Graphene mode-locked femtosecond laser at 2 μm wavelength

High-performance Mach-Zehnder modulator using tailored plasma dispersion effects in an ITO/graphene-based waveguide

A high-performance electro-optic Mach-Zehnder modulator (MZM) with outstanding characteristics is proposed. The MZM is in a push-pull configuration that is constructed using an ITO/graphene-based silicon waveguide. A novel idea for engineering of the plasma dispersion effect in an ITO/graphene-based waveguide is proposed so that the modulation characteristics of the MZM are highly improved. Plasma dispersion effects of ITO and graphene layers are tailored in such a way that a large difference between real parts of guided mode effective index of the two arms is achieved while their corresponding imaginary parts are equal. As a result, a very low [Formula: see text] of [Formula: see text] is achieved. To the best of our knowledge, this is one of the lowest [Formula: see text] reported for an electro-optic modulator. In addition, the proposed modulator exhibits a very high extinction ratio of more than 30 dB, low insertion loss of 2.8 dB and energy consumption of as low as 10 fJ/bit, which are all promising for optical communication and processing systems.

Black Phosphorus/Polymers: Status and Challenges

As a newly emerged mono-elemental nanomaterial, black phosphorus (BP) has been widely investigated for its fascinating physical properties, including layer-dependent tunable band gap (0.3-1.5 eV), high ON/OFF ratio (10⁴ ), high carrier mobility (10³ cm² V^-1 s^-1 ), excellent mechanical resistance, as well as special in-plane anisotropic optical, thermal, and vibrational characteristics. However, the instability caused by chemical degradation of its surface has posed a severe challenge for its further applications. A focused BP/polymer strategy has more recently been developed and implemented to hurdle this issue, so at present BP/polymers have been developed that exhibit enhanced stability, as well as outstanding optical, thermal, mechanical, and electrical properties. This has promoted researchers to further explore the potential applications of black phosphorous. In this review, the preparation processes and the key properties of BP/polymers are reviewed, followed by a detailed account of their diversified applications, including areas like optoelectronics, bio-medicine, and energy storage. Finally, in accordance with the current progress, the prospective challenges and future directions are highlighted and discussed.

Recent Progress of Two-Dimensional Materials for Ultrafast Photonics

Owing to their extraordinary physical and chemical properties, two-dimensional (2D) materials have aroused extensive attention and have been widely used in photonic and optoelectronic devices, catalytic reactions, and biomedicine. In particular, 2D materials possess a unique bandgap structure and nonlinear optical properties, which can be used as saturable absorbers in ultrafast lasers. Here, we mainly review the top-down and bottom-up methods for preparing 2D materials, such as graphene, topological insulators, transition metal dichalcogenides, black phosphorus, and MXenes. Then, we focus on the ultrafast applications of 2D materials at the typical operating wavelengths of 1, 1.5, 2, and 3 μm. The key parameters and output performance of ultrafast pulsed lasers based on 2D materials are discussed. Furthermore, an outlook regarding the fabrication methods and the development of 2D materials in ultrafast photonics is also presented.

High-order mode conversion in a few-mode fiber via laser-inscribed long-period gratings at 1.55 µm and 2 µm wavebands

We demonstrate high-order mode conversion in a few-mode fiber (FMF) via CO₂ laser inscribed long-period fiber gratings (LPFGs) at both the 1.55 µm and 2 µm wavebands. At the 1.55 µm waveband, five high-order core modes (the LP₁₁, LP₂₁, LP₀₂, LP₃₁, and LP₁₂ modes) can be coupled from the LP₀₁ mode with high efficiency by the FMF-LPFGs. The orbital angular momentum beams with different topological charges (±1,±2,±3) are experimentally generated by adjusting the polarization controllers. At the 2 µm waveband, three high-order modes (the LP₁₁, LP₂₁, and LP₀₂ mode) can be coupled by the FMF-LPFGs with different grating periods. The proposed LPFG-based mode converters could have a potential prospects in mode-division multiplexing and multiwindow broadband optical communication applications.

2.8 µm passively Q-switched Er:ZBLAN fiber laser with an Sb saturable absorber mirror

A Q-switched Er:ZBLAN fiber laser operating at 2.8 µm was realized by employing Sb as the saturable material. The Sb material was deposited on a gold mirror by the magnetron-sputtering deposition method to develop a saturable absorber mirror (SAM). By employing the Sb-SAM in an Er:ZBLAN fiber laser, stable Q-switching operation was achieved at central wavelength of 2799.7 nm with the repetition rates ranging from 33.3 to 58.8 kHz and the pulse duration ranging from 5.7 to 1.7 µs. The Sb-SAM still works stably under the maximum pump power of 5.6 W, with an output power of 59 mW corresponding to the pulse energy of 1.03 µJ. To our knowledge, this was the first demonstration of Sb-based saturable material in Er:ZBLAN fiber laser for mid-infrared Q-switched pulse generation operating in the 2.8 µm regime, indicating its potential applications in the mid-infrared waveband.

Tellurium as the saturable absorber for the passively Q-switched laser at 1.34 µm

The novel two-dimensional (2D) elementary tellurium is currently of great interest in optoelectronic and photonic applications. In this contribution, 2D tellurium nanosheets were successfully created by using the liquid-phase exfoliation method. With the as-prepared tellurium nanosheets as the saturable absorber (SA), we realized a passively $ Q $Q-switched ${\rm Nd} \text:{{\rm YVO}_4}$Nd:YVO₄ laser operating at 1342 nm with a pulse width of 947 ns and single pulse energy of 2.25 µJ. Our work indicated the tellurium SA could be an efficient $ Q $Q-switcher for a near-infrared solid-state laser.

1886-nm mode-locked and wavelength tunable Tm-doped CaF2 lasers

A 3 at.% Tm-doped CaF₂ crystal was grown successfully and used as a gain medium. A high-efficiency continuous-wave laser and wide tuning performance were demonstrated in this crystal, and passive mode-locking laser operation was realized for the first time, to the best of our knowledge. For continuous-wave operation, the maximum output power was 2.71 W with a high slope efficiency of 70.3%. Using a quartz birefringent filter, a continuous tuning range of approximately 190 nm was observed in the tuning mode. In addition, a passively mode-locked Tm³⁺:CaF₂ laser emitting at 1886.8 nm was achieved with a semiconductor saturable absorber mirror. At an absorbed pump power of 2.65 W, a pulse duration with tens of picoseconds was obtained at a pulse repetition rate of 96.35 MHz.

Gold nanostars as a Q-switcher for the mid-infrared erbium-doped fluoride fiber laser

We demonstrated passively Q-switched mid-infrared (mid-IR) erbium-doped fiber lasers by using gold nanostars (GNSs) as the Q-switcher. The nonlinear optical responses of the GNSs synthesized via the seed-mediated method have been characterized via a Z-scan technique, and the modulation depth and saturation intensity of the GNSs are measured to be 25% and 15.75  kW/cm², respectively. The Q-switched fiber laser can deliver a maximum average power of 454 mW with corresponding pulse energy of 3.6 μJ and pulse duration of 536 ns at a repetition rate of 125 kHz under the incident pump power 3.5 W. To the best of our knowledge, this is the first Letter that reports that the GNSs can act as a Q-switcher for the mid-IR erbium-doped ZBLAN fiber lasers. This Letter can deepen the understanding of the nonlinear optical behavior of the gold nanomaterials and may make inroads for the excellent mid-infrared optoelectronic devices.

Black phosphorus Q-switched and mode-locked mid-infrared Er:ZBLAN fiber laser at 3.5 μm wavelength

With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber lasers at 3.5 μm have become a fascinating area of research. However, limited by the absence of suitable saturable absorber, passively Q-switched and mode-locked fiber lasers have not been realized in this spectral region. Based on the layer-dependent bandgap and excellent photoelectric characteristics of black phosphorus (BP), BP is a promising candidate for saturable absorber near 3.5 μm. Here, we fabricated a 3.5-μm saturable absorber mirror (SAM) by transferring BP flakes onto a Au-coated mirror. With the as-prepared BP SAM, we realized Q-switching and mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 μm. To the best of our knowledge, it is the first time to achieve passively Q-switched and mode-locked pulses in 3.5 μm spectral region. The research results will not only promote the development of 3.5-μm pulsed fiber lasers but also open the photonics application of two-dimensional materials in this spectral region.

Sub-200 femtosecond dispersion-managed soliton ytterbium-doped fiber laser based on carbon nanotubes saturable absorber

Ultrafast fiber laser light sources attract enormous interest due to the booming applications they are enabling, including long-distance communication, optical metrology, detecting technology of infra-biophotons, and novel material processing. In this paper, we demonstrate 175 fs dispersion-managed soliton (DMS) mode-locked ytterbium-doped fiber (YDF) laser based on single-walled carbon nanotubes (SWCNTs) saturable absorber (SA). The output DMSs have been achieved with repetition rate of 21.2 MHz, center wavelength of 1025.5 nm, and a spectral width of 32.7 nm. The operation directly pulse duration of 300 fs for generated pulse is the reported shortest pulse width for broadband SA based YDF lasers. By using an external grating-based compressor, the pulse duration could be compressed down to 175 fs. To the best of our knowledge, it is the shortest pulse duration obtained directly from YDF laser based on broadband SAs. In this paper, SWCNTs-SA has been utilized as the key optical component (mode locker) and the grating pair providing negative dispersion acts as the dispersion controller.

Magnetron-sputtering deposited WTe2for an ultrafast thulium-doped fiber laser

Ultrafast pulse generation was demonstrated in a thulium-doped fiber laser mode-locked by magnetron-sputtering deposited WTe₂ with a modulation depth, a nonsaturable loss, and a saturable intensity of 31%, 34.3%, and 7.6  MW/cm², respectively. Stable soliton pulses could be obtained at a 1915.5 nm central wavelength with a pulse duration of 1.25 ps, an average output power of 39.9 mW, and a signal-to-noise ratio of 95 dB. To the best of our knowledge, this was the first demonstration of WTe₂-based saturable absorbers in fiber lasers at a 2 μm regime.

Large-area highly crystalline WSe2 atomic layers for ultrafast pulsed lasers

Large-area and highly crystalline transition metal dichalcogenides (TMDs) films possess superior saturable absorption compared to the TMDs nanosheet counterparts, which make them more suitable as excellent saturable absorbers (SA) for ultrafast laser technology. Thus far, the nonlinear optical properties of large-scale WSe₂ and its applications in ultrafast photonics have not yet been fully investigated. In this work, the saturable absorption of chemical vapor deposition (CVD) grown WSe₂ films with large-scale and high quality are studied and the use of WSe₂ films as a broadband SA for passively mode-locked fiber lasers at both 1.5 and 2 μm ranges is demonstrated. To enhance the light-material interaction, large-area WSe₂ film is tightly transferred onto the side wall of a microfiber to form a hybrid structure, which realizes strong evanescent wave interaction between light and WSe₂ film. The integrated microfiber-WSe₂ device shows a large modulation depth of 54.5%. Using the large-area WSe₂ as a mode-locker, stable soliton mode-locked pulse generation is achieved and the pulse durations of 477 fs (at 1.5 μm) and 1.18 ps (at 2.0 μm) are demonstrated, which suggests that the large-area and highly crystalline WSe₂ films afford an excellent broadband SA for ultrafast photonic applications.

Diode-pumped Tm:KY(WO4)2 laser passively modelocked with a GaSb-SESAM

We present the first diode-pumped modelocked thulium (Tm³⁺) laser based on a double-tungstate crystalline gain material. The solid-state laser consists of a Tm:KY(WO₄)₂ crystal as gain medium and a GaInSb/GaSb quantum well saturable absorber for self-starting passive mode locking. The laser is pumped by a multi-mode fiber-coupled laser diode at a wavelength of 793 nm. An average output power of 202 mW is achieved at a center wavelength of 2032 nm. Pulses with duration of 3 ps are generated at a repetition rate of 139.6 MHz. We also report on the first noise evaluation of a modelocked solid-state laser operating in the 2-µm wavelength range. We measured a timing jitter of sub-100 fs and a relative intensity noise of only 0.04% (frequency range from 500 Hz to 1 MHz).

Kerr-lens mode-locked Tm3+:Sc2O3 single-crystal laser in-band pumped by an Er:Yb fiber MOPA at 1611 nm

We demonstrate a Kerr-lens mode-locked Tm³⁺:Sc₂O₃ single-crystal laser in-band pumped by an Er³⁺:Yb³⁺ fiber master oscillator power amplifier at 1611 nm. Pulses as short as 166 fs with an average output power of 440 mW are obtained. The spectral bandwidth and center wavelength are 29.3 and 2124 nm, respectively. At a longer pulse duration of 298 fs, we obtain 1 W of average output power. The repetition rate is 95 MHz, and the conversion efficiency against the absorbed pump power is as high as 47%. To the best of our knowledge, this is the first Kerr-lens mode-locked Tm³⁺-doped solid state laser.

Graphene mode-locked femtosecond Cr2+:ZnS laser with ~300 nm tuning range

Graphene has proved to be an excellent broadband saturable absorber for mode-locked operation of ultrafast lasers. However, for the mid-infrared (mid-IR) range where broadly tunable sources are in great needs, graphene-based broadly tunable ultrafast mid-IR lasers have not been demonstrated so far. Here, we report on passive mode-locking of a mid-IR Cr:ZnS laser by utilizing a transmission-type monolayer graphene saturable absorber and broad spectral tunability between 2120 nm and 2408 nm, which is the broadest tuning bandwidth ever reported for graphene mode-locked mid-IR solid-state lasers. The recovery time of the saturable absorber is measured to be ~2.4 ps by pump-probe technique at a wavelength of 2350 nm. Stably mode-locked Cr:ZnS laser delivers Fourier transform-limited 220-fs pulses with a pulse energy of up to 7.8 nJ.

Generation of 30 fs pulses from a diode-pumped graphene mode-locked Yb:CaYAlO4 laser

Stable 30 fs pulses centered at 1068 nm (less than 10 optical cycles) are demonstrated in a diode pumped Yb:CaYAlO4 laser by using high-quality chemical vapor deposited monolayer graphene as the saturable absorber. The mode-locked 8.43 optical-cycle pulses have a spectral bandwidth of ∼50  nm and a pulse repetition frequency of ∼113.5  MHz. To the best of our knowledge, this is the shortest pulse ever reported for graphene mode-locked lasers and mode-locked Yb-doped bulk lasers. Our experimental results demonstrate that graphene mode locking is a very promising practical technique for directly generating few-cycle optical pulses from a laser oscillator.

Graphite saturable absorber based on the pencil-sketching method for Q-switching of an erbium fiber laser

We experimentally demonstrate a practical and simple method for the preparation of a graphite-based, fiberized saturable absorber (SA). Our SA is prepared by using a low-cost graphite-core pencil that is commercially available from stationary stores to uniformly shade the flat end of a fiber ferrule. The saturable-absorption performance of the prepared SA was experimentally tested, and the feasibility of using the SA as a passive Q-switch was investigated through its incorporation into an erbium-doped-fiber ring cavity. The modulation depth of the SA is ∼1%, and the Q-switched pulses of a 1.98 μs temporal width were readily obtained at a repetition rate of 46.08 kHz.

Mid-infrared mode-locked pulse generation with multilayer black phosphorus as saturable absorber

A mid-infrared saturable absorber mirror is successfully fabricated by transferring the mechanically exfoliated black phosphorus onto the gold-coated mirror. With the as-prepared black phosphorus saturable absorber mirror, a continuous-wave passively mode-locked Er:ZBLAN fiber laser is demonstrated at the wavelength of 2.8 μm, which delivers a maximum average output power of 613 mW, a repetition rate of 24 MHz, and a pulse duration of 42 ps. To the best of our knowledge, this is the first time a black phosphorus mode-locked laser at 2.8 μm wavelength has been demonstrated. Our results demonstrate the feasibility of black phosphorus flake as a new two-dimensional material for application in mid-infrared ultrafast photonics.

Ultrasensitive nonlinear absorption response of large-size topological insulator and application in low-threshold bulk pulsed lasers

Dirac-like topological insulators have attracted strong interest in optoelectronic application because of their unusual and startling properties. Here we report for the first time that the pure topological insulator Bi₂Te₃ exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation. The Bi₂Te₃ sheets with lateral size up to a few micrometers showed extremely low saturation absorption intensities of only 1.1 W/cm² at 1.0 and 1.3 μm, respectively. Benefiting from this sensitive response, a Q-switching pulsed laser was achieved in a 1.0 μm Nd:YVO₄ laser where the threshold absorbed pump power was only 31 mW. This is the lowest threshold in Q-switched solid-state bulk lasers to the best of our knowledge. A pulse duration of 97 ns was observed with an average power of 26.1 mW. A Q-switched laser at 1.3 μm was also realized with a pulse duration as short as 93 ns. Moreover, the mode locking operation was demonstrated. These results strongly exhibit that Bi₂Te₃ is a promising optical device for constructing broadband, miniature and integrated high-energy pulsed laser systems with low power consumption. Our work clearly points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.

Black phosphorus as saturable absorber for the Q-switched Er:ZBLAN fiber laser at 2.8 μm

Black phosphorus, a newly emerged two-dimensional material, has attracted wide attention as novel photonic material. Here, multilayer black phosphorus is successfully fabricated by liquid phase exfoliation method. By employing black phosphorus as saturable absorber, we demonstrate a passively Q-switched Er-doped ZBLAN fiber laser at the wavelength of 2.8 μm. The modulation depth and saturation fluence of the black phosphorus saturable absorber are measured to be 15% and 9 μJ/cm(2), respectively. The Q-switched fiber laser delivers a maximum average power of 485 mW with corresponding pulse energy of 7.7 μJ and pulse width of 1.18 μs at repetition rate of 63 kHz. To the best of our knowledge, this is the first time to demonstrate that black phosphorus can realize Q-switching of 2.8-μm fiber laser. Our research results show that black phosphorus is a promising saturable absorber for mid-infrared pulsed lasers.

1.21 W passively mode-locked Tm:LuAG laser

A watt-level output passively mode-locked Tm:LuAG bulk laser with an InGaAs semiconductor saturable absorber mirror (SESAM) is demonstrated for the first time. A maximum average output power of 1.21 W at 2022.9 nm has been achieved with a pulse duration of 38 ps and a repetition rate of 129.2 MHz. The results indicate the potential of Tm:LuAG crystals as candidate for realizing high power ultrafast lasers at 2 μm.

463-MHz fundamental mode-locked fiber laser based on few-layer MoS(2) saturable absorber

We report on the passive-mode-locking operation of a fiber laser with a fundamental repetition rate of 463 MHz based on molybdenum disulfide (MoS(2)) saturable absorber (SA). By embedding MoS(2) into polyvinyl alcohol (PVA) thin film, MoS(2)-PVA SA was prepared with a modulation depth of 2.7% and a saturation intensity of 137  MW/cm(2). The mode-locked fiber laser-employed MoS(2)-PVA SA was achieved with center wavelength of 1556.3 nm, 3-dB bandwidth of 6.1 nm, output power of 5.9 mW, and an extinction ratio of up to 97 dB in the RF spectrum. The demonstration of mode-locking operation with high fundamental repetition rate and high spectral purity indicates that MoS(2)-PVA SA can be a good candidate for high-precision ultrafast applications.

Towards low timing phase noise operation in fiber lasers mode locked by graphene oxide and carbon nanotubes at 1.5 µm

We investigate the timing phase noise of fiber lasers mode locked by graphene oxide (GO) and carbon nanotubes (CNTs), respectively, integrated in a linear cavity fiber laser in the reflecting operation. Due to the shorter decay time of the GO and CNTs, weaker slow saturable absorber effects are expected and mode-locked lasers based on these two saturable absorbers exhibit low excess timing phase noise coupled from the laser intensity noise. Compared with a reference laser mode locked by semiconductor saturable absorber mirror (SESAM), GO based laser obtains a timing phase noise reduction of 7 dB at 1 kHz and a timing jitter reduction of 45% experimentally whereas CNTs based laser obtains a timing phase noise reduction of 3 dB and a timing jitter reduction of 29%. This finding suggests that saturable absorbers with short decay time have the potential for achieving mode locking operation with low timing phase noise, which is important for applications including frequency metrology, high-precision optical sampling, clock distribution and optical sensing.

A 2.95 GHz, femtosecond passive harmonic mode-locked fiber laser based on evanescent field interaction with topological insulator film

By utilizing the pulsed laser deposition (PLD) method, we fabricated a kind of microfiber-based topological insulator (TI) saturable absorber (SA) which has inherent merits of effective and robust properties. We also proposed a newly explanation for the impact of nonlinear effect of SA on the harmonic mode-locking (HML) behavior. Upon employing on the SA, we achieved stable fundamental mode-locking (FML) at central wavelength of 1562.4 nm with pulse duration as short as 320 fs. By adjusting the intracavity polarization state at maximum pump power of 395 mW, we obtained stable femtosecond harmonic soliton pulse generation with repetition rate of 2.95 GHz and output power of 45.3 mW. Our results demonstrated that the microfiber-based TI PLD film SA is a promising device for practical multi-GHz ultrashort pulses generation.

Passively Q-switched 2 μm Tm:YAP laser based on graphene saturable absorber mirror

Using high-quality single-layer graphene as a saturable absorber, Tm:YAlO₃ (Tm:YAP) crystal as the gain medium, we demonstrated a laser-diode-pumped, compact, passively Q-switched (PQS) solid-state laser in the 2 μm region. The maximum average output power was 362 mW, with the corresponding largest pulse repetition rate and pulse energy of 42.4 kHz and 8.5 μJ, respectively. Under the same pump power, the pulse width of 735 ns was obtained, which is, to our best knowledge, the shortest pulse width among Tm-doped solid-state PQS lasers using graphene saturable absorber mirrors.

Wavelength-versatile graphene-gold film saturable absorber mirror for ultra-broadband mode-locking of bulk lasers

An ultra-broadband graphene-gold film saturable absorber mirror (GG-SAM) with a spectral coverage exceeding 1300 nm is experimentally demonstrated for mode-locking of bulk solid-state lasers. Owing to the p-type doping effect caused by graphene-gold film interaction, the graphene on gold-film substrate shows a remarkably lower light absorption relative to pristine graphene, which is very helpful to achieve continuous-wave mode-locking in low-gain bulk lasers. Using the GG-SAM sample, stable mode-locking is realized in a Yb:YCOB bulk laser near 1 μm, a Tm:CLNGG bulk laser near 2 μm and a Cr:ZnSe bulk laser near 2.4 μm. The saturable absorption is characterised at an intermediate wavelength of 1.56 μm by pump-probe measurements. The as-fabricated GG-SAM with ultra-broad bandwidth, ultrafast recovery time, low absorption, and low cost has great potential as a universal saturable absorber mirror for mode-locking of various bulk lasers with unprecedented spectral coverage.

Sapphire-based graphene saturable absorber for long-time working femtosecond lasers

We report a long-time working femtosecond laser using metal-free sapphire-based graphene as a saturable absorber (SA). The sapphire-based graphene yielded excellent nonlinear saturable absorption properties and was demonstrated to be suitable as an SA for an ultrafast solid-state laser. Stable mode-locked pulses of 325 fs were obtained at a central wavelength of 1032 nm with a repetition rate of 66.3 MHz. At pump power of 8.23 W the average output power was 1.78 W and the highest pulse energy reached 26.8 nJ with a peak power of 72.6 kW. Our work opens up a facile route for making reliable graphene SA in the mode-locking technique and also displays an exciting prospect in making low-cost and ultrafast lasers.

A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi2Te3 topological insulator

We experimentally demonstrate a femtosecond mode-locked, all-fiberized laser that operates in the 2 μm region and that incorporates a saturable absorber based on a bulk-structured bismuth telluride (Bi(2)Te(3)) topological insulator (TI). Our fiberized saturable absorber was prepared by depositing a mechanically exfoliated, ~30 μm-thick Bi(2)Te(3) TI layer on a side-polished optical fiber platform. The bulk crystalline structure of the prepared Bi(2)Te(3) layer was confirmed by Raman and X-ray photoelectron spectroscopy measurements. The modulation depth of the prepared saturable absorber was measured to be ~20.6%. Using the saturable absorber, it is shown that stable, ultrafast pulses with a temporal width of ~795 fs could readily be generated at a wavelength of 1935 nm from a thulium/holmium co-doped fiber ring cavity. This experimental demonstration confirms that bulk structured, TI-based saturable absorbers can readily be used as an ultra-fast mode-locker for 2 μm lasers.

Diode-pumped 1988-nm Tm:YAP laser mode-locked by intracavity second-harmonic generation in periodically poled LiNbO₃

We report a diode-pumped intracavity second-harmonic generation mode-locked solid-state Tm:YAP laser operating at 1988 nm using a periodically poled congruent LiNbO3 as the nonlinear crystal. The threshold of continuous wave mode locking is 11.6 W. The maximum output power is 1.67 W, while the shortest pulse obtained is 4.7 ps at a repetition rate of 97.09 MHz.

Graphene mode-locked Cr:ZnS chirped-pulse oscillator

We report the first to our knowledge high-energy graphene mode-locked solid-state laser operating in the positive dispersion regime. Pulses with 15.5 nJ energy and 42 nm spectral bandwidth with 0.87 ps duration were obtained at 2.4 μm wavelength. The output can be compressed down to 189 fs. The graphene absorber damage threshold was established at fluence approaching 1 mJ/cm².

High-efficiency femtosecond Yb:Gd3Al(0.5)Ga(4.5)O12 mode-locked laser based on reduced graphene oxide

A diode-pumped Yb-doped Gd(3)Al(0.5)Ga(4.5)O(12) mode-locked bulk laser based on chemically reduced graphene oxide (RGO) has been demonstrated for the first time to our best knowledge. Pulses with duration of 643 fs were produced at the central wavelength of 1041.1 nm. A maximum average output power of 0.8 W was obtained from the RGO mode-locked laser, corresponding to a slope efficiency of 20.1% and a peak power of 27.6 kW. The results indicate that RGO is suitable for obtaining high-power and high-efficiency ultrafast lasers.

Mode-locked pulse generation from an all-fiberized, Tm-Ho-codoped fiber laser incorporating a graphene oxide-deposited side-polished fiber

An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated. It showed that the higher-order soliton compression effect caused by the combination of anomalous dispersion and Kerr nonlinearity can provide incorrect pulse-width information. Third, an experimental investigation into the precise role of the graphene oxide-deposited side-polished fiber was carried out to determine whether its polarization-dependent loss (PDL) can be a substantial contributor to mode-locking through nonlinear polarization rotation. By comparing its performance with that of a gold-deposited side-polished fiber, the PDL contribution to mode-locking was found to be insignificant, and the dominant mode-locking mechanism was shown to be saturable absorption due to mutual interaction between the evanescent field of the oscillated beam and the deposited graphene oxide particles.

Spectral hole burning in silicon waveguides with a graphene layer on top

We present an experimental study of the nonlinear absorption of graphene-on-silicon waveguides. The wavelength dependence of absorption saturation from a narrow linewidth optical pump is measured. Spectral hole burning (SHB) introduces a decrease in the probe absorption near the pump wavelength, which may be distinguished from the free carrier absorption (FCA) by using the time dependence of the buildup of the free carrier population. Beyond SHB bandwidth, only FCA dominates the waveguide loss. The spectral bandwidth of absorption bleaching from SHB is measured to have a full width at half-maximum of ~12 meV (~20 nm) at 16.8 dBm pump power.

Sub-100-fs Cr:YAG laser mode-locked by monolayer graphene saturable absorber

We report on mode-locking of a Cr:YAG laser at 1516 nm using a monolayer graphene-based saturable absorber of transmission type generating 91 fs pulses with a Fourier product of 0.38 at an average output power exceeding 100 mW. Stable single-pulse mode-locked operation without any sign of Q-switching instabilities or multiple pulses is achieved.

1.5 GHz picosecond pulse generation from a monolithic waveguide laser with a graphene-film saturable output coupler

We fabricate a saturable absorber mirror by coating a graphene- film on an output coupler mirror. This is then used to obtain Q-switched mode-locking from a diode-pumped linear cavity channel waveguide laser inscribed in Ytterbium-doped Bismuthate Glass. The laser produces 1.06 ps pulses at ~1039 nm, with a 1.5 GHz repetition rate, 48% slope efficiency and 202 mW average output power. This performance is due to the combination of the graphene saturable absorber and the high quality optical waveguides in the laser glass.

Graphene mode-locked femtosecond Cr:ZnSe laser at 2500 nm

We report, for the first time to our knowledge, femtosecond pulse generation from a graphene mode-locked Cr:ZnSe laser at 2500 nm. To minimize the insertion losses at the lasing wavelength, high-quality monolayer graphene transferred on a CaF(2) substrate was used in the experiments. Once mode-locking was initiated, the laser generated a stable train of 226 fs pulses with a time-bandwidth product of 0.39. The mode-locked laser operated at a pulse repetition rate of 77 MHz and produced 80 mW output power with an incident pump power of 1.6 W. To our knowledge, this is the longest laser wavelength at which graphene-based passive mode-locking has been demonstrated to date.

Polarization rotation vector solitons in a graphene mode-locked fiber laser

Polarization rotation vector solitons formed in a fiber laser passively mode locked with atomic layer graphene were experimentally investigated. It was found that different from the case of the polarization locked vector soliton formed in the laser, two extra sets of spectral sidebands always appear on the soliton spectrum of the polarization rotating vector solitons. We confirm that the new sets of spectral sidebands have the same formation mechanism as that of the Kelly sidebands.

Broadly tunable femtosecond Tm:Lu2O3 ceramic laser operating around 2070 nm

Femtosecond mode locking of a Tm-doped Lu2O3 ceramic laser is reported. Transform-limited pulses as short as 180 fs are generated at 2076 nm with an average output power of 400 mW and a pulse repetition frequency of 121.2 MHz. An output power up to 750 mW can be reached at the somewhat longer pulse duration of 382 fs. Femtosecond pulse generation is realized in the 2030-2100 nm spectral range. Passive mode locking was achieved using an ion-implanted InGaAsSb quantum-well-based SESAM.