Mode-locked Waveguide Laser Research Articles

Characterization of noise spectra in low-jitter GHz mode-locked fs-laser-inscribed waveguide lasers

We demonstrate low-noise, continuous-wave mode-locking of a diode-pumped Yb:KLuW waveguide laser operating at fundamental repetition rates in the GHz range. Utilizing a femtosecond-laser-inscribed Yb:KLuW channel waveguide laser with a tunable cavity length of a few centimeters, we successfully generate femtosecond pulses near 1030 nm, employing either single-walled carbon nanotubes or semiconductor saturable absorbers. Although timing noise is one of the most critical factors in the implementation of high-repetition-rate laser sources for various applications, investigations into timing noise characteristics in waveguide lasers remain limited. This study fills this gap by presenting timing jitter measurements for GHz mode-locked waveguide lasers with diverse cavity parameters. To quantitatively analyze noise spectral characteristics, including relaxation oscillation processes induced by intensity noise features, we introduce a theoretical modeling approach. The present investigation directly enables the provision of strategies for further suppression of timing jitter and designing high-performance, low-noise mode-locked lasers.

Dual-wavelength self-Q-switched mode-locked waveguide lasers based on Nd:LGGG cladding waveguides

We report a self-Q-switched mode-locked Nd:LGGG waveguide laser with tunable dual-wavelength emission fabricated by femtosecond laser direct writing (FsLDW). The waveguide laser delivers pulses with a minimum temporal duration of approximately 30 ps at a fundamental repetition rate of up to 8.03 GHz, without using any modulation element. The maximum output power is determined to be 226 mW with a slope efficiency of 25.38%. This work indicates the promising applications of waveguide lasers based on mixed crystals for integrated optics.

A Novel Hierarchical Nanostructure for Enhanced Optical Nonlinearity Based on Scattering Mechanism.

Surface modification of nonlinear optical materials (NOMs) is widely applied to fabricate diverse photonic devices, such as frequency combs, modulators, and all-optical switches. In this work, a double-layer nanostructure with heterogeneous nanoparticles (NPs) is proposed to achieve enhanced third-order optical nonlinearity of NOMs. The mechanism of modified optical nonlinearity is elucidated to be the scattering-induced energy transfer between adjacent NPs layers. Based on the LiNbO3 platform, as a typical example, double layers of embedded Cu and Ag NPs are synthesized by sequential ion implantation, demonstrating twofold magnitude of near-infrared enhancement factor and modulation depth in comparison with a single layer of Cu NPs. With the elastic collision model and thermolysis theory being considered, the shift of the localized surface plasmon resonance (LSPR) peak reveals the formation mechanism of the double-layer nanostructure. Utilizing the enhanced optical nonlinearity of LiNbO3 as modulators, a Q-switched mode-locked waveguide laser at 1µm is achieved with shorter pulse duration. It suggests potential applications to improve the performance of nonlinear photonic devices by using double-layer metallic nanostructures.

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

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.

Monolithic waveguide laser mode-locked by embedded Ag nanoparticles operating at 1 μm

Abstract Monolithic waveguide laser devices are required to achieve on-chip lasing. In this work, a new design of a monolithic device with embedded Ag nanoparticles (NPs) plus the Nd:YAG ridge waveguide has been proposed and implemented. By using Ag+ ion implantation, the embedded Ag NPs are synthesized on the near-surface region of the Nd:YAG crystal, resulting in the significant enhancement of the optical nonlinearity of Nd:YAG and offering saturable absorption properties of the crystal at a wide wavelength band. The subsequent processing of the O5+ ion implantation and diamond saw dicing of crystal finally leads to the fabrication of monolithic waveguide with embedded Ag NPs. Under an optical pump, the Q-switched mode-locked waveguide lasers operating at 1 μm is realized with the pulse duration of 29.5 ps and fundamental repetition rate of 10.53 GHz, owing to the modulation of Ag NPs through evanescent field interaction with waveguide modes. This work introduces a new approach in the application of monolithic ultrafast laser devices by using embedded metallic NPs.

WSe2 as a saturable absorber for multi-gigahertz Q-switched mode-locked waveguide lasers [Invited

Graphene and other extraordinary two-dimensional materials together with recent advances in optical modulators have set the foundations for the widespread applications of next-generation optoelectronic devices. In this work, we report on the high-performance fundamentally mode-locked waveguide laser modulated by chemical-vapor-deposition-grown WSe2 as a saturable absorber. By incorporating a WSe2 sample into a monolithic Nd:YVO4 waveguide platform, 6.526 GHz picosecond pulsed laser generation has been achieved at the wavelength of 1 μm with pulse duration of 47 ps.

Epsilon-near-zero medium for optical switches in a monolithic waveguide chip at 1.9 μm

Abstract A saturable absorber is a building block for integrated ultrafast photonics and passive optical circuits. However, options currently available suffer from the bottlenecks of the necessity for fine control of the material preparation, large optical losses, and compatibility. This paper presents a complementary metal–oxide–semiconductor (CMOS)-compatible alternative based on an epsilon-near-zero (ENZ) medium, in which the real part of the dielectric constant vanishes. Excellent nonlinear optical modulations, including low linear optical losses, low bleaching threshold, moderate optical amplitude modulation, and high modulation speed of indium tin oxide (ITO) in its ENZ region are achieved. The use of ITO as an intracavity saturable absorber for optical switches of integrated waveguide chip lasers at 1.9 μm has been realized. A stable mode-locked waveguide laser with a repetition rate of 6.4 GHz and an average output power of 28.6 mW is achieved via carefully adjusting the intracavity three-surface interferometer (TSI). This work may pave the way for integrated photonics and electro-optics using a CMOS-compatible ENZ medium.

Invited Article: Mode-locked waveguide lasers modulated by rhenium diselenide as a new saturable absorber

The layered two-dimensional (2D) materials with extraordinary optical properties play important roles in the development of ultrafast photonics, in which mode-locking lasers with a high fundamental repetition rate (>1 GHz) are of particular interest. The nonlinear optical properties of one of the emerging 2D materials, rhenium diselenide (ReSe2), have been investigated for the first time. Broadband ultrafast saturable absorption of ReSe2 from the visible to the near infrared wavelength regimes has been observed, which enables potential applications in ultrafast lasing. With typical end-pump arrangement, continuous-wave mode-locking based on the ReSe2 saturable absorber has been realized, reaching a fundamental repetition-rate of 6.5 GHz and pulse duration as short as 29 ps at 1 μm in a monolithic waveguide platform. This work indicates intriguing applications of ReSe2 for the development of on-chip ultrafast photonic devices.

Enhanced nonlinear optical response of graphene by silver-based nanoparticle modification for pulsed lasing

In this work, we report on the synthesis and characterization of a functionalized graphene modified by Ag based nanoparticles (Ag2S@Ag) and the applications as an optical modulator for pulsed laser generation at 1μm in the compact waveguide platform written by a femtosecond laser. The nonlinear optical response of the Ag2S@Ag nanoparticle modified graphene has been explored by the Z-scan technique, which exhibits an enhanced ultrafast saturable absorption response with higher modulation depth and lower saturation intensity. The Q-switching and Q-switched mode locking have been realized in a waveguide laser system by using Ag nanoparticle modified graphene as a saturable absorber (SA) mirror. Fundamental Q-switched mode-locked waveguide lasers with a repetition rate of 6.44 GHz have been achieved, reaching shorter pulse duration (33 ps) in comparison to that (52 ps) through unmodified graphene SA. This work suggests potential applications of functionalized graphene in ultrafast photonics.

65 GHz Q-switched mode-locked waveguide lasers based on two-dimensional materials as saturable absorbers

Two-dimensional (2D) materials have generated great interest in the past few years opening up a new dimension in the development of optoelectronics and photonics. In this paper, we demonstrate 6.5 GHz fundamentally Q-switched mode-locked lasers with high performances in the femtosecond laser-written waveguide platform by applying graphene, MoS2 and Bi2Se3 as saturable absorbers (SAs). The minimum mode-locked pulse duration was measured to be as short as 26 ps in the case of Bi2Se3 SA. The maximum slope efficiency reached 53% in the case of MoS2 SA. This is the first demonstration of Q-switched mode-locked waveguide lasers based on MoS2 and Bi2Se3 in the waveguide platform. These high-performance Q-switched mode-locked waveguide lasers based on 2D materials pave the way for practical applications of compact ultrafast photonics.

Highly coherent free-running dual-comb chip platform.

We characterize the frequency noise performance of a free-running dual-comb source based on an erbium-doped glass chip running two adjacent mode-locked waveguide lasers. This compact laser platform, contained only in a 1.2L volume, rejects common-mode environmental noise by 20dB thanks to the proximity of the two laser cavities. Furthermore, it displays a remarkably low mutual frequency noise floor around 10 Hz2/Hz, which is enabled by its large-mode-area waveguides and low Kerr nonlinearity. As a result, it reaches a free-running mutual coherence time of 1s since mode-resolved dual-comb spectra are generated even on this time scale. This design greatly simplifies dual-comb interferometers by enabling mode-resolved measurements without any phase lock.

2-GHz carbon nanotube mode-locked Yb:YAG channel waveguide laser.

We demonstrate GHz-repetition rate mode-locked operation of a femtosecond-laser-inscribed Yb:YAG channel waveguide laser using single-walled carbon nanotube saturable absorber mirror (SWCNT-SAM). A 6.3-mm-long, type II Yb:YAG waveguide laser with an extended cavity configuration delivers mode-locked picosecond (ps) pulses at GHz repetition rates. The dispersion of the laser cavity is compensated by the combination of a multi-functional output coupler and the Gires-Tournois interferometer (GTI) effect arising from an air-gap between the facet of the waveguide and the output coupler. The incident beam fluence on the SWNCNT-SAM is controlled by adjusting two intracavity lenses to avoid optical damage on the polymer nanocomposite matrix containing the SWCNTs. The average output power of our mode-locked waveguide laser is 322 mW at a pump power of 3.2 W. Nearly Fourier-limited, stable 2-ps-short pulses are generated at a repetition rate of 2.08 GHz.

Self-corrected chip-based dual-comb spectrometer.

We present a dual-comb spectrometer based on two passively mode-locked waveguide lasers integrated in a single Er-doped ZBLAN chip. This original design yields two free-running frequency combs having a high level of mutual stability. We developed in parallel a self-correction algorithm that compensates residual relative fluctuations and yields mode-resolved spectra without the help of any reference laser or control system. Fluctuations are extracted directly from the interferograms using the concept of ambiguity function, which leads to a significant simplification of the instrument that will greatly ease its widespread adoption and commercial deployment. Comparison with a correction algorithm relying on a single-frequency laser indicates discrepancies of only 50 attoseconds on optical timings. The capacities of this instrument are finally demonstrated with the acquisition of a high-resolution molecular spectrum covering 20 nm. This new chip-based multi-laser platform is ideal for the development of high-repetition-rate, compact and fieldable comb spectrometers in the near- and mid-infrared.

Ultrafast High-Repetition-Rate Waveguide Lasers

We report on progress in the field of integrated mode-locked waveguide lasers with an emphasis on compact monolithic designs producing picosecond and femtosecond optical pulses at multi-GHz repetition rates.

Integrated Low-Jitter 400-MHz Femtosecond Waveguide Laser

An integrated passively mode-locked waveguide laser generating 440-fs pulses at 394-MHz repetition rate is demonstrated on an 18 mm times 44 mm silica waveguide chip. The laser self-starts, and uses a saturable Bragg reflector for mode-locking.

Harmonically mode-locked glass waveguide laser with 21-fs timing jitter

We report on experimental jitter results of a 10-GHz mode-locked laser. The laser is an actively harmonically mode-locked fiber laser using an erbium-doped glass waveguide as the gain medium. Amplitude noise and corresponding phase noise effects are greatly reduced by the inclusion of an intracavity high-finesse fiber Fabry-Pe/spl acute/rot etalon. Typical results show timing jitter of 21-fs root mean square, integrated from 10 Hz to 100 MHz.

Optimisation and regime characterisation of monolithic semiconductor mode-locked lasers and colliding-pulse mode-locked lasers at microwave and millimetre-wave frequencies

The optimisation of the saturable absorber section length for mode-locked ridge waveguide lasers in GaAs/AlGaAs double quantum-well material is reported. Mode-locked lasers and colliding-pulse mode-locked lasers were fabricated using a simple self-alignment process. Regime analysis and signal characterisation are performed as a function of the laser cavity and saturable absorber section lengths. Device degradation is evaluated and compared in both configurations. Device performance in the frequency domain is assessed using both an external fast photodiode and the saturable absorber section, and the direct generation of millimetre-wave signal through the saturable section is discussed.

Passively mode-locked glass waveguide laser with 14-fs timing jitter.

Ultralow jitter pulse trains are produced from a passively mode-locked, erbium/ytterbium co-doped, planar waveguide laser by use of high-bandwidth feedback control acting on the physical cavity length and optical pump power. Synchronization of a 750-MHz, fundamentally mode-locked laser to an external clock signal yields an ultralow, root-mean-square relative timing jitter of 14.4 fs integrated from 10 Hz to the Nyquist frequency of 375 MHz.

Passively mode-locked waveguide laser with low residual jitter

Picosecond pulses at 1.53 /spl mu/m with low residual jitter are generated from a passively mode-locked erbium/ytterbium codoped planar waveguide laser in an extended cavity configuration. The round-trip frequency of the laser cavity is actively referenced to the frequency of a stable electronic oscillator; this lowers the residual root-mean-square timing jitter to 83 fs over the frequency range of our phase-noise measurement system 100 Hz-10 MHz.