementation, and low-cost [9–12],
and thus have been widely deployed in a variety of applications.
In recent years, remarkable progress has been made on two-
dimensional (2D) layered materials due to their extraordinary
physical properties that provide exciting opportunities for di-
verse photonic and optoelectronic applications, such as field
effect transistors, saturable absorbers, photodetectors, polar-
izers, and optical modulators [13–17]. Optical modulation
effects in 2D materials have been widely studied as the signal
processing can be fully realized in the photonic domain. All-
optical modulators (AOMs) based on the photothermal effect
of 2D materials (such as graphene [18], WS
2
[19], phosphor-
ene [20], bismuthine [21], antimonene [12], and MXenes [22])
have been demonstrated to exhibit large modulation depth,
broad bandwidth operation, and ease of integration for all-fiber
structures. A previous report has shown an all-optical active
Q-switching utilizing an antimonene-based AOM with a high
modulation depth and broad operating bandwidth [12].
However, this Q-switch has its own limitations, including poor
structure stability, limited tunability of repetition rate, and
complexity.
AOMs based on a microfiber knot resonator (MKR) have
been successfully implemented for many applications, such as
optical routing and switching, demonstrating superior perfor-
mances due to their prominent advantages, including flexible
configurability, compact configuration, good environmental sta-
bility, and strong light–matter interaction [23–25]. The strong
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Vol. 8, No. 7 / July 2020 / Photonics Rese arch
Research Article
2327-9125/20/071140-08 Journal © 2020 Chinese Laser Press