Maximizing the bandwidth of coherent,mid-IR supercontinuum using highly nonlinear aperiodic nanofibers

We describe in detail a new procedure of maximizing the bandwidth of mid-infrared (mid-IR) supercontinuum (SC) in highly nonlinear microstructured As₂Se₃ and tellurite aperiodic nanofibers. By introducing aperiodic rings of first and secondary air holes into the cross-sections of our microstructured fiber designs, we achieve flattened and all-normal dispersion profiles over much broader bandwidths than would be possible with simple periodic designs. These fiber designs are optimized for efficient, broadband, and coherent SC generation in the mid-IR spectral region. Numerical simulations show that these designs enable the generation of a SC spanning over 2290?nm extending from 1140 to 3430?nm in 8?cm length of tellurite nanofiber with input energy of E?=?200?pJ and a SC bandwidth of over 4700?nm extending from 1795 to 6525?nm generated in only 8?mm-length of As₂Se₃-based nanofiber with input energy as low as E?=?100?pJ. This work provides a new type of broadband mid-IR SC source with flat spectral shape as well as excellent coherence and temporal properties by using aperiodic nanofibers with all-normal dispersion suitable for applications in ultrafast science, metrology, coherent control, non-destructive testing, spectroscopy, and optical coherence tomography in the mid-IR region.     

Dispersion engineering of a silicon-nanocrystal-based slot waveguide for broadband wavelength conversion

A proposal for broadband wavelength conversion using four-wave mixing is presented based on a slot waveguide with silicon nanocrystals (Si-nc's) as the optical nonlinear material. The dispersion of the waveguide is engineered to realize a flat dispersion as well as a small effective mode area for better nonlinear interaction by optimizing the waveguide dimensions. The conversion performance is synthetically analyzed and numerical results show that a bandwidth of over 400?nm and an efficiency of -2.38?dB can be achieved using a pump power of 150?mW in a 4?mm long Si-nc slot waveguide with slot width of 50?nm, slab width of 310?nm, and height of 305?nm.     

Ultrabroad supercontinuum generation in tellurite equiangular spiral photonic crystal fiber

Simulations are presented of a very broad and flat supercontinuum (SC) in both the normal and anomalous group velocity dispersion regimes of the same equiangular spiral photonic crystal fiber at low pumping powers. For a pump wavelength at 1557?nm and average pump power of 11.2?mW, we obtained a bandwidth >3?μm (970?nm–4100?nm) at 40 dB below the peak spectral power with fiber dispersion ～2.1?ps/km nm at 1557?nm. In the same fiber, at pump wavelength 1930?nm and average pump power of 12?mW the SC bandwidth was more than two octaves (1300?nm–3700?nm) and dispersion was ～1.3?ps/km nm at 1930?nm. This demonstrates the potential use of the fiber for multi-wavelength pumping with commercially available sources at fairly low power.     

Broadband and efficient wavelength conversion in a slot-width switching silicon–organic hybrid waveguide

We propose a slot-width switching (SWS) silicon–organic hybrid waveguide for broadband and efficient wavelength conversion. By switching the slot width of different lengths, the quasi-phase-matching can be obtained. Compared with width-modulated silicon-on-insulator (SOI) waveguide, the non-linear absorption can be ignored in slot waveguide which is filled with p-toluene sulphonate. Consequently, the conversion efficiency at a particular signal wavelength is improved, and the 3-dB conversion bandwidth is also extended. The numerical simulation results indicate that, for a continuous-wave pump at 1550 nm, a conversion bandwidth of 570 nm and a peak conversion efficiency of 11.32 dB can be realized in a 7.5-mm-long SWS waveguide, which is better than that of width-modulated SOI waveguide.     

All-fiber broadband supercontinuum source with high efficiency in a step-index high nonlinear silica fiber

We demonstrate an all-fiber broadband supercontinuum (SC) source with high efficiency in a step-index high nonlinear silica fiber, which was pumped by a 1557 nm subpicosecond-pulse laser in the normal dispersion region. The broad SC spectrum covers the spectral range from 840 to 2390 nm, and the 10 dB bandwidth from 1120 nm to 2245 nm of the SC covers one octave, assuming the peaks near 1550 nm were filtered. The SC source system is constructed by all-fiber components, which can be fusion-spliced together directly with low loss, less than 0.1 dB. Thus the SC source has high energy transfer efficiency from the pump source. The maximum SC average power of 332 mW is obtained, including the peaks near 1550 nm. The spectral density for the 10 dB bandwidth is in the range from -17.3 to -7.3 dBm/nm.     

Analysis and design of a rib-like-based slot waveguide for nonlinear silicon nanophotonics

Design of efficient nonlinear optical waveguides is an essential requirement for development of silicon nanophotonics. These waveguides should have a unique capability to play the main role in realization of both passive and active optical devices. A high-performance dielectric rib-like-based slot waveguide is proposed for nonlinear silicon nanophotonics. Its slot region can be filled with Si-nc:SiO₂ which exhibits a high third-order nonlinear effect. Study of numerical results shows that this new slot waveguide has a nonlinear parameter of the same order of magnitude as an equally sized silicon nanophotonics strip-based slot waveguide. The new waveguide can be fabricated easily by etching a slot in the core region of the silicon-on-insulator (SOI)-based rib-like waveguide.     

Ultrawide spectral range group-velocity dispersion measurementutilizing supercontinuum in an optical fiber pumped by a 1.5 μmcompact laser source

Group velocity dispersion (GVD) measurement is presented utilizing supercontinuum (SC) white pulses generated in an optical fiber by 15 μm compact laser sources. This provides 1) ultrawide continuous spectral measurement range >600 nm from a single optical source without the use of interpolation formulae and 2) stable far-end measurements by the simultaneous multi-wavelength nature of the SC pulses. A novel method that is independent of the detector bandwidth is proposed which measures λ-dependent phase shifts of one of the Fourier components of a short pulse train. Fiber GVD's of unusual dispersion characteristics were measured using SC pulses extended over the spectral range of 1150-1770 nm. It is shown that fiber lengths of up to 130 km can be measured with a group delay resolution of 0.01 ps/km     

Effect of intrapulse Raman scattering on broadband amplitude noise of supercontinuum generated in fiber normal dispersion region

Based on the generalized stochastic nonlinear Schr?dinger equation, the effect of intrapulse Raman scattering (IRS) on broadband amplitude noise of supercontinuum (SC) generated in the normal dispersion regime is investigated numerically. The results show that, in the normal dispersion regime, where the IRS contributes less to the bandwidth of the SC spectrum, the broadband amplitude noise of SC is amplified significantly in the process of SC generation because of the existence of IRS effect. Using fiber with an optimal negative dispersion slope, the IRS effect can be suppressed, and thus the SC amplitude noise is reduced without spectral bandwidth loss.     

Slow light with large group index – bandwidth product in lattice-shifted photonic crystal waveguides

Abstract

This study presents a systematic optimization procedure to generate slow light with large group index, wideband, and low dispersion in an lattice-shifted photonic crystal waveguide. The waveguide is based on triangular lattice photonic crystal imposed by selectively altering the locations of the holes adjacent to the line defect. Under a constant group index criterion of ± 10% variation, when group indices are nearly constants of 24, 33, 46, 57, and 66, their corresponding bandwidths of flat band reach 24.2, 17.6, 12.8, 10.1 and 8.6 nm around 1550 nm, respectively. A nearly constant large group index – bandwidth product (GBP) of 0.37 is achieved for all cases. Low dispersion slow light propagation is confirmed by studying the relative temporal pulse-width spreading with the 2-D finite-difference time-domain method.     

Magnetic Proximity Effects in V/Fe Superconductor/Ferromagnet Single Bilayer Revealed by Waveguide-Enhanced Polarized Neutron Reflectometry

Polarized neutron reflectometry is used to study the magnetic proximity effect in a superconductor/ferromagnet (SC/FM) system of composition Cu(32 nm)/ V(40 nm)/Fe(1 nm)/MgO. In contrast to previous studies, here a single SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary signal enhancement is achieved by waveguide resonance, i.e., preparing the V(40 nm)/Fe(1 nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate and Cu top layer, respectively. A new magnetic state of the system was observed at temperatures below 0.7T _C manifested in a systematic change in the height and width of the waveguide resonance peak. Upon increasing the temperature from 0.7T _C to T _C, a gradual decay of this state is observed, accompanied by a 5% growth of the diffuse scattering. This behavior can be explained in a natural way by the polarization of the superconducting electrons upon the SC transition, i.e., an appearance of additional induced magnetization within the SC, due to the proximity of the FM layer.     

Mid-infrared supercontinuum generation in tapered As2S3 chalcogenide planar waveguide

Abstract

We numerically demonstrate mid-infrared supercontinuum generation in a non-uniformly tapered chalcogenide planar waveguide. This planar rib waveguide of As₂S₃ glass on MgF₂ is 2 cm long with increasing etch depth longitudinally to manage the total dispersion. This waveguide has zero dispersion at two wavelengths. The dispersion profile varies along the propagation distance, leading to continuous modification of the phase-matching condition for dispersive wave emission and enhancement of energy transfer efficiency between solitons and dispersive waves. Numerical simulations are conducted for secant input pulses at a wavelength of 1.55 μm with a width of 50 fs and peak power of 2 kW. Results show this proposed scheme significantly broadens the generated continuum, extending from ~1 to ~7 μm.     

Efficient poling of electro-optic polymers in thin films and silicon slot waveguides by detachable pyroelectric crystals

Pyroelectric crystals are used as a conformal and detachable electric field source to efficiently pole electro-optic (E-O) polymers in both parallel-plate (transverse) and in-plane (quasi-longitudinal) configurations. Large Pockels coefficients in poled thin films and high tunability of resonance wavelength shift in hybrid polymer silicon slot waveguide ring-resonator modulators have been achieved using this method.     

Hybrid integrated photodetector with flat-top steep-edge spectral response

Hybrid integrated photodetectors with flat-top steep-edge spectral responses that consist of an Si-based multicavity Fabry-Perot (F-P) filter and an InP-based p-i-n absorption structure (with a 0.2?μm In_0.53Ga_0.47As absorption layer), have been designed and fabricated. The performance of the hybrid integrated photodetectors is theoretically investigated by including key factors such as the thickness of each cavity, the pairs of each reflecting mirror, and the thickness of the benzocyclobutene bonding layer. The device is fabricated by bonding an Si-based multicavity F-P filter with an InP-based p-i-n absorption structure. A hybrid integrated photodetector with a peak quantum efficiency of 55% around 1549.2?nm, the -0.5 dB band of 0.43?nm, the 25?dB band of 1.06?nm, and 3?dB bandwidth more than 16?GHz, is simultaneously obtained. Based on multicavity F-P structure, this device has good flat-top steep-edge spectral response.     

Fluorescence and nonlinear optical properties of non-aggregating hexadeca-substituted phthalocyanine

Highly non-aggregating hexadeca-substituted phthalocyanine (Pc) complexes were prepared and their fluorescence and nonlinear optical properties were studied. Three visible fluorescence bands were observed when the Pc complexes were excited at 355 nm and found to be concentration dependent. They are attributed to the optical transitions S₂ → S₀ at 415 nm, T₂ → T₁ at 630 nm, and S₂ → S₁ at 755 nm. Nonlinear absorptive and refractive effects were measured with the help of Z-scan technique. Saturation absorption was observed at 632.8 nm where the nonlinear absorption coefficient is found to be very large (β = −2.8 × 10⁻² cm/W) and the refractive nonlinear coefficient γ = −9.5 × 10⁻¹¹ cm²/W. In the transparency domain at 532 nm, reverse absorption saturation is observed and β and γ are found to be 17.5 and 15.5 times smaller, respectively. Optical limiting performances are measured in the absorption and transparency domains. Purely refractive-based optical limiting at 632.8 nm is found to have a threshold of 0.16 kW/cm², lower than the reverse absorption saturation and refractive-based optical limiting of 0.90 kW/cm² at 532 nm.     

An all solid-state narrow bandwidth optical parametric oscillator and its applications to the high resolution spectroscopy of free radicals

The paper describes the design, performance and illustrative spectroscopic applications of a high power, pulsed, injection seeded, narrow bandwidth and continuously tuneable optical parametric oscillator (OPO) based on two β-barium borate (BBO) nonlinear crystals. A ring cavity OPO was injection seeded with an external cavity diode laser in the spectral range 755–855 nm. The OPO generated high power transform limited nanosecond light pulses in this range and, simultaneously, at 606–667 nm. Spectral parameters of the OPO were investigated as a function of pump power for two different cavity lengths. A bandwidth of ～120 MHz (0.004 cm^-1) in the visible has been achieved with a 40-cm-long cavity. The potential of the OPO system is demonstrated by recording high resolution sub-Doppler spectra in the UV of PF and C₃ radicals in a pulsed supersonic jet expansion.     

Three octave spanning supercontinuum by red-shifted dispersive wave in photonic crystal fibers

This article presents a three-layer index guided lead silicate (SF57) photonic crystal fiber which simultaneously promises to yield large effective optical nonlinear coefficient and low anomalous dispersion that makes it suitable for supercontinuum (SC) generation. At an operating wavelength 1550 nm, the typical optimized value of anomalous dispersion and effective nonlinear coefficient turns out to be ~4 ps/km/nm and ~1078 W^?1km^?1, respectively. Through numerical simulation, it is realized that the designed fiber promises to exhibit three octave spanning SC from 900 to 7200 nm using 50 fs ‘sech’ optical pulses of 5 kW peak power. Due to the cross-phase modulation and four-wave mixing processes, a long range of red-shifted dispersive wave generated, which assists to achieve such large broadening. In addition, we have investigated the compatibility of SC generation with input pulse peak power increment and briefly discussed the impact of nonlinear processes on SC generation.     

All-fiber quasi-continuous wave supercontinuum generation in single-mode high-nonlinear fiber pumped by submicrosecond pulse with low peak power

We demonstrate quasi-continuous wave supercontinuum generation in a single-mode high-nonlinear fiber (HNLF) in 1.55 μm band, which is pumped by the amplified passively Q-switched submicrosecond pulse. The pump wavelength is in the normal dispersion region of HNLF and near to the zero-dispersion wavelength. The broad SC spectral range from 1200 to 2260 nm is obtained with the low pump peak power of 17.8 W. The 20 dB bandwidth of 922 nm from 1285 to 2207 nm is obtained with the assumption that the peak near 1560 nm is filtered. The spectrum density for the 20 dB bandwidth is from -27.5 to -7.5 dbm/nm.     

Diode-pumped passively mode-locked Nd:GYSGG laser at 1061 nm with periodically poled LiNbO3 nonlinear mirror

ABSTRACT

We report a nonlinear-mirror mode-locked diode-pumped solid-state Nd:GYSGG laser operating at 1061?nm. The nonlinear mirror comprises a periodically poled LiNbO₃(PPLN) crystal and a dichroic mirror. Continuous-wave mode-locked laser with an output power of 450?mw is obtained under a diode pump power of 5.5?W at 808?nm. The repetition rate of the mode-locked laser is 97.1?MHz and the bandwidth of spectral is 1.3?nm. Considering the group velocity mismatch (GVM) of PPLN, we estimate the minimum pulse width is about 9?ps.     

Synthesis of iron red hybrid pigments from oil shale semi-coke waste

Oil shale semi-coke (SC) is a bulk solid waste produced after shale oil being extracted from oil shale. It is abundant on the earth, but most of them are discarded or piled up as solid waste, and their reuse as resources is very limited. In this paper, adhering to the concept of “waste to materials“, the α-Fe₂O₃/SC hybrid pigments with the red color (a* = 29.68) better than commercial iron red pigments (a* = 26.92) were synthesized by an one-pot hydrothermal reaction of pretreated SC with Fe(III), using SC as a cheap starting material. The microscopic structure, chemical composition and color of the hybrid pigments were studied, and the reaction parameters for synthesizing the best hybrid pigments from SC were optimized. The results indicate that the hybrid pigments are mainly composed of SiO₂ and Fe₂O₃, where α-Fe₂O₃ particles grow on the surface of SC-derived silicate substrate with a better dispersion. The hybrid pigments showed a good stability, especially an outstanding high temperature-resistant stability. The secondary heat treatment induced the further improvement of red color value of the hybrid pigments. This work provides a new way and solution for the rational disposal and functional application of SC waste.     

Slab waveguide theory for general multi-slot waveguide

Abstract

Optical devices based on slot waveguide are of considerable interest in numerous applications due to the distinct feature of strong electric field confinement in a low-refractive index region. A theoretical model based on multi-slab waveguide theory is used to reveal the physical mechanism of the slot waveguide. The calculation results derived from the basic Helmholtz equation for the conventional single-slot waveguide with a ~2% validation of the effective refractive index are compared to the former experiment results by the Cornell University group. Moreover, we extend the theoretical model to a general multi-slot waveguide. Its electric field distribution and key properties such as optical power confinement factor and enhancement factor in slot are deduced theoretically and fully discussed.