Waveguide Laser Research Articles

Femtosecond laser fabricated semi-tapered waveguide for Q-switched vortex laser generation.

Dielectric waveguides are widely recognized as excellent and versatile components for integrated multifunctional photonic chips, thanks to their strong optical confinement capabilities. In this study, we present a novel semi-tapered depressed-cladding waveguide structure, designed and fabricated using femtosecond laser direct writing technology. The optical guiding performance of this semi-tapered waveguide is systematically analyzed by characterizing its loss characteristics. Leveraging the high gain and superior laser performance of the semi-tapered waveguide platform, we successfully demonstrate an efficient vortex waveguide laser. Moreover, we achieve a stable Q-switched vortex laser with short pulse duration and high repetition rate by utilizing an Sb2Te3 thin film as a saturable absorber. This work exemplifies the potential for developing three-dimensional waveguides for on-chip integrated pulsed lasers.

Ta<sub>2</sub>O<sub>5</sub> 980/1550 nm wavelength multiplexer/demultiplexer based on segmented cascaded multimode interference

On-chip erbium-doped/erbium-ytterbium co-doped waveguide amplifiers (EDWAs/EYCDWAs) have received extensive research attention in recent years, As an important component of EDWA, there has been relatively little research on integrated wavelength division multiplexing/demultiplexing devices for 980 nm pump light and 1550 nm signal light. This article aims to propose a compact Ta<sub>2</sub>O<sub>5</sub> 980 / 1550 nm wavelength diplexer based on multimode interference effects. The device employs a structure of symmetric interference and paired interference cascade, which reduces the total length of the segmented multimode interference waveguide to one-third of the ordinary paired multimode interference waveguide without using any complex structures such as subwavelength gratings to regulate the beat length of the pump and signal light. The three-dimensional finite difference time domain (3D-FDTD) tool was used to analyze and optimize the established model. The results demonstrate that the designed MMI diplexer has low insertion loss and high process tolerance, with an insertion loss of 0.4 dB at 980 nm and 0.8 dB at 1550 nm, and the extinction ratios are both better than 16 dB. Moreover, the 1-dB bandwidth is up to 150 nm around the 1550 nm wavelength and up to 70 nm around the 980 nm wavelength. The segmented structure designed in the article greatly reduces the design difficulty of MMI devices and reduces the overall size of 980 / 1550 nm wavelength division multiplexers/demultiplexers. It is expected to be applied in on-chip integrated erbium-doped waveguide amplifiers and lasers. In addition, the segmented design approach of cascading the hybrid multimode interference mechanism provides a technical reference for separating two optical signals with far apart center wavelengths such as 800 / 1310 nm and 1550 / 2000 nm, and has potential application value in communication and mid infrared diplexing devices.

Enhancement of harmonic generation by an intense driving laser with high-order waveguide modes in a high-pressure gas-filled hollow waveguide.

High-order harmonics have been widely used as reliable tabletop coherent radiation sources recently, but their applications have often been limited by the available pulse energy. Here, we report that by using an overdriven intense laser in a long waveguide with high-pressure gas, phase matching can be achieved in three distinct "regimes". In the third regime, favorable phase matching is achieved at near-axis positions to enhance harmonic yields. Our results are supported by a full theoretical analysis, and we demonstrate that coupling of the driving laser with the high-order waveguide modes (instead of the fundamental mode used in most prior experiments) is responsible for achieving phase matching. Furthermore, we establish that this phase matching (and harmonic enhancement) is robust, and a scaling relation is derived for the necessary waveguide and gas parameters, allowing our predictions to be tested immediately in any laboratory today.

2-W continuous-wave and passively Q-switched Tm,Ho:YLF channeled waveguide laser at 2.05 µm.

We report on the operation of an efficient Tm,Ho:YLF depressed cladding, channeled waveguide laser in both continuous-wave (CW) and passively Q-switched (PQS) regimes, producing laser emission at the wavelength of 2.05 µm. The 70-µm diameter depressed cladding waveguide, fabricated using femtosecond laser inscription, had a low propagation loss value of 0.14 dB/cm and a refractive index contrast of 8.3 × 10-4. In the CW regime, the waveguide laser was excited at 780 nm, and an output power of up to 2 W was generated at the incident pump power of 4.14 W with a power slope efficiency of 50.0%. PQS operation was further realized by utilizing a Cr:ZnSe saturable absorber (SA), whereby the waveguide laser generated as short as 19.6-ns pulses with a power slope efficiency of 18.9%.

A low quantum defect and power scalable Yb-doped glass waveguide laser

We present a continuous wave laser action in ytterbium (Yb)-doped phosphate glass buried channel waveguides. The 25 mm long waveguides were fabricated by the standard ion exchange method. When pumped with a 976 nm laser diode, the waveguide laser emits at 982.4 nm, yielding an ultralow quantum defect of 0.66 %. The impact of coupling and pump power variation on the laser emission wavelengths is demonstrated. Furthermore, the results of pulsing using a monolayer graphene as a saturable absorber (SA) are presented and a pulse train with a repetition rate of 1 MHz and a pulse width of 700 ns was obtained.

Design of a broadband Si3N4 waveguide amplifier based on a gain medium of ion-sliced titanium-doped sapphire.

In recent years, significant progress has been made in the on-chip integration of Ti:sapphire amplifiers and lasers, showing great potential in device miniaturization, cost reduction, and mass production. However, the further integration of such devices on standard CMOS platforms has been challenging due to its limits on the wafer bonding method between gain materials and substrates. Here, we present a novel, to the best of our knowledge, Si3N4 on-chip broadband optical waveguide amplifier scheme with an ultra-wide bandwidth of 650-900 nm and a peak gain of 28 dB based on an ion-sliced Ti:sapphire platform. The difficulty of heterogeneous integration is significantly reduced by growing Si3N4 thin films on Ti:sapphire. Moreover, by using homogeneous bonding combined with ion slicing technology, the target thickness of Ti:sapphire is expected to be easily controlled to less than 1 µm, greatly reducing the device volume and improving its practicality. Through subsequent experimental optimization, this work is expected to provide a new approach for the optimized design and experimental realization of on-chip Ti:sapphire waveguide amplifiers and lasers.

Near infrared diode-pumped lasing of femtosecond-laser-written Pr:LiLuF4 waveguide

In this Letter we report the near infrared operation of a femtosecond-laser-written diode-pumped Pr:LiLuF4 waveguide laser. By employing a circular depressed-cladding waveguide with propagation losses as low as 0.19dB/cm, we demonstrated lasing at 914 nm, with a maximum output power of 140mW and a slope efficiency of 24%. Moreover, we demonstrated the possibility of lasing in a waveguide device at 894 nm, 922 nm and 933 nm. To the authors knowledge, this is the first demonstration of a Pr-based waveguide laser operating in this spectral region.

Integrated thermo-optic phase shifters for laser-written photonic circuits operating at cryogenic temperatures

Abstract Integrated photonics offers compact and stable manipulation of optical signals in miniaturized chips, with the possibility of changing dynamically their functionality by means of integrated phase shifters. Cryogenic operation of these devices is becoming essential for advancing photonic quantum technologies, accommodating components like quantum light sources, single photon detectors and quantum memories operating at liquid helium temperatures. In this work, we report on a programmable glass photonic integrated circuit (PIC) fabricated through femtosecond laser waveguide writing (FLW) and controlled by thermo-optic phase shifters both in a room-temperature and in a cryogenic setting. By taking advantage of a femtosecond laser microstructuring process, we achieved reliable PIC operation with minimal power consumption and confined temperature gradients in both conditions. This advancement marks the first cryogenically-compatible programmable FLW PIC, paving the way for fully integrated quantum architectures realized on a laser-written photonic chip.

Dissipative spatiotemporal soliton in a driven waveguide laser

A distributed Kerr-lens mode locking regime can be realized in a waveguide laser by spatial profiling of the pump beam, thus creating a spatio-temporal soliton. Additional slow temporal modulation of the pump source stabilizes the spatio-temporal solution in a broad range of parameters defined by the dynamic gain saturation. We choose a Cr:ZnS waveguide laser as a practical example, but such a regime is feasible in various waveguide and fiber oscillators. A far-reaching analogy with Bose–Einstein condensates allows this approach to stabilize the weakly dissipative BECs.

Developments of Waveguide Lasers by Femtosecond Laser Direct–Writing Technology

Waveguide lasers have the advantages of miniature and compact structure and have broad application prospects in photonic integration and on–chip laboratories. The development of femtosecond laser direct–writing technology makes the processing of transparent materials more flexible and controllable. This paper mainly introduces a waveguide laser based on femtosecond laser direct–writing technology. Firstly, the applications of femtosecond laser direct–writing technology in an optical waveguide are introduced, including the principles of femtosecond laser direct–writing technology, common optical wave scanning methods, and types of optical waveguides. After that, we summarize the development of a waveguide continuous–wave laser, a Q–switched laser and a mode–locked laser from visible to mid–infrared wavebands and analyze some new representative work. Finally, we explain the difficulty of compensating for dispersion in pulse waveguide lasers and summarize some new ideas that have been proposed to solve the problem.

Er:LiYF4 planar waveguide laser at 2.8 μm

We report on a mid-infrared erbium planar waveguide laser operating on the 4I11/2 → 4I13/2 transition. It employs a heavily doped 10.6 at. % Er3+:LiYF4 single-crystalline layer grown by liquid-phase epitaxy. The waveguide laser delivers a maximum output power of 191 mW at ∼2809 nm with a slope efficiency of 15%, a linear polarization, and a laser threshold of 134 mW. The waveguide propagation losses are 0.4 ± 0.2 dB/cm. The polarized spectroscopic properties of the Er3+:LiYF4 layers are also investigated. The stimulated-emission cross section of Er3+ ions amounts to 0.87 × 10−20 cm2 at 2809 nm for π-polarization. Er3+:LiYF4 epitaxial layers represent a promising platform for integrated low-loss mid-infrared light sources.

Continuous wave operation of broad area and ridge waveguide laser diodes at 626 nm

AbstractThe authors present continuous wave (CW) high‐power broad area and ridge waveguide lasers with laser emission at 626 nm at room temperature. For this, the authors employ GaAs‐based diode lasers in the AlGaInP system for laser emission at 626 nm at room temperature. The laser structure is grown on three‐inch wafers by metal organic vapour phase epitaxy. Broad area and ridge waveguide lasers are fabricated. Pulsed broad area laser characterisation on bar level shows laser operation at 20 C heat sink temperature. The authors measured peak lasing wavelengths as short as 625 nm and total maximum output power of both facets up to 1.4 W at an injection current of 2 A. Both, broad area and ridge waveguide lasers show laser operation and CW excitation at room temperature. The ridge waveguide lasers emit output powers of over 90 mW at 626 nm at a maximum injection current of 200 mA with a nearly diffraction‐limited beam profile.

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.

Compact Q-switched vortex waveguide laser modulated by buried Ag nanoparticles in SiO2

Vortex beam, particularly pulsed vortex laser, has expanded the potential applications in optics due to their unique wave-front phase structure and the determined photon orbital angular momentum. In this study, we present a novel approach including the integration of fused silica embedded with silver nanoparticles (Ag:SiO2) into the Nd:YAG waveguide platform for achieving nanosecond vortex pulses. Using a spiral phase plate for in-cavity phase modulation, we successfully demonstrate a Q-switched vortex laser with a high repetition rate in the megahertz range and short pulse width in the nanosecond regime. Additionally, we conduct a comprehensive analysis of the near-field distributions of Ag nanoparticles with varying sizes and distributions using COMSOL simulation. This study exemplifies the integration of silica-based photonic elements for realizing a high-stability and cost-effective nanosecond vortex laser system.

Integrated graphene-based semimetal/metallic-like MSe2 (M = Pt, Re) heterostructures for mid-infrared ultrafast photonics

Mid-infrared (MIR) ultrafast photonics has received significant interest due to the development of compact and robust MIR laser sources capable of emitting wavelengths beyond 2 μm. Transition metal selenides (TMSes), with the properties of feasibly tunable bandgaps, desirable photocarrier transmission property, and broadband nonlinear optical response, have become a research focus on ultrafast photonic applications. However, the relatively large bandgap (around 1 eV) of the TMSes greatly restricts their applications in the MIR region. Here, the synergetic interaction between multilayer graphene (Gr) and semimetal or metallic-like (PtSe2 and ReSe2) is employed to tune the optical properties and to further optimize the optical performance of TMSes in the MIR region. Benefiting from the ultrafast photocarrier relaxation time, appropriate modulation depth, and almost zero non-saturated loss of Gr-PtSe2 and Gr-ReSe2 heterostructures, stable Q-switched laser operation at 1.9 μm has been achieved in an integrated design based on waveguide laser platform. The results demonstrate that combining the semimetal or metallic-like TMSes with van der Waals (vdW) heterostructures is a promising strategy to extend the photonic applications of TMSes into the MIR region, indicating the potential applications of graphene-based TMSes vdW heterostructures for MIR integrated photonics.

Efficient sum-frequency generation of a yellow laser in a thin-film lithium niobate waveguide.

Yellow lasers with high efficiency and tunability play an essential role in many applications. Here, we demonstrate the sum-frequency generation (SFG) of yellow light on a periodically poled thin-film lithium niobate (PP-TFLN) waveguide. Taking advantage of large χ(2) nonlinearity, a high normalized conversion efficiency of 10,097% (W·cm2) is obtained with pump wavelengths of 1317.7 and 1064 nm. An absolute conversion efficiency of 24.17% is recorded with on-chip pump powers of 10.4 dBm (O-band) and 13.5 dBm (1064 nm).

Fundamental spatial mode high power 808 nm double trench wide ridge waveguide laser

—Lasers operating at a wavelength of 808 nm, with watt-level output power and high beam quality in the fundamental spatial mode, have garnered significant attention due to their potential applications across various fields. Transverse optical confinement in double trench ridge waveguide lasers is determined by the width of the ridge and the refractive index difference between the ridge and trench. In this study, we have designed and fabricated a wide ridge laser operating at 808 nm with high power output and stable fundamental spatial mode based on this principle. The fundamental spatial mode operation was successfully achieved with an 8 μm ridge waveguide laser, producing an impressive output power of 1.3 W. The device exhibits a stable far-field as the current was increased from 0.3 A to 1.8 A. The laser's output power exhibits a 14% reduction with an increase in temperature of 80 °C, demonstrating a decrease rate of only 1.25 mW/°C and a wavelength variation rate of 0.22 nm/°C, indicating low sensitivity to temperature changes.

Monolithically integrated multimode interference coupler-based master oscillator power amplifier with dual-wavelength emission around 830 nm

A monolithically integrated dual-wavelength multimode interference coupler-based master oscillator power amplifier is presented. It consists of two shallowly etched, laterally separated ridge waveguide laser cavities as master oscillators with individual distributed Bragg reflector gratings as cavity mirrors. A deeply etched coupling section containing S-bend shaped waveguides and a multimode interference coupler is used to couple the laser emission of the master oscillators into a shallowly etched single waveguide serving as power amplifier. Changing the etch depth for the coupling section enables a compact device layout. In addition, increased radiation angles of modes not coupled into the power amplifier help to suppress beam steering, otherwise indicated by laterally separated far-field intensity distributions. The device provides 0.5 W of dual-wavelength emission around 830 nm in individual and common operation. As designed, both emission wavelengths are separated by 0.5 nm with spectral widths below 20 pm, limited by the spectral resolution of the spectrometer. Both peak wavelengths remain within spectral windows of 50 pm within the available power range. This enables full flexibility selecting operating points for applications such as shifted excitation Raman difference spectroscopy and the generation of THz emission by photomixing. The emission wavelengths can additionally be non-continuously tuned by applying a heater current to resistors implemented next to the distributed Bragg reflector gratings. As an example, selected spectral distances of 0.5 nm, 1.0 nm, 1.5 nm, and 2.0 nm are demonstrated. Near field widths of 5 μm and far field angles of 17° result in beam propagation ratios of 1.4 (1/e2) in all operation modes and enable easy beam shaping or optical single-mode fiber coupling.

Nonlinear-mirror mode-locked crystal waveguide laser by intracavity fourth-harmonic loss modulation: publisher's note.

This publisher's note contains a correction to Opt. Lett.48, 6064 (2024)10.1364/OL.509275.

Miniaturizing a coherent beam combining system into a compact laser diode module.

We present a laser module with dimensions of 76×43×15m m 3 that for the first time to our knowledge realizes a coherent beam combination in such a compact device, using two tapered amplifiers seeded by a distributed Bragg reflector ridge waveguide laser diode operating at 761nm in a single longitudinal mode. The generated combined optical power is up to 5W continuous wave with a combing efficiency of 85%. The phase of the system is controlled by the current in the ridge waveguide section of one of the tapered amplifiers. The phase-stabilization process is automated using a reverse hill-climbing algorithm and an ATmega328P microcontroller.