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100?GHz free spectral range-tunable multi-wavelength fiber laser using single–multi–single mode fiber interferometer
摘要： Six single–multi–single (SMS) mode fiber-based Mach–Zehnder Interferometers (MZI) with different spooling radii are demonstrated as spatial mode filtering elements for multi-wavelength laser generation. Free spectral range (FSR) tuning of the multi-wavelength output generated is realized by alternating between the six MZIs, which have different macro-bending losses. Additional FSR tuning is also realized by changing the spooling radius of the two-mode step index fiber section within the MZI setups from 80 mm to 30 mm, giving an FSR tuning range of 0.89–0.99 nm. All generated multi-wavelength outputs show high stability over a test period of 100 min. The proposed multi-wavelength lasers are highly suitable for various microwave photonics applications the field of such as microwave signal source generation and microwave photonic filtering.
关键词： free spectral range tuning,Mach–Zehnder Interferometer,microwave photonics,multi-wavelength fiber laser
更新于2025-11-28 14:23:57
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Direct laser writing of birefringent photonic crystals for the infrared spectral range
摘要： Infrared optical photonic crystals fabricated using direct laser writing, which is based on the two-photon polymerization of suitable monomers, have received substantial interest since the emergence of this process. Two-photon polymerization could be a disruptive technology for the fabrication of all-dielectric photonic crystals in the infrared spectral range, as it allows the synthesis of large scale arrays of uniform structures with arbitrary geometries and arrangements. However, all-dielectric photonic crystals that provide birefringent optical responses in the infrared spectral range have not yet been demonstrated using direct laser writing techniques. Here, the authors explore the form birefringence observed in photonic crystals composed of arrays of subwavelength-sized slanted polymer microwires. The photonic crystals investigated here were fabricated in a single fabrication step using direct laser writing of an infrared transparent photoresist (IP-Dip). A strong contrast of the cross-polarized re?ectance of photonic crystals as a function of the in-plane orientation is observed in the mid-infrared spectral range at λ ≈ 6:5 μm. This observation is indicative of an anisotropic optical behavior. Finite element based techniques corroborate the experimentally observed responses qualitatively.
关键词： two-photon polymerization,direct laser writing,infrared spectral range,birefringent photonic crystals,all-dielectric photonic crystals
更新于2025-11-14 15:18:02
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Adaption of an array spectroradiometer for total ozone column retrieval using direct solar irradiance measurements in the UV spectral range
摘要： A compact array spectroradiometer that enables precise and robust measurements of solar UV spectral direct irradiance is presented. We show that this instrument can retrieve total ozone column (TOC) accurately. The internal stray light, which is often the limiting factor for measurements in the UV spectral range and increases the uncertainty for TOC analysis, is physically reduced so that no other stray-light reduction methods, such as mathematical corrections, are necessary. The instrument has been extensively characterised at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. During an international total ozone measurement intercomparison at the Iza?a Atmospheric Observatory in Tenerife, the high-quality applicability of the instrument was verified with measurements of the direct solar irradiance and subsequent TOC evaluations based on the spectral data measured between 12 and 30 September 2016. The results showed deviations of the TOC of less than 1.5 % from most other instruments in most situations and not exceeding 3 % from established TOC measurement systems such as Dobson or Brewer.
关键词： stray-light reduction,direct solar irradiance measurements,array spectroradiometer,total ozone column,UV spectral range
更新于2025-09-23 15:21:21
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LED Structures Based on ZnO Films Obtained by RF Magnetron Sputtering for the UV Spectral Range
摘要： Data for the influence of different defects on the photoluminescence and electroluminescence spectra (emission intensity and wavelength) of n-ZnO/p-GaN structures are reported.
关键词： ZnO films,photoluminescence,RF magnetron sputtering,UV spectral range,electroluminescence
更新于2025-09-23 15:21:01
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Tunability of the Freea??Spectral Range by Microwave Injection into a Mida??Infrared Quantum Cascade Laser
摘要： The free-spectral range (FSR) of quantum cascade lasers (QCLs) emitting at 4.7 μm can be tuned through direct microwave modulation. The intrinsic short carrier lifetime of inter-subband transitions, along with impedance matched electrical packaging, allows a high-speed modulation up to more than 30 GHz. A signi?cant broadening and ?attening of the lasing spectrum is observed under radio frequency (RF) injection with frequencies close to the round-trip cavity. An accurate analysis of the high resolution spectra of the laser shows a comb-like regime for both free-running and RF modulated QCLs, if the modulation frequency is within the locking-range of the device. One of the main advantages of collecting high-resolution mid-infrared spectra, over the plain investigation of the beatnote in the microwave region, is the access to all the longitudinal modes and thus the accurate measure of the FSR over the whole optical spectrum. The use of high-resolution spectroscopy provides an in-depth and comprehensive analysis of lasing spectra under microwave modulations.
关键词： quantum devices,mid-infrared region,injection locking,tunability of the free-spectral-range,ultrafast devices
更新于2025-09-23 15:19:57
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Surface Polariton‐Like s‐Polarized Waveguide Modes in Switchable Dielectric Thin Films on Polar Crystals
摘要： Surface phonon polaritons (SPhPs) and surface plasmon polaritons (SPPs), evanescent modes supported by media with negative permittivity, are a fundamental building block of nanophotonics. These modes are unmatched in terms of field enhancement and spatial confinement, and dynamical all-optical control can be achieved, e.g., by employing phase-change materials. However, the excitation of surface polaritons in planar structures is intrinsically limited to p-polarization. On the contrary, waveguide modes in high-permittivity films can couple to both p- and s-polarized light, and in thin films, their confinement can become comparable to surface polaritons. Here, it is demonstrated that the s-polarized waveguide mode in a thin Ge3Sb2Te6 (GST) film features a similar dispersion, confinement, and electric field enhancement as the SPhP mode of the silicon carbide (SiC) substrate, while even expanding the allowed frequency range. Moreover, it is experimentally shown that switching the GST film grants nonvolatile control over the SPhP and the waveguide mode dispersions. An analytical model is provided for the description of the GST/SiC waveguide mode and it is shown that the concept is applicable to the broad variety of polar crystals throughout the infrared spectral range. As such, complementarily to the polarization-limited surface polaritons, the s-polarized waveguide mode constitutes a promising additional building block for nanophotonic applications.
关键词： waveguide modes,infrared spectral range,phase-change materials,surface plasmon polaritons,silicon carbide,nanophotonics,Ge3Sb2Te6,surface phonon polaritons,s-polarized light
更新于2025-09-19 17:13:59
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Chalcogenide || Lead salt photodetectors and their optoelectronic characterization
摘要： Lead salt photoconductors produced by chemical bath deposition are popular IR photodetectors due to their outstanding performance-to-cost ratio, high room temperature performance (D(cid:3) . 1E10) and availability of large area detectors. History of lead salt detectors has been reviewed recognizing some more recent research developments. The chemical bath deposition technique for production of the lead salt detectors has been outlined, followed by a review of the basics for their characterization. Spectral responses of both PbS and PbSe detectors collected in a wide temperature range and properly corrected have been presented.
关键词： PbSe,chemical bath deposition,photoconductors,Lead salt photodetectors,PbS,infrared spectral range
更新于2025-09-16 10:30:52
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Quartz Optical Fibers with Increased Content of Fluorine for Fluorimeter Probes
摘要： A method to fabricate quartz optical fibers for probes employed in fluorescence diagnostics of tumors is proposed. It is shown that the sensitivity of fluorimeters in the near-IR spectral range can be increased using quartz–quartz optical fiber probes with the core made of the Heraeus glass and the SiO2–F cladding with an increased content of fluorine in the glass of up 7 wt %. The numerical aperture of such optical fibers amounts to 0.32. The optical fibers are used to develop a prototype of a multifiber high-aperture probe for a laser oncofluorimeter with a relatively high sensitivity in a spectral interval of 900–1100 nm.
关键词： fluorimeter probes,fluorescence diagnostics,quartz optical fibers,fluorine,near-IR spectral range
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Long Length Fibre Fabry-Perot Interferometers and their Applications in Fibre Characterization and Temperature Sensing
摘要： Since the free spectral range (FSR) of a fibre Fabry-Perot (f-FP) is the reciprocal of the time delay inside the interferometer, it can be used for the precise measurement of fibre properties (chromatic dispersion when measured as a function of wavelength, birefringence, etc.) or for the measurement of environmental changes (such as temperature, pressure, stress, etc.) which alter the fibre’s parameters. Here we propose a method to precisely measure the FSR of long-length f-FP based on an incoherent optical source and RF beat signal analysis. We built a 7-m long f-FP made of a single mode fibre (SMF) and investigated the use of several algorithms to evaluate the FSR. When measuring over time, we achieved an excellent accuracy down to 2.4 Hz (corresponding to a relative error of 1.5× 10??). To demonstrate its use in sensing application, we varied the f-FP temperature and monitored the associated FSR. We achieved a sensitivity of 345 Hz/K, leading to an excellent temperature resolution below 10 mK. Additionally, the achieved high accuracy in the measured FSR can also be used to measure fibre’s properties very precisely (e.g., zero chromatic dispersion wavelength) or to determine their temperature dependence. The method requires no alignment and requires only a few off-the-shelf components and instruments.
关键词： fibre characterization,temperature sensing,RF beat signal analysis,free spectral range,fibre Fabry-Perot interferometers
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - GaSb-Based Swept-Wavelength Lasers for Spectroscopic Sensing Applications in the 1.7–2.5 Micron Spectral Range
摘要： 1.7-2.5 micron spectral region is particularly interesting for spectroscopic sensing due to the presence of strong and molecule-specific ro-vibrational absorption bands. These absorption bands correspond to the first overtone of the C-H stretching vibrations and the combination of stretching and bending vibrations of C-H, N-H and O-H bonds, acting as a unique molecular fingerprint for sensing applications and can be read by means of direct photon-phonon (target molecule vibration) interaction [1]. This provides an opportunity for laser based spectroscopic sensing for both gases and liquids. In the field of biomedical application, laser-based sensing of critical biomolecules such as glucose, lactate, urea, serum albumin as they provide key insights into the person’s metabolism as well as allow tracking patient’s condition in case of difficult chronic diseases such as diabetes, chronic renal failure or act as an important marker in case sepsis. In this work, we provide our recent results in developing fast, miniature and potentially low-cost swept-wavelength laser technology based on GaSb type-I gain-chips embedded in external cavity. We demonstrate excellent performance in the entire 1.7-2.5 micron spectral band both in terms of output power, bandwidth and speed [2]. From the application provide experimental data for realizing swept-laser based spectroscopic sensor for sensing the main critical biomolecules both in-vitro and in-vivo in the entire physiologically relevant concentration level range. Moreover we present a pathway to transfer this technology for volume manufacturing, opening opportunity to the consumer and personalized healthcare markets.
关键词： GaSb-based,1.7-2.5 micron Spectral Range,Swept-Wavelength Lasers,Spectroscopic Sensing
更新于2025-09-12 10:27:22