PbS量子点：超快激光的新型饱和吸收体

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"PbS量子点可作为超快激光的饱和吸收体，研究论文" 在光学和光电子学领域，低维纳米材料因其独特的性质和广泛的应用潜力而备受关注。PbS量子点（Quantum Dots, QDs）作为一种重要的纳米材料，其大玻尔半径和可调的带隙特性使其在近红外区域的光子应用中具有特别的吸引力。这篇研究论文探讨了 oleic acid 包裹的胶体PbS量子点作为超快激光的饱和吸收体的潜力。饱和吸收体是超快激光脉冲产生的重要组成部分，它能够通过非线性吸收机制控制激光的脉冲宽度和峰值功率。在该研究中，PbS量子点表现出优异的饱和吸收性能，这得益于它们的尺寸量子限制效应，使得在特定能量下，光吸收会随着入射光强的增加而达到饱和，从而有效地缩短激光的脉冲持续时间。实验结果显示，这些PbS量子点能够有效降低激光的阈值，促进超短脉冲的产生。由于PbS QDs的尺寸可调性，研究人员可以精确地控制它们的能带结构，进而调整饱和吸收的特性，以适应不同波长的激光系统。此外，oleic acid 的包覆层为量子点提供了稳定的化学环境，增强了它们在激光器中的长期稳定性和可重复使用性。通过这种基于PbS量子点的饱和吸收体，研究团队成功地实现了超短脉冲激光的产生，这在光通信、生物成像、光学数据处理以及高精度材料加工等众多领域具有潜在的应用价值。这项工作不仅展示了PbS量子点在超快激光技术中的新应用，也为设计新型光子器件提供了新的思路和方法。这篇研究论文深入研究了PbS量子点作为超快激光饱和吸收体的性能和工作机制，为开发高性能、可调谐的超快激光系统开辟了新的道路，并可能推动光电子技术领域的进步。同时，这也证明了纳米材料在光学领域中所展现出的巨大创新潜力和实用价值。

PbS quantum dots as a saturable absorber

for ultrafast laser

LING YUN,

1,†

YANG QIU,

1,†

CONGHAO YANG,

JIE XING,

KEHAN YU,

*XIANGXING XU,

2,3

AND WEI WEI

College of Electronic and Optical Engineering & College of Microelectronics, Nanjing University of Posts and Telecommunications,

Nanjing 210046, China

Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University,

Nanjing 210046, China

e-mail: xuxx@njnu.edu.cn

*Corresponding author: kehanyu@njupt.edu.cn

Received 23 July 2018; revised 31 August 2018; accepted 11 September 2018; posted 13 September 2018 (Doc. ID 340424);

published 16 October 2018

Low-dimensional nanomaterials, owing to their unique and versatile properties, are very attractive for enormous

electronic and optoelectronic applications. PbS quantum dots (QDs), characterized by a large Bohr radius and

size-tunable bandgap, are especially interesting for photonic applications in the near-infrared region. Here, oleic

acid capped colloidal PbS QDs as a saturable absorber are investigated for ultrashort-pulse generation. The PbS

QDs exhibit outstanding nonlinear saturable absorption properties at 1550 nm: a modulation depth up to 44.5%

and a thermal damage threshold larger than 30 mJ∕cm

. By incorporating PbS QDs into a fiber laser, a trans-

form-limited soliton pulse as short as 559 fs with a bandwidth of 4.78 nm is realized at 1563 nm. Numerous

applications may benefit from the nonlinear saturable absorption properties of PbS QDs, such as near-infrared

pulsed lasers and modulators.

https://doi.org/10.1364/PRJ.6.001028

1. INTRODUCTION

Ultrafast pulsed lasers that generate picosecond to femtosecond

optical pulses have been extensively investigated in the fields of

medicine, frequency combs, materials processing, and telecom-

munication [1–4]. Currently, the most-widely used ultrashort

pulse laser adopts a passive mode-locking technique, which uses

a nonlinear optical element called a saturable absorber (SA) to

transform the continuous wave into optical pulses [5–8]. Key

demands for SAs are broad bandwidth, fast charge carrier

relaxation, large modulation depth, high thermal damage

threshold, and simple fabrication and integration into an opti-

cal fiber system [9–13].

Low-dimensional nanomaterials have attracted tremendous

interest from the applied physics community due to their

excellent optoelectronic features [14–18]. Owing to short

recovery time and high third-order nonlinear susceptibility,

one-dimensional (1D) carbon nanotubes and two-dimensional

(2D) graphene and graphene-like materials with ultrashort

pulse generation in extremely wide wavelength range have been

discovered one after another in the past few years [19–23].

Among these SAs, the main challenge is that the fast charge

carrier relaxation, large modulation depth, and high damage

threshold usually cannot be endued simultaneously on an

individual material [24–28]. Therefore, it is necessary to find

a novel SA that can overcome all the above challenges and pro-

vide saturable absorption over a wider wavelength range.

PbS quantum dots (QDs) have been widely researched due

to their tunable optical properties via control of size, structure,

and composition [29,30]. Given to the large exciton Bohr

radius (18 nm), narrow bandgap energy (0.41 eV for bulk

material), and quantum confinement effect, adjustable absorp-

tion of PbS QDs over the entire near-infrared (NIR) spectral

range can be easily achieved [31 ], resulting in the advancement

of fascinating applications as transistors, photodetectors, and

photovoltaic cells [29,32,33]. In the field of nonlinear saturable

absorption, Asunskis et al. revealed that nonlinear optical ab-

sorption of PbS QDs depended on their surface properties [34].

Later, a 2.6-ps pulse at around 1 μm with an out put power

of 250 mW was observed in PbS QD-doped glass SAs [35].

Gumenyuk et al. demonstrated a vector soliton fiber laser cen-

tered at 2 μm with a modulation depth >40% [36]. The gen-

eration of transform-limited fs optical pulses with QDs was

predicted almost two decades ago [37]; however, experimental

study on PbS QD mode-locked fs fiber lasers is still rarely

reported.

Here, we demonstrate saturable absorption of PbS QDs and

generation of a high-power ultrafast-pulse erbium-doped fiber

(EDF) laser. Results show a nonlinear saturable absorption fea-

ture at 1550 nm with modulation depth up to 44.5%. In a PbS

1028

Vol. 6, No. 11 / November 2018 / Photonics Research

Research Article

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