In this paper, a fiber amplifier based on ZBLAN fiber doped with dysprosium is designed and optimized considering an in-band pumping scheme. The model is validated by comparing the simulated amplified spontaneous emission with the experimental curves reported in the literature. It allows to investigate the amplification of the signal of a continuous-wave fiber laser emitting in the wavelength range from 2.9 μm to 3.25 μm. The numerical analysis is carried out via home-made code that accurately takes into account the rate equations and the power propagation equations for the signal, pump, and amplified spontaneous emission. The finite element method (FEM) is used to calculate the modal overlap in the designed pump fiber combiner with the Dy3+-doped core. By employing an input pump power Pp = 5 W at the wavelength λ = 2.82 μm, a signal power Ps = 2 mW at the wavelength λ = 2.95 μm, a fiber length L = 3 m an amplifier output power of 0.5 W and an optical gain of about 24 dB are achieved. The obtained results are attractive for feasible innovative applications, e.g. the development of all-in-fiber systems. For instance, the pump and signal beams can be obtained via an Er:ZBLAN fiber laser and coupled with the dysprosium fiber through a single-mode fluoride coupler.
KEYWORDS: Free space optics, Visibility through fog, Visibility, Mid infrared, Data modeling, Signal attenuation, Attenuation, Atmospheric propagation, Wave propagation, Near infrared
A Free-Space Optics (FSO) propagation experiment is running in Milan, Italy, since September 2022, in the framework of the Joint Lab between Huawei and Politecnico di Milano in collaboration with Consiglio Nazionale delle Ricerche (CNR). The set-up includes two co-located FSO links: a prototype mid-IR link (10.6 μm) and a commercial near-IR link (1.550 μm) over an 800-m path. Meteorological data are collected by two visibility sensors, two disdrometers, and a weather station. Data from a case study of moderate fog that occurred in winter 2022 highlights that the spatial distribution of fog is highly non-homogeneous along the path, hence, simple prediction models based on single-point measurements of the visibility may incur in large errors. Moreover, the comparison of path attenuation time series shows that the mid-IR link performs better than near-IR.
A Dy3+-doped ZBLAN fiber amplifier based on an in-band pumped configuration is designed and optimized via an evolutionary approach. In the proposed model, the rate equations are coupled with the power propagation equations for the pump and signal beams. The complete amplifier model allows the definition of the fitness function to be optimized. Realistic values for optical and spectroscopic parameters are considered. For a fiber with dopant concentration of 2000 ppm, by employing an input pump power of 1 W at 2.72 μm wavelength, an optical gain of about 15.56 dB at 2.95 μm wavelength is obtained.
Measurement of carbon dioxide isotopic ratio on a gas sample through Tunable Diode Laser Absorption Spectroscopy over the 2000nm band is a task that poses different kinds of challenges depending on the required resolution or stability. With the particular application of an instrument for the analysis of human breath samples for the diagnosis of Helicobacter Pylori in mind, the performances of such a system have been investigated.
This measurement has to performed before and after ingestion of a test meal and an accuracy within a few parts per mille needs to be reached for a new instrument to be considered as an alternative to the other, more complex and expensive techniques currently used as a diagnostic test.
The considered instrument is based on a 29m Herriott type multi pass cell, direct absorption setup with a VCSEL source and piezoelectric fringe dithering. Effects of temperature and pressure of the sample on line cross sections and broadening are discussed.
The use of a beam splitter and a second photodetector for a live background signal acquisition and spectra normalization was considered and tested against a simpler approach based on only one channel and using more complex fitting techniques to extract the background waveform from the absorption signal itself. For each case, an evaluation of the obtainable performance with different measurement and/or fitting algorithms is presented.
The work has been done with the ultimate goal of measuring small (0.1 liters) samples collected from exhaled breath (usually saturated in water vapor and containing 4 to 10 vol. % carbon dioxide) without any preprocessing other than lowering the measurement cell pressure; for this reason particular attention to isotope ratio measurement stability against variable sample concentration has been put. At the desired accuracy levels, even the differences in collisional broadening coefficients due to gas mixture composition are non negligible; temperature effects can be neglected only by considering proper line pairs for the ratio evaluation.
The current setup shows a resolution of about 0.2% on the δ13CO2 isotopic ratio measurement around the ambient level with a day-to-day reproducibility better than 1.5% on the single channel approach.
The combination of frequency combs and quantum cascade lasers is opening new opportunities in the field of precision spectroscopy in the mid-infrared. Frequency combs allow quantum cascade lasers to be referenced to a highly repeatable, precise and absolute frequency axis. Repeatability is a key feature to obtain high quality measurements of absorption profiles and thus accurate determination of spectroscopic parameters, while absolute frequency calibration makes it possible the comparison of spectroscopic data acquired in different laboratories and at different times, as well as comparison with theoretical predictions or existing databases. This work reviews some of the main results achieved at 4.3 μm by investigation of a manifold of rovibrational lines of CO2. Spectroscopic parameters such as line-centre frequencies, line intensity factors, pressure shift and pressure broadening coefficients are retrieved with an unprecedented quality from the metrological point of view.
Recently, great effort has been devoted to waveguide lasers, because of their inherent simplicity with respect to
fiber lasers. Actually, due to their compactness, such lasers are expected to achieve a higher temporal coherence,
making them attracting for fiber optical reflectometry, distribute sensing, and range finding applications. Furthermore,
the availablity of fast saturable absorbers based on carbon nanotubes allows for a cheap and reliable
implementation of the passive mode-locking technique with the potential for generating high repetition rate pulse
trains. Such lasers will provide low-noise and inexpensive pulsed sources for applications in optical communications,
optically sampled analog-to-digital converters, and spectral line-by-line pulse shaping. We report here on
advanced waveguide lasers, operating both in continuous wave and pulsed regimes, based on active waveguides
fabricated by femtosecond laser writing in a phosphate glass substrate. A single longitudinal mode waveguide
laser providing more than 50 mW with 21% slope efficiency was demonstrated. Furthermore, by combining a high
gain waveguide and an innovated fiber-pigtailed saturable absorber based on carbon nanotubes, a mode-locked
ring laser providing transform limited 1.6-ps pulses was also demonstrated.
A theoretical and experimental analysis of group velocity reduction in periodic super-structured Bragg gratings
is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the 1.5 μm wavelength of optical communications is reported using either a 20-cm-long Moire and a periodically-spaced πphase shift fiber gratings. Time delays up to approximately 690 ps for 250-ps-duration optical pulses have been achieved leading to the realization of an optical buffer.
A review on the results achieved by our group in the development of novel solid-state lasers for Lidar applications at 2 μm is presented. These lasers, based on fluoride crystals (YLF4, BaY2F8, and KYF4) doped with Tm and Ho ions, are characterized by high-efficiency and wide wavelength tunability around 2 μm. Single crystals of LiYF4, BaY2F8, and KYF4 codoped with the same Tm3+ and Ho3+ concentrations were successfully grown by the Czochralski method. The full spectroscopic characterization of the different laser crystals and the comparison between the laser performance are presented. Continuous wave operation was efficiently demonstrated by means of a CW diode-pumping. These oscillators find interesting applications in the field of remote sensing (Lidar and Dial systems) as well as in high-resolution molecular spectroscopy, frequency metrology, and biomedical applications.
Preliminary results on absolute frequency stabilization of Distributed Bragg Reflector (DBR) diode-lasers with emission wavelength at 852 nm will be reported. Saturated absorption D2 lines of cesium atom have been adopted as a frequency reference and the nonlinear spectroscopy method of Modulation Transfer has been used to lock the laser frequency against the resonance. From the preliminary results on the beat signal between two independent laser systems a relative frequency stability of 10-11 has been reached at an integration time of 0.1 s. The analysis on the obtained signal to noise ratio shows a frequency noise floor in the order of approximately 10-12 which should be achieved in an integration time of 1 s.
A novel Er-Yb:glass quasi-monolithic diode-pumped laser has been developed to realize a high-accuracy frequency standard at 1.54 micrometer based on saturated absorption of isotopic acetylene. This compact oscillator shows low amplitude- and frequency-noise, wide wavelength tunability (approximately 20 nm), and continuous output power in excess of 20 mW with excellent linear polarization (approximately 30 dB extinction ratio). Employing this laser source sub-Doppler spectroscopy of the acetylene around 1.54 micrometer has been performed. To obtain the necessary saturation intensity (approximately 3.5 W/mm2), the absorbing sample is placed inside a Fabry- Perot cavity with a Finesse of approximately 150. The dispersion signal of the sub-Doppler resonance, useful to stabilize the laser frequency, has been obtained by dithering the Fabry-Perot piezo and employing a lock-in detection scheme.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.