scispace - formally typeset
Search or ask a question

Showing papers in "IEEE Journal of Selected Topics in Quantum Electronics in 2017"


Journal ArticleDOI
TL;DR: In this article, the current state in the field of laser-induced periodic surface structures (LIPSS) is reviewed, and the formation mechanisms are analyzed in ultrafast time-resolved scattering, diffraction, and polarization constrained double-pulse experiments.
Abstract: Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon and can be generated on almost any material upon irradiation with linearly polarized radiation. With the availability of ultrashort laser pulses, LIPSS have gained an increasing attraction during the past decade, since these structures can be generated in a simple single-step process, which allows a surface nanostructuring for tailoring optical, mechanical, and chemical surface properties. In this study, the current state in the field of LIPSS is reviewed. Their formation mechanisms are analyzed in ultrafast time-resolved scattering, diffraction, and polarization constrained double-pulse experiments. These experiments allow us to address the question whether the LIPSS are seeded via ultrafast energy deposition mechanisms acting during the absorption of optical radiation or via self-organization after the irradiation process. Relevant control parameters of LIPSS are identified, and technological applications featuring surface functionalization in the fields of optics, fluidics, medicine, and tribology are discussed.

607 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the color gamut difference between the commonly used Gaussian fitting method and that using real emission spectra and investigated the Helmholtz-Kohlrausch effect.
Abstract: We review recent advances in quantum dot (QD)- enhanced liquid crystal displays (LCDs), including material formulation, device configuration, and system integration. For the LCD system, we first compare the color gamut difference between the commonly used Gaussian fitting method and that using real emission spectra. Next, we investigate the Helmholtz–Kohlrausch effect. Our simulation results indicate that QD-enhanced LCD appears 1.26X more efficient than organic light-emitting diode (OLED) display due to its wider color gamut. Finally, two new trends for QD-LCDs are discussed: 1) replacing conventional color filters with a QD array, and 2) emerging quantum rod (QR)-enhanced backlight. Their inherent advantages, technical challenges, and potential solutions are presented. We believe the prime time for QD-enhanced LCDs is around the corner.

149 citations


Journal ArticleDOI
Ben-Xin Wang1
TL;DR: In this paper, a new type of quad-band terahertz metamaterial absorber based on a common sandwich structure is investigated, which enables near-unity absorption in four distinct peaks by utilizing the dipole and quadrupole resonances of the patterns.
Abstract: A new type of quad-band terahertz metamaterial absorber based on a common sandwich structure is investigated. In sharp contrast to the most previous studies focused on only combining of fundamental resonance (or LC resonance) of the metamaterial structure to obtain the quad-band response, we directly enable near-unity absorption in four distinct peaks by utilizing the dipole and quadrupole resonances of the patterns. The design also has the ability to tune the frequencies of the absorption peaks by merely changing the angle of polarization. The proposed platform has potential application perspectives in imaging, sensing, and detection.

145 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the generation of mode-locked pulses from a double-clad ytterbium-doped fiber laser employing a saturable absorber (SA) made of a few layers of black phosphorus (BP).
Abstract: We demonstrate the generation of mode-locked pulses from a double-clad ytterbium-doped fiber laser (YDFL) employing a saturable absorber (SA) made of a few layers of black phosphorus (BP). The BP SA was prepared by mechanically exfoliating BP crystal and spreading the acquired BP flakes on a piece of scotch tape. The tape was then sandwiched between two ferrules and incorporated in a YDFL cavity to achieve a stable mode-locked operation at 1085.58 nm with a repetition rate of 13.5 MHz. A maximum pulse energy of 5.93 nJ was obtained at pump power of 1322 mW with the output power of 80 mW. Our study may well be the first demonstration of the BP-based mode-locked fiber laser that should shed some new insights into two-dimensional layer materials related photonics.

91 citations


Journal ArticleDOI
TL;DR: In this article, a review and discussion of the applications of microwave photonic techniques and functionalities to the field of optical fiber sensors is presented and a specific end-to-end model for its characterization is presented.
Abstract: This paper presents a review and discussion of the applications of microwave photonic techniques and functionalities to the field of optical fiber sensors. A specific end-to end model for its characterization is presented here for the first time that yields the sensitivity of the different figures of merit in terms of measured variations. Experimental techniques to characterize these systems are presented and applications of two specific microwave photonic functionalities to high-resolution discrete and quasidistributed optical sensing are illustrated. Future directions of research are also highlighted.

90 citations


Journal ArticleDOI
TL;DR: In this paper, a modulated photonic-crystal surface-emitting laser (M-PCSEL) is proposed to realize both lasing oscillation and on demand, beam diffraction for any two-dimensional direction in free space without the need for external elements.
Abstract: Photonic-crystal surface-emitting lasers (PCSELs) have attracted much attention for their unrivaled capabilities, such as broad area, coherent resonance, tailored beam patterns, and beam steering. In this paper, we first review the progress of PCSELs, then introduce a novel concept of modulated photonic-crystal surface-emitting lasers (M-PCSELs) for realizing both lasing oscillation and on demand, beam diffraction for any two-dimensional direction in free space without the need for external elements. This unique concept paves the way toward the development of semiconductor lasers with completely controllable beams.

89 citations


Journal ArticleDOI
TL;DR: The penetration depth has been enhanced sufficiently to observe cancer lesions deep inside tissues by using freezing and penetration-enhancing agents; the biochemical modification of DNA can be utilized to track the resonance fingerprints of carcinogenesis at the genomic DNA level; and nanoparticles can increase the THz imaging contrast if they are employed similarly to how they are used in magnetic resonance imaging.
Abstract: Cancer imaging using terahertz (THz) electromagnetic waves has the potential to overcome the drawbacks of existing cancer imaging techniques because of the unique properties of THz radiation. It is nonionizing, highly sensitive to water molecules, and suitable for the observation of many biomolecular characteristics based on low-energy vibrational modes. Consequently, it is advantageous to use THz cancer imaging for detection, especially of superficial carcinomas in soft tissues. However, there are three primary challenges facing this type of cancer imaging that must be addressed before it can be applied medically: the limited penetration depth in hydrated tissues, the difficulty of obtaining molecular resonance fingerprints of cancers, and the low image contrast between tissues. These challenges can be overcome by applying several state-of-the-art techniques; the penetration depth has been enhanced sufficiently to observe cancer lesions deep inside tissues by using freezing and penetration-enhancing agents: the biochemical modification of DNA can be utilized to track the resonance fingerprints of carcinogenesis at the genomic DNA level; and nanoparticles can increase the THz imaging contrast if they are employed similarly to how they are used in magnetic resonance imaging. These solutions are important to enable THz cancer imaging to be performed in clinical settings.

85 citations


Journal ArticleDOI
TL;DR: In this paper, the Pancharatnam-Berry phase approach was used for the realization of high performance planar lenses (metalenses) in the visible spectrum, which have efficiencies as high as 86% and provide high imaging resolution.
Abstract: We present recent advances in metasurface-based photonics, which enables the realization of high performance planar lenses (metalenses) in the visible spectrum. They are enabled by a technique based on atomic layer deposition of titanium dioxide allowing for the fabrication of nanostructures with high fidelity. First, we demonstrate highly efficient metalenses with numerical aperture ${\rm{NA\,= \,0.8}}$ using the Pancharatnam-Berry phase approach. These metalenses can focus light into a diffraction-limited spot. They have efficiencies as high as 86% and provide high imaging resolution. Furthermore, by judicious design of the phase-shifting elements, we achieve a multispectral chiral metalens realized with a single metasurface layer. This chiral metalens can resolve both the chiral and spectral information of an object without the requirement of any additional optical components. Finally, we discuss the experimental realization of polarization-insensitive metalenses with NAs as high as 0.85. They are able to focus incident light to a spot as small as ∼0.64 λ with efficiencies up to 60%. Due to its straightforward and CMOS-compatible fabrication, this platform is promising for a wide range of applications ranging from camera modules, displays, laser-based imaging, microscopy, and spectroscopy to laser fabrication and lithography.

84 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that the modal confinement and hence the modulation strength of a single-layer modulated 2D material in a plasmonically confined mode is able to improve by more than 10× compared to diffraction-limited modes.
Abstract: The ability to modulate light using 2-dimensional (2D) materials is fundamentally challenged by their small optical cross-section leading to miniscule modal confinements in diffraction-limited photonics despite intrinsically high electro-optic absorption modulation (EAM) potential given by their strong exciton binding energies. However the inherent polarization anisotropy in 2D materials and device tradeoffs lead to additional requirements with respect to electric field directions and modal confinement. A detailed relationship between modal confinement factor and obtainable modulation strength including definitions on bounding limits are outstanding. Here, we show that the modal confinement factor is a key parameter determining both the modulation strength and the modulator extinction ratio-to-insertion loss metric. We show that the modal confinement and hence the modulation strength of a single-layer modulated 2D material in a plasmonically confined mode is able to improve by more than 10× compared to diffraction-limited modes. Combined with the strong-index modulation of graphene, the modulation strength can be more than 2-orders of magnitude higher compared to Silicon-based EAMs. Furthermore, modal confinement was found to be synergistic with performance optimization via enhanced light-matter-interactions. These results show that there is room for scaling 2D-material EAMs with respect to modal engineering toward realizing synergistic designs leading to high-performance modulators.

84 citations


Journal ArticleDOI
TL;DR: In this paper, the design and fabrication of terahertz (THz) metamaterial (MM) absorbers and their monolithic integration into a commercial CMOS technology along with its respective readout electronics to produce a low-cost, uncooled, and high resolution THz camera are presented.
Abstract: We present the design and fabrication of terahertz (THz) metamaterial (MM) absorbers and their monolithic integration into a commercial CMOS technology along with its respective readout electronics to produce a low-cost, uncooled, and high resolution THz camera. We first describe the work done on single band and broadband MM absorbers on custom substrates, then progress with a description of the integration of such resonators into a six metal layer 180 nm CMOS process and its coupling with two types of microbolometer sensors: Vanadium oxide (VOx) and silicon (Si) pn diode. Additionally, we demonstrate the integration of the THz sensors with readout electronics to form a monolithic THz focal plane array (FPA). Reflection images of a metallic object hidden in a manila envelope are recorded using both the VOx and Si pn diode detectors, demonstrating the suitability of the technology for stand-off detection of concealed objects. Finally, we present the current work toward scaling this technology into a 64 × 64 FPA.

80 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical description of the third-order response induced by an elliptically-polarized terahertz beam normally-incident on intrinsic and extrinsic metallic armchair graphene nanoribbons is presented.
Abstract: We present a theoretical description of the third-order response induced by an elliptically-polarized terahertz beam normally-incident on intrinsic and extrinsic metallic armchair graphene nanoribbons. Our results show that using a straightforward experimental setup, it should be possible to observe novel polarization-dependent nonlinearities at low excitation field strengths of the order of ${\text{10}}^4 \; \text{V/m}$ . At low temperatures the Kerr nonlinearities in extrinsic nanoribbons persist to significantly higher excitation frequencies than they do for linear polarizations, and at room temperatures, the third-harmonic nonlinearities are enhanced by $2\hbox{--}3$ orders of magnitude. Finally, the Fermi-level and temperature dependence of the nonlinear response is characterized.

Journal ArticleDOI
TL;DR: In this article, the necessary conditions of forming non-reciprocal transmission in magneto-optical microstructure devices were concluded, and the tunability of these devices was also analyzed, which strongly depends on the magnetooptical property of material and the symmetry of structure.
Abstract: Recent research work on magneto-optical micro- structure devices in terahertz (THz) regime has been reviewed. Some magneto-optical materials responding at THz frequency range were introduced. Based on these magneto-optical materials, MO microstructures devices were reviewed, including magnetic photonic crystals, magneto-plasmonics, and magneto-metasurface all in the submillimetre scale. These devices can realize several functions of isolating, modulation, sensing, and directional beam scanning. Moreover, the necessary conditions of forming THz nonreciprocal transmission in magneto-optical microstructure devices were concluded, and the tunability of these devices was also analysed, which strongly depends on the magneto-optical property of material and the symmetry of structure. The unique magneto-optical effects make it play an irreplaceable role in the high performance THz applications of communication, imaging, and sensing systems.

Journal ArticleDOI
TL;DR: In this article, the authors report experimentally and in theory on the controllable propagation of spiking regimes between two interlinked vertical-cavity surface-emitting lasers (VCSELs).
Abstract: We report experimentally and in theory on the controllable propagation of spiking regimes between two interlinked vertical-cavity surface-emitting lasers (VCSELs). We show that spiking patterns generated in a first transmitter VCSEL (T-VCSEL) are communicated to a second receiver VCSEL (R-VCSEL), which responds by firing the same spiking response. Importantly, the spiking regimes from both devices had analogous temporal and amplitude characteristics, including equal number of spikes fired, same spike and interspike temporal durations, and similar spike intensity properties. These responses are analogous to the spiking communication patterns of biological neurons yet at subnanosecond speeds, this is several (up to 8) orders of magnitude faster than the timescales of biological neurons. We have also carried out numerical simulations reproducing with high degree of agreement the experimental findings. These results obtained with inexpensive, commercially available VCSELs operating at important telecom wavelengths (1300 nm) offer great prospects for the scaling of emerging VCSEL-based photonic neuronal models into network configurations for use in novel neuromorphic photonic systems. This offers high potentials for nontraditional computing paradigms beyond digital systems and able to operate at ultrafast speeds.

Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the progress regarding the optical, transport, and photodetection properties of thin film based on colloidal nanoparticles, and the three different ways by which infrared resonances have been realized with colloidal nano-nodes: interband absorption with small gap semiconductor quantum dots, intraband absorption in lightly doped quantum dots and plasmonic resonances in heavily doped nanocrystals.
Abstract: Over the past few years, colloidal nanoparticles have started to be investigated for their optical properties in the mid-infrared, past 3 μ m. Research on detector application has led to background limited detection and fast video imaging at 5 μ m. With further development, one could imagine that these new materials could vastly reduce the costs of infrared technology and this would lead to a trove of new applications for infrared imaging into our daily lives. This paper reviews the progress regarding the optical, transport, and photodetection properties of thin film based on these materials, and the three different ways by which infrared resonances have been realized with colloidal nanoparticles: interband absorption with small gap semiconductor quantum dots, intraband absorption in lightly doped quantum dots, and plasmonic resonances in heavily doped nanocrystals.

Journal ArticleDOI
TL;DR: In this article, the authors leverage strong optical and thermal confinement in judiciously designed microcavities to circumvent the thermal diffusion and optical diffraction limits in conventional photothermal sensors and achieve parts-per-billion level gas molecule limit of detection.
Abstract: Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical analysis. Recent strides in photonic integration technologies offer a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. Here we show that simple size scaling by replacing bulky discrete optical elements used in conventional IR spectroscopy with their on-chip counterparts is not a viable route for on-chip infrared spectroscopic sensing, as it cripples the system performance due to the limited optical path length accessible on a chip. In this context, we discuss two novel photonic sensor designs uniquely suited for microphotonic integration. We leverage strong optical and thermal confinement in judiciously designed microcavities to circumvent the thermal diffusion and optical diffraction limits in conventional photothermal sensors and achieve parts-per-billion level gas molecule limit of detection. In the second example, an on-chip spectrometer design with Fellgett's advantage is proposed for the first time. The design enables sub-nm spectral resolution on a millimeter-sized, fully packaged chip without mechanical moving parts.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that the sensitivity can be significantly enhanced by a factor of 19 reaching a value of 5.7 × 105 nm/RIU/unit-volume when selected spots are covered with the analyte.
Abstract: Metamaterials that can support ultrasharp resonances using conductively coupled split ring resonators are potential candidates for designing label-free biomedical sensors. The sharp spectral response, as well as the ability to confine the field, increases the interaction between the electromagnetic field and unidentified analytes. A sensitivity level of 3 × 104 nm/RIU/unit-volume is achieved when the whole area of the sensor is covered with the analyte. More interestingly, we demonstrate that the sensitivity can be significantly enhanced by a factor of 19 reaching a value of 5.7 × 105 nm/RIU/unit-volume when selected spots are covered with the analyte. These results will pave the way for designing practical biomedical sensors in the terahertz frequency range.

Journal ArticleDOI
TL;DR: In this article, the authors compare four representative hybrid graphene-waveguide configurations, focusing on optimizing their dimensions, the gate-oxide thickness, the polarization, the operating wavelength, and contact definition.
Abstract: The optoelectronic properties of graphene attracted a lot of interest in recent years. Several demonstrations of integrated graphene based modulators, switches, detectors, and nonlinear devices have been reported. We present here a comprehensive study investigating the different design tradeoffs involved in realizing, in particular, graphene-based modulators and switches. We compare four representative hybrid graphene-waveguide configurations, focusing on optimizing their dimensions, the gate-oxide thickness, the polarization, the operating wavelength, and contact definition. We study both static and dynamic behavior, defining a relevant figure of merit. We find that a 20-μm device based on silicon waveguides should allow for 25-GBit/s modulation rate and an extinction ratio of 5 dB. A 200-μm long SiN device on the other hand should allow for 23-dB extinction ratio and switching speeds down to 0.4 ns.

Journal ArticleDOI
TL;DR: In this paper, the evolution of QDs, as well as improved device performances for novel application fields are discussed, where the authors discuss the use of QD lasers for resource searching by utilizing high-temperature operation such as lasing at higher than 200°C.
Abstract: The device characteristics of semiconductor lasers have been improved with progress in active layer structures. Carrier confinement dimension plays an important role especially in temperature sensitivity as well as slope efficiency. Three-dimensional carrier confinement to nano-scale semiconductor crystal, known as “quantum dots (QDs)” had been predicted to show ultimately superior device performances. Self-assembly formed InAs QDs grown on GaAs had been intensively promoted in order to achieve QD lasers with superior device performances. Now high-density, high-optical quality QDs have been realized through improved molecular beam epitaxy growths and QD lasers with better temperature characteristics are in the stage of mass-production for a data-com market. Fabry–Perot type, as well as distributed feedback type QD lasers show quite improved laser characteristics. Also, the unique device characteristics of QD lasers opened new application fields such as the use for resource searching by utilizing high-temperature operation such as lasing at higher than 200 °C. For silicon-photonics, QD lasers are used as an optical source for athermal operation. In this paper, the evolution of QDs, as well as improved device performances for novel application fields are discussed.

Journal ArticleDOI
TL;DR: In this article, the scattering and absorption of the H and E-polarized plane waves by an infinite flat graphene strip grating placed in a dielectric slab, in the THz range, were considered.
Abstract: We considered the scattering and absorption of the H and E-polarized plane waves by an infinite flat graphene strip grating placed in a dielectric slab, in the THz range. Accurate numerical treatment was based on the singular integral equations and their projection to specially tailored orthogonal polynomials. The resulting numerical algorithm possessed guaranteed convergence and provided controlled accuracy. Reflectance, transmittance, and absorbance were studied, and the resonances on the surface-plasmon modes, the grating modes, and the slab modes were identified. The grating or lattice modes are caused by the periodicity. Their complex frequencies are extremely close to Rayleigh anomalies and therefore the Q-factors are extraordinarily high, which makes them promising in various applications.

Journal ArticleDOI
TL;DR: In this article, a nanostructured metal-insulator-metal metamaterial (NMIM2) was constructed by electron beam lithography and the liftoff technique.
Abstract: Nanofabrication of nanostructured metal–insulator–metal metamaterial (NMIM2) by the electron beam lithography and the liftoff technique is reported in this paper. The NMIM2 consists of periodic arrays of gold (Au) nanotriangles deposited on a gold layer (acting as a mirror) separated by a thin dielectric insulator. Such an NMIM2 stack was fabricated on a silicon wafer. Reflection of the NMIM2 was measured by the Fourier transform infrared spectroscope. The experimental measurement for reflection coefficients are in good agreement with the full-wave finite-different time-domain simulation results. At resonance, we numerically observed a strong field localized inside the gap between the Au nanostructures and the Au mirror, resulting in a strong confinement of incoming light within the insulator spacer and, thus, a pronounced absorption at telecommunication wavelengths. This resonant spectral response is investigated for sensitive label-free refractive index biosensing applications.

Journal ArticleDOI
TL;DR: In this paper, the first electrically pumped continuous-wave (c.w.) InAs/GaAs QD laser was fabricated on on-axis GaAs/Si (001) substrates without any intermediate buffer layers.
Abstract: In this paper, we report monolithically integrated III-V quantum dot (QD) light-emitting sources on silicon substrates for silicon photonics. We describe the first practical InAs/GaAs QD lasers monolithically grown on an offcut silicon (001) substrate due to the realization of high quality III-V epilayers on silicon with low defect density, indicating that the large material dissimilarity between III-Vs and silicon is no longer a fundamental barrier limiting monolithic growth of III-V lasers on Si substrates. Although the use of offcut silicon substrates overcomes the antiphase boundary (APB) problem, it has the disadvantage of not being readily compatible with standard microelectronics fabrication, where wafers with on-axis silicon (001) substrates are used. We therefore report, to the best of our knowledge, the first electrically pumped continuous-wave (c.w.) InAs/GaAs QD lasers fabricated on on-axis GaAs/Si (001) substrates without any intermediate buffer layers. Based on the achievements described above, we move on to report the first study of post-fabrication and prototyping of various Si-based light emitting sources by utilizing the focused ion beam (FIB) technique, with the intention of expediting the progress toward large-scale and low-cost photonic integrated circuits monolithically integrated on a silicon platform. We compare two Si-based QD lasers with as-cleaved and FIB-made facets, and prove that FIB is a powerful tool to fabricate integrated lasers on silicon substrates. Using angled facet structures, which effectively reduce facet reflectivity, we demonstrate Si-based InAs/GaAs QD superluminescent light emitting diodes (SLDs) operating under c.w. conditions at room temperature for the first time. The work described represents significant advances towards the realization of a comprehensive silicon photonics technology.

Journal ArticleDOI
TL;DR: In this paper, van der Waals heterostructures with clean, atomically sharp interfaces have been used for solar energy harvesting, and the observed electrical and photovoltaic properties are analyzed.
Abstract: The peculiar nature of light-matter interaction in atomically thin transition metal dichalcogenides is recently under examination for application in novel optoelectronic devices. Here, we show that heterostructures composed of two or more such layers can be used for solar energy harvesting. The strong absorption in these atomically thin layers makes it possible to achieve an efficient power conversion with a minimal amount of active material. We describe in detail two different fabrication techniques that allow to realize heterostructures with clean, atomically sharp interfaces. The observed electrical and photovoltaic properties are analyzed. Our findings suggest that, accompanied by the advances in large area fabrication of atomically thin transition metal dichalcogenides, van der Waals heterostructures are promising candidates for a new generation of excitonic solar cells.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the potential for 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the fundamental material challenges for the fabrication of photonic and opto-electronic devices in the mid-infrared are discussed, and an approach for development, characterization, and integration of numerous photonic components for the spectral range λ = 4-6 μm is presented.
Abstract: Photonics has been extensively exploited in the visible and near-infrared spectral ranges. Sensing of liquids and gases is a promising area for advancing of the photonics also in the mid-infrared spectral range (MIR). Of particular interest is the realization of Si-based MIR devices and their integration on a single chip. In this paper, the fundamental material challenges for the fabrication of photonic and opto-electronic devices in the mid-infrared are discussed. An approach for development, characterization, and integration of numerous photonic components for the spectral range λ = 4–6 μm is presented. Using Si, SiOx, and Si3N 4 as a material base, it is illustrated that fully Si-compatible active and passive devices are possible, which can be readily integrated onto a silicon chip. Finally, a compact mathematical model is provided for evanescent sensing of fluids with rib and photonic crystal waveguides.

Journal ArticleDOI
TL;DR: The design of such terahertz imaging systems from a general point of view is addressed with the focus on the design of sparse line arrays, while considering objects scattering properties, and the realization of a novel highly sparse 3D teraHertz imaging system is discussed.
Abstract: Many established terahertz imaging modalities are on one side restricted by the tradeoff between resolution and field of view such as in the case of focal plane arrays and on the other side suffer from a limited depth of field such as in the case of quasi-optical terahertz imaging configurations. Furthermore, typical scanning solutions require time-consuming measurement procedures and restrict significant potential industrial deployments of terahertz imaging technology. Imaging with sparse multistatic line arrays in combination with digital beam forming (DBF) techniques enables us to overcome these limitations and offer three-dimensional (3D) terahertz image reconstructions of the object. This contribution addresses the design of such terahertz imaging systems from a general point of view with the focus on the design of sparse line arrays, while considering objects scattering properties. Based on this design concept, the realization of a novel highly sparse 3D terahertz imaging system is discussed. The sparse line array of the system is operating within a frequency range from 75 to 110 GHz and is used in combination with a conveyor in order to generate a synthetic sampling aperture. The system is capable to generate 3D terahertz images with tens of megavoxels at feed motions of up to a few 10 cm/s. Also, a sparse array design in regard to an imaging system operating at 240 GHz with integrated SiGe sensor elements is discussed. In addition, three different DBF algorithms are compared in regard to their computational efficiency.

Journal ArticleDOI
TL;DR: In this article, the authors review various structures and recent progress of MEMS-VCSELs and summarize some of the early breakthroughs in designs and properties of micromechanical tunable VCSEL, including advances in HCG/HCM-based MEMS, which emit at 850, 1060, and 1550 nm wavelength regimes.
Abstract: The ability to continuously tune the wavelength of a laser is of critical importance and is a fundamental building block for many optical systems, including wavelength division multiplexed optical fiber communication systems. Vertical cavity surface emitting laser (VCSEL) structure offers a unique advantage to engineer the lasing wavelength because of its ultrashort cavity length, inherently supporting a single Fabry–Perot mode. Hence, a continuous change in VCSEL cavity thickness leads to a continuous sweep of VCSEL wavelength. Wavelength-tunable VCSELs have been a subject of intense interest for the last two decades. Incorporating part or entire top mirror of a VCSEL in an optical microelectromechanical structure (MEMS), continuous wavelength sweeps have been reported. The monolithic integration brings together the best of both technologies and leads to an unprecedented performance in the continuously swept wavelength range. In addition, with the advances of ultrathin high contrast gratings and metastructures (HCG/HCM), the wavelength tuning speed of MEMS-VCSELs has been increased to 1–10 MHz range. Such lasers, now referred as wavelength-swept lasers, are enabling new applications in optical coherent tomography and light detection and ranging systems. In this paper, we review various structures and recent progress of MEMS-VCSELs. We summarize some of the early breakthroughs in designs and properties of micromechanical tunable VCSELs, including advances in HCG/HCM-based MEMS-VCSELs emitting at 850, 1060, and 1550 nm wavelength regimes. In addition, we report a brand new design leading to a record high Δλ/λo = 6.9% tuning ratio with 600 kHz speed at center wavelength of 1060 nm.

Journal ArticleDOI
TL;DR: In this article, the femtosecond fundamental and harmonic mode-locked Er-doped fiber laser with WS2 solution saturable absorber (SSA) is presented.
Abstract: This study presents the femtosecond fundamental and harmonic mode-locked Er-doped fiber laser with WS2 solution saturable absorber (SSA). The SA is fabricated based on a D-shaped fiber (DF) embedded in WS2 nanosheets solution. Such WS2 solution has virtues of good antioxidant capacity, excellent scattering resistance, high heat dissipation, and high damage threshold. This kind of SA shows a modulation depth of 11%, a saturable intensity ${\rm I_{sat}}$ of 5 MW/cm2, and nonsaturable loss of 18%. By employing DF-WS2 SSA, a stable mode-locked fiber laser is achieved with repetition rate of 10.2 MHz and pulse duration of 660 fs. At the pump power of 350 mW, 460.7-MHz repetition rate harmonic mode-locking (HML) operation is also obtained, which corresponds to 45th harmonics of the fundamental cavity repetition rate. The pulse duration is 710 fs and signal-to-noise ratio is 66 dB, showing the excellent performance in HML fiber laser with SA. The results indicate that DF-WS2 solution can work as a potential SA for ultrafast nonlinear optics.

Journal ArticleDOI
TL;DR: In this article, a low-cost, flexible, and highly efficient wheel polishing technique for the fabrication of side-polished single mode-multimode-single mode fiber (SP-SMSF) is presented.
Abstract: This paper presents a low-cost, flexible, and highly efficient wheel polishing techniques for the fabrication of side-polished single mode-multimode-single mode fiber (SP-SMSF). The evolution of transmission spectrum of SP-SMSF is measured, simulated, and discussed. The good linear relationship between polished depth (PD) and polish-induced loss has relatively high linear correlation at 95%, allowing us to monitor and control the critical parameter PD in line and in real time. Several desirable SP-SMSF with ${\rm{PD\,= \,9.6\,}}$ , 15, 20.6 μm were fabricated successfully. Their characteristics of refractive index (RI) sensing are investigated experimentally. The results show that SP-SMS sensitivity increases as RI increases, approaching its maximum when the latter gets close to its core. The maximum sensitivity of the SP-SMSF with ${\rm{PD\,= \,20.6\; \mu m}}$ is ${\rm{1190\; nm/ RIU}}$ , comparable to that of chemically etched SMSF. The dependence of the sensitivity on the PD of SP-SMSF is also measured and discussed, showing that an increase in PD can improve the sensitivity of SP-SMSF. In addition, such novel structure of SP-SMSF will provide a flat platform to implement various fiber devices.

Journal ArticleDOI
TL;DR: In this article, a frequency-selective surface filter (FSS) for terahertz (THz) applications is proposed and investigated both numerically and experimentally, and the effect of the filter's geometrical parameters on its performance is systematically studied via finite-element method simulation and confirmed by time-domain spectroscopy characterization of the fabricated samples.
Abstract: A new class of frequency-selective surface filters (FSS) for terahertz (THz) applications is proposed and investigated both numerically and experimentally. A periodic FSS array of cross-shaped apertures is patterned on aluminum, deposited on thin foils of the low-loss cyclo-olefin polymer Zeonor. Apart from the fundamental filtering response of the FSS elements, we also observe very narrow-linewidth peaks with high transmittance, associated with guided-mode resonances in the dielectric substrate. The effect of the filter's geometrical parameters on its performance is systematically studied via finite-element method simulation and confirmed by time-domain spectroscopy characterization of the fabricated samples. Finally, thanks to the flexibility of the employed substrates, THz-FSS filters are also characterized in bent configuration, revealing a robust response in terms of the fundamental FSS passband filter and a high sensitivity of the GMR peaks. These features can be exploited in the design of novel THz filters or sensors.

Journal ArticleDOI
TL;DR: This paper covers the recent work on terahertz reflectarray antennas, providing a broad, critical perspective, and contrasting different approaches, based on two different classes of terAhertz resonator.
Abstract: This paper covers our recent work on terahertz reflectarray antennas, providing a broad, critical perspective, and contrasting different approaches. The reflectarray antenna is a well-established device that offers significant control and freedom over the directionality and characteristics of its radiation pattern. Such a capability is critical to the successful development of commercially viable terahertz technologies. In this paper, the design, fabrication, and experimental characterization of four terahertz reflectarray devices is presented, based on two different classes of terahertz resonator. The first class is the metallic resonator, and three such reflectarray devices are presented, with each offering its own particular birefringent behavior. The second class is the dielectric resonator, which promises higher efficiency than the metallic resonator, and one such reflectarray device is presented. Devices such as these provide significant design freedom for defining particular beam-shaping operations for diverse application requirements. It is hoped that, with future advances in terahertz resonator technology, reflectarray antennas will prove instrumental in facilitating numerous promising applications of the terahertz range, including high-volume communications, noninvasive medical imaging, and security screening.