Channel 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.

Controllable Dynamic Single‐ and Dual‐Channel Graphene Q‐Switching in a Beam‐Splitter‐Type Channel Waveguide Laser (Laser Photonics Rev. 16(4)/2022)

Waveguide Lasers In article number 2100501, Fabian Rotermund and colleagues present the dynamically Q-switched operation of a graphene-integrated beam-splitter-type channel waveguide laser. Controlled single- and dual-channel Q-switching can be achieved based on selective excitation of the desired channel by widely tunable power splitting ratio. In particular, dual-channel Q-switching with a single pumping source generates a hybrid pulse train with two separately Q-switched modes simultaneously.

Controllable Dynamic Single‐ and Dual‐Channel Graphene Q‐Switching in a Beam‐Splitter‐Type Channel Waveguide Laser

AbstractDirect inscription of structures by femtosecond‐laser pulses facilitates the flexible fabrication of diverse optical channel waveguides in dielectric laser gain media. Among them, beam‐splitter‐type waveguide lasers have been recently studied; however, there is a lack of investigations on the effect of unique characteristics of such waveguides, such as controlled splitting ratios of output powers and selectable excitation of individual channels, for pulsed laser operation. Here, dynamic single‐ and dual‐channel graphene Q‐switching of an Yb:YAG waveguide consisting of one input and two output channels is demonstrated by controlling the power‐splitting ratio. Single‐channel Q‐switched operation, exhibiting typical Q‐switched pulses, is achieved by interaction between the graphene saturable absorber and the desired one of the two channels. When both channels exceed the Q‐switching threshold, dual‐channel Q‐switching generates a pulse train that simultaneously combines the separately Q‐switched pulses induced from each channel under excitation with a single pump source. At a fixed power‐splitting ratio, the pulsed mode can be dynamically switched between the single‐ and dual‐channel Q‐switched operations by varying the pump power. The beam‐splitter‐type waveguide laser demonstrated in this study can be further developed for multiple‐channel Q‐switching, high‐repetition‐rate mode‐locking, and on‐chip dual‐comb sources advantageous for diverse applications in optical communication, metrology, and sensing.

Channel waveguide lasers in bulk Tm:LiYF4 produced by deep diamond-saw dicing.

We report on a novel approach to fabricate channel (ridge) waveguides (WGs) in bulk crystals using precision diamond saw dicing. The channels feature a high depth-to-width aspect ratio (deep dicing). The proof-of-the-concept is shown for a Tm3+:LiYF4 fluoride crystal. Channels with a depth of 200 µm and widths of 10-50 µm are diced and characterized by confocal laser microscopy revealing a r.m.s. roughness of the walls well below 100 nm. The channels obtained possess waveguiding properties at ∼815 nm with almost no leakage of the guided mode having a vertical stripe intensity profile into the bulk crystal volume and relatively low propagation losses (0.20-0.43 dB/cm). Laser operation is achieved in quasi-CW regime by pumping at 780 nm. The maximum peak output power reaches 0.68 W at ∼1.91 µm with a slope efficiency of 53.3% (in σ-polarization). The proposed concept is applicable to a variety of laser crystals with different rare-earth dopants.

Passive Q-switching of a Tm3+:LiYF4 waveguide laser by Cr2+:ZnSe and Co2+:ZnSe saturable absorbers

Abstract A Tm3+:LiYF4/LiYF4 channel waveguide laser produced by Liquid Phase Epitaxy and diamond-saw dicing is passively Q-switched by Cr2+:ZnSe and Co2+:ZnSe saturable absorbers. For Cr2+:ZnSe, the laser generated a maximum average output power of 0.59 W at 1876.5 nm with a slope efficiency of 36.1% (with respect to the absorbed pump power) and a linearly polarized output (π-polarization). The pulse characteristics (duration/energy) were 9 ns/2.1 μJ at a repetition rate of 0.29 MHz. The laser performance was modelled within a “slow” saturable absorber model showing good agreement with the experiment. We also revisited Co2+:ZnSe for passive Q-switching applications in the spectral range of ~2 μm. It allowed to operate the laser in a high-repetition-rate regime (0.91 MHz) while preserving the benefits of short pulses (30 ns/0.9 μJ). For Co2+:ZnSe, the average output power of the waveguide laser reached 0.81 W with a record-high slope efficiency of 49.6%.

Transition of pulsed operation from Q-switching to continuous-wave mode-locking in a Yb:KLuW waveguide laser.

We report on the diverse pulsed operation regimes of a femtosecond-laser-written Yb:KLuW channel waveguide laser emitting near 1040 nm. By the precise position tuning of a carbon-nanotube-coated saturable absorber (SA) mirror, the transition of the pulsed operation from Q-switching, Q-switched mode-locking and finally sub-GHz continuous-wave mode-locking are obtained based on the interplay of dispersion and mode area control. The Q-switched pulses exhibit typical fast SA Q-switched pulse characteristics depending on absorbed pump powers. In the Q-switched mode-locking, amplitude modulations of the mode-locked pulses on the Q-switched envelope are observed. The radio-frequency spectrum represents the coexistence of Q-switching and mode-locking signals. In the purely mode-locked operation, the waveguide laser generates 2.05-ps pulses at 0.5 GHz.

MXene Ti3C2Tx saturable absorber for passively Q-switched mid-infrared laser operation of femtosecond-laser–inscribed Er:Y2O3 ceramic channel waveguide

Abstract We report on an Er:Y2O3 ceramic channel waveguide laser operating at continuous-wave and passively Q-switched regimes, for the first time to the best of our knowledge. The Er:Y2O3 ceramic channel waveguide has been fabricated by a femtosecond laser direct-writing technique. The maximum output power reached 123.5 mW in continuous-wave mode with a slope efficiency of about 21%, and the lasing behavior has been found simultaneously at 2710.28, 2716.76, and 2723.18 nm. We have further fabricated an MXene Ti3C2Tx saturable absorber mirror to operate the Er:Y2O3 waveguide in passively Q-switched regime. At the same time, property of the MXene Ti3C2Tx saturable absorber has been characterized, and nonlinear saturable absorption of the saturable absorber has also been measured. The average output power is about 67.6 mW, and the shortest pulse width is about 58.1 ns. This work indicates that femtosecond laser direct writing is a reliable technique for processing mid-infrared ceramic waveguides, and MXene Ti3C2Tx is promising for operating pulsed mid-infrared lasers.

Ultrafast laser inscribed waveguide lasers in Tm:CALGO with depressed-index cladding.

Depressed-index buried and surface channel waveguides (type III) are produced in a bulk 3.5 at.% Tm3+:CALGO crystal by femtosecond direct-laser-writing at kHz repetition rate. The waveguides are characterized by confocal microscopy and µ-Raman spectroscopy. Under in-band-pumping at 1679 nm (3H6 → 3F4 transition) by a Raman fiber laser, the buried channel waveguide laser with a circular cladding (diameter: 60 µm) generated a continuous-wave output power of 0.81 W at 1866-1947 nm with a slope efficiency of 71.2% (versus the absorbed pump power) and showed a laser threshold of 200 mW. The waveguide propagation losses were as low as 0.3 ± 0.2 dB/cm. The laser performance under in-band pumping was superior compared pumping at ∼800 nm (3H6 → 3H4 transition), i.e., the convetional pump wavelength. Vibronic laser emission from the WG laser above 2 µm is also achieved. The low-loss behavior, the broadband emission properties and good power scaling capabilities indicate the suitability of Tm3+:CALGO waveguides for mode-locked laser operation at ∼2 µm.

Carbon nanotube Q-switched Yb:KLuW surface channel waveguide lasers

A channel waveguide (WG) buried immediately below the surface of a Yb:KLuW crystal is used as a laser gain medium for passive Q -switching by both evanescent- and direct-field interactions with single-walled carbon nanotubes (SWCNTs) near 1040 nm. The SWCNTs used as saturable absorbers (SAs) are deposited on top of the half-ring-type channel WG fabricated via femtosecond direct laser writing. The Q -switched WG laser delivers 88.5 ns pulses at a 1.16 MHz repetition rate with a maximum average output power of 680 mW. For the two different interaction schemes with SWCNT-SAs, the pulse characteristics, depending on the output coupling ratio and absorbed pump power, are experimentally investigated and compared to the results of theoretical analyses of the SA Q -switched operation.

Diamond saw dicing of thulium channel waveguide lasers in monoclinic crystalline films.

A surface channel waveguide (WG) laser is produced by diamond saw dicing of a 15μm thick 10at. % Tm:KY1-x-yGdxLuy(WO4)2 monoclinic double tungstate thin film grown by liquid phase epitaxy on an undoped KY(WO4)2 substrate. The WG propagation losses are 1.1±0.5 dB/cm. When pumped at 802nm, laser operation is achieved with a maximum output power of 262mW at 1833nm with a record slope efficiency of 82.6% (versus the absorbed pump power) in a TE10 spatial mode (linear laser polarization, E‖Nm). Diamond saw dicing of double tungstate epitaxies is a promising technology for manufacturing WGs for sensing applications.

Room temperature operation of InAsSb quantum dashes laser near 1.8 μm based on InP (001) substrate

Single-stack InAsSb self-assembled quantum dashes (QDashes) laser grown by metalorganic vapor phase epitaxy based on InP (001) substrate is reported. High-quality InAsSb quantum dashes have been acquired under the optimized growth conditions, such as substrate temperature, growth rate, deposition thickness and V/III ratio. Surface QDashes morphologies have been characterized by atomic force microscopy whereas the ones buried in active region have been investigated by transmission electron microscope with high resolution X-ray Energy Dispersive Spectroscopy to confirm the antimony composition. Double channel waveguide laser with 40 μm width ridge has been fabricated by standard optical lithography and wet etching. Pulsed room temperature operation demonstrates the wavelength from 1.72 to 1.79 μm for different injection currents. In addition, the laser peak output power can exceed 600 mW with 12.8% of differential quantum efficiency and even under continuous wave operation, the maximum optical power still remains 26 mW.

Watt-level Tm:LiYF4 channel waveguide laser produced by diamond saw dicing.

Low-loss surface channel waveguides with a cross-section of 30 × 30 μm2 are produced by diamond saw dicing of 6.2 at.% Tm3+, 3.5 at.% Gd3+:LiYF4 films grown by liquid phase epitaxy (LPE) on (001)-oriented bulk undoped LiYF4 substrates. Pumped by a Ti:Sapphire laser at 783 nm, a continuous-wave Tm:LiYF4 waveguide laser generated 1.30 W at 1880 nm (for π-polarization) with a slope efficiency of 80% with respect to the absorbed pump power. The laser threshold was at 80 mW. The waveguide morphology was studied revealing low roughness (3 ± 2 μm) as expressed by the propagation losses of <0.3 dB/cm. A combination of LPE and diamond saw dicing is a promising technology for multi-watt single-mode channel waveguide lasers and amplifiers.

Optically pumped rare-earth-doped Al2O3 distributed-feedback lasers on silicon [Invited

This paper reviews recent progress in the field of optically pumped rare-earth-doped channel waveguide lasers, with a focus on operation utilizing distributed-feedback resonators on silicon wafers. Rare-earth-doped amorphous aluminum oxide thin films have been deposited onto silicon wafers by RF reactive co-sputtering from metallic Al and rare-earth targets, the spectroscopy and optical gain of Er3+, Yb3+, Nd3+, and Tm3+ ions has been investigated, and the near-infrared laser transitions near 1 μm in Yb3+, 1.5 μm in Er3+, and 2 μm in Tm3+ and Ho3+ have been demonstrated. Output power between a few μW and hundreds of mW have been achieved in different waveguide geometries, and ultranarrow-linewidth laser operation has been demonstrated.

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.

Femtosecond-laser-written hexagonal cladding waveguide in Tm:KLu(WO_4)_2: µ-Raman study and laser operation

We report on the fabrication, µ-Raman characterization, and continuous-wave laser operation of a channel waveguide with a hexagonal optical-lattice-like cladding fabricated in monoclinic Tm:KLu(WO4)2 crystal by femtosecond direct laser writing. µ-Raman spectroscopy indicates preservation of the crystalline quality in the core region and an anisotropic residual stress field. When pumped by a Ti:Sapphire laser at 802 nm, the Tm:KLu(WO4)2 buried channel waveguide laser generated 136 mW at 1843.7 nm with a slope efficiency of 34.2% and a threshold as low as 21 mW, which are the record characteristics for femtosecond-laser-written Tm crystalline waveguide lasers. The variation of the output coupling resulted in discrete wavelength tuning of the laser emission from 1785 to 1862 nm. The propagation losses in the waveguide are ~1.2 ± 0.3 dB/cm.

Highly efficient Q-switched Yb:YAG channel waveguide laser with 5.6 W of average output power.

In this Letter, we present high-power continuous wave (CW) and Q-switched femtosecond laser-written Yb:YAG channel waveguide lasers. In Q-switched operation, obtained by a semiconductor saturable absorber mirror (SESAM), as well as in CW operation, the laser generates average output powers of more than 5.6 W and reaches slope efficiencies above 74%. The Q-switched laser operated at a maximum repetition rate of 5.4 MHz with a minimum pulse duration of 11 ns, and with a maximum pulse energy of 1 μJ. This laser has almost an order of magnitude higher average output power than previously reported Q-switched channel waveguide lasers.

Monolayer graphene coated Yb:YAG channel waveguides for Q-switched laser operation

We studied operation characteristics of an Yb:YAG channel waveguide laser, Q-switched by employing monolayer graphene. Uniform monolayer graphene grown by thermal chemical vapor deposition is transferred directly onto one end facet of the channel waveguide which simultaneously serves as an output coupling mirror (OC), making a monolithic Q-switched waveguide laser possible. In this cavity configuration, the Q-switched laser delivers a maximum average output power of 85 mW, corresponding to a pulse energy of 64 nJ at 1.33-MHz repetition rate. The laser performance of this device is compared with another cavity configuration, in which the monolayer graphene is coated onto separate OCs. In this case a shorter pulse duration of 79 ns is achieved, but the laser operation performance is worse with respect to efficiency and output power. The proposed monolithic approach demonstrates the potential for developing more compact Q-switched laser devices.

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.

Femtosecond laser-written lithium niobate waveguide laser operating at 1085 nm

We report on the channel waveguide lasers at 1085 nm in femtosecond laser written Type II waveguides in an Nd:MgO:LiNbO3 crystal. The waveguide was constructed in a typical dual-line approach. In the geometry, we found that four vicinal regions of the track pair could guide light propagation. In addition, these guiding cores support polarization-dependent-guided modes. The propagation losses of the waveguides were measured to be as low as 1 dB/cm. Under an optical pump at 808 nm, the continuous-wave waveguide lasing at 1085 nm was generated, reaching a slope efficiency of 27% and maximum output power of 8 mW. The lasing threshold was 71 mW. Our results show that with the femtosecond laser written Nd:MgO:LiNbO3 waveguide as the miniature light source, it was possible to construct all-LiNbO3-based integrated devices for diverse photonic applications.

Q-switched Nd:YAG channel waveguide laser through evanescent field interaction with surface coated graphene

We demonstrate a compact passively Q-switched channel waveguide laser based on the interaction of the evanescent-field and the graphene coated surface. The graphene layer is transferred onto the surface of a femtosecond laser inscribed Nd:YAG surface waveguide for a simple integration of the saturable absorber and waveguide structure. The passive Q-switching configuration is based on the evanescent-field interaction with graphene. A 1064 nm pulsed waveguide laser with a maximum repetition rate of 10.4 MHz has been achieved, reaching an output power of 48 mW. The shortest pulse duration of the channel waveguide laser is 52 ns.