In this work, we present an all-polarization-maintaining, all-large-mode-area fiber laser oscillator passively mode-locked using a nonlinear optical loop mirror. The ytterbium-doped system, working in a Raman-free regime, operates at a central wavelength of 1.03 μ;m. The oscillator emits 12 nJ pulses at a repetition rate of 7.56 MHz. Positively chirped pulses from an all-normal-dispersion cavity can be externally compressed to the duration of 250 fs.

Controlling an ultrafast laser oscillator repetition rate is crucial for the emerging laser burst micromachining. The efficiency of a material surface treatment process as well as the quality of live tissue ablation depends, to a considerable extent, on the number of laser pulses in a burst window. In the following article, we present an all-PM fiber harmonically mode-locked Mamyshev ring oscillator capable of producing laser pulses with a tunable period. The oscillator can be operated at any frequency, being a multiple of the fundamental repetition rate up to 305 MHz at 19th harmonic. We found that the operation frequency is limited by the available pump power only. What is worth noting is that the energy of the emitted pulses is independent of the operating frequency. The essential laser parameters are excellent: an amplitude noise of 0.1% and fundamental frequency suppression levels of 70 dB at every repetition rate. Additionally, the mechanism of harmonic mode-locking is discussed in detail and is found to be caused by gain depletion and recovery effect.

We present the first o bservation of h armonic m ode l ocking i n Mamyshev oscillator. The Yb-doped all-PM oscillator emits 2 nJ pulses with repetition rate up to 229 MHz at 14th harmonic, limited by available pump power.

We present an all-PM fiber Mamyshev oscillator with the tunable repetition rate through harmonic mode-locking. It emits 2 nJ pulses at 1022nm with repetition rate ranging from 16.3 through 229 MHz tuned by pump power.

In this article we demonstrate the first, to the best of our knowledge, all-fiber self-starting laser oscillator consisting entirely of polarization-maintaining large mode area (PLMA) fibers mode-locked with nonlinear optical loop mirror (NOLM). The system works in a Raman-free dissipative soliton regime and operates at a central wavelength of 1030 nm. It delivers stable ultrashort pulses of high energy of 12 nJ at a 7.56 MHz repetition rate which can be compressed down to the Fourier transform limit of ~250 fs. Higher energies were limited by the formation of multiple pulses in the cavity.

We present an environmentally stable ultrafast oscillator employing a novel implementation of a multi-segment All Polarization-Maintaining-Fiber Nonlinear Polarization Evolution reflective artificial Saturable Absorber. Oscillator emits 1 nJ pulses with duration of 230 fs after compression. © 2019 The Author(s)

We present a development of microlenses achromatically corrected in near-infrared spectral windows. We show that the standard fiber drawing technology can be successfully applied to the development achromatic gradient index microlenses by means of internal nanostructurization. These gradient index microlenses can achieve similar performance to standard aspheric doublets, while utilizing a simpler, singlet element geometry with flat surfaces. A nanostructured lens with a parabolic profile was designed using a combination of the simulated annealing method and the effective medium approximation theory. Measurements on the fabricated lenses show that the microlenses have a nearly wavelength-independent focal plane at a distance of about 35 μm from the lens facet over the wavelength range of 600-1550 nm. The successful design and fabrication of achromatic flat-parallel rod microlenses opens new perspectives for micro-imaging systems and wavelength-independent coupling into optical fibers.

We report on a ytterbium-doped phosphate glass single-mode fibre laser, 4 cm long, with a maximum output power of 11.6 W and a slope efficiency of 66.6%. We developed the double-clad fibre with a 19 µm diameter step-index core and a pump waveguide with a high numerical aperture due to external air-cladding. The estimated pump absorption in the fibre exceeded 700 dB m−1.

We have developed a new type of an optical fiber probe which integrates the standard single mode fiber with a gradient index (GRIN) microlens. The system is perfectly suited for optofluidic sensor applications since the diameter of the lens module is exactly the same as the diameter of the optical fiber. Moreover, the performance of the GRIN lens is not degraded by low contrast of the refractive index between of the lens and the fluidic environment. The GRIN lens is made with novel technology of nanostructured optics. Full Text: PDF References M. Woerdemann, C. Alpmann, M. Esseling, C. Denz, "Advanced optical trapping by complex beam shaping", Laser Photonics Rev. 7, 839 (2013). CrossRef E. Weber, F. Keplinger, and M. J. Vellekoop, "On-Chip Light Modulation Applying Optofluidic Principles", IEEE Sensors Journal 13 4773 (2013). CrossRef F. Hudelist, J. M. Nowosielski, R. Buczynski, A. J. Waddie, M. R. Taghizadeh, "Nanostructured elliptical gradient-index microlenses", Optics Letters 35, 130 (2010) CrossRef J. M. Nowosielski, R. Buczynski, F. Hudelist, A. J. Waddie, M. R. Taghizadeh, "Nanostructured GRIN microlenses for Gaussian beam focusing", Opt. Comm. 283 1938 (2010). CrossRef A.Sihvola, Electromagnetic Mixing Formulas and Applications (London: The Institution of Electrical Engineers 1999). J. Nowosielski, R. Buczynski, A. J. Waddie, A. Filipkowski, D. Pysz, A. McCarthy, R. Stepien, M. R. Taghizadeh, "Large diameter nanostructured gradient index lens", Opt. Ex. 20 11767 (2012). CrossRef R. Stepien, J. Cimek, D. Pysz, I. Kujawa, M. Klimczak, R. Buczynski, "Soft glasses for photonic crystal fibers and microstructured optical components", Opt. Eng. 53, 071815 (2014). CrossRef A. Filipkowski, B. Piechal, D. Pysz, R. Stepien, A. Waddie, M. R. Taghizadeh, R. Buczynski, "Nanostructured gradient index microaxicons made by a modified stack and draw method", Opt. Lett. 40, 5200-5203 (2015). CrossRef

We report the design and fabrication of nanostructured gradient index microaxicons suitable for integration with optical fibers. A structure with the effective refractive index decreasing linearly from the center to the edges (i.e., an axicon) was designed using a combination of a simulated annealing method and the effective medium theory. The design was verified numerically with beam propagation method simulations. The axicons were made by the modified stack and draw method and integrated with optical fibers. The optical properties of the fabricated elements were measured and showed good agreement with the numerical simulations. The fabricated axicons produced an extended line focus at a distance from about 70 to 160 μm from the lens facet with a minimum FWHM diameter of 8 μm at 90 μm. At smaller distances, an interference pattern is observed both in the experiment and in simulations, which is attributed to the uneven effective refractive index profile at the structure.

Pressure-tuned laser diodes in external cavity were used as tunable sources for photoluminescence excitation (PLE) spectroscopy. The method was demonstrated in the 720 nm-1070 nm spectral range using a few commercial laser diodes. The samples for PLE measurements were quantum-well structures grown on GaAs and on InP. The method is superior to standard PLE measurements using titanium sapphire laser because it can be extended to any spectral range where anti-reflection coated laser diodes are available.

Nanostructured gradient index (nGRIN) elements are a new class of planar-surface micro-optical components which transform optical wavefront by discrete, subwavelength changes in the refractive index perpendicular to the optical axis. We have developed a series of various nanostructured micro-optical components with various functionalities using modified stack-and -draw method. All nanostructured components are developed with two types of thermally matched soft glasses with refractive index difference of 0.04 - 0.1. In this paper we present experimental and modelling results for various type of microcomponets, including spherical, elliptical and axicon lenses.

Most of the research work related to photonic crystal fibres has to date been focused on silica based fibres. Only in the recent years has there been a fraction of research devoted to fibres based on soft glasses, since some of them offer interesting properties as significantly higher nonlinearity than silica glass and wide transparency in the infrared range. On the other hand, attenuation in those glasses is usually one or more orders of magnitude higher that in silica glass, which limits their application area due to limited length of the fibres, which can be practically used. We report on the development of single-mode photonic crystal fibres made of highly nonlinear lead-bismuth-gallate glass with a zero dispersion wavelength at 1460 nm and flat anomalous dispersion. A two-octave spanning supercontinuum in the range 700–3000 nm was generated in 2 cm of the fibre. In contrast to the silica glass, various oxide based soft glasses with large refractive index difference can jointly undergo multiple thermal processing steps without degradation. The use of two soft glasses gives additional degrees of freedom in the design of photonic crystal fibres. As a result, highly nonlinear fibres with unique dispersion characteristics can be obtained. Soft glass allow also development of fibres with complex subwavelength refractive index distribution inside core of the fibre. A highly birefringent fibre with anisotropic core composed of subwavelength glass layers ordered in a rectangular structure was developed and is demonstrated

We demonstrate the feasibility of the development of a gradient-index elliptical microlens with a size of 75×125  μm using nanostructured glass technology. The gradient index is obtained by means of a discrete internal structure composed of two glasses with feature sizes much smaller than the wavelength of the incident light. A modified photonic crystal fiber-drawing technique is used for the lens fabrication. The elliptical shape of the lens is obtained by a novel final drawing stage where the spherically symmetric lens preform is drawn into an elliptical form by collapsing two large air holes placed in the preform during assembly. The effective focal lengths of 160 and 260 μm for the orthogonal axes are obtained experimentally for the fabricated lens, and show good agreement with those predicted by the effective medium theory and the full-wave beam propagation simulations.

Wavelength tuning of infrared laser diodes in the high-hydrostatic pressure setup is demonstrated and its reliability is discussed in detail. Major reliability issues concern the photochemical reactions on the laser facet and the presence of strong absorption bands above 1650 nm in typical pressure liquids that do not undergo phase transitions up to 20 kbar. Despite these difficulties spectrally wide-range pressure tuning can be achieved with sufficient reliability for spectroscopic applications.

A modified gradient index (GRIN) lens is optimised for use in a liquid-type high pressure cell. It was found that high pressure changes the optical power of the gradient-index lenses by changing the index profile of the glass. In this paper, we present a modified GRIN lens in which these changes are compensated by the pressure-induced changes of the refraction index of the liquid used as a pressure medium. New lens was used for the collimation of the pressure tuned tapered laser working in external resonator. The lens proved to have the optical power almost independent of the pressure up to 1.6 GPa, as it allowed to obtain tuning range almost independent on pressure without the need of any modification of the optical setup.

Diode lasers are coupled to a multi-mode fiber (with 100-400 μm core) using a reflector in the form of a regular pyramid. The optimization of the optical setup allows to couple 60%-90% of light into the fiber. The demonstrator achieves 3.5 W in the 100/125 μm fiber with 8 violet (405 nm) diodes, 5.5 W in the 100/125 μm fiber with 8 blue (445 nm) diodes, and 3.3 W in the 200/250 μm fiber with red (638 nm) diodes. The device can work with lasers emitting at many different wavelengths, including green (532 nm) frequency-doubled lasers. Our work was motivated by potential medical applications of these laser sources.

Threshold current in 808 nm GaAsP/AlGaAs laser diode has been measured as a function of pressure (up to 1.8 GPa) and temperature (from 80 to 300 K). The results have been analyzed in order to separate leakage current from radiative current and to determine the effective barrier for leakage and its pressure dependence. Our data indicates that both X and L minima in the barriers and in the claddings contribute to leakage. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Photoreflectance (PR) and photocurrent (PC) measurements have been demonstrated in the 1250-1600 nm spectral range using an external-cavity pressure-tuned laser diode as the source of monochromatic light. Compared to conventional PR and PC methods using monochromated light from the lamp, it allows to achieve a smaller spot so that micro-PR and micro-PC are possible either directly or with fiber coupled beam. In case of PR, it also allows to eliminate spurious photoluminescence signal. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Laser diodes with output powers of 1–2 W and emission wavelengths of 808, 860, 975, 1060, 1120, 1210, and 1540 nm have been tuned with pressure up to 2 GPa. Pressure tuning might become a practical method for tuning near‐infrared lasers in spectroscopic applications, such as photoluminescence excitation, photoreflectance, and resonant Raman scattering, as well as in applications as optical pumps at unique wavelengths.