Guided continuous-wave and graphene-based Q-switched lasers in carbon ion irradiated Nd:YAG ceramic channel waveguide

Femtosecond Laser Written Depressed-Cladding Waveguide 2 × 2, 1 × 2 and 3 × 3 Directional Couplers in Tm3+:YAG Crystal

Ion-doped crystal-based compact devices capable of beam splitting and coupling are enthralling for a broad range of classical and quantum integrated photonics applications. In this work, we report on the fabrication of depressed-cladding waveguide 2D 2 × 2, 1 × 2 and 3D 3 × 3 directional couplers in Tm3+:YAG crystal by femtosecond laser writing. The performances of the couplers are characterized at 810 nm, showing single-mode guidance, polarization independence, finely matched splitting ratios. These results open up new opportunities in the beneficial fabrication of 3D circuits and devices in crystals.

Designing MMI structured beam-splitter in LiNbO3 crystal based on a combination of ion implantation and femtosecond laser ablation

In this work, the design and numerical study of a MMI-based LiNbO₃ beam splitter were presented, with a combination of ion implantation and femtosecond laser ablation as a fabricating strategy. The designed splitters show advantages such as good fabrication tolerance, low insertion loss, compactness, and simple fabrication processes. We also demonstrated that the self-imaging principle could be applied to design low-loss MMI beam splitters for multi-mode input with mode number m = 1 and n>1 by carefully choosing the geometry parameters. The presented fabrication strategy provides an alternative choice for the fabrication of power splitters also with other MMI-based devices in various optical monocrystal chips.

Tailoring the optical properties of atomically-thin WS2via ion irradiation

Two-dimensional transition metal dichalcogenides (TMDCs) exhibit excellent optoelectronic properties. However, the large band gaps in many semiconducting TMDCs make optical absorption in the near-infrared (NIR) wavelength regime impossible, which prevents applications of these materials in optical communications. In this work, we demonstrate that Ar⁺ ion irradiation is a powerful post-synthesis technique to tailor the optical properties of the semiconducting tungsten disulfide (WS₂) by creating S-vacancies and thus controlling material stoichiometry. First-principles calculations reveal that the S-vacancies give rise to deep states in the band gap, which determine the NIR optical absorption of the WS₂ monolayer. As the density of the S-vacancies increases, the enhanced NIR linear and saturable absorption of WS₂ is observed, which is explained by the results of first-principles calculations. We further demonstrate that by using the irradiated WS₂ as a saturable absorber in a waveguide system, the passively Q-switched laser operations can be optimized, thus opening new avenues for tailoring the optical response of TMDCs by defect-engineering through ion irradiation.

Electrically Tunable Nd:YAG waveguide laser based on Graphene

We demonstrate a tunable hybrid Graphene-Nd:YAG cladding waveguide laser exploiting the electro-optic and the Joule heating effects of Graphene. A cladding Nd:YAG waveguide was fabricated by the ion irradiation. The multi-layer graphene were transferred onto the waveguide surface as the saturable absorber to get the Q-switched pulsed laser oscillation in the waveguide. Composing with appropriate electrodes, graphene based capacitance and heater were formed on the surface of the Nd:YAG waveguide. Through electrical control of graphene, the state of the hybrid waveguide laser was turned on or off. And the laser operation of the hybrid waveguide was electrically tuned between the continuous wave laser and the nanosecond pulsed laser.

Tunable Picosecond Laser Pulses via the Contrast of Two Reverse Saturable Absorption Phases in a Waveguide Platform

How to enhance the optical nonlinearity of saturable absorption materials is an important question to improve the functionality of various applications ranging from the high power laser to photonic computational devices. We demonstrate the saturable absorption (SA) of VO2 film attributed to the large difference of optical nonlinearities between the two states of the phase-transition materials (VO2). Such VO2 film demonstrated significantly improved performance with saturation intensity higher than other existing ultrathin saturable absorbers by 3 orders due to its unique nonlinear optical mechanisms in the ultrafast phase change process. Owing to this feature, a Q-switched pulsed laser was fabricated in a waveguide platform, which is the first time to achieve picosecond pulse duration and maintain high peak power. Furthermore, the emission of this VO2 waveguide laser can be flexibly switched between the continuous-wave (CW) and pulsed operation regimes by tuning the temperature of the VO2 film, which enables VO2-based miniature laser devices with unique and versatile functions.

Tailoring nonlinear optical properties of Bi2Se3 through ion irradiation

The nonlinear optical property of topological insulator bismuth selenide (Bi₂Se₃) is found to be well-tailored through ion irradiation by intentionally introducing defects. The increase of the optical modulation depth sensitively depends on the careful selection of the irradiation condition. By implementing the ion irradiated Bi₂Se₃ film as an optical saturable absorber device for the Q-switched wave-guide laser, an enhanced laser performance has been obtained including narrower pulse duration and higher peak power. Our work provides a new approach of tailoring the nonlinear optical properties of materials through ion irradiation, a well-developed chip-technology, which could find wider applicability to other layered two-dimensional materials beyond topological insulators, such as graphene, MoS₂, black phosphours etc.

Q-switched waveguide laser based on two-dimensional semiconducting materials: tungsten disulfide and black phosphorous

Owing to their unique properties, graphene-like two dimensional semiconducting materials, including Tungsten Disulfide (WS2) and Black Phosphorous (BP), have attracted increasing interest from basic research to practical applications. Herein, we demonstrated the ultrafast nonlinear saturable absorption response of WS2 and BP films in the waveguide structure. Through fabricating WS2 and BP films by evaporating the solutions on glass wafers. Saturable absorber films were attached onto the end-facet of the waveguide, which therefore constitutes a resonant cavity for the waveguide laser. Under a pump laser at 810 nm, we could obtain a stable Q-switched operation in the waveguide structure. This work indicated the significant potential of WS2 and BP for the ultrafast waveguide laser.

Cladding-like waveguide structure in Nd:YAG crystal fabricated by multiple ion irradiation for enhanced waveguide lasing

We report on a cladding-like waveguide structure in Nd:YAG crystal fabricated by the multiple carbon ion beam irradiation. After the designed multiple irradiation process, the cladding-like waveguide with triple refractive-index layers were constructed in the region near the surface of the crystal. With such a structure, the waveguiding core was compressed and refractive index profile was modified, resulting in a higher light intensity than that of the single ion-beam-irradiated monolayer waveguide. The waveguide lasing at wavelength of 1064 nm was achieved with enhanced performance in the cladding-like structures with both planar and ridge configurations by the optical pump at 810 nm.

High-gain optical waveguide amplifier based on proton beam writing of Nd:YAG crystal

We report on an optical amplifier based on a Nd:YAG channel waveguide, which was fabricated by proton beam writing. Under the pumping of a continuous wave laser, the high-gain optical amplifications at single wavelength of 1064 nm and wavelength band of 1300 nm -1360 nm were obtained. The maximum gain was 24 dB/cm at 1064 nm and 6 dB/cm at 1319 nm, respectively. This work paves a way to apply proton beam written Nd:YAG waveguides as integrated optical amplifiers for the efficient amplification.

456-mW graphene Q-switched Yb:yttria waveguide laser by evanescent-field interaction

In this Letter, we present a passively Q-switched Yb:Y2O3 waveguide laser using evanescent-field interaction with an atmospheric-pressure-chemical-vapor-deposited graphene saturable absorber. The waveguide, pumped by a broad area diode laser, produced an average output power of 456 mW at an absorbed power of 4.1 W. The corresponding pulse energy and peak power were 330 nJ and 2 W, respectively. No graphene damage was observed, demonstrating the suitability of top-deposited graphene for high-power operation.

Diode-pumped tape casting planar waveguide YAG/Nd:YAG/YAG ceramic laser

We demonstrated the efficient guided laser action in a diode-pumped YAG/Nd:YAG/YAG ceramic planar waveguide produced by tape casting and vacuum sintering technology for the first time to the best of our knowledge. In the regime of continuous wave operation, a maximum output power of 840 mW corresponding to the slope efficiency of 65% was achieved. During passively Q-switched operation, by replacing the dichroic mirror with graphene-oxide based output coupler, we obtained the stable pulse trains with the shortest pulse duration of 179 ns at a pulse repetition rate of 930 kHz which resulted in the single pulse energy of 221 nJ.

Q-switched operation of a femtosecond-laser-inscribed Yb:YAG channel waveguide laser using carbon nanotubes

We demonstrate a diode-pumped femtosecond-laser-inscribed Yb:YAG channel waveguide laser, Q-switched by using single-walled carbon nanotubes (SWCNTs) near 1029 nm. We used saturable absorber mirrors (SAMs) fabricated by depositing SWCNTs on three different output couplers. Best performance of the 9.3-mm-long ultra-compact Q-switched waveguide laser is obtained with an output coupling transmission of 20%. In this case, a maximum average output power of 60 mW with a corresponding pulse energy of 37.7 nJ and a pulse duration of 88 ns at 1.59-MHz repetition rate were achieved. The highest pulse energy of 39.2 nJ and the shortest pulse duration of 78 ns were obtained with 30% and 10% output couplers, respectively.

Bi₂Se₃ Q-switched Nd:YAG ceramic waveguide laser

Using a topological insulator (TI) Bi2Se3 as a saturable absorber, highly stable Q-switched laser pulses were realized in an Nd:YAG ceramic waveguide fabricated by carbon ion irradiation. The laser operation was at a wavelength of 1064 nm, with a repetition rate ranging from 2.7 to 4.7 MHz. The minimum pulsed duration was 46 ns. The maximum output power was up to 168.6 mW corresponding to the pulse energy of 31.3 nJ. This work opens up a practical way for implementation of TI modulated pulsed laser devices in dielectric waveguide platforms.

Q-switched operation of a pulsed-laser-deposited Yb:Y(2)O(3) waveguide using graphene as a saturable absorber

The first, to the best of our knowledge, Q-switched operation of a pulsed-laser-deposited waveguide laser is presented. A clad Yb:Y(2)O(3) waveguide was Q-switched using an output coupling mirror coated with a single layer of graphene deposited by atmospheric pressure chemical vapor deposition. During continuous-wave operation, a maximum power of 83 mW at a slope efficiency of 25% was obtained. During Q-switched operation, pulses as short as 98 ns were obtained at a repetition rate of 1.04 MHz and a central wavelength of 1030.8 nm.

Efficient lasing in continuous wave and graphene Q-switched regimes from Nd:YAG ridge waveguides produced by combination of swift heavy ion irradiation and femtosecond laser ablation

We report on the continuous wave and passively Q-switched lasers in Nd:YAG ridge waveguides fabricated by a combination of swift Kr ion irradiation and femtosecond laser ablation. Owing to the deep penetration length (~50 μm) of 670 MeV Kr(8+) ions into the crystal, ridge waveguides with large-area cross section, supporting nearly symmetric guiding modes, were produced. Continuous wave lasers with maximum 182 mW output power at ~1064 nm have been realized at 808-nm optical pump. Using graphene as a saturable absorber, passively Q-switched waveguide laser operations were achieved. The pulsed laser produces 90 ns pulses, with a ~4.2 MHz repetition rate, 19% slope efficiency and 110 mW average output power, corresponding to single-pulse energy of 26.5 nJ.

Nd:YAG waveguide laser Q-switched by evanescent-field interaction with graphene

We report on the Q-switched laser operation by the evanescent-field interaction with the graphene layers deposited on a Nd:YAG surface planar waveguide, which was fabricated by the 15 MeV carbon ion irradiation. Based on the simple and compact design of the cavity with saturable-absorber features, the Q-switched pulsed waveguide laser operation was achieved at the wavelength of 1064 nm through the interaction between the graphene layer and the evanescent-field of the waveguide mode. The maximum output pulse repetition rate was ~29 kHz with the pulse duration of ~9.8 µs.