Chinese Optics Letters
Co-Editors-in-Chief
Han Zhang, Haibo Zeng, Qiaoliang Bao
Vol. 16, Issue 16, 2018
Editor(s): Han Zhang, Haibo Zeng, Qiaoliang Bao
Year: 2018
Status: Published

Two-dimensional (2D) noncarbon materials with outstanding optical properties are catching worldwide attentions on the heels of the discovery of graphene. Besides the large 2D family of transition metal dichalcogenides (TMDs), a series of new kind of mono-elemental 2D noncarbon materials, such as phosphorene, arsenene, antimonene and silicene, were recently emerging. The mentioned mono-elemental 2D materials shows unique properties like light emitting, non-linear optics, ultrafast optics, bio-related photonics and etc. The potential applications of these materials are in laser, ultrafast phtonics, biophotonics, optical modulation and optical devices. The scope of this special focus, covers all aspects of experimental research related to 2D noncarbon materials beyond graphene for optics, photonics and optoelectronics.

Contents 20 article(s)
Editorial for special issue on photonics based on two-dimensional noncarbon materials
Han Zhang, Haibo Zeng, and Qiaoliang Bao

Scientists are in the constant search of novel materials, or innovative applications of existing materials to solve problems we face in our everyday life. Although graphene, the two-dimensional (2D) form of carbon, has been a star player for the past decade, there is a significant shift towards other noncarbon materials in recent years. Apart from the large family of transition metal dichalcogenides (TMDs), mono-elemental materials, such as phosphorene, arsenene, antimonene, and silicene, are rapidly gaining attention. Composites and heterogenous layered structures are also worthy of interest.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020001 (2018)
Highly responsive broadband black phosphorus photodetectors
Yan Liu, Tian Sun, Weiliang Ma, Wenzhi Yu, Shivananju B. Nanjunda, Shaojuan Li, and Qiaoliang Bao

Black phosphorus (BP) is a promising material for ultrafast and broadband photodetection because of its narrow bandgap from 0.35 eV (bulk) to 1.8 eV (monolayer) and high carrier mobility. Although photodetectors based on BP with different configurations have been reported, high photosensitivity was mostly observed in the visible range. A highly efficient BP-based infrared photodetector operated in the telecom spectral range, especially at 1550 nm, has not been demonstrated. Here, we report a Schottky-type photodetector based on thin BP flakes, operating in a broad spectral range from visible (635 nm) to infrared (1550 nm). A responsivity as high as 230 A·W 1 was achieved at 1550 nm with a source-drain bias of 1 V. The rise time is 4.8 ms, and the fall time is 6.8 ms. Under light illumination and external bias, the Schottky barrier between the BP and metal was reduced, leading to efficient photocurrent extraction. The unprecedented performance of the BP photodetector indicates intriguing potential for sensing, imaging, and optical communication.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020002 (2018)
All-optical modulator based on MoS2-PVA thin film
Yifang Wang, Kan Wu, and Jianping Chen

The all-optical approach plays an important role in ultrafast all-optical signal processing, and the all-fiber scheme has a wide application in optical communications. In this letter, we investigate an all-optical modulator using few-layer molybdenum disulfide (MoS2)-polyvinyl alcohol (PVA) thin films based on the thermo-optic effect and obtain a long-time stable modulated output by applying polarization interference. By absorbing the injected 980 nm pump (control light), MoS2 generates heat, changes the refractive index of MoS2, and modulates the polarization of light. The obtained thermal all-optical modulator has a rise time of 526 μs.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020003 (2018)
2D noncarbon materials-based nonlinear optical devices for ultrafast photonics [Invited]
Bo Guo

Ultrafast lasers play an important role in a variety of applications ranging from optical communications to medical diagnostics and industrial materials processing. Graphene and other two-dimensional (2D) noncarbon materials, including topological insulators (TIs), transition metal dichalcogenides (TMDCs), phosphorene, bismuthene, and antimonene, have witnessed a very fast development of both fundamental and practical aspects in ultrafast photonics since 2009. Their unique nonlinear optical properties enable them to be used as excellent saturable absorbers (SAs) that have fast responses and broadband operation, and can be easily integrated into lasers. Here, we catalog and review recent progress in the exploitation of these 2D noncarbon materials in this emerging field. The fabrication techniques, nonlinear optical properties, and device integration strategies of 2D noncarbon materials are first introduced with a comprehensive view. Then, various mode-locked/Q-switched lasers (e.g., fiber, solid-state, disk, and waveguide lasers) based on 2D noncarbon materials are reviewed. In addition, versatile soliton pulses generated from the mode-locked fiber lasers based on 2D noncarbon materials are also summarized. Finally, future challenges and perspectives of 2D materials-based lasers are addressed.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020004 (2018)
Passively Q-switched green laser operation using CdTe/CdS quantum dots (Invited Paper)
Xigun Yan, Saiyu Luo, Bin Xu, Huiying Xu, Zhiping Cai, Jingzhou Li, Hongxing Dong, Long Zhang, and Zhengqian Luo

The direct generation of passively Q-switched lasers at a green wavelength has rarely been investigated in the past. In this Letter, we demonstrate a passively Q-switched praseodymium-doped yttrium lithium fluoride green laser at 522 nm using CdTe/CdS quantum dots as a saturable absorber. A maximum average output power of 33.6 mW is achieved with the shortest pulse width of 840 ns. The corresponding pulse energy and peak power reached 0.18 μJ and 0.21 W, respectively. To the best of our knowledge, this is the first demonstration in regard to a quantum dots saturable absorber operating in the green spectral region.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020005 (2018)
Layer-number determination of two-dimensional materials by optical characterization
You Zheng, Changyong Lan, Zhifei Zhou, Xiaoying Hu, Tianying He, and Chun Li

Initiated by graphene, two-dimensional (2D) layered materials have attracted much attention owing to their novel layer-number-dependent physical and chemical properties. To fully utilize those properties, a fast and accurate determination of their layer number is the priority. Compared with conventional structural characterization tools, including atomic force microscopy, scanning electron microscopy, and transmission electron microscopy, the optical characterization methods such as optical contrast, Raman spectroscopy, photoluminescence, multiphoton imaging, and hyperspectral imaging have the distinctive advantages of a high-throughput and nondestructive examination. Here, taking the most studied 2D materials like graphene, MoS2, and black phosphorus as examples, we summarize the principles and applications of those optical characterization methods. The comparison of those methods may help us to select proper ones in a cost-effective way.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020006 (2018)
High-power MoTe2-based passively Q-switched erbium-doped fiber laser
Mengli Liu, Wenjun Liu, Peiguang Yan, Shaobo Fang, Hao Teng, and Zhiyi Wei

Materials in the transition metal dichalcogenide family, including WS2, MoS2, WSe2, and MoSe2, etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties. Compared with WS2 and MoS2, the monolayered MoTe2 owns a smaller direct bandgap of 1.1 eV. It is beneficial for the applications in broadband absorption. In this letter, using the magnetron sputtering technique, MoTe2 is deposited on the surface of the tapered fiber to be assembled into the saturable absorber. We first implement the MoTe2-based Q-switched fiber laser operating at the wavelength of 1559 nm. The minimum pulse duration and signal-to-noise ratio are 677 ns and 63 dB, respectively. Moreover, the output power of 25 mW is impressive compared with previous work. We believe that MoTe2 is a promising 2D material for ultrafast photonic devices in the high-power Q-switched fiber lasers.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020007 (2018)
Coexistence of bound soliton and harmonic mode-locking soliton in an ultrafast fiber laser based on MoS2-deposited microfiber photonic device
Meng Liu, Aiping Luo, Wencheng Xu, and Zhichao Luo

As the typical material of two-dimensional transition metal dichalcogenides (TMDs), few-layered MoS2 possesses broadband saturable absorption and a large nonlinear refractive index, which could be regarded as a promising candidate for dual-function photonic device fabrication. In this work, the coexistence of a bound soliton and harmonic mode-locking soliton was demonstrated in an ultrafast fiber laser based on a MoS2-deposited microfiber photonic device. Through a band-pass filter, each multi-soliton state was investigated separately. The bound soliton has periodic spectral modulation of 1.55 nm with a corresponding pulse separation of 5.16 ps. The harmonic mode-locking soliton has the repetition rate of 479 MHz, corresponding to the 65th harmonic of the fundamental repetition rate. The results indicated that there exist more possibilities of different multi-soliton composites, which would enhance our understanding of multi-soliton dynamics.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020008 (2018)
Passive Q-switching in an erbium-doped fiber laser using tungsten sulphoselenide as a saturable absorber
H. Ahmad, Z. C. Tiu, and S. I. Ooi

A highly stable Q-switched laser incorporating a mechanically exfoliated tungsten sulphoselenide (WSSe) thin sheet saturable absorber (SA) is proposed and demonstrated. The SA assembly, formed by sandwiching a thin WSSe sheet between two fiber ferrules within the erbium-doped fiber laser, is used to effectively modulate the laser cavity losses. The WSSe-based SA has a saturation intensity of ～0.006 MW/cm2 and a modulation depth of 7.8%, giving an optimum Q-switched laser output with a maximum repetition rate of 61.81 kHz and a minimum pulse width of 2.6 μs. The laser’s highest output power of 0.45 mW and highest pulse energy of 7.31 nJ are achieved at the maximum pump power of 280.5 mW. The tunability of the cavity’s output at the maximum pump power is analyzed with a C-band tunable bandpass filter, giving a broad tunable range of ～40 nm, from 1530 nm to 1570 nm. The output performance of the tunable Q-switched laser correlates well with the gain spectrum of erbium-doped fibers, with the shift in the gain profile as a result of the saturated SA.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020009 (2018)
High-power all-fiber 1.0/1.5 μm dual-band pulsed MOPA source
Xiaogang Ge, Jun Yu, Weiqi Liu, Shuangchen Ruan, Chunyu Guo, Yewang Chen, Peiguang Yan, and Ping Hua

The simultaneous dual-band pulsed amplification is demonstrated from an Er/Yb co-doped fiber (EYDF), and consequently a high-power all-fiber single-mode 1.0/1.5 μm dual-band pulsed master oscillator power amplifier (MOPA) laser source is realized for the first time, to the best of our knowledge, based on one singlegain fiber. The simultaneous outputs at 1061 and 1548 nm of the laser source have the maximum powers of 10.7 and 25.8 W with the pulse widths of 9.5 ps and 2 ns and the pulse repetition rates of 178 and 25 MHz, respectively. This EYDF MOPA laser source is seeded by two separate preamplifier chains operating at 1.0 and 1.5 μm wavebands. The dependence of the laser output powers on the length of the large-mode area EYDF, the ratio of the powers of the two signals launched into the booster amplifier, and the wavelength of the 1 μm seed signal are also investigated experimentally.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020010 (2018)
516 mW, nanosecond Nd:LuAG laser Q-switched by gold nanorods
Guangju Zhang, Tinghao Liu, Yijie Shen, Chujun Zhao, Bin Huang, Zhe Kang, Guanshi Qin, Qiang Liu, and Xing Fu

Q-switched operation of an Nd:LuAG laser using gold nanorods (GNRs) as the saturable absorber (SA) is reported, which also produces the highest average power among the nanosecond Nd-doped Q-switched lasers by GNRs-based SA. The applied GNRs are prepared using a seed-mediated growth method and then dropped onto the quartz substrate to fabricate the SA. The average power of the Q-switched laser is 516 mW with the shortest pulse duration of 606.7 ns and the repetition rate of 265.1 kHz.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020011 (2018)
Graphene/MoS2 heterostructure: a robust mid-infrared optical modulator for Er3+-doped ZBLAN fiber laser
Pinghua Tang, Yue Tao, Yuliang Mao, Man Wu, Zongyu Huang, Shengnan Liang, Xinhang Chen, Xiang Qi, Bin Huang, Jun Liu, and Chujun Zhao

We have prepared the graphene/MoS2 heterostructure by a hydrothermal method, and presented its nonlinear absorption parameters and application as a nonlinear optical modulator in the mid-infrared region. Using the nonlinear optical modulator, stable passively Q-switched operation of an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser at ～2.8 μm can be obtained. The Q-switched Er3+-doped ZBLAN fiber laser can yield per-pulse energy up to 2.2 μJ with the corresponding pulse width and pulse repetition rate of 1.9 μs and 45 kHz, respectively. Our results indicate that the graphene/MoS2 heterostructure can be a robust optical modulator for pulsed lasers in the mid-infrared spectral range.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020012 (2018)
Graphene oxide for diode-pumped Tm:YLF passively Q-switched laser at 2 μm
Yuqian Zu, Cheng Zhang, Yongjing Wu, Jingjing Liu, Jie Liu, and Yonggang Wang

A diode-pumped Tm:YLF passively Q-switched laser at 2 μm was first demonstrated by using graphene oxide (GO) as a saturable absorber (SA). In this letter, continuous-wave (CW) laser and pulse laser performances were studied meticulously and systematically. It reasonably showed the dependence of the pulse duration, pulse energy, and pulse repetition rate on the absorbed power. A maximum repetition rate of 38.33 kHz and a single pulse energy of 9.89 μJ were obtained.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020013 (2018)
Tunable passively Q-switched ytterbium-doped fiber laser with mechanically exfoliated GaSe saturable absorber
H. Ahmad, S. N. Aidit, S. I. Ooi, and Z. C. Tiu

A tunable passively Q-switched ytterbium-doped fiber laser using few-layer gallium selenide (GaSe) as a saturable absorber (SA) is demonstrated. The few-layer GaSe SA, which is fabricated by the mechanical exfoliation method, is able to generate a Q-switched fiber laser that has a maximum repetition rate of 92.6 kHz and a minimum pulsed width of 2.3 μs. The highest pulse energy exhibited by the generated pulse is 18.8 nJ with a signal to noise ratio of ～40 dB. The tunability of the proposed laser covers from 1042 to 1082 nm, giving a tuning range of 40 nm.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020014 (2018)
Silver nanorods absorber for passively Q-switched Nd,$Gd:CaF2$ laser
Yongjing Wu, Siyuan Pang, Yuqian Zu, Qianqian Peng, Jimin Yang, Jie Liu, and Liangbi Su

Using a novel silver nanorods absorber with a localized surface plasmon resonance absorption peak at 1.06 μm, we obtain a diode-pumped passively Q-switched (PQS) Nd,Gd:CaF2 disordered crystal laser output. Its PQS pulse laser performances are studied comprehensively and systematically in this Letter. The single pulse energy and peak power can be attained to 2.15 μJ and 2.06 W, respectively.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020015 (2018)
Dual-wavelength $Bi2Se3$-based passively Q-switching $Nd3+$-doped glass all-fiber laser
Xiaofeng Rong, Saiyu Luo, Wensong Li, Shuisen Jiang, Xigun Yan, Xiaofeng Guan, Zhiyong Zhou, Bin Xu, Nan Chen, Degui Wang, Huiying Xu, and Zhiping Cai

We demonstrate a dual-wavelength passively Q-switched Nd3+-doped glass fiber laser using a few-layer topological insulator Bi2Se3 as a saturable absorber (SA) for the first time, to the best of our knowledge. The laser resonator is a simple and compact linear cavity using two fiber end-facet mirrors. The SA is fabricated by Bi2Se3/polyvinyl alcohol composite film. By inserting the SA into the laser cavity, a stable Q-switching operation is achieved with the shortest pulse width and maximum pulse repetition rate of 601 ns and 205.2 kHz, respectively. The maximum average output power and maximum pulse energy obtained are about 6.6 mW and 38.8 nJ, respectively.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020016 (2018)
Passively Q-switched ytterbium-doped fiber laser using the evanescent field interaction with bulk-like WTe2 particles
Seunghwan Ko, Jinho Lee, and Ju Han Lee

The potential of bulk-like WTe2 particles for the realization of a passive Q-switch operating at the 1 μm wavelength was investigated. The WTe2 particles were prepared using a simple mechanical exfoliation method together with Scotch tape. By attaching bulk-like WTe2 particles, which remained on the top of the sticky surface of a small segment of the Scotch tape, to the flat side of a side-polished fiber, a saturable absorber (SA) was readily implemented. A strong saturable absorption was then readily obtained through an evanescent field interaction with the WTe2 particles. The modulation depth of the prepared SA was measured as ～2.18% at 1.03 μm. By incorporating the proposed SA into an all-fiberized ytterbium-doped fiber ring cavity, stable Q-switched pulses were readily achieved.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020017 (2018)
Enhanced saturable absorption of $MoS2$ black phosphorus composite in 2 μm passively Q-switched Tm: YAP laser
Yang Xue, Zhenda Xie, Zhilin Ye, Xiaopeng Hu, Jinlong Xu, and Han Zhang

We report the fabrication of an MoS2 black phosphorus (BP) composite saturable absorber by liquid phase exfoliation and the spin-coating method and further exploitation to build a 2 μm passively Q-switched Tm:YAP laser. Such a composite based Q-switched laser with a duration of 488 ns and corresponding peak power of 85.9 W is obtained, which shows an improved saturable absorption effect than that of single MoS2 (616 ns, 68.7 W) and BP (932 ns, 22.4 W). The results indicate that simple and reasonable fabrication of the vertical composite from two-dimensional atomic layer materials opens up the possibility to create an unprecedented saturable absorber with exciting properties.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020018 (2018)
Passively harmonic mode-locked erbium-doped fiber laser at a 580  MHz repetition rate based on carbon nanotubes film
Qianqian Huang, Tianxing Wang, Chuanhang Zou, Mohammed AlAraimi, Aleksey Rozhin, and Chengbo Mou

We propose and demonstrate a passively harmonic mode-locked erbium-doped fiber laser (EDFL) using carbon nanotubes polyvinyl alcohol (CNTs-PVA) film. The laser allows generation of the pulses with a repetition rate of 580 MHz, which corresponds to the 22nd harmonics of a 26.3 MHz fundamental repetition rate under 323 mW pump power. A particularly noteworthy feature of the pulses is the super-mode suppression ratio (SMSR), which is over 40 dB, indicating a stable operation.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020019 (2018)
2  μm mode-locking laser performances of sol-gel-fabricated large-core Tm-doped silica fiber
Yan Ren, Zhipeng Qin, Guoqiang Xie, Zhen Qiao, Ting Hai, Peng Yuan, Jingui Ma, Liejia Qian, Shikai Wang, Chunlei Yu, and Lili Hu

High-power ultrafast fiber lasers operating at the 2 μm wavelength are extremely desirable for material processing, laser surgery, and nonlinear optics. Here we fabricated large-core (LC) double-cladding Tm-doped silica fiber via the sol-gel method. The sol-gel-fabricated Tm-doped silica (SGTS) fiber had a large core diameter of 30 μm with a high refractive index homogeneity (Δn=2×10 4). With the newly developed LC SGTS fiber as the gain fiber, high-power mode-locking was realized. By using a semiconductor saturable absorber mirror (SESAM) as a mode locker, the LC SGTS fiber oscillator generated mode-locked pulses with an average output power as high as 1.0 W and a pulse duration of 23.9 ps at the wavelength of 1955.0 nm. Our research results show that the self-developed LC Tm-doped silica fiber via the sol-gel method is a promising gain fiber for generating high-power ultrafast lasers in the 2 μm spectral region.

Chinese Optics Letters
Feb. 10, 2018, Vol. 16 Issue 2 020020 (2018)
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