2018, 16(2) Column
Chinese Optics Letters 第16卷 第2期
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.
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.
040.5160 Photodetectors 160.1890 Detector materials 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 (MoS 2 )-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), MoS 2 generates heat, changes the refractive index of MoS 2 , and modulates the polarization of light. The obtained thermal all-optical modulator has a rise time of 526 μs.
230.1150 All-optical devices 160.4330 Nonlinear optical materials 130.4815 Optical switching devices 2D noncarbon materials-based nonlinear optical devices for ultrafast photonics [Invited]Download:1034次
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.
140.3510 Lasers, fiber 140.4050 Mode-locked lasers 140.3540 Lasers, Q-switched 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.
140.3480 Lasers, diode-pumped 140.3540 Lasers, Q-switched 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, MoS 2 , 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.
120.6200 Spectrometers and spectroscopic instrumentation 160.4760 Optical properties 180.5655 Raman microscopy Materials in the transition metal dichalcogenide family, including WS 2 , MoS 2 , WSe 2 , and MoSe 2 , etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties. Compared with WS 2 and MoS 2 , the monolayered MoTe 2 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, MoTe 2 is deposited on the surface of the tapered fiber to be assembled into the saturable absorber. We first implement the MoTe 2 -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 MoTe 2 is a promising 2D material for ultrafast photonic devices in the high-power Q -switched fiber lasers.
160.4330 Nonlinear optical materials 140.3540 Lasers, Q-switched As the typical material of two-dimensional transition metal dichalcogenides (TMDs), few-layered MoS 2 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 MoS 2 -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.
160.4330 Nonlinear optical materials 140.4050 Mode-locked lasers 140.3510 Lasers, fiber 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 / cm 2 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.
140.3500 Lasers, erbium 140.3510 Lasers, fiber 140.3540 Lasers, Q-switched 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.
140.3510 Lasers, fiber 140.3280 Laser amplifiers 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.
160.3380 Laser materials 140.3540 Lasers, Q-switched 160.4236 Nanomaterials We have prepared the graphene / MoS 2 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 Er 3 + -doped ZrF 4 - BaF 2 - LaF 3 - AlF 3 - NaF (ZBLAN) fiber laser at ~ 2.8 μ m can be obtained. The Q -switched Er 3 + -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 / MoS 2 heterostructure can be a robust optical modulator for pulsed lasers in the mid-infrared spectral range.
160.4330 Nonlinear optical materials 140.3070 Infrared and far-infrared lasers 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.
140.3380 Laser materials 140.3480 Lasers, diode-pumped 140.3540 Lasers, Q-switched 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.
060.3510 Lasers, fiber 140.3540 Lasers, Q-switched 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 : CaF 2 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.
140.0140 Lasers and laser optics 140.3380 Laser materials 140.3480 Lasers, diode-pumped 140.3540 Lasers, Q-switched We demonstrate a dual-wavelength passively Q-switched Nd 3 + -doped glass fiber laser using a few-layer topological insulator Bi 2 Se 3 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 Bi 2 Se 3 /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.
060.3510 Lasers, fiber 140.3540 Lasers, Q-switched 140.3530 Lasers, neodymium The potential of bulk-like WTe 2 particles for the realization of a passive Q -switch operating at the 1 μm wavelength was investigated. The WTe 2 particles were prepared using a simple mechanical exfoliation method together with Scotch tape. By attaching bulk-like WTe 2 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 WTe 2 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.
140.3510 Lasers, fiber 140.3540 Lasers, Q-switched We report the fabrication of an MoS 2 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 MoS 2 (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.
140.3540 Lasers, Q-switched 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.
140.3500 Lasers, erbium 160.4236 Nanomaterials 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 (Δ n = 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.
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