Ultrabroad Wavelength Range Research Articles

Ultrahigh Extinction Ratio Leaky-Guided Hollow Core Fiber Mach-Zehnder Interferometer Assisted by a Large Core Hollow Fiber Beam Splitter.

We proposed a novel fiber Mach-Zehnder interferometer (FMZI) that can perform an ultrahigh extinction ratio (ER), ultracompact, and ultra-broadband interference characteristics. The FMZI structure is based on an extremely tiny hollow core fiber (HCF) with a small diameter of 10 μm (named HCF10) connected with a beam splitter of a large core of 50 μm HCF (named HCF50). The refractive index (RI) of the air core is lower than that of the HCF cladding; a leaky-guided fiber waveguide (LGFW) occurs in such a short-section HCF10 waveguide to simultaneously have the core and cladding modes. To achieve better fringe visibility of the interference, the section of HCF50 assists in splitting the optical light into core and cladding beams launched into the HCF10 with appropriate intensities. Experimental and simulation results show that the optical characteristics of the proposed LGFW-FMZI are very similar. Based on the results of the study, the length of the HCF10 primarily influences the free spectral range (FSR) of the interference spectra, and the HCF50 splitter significantly controls the optimal extinction ratio (ER) of the interference fringes. By exactly adjusting the lengths of HCF10 and HCF50, the proposed fiber interferometers can perform the capability of an ultrahigh ER over 50 dB with the arbitrary FSR in the transmitted interference spectra over an ultra-broad wavelength range of 1250 nm to 1650 nm.

Room‐Temperature Blackbody‐Sensitive Photodetector with Visible‐To‐Long‐Wavelength‐Infrared Photoresponse and Ultrafast Speed Based on a Te/PtSe2 Heterostructure

AbstractRoom‐temperature blackbody‐sensitive infrared photodetectors with ultra‐broadband and ultrafast photoresponses are highly desired in numerous scientific and technical fields. However, it is challenging for an infrared photodetector to simultaneously possess all the aforementioned characteristics. In this study, a room‐temperature Te/PtSe2 heterostructure photodetector is established to address this challenge, utilizing the built‐in field of the heterostructure, the crossing conduction and valence bands of PtSe2, the high mobilities of both materials, and a considerable photogain. The device is photoresponsive over the ultrabroad wavelength range (519 nm–10 µm). The peak responsivity and specific detectivity reach 196.8 A W−1, and 4.3 × 109 cm Hz1/2 W−1, respectively, at the wavelength of 3.32 µm. The device also exhibits blackbody sensitivity, with a responsivity of 24.8 A W−1, and a specific detectivity of 7.4 × 108 cm Hz1/2 W−1. The photoresponse is ultrafast, corresponding to a 3 dB bandwidth of 160 kHz. The study provides new possibilities for high‐performance room‐temperature infrared detection.

Theoretical analysis of composite nanostructure with three-dimensional photonic lattice for ultra-broadband and polarization-independent absorption

In this study, we present a composite nanopillar array with an average absorption efficiency near 100% in an ultra-broad wavelength range from 300 nm to 2000 nm. In particular, the average absorption in the band range from 400 nm to 1000 nm is close to 99% due to the strong coupling between the composite nanopillars and a complementary absorption generated by the two kinds of nanopillars in one period. The real and imaginary parts of the absorber’s impedance present a fluctuation near 1 and 0 in the entire wavelength range, which indicates an ultra-weak reflection of the absorber. The device also shows insensitivity to the polarization state and angle of incidence. The research offers a novel strategy for achieving high-efficiency light absorption in an ultra-broad wavelength range and boosts the potential value of composite nanostructures for thermophotovoltaic cells, electromagnetic stealth, and stray light suppression.

Ultra-Broadband, Omnidirectional, High-Efficiency Metamaterial Absorber for Capturing Solar Energy.

In this study, we investigated an absorber based on a center-aligned tandem nanopillar array for ultra-broadband solar energy harvesting theoretically. A high-efficiency, omnidirectional absorber was obtained by introducing the center-aligned tandem nanopillar array embedded in an Al2O3 dielectric layer. The multi-coupling modes at different wavelengths were interpreted. The strong absorption can be adjusted by changing the radii and heights of nanopillars. According to the simulation results, the average absorptance of the absorber exceeded 94% in the wavelength range from 300 nm to 2000 nm. In addition, the high-efficiency absorption was insensitive to the incident angle and polarization state. The research not only proposed an absorber which possesses a huge potential value for application areas, such as thermal photovoltaic systems, infrared detection, and isotropic absorption sensors, but also pointed out a new way to design an absorber with high efficiency in an ultrabroad wavelength range.

Investigation and process control of the grating fill-factor and sidewall angle impacts on 2-D metamaterial infrared mirrors

We report the first study of the effects of grating fill-factor variation and sidewall angle on 2-D subwavelength grating shortwave infrared mirrors, and the first development of a geometry compensation approach to correct for the grating fill-factor patterning error caused by EBL proximity effect and a plasma etching process based on CHF3 passivation to control grating sidewall angle. Mirrors with a large grating air-hole diameter-to-pitch ratio of 0.954 and vertical sidewall angle of 89.8° are demonstrated with an average reflectivity of 99% over an ultrabroad wavelength range of 560 nm (1.92-2.48 µm), which represents an unprecedented fractional bandwidth of 26%.

Group-velocity symmetry in photonic crystal fibre for ultra-tunable quantum frequency conversion

Low-noise frequency conversion of single photons is a critical tool in establishing fibre-based quantum networks. We show that a single photonic crystal fibre can achieve frequency conversion by Bragg-scattering four-wave mixing of source photons from an ultra-broad wavelength range by engineering a symmetric group velocity profile. Furthermore, we discuss how pump tuning can mitigate realistic discrepancies in device fabrication. This enables a single highly adaptable frequency conversion interface to link disparate nodes in a quantum network via the telecoms band.

A new type of ultra-broadband microstructured fiber sensor based on surface plasmon resonance

Microstructured fiber (MF) sensors based on surface plasmon resonance (SPR) have been widely investigated because they have many merits including high sensitivity, label-free and real-time detection and so on, thus they possess extensive applications such as in food safety control, environmental monitoring, biomolecular analytes detection, antibody-antigen interaction, liquid detection and many others. However, most of reported SPR-based MF sensors can only work in the visible or near-infrared wavelength region. Hence, the investigation of high-performance mid-infrared SPR-based MF sensors is a challenge task. In this paper, with the aim of overcoming the above limitation, a new type of high-sensitivity SPR-based MF sensor coated with indium tin oxide (ITO) layer is proposed. The proposed sensor can work in both the near-infrared and mid-infrared wavelength region. Benefitting from its two-core and single analyte channel structure, our proposed sensor can effectively eliminate the interference among neighboring analyte channels, improving its signal-to-noise ratio, and achieving high-sensitivity detection in ultra-broadband wavelength range. By using the full-vector finite method with the PML boundary conditions, the sensing properties of our proposed sensor are numerically studied in detail. The numerical results show that the resonance wavelength of the proposed sensor shifts toward a long wavelength region as the refractive index of analyte increases from 1.423 to 1.513, and a similar phenomenon can be found if the thickness of the ITO layer increases from 40 nm to 60 nm. Nevertheless, the wavelength sensitivity of the proposed sensor decreases with the increase of the diameter of the hole located in the fiber core region. On the other hand, when the refractive index of analyte varies in a large range of 1.423–1.513, the proposed sensor can operate in an ultra-broad wavelength range of 1.548–2.796 μm, and the average wavelength sensitivity is as high as 13964 nm/refractive index unit (RIU). Moreover, the maximum wavelength sensitivity and refractive index resolution increase up to 17900 nm/RIU and 5.59 × 10<sup>–7</sup> RIU, respectively. Hence, our proposed SPR-based MF sensor can be applied to environmental monitoring, biomolecular analyte detection and chemical detection.

Compact and broadband multimode waveguide bend by shape-optimizing with transformation optics

Multimode waveguide bend is one of the key components for realizing high-density mode-division multiplexing systems on chip. However, the reported multimode waveguide bends are either large, bandwidth-limited or fabrication-complicated, which hinders their applications in future high-density multimode photonic circuits. Here we propose a compact multimode waveguide bend supporting four TE modes simply by shape-optimizing with transformation optics. The shape of the waveguide is optimized in the virtual space with gradient distribution of the refractive index, so that the scattering loss and intermode cross talk are well suppressed. After conformal mapping back into the physical space, a compact (effective radius of 17 μm) multimode bending waveguide is obtained. Simulations show that the proposed multimode waveguide bend has little loss ( < 0.1 dB ) and low cross talk ( < − 20 dB ) throughout an ultrabroad wavelength range of 1.16–1.66 μm. We also fabricated the shape-optimized multimode bending waveguide on a silicon-on-insulator wafer. At 1550 nm wavelength, the measured excess losses for the four lowest-order TE modes are less than 0.6 dB, and the intermode cross talks are all below − 17 dB . Our study paves the way for realizing high-density and large-scale multimode integrated optical circuits for optical interconnect.

Ultra-broadband and highly sensitive surface plasmon resonance sensor based on four-core photonic crystal fibers

An ultra-broadband surface plasmon resonance (SPR) sensor with high sensitivity adopting four-core photonic crystal fiber is designed. The impacts of fiber structure parameters on the sensing performance are theoretically studied in detail. The investigation results demonstrate that, the average wavelength sensitivity of our proposed sensor is up to 1.135 × 104 nm/refractive index unit (RIU) within the ultra-broad wavelength range of 1.548–2.683 μm when the refractive index (RI) of analyte varies in a large range of 1.423–1.523. Furthermore, the maximum amplitude sensitivity of 550 RIU−1 is achieved if RI changes from 1.423 to 1.433. Therefore, the proposed sensor can work both in the telecommunication window, and the mid-infrared wavelength regime.

Optical Thouless conductance and level-spacing statistics in two-dimensional Anderson localizing systems

We experimentally investigate spectral statistics in Anderson localization in two-dimensional amorphous disordered media. Intensity distributions captured over an ultrabroad wavelength range of $\sim 600$~nm and averaged over numerous configurations provided the Ioffe-Regel parameter to be $\sim2.5$ over the investigated wavelength range. The spectra of the disordered structures provided access to several quasimodes, whose widths and separations allowed to directly estimate the optical Thouless conductance $g_{Th}$, consistently observed to be below unity. The probability distribution of $g_{Th}$ was measured to be a log-normal. Despite being in the Anderson localization regime, the spacings of energy levels of the system was seen to follow a near Wigner-Dyson function. Theoretical calculations based on the tight-binding model, modified to include coupling to a bath, yielded results that were in excellent agreement with experiments. From the model, the level-spacing behavior was attributed to the degree of localization obtained in the optical disordered system.

Graphene Heterostructure Integrated Optical Fiber Bragg Grating for Light Motion Tracking and Ultrabroadband Photodetection from 400 nm to 10.768 µm

AbstractIntegrated photonics and optoelectronics devices based on graphene and related 2D materials are at the core of the future industrial revolution, facilitating compact and flexible nanophotonic devices. Tracking and detecting the motion of broadband light in millimeter to nanometer scale is an unfold science which has not been fully explored. In this work, tracking and detecting the motion of light (millimeter precision) is first demonstrated by integrating graphene with an optical fiber Bragg grating device (graphene‐FBG). When the incident light moves toward and away from the graphene‐FBG device, the Bragg wavelength red‐shifts and blue‐shifts, indicating its light motion tracking ability. Such light tracking capability can be further extended to an ultrabroad wavelength range as all‐optical photodetectors show the robust response from 400 nm to 10.768 µm with a linear optical response. Interestingly, it is found that graphene‐Bi2Te3 heterostructure on FBG shows 87% higher photoresponse than graphene‐FBG at both visible and telecom wavelengths, due to stronger phonon‐electron coupling and photo‐thermal conversion in the heterostructure. The device also shows superior stability even after 100 d. This work may open up amazing integrated nanophotonics applications such as astrophysics, optical communication, optical computing, optical logic gating, spectroscopy, and laser biology.

Universal multimode waveguide crossing based on transformation optics

Mode-division multiplexing is a promising and cost-effective way to increase the communication capability of integrated photonic circuits, for both classical and quantum information processing. To construct large-scale on-chip multimode routing systems, the multimode waveguide crossing is one of the key components. However, there have been only a few dual-mode waveguide crossings reported, which can support merely two waveguide modes or two crossing channels. This severely limits the density and capacity of multimode routing systems. Here we demonstrate for the first time, to the best of our knowledge, a universal multimode waveguide star crossing based on transformation optics, which can handle, in principle, any number of waveguide modes and any number of crossing channels as well. The structure is transformed from a Maxwell fisheye and can realize aberration-free imaging for each waveguide mode. A gray-scale electron-beam lithography is adopted to fabricate it on a commercial silicon-on-insulator wafer. The proposed multimode waveguide star crossing has little loss and low crosstalk throughout an ultra-broad wavelength range of ∼400 nm. Our study paves the way for realizing highly integrated and large capacity on-chip multimode routing and communication systems.

Transmittance and phase matching of BBO crystal in the 3−5 μm range and its application for the characterization of mid-infrared laser pulses

We uncover that thin (of few tens of μm thickness) BBO crystal exhibits reasonable transmittance and phase matching in the 3 − 5.2 μm range. We also provide refined dispersion equations of the ordinary and extraordinary refractive indexes for the 0.188 − 5.2 μm wavelength range, which were derived using an extended set of the refractive index values from direct measurements available in the literature and from indirect refractive index evaluation based on large collection of tuning curves provided by Light Conversion Ltd., and our own measurements of the sum-frequency mixing between the fundamental wavelength of Ti:sapphire laser and wavelength-tunable mid-infrared pulses. In particular, the uncovered mid-infrared features of BBO were exploited for the characterization of the ultrashort laser pulses at 4 μm and over an ultrabroad wavelength range, demonstrating simultaneous sum-frequency generation-based frequency-resolved optical gating of the signal and idler pulses from an optical parametric amplifier, and difference frequency pulse with central wavelengths of 1.3, 2.1 and 3.5 μm, respectively, using BBO crystal of 20 μm thickness.

Ultra-broadband and low-loss 3 dB optical power splitter based on adiabatic tapered silicon waveguides.

A broadband, low-loss and polarization-insensitive 3 dB optical power splitter based on adiabatic tapered silicon waveguides is proposed and investigated. 3D-FDTD simulation results show that the splitter achieves an output transmission efficiency of nearly 50% over an ultra-broad wavelength range from 1200 to 1700 nm. The device is fabricated, and experimental results show that the splitter exhibits a low excess loss of <0.19 dB for the TE polarization and <0.14 dB for the TM polarization over the entire measured wavelength range from 1530 to 1600 nm, while having an adiabatic taper length of only 5 μm. In addition, the measured power uniformity of the cascaded 1×8 splitter is only 0.47 dB, and 0.17 dB for the TE and TM polarizations, respectively. With the advantages of low loss, broad bandwidth, and compact size, the proposed splitter is a promising element for large-scale silicon integrated photonic circuits.

Ultrabroadband Silicon-on-Insulator Polarization Beam Splitter Based on Cascaded Mode-Sorting Asymmetric Y-Junctions

A very novel silicon-on-insulator polarization beam splitter is proposed based on cascaded mode-sorting asymmetric Y-junctions. The width and length of each Y-junction are optimized to achieve correct mode sorting with high conversion efficiency. The numerical simulation results show that the mode conversion efficiency increases with the length of the Y-junction for the waveguide widths varying in a large range. This proposed device has $ 0.7 dB insertion loss with $>$ 22 dB polarization extinction ratio in an ultrabroad wavelength range from 1450 to 1750 nm. Fabrication tolerance analysis is also performed with respect to the deviation in device width and height. With such a broad operating bandwidth and robust fabrication tolerance, this device offers potential applications for complementary metal oxide semiconductor (CMOS)-compatible polarization diversity operating across the S, C, L, and U optical communication bands, particularly in the booming 100-Gb/s coherent optical communications based on silicon photonics technology.

Novel ultra-broadband polarization splitter-rotator based on mode-evolution tapers and a mode-sorting asymmetric Y-junction.

A novel silicon-on-insulator (SOI) polarization splitter-rotator is proposed based on mode-evolution tapers and a mode-sorting asymmetric Y-junction. The tapers are designed to adiabatically convert the input TM0 mode into the TE1 mode, which will evolve into the TE0 mode in the wide output arm while the input TE0 mode excites the TE0 mode in the narrow arm. The numerical simulation results show that the mode conversion efficiency increases with the lengths of the tapers and the Y-junction for the output waveguide widths in a large range. This proposed device has < 0.4 dB insertion loss with > 12 dB extinction ratio in an ultra-broad wavelength range from 1350 nm to 1750 nm. With such a broad operating bandwidth, this device offers potential applications for polarization diversity operating across every communication bands. Fabrication tolerance analysis is also performed in terms of the device width variation, the slab height variation and the variation of the upper-cladding refractive index.

Ultra-broadband wide-angle unidirectional plasmonic coupler based on joint effects of plasmonic critical angles and subwavelength metallic gratings.

A unidirectional plasmonic coupler with ultra-broadband and wide-angle coupling efficiency is proposed and demonstrated. Employing the plasmonic critical angle (PCA) phenomenon in conjunction with the effect of subwavelength metallic gratings, a wide incident angular full-width-half-maximum (AFWHM >28°) coupling efficiency larger than 50% and extinction ratio better than 15dB over an ultrabroad wavelength range 725-985nm (bandwidth >260 nm) are achieved. The operation principle and performance of the structure are clarified and theoretically illustrated.

Ultrawide‐Band Unidirectional Surface Plasmon Polariton Launchers

Plasmonic devices and circuits, bridging the gap between integrated photonic and microelectronic technology, are promising candidates to realize on-chip ultrawide-band and ultrahigh-speed information processing. Unfortunately, the wideband surface plasmon source, one of the most important core components of integrated plasmonic circuits, is still unavailable up to now. This has seriously restricted the practical applications of plasmonic circuits. Here, we report an ultrawide-band unidirectional surface plasmon polariton launcher with high launching efficiency ratio and large extinction ratio, realized by combining plasmonic bandgap engineering and linear interference effect. This device offers excellent performances over an ultrabroad wavelength range from 690 to 900 nm, together with a high average launching efficiency ratio of 1.25, large average extinction ratio of 30 dB, and ultracompact lateral dimension of less than 4 um. Compared with previous reports, the operating bandwidth is enlarged 210 folds, while the largest launching efficiency ratio, largest extinction ratio, and small feature size are maintained simultaneously. This provides a strategy for constructing on-chip surface plasmon source, and also paving the way for the study of integrated plasmonic circuits.

High birefringence low-dispersion of nonlinear photonic crystal fiber

The paper presents a theoretical design of high nonlinear photonic crystal fiber (PCF) with high birefringence and low dispersion. Its birefringence, dispersion and nonlinear coefficient are investigated simultaneously by using the full vectorial finite element method with anisotropic perfectly matched layers. Numerical results show that the proposed highly nonlinear low-dispersion fiber has a total dispersion as low as ±12.6pskm−1nm−1 over ultrabroad wavelength range from 1.21 to 1.61μm, and the corresponding birefringence and nonlinear coefficient are about 2.1×10−3 and 28W−1km−1 at 1.55μm, respectively. The proposed PCF with high birefringence, low dispersion and high nonlinearity can have important application in supercontinuum (SC) generation, dispersion compensation, wavelength (frequency) converter, polarization maintaining transmission and Raman amplifier.

Design and optimization of highly nonlinear low-dispersion crystal fiber with high birefringence for four-wave mixing

We have proposed a novel type of photonic crystal fiber (PCF) with low dispersion and high nonlinearity for four-wave mixing. This type of fiber is composed of a solid silica core and a cladding with a squeezed hexagonal lattice elliptical airhole along the fiber length. Its dispersion and nonlinearity coefficient are investigated simultaneously by using the full vectorial finite element method. Numerical results show that the proposed highly nonlinear low-dispersion fiber has a total dispersion as low as +/-2.5 ps nm(-1) km(-1) over an ultrabroad wavelength range from 1.43 to 1.8 microm, and the corresponding nonlinearity coefficient and birefringence are about 150 W(-1) km(-1) and 2.5x10(-3) at 1.55 microm, respectively. The proposed PCF with low ultraflattened dispersion, high nonlinearity, and high birefringence can have important application in four-wave mixing.