Mode-locked and Q-switched all-fiber lasers using nanostructured core silica fiber are demonstrated. A novel active fiber has been developed, consisting of a collection of discrete nanorods doped with ytterbium and erbium within an aluminosilicate matrix. The arrangement of nanorods within the fiber core dictates the spatial distribution of amplification and refractive index, enabling the tailored design of the fiber's modal characteristics and dispersion properties. We demonstrate that the employed pumping strategy, which involves stimulating Yb3+ ions situated in nanorods and leveraging a non-radiative energy transfer from Yb3+ to Er3+ ions in distinct nanorods, is effective. This approach facilitates efficient laser performance comparable to fibers with a continuous dispersion of active ions throughout the core. The femtosecond mode-locked pulse at wavelength of 1560 nm, featuring a bandwidth of 5.2 nm, a pulse duration of 860 femtoseconds, and an RF spectral purity with an extinction ratio of 80 dB has been successfully obtained. These results underscore the potential of the nanostructured core fiber concept as an active medium in ultrafast, all-fiber devices

Although Four-Wave Mixing (FWM) has been extensively investigated, recent advancements in nonlinear imaging and spectroscopy have renewed interest in this area. This resurgent focus is driven by the need for ultrashort pulses at specific wavelengths, essentially for deep-tissue imaging and matching the spectral response of fluorophores and molecular vibrations [1]. FWM provides wide and selective wavelength tunability with high power, particularly in resonant cavity configuration. Fiber optical parametric oscillators (FOPOs) based on FWM demonstrate broad tunability by varying the wavelength of the pump beam from tunable ultrafast fiber oscillators [2]. However, most commercially available mode-locked fiber lasers have fixed or slightly tunable wavelengths.

Maximizing the transmission of high-peak-power ultrashort pulses through joints between polarization-maintaining optical fibers with different mode field diameters is crucial for improving the efficiency of all-fiber laser systems. Here, we propose a method of fabricating a thermally expanded core by using a CO2 laser as a heating source that does not require a priori splicing of fibers. Unlike standard methods utilizing continuous heating of the fiber, usually on the time scale of minutes, we present the pulsed approach, which can reduce the duration of the whole process to below 30 s. Via fiber rotation, we tailor our method to polarization-maintaining optical fibers. Furthermore, we apply the thermally expanded core method to manufacturing mode field adapters between commercially available polarization-maintaining optical fibers. Exemplary splices reveal an increase in transmission of 30 %, enabling insertion losses lower than 0.4 dB. The presented methods of fabricating a thermally expanded core and mode field adapters show high potential for large-volume production, especially for high-power applications, as the splices can withstand peak powers as high as 50 kW.

Artificial saturable absorbers based on loop mirrors often suffer from a not self-starting mode-locking operation. It is usually necessary to provide an additional phase shift in the loop, guaranteeing repeatable initiation of the pulsed regime. 3x3 even fiber couplers have recently enabled the introduction of a phase shift in an all-fiber loop mirror architecture. Until now, mode-locking induced by a 3x3 fiber coupler has been associated only with nonlinear amplifying loop mirrors. Here, we present a self-starting ultrafast dispersion-managed all-polarization-maintaining Yb-doped oscillator that utilizes a nonlinear optical lossy loop mirror instead. We show three ways of introducing asymmetric losses in a loop via a variable optical attenuator, a fiber coupler, and a very simple lossy splice. Complete characterization of all output ports of the oscillator proves significant spectral and temporal breathing of the pulse when circulating through the net normal dispersion cavity, which can deliver nJ-level pulse energy. The system guarantees excellent stability and performance comparable to nonlinear amplifying loop mirrors while being simpler, cheaper, and providing more usable output ports with different characteristics.

Mode-locking operation is demonstrated in all-fiber laser incorporating a nanostructured Yb+Er co-doped silica SMF. The femtosecond pulses with 6nm bandwidth, 850fs pulse-width and high RF spectral purity of 80dB extinction ratio have been obtained.

Plasmonic structural color originates from the scattering and absorption of visible light by metallic nanostructures. Stacks consisting of thin, disordered semicontinuous metal films are attractive plasmonic color media, as they can be mass-produced using industry-proven physical vapor deposition techniques. These films are comprised of random nano-island structures of various sizes and shapes resonating at different wavelengths. When irradiated with short-pulse lasers, the nanostructures are locally restructured, and their optical response is altered in a spectrally selective manner. Therefore, various colors are obtained. We demonstrate the generation of structural plasmonic colors through femtosecond laser modification of a thin aluminum film–isolator–metal mirror (TAFIM) structure. Laser-induced structuring of TAFIM’s top aluminum film significantly alters the sample’s specular and diffuse reflectance depending on the fluence value and the number of times a region is scanned. A “negative image” effect is possible, where a dark field observation mode image is a negative of a bright field mode image. This effect is visible using an optical microscope, the naked eye, and a digital camera. The use of self-passivating aluminum results in a long-lasting, non-fading coloration effect. The reported technique could be used in anti-counterfeiting and security applications, as well as in plasmonic color printing and macroscopic and microscopic marking for personalized fine arts and aesthetic products such as jewelry.

Femtosecond lasers play a significant role in the industrial processing of metals, including cutting masks, drilling foils, texturing molds, and engraving. This research explores methods for maximizing the removal rate of metals. The highest removal rate and best quality can be achieved using pulses shorter than 300 fs and optimal laser fluence. We also demonstrate the potential of femtosecond laser polishing of laser-machined surface, resulting in surface roughness well below Sa<1 mu m. Examples to be showcased include manufacturing gratings for FIR spectroscopy, drilling stainless steel, deep engraving, and polishing dies for coin minting.

We fabricate a nanodiamond-doped silica step-index fiber exhibiting a highly dispersive nonlinearity across near-infrared wavelengths. This is achieved without altering chromatic dispersion, which resembles SMF-28 fiber.

We discuss new ideas for developing fiber light sources for nonlinear imaging. We demonstrate high-power SC-based laser tunable within fingerprint region, as well as new methods of tuning FWM sidebands.

This erratum corrects errors in Fig. 3 and Fig. 4 of the original publication [Opt. Express32, 31672 (2024)10.1364/OE.530457] caused by incorrect values of the vertical axes in logarithmic scales. The corrections do not influence the conclusions of the original article.

Ultrafast all-fiber Yb-doped fiber oscillators are usually associated with all-normal-dispersion cavities, which operate in a dissipative soliton regime, quintessential for pulsed operation at the wavelength of 1 $\mu$m. This work presents an all-polarization-maintaining Yb-doped fiber laser oscillator that operates in a dispersion-managed dissipative soliton regime, thanks to incorporating a chirped fiber Bragg grating. The oscillator, mode-locked via a nonlinear optical loop mirror, has an unconventional semi-linear cavity of net anomalous dispersion. Unlike in standard ring resonators, the ultrashort pulse undergoes amplification twice per cavity roundtrip. Additionally, we report a duality of pulsed operation states depending on the pumping power. Strikingly, the oscillator can work in a subregime similar to the standard dissipative soliton, facilitating further energy scaling at anomalous dispersion. We characterize the low-noise setup capable of delivering pulse energy as high as 6.4 nJ using standard single-mode polarization-maintaining optical fibers.

3x3 fiber couplers introduce a 2π/3 phase shift, which helps initiate the mode-locking operation. Here, we provide more in-depth insight into the performance of the 3x3 nonlinear loop mirror with an asymmetrically placed lossy splice.

We present a stimulated Raman scattering (SRS) microscope integrated with a novel fiber-based light source. Our light source provides two synchronized pulse trains with 100 mW average power each, independently tunable in the range of 913 to 930 nm and 1024 to 1034 nm, respectively, thus enabling SRS measurements across the 990 to 1300 cm-1 spectral range with a spectral resolution of 15 cm-1. We demonstrate the SRS imaging of leukemic cells recorded in a few seconds. Our system may find potential application in biomedicine, in particular, helping to accelerate the diagnostics and follow-up treatment of leukemia patients.

Nanodiamond integration with optical fibers has proved a compelling methodology for magneto-optics. We reveal that the applicability of nanodiamonds in nonlinear optics goes beyond the previous demonstrations of frequency converters. Instead, we exploit the recently reported volumetric integration of nanodiamonds along the optical fiber core and show that the nonlinear response of glasses can be manipulated by nanodiamonds. By taking the mature z-scan approach we measure the nonlinear absorption and nonlinear refraction of three dielectric materials containing nanodiamonds in different concentrations and sizes. The work begins with nanodiamond-water suspensions, which offer the advantage of rapidly assessing the dependence of the nonlinear refractive index on the nano-particle concentration and size. Subsequently we investigate two fiber preforms based on silica and soft glass doped with nanodiamonds to evaluate the feasibility of nonlinearity shaping. We achieve a nearly 20% reduction of the nonlinear refractive index of fused silica containing trace amounts of nanodiamonds relative to a pristine reference. The demonstration of such a noticeable impact on the nonlinear response of the key optical material widely accepted by ultrafast optics practitioners provides a guideline for future work on the novel concept of negative nonlinearity fibers, which could disrupt the established chromatic dispersion-nonlinearity landscape.

Chirped fiber Bragg gratings opened up a way towards investigating dispersion-managed dissipative soliton regime in all-fiber cavities at the wavelength of 1 µm. It has been shown that dispersion management can decrease the chirped pulse duration compared to all-normal-dispersion oscillators. Recent works also prove that operation near-zero net cavity dispersion can reduce the relative intensity noise. Building such systems using only polarization-maintaining optical fibers is of great interest because of their robustness in extreme environmental conditions resulting in various applications outside research laboratories. This work presents an ultrafast Ybdoped fiber laser oscillator made entirely of polarization-maintaining optical fibers and fiberized components. Unlike in typical ring cavities, the ultrashort pulse passes through the rare-earth-doped fiber twice per cavity roundtrip. The system operates in a Raman-free dispersion-managed dissipative soliton regime at the central wavelength of 1031 nm. The negative dispersion is introduced to the cavity via a chirped fiber Bragg grating. At net cavity dispersion of –0.037 ps2, the setup delivers stable 3 nJ pulses at a repetition rate of 23.781 MHz. The oscillator, passively mode-locked with a nonlinear optical loop mirror, generates positively chirped 8.2 ps pulses, which can be compressed down to 125 fs with a temporal Strehl ratio of 0.77.

Glass cleaving by Bessel-like beams is one of the leading techniques providing high processing throughput and high edge quality. With the possibility to apply it to different transparent materials, this method has great potential in the high-volume production of flat panel displays, camera windows, medical devices, and others. The principle of glass cleaving is the controlled weakening of a hard transparent material by the induction of microcracks along a tight, elongated focus. These microcracks are oriented in a predefined, constant direction, limiting the flexibility of round shape fabrication. In contrast to dynamic beam manipulation techniques, the regime of direction-independent cutting was achieved through proper temporal pulse shaping. The setup does not consist of any active components in the beam path. The obtained quality and process speed are comparable with other, more complex laser cleaving techniques. Additionally, the successful cutting of polymers is presented, which are difficult to separate by the Bessel beam due to the limited possibility of microcrack generation.

Fiber-based light sources with a tunability range well beyond the gain bandwidth allowed by the available doped-fiber media are highly demanded for numerous applications including biomedical nonlinear imaging. For instance, coherent Raman microscopy requires the combination of at least two beams at two different wavelengths with one of them spectrally tunable, to explore the resonances of the different molecules in the sample [1]. Nonlinear frequency conversion based on four-wave-mixing (FWM) in microstructure fibers offers a flexible tool allowing to obtain wide wavelength tunability, with impressive performances [2]–[4]. To date, such a spectral tunability has been enabled exclusively by tuning the pump wavelength. Here, we demonstrate that an analogous effect and with a comparable spectral range can be obtain also by stretching an ultrashort pulsed pump at fixed wavelength.