Abstract ：

Stable polarization has been regarded as a key element for improving the beam quality of vertical cavity surface emitting lasers (VCSELs). However, gain isotropy in the active layer of VCSELs ineluctably leads to the uncertainty of the polarization direction. In this paper, a liquid crystal (LC)-VCSEL laser with polarization control characteristics is designed and fabricated based on the optical rotation effect and electrically controlled birefringence characteristics of orthogonal LC. The experimental results show that, electrically controlled LC could flexibly realize the scheme of polarization stable output and the switching ratio of polarization output could reach 164:1. Based on the electrically controlled birefringence characteristics of LC, the linear polarization angle of VCSEL is further regulated by applying a deflection voltage, and the polarization angle tuning range is between 0° and 90°. © 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.

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Surface emitting lasers Transceivers Liquid crystals Birefringence Polarization

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Low-dimensional hybrid halide perovskite materials with self-trapped exciton (STE) emissions and anisotropic properties are highly attractive for their great potential in many applications. However, to date, reports on large one-dimensional (1D) perovskite single crystals have been limited. Here, centimeter-sized 1D single crystals of trimethylammonium lead iodide (TMAPbI(3)) with typical STE emission are synthesized by an antisolvent vapor-assisted crystallization method. Thermal quenching and antiquenching with a high relative sensitivity of photoluminescence (PL) are observed and studied via temperature-dependent photoluminescence spectroscopy. Further analysis indicates that the temperature-dependent PL behaviors are influenced by the self-trapping of the free exciton and the migrations between self-trapped excitons and intermediate nonradiative states. The TNIAPbI(3) single crystal also exhibits a linearly polarized emission and a large birefringence that is higher than those of commercial birefringent crystals. This 1D perovskite with high structural anisotropy has promise for applications in versatile optical- and luminescence-related fields.

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We report the first high-birefringence hollow-core anti-resonant fiber with a pseudo-C4v symmetry. The resulted fiber shows a phase birefringence, polarization extinction ratio, and loss of 0.9 × 10-4, 25 dB, and 250 dB/km, respectively, at 1550 nm. © 2020 OSA.

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Optical properties Optics Lasers Birefringence

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Abstract ：

We report the first high-birefringence hollow-core anti-resonant fiber with a pseudo-C4ν symmetry. The resulted fiber shows a phase birefringence, polarization extinction ratio, and loss of 0.9×10-4, 25 dB, and 250 dB/km, respectively, at 1550 nm. © OSA 2020 © 2020 The Author(s)

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Birefringence

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We report the first high-birefringence hollow-core anti-resonant fiber with a pseudo-C-4 nu symmetry. The resulted fiber shows a phase birefringence, polarization extinction ratio, and loss of 0.9 x 10(-4), 25 dB, and 250 dB/km, respectively, at 1550 nm. (C) 2020 The Author(s)

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The ability of loosely focused picosecond laser to induce filamentation (4.8 times the Rayleigh length) in sapphire was confirmed. The morphology and microstructure of the filamentary traces under typical pulse energy were studied, in which the colorful birefringence phenomenon and damage defects were detected in sapphire. Irreversible ceramic-like polycrystalline microstructures were formed in filamentary traces, and the phase transition from alpha-Al2O3 to gamma-Al2O3 directly reflected the thermal effect of picosecond laser filamentation. According to the filamentary characteristics, a continuous filamentary channel with a uniform diameter of 33 mu m and a length of 7443 mu m was obtained by gradually raising the focal position. The research provides first-hand information for the high throughput micro-cutting, micro drilling and thin slicing of sapphire based on ultrafast laser non-linear effects.

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Sapphire Modification Phase transition Picosecond laser Filamentation

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We demonstrate an all fiber mode-locked ultrafast erbium laser oscillator by means of nonlinear polarization evolution (NPE) in polarization maintaining (PM) fibers. Here, the artificial saturable absorber (SA) is formed by a piece of PM active fiber and a Faraday mirror (FM). High repetition rate could be obtained thanks to the introduction of the PM active fiber. The transmission characteristics of the SA are studied through theoretical analyses as well as experimental demonstration. Channeled spectra caused by soliton-soliton interaction and birefringence-induced filter are also studied and discussed. A good agreement is achieved between the theoretical analyses and experimental results.

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Mode-locked lasers polarization-maintaining lasers

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The explosive market growth of consumer electronic devices has made a great demand for the precise processing of sapphire by using ultrafast lasers. Ultrafast lasers can induce nonlinear multiphoton absorption, and thereby leads to the precise and defined microfabrication inside transparent materials with minimum heating effects. The induction of these structural modifications by tightly focused high intensity laser pulses is a versatile technique for the fabrication of three-dimensional photonic devices. Ultrafast lasers are therefore widely used for fundamental research as well as practical applications. This paper presents the laser induced damage mechanisms and absorption phenomena that lead to structural modifications in sapphire. For the given parameters, the electron density growth as a result of plasma generation through multiphoton and avalanche processes is predicted theoretically and is found to be greater than the critical electron density required to induce breakdown in sapphire. Structural modifications, from small change of refractive index to birefringence, cracks and voids are observed when sapphire was irradiated experimentally under the same parameters. Observations revealed the creation of a highly crack region at the focal volume surrounded by local refractive index change which enhances in radial as well as longitudinal direction with increase in the incident laser power and pulse number. Followed by this highly crack region, a birefringent region associated with the nonlinear propagation of laser beam is observed, length of which increases with increasing input power however no significant effect is observed with changing number of pulses. Depending on the input beam powers, this region has length of several hundred-micron and diameter smaller than two microns.

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microfabrication sapphire three-dimensional photonic devices Ultrafast lasers

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A single pulse energy 6.77mJ, repetition rate of 1kHz, pulse width of 11ps at 532nm wavelength with the near top-hat intensity profile in the near filed picosecond laser amplification system is realized using a semiconductor laser side pumped Nd:YAG crystal. The seed pulse is generated in a home-built Nd:YVO4 oscillator, pumped with a 808 nm CW diode laser. The oscillator provides 2.8nJ, 11ps pulse width, 86 MHz repetition rate at 1064 nm wavelength. Pulse from the Nd:YVO4 oscillator is first amplified to 1.5mJ by a diode side-pump Nd:YAG regenerative amplifier. Then the pulse, increased in size by a negative lens, sequentially passed through a circular aperture and a spatial filter-image relaying system to produce a top-hat intensity profile in the modules, and an 8th order super-Gaussian beam is obtained, and total transmission of beam shaping set-up is about 30%. The beam, passed through a double-pass preamplifier of single rod and a double-pass main amplifier of single rod, is amplified up to 17.3mJ, corresponding peak power is 1.57 GW. A 4F relay-imaging system is used in the amplification stages to preserve the top-hat intensity profile and compensate the thermally induced birefringence of Nd:YAG rod. The amplified output beam leaving the double-pass Nd:YAG module is decreased in size and imaged on a 5x5x13 m<^>3 second-harmonic generation (SHG) crystal-LBO by a 4F relay-imaging system, finally a 532nm approximate top-hat intensity profile in the near filed, which single pulse energy is 6.77mJ, is obtained after double-frequency. The second-harmonic generation efficiency is over 51%.

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Second-harmonic generation Spatial filter-image relaying system Super-Gaussian beam Ultrafast laser

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Pulse-burst 1064-nm picosecond azimuthal polarization beam amplification up to an average power of 16.32 W using side-pumped Nd: YAG amplifiers has been demonstrated. The maximum envelop energy as much as 16.32 mJ, corresponding to a power amplification factor of 299.5%. A simple criterion was defined to help estimate the amount of depolarization in Nd:YAG amplifier stages. The degree of depolarization of the beam was 7.1% and the beam quality was measured to be M-2 = 3.69. The reason for the azimuthal polarization depolarization and beam quality degradation were explained theoretically and experimentally during the amplification process.

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azimuthal polarization Nd:YAG amplifiers picosecond laser thermally induced birefringence

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