Μm Regime Research Articles

A slot-waveguide-based polarization beam splitter assisted by epsilon-near-zero material

A slot-waveguide-based polarization beam splitter (PBS) assisted by “epsilon-near-zero” (ENZ) material is proposed and investigated. Because of the tunable complex refractive indices of indium tin oxide (ITO), ENZ effect can be achieved in the 1.55 μm regime. By embedding ITO in the slot region of the silicon waveguide, the modal characteristics of the TM mode are significantly modified, whereas that of the TE mode is nearly unchanged. Based on this feature, an asymmetric directional coupler is constructed as a PBS in which the TE mode undergoes a strong coupling to the slot waveguide nearby while the TM mode can pass through the waveguide directly. The results show that with 5.6 μm coupling length and 200 nm gap, the PBS offers 31.1 dB and 31.9 dB extinction ratio (ER) and 0.69 dB and 0.97 dB insertion loss (IL) for TE mode and TM mode, respectively. Furthermore, the impact of carrier concentration and operation wavelength on the PBS performance are investigated in detail. The proposed PBS is compatible with most of the newly developed ITO-based active photonic devices and can be a useful component for on-chip signal processing.

A search for possible long range spin dependent interactions of the neutron from exotic vector boson exchange

We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that interactions would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, ϕ′=[2.8±4.6(stat.)±4.0(sys.)]×10−5 rad/m is consistent with zero. This result improves the upper bounds on the neutron-matter coupling gA2 by about three orders of magnitude for force ranges in the mm– μm regime.

The Effect of Arctic Dust on the Retrieval of Satellite Derived Sea and Ice Surface Temperatures

Large quantities of dust are transported annually to the Arctic, primarily from Asian deserts. The influx of dust into the polar environment changes the radiative properties of clouds while the deposition of dust onto ice and snow decreases the surface albedo. Atmospheric and surface dust may be identified with space borne radiometers by comparing infrared energy in the 11 μm and 12 μm regime. Between 2007 and 2017 satellite infrared data revealed persistent low-level dust clouds in the vicinity of Amundsen Gulf in the Western Canadian Arctic during the melting season. Evidence suggests that the subsequent deposition of atmospheric dust in the region affected the surface emissivity in the thermal infrared regime. As a result, satellite derived sea and ice surface temperature algorithms were rendered inaccurate in these areas. Moreover, the ubiquitous nature of dust in the region may play a role in the rapidly vanishing cryosphere.

Actively Q-switched dual-wavelength pumped Er3+ :ZBLAN fiber laser at 3.47 µm.

We demonstrate the first actively Q-switched fiber laser operating in the 3.5μm regime. The dual-wavelength pumped system makes use of an Er3+ doped ZBLAN fiber and a germanium acousto-optic modulator. Robust Q-switching saw a pulse energy of 7.8μJ achieved at a repetition rate of 15kHz, corresponding to a peak power of 14.5W.

High energy soliton pulse generation by a magnetron-sputtering-deposition-grown MoTe2 saturable absorber

The pulse energy in the ultrafast soliton fiber laser oscillators is usually limited by the well-known wave-breaking phenomenon owing to the absence of a desirable real saturable absorber (SA) with high power tolerance and large modulation depth. Here, we report a type of microfiber-based MoTe2 SA fabricated by the magnetron-sputtering deposition (MSD) method. High-energy wave-breaking free soliton pulses were generated with pulse duration/pulse energy/average output power of 229 fs/2.14 nJ/57 mW in the 1.5 μm regime and 1.3 ps/13.8 nJ/212 mW in the 2 μm regime, respectively. To our knowledge, the generated soliton pulses at 1.5 μm had the shortest pulse duration and the highest output power among the reported erbium-doped fiber lasers mode locked by transition metal dichalcogenides. Moreover, this was the first demonstration of a MoTe2-based SA in fiber lasers in the 2 μm regime, and the pulse energy/output power are the highest in the reported thulium-doped fiber lasers mode locked by two-dimensional materials. Our results suggest that a microfiber-based MoTe2 SA could be used as an excellent photonic device for ultrafast pulse generation, and the MSD technique opens a promising route to produce a high-performance SA with high power tolerance and large modulation depth, which are beneficial for high-energy wave-breaking free pulse generation.

Design and analysis of a hexagonal tellurite photonic crystal fiber with broadband ultra-flattened dispersion in mid-IR

We propose a modified hexagonal tellurite photonic crystal fiber (PCF) with broadband ultra-flattened dispersion near 2 μm regime. By optimizing various structural parameters, the dispersion of the proposed PCF can be kept within 60.47 ps nm−1 km−1 to 61.33 ps nm−1 km−1 from 2.15 μm to 2.85 μm wavelength. More importantly, the corresponding nonlinear coefficients can be as high as 378.1 W−1 km−1. Leveraging on these advantages, this fiber is suitable for supercontinuum generation toward mid-infrared (MIR) wavelength range. By injecting the hyperbolic secant pulse with peak power of 5 kW and full width at half maximum (FWHM) of 176 fs into the fiber, supercontinuum spectrum covering 2000–4900 nm together with the dispersive wave locating near 933 nm can be produced.

Few-layer bismuthene for ultrashort pulse generation in a dissipative system based on an evanescent field

Bismuthene has attracted a great deal of attention because of its unique electronic and optical properties. However, there are few reported applications of bismuthene in nonlinear optical applications. In this research, a dissipative soliton ytterbium-doped mode-locked fiber laser at 1 μm regime with a bismuthene saturable absorber (SA) by using evanescent field interaction for the first time is demonstrated. The nonlinear optical absorption of microfiber-based bismuthene SA is shown experimentally by using a homemade ultrafast fiber laser, whose saturation intensity and modulation depth are about 13 MW cm-2 and 2.2%, respectively. Relying on the excellent nonlinear optical property of the bismuthene SA, the typical dissipative solitons with a repetition rate of 21.74 MHz are generated at a center wavelength of 1034.4 nm. The time-bandwidth product of the pulse is about 23.07 with a pulse width of 30.25 ps. The results demonstrate that bismuthene is a good candidate for application in a 1 μm wave-breaking-free mode-locked fiber laser and nonlinear photonic components.

Slotted rotatable target assembly and systematic error analysis for a search for long range spin dependent interactions from exotic vector boson exchange using neutron spin rotation

We discuss the design and construction of a novel target array of nonmagnetic test masses used in a neutron polarimetry measurement made in search for new possible exotic spin dependent neutron–atominteractions of Nature at sub-mm length scales. This target was designed to accept and efficiently transmit a transversely polarized slow neutron beam through a series of long open parallel slots bounded by flat rectangular plates. These openings possessed equal atom density gradients normal to the slots from the flat test masses with dimensions optimized to achieve maximum sensitivity to an exotic spin-dependent interaction from vector boson exchanges with ranges in the mm - μm regime. The parallel slots were oriented differently in four quadrants that can be rotated about the neutron beam axis in discrete 90°increments using a Geneva drive. The spin rotation signals from the 4 quadrants were measured using a segmented neutron ion chamber to suppress possible systematic errors from stray magnetic fields in the target region. We discuss the per-neutron sensitivity of the target to the exotic interaction, the design constraints, the potential sources of systematic errors which could be present in this design, and our estimate of the achievable sensitivity using this method.

Magnetron-sputtering deposited WTe2for an ultrafast thulium-doped fiber laser.

Ultrafast pulse generation was demonstrated in a thulium-doped fiber laser mode-locked by magnetron-sputtering deposited WTe2 with a modulation depth, a nonsaturable loss, and a saturable intensity of 31%, 34.3%, and 7.6 MW/cm2, respectively. Stable soliton pulses could be obtained at a 1915.5 nm central wavelength with a pulse duration of 1.25 ps, an average output power of 39.9 mW, and a signal-to-noise ratio of 95 dB. To the best of our knowledge, this was the first demonstration of WTe2-based saturable absorbers in fiber lasers at a 2 μm regime.

Heterogeneous Integration for Mid-infrared Silicon Photonics

Heterogeneous integration enables the construction of silicon (Si) photonic systems, which are fully integrated with a range of passive and active elements including lasers and detectors. Numerous advancements in recent years have shown that heterogeneous Si platforms can be extended beyond near-infrared telecommunication wavelengths to the mid-infrared (MIR) (2-20 μm) regime. These wavelengths hold potential for an extensive range of sensing applications and the necessary components for fully integrated heterogeneous MIR Si photonic technologies have now been demonstrated. However, due to the broad wavelength range and the diverse assortment of MIR technologies, the optimal platform for each specific application is unclear. Here, we overview Si photonic waveguide platforms and lasers at the MIR, including quantum cascade lasers on Si. We also discuss progress toward building an integrated multispectral source, which can be constructed by wavelength beam combining the outputs from multiple lasers with arrayed waveguide gratings and duplexing adiabatic couplers.

Silk‐Based Fine Dust Filters for Air Filtration

AbstractState‐of‐the‐art air filter devices have been well‐characterized and optimized for particle deposition of a huge range of particle sizes. However, sustainability of the employed filter materials is usually neglected. In this study, several polymers (recombinant spider silk, recombinant lacewing silk, poly(lactic acid), and poly(ethylene oxide)) are electrospun into fine dust filter layers to evaluate relevant filter parameters such as particle deposition, air permeability, and pressure drop for sub‐micrometer fiber materials. Filters comprising silk proteins show a much lower demand on fine‐dust‐layer material (40–210 mg m−2) in comparison to that of conventional filters (50 g m−2). Filters equipped with silk meshes with fiber diameters in the sub‐micrometer regime (<250 nm) show improved filter qualities in comparison to that of commercially available air filter devices (with melt blown fibers in the >20 µm regime). In particular, sub‐micrometer particles (0.2–1 µm) are filtered more efficiently by the silk‐based filters due to interception and impaction effects yielding a low pressure drop, and therefore these filters show an improved air permeability and lowered pressure drop of, for example, a vacuum cleaner bag in which they can be employed.

Fully High‐Speed Gravure Printed, Low‐Variability, High‐Performance Organic Polymer Transistors with Sub‐5 V Operation

Printed transistors will be a key component in low‐cost, large area, flexible printed systems such as flexible displays, sensor networks, or radio‐frequency identification (RFID) tags. In any such applications, these printed organic thin‐film transistors (OTFTs) will have to operate at low voltages, exhibit good uniformity, and deliver relatively high performance by using scaled source and drain electrodes. In addition, devices need to be printed at high speeds to fully harness the potential of low‐cost fabrication that printed electronics promises. Gravure printing is a particularly promising technique because it combines high resolution in the sub‐10 μm regime with high printing speed on the order of 1 m s–1. Here, for the first time, fully gravure‐printed OTFTs are demonstrated that use highly scaled source and drain electrodes with linewidth and spacing of 5 μm. All layers are printed at 1 m s–1. An amorphous polymer semiconductor is used to achieve good uniformity. By patterning the semiconductor and scaling the dielectric, good off‐state performance and sub‐5 V operation are achieved, thus providing a promising path for the realization of functional printed systems.

Highly efficient passively Q-switched solid-state 2 μm laser with monolayer Graphene

By using monolayer graphene as saturable absorber, a passively Q-switched Tm:LuAG laser with high efficiency at 2 μm is demonstrated. At the incident pump power of 5.8 W, pulses with duration of 235 ns and maximum average output power of 873 mW were obtained at a repetition rate of 72 kHz. This is, to the best of our knowledge, the highest average output power, as well as the narrowest pulse width, ever obtained among graphene-based passively Q-switched solid-state bulk lasers at 2 μm regime.

Optical characterization of In-flushed InAs/GaAs quantum dots emitting a broadband spectrum with multiple peaks at ~1 μm.

We investigated optical properties of In-flushed InAs quantum dots (QDs) grown on a GaAs substrate by molecular beam epitaxy. By using the In-flush technique for setting the height of self-assembled InAs QDs, we have tuned the emission wavelength of InAs QDs to the ~1 μm regime, which can be utilized as a non-invasive and deeply penetrative probe for biological and medical imaging systems. The controlled emission exhibited a broadband spectrum comprising multiple peaks with an interval of approximately 30 meV. We examined the origin of the multiple peaks using spectral and time-resolved photoluminescence, and concluded that it is attributed to monolayer step fluctuations in the height of the In-flushed QDs. This feature can be advantageous for realizing a broadband light source centered at the ~1 μm regime, which is especially suitable for the non-invasive cross-sectional biological and medical imaging system known as optical coherence tomography.

GHz response of metamorphic InAlAs metal–semiconductor–metal photodetector on GaAs substrate

We fabricated metal–semiconductor–metal (MSM) photodetectors on the metamorphic InAlAs layer grown on a GaAs substrate. The devices were measured at a wavelength in the 0.8 µm regime. The receiving area is 30 × 30 µm2 and the electrode spacings are 2, 1, and 0.4 µm. At the electrode spacing of 1 µm, a dark current of 125 nA was obtained at a bias voltage of −15 V. At a wavelength of 830 nm, a responsivity of 0.13 A/W was obtained at a bias voltage of −15 V. At a wavelength of 850 nm, the maximum bandwidth of 9 GHz was obtained at a bias voltage of −15 V.

Progress Report on the Generation of Polyfunctional Microscale Particles for Programmed Self-Assembly.

A process for 3D programmed self-assembly of lithographically printable microscale polymer particles using ssDNA hybridization as the associative force is described. We report our progress in establishing the unit processes required for 3D programmed self-assembly and demonstrate the successful fabrication and sequence-specific self-assembly of covalent ssDNA-functionalized parallelepipeds with dimensions in the sub 10 μm regime characterized by optical microscopy and imaging flow cytometry. This technology has the potential to produce parallelepiped particles with different ssDNA on each facet.

Demonstration of optical parametric gain generation in the 1 μm regime based on a photonic crystal fiber pumped by a picosecond mode-locked ytterbium-doped fiber laser

We report the experimental demonstration of the optical parametric gain generation in the 1 μm regime based on a photonic crystal fiber (PCF) with a zero group velocity dispersion (GVD) wavelength of 1062 nm pumped by a homemade tunable picosecond mode-locked ytterbium-doped fiber laser. A broad parametric gain band is obtained by pumping the PCF in the anomalous GVD regime with a relatively low power. Two separated narrow parametric gain bands are observed by pumping the PCF in the normal GVD regime. The peak of the parametric gain profile can be tuned from 927 to 1038 nm and from 1099 to 1228 nm. This widely tunable parametric gain band can be used for a broad band optical parametric amplifier, large span wavelength conversion or a tunable optical parametric oscillator.

Mid-infrared supercontinuum generation to 45 μm in uniform and tapered ZBLAN step-index fibers by direct pumping at 1064 or 1550 nm

We present a numerical design optimization of step-index ZBLAN fibers for developing mid-infrared (IR) supercontinuum sources with spectra covering the 1–4.5 μm regime using direct pumping with 10 ps pulses (FWHM) from mode-locked Yb (12.5 kW peak power) and Er lasers (10 kW peak power). Even with optimum NA and core diameter to minimize confinement loss and give the most suitable dispersion and nonlinearity, the Yb pump-laser cannot push the spectrum beyond 1.52 μm, whereas the Er laser can push the spectrum to 4.15 μm. We further consider the optimum placement of a 20 cm taper to broaden the spectrum. This does not considerably broaden the Yb-pumped spectrum, whereas the Er-pumped spectrum can be extended to 4.5 μm through mid-IR dispersive waves and tunneling solitons.

High power single frequency solid state master oscillator power amplifier for gravitational wave detection

High power single frequency, single mode, linearly polarized laser output at the 1 μm regime is in demand for the interferometric gravitational wave detectors (GWDs). A robust single frequency solid state master oscillator power amplifier (MOPA) is a promising candidate for such applications. We present a single frequency solid state multistage MOPA system delivering 177 W of linearly polarized output power at 1 μm with 83.5% TEM(00) mode content.

High average power 2 μm generation using an intracavity PPMgLN optical parametric oscillator

An intracavity quasi-phase-matched optical parametric oscillator (OPO) has been developed for the purpose of generating radiation with high average power and high repetition rate in the 2 μm regime. The device is a degenerate OPO based on a 3 mm thick MgO-doped periodically poled LiNbO(3) (PPMgLN) crystal, which is pumped in turn within the cavity by a diode side-pumped, Q-switched 1 μm Nd:YAG laser operating at 10 kHz. Up to 20 W broadband 2 μm radiation can be generated with a compact configuration under the crystal temperature of 115 °C. The beam profile is close to circularly symmetric with M(2) ~ 10.