In this paper, a directly pumped passively Q-switched Nd3+ -doped phosphate fiber laser using Cr4+:YAG as a saturable absorber is reported. The Nd3+ -doped phosphate fiber preform with minimal internal defects were prepared by the double-peeled isolation extrusion method and drawn into optical fibers. The core-clad size of the fiber was 234/356 μm, with a transmission loss of 1.1 dB/m at 1053 nm. Subsequently, a passively Q-switched fiber laser was constructed based on the homemade Nd3+ -doped phosphate fiber, and the effects of parameters such as the reflectivity of the output coupler mirror, the transmittance of the saturable absorber, the length of the fiber, and the pumping power on the characteristics of the output laser pulse were investigated. After optimizing the key parameters, the laser achieved a peak pulse energy of 388 μJ and a maximum peak power of 21.8 kW. The results provide fundamental theoretical and experimental guidance for the development of passively Q-switched fiber lasers with high peak power, demonstrating significant practical value and theoretical significance.
A long-wave infrared (LWIR) on-chip gas sensor based on subwavelength grating waveguide is proposed. By optimizing the grating structural parameters, the corresponding slow-light region is overlapped with the absorption spectrum of methane, which can greatly improve the light–gas interaction to achieve excellent sensing performance. The presented waveguide gas sensor is designed to operate at the wavelength of 7.70 μm, which corresponds to the methane absorption peak in the LWIR and exhibits a high slow-light enhancement factor of 7.514. The related sensitivity and limit of detection are, respectively, 26.54393 and 0.1327 ppm.
A non-volatile flexible-grid wavelength-selective switch (NVFGWSS) based on subwavelength-grating-Ge2Sb2Te5 (GST)-assisted silicon microring resonators (MRRs) is proposed. By controlling the state of the subwavelength grating GST and the phase shifter, the transmission spectra of the designed subwavelength-grating-GST-assisted silicon MRRs are combined, and thus tunable bandwidths (BWs) are generated as required. A comprehensive analysis of the presented subwavelength-grating-GST-assisted silicon MRRs and the corresponding NVFGWSS is given. Numerical simulations reveal that, for the designed module comprising a subwavelength-grating-GST-assisted silicon MMR and an ellipse-based crossing waveguide, its maximum crosstalk (CT) and insertion loss are −18.08 and 0.50 dB, respectively. For the designed NVFGWSS, as the channel spacing is 0.8 nm, the in-band ripple and CT are <0.895 and −13.006 dB, respectively, and the 3-dB BW changes from 0.51 to 3.2 nm.
KEYWORDS: Phase unwrapping, Deformation, Tunable filters, Fringe analysis, 3D metrology, Signal to noise ratio, 3D projection, Error analysis, 3D mask effects, Optical filters
An improved composite Fourier transform profilometry is proposed in this study to quickly measure the three-dimensional (3D) contour of an object. Three groups of fringe patterns with different frequencies are combined in this method. Compared with the other composite profilometry, it solves the problem of phase error propagation in phase unwrapping. The absolute phase of the object is accurately calculated and the measuring accuracy is improved greatly by filtering out the background direct current noise. Both simulation and experiment results show that the 3D contour of the measured object can be reconstructed quickly and accurately by this method. It has great application potential in the field of real-time 3D measurement.
A highly sensitive long-period fiber gratings (LPFGs) temperature sensor based on dual-peak resonance operating near the phase-matching turning point in chalcogenide fiber is proposed. The Ge-As-Se chalcogenide glasses with a high linear refractive index, large thermo-optic coefficient, and wide transmission window was prepared and characterized for temperature sensors. Combined with PMTP and cladding etching, the temperature sensing characteristics of different cladding modes were examined systematically. The results of theoretical simulation indicated that different cladding modes show relatively high-temperature sensitivities, and the temperature sensitivity of the seventh cladding mode was as high as 9.296 nm/°C operating near PMTP, which is about two orders of magnitude higher than that of the traditional silica LPFGs. Therefore, this temperature sensor with high sensitivity and simplified design can be applied to high-precision temperature sensing.
A method based on Mach–Zehnder interferometer and stress optical coefficients theory was proposed for measuring the photoelastic coefficients of optical glasses. The corresponding apparatus is built to measure the photoelastic coefficients of fused silica and As2S3 glasses, with p12 = 0.27 and 0.26 at 632.8 nm, respectively. The validity and accuracy of the present technique were tested on the samples of fused silica and As2S3 glass, with the relative error not exceeding 10% compared to that in previous studies and the causes of errors were analyzed. The photoelastic coefficients of tellurite glasses with component 75TeO2-20ZnO-5Na2O were measured, with p11 = 0.23 and p12 = 0.22. The acousto-optic (AO) figure of merit M2 of the three types of glass was calculated and the role of photoelastic coefficient in the equation was discussed, providing an effective technique for investigating the AO interaction in a glass.
We demonstrated a robust Watt-level mid-infrared supercontinuum (MIR-SC) source from 2 to 6.5 μm in an all-fiber structured cascade infrared transmission system. In combination with an optimized ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber-based high-power MIR-SC source and an advanced fiber coupling system, we achieved a SC with 30 dB spectral bandwidth spanning from 2000 to 6500 nm SC, with an output power scaled up to 1.13 W in a segment of 4- meter-long As2S3 fiber. And the maximum output power of 1.28W was achieved in a segment of 2-meter-long As2S3 fiber. To the best of our knowledge, this is the first report of an all-fiber supercontinuum based on commercial As2S3 step-index fiber with both watt-level output power and systematically investigation of the output characteristics. And in the meantime, we provided a feasible idea for fiber coupling under high power condition.
We have experimentally reported an ultrabroadband midinfrared (MIR) supercontinuum (SC) generation with high coherence property in chalcogenide tapered fiber with all normal dispersion (ANDi). The fibers, fabricated by an isolated extrusion method, made of Ge20As20Se15Te45 core and Ge20As20Se20Te40 cladding glasses. A homemade tapering platform allows us to accurately control the core diameters of the tapered fibers to realize ANDi characteristic. A coherent MIR SC spectrum spanning from 1.7–12.7 Μm was generated in a 7 cm long tapered fiber pumped at 5.5 μm. And high coherence property of the generated SC spectrum was investigated and verified by the simulation.
Phase change memory is regarded as one of the most promising candidates for the next-generation non-volatile memory. Zr9(Ge2Sb2Te5)91 film was investigated as storage material for phase-change memory application. The crystallization temperature (Tc) and 10 years data retention temperature of the Zr9(Ge2Sb2Te5)91 film are about 195 and 106.7°C, respectively, and both higher than that of Ge2Sb2Te5 (GST). The sheet resistance ratio between amorphous and crystalline states is up to four orders of magnitude. The crystalline resistance of Zr9(Ge2Sb2Te5)91 film is higher than GST for one order of magnitude, which contribute to reduce the power consumption for PCM device. Zr9(Ge2Sb2Te5)91 film exhibit larger optical band gap in comparison with GST. Zr9(Ge2Sb2Te5)91 is considered to be a promising material for phase change memory.
We developed the extrusion method to prepare arsenic-free chalcogenide glass fibers with glass cladding. By using the double nested extrusion molds and the corresponding isolated stacked extrusion method, the utilization rate of glass materials was greatly improved compared with the conventional extrusion method. Fiber preforms with optimal stability of core/cladding ratio throughout the 160 mm length were prepared using the developed extrusion method. Typical fiber structure defects between the core/cladding interface, such as bubbles, cracks, and core diameter variation, were effectively eliminated. Ge-Sb-Se/S chalcogenide glasses were used to form a core/cladding pair and fibers with core/cladding structure were prepared by thermally drawing the extruded preforms. The transmission loss, fiber bending loss, and other optical characters of the fibers were also investigated.
Chalcogenide glasses (ChGs) have a relatively small temperature coefficient of refractive index, broad transmission
range from almost visible to mid-infrared. It is suitable for precision molding. With the help of above mentioned merits,
ChGs have a vast reservoir of value in the field of military and civilian infrared imaging. However, the internal defects of
ChGs are caused by melting, cool-demoulding and annealing in a high vacuumed ampoule. The defects include the
optical inhomogeneity, chemical inhomogeneity and built-in stress which trouble the homogeneity of ChGs and directly
affect the imaging quality of infrared imaging devices. The detection and control of internal defects is a key technique. In
this paper the platform for testing, characterization and evaluation of the inhomogeneity of ChGs will be designed and
built. The appropriate testing and evaluation criteria of inhomogeneity during the preparation procedure of ChGs in the
vacuumed ampoule will be studied. The transmittance of ChGs sample is measured repeatedly. The factor of internal
multple reflection in ChGs sample is analysed and discussed. Analysis shows that the mean transmissivity of ChGs
sample (Ge28Sb12Se60) with thick of 1 cm is approximately 66% in 8 to 11 microns. The loss is less than 2.40%/cm. The
optical path difference (OPD) caused by residual stress in ChGs sample is less than 5.2 nm/cm. The results will provide a
technical support to optimize the ChGs preparation process and improve the ChGs homogeneity.
In this paper, the methods of preparation of Ge-Se-Sb glasses with low impurity content were developed, and a
large Ge-Sb-Se glass rod (φ85×80mm) with good quality was obtained. The physical and optical properties of
the glass were measured. The optical homogeneity (Δn) at 2μm at different places inside the same bulk was less
±2×10-4. In order to accurately evaluate the infrared resolution of our prepared glass, a lens of f 19mm F/#1.3
was used to evalue its modulation transfer function (MTF) performance. The MTF value at 20cycles/mm for
20°C was 0.52. The area under MTF curve covers 82.466% of the image space, and has a value of 21.8 cycles/mm.
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