mid-IR Wavelength Region Research Articles

Brillouin laser pumped tunable low-threshold mid-IR Kerr comb at 2 μm

Optical frequency combs in the 2 μm wavelength region are important for applications ranging from sensing of gases such as CO2 and CO to optical communications, LIDAR, and gravitational wave detection. The development of low-loss waveguides and high-Q microresonators with anomalous dispersion and the availability of tunable narrow linewidth lasers around 1.55 μm have enabled the realization of small footprint soliton combs and low-threshold Kerr combs in this wavelength region; demonstrations of microresonator frequency combs in the 2 μm wavelength region have been limited. Here, we harness an intracavity pumping scheme to demonstrate a low-threshold (<100 mW) microresonator Kerr comb at 2 μm. We exploit Brillouin lasing in a silica microsphere (∼310 μm diameter) to create an intracavity pump, which then generates a ∼140 nm wide Kerr comb in the backscattered Stokes direction. We demonstrate the tolerance of the comb generation scheme to microsphere dimensions and the input pump wavelength by achieving Kerr comb generation in microspheres of diameters ranging from 295 to 318 μm and also at different input pump wavelengths for a particular microsphere diameter. Intracavity pumping opens up opportunities for the development of soliton combs and Kerr combs in the mid-IR wavelength region for applications such as dual-comb spectroscopy, LIDAR, and optical communications.

Optical mid-infrared modulator based on D-shaped photonic crystal fiber and GST phase changing material

Photonic crystal fibers (PCFs) have recently attracted compelling attention because of their numerous applications, particularly in the mid-infrared (mid-IR) wavelength region. In this paper, we have presented and analyzed mid-IR optical modulator based on phase-changing material (PCM) known as germanium-antimony-tellurium (GST) and D-shaped PCF. The modulation process can be performed as the GST material’s phase undergoes a transition between amorphous (on) and crystalline (off) states. To analyze the proposed design numerically, full vectorial finite element method (FVFEM) is employed. Further, we studied the light propagation through the suggested structure using 3D finite difference time domain (FDTD) method. The optical losses of the fundamental transverse electric (TE) mode supported by the reported structure in the two GST states are studied. The obtained extinction ratio (ER) of the proposed modulator approaches 302.61 dB, whereas the insertion loss (IL) is less than 0.00014 dB throughout the wavelength range from 3 to 5.8 μm at a device length (LD) of 0.2 mm. Therefore, the suggested modulator can be utilized in photonic integrated circuits that require high ER, very low IL, and large optical bandwidth.

Design of hexagonal chalcogenide photonic crystal fiber with ultra-flattened dispersion in mid-infrared wavelength spectrum

In the last few decades, silica-based photonic crystal fibers (PCFs) have been the subject of extensive research. Traditional silica-based PCFs, however, experience considerable propagation loss when used beyond 3000 nm. On the other hand, soft glasses, notably tellurite, fluoride, and chalcogenide glasses, offer exceptional optical transparency in the mid-IR wavelength region and are a desirable replacement for silica in MIR applications. A comprehensive investigation of chromatic dispersion properties in the hexagonal chalcogenide photonic crystal fibers is presented. The dependency of fiber dispersion on the structural parameters of photonic crystal fibers is thoroughly described in this study. Utilizing the interaction between material and geometrical dispersion, we were able to develop a well-defined framework for making specific predefined dispersion curves. In the mid-infrared wavelength spectrum, we are concerned with flattened, if not ultra-flattened, dispersion behaviors. In the wavelength range of 3500–6500 nm, the hexagonal chalcogenide microstructured fiber was engineered to achieve a typical dispersion profile flattened to within −3.41 to 9.5 ps/[nm–km] for the six-ring structure and −3.91 to 8.17 ps/[nm–km] for the four-ring structure. This proposed chalcogenide PCF can be used for soliton generation, gas sensing, biomedical imaging, supercontinuum generation, and long-distance high-speed communication applications in the mid-infrared wavelength range due to its nearly zero ultra-flattened dispersion characteristics.

Multifunctional chalcogenide (As[formula omitted]S[formula omitted], As[formula omitted]Se[formula omitted]) dual-core photonic crystal fiber with elliptical air-hole for mid-IR optical communications: Design and analysis

This work presents an integrated design of a multifunctional hexagonal lattice dual-core photonic crystal fiber (DC-PCF) with elliptical air-hole surrounding the cores, using two different chalcogenides (As2S3-Arsenic sulfide and As2Se3-Arsenic selenide) for mid-infrared (mid-IR) optical communications. Numerical study of both chalcogenide DC-PCF structures exhibits that the DC-PCFs are highly birefringent and single-moded in the mid-IR wavelength region (5 μm to 13 μm) of optical communications. Results show that both DC-PCFs can be operated as polarization splitters at 9 μm wavelength for two orthogonal modes and they can also be used as WDM MUX-DeMUX for both X- and Y-polarization fundamental supermodes separating 9 μm/10 μm wavelengths (As2S3 DC-PCF) and 8 μm/9 μm wavelengths (As2Se3 DC-PCF). Moreover, the proposed chalcogenide DC-PCFs, with much lower splice loss at 8–10 μm wavelength region, are appropriate enough for the practical applications in integrated optics and photonics.

3.46 μm Q-switched Er3+:ZBLAN fiber laser based on a semiconductor saturable absorber mirror

By adopting a InAs based semiconductor saturable absorber mirror (SESAM), we have demonstrated a 3.46 μm passively Q-switched Er3+:ZBLAN fiber laser. An amplified spontaneous emission (ASE) seeded 1973 nm pump source is introduced to enhance the temporal stability. Stable 3.46 μm Q-switched pulse trains are obtained with a maximum repetition rate of 58.71 kHz and corresponding pulse width of 2.47 μs. The maximum average output power and single pulse energy are 63 mW and 1.4 μJ, respectively. The pulse characteristics with respect to the two pump powers are also evaluated. The results prove that the commercial SESAMs in stock have the capacity to extend the operation wavelength to the mid-infrared (mid-IR) wavelength region beyond 3.0 μm.

MoS2 Q-switched 2.8 µm Er:ZBLAN fiber laser

Since the invention of graphene, two-dimensional (2D) materials have attracted great interest in both fundamental science and potential applications. Here, we report the saturable absorption features of 2D (multilayered structure) molybdenum disulfide (MoS2) in the mid-infrared (mid-IR) wavelength region, and use it to passively Q-switch an Er3+-doped ZBLAN fiber laser at 2.8 µm. This MoS2 saturable absorber has a moderate modulation depth of 5% at 2.8 µm, making it an appropriate candidate for light modulating in the mid-IR spectral range. In stable Q-switching, the Er3+-doped ZBLAN fiber laser is widely tuned in both repetition rate and pulse width. Through increasing pump power, the repetition rate and pulse duration are monotonically tuned from 36 to 70 kHz and from 1.84 µs to 806 ns, respectively. The maximum average power is 140 mW (at 70 kHz), giving a pulse energy of 2 µJ and peak power of ~2.48 W. Successful Q-switching operation of this 2.8 µm fiber laser confirms that 2D MoS2 has great potentials as efficient light modulating elements in mid-IR regions.

Theoretical study of leaky-mode resonant gratings for improving the absorption efficiency of the uncooled mid-infrared photodetectors

In this work, we studied a new theoretical approach to enhance the PbSe-based uncooled photodetector's performance in the mid-infrared (mid-IR) wavelength region. A one-dimensional grating layer was proposed to be implemented and inserted under the PbSe photosensitive layer. Due to the leaky-mode resonance tuning mechanism, this grating layer could manipulate mid-IR light-and-matter interactions in a unique way. It not only prevents the light transmission loss from the backside of the device but also tunes the destructive interference in the reflectance spectra, which consequently maximize the light absorption in the weak-absorbing energy band-tail region. By combining these two capabilities, it is possible to improve detector's sensitivity significantly. With this goal, several grating parameters including grating period, fill factor, and grating thickness were systematically investigated and optimized by using the rigorous coupled wave analysis method. Through the optimization, a 33% broadband absorption enhancement was achieved by using a Si (n = 3.489)/SiO2 grating on a soda-lime glass (n = 1.45) substrate with the listed parameters: grating period = 2.4 μm, fill factor = 0.49, and thickness = 1.22 μm. Apparently, this simple and effective method could practically advance the uncooled mid-IR PbSe detector's performance. But more importantly, this photonic-design concept can be used in and impact many other light-matter interaction related research fields.

Tuning direct bandgap GeSn/Ge quantum dots' interband and intraband useful emission wavelength: Towards CMOS compatible infrared optical devices

In this work, interband and intraband optical transitions from direct bandgap strained GeSn/Ge quantum dots are numerically tuned by evaluating the confined energies for heavy holes and electrons in Г-and L-valley. The practically exploitable emission wavelength ranges for efficient use in light emission and sensing should fulfill specific criteria imposing the electrons confined states in Г-valley to be sufficiently below those in L-valley. This study shows that GeSn quantum dots offer promising opportunity towards high efficient group IV based infrared optical devices operating in the mid-IR and far-IR wavelength regions.

Silicon-on-nitride slot waveguide: A promising platform as mid-IR trace gas sensor

We propose design of a chip-scale evanescent field absorption-based trace gas sensor, exploiting silicon-on-nitride (SON) slot waveguide structure at mid-IR wavelength region. As an example, we numerically demonstrate detectability of NH3 gas in the atmosphere at its characteristic absorption wavelength of 3μm. Using the optimum sensor design, detection down to 5ppm including loss is viable in just ∼8.7mm length of the proposed slot waveguide. The achievable evanescent field fraction (η) is upto ∼43%. Our tolerance studies show that η is relatively more critical to the slot width as compared to its height.

中红外Fe:ZnSe激光技术最新研究进展

Mid-IR laser in 3-5 m wavelength region is in the range of atmospheric transmission window, it is in great demand for a variety of applications including molecular spectroscopy, remote sensing for environmental monitoring, industrial process, free space communication, optoelectronic countermeasures. One of the most promising approaches to reach mid-IR spectral range is based on direct lasing of Transition Metal (TM) doped II-VI chalcogenide crystals. Fe2+ ions doped ZnSe laser crystals offer a special blend of physical and spectroscopic parameters that make them the gain media of choice for cost effective broadly tunable lasing in Mid-IR wavelength region. Spectroscopic properties and fabrication methods of Fe:ZnSe crystal were introduced, the development history and technology status of Fe:ZnSe laser were summarized. There are still several challenges to be overcome in the development of affordable room temperature Fe:ZnSe laser including fabrication of high optical quality gain elements and developing high efficient, high energy short pulse pump sources in 3 m wavelength region. The key problems developing high energy, high power Fe:ZnSe laser at room temperature were analyzed.

Modeling and analysis of a highly birefringent chalcogenide photonic crystal fiber

In the present investigation, a highly elliptic chalcogenide core photonic crystal fiber with anisotropic perfectly matched layer (PML) is designed and simulated. Variation of different optical properties of the fiber such as effective refractive index, birefringence, beat length, confinement loss, effective mode area, dispersion and nonlinear coefficient are studied. The unique properties of chalcogenide glass and the structural characteristics of the fiber give high value of nonlinear coefficient, ultra high birefringence, low confinement loss and flat dispersion profile with negative dispersion in the mid-IR wavelength region of the electromagnetic spectrum which is extremely suitable for telecommunication purpose.

Exfoliated layers of black phosphorus as saturable absorber for ultrafast solid-state laser.

High-quality black phosphorus (BP) saturable absorber mirror (SAM) was successfully fabricated with few-layered BP (phosphorene). By employing the prepared phosphorene SAM, we have demonstrated ultrafast pulse generation from a BP mode-locked bulk laser for the first time to our best knowledge. Pulses as short as 6.1ps with an average power of 460mW were obtained at the central wavelength of 1064.1nm. Considering the direct and flexible band gap for different layers of phosphorene, this work may provide a possible method for fabricating BP SAM to achieve ultrafast solid-state lasers in IR and mid-IR wavelength region.

Plasmonic Nanoantennas for Multispectral Surface-Enhanced Spectroscopies

Plasmonic nanoantennas provide new routes for efficiently detecting, analyzing, and monitoring single biomolecules via fluorescence, Raman, and infrared absorption spectroscopies. The development of efficient biosensors for multispectral spectroscopy remains nevertheless limited by the narrowband responses of plasmonic devices, as they are generally designed to operate in a specific bandwidth, matching with the absorption, scattering, or emission frequency of target biomolecules under investigation. Therefore, performing biosensing from visible to infrared frequencies systematically requires designing and fabricating multiple plasmonic nanoantenna configurations and prevents the development of nanoscale integrated sensors for multispectral probing of random chemical species. Here, we propose to overcome these limitations by using broadband log-periodic nanoantennas designed to generate significant electromagnetic intensity enhancements from the visible to the mid-IR wavelength regions. We demonstrate simu...

Ultra-sensitive bio-sensor based on GMR in self-suspended-membrane-type germanium grating

In this paper, an ultra-sensitive bio-sensor based on the GMR effect in self-suspended-membrane-type gratings (SSGs) is proposed using multilayer plane waveguide theory. It is demonstrated from our calculations that the sensitivity of our bio-sensor is near the theoretical limit compared with a conventional GMR sensor. Based on the normalized eigenfunction of a single-layer homogeneous grating, the resonance curves with respect to different refractive indices of surrounding media are calculated, which confirm the estimated sensitivity. In addition, we design a highly sensitive bio-sensor in the near- and mid-IR wavelength region for liquid and gas detection respectively, the sensor can deliver a resolution over 1 × 10−5 in the near-IR region in a large refractive index (1.3–1.7) range and provide better than 1 × 10−6 in the mid-IR region, which is enough for various bio-material detections. Therefore, the bio-sensor we proposed is one or two orders more sensitive than conventional GMR sensors.

In-Vitro Near-Field Ablation of Biological Samples in the Mid-IR Wavelength Region

As a first step towards the chemical analysis of biological samples with sub-micron resolution, we report our experiments on the sub-cellular ablation of biological samples in their native environment. This has the potential to combine the near-field IR ablation with mass spectrometry, thus facilitating the study of the spatial distribution of proteins in cellular samples, at sub-cellular length scales. We report the ablation of hard and soft materials: cellular acetate cover slips in water and myoblast cell samples in growth media, with spot sizes as small as 1.5um under 3um wavelength radiation. The ablation threshold and fluence in these processes have been measured. We found that there is a dramatic increase in the ablation threshold fluences when we go from far-field to the near-field region. We will also report on the difference in the ablation mechanism in air and water medium. This approach has the potential to identify the protein expressed in cells in a relatively non-destructive manner.

High-resolution two-dimensional image upconversion of incoherent light

We consider a technique for high-resolution image upconversion of thermal light. Experimentally, we demonstrate cw upconversion with a resolution of more than 200 × 1000 pixels of thermally illuminated objects. This is the first demonstration (to our knowledge) of high-resolution cw image upconversion. The upconversion method promises an alternative route to high-quantum-efficiency all-optical imaging in the mid-IR wavelength region and beyond using standard CCD cameras. A particular advantage of CCD cameras compared to state-of-the-art thermal cameras is the possibility to tailor and tune the spectral response leading to functional spectral imaging.

Mid infrared resonant cavity detectors and lasers with epitaxial lead-chalcogenides

AbstractWavelength tunable emitters and detectors in the mid-IR wavelength region allow applications including thermal imaging and gas spectroscopy. One way to realize such tunable devices is by using a resonant cavity. By mechanically changing the cavity length with MEMS mirror techniques, the wavelengths may be tuned over a considerable range.Resonant cavity enhanced detectors (RCED) are sensitive at the cavity resonance only. They may be applied for low resolution spectroscopy, and, when arrays of such detectors are realized, as multicolour IR-FPA or “IR-AFPA”, adaptive focal plane arrays.We report the first room temperature mid-IR VECSEL (vertical external cavity surface emitting laser) with a wavelength above 3 μm. The active region is just 850 nm PbSe, followed by a 2.5 pair Bragg mirror. Output power is > 10 mW at RT.

Mid-IR multiwavelength difference frequency generation laser source based on fiber lasers

The quasi-phase-matched (QPM) wavelength acceptation bandwidth for a difference frequency generation (DFG)mid-IR laser source with fiber lasers as the fundamental sources is effectively broadened by using the dispersion relations and its temperature characteristic of periodically poled MgO-doped LiNbO3 (PPMgLN). Our simulation results show that, with an erbium-doped fiber laser (EDFL) and a ytterbium-doped fiber laser (YDFL) respectively operating near 1550 and 1060 nm wave-bands as the signal source and pump source, for the same mid-IR wavelength regions, the allowable wavelength range given by the QPM condition for the pump wave is much larger than that for the signal wave. When the wavelength of the signal wave is fixed at 1560 nm, for a given optimized crystal temperature, the acceptance bandwidth for the pump wave is over 17 nm, corresponding to the acceptance bandwidth for the idler wave of about 180 nm. Based on it, by using a multiwavelength YDFL and a single wavelength EDFL cascaded by an erbium-doped fiber amplifier (EDFA) respectively as the pump source and the signal source, 14-wavelength mid-IR laser lines, with a spacing of about 14 nm in between, are obtained simultaneously with our QPM-DFG laser system when both the temperature and the grating period of the PPMgLN used being kept unchanged at 73.5 ℃ and 30 μm respectively. Moreover, the mid-IR multiwavelength laser lines may be tuned synchronously by varying the signal wavelength.

Birefringent- and quasi phase-matching with BaMgF_4 for vacuum-UV/UV and mid-IR all solid-state lasers

BaMgF(4) is a ferroelectric fluoride which shows a very wide transparency range extending from 125 nm to 13 microm. The conjunction of these properties confers to BaMgF(4) a unique chance for optical applications in the UV and mid-IR wavelength regions, where other nonlinear materials cannot be used. In particular its application as frequency converter in all solid-state lasers is considered. The wavelength dispersion of the refractive indices along the three optical principal axes is measured in the transparent region, and the Sellmeier coefficients for the three refractive indices are determined. The conditions for nonlinear optical processes are calculated for birefringent-matching and quasi phase-matching, with special emphasis in the UV and IR wavelength regions. Quasi phase-matching can be achieved in the whole transparent wavelength region, in contrast to birefringent-matching, which can be obtained in a limited range 573-5634 nm. First demonstration of second harmonic generation by quasi phase-matching with a ferroelectric fluoride is shown by frequency-doubling the emissions of a 1064 nm Nd:YAG laser and a tunable Ti:sapphire laser. The shortest emission is obtained in the UV at 368 nm, indicating the potential of BaMgF(4) as nonlinear medium for the fabrication of all solid-state lasers in the vacuum-UV/UV and mid-IR wavelength regions.

Phase-stabilized, 15 W frequency comb at 28–48 μm

We present a high-power optical-parametric-oscillator (OPO) based frequency comb in the mid-IR wavelength region. The system employs periodically poled lithium niobate and is singly resonant for the signal. It is synchronously pumped by a 10 W femtosecond Yb:fiber laser centered at 1.07 microm. The idler (signal) wavelength can be continuously tuned from 2.8 to 4.8 microm (1.76 to 1.37 microm) with a simultaneous bandwidth as high as 0.3 microm and a maximum average idler output power of 1.50 W. We also demonstrate the performance of the stabilized comb by recording the heterodyne beat with a narrow-linewidth diode laser. This OPO is an ideal source for frequency comb spectroscopy in the mid-IR.