Mid-infrared Light Generation Research Articles

Electrical generation of surface phonon polaritons.

Efficient electrical generation of mid-infrared light is challenging because of the dearth of materials with natural dipole-active electronic transitions in this spectral region. One approach to solve this problem is through quantum-engineering of the electron dispersion to create artificial transitions, as in quantum cascade devices. In this work we propose an alternative method to generate mid-infrared light, utilizing the coupling between longitudinal and transverse degrees of freedom due to the nonlocal optical response of nanoscopic polar dielectric crystals. Polar crystals support sub-diffraction photonic modes in the mid-infrared. They also support longitudinal phonons, which couple efficiently with electrical currents through the Fröhlich interaction. As we have shown in previous theoretical and experimental works, these two degrees of freedom can hybridize forming longitudinal-transverse polaritons. Here we theoretically demonstrate that longitudinal-transverse polaritons can be efficiently generated by electrical currents, leading to resonant narrowband photonic emission. This approach can therefore be utilised to electrically generate far-field mid-infrared photons in the absence of dipole-active electronic transitions, potentially underpinning a novel generation of mid-infrared optoelectronic devices.

Widely tunable continuous-wave visible and mid-infrared light generation based on a dual-wavelength switchable and tunable random Raman fiber laser

Nonlinear frequency conversion of wavelength agile and high-power random fiber lasers can provide a promising way to generate continuous-wave (CW) visible and mid-infrared (MIR) light with unique properties such as the continuous modeless spectrum, low temporal/spatial coherence, and high temporal stability. Here, we report a dual-wavelength switchable and tunable random Raman fiber laser (RRFL) based on a phosphosilicate fiber that has two Raman gain peaks for the first time and demonstrate its superior capability to generate widely tunable CW visible and mid-infrared light via nonlinear frequency conversions. By using the combination of a tunable pump and two tunable gratings in Littrow configuration that can provide separated point feedback for the two Stokes wavelengths corresponding to silica- and phosphorus-related Raman peaks, the spectrum of an RRFL can be flexibly manipulated for the aim of nonlinear frequency conversions, including single-wavelength tunable emission at the 1.1 μm or 1.2 μm band for second-harmonic generation (SHG), dual-wavelength simultaneously tunable emission at the 1.1 μm and 1.2 μm bands for the sum-frequency generation (SFG), and dual-wavelength separation tunable emission for difference-frequency generation (DFG). As a result, with the combination of SHG and SFG in a periodically poled lithium niobate crystal array, we experimentally demonstrate the broadest tuning range (560–630 nm) of visible light generated from an RRFL, to the best of our knowledge. The tunable MIR light in the range of 10.7–12.3 μm is also demonstrated through DFG of an RRFL operating in separation tunable dual-wavelength emission mode in a BaGa4Se7 (BGSe) crystal, which is the first realization of >10 μm CW DFG in the BGSe crystal. We believe the developed dual-wavelength switchable and tunable RRFL can provide a new compact, robust, and cost-effective platform to realize broadly tunable light in both the visible and MIR regions, which can also find potential applications in imaging, sensing, and temporal ghost imaging in various spectral bands.

Parametrically Tunable Mid-Infrared Resonant Radiation by Four-Wave Mixing in Silicon Nitride Nanophotonic Waveguides

The direct generation of mid-infrared light is of significant interest for various applications including spectroscopy, detection system, optical sensing and biophotonics. Ultrashort-pulse nonlinear interaction can be viewed as four-wave mixing process, which can generate new spectral components under appropriate conditions. Here, we numerically demonstrate a fully, yet effective, spectral conversion scheme where the effective portion and components of femtosecond pulses can access the mid-infrared region directly by four-wave mixing process in silicon nitride integrated photonics waveguide. Wideband conversions occur mainly towards the mid-infrared region around the traditional red-shift phase-matching point without the adjustment of waveguide geometry. The corresponding conversion mechanisms can be attributed to nonlinear interaction of optical waves, resulting in the dispersive wave generation, the soliton-probe collision and the phase-sensitive scattering process. Our results provide an alternative route to realize wideband tunable mid-infrared frequency conversion in silicon nitride system on a chip.

Mode-locked short pulses from an 8\xa0\u03bcm wavelength semiconductor laser

Quantum cascade lasers (QCL) have revolutionized the generation of mid-infrared light. Yet, the ultrafast carrier transport in mid-infrared QCLs has so far constituted a seemingly insurmountable obstacle for the formation of ultrashort light pulses. Here, we demonstrate that careful quantum design of the gain medium and control over the intermode beat synchronization enable transform-limited picosecond pulses from QCL frequency combs. Both an interferometric radio-frequency technique and second-order autocorrelation shed light on the pulse dynamics and confirm that mode-locked operation is achieved from threshold to rollover current. Furthermore, we show that both anti-phase and in-phase synchronized states exist in QCLs. Being electrically pumped and compact, mode-locked QCLs pave the way towards monolithically integrated non-linear photonics in the molecular fingerprint region beyond 6 μm wavelength.

Mid-infrared heterodyne phase-sensitive dispersion spectroscopy using difference frequency generation

Difference frequency generation is a flexible method for the generation of mid-infrared light. It allows downshifting a near-infrared optical signal to the mid-infrared region by means of a nonlinear process, enabling to take full advantage of the availability of optical communications components for the generation of the multi-tone signals that are characteristic of molecular dispersion spectroscopic methods. In this way, it is possible to avoid several issues associated with optical instruments in which directly modulated mid-infrared quantum cascade lasers are employed. In this paper, we take full advantage of this benefit to implement the first heterodyne phase sensitive dispersion spectroscopy gas sensor based on a difference frequency generation source. The performance of the instrument is validated by detecting with high sensitivity methane in the 3.4 µm mid-infrared band.

Investigation of Germanium-Loaded Slot Waveguides for Mid-Infrared Third Harmonic Generation

In this paper, we propose a metal-semiconductor-metal slot waveguide (MSMSW) for producing mid-infrared (MIR) light from 10.2 μm by means of third harmonic generation (THG). In this waveguide, the required interaction length is limited by the large Ohmic loss, and therefore, perfect phase-matching condition (PMC) which ensures long coherent length is not necessary. Without the limitation of perfect PMC, the THG interaction mainly occurs between two fundamental modes at pump and harmonic wavelength, respectively leading to high nonlinear coefficient. According to our simulation, the conversion up to ~ 9.1 × 10−4 can be achieved within micron-scale waveguide under 1 W pump power. Furthermore, the waveguide demonstrates both large fabrication error and wavelength shift tolerance. The proposed waveguide can be a promising candidate for MIR light generation with large integration capability.

Giant spectral transformations in plasmon-enhanced difference-frequency generation with polychromatic light

We theoretically study the generation of mid-infrared light through difference-frequency excitation using a single dual-wavelength coherent femtosecond laser source. The difference-frequency wave is generated from the surface of a thin gold film in the Kretschmann coupling geometry due to the surface nonlinearity of the film. We show a clear enhancement of the difference-frequency wave around the surface plasmon polariton coupling angle of the incident fundamental wave. We also show an enormous shift and modification of the difference-frequency spectrum near surface plasmon resonance. We discuss the discovered spectral change dependence on the source pulse duration and incidence angle of the fundamental wave. Our findings have an enormous potential for use in difference-frequency surface sensing and spectroscopy applications.

Energy transfer and energy level decay processes of Er3+ in water-free tellurite glass

This report details the fundamental spectroscopic properties of a new class of water-free tellurite glasses studied for future applications in mid-infrared light generation. The fundamental excited state decay processes relating to the 4I11/2→4I13/2 transition in singly Er3+-doped Tellurium Zinc Lanthanum glass have been investigated using time-resolved fluorescence spectroscopy. The excited state dynamics was analyzed for Er2O3 concentrations between 0.5mol% and 4mol%. Selective laser excitation of the 4I11/2 energy level at 972nm and selective laser excitation of the 4I13/2 energy level at 1485nm has established that in a similar way to other Er3+-doped glasses, a strong energy-transfer upconversion by way of a dipole–dipole interaction between two excited erbium ions in the 4I13/2 level populates the 4I11/2 upper laser level of the 3μm transition. The 4I13/2 and 4I11/2 energy levels emitted luminescence with peaks located at 1532nm and 2734nm respectively with luminescence efficiencies of 100% and 8% for the higher (4mol.%) concentration sample. Results from numerical simulations showed that a population inversion is reached at a threshold pumping intensity of ∼57kWcm−2 for a CW laser pump at 976nm for [Er2O3]=2mol.%.

Design of erbium doped double clad ZBLAN Fibre laser

A high powered octagonal double clad ZBLAN (33 μm/330 μm, NA=0.13) glass fibre for mid-infrared light generation is studied using a one dimensional rate equation model. The fibre laser design employs the concept of cascade lasing and includes up-conversion phenomena. The results obtained demonstrate that efficient cascade lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser action is provided by Fresnel light reflection at ZBLAN glass fibre air interfaces. Further enhancement of the laser efficiency can be achieved by terminating one of the fibre ends with a mirror. Simulation results show that the laser operation with 20 W of pump power at 0.98 μm wavelength can be achieved at 2.75 μm operating wavelength with Er3+ ion concentrations of 60,000 ppm.

Generation of 36 μm radiation and telecom-band amplification by four-wave mixing in a silicon waveguide with normal group velocity dispersion

Mid-infrared light generation through four-wave mixing-based frequency down-conversion in a normal group velocity dispersion silicon waveguide is demonstrated. A telecom-wavelength signal is down-converted across more than 1.2 octaves using a pump at 2190nm in a 1cm-long waveguide. At the same time, a 13dB on-chip parametric gain of the telecom signal is obtained.

Control of signal coherence in parametric frequency mixing with incoherent pumps: narrowband mid-infrared light generation by downconversion of broadband amplified spontaneous emission source at 1550 nm

We study, with numerical simulations using the generalized nonlinear envelope equation, the processes of optical parametric and difference- and sum-frequency generation (SFG) with incoherent pumps in optical media with both quadratic and third-order nonlinearity, such as periodically poled lithium niobate. With ultrabroadband amplified spontaneous emission pumps or continua (spectral widths > 10 THz), group-velocity matching of a near-IR pump and a short-wavelength mid-IR (MIR) idler in optical parametric generation may lead to more than 15-fold relative spectral narrowing of the generated MIR signal. Moreover, the SFG process may also lead to 6-fold signal coherence improvements. When using relatively narrowband filtered noise pumps (e.g., spectral widths < 1 THz), the signal from optical parametric, sum-frequency, and difference- frequency generation has nearly the same spectral width as that of the incoherent pump.

Mid-infrared light generation by high order SRS effect in silicon ring cavity

We have numerically investigated the generation of a fourth order stimulated Raman scattering (SRS) signal in a silicon ring cavity. Output power saturation of the silicon Raman laser has been observed. The influences of effective free carrier life, length of ring cavity and coupling ratio on the signal generation are discussed based on our simulation work. Finally, we put forward a double ring cavity scheme to improve the output characteristics of the silicon Raman laser.

Modelling of a simple Dy3+ doped chalcogenide glass fibre laser for mid-infrared light generation

A simple Dy3+-doped chalcogenide glass fibre laser design for mid-infrared light generation is studied using a one dimensional rate equation model. The fibre laser design employs the concept of cascade lasing. The results obtained demonstrate that efficient cascade lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser action is provided by Fresnel light reflection at chalcogenide glass fibre–air interfaces. Further enhancement of the laser efficiency can be achieved by terminating one of the fibre ends with a mirror. A numerical analysis of the effect of the Dy3+ doping concentration and fibre loss on the laser operation shows that with 5 W of pump power, at 1.71 μm wavelength, output powers above 100 mW at ∼ 4.5 μm wavelength can be achieved with Dy3+ ion concentrations as low as 3 × 1019 cm−3, when fibre loss is of the order 1dB/m.

Tunable-narrow-linewidth continuous-wave mid-infrared light generation by difference-frequency mixing

The generation of tunable narrow-band mid-infrared light by difference-frequency mixing of two kinds of continuous-wave ring-laser radiation in potassium titanyl phosphate is described. The system produces infrared powers of ∼20 µW of difference-frequency light continuously tunable from 1.05 to 2.8 µm (3500–9500 cm-1). Continuous scans over a range of 100 cm-1 with a spectral precision better than 10 MHz (0.0003 cm-1) are achieved. The high-resolution characteristics of the laser system are evaluated by use of a portion of Q2(0) overtone vibration–rotation spectrum of a solid parahydrogen crystal.