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Sensor fusion based localization techniques often need accurate estimate of the fast and uncertain scene change in environment. To determine the scene change from two consecutive LIDAR scans, this paper proposes a novel technique called 'keep zero as zero' polar correlation. As it name implies any zero in the scan data is kept isolated from scene change estimation as it do not carry any information about scene change. Unlike existing techniques, the proposed methodology employs minimization of selective horizontal and vertically shifted sum of difference between the scans to estimate scene change in terms of rotation and translation. Minimization of the proposed correlation function across the specified search space can guarantee an accurate estimate of scene change without any ambiguity. The performance of the proposed method is tested experimentally on a mobile robot in two modes depending on the scene change. In the first mode, scene change is detected using dynamic LIDAR, whereas static LIDAR is used in the second mode. The proposed methodology is found to be more robust to environmental uncertainties with a reliable level of localization accuracy.

Wheel slip compensation is vital for building accurate and reliable dead reckoning based robot localization and mapping algorithms. This investigation presents stochastic slip compensation scheme for robot localization and mapping. Main idea of the slip compensation technique is to use wheel-slip data obtained from experiments to model the variations in slip velocity as Gaussian distributions. This leads to a family of models that are switched depending on the input command. To obtain the wheel-slip measurements, experiments are conducted on a wheeled mobile robot and the measurements thus obtained are used to build the Gaussian models. Then the localization and mapping algorithm is tested on an experimental terrain and a new metric called the map spread factor is used to evaluate the ability of the slip compensation technique. Our results clearly indicate that the proposed methodology improves the accuracy by 72.55% for rotation and 66.67% for translation motion as against an uncompensated mapping system. The proposed compensation technique eliminates the need for extro receptive sensors for slip compensation, complex feature extraction and association algorithms. As a result, we obtain a simple slip compensation scheme for localization and mapping.

Ultrashort pulse generation at the short-wave infrared (SWIR) wavelength ranges from 1.6 to 2.5 μ m and together with benefits of the all-fiber design has transformed lasers into an essential tool for industrial, technological, scientific, environmental, and medical applications. With the development of pumping sources and fiber components, ultrafast SWIR fiber lasers have drawn exceptional research and industrial attention over the last decade, resulting in the achievement of comparable performance or even surpassing well-established near-IR sources. Exceptionally compact, highly stable, cost-effective, and maintenance-free ultrafast fiber lasers operating at the SWIR range are currently well on the way to be commercially employed. This invited Perspective article gives a comprehensive overview of the most significant achievements enabling ultrafast generation at SWIR, including up-to-date gain fibers and saturable absorbers, nonlinear process, and laser architectures. This article highlights the perspectives and strategies for further maturing of the field of SWIR fiber lasers and pathways for the improvement of the performance, overcoming existing bottlenecks and challenges toward reducing pulse durations, tunability of repetition rate, and power upscaling. The advancement of the ultrafast SWIR laser development is projected until the landscape of existing technologies, driven by these ultimate sources, and potential applications, emerging on the horizon. [ABSTRACT FROM AUTHOR]

In this paper, gap modes assisted enhanced broadband light localization and possible absorption in a thin film silicon solar cell is presented. The existence of gap modes in metal particle-surface based thin film silicon solar cell is numerically investigated for improved light absorption. About 10.2% increment in light absorption compared to bare thin film silicon solar cell is obtained and enhanced light absorption at longer wavelength range is observed. The enhancement is due to the modification of localized surface plasmon modes around the nanoparticles via exciting the gap modes in the space between the nanoparticle and the surface. [ABSTRACT FROM AUTHOR]

We propose a parabolic W-type thulium-doped fiber for the 1.7 µm high-energy femtosecond pulsed laser. Despite its attractive normal dispersion, the fiber offers high gain in 1.7 µm region thanks to its distributed short-pass filtering effect. With a proper dispersion management in an all-fiber chirped pulse amplification (CPA) scheme, we demonstrate so far the highest pulse energy of 128.0 nJ in a stable pulse of 174 fs in the 1.7-1.8 µm region, which marks above an order of magnitude improvement in pulse energy while exhibiting the shortest pulse duration among fiber-based CPA works at 1.7 µm. Hence, we provide a pathway to an energy scalable and efficient femtosecond laser at 1.7 µm via a compact and elegant all-fiber solution.

We demonstrate a simple and power stable 1.5-10.5 µm cascaded mid-infrared 3 MHz supercontinuum fiber laser. To increase simplicity and decrease cost, the design of the fiber cascade is optimized so that no thulium amplifier is needed. Despite the simple design with no thulium amplifier, we demonstrate a high average output power of 86.6 mW. Stability measurements for seven days with 8-9 h operation daily revealed fluctuations in the average power with a standard deviation of only 0.43% and a power spectral density stability of ±0.18 d B m / n m for wavelengths <10µ m . The high-repetition-rate, robust, and cheap all-fiber design makes this source ideal for applications in spectroscopy and imaging.

We experimentally investigate the influence of varying pulse parameters on the spectral broadening, power spectral density, and relative intensity noise of mid-infrared (mid-IR) in-amplifier cascaded supercontinuum generation (SCG) by varying the pulse duration (35 ps, 1 ns, 3 ns) and repetition rate (100, 500, 1000 kHz). The system is characterized at the output of the erbium-ytterbium-doped in-amplifier SCG stage, the thulium/germanium power redistribution stage, and the passive ZBLAN fiber stage. In doing so, we demonstrate that the output of the later stages depends critically on the in-amplifier stage, and relate this to the onset of modulation instability.

We demonstrate a direct inscription of a fiber Bragg grating (FBG) in the active cores of an Yb-doped large mode area multicore fiber (MCF). An ultrashort pulsed laser is used to inscribe the FBG simultaneously in all six cores. In order to validate the FBG reflection and uniformity, the FBG is incorporated as a rear mirror in a fiber laser oscillator setup. The MCF, which has been fabricated in-house, has six cores located in a hexagonal-ring shape, each with a 19 µm diameter and an NA of ∼0.067. A reflection of ∼96 % was measured at a center Bragg wavelength of ∼1062 n m for the inscribed FBG. The laser performance of the MCF with the femtosecond inscribed FBG at its end shows a similar performance to lasing with a free-space commercial volume Bragg grating as the rear-reflector. A slope efficiency of ∼72.4 % and a maximum (pump limited) output power of 51.8 W have been obtained for the FBG setup. An effective M 2 of 3.88, indicating a somewhat multimode operation and a narrow bandwidth of ∼0.19 n m , has been measured for this fiber laser.

High concentration rare earth doped, large mode area (LMA) step-index fibers, which feature a very high cladding absorption per unit length at the pump wavelength, high efficiency, and excellent beam quality, are ideal for high power pulsed fiber lasers/amplifiers where large effective mode areas and short device lengths are crucial in order to reduce detrimental nonlinear effects associated with high peak power operation. In this Letter, we realize low numerical aperture (NA) high absorption fibers, simply by employing a germanium (Ge)-doped cladding rather than a pure silica cladding to offset the high refractive index associated with using a high concentration of ytterbium (Yb) in the core. This approach allows us to separate the two inter-linked fiber design parameters of pump absorption and NA in a step-index fiber. Using a conventional modified chemical vapor deposition process combined with solution doping, a low NA (0.04), LMA (475µ m 2 ) silica fiber is fabricated with a cladding absorption value of >20 d B / m , which is the highest value among LMA step-index fibers with N A <0.06 so far reported to the best of our knowledge. The fabricated Yb-doped fiber was tested in a high-power picosecond amplifier system and enabled the generation of 190 ps laser pulses with a 101 µJ pulse energy and 0.5 MW peak power at an average power of 150 W.

We report an all-fiber high pulse energy ultrafast laser and amplifier operating at the short wavelength side of the thulium (Tm) emission band. An in-house W-type normal dispersion Tm-doped fiber (NDTDF) exhibits a bending-induced distributed short-pass filtering effect that efficiently suppresses the otherwise dominant long wavelength emission. By changing the bending diameter of the fiber, we demonstrated a tunable mode-locked Tm-doped fiber laser with a very wide tunable range of 152 nm spanning from 1740 nm to 1892 nm. Pulses at a central wavelength of 1755 nm were able to be amplified in an all-fiber configuration using the W-type NDTDF, without the use of any artificial short-pass filter or pulse stretcher. The all-fiber amplifier delivers 2.76 ps pulses with an energy of ∼32.7 nJ without pulse break-up, due to the normal dispersion nature of the gain fiber, which marks so far, the highest energy amongst fiber lasers in the 1700 nm-1800 nm region.

A reconfigurable multiwavelength erbium-doped fiber laser based on an all-fiber multimode interferometer (MMI) is proposed and experimentally demonstrated. The interferometer is constructed by sandwiching a section of highly germanium-doped fiber (HGDF) between two sections of single-mode fiber. The insertion loss of the interferometer is as low as 2 dB. Due to the polarization-dependent spectral filtering effect formed by the MMI, by rotating the intracavity polarization controller, the laser output can be switched among single-, dual-, and triple-wavelength lasing states with optical signal-to-noise ratio up to 50 dB. In particular, the obtained dual-wavelength state shows high stability with wavelength shift within $ \pm {0.04}\;{\rm nm}$±0.04nm, wavelength spacing variation within $ \pm {0.03}\;{\rm nm}$±0.03nm, and power fluctuation within $ \pm {0.04}\;{\rm dB}$±0.04dB by monitoring the output spectra over 8 h at room temperature. By changing the length of the HGDF, the wavelength spacing can also be flexibly manipulated. Taking the advantages of reconfiguration, low cost, and easy fabrication, this fiber laser may have great potential in various optical applications.

We fabricate and characterize a germanium/thulium (Ge/Tm) co-doped silica fiber in order to enhance the gain at the short wavelength edge of the thulium emission band (i.e. 1620-1660 nm). The Ge/Tm doped fiber shows an intrinsic blue-shifted absorption/emission cross-section compared to aluminum/thulium (Al/Tm) co-doped fiber, which greatly improves the short wavelength amplification and has enabled us to further extend the shortest wavelength of emission towards 1600 nm. Using this glass fiber composition, we have demonstrated both a silica-based thulium doped fiber amplifier (TDFA) in the 1628-1655 nm waveband and a tunable thulium-doped fiber laser (TDFL) capable of accessing the telecom U-band wavelength region. These results represent by far the shortest amplifier/laser wavelengths reported to-date from TDFAs/TDFLs.

We report an all-solid large-mode-area (LMA) step-index fiber offering high absorption and low core numerical aperture (NA) by introducing a highly ytterbium-doped P:Al core and germanium-doped cladding. The fiber provides core absorption of ∼1200  dB/m at 976 nm with a low 0.07 core NA, due to the raised Ge cladding. Furthermore, matched profiles of P and Al across the core are successfully obtained with high concentration of Yb 2 O 3 around 0.4 mol%. The fiber characteristics are routinely achievable by conventional modified chemical vapor deposition with a solution doping technique. A highly efficient laser with >100  W output power, 86% slope efficiency with respect to launched pump power, and a mean M 2 of 1.34 has been demonstrated using the fabricated LMA step-index fiber. We also report 80% laser slope efficiency with 58 W output power (pump power limited) within only 0.5 m of the fiber when pumped by a wavelength-stabilized laser diode.

This publisher's note amends the spelling of the second author's name in Appl. Opt.57, 6388 (2018)APOPAI0003-693510.1364/AO.57.006388.

We report the first demonstration of Raman amplification in a fiber of a single Bessel-like higher order mode using a multimode pump source. We amplify the LP 08 -mode with a 559-µm 2 effective mode area at a signal wavelength of 1115 nm in a pure-silica-core step-index fiber. A maximum of 18 dB average power gain is achieved in a 9-m long gain fiber, with output pulse energy of 115 µJ. The Raman pump source comprises a pulsed 1060 nm ytterbium-doped fiber amplifier with V-value ~30, which is matched to the Raman gain fiber. The pump depletion as averaged over the signal pulses reaches 36.7%. The conversion of power from the multimode pump into the signal mode demonstrates the potential for efficient brightness enhancement with low amplification-induced signal mode purity degradation.