Elsevier

Optical Materials

Volume 100, February 2020, 109702
Optical Materials

Q-switched mode-locked Nd:GGG waveguide laser with tin disulfide as saturable absorber

https://doi.org/10.1016/j.optmat.2020.109702Get rights and content

Highlights

  • The first Nd:GGG Q-switched mode-locked waveguide laser.

  • Fundamental repetition rate up to 17.9 GHz.

  • SnS2 as saturable absorber.

Abstract

We demonstrate a Q-switched mode-locked waveguide laser operation with high fundamental repetition rate based on the few-layer tin disulfide (SnS2) as a saturable absorber. The excellent nonlinear optical property of SnS2 enables efficient pulsed laser generation. By using Nd:GGG ridge waveguide, the fundamental repetition rate up to 17.9 GHz has been achieved for the mode-locked pulses with duration as short as 30 ps. In addition, this Nd:GGG-based waveguide laser exhibits excellent lasing properties (maximum output power of 115 mW at 1064 nm) by modulation of SnS2, suggesting promising application as miniature ultrafast light sources.

Introduction

Since the discovery of graphene in 2004, two-dimensional (2D) materials have rapidly become the research hot points in the world [1]. The unique and excellent properties of 2D materials in optics and electronics provided unprecedented technological application possibilities in the nonlinear optics, optoelectronics, and electronics [2,3]. As a prime category of emerging 2D materials, transition-metal dichalcogenides (TMDs) has attached much scientific interests for its distinct optical properties, exhibiting a bright developing prospect in photonics [4], chemical sensing [5], catalysis [6] and many other application fields. Particularly, with intriguing nonlinear saturable absorption, TMDs have been widely used in the generation of pulsed lasers as efficient saturable absorbers (SAs) [[7], [8], [9], [10]]. Tin disulfide (SnS2), as a kind of newly-developed TMDs, possesses a sizeable bandgap [11] as well as an ideal absorbance in near-infrared region [12], indicating bright potential as effective SAs.

With dimensions of micrometer or sub-micrometric scales, optical waveguides could confine the propagation of light within extremely small volumes, thus the optical intensities could achieve a much higher level with respect to the bulks [13,14]. Based on these features, waveguides receive a broad variety of applications in many areas. For example, waveguides have exhibited a great developing prospect in medical ultrasonography, radar, and augment reality [15,16]. In quantum photonics, waveguides play a crucial role of the light guidance and on-chip quantum elements [17,18]. In laser technology, by altering surface refractive index of gain materials, waveguide lasers have been implemented with on-chip integration towards miniature and compact laser sources [[19], [20], [21], [22], [23], [24], [25], [26], [27]]. The Q-switched as well as mode-locked (i.e., Q-switched mode-locked, QML or continuous-wave mode-locked, CWML) laser operations both have been achieved in varieties of laser gain media based on the waveguide platform and nanomaterial SAs [[28], [29], [30], [31], [32]]. Nowadays, mode-locked waveguide lasers have caught growing research interest to the relatively great stability and high repetition rate, for which they possess a great application potential in ultrafast nonlinear spectroscopy, precision metrology and high-speed optical communication [[33], [34], [35]]. In recent years, it has achieved repetition rate up to 1.5, 5.9, 6.5, and 8.8 GHz for different QML lasers [28,[36], [37], [38], [39]] as well as 6.5, 11, 15.2, and 21.25 GHz for diverse CWML lasers [[40], [41], [42], [43]]. As a widely-used laser crystal, Nd:GGG possesses outstanding optical advantages such as high slope efficiency and low propagation losses [44,45].

In this work, we report on a 1-μm QML with a few-layer SnS2 as SA. The system is based on a ridge Nd:GGG waveguide produced by C ion implantation and femtosecond laser ablation. As the first successful attempt for applying Nd:GGG waveguides in pulsed laser operations as well as SnS2 film in waveguide lasers, it achieved a fundamental repetition rate as high as 17.9 GHz and the output power of Q-switched envelopes is 115 mW on average. The mode-locked lasing performances have also been investigated in details.

Section snippets

Properties of SnS2 saturable absorber

The high-quality few-layer SnS2 SA, which was synthesized by chemical vapor deposition (CVD), was customized from 6 Carbon Technology Co., Ltd. (Shenzhen, China). Fig. 1a indicates a good linear optical absorption of the as-synthesized SnS2 sample in visible to near-infrared region. The absorption decreases as wavelength increases, possessing a threshold photon energy lower than 0.83 eV. These absorption properties illustrate a great potential for the SnS2 film as a broadband SA. An atomic

Results and discussion

Based on the monolithic Nd:GGG cladding waveguide, we have achieved a 1-μm mode-locked pulse laser operation, which is modulated by a CVD-grown SnS2 sample as the SA. Fig. 4 shows the performances of the pulses modulated by SnS2 sample. The linear fit in Fig. 4a indicates a 60-mW threshold pump power while the maximum power output is 115 mW and the corresponding slope efficiency is ~12.5%. The inset illustrates a near-field intensity image of the output laser. With pump power is 484 mW, a

Conclusions

In summary, based on the nonlinear optical properties of SnS2 we investigated, a 1-μm Q-switched mode-locked laser operation was achieved. The laser was modulated by a few-layer SnS2 saturable absorber and integrated in a Nd:GGG waveguide system. The fundamental repetition rate of the laser has reached 17.9 GHz with relatively low lasing threshold and high peak power, exhibiting bright prospects of SnS2 SAs as well as Nd:GGG waveguides in future ultrafast optical applications.

CRediT authorship contribution statement

Xuejian Dong: Formal analysis, Writing - original draft. Ziqi Li: Formal analysis, Writing - original draft. Chi Pang: Formal analysis, Writing - original draft. Ningning Dong: Writing - original draft. Hailing Jiang: Formal analysis, Writing - original draft. Jun Wang: Writing - original draft, Formal analysis. Feng Chen: Writing - original draft, Formal analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by National Natural Science Foundation of China (No. 61775120, 61875213) and STCSM Excellent Academic Leader of Shanghai (No. 17XD1403900).

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