Showing papers in "Photonics Research in 2014"
TL;DR: In this paper, a silicon-on-insulator-based adiabatic waveguide taper with a high coupling efficiency and small footprint is presented to reduce the incidence of mode conversion to higher-order and radiation modes inside the waveguide.
Abstract: A silicon-on-insulator-based adiabatic waveguide taper with a high coupling efficiency and small footprint is presented. The taper was designed to reduce the incidence of mode conversion to higher-order and radiation modes inside the waveguide. In connecting a 0.5-μm-wide output waveguide and a 12-μm-wide input waveguide of a grating coupler, a compact 120-μm-long taper was demonstrated, achieving a transmission of 98.3%. Previously, this transmission level could only be achieved using a conventional linear taper with a length of more than 300 μm.
171 citations
TL;DR: In this paper, the authors reported uniaxial tensile strains up to 5.7% along germanium wires on a silicon substrate, measured using Raman spectroscopy.
Abstract: We report uniaxial tensile strains up to 5.7% along 〈100〉 in suspended germanium (Ge) wires on a silicon substrate, measured using Raman spectroscopy. This strain is sufficient to make Ge a direct bandgap semiconductor. Theoretical calculations show that a significant fraction of electrons remain in the indirect conduction valley despite the direct bandgap due to the much larger density of states; however, recombination can nevertheless be dominated by radiative direct bandgap transitions if defects are minimized. We then calculate the theoretical efficiency of direct bandgap Ge LEDs and lasers. These strained Ge wires represent a direct bandgap Group IV semiconductor integrated directly on a silicon platform.
155 citations
TL;DR: Some of the notable challenges in MWP are identified and the recent work is reviewed and applications and future direction of research are also discussed.
Abstract: Microwave photonics (MWPs) uses the strength of photonic techniques to generate, process, control, and distribute microwave signals, combining the advantages of microwaves and photonics. As one of the main topics of MWP, radio-over-fiber (RoF) links can provide features that are very difficult or even impossible to achieve with traditional technologies. Meanwhile, a considerable number of signal-processing subsystems have been carried out in the field of MWP as they are instrumental for the implementation of many functionalities. However, there are still several challenges in strengthening the performance of the technology to support systems and applications with more complex structures, multiple functionality, larger bandwidth, and larger processing capability. In this paper, we identify some of the notable challenges in MWP and review our recent work. Applications and future direction of research are also discussed.
103 citations
TL;DR: In this paper, the authors reported a significant enhancement in the selectivity of SBS-based microwave-photonic (MWP) filters with a single passband of 250 MHz-1 GHz bandwidth.
Abstract: Stimulated Brillouin scattering (SBS) in optical fibers has long been used in frequency-selective optical signal processing, including in the realization of microwave-photonic (MWP) filters. In this work, we report a significant enhancement in the selectivity of SBS-based MWP filters. Filters having a single passband of 250 MHz–1 GHz bandwidth are demonstrated, with selectivity of up to 44 dB. The selectivity of the filters is better than that of the corresponding previous arrangements by about 15 dB. The shape factor of the filters, defined as the ratio between their −20 dB bandwidth and their −3 dB bandwidth, is between 1.35 and 1.5. The central transmission frequency, bandwidth, and spectral shape of the passband are all independently adjusted. Performance enhancement is based on two advances, compared with previous demonstrations of tunable SBS-based MWP filters: (a) the polarization attributes of SBS in standard, weakly birefringent fibers are used to discriminate between in-band and out-of-band components and (b) a sharp and uniform power spectral density of the SBS pump waves is synthesized through external modulation of an optical carrier by broadband, frequency-swept waveforms. The signal-to-noise ratio of filtered radio-frequency waveforms and the linear dynamic range of the filters are estimated analytically and quantified experimentally. Lastly, a figure of merit for the performance of the filters is proposed and discussed. The filters are applicable to radio-over-fiber transmission systems.
100 citations
TL;DR: In this paper, the authors summarize the recent exciting development in perovskite solar cells, and discuss the fundamental mechanisms of perovsite materials in solar cells and their structural evolution.
Abstract: A cost-effective and high-throughput material named perovskite has proven to be capable of converting 15.9% of the solar energy to electricity, compared to an efficiency of 3.8% that was obtained only four years ago. It has already outperformed most of the thin-film solar cell technologies that researchers have been studying for decades. Currently, the architecture of perovskite solar cells has been simplified from the traditional dye-sensitized solar cells to planar-heterojunction solar cells. Recently, the performance of perovskite in solar cells has attracted intensive attention and studies. Foreseeably, many transformative steps will be put forward over the coming few years. In this review, we summarize the recent exciting development in perovskite solar cells, and discuss the fundamental mechanisms of perovskite materials in solar cells and their structural evolution. In addition, future directions and prospects are proposed toward high-efficiency perovskite solar cells for practical applications.
96 citations
TL;DR: In this paper, the authors review the emergence and development of integrated photonics and its status today, focusing on information and communications technology (ICT) applications, but the technology is generically employable for a wealth of other applications, such as sensors.
Abstract: We review the emergence and development of integrated photonics and its status today. The treatise is focused on information and communications technology (ICT) applications, but the technology is generically employable for a wealth of other applications, such as sensors. General properties of the waveguides that form the basis of integrated photonics are reviewed, and several examples of integrated photonics based on silicon and plasmonics are presented. The all-important development of integrated low-power nanophotonics is discussed and current challenges and prospects of the field are elucidated. The treatment is focused on the photonic fabric between source and detector.
66 citations
TL;DR: A novel polarimetric dehazing method based on three linear polarization images based on the polarization orientation angle of the light scattered by the haze particles is proposed and it is found that the dehazed image suffers from little noise and the details of the objects close to the observer can be preserved well.
Abstract: A novel polarimetric dehazing method is proposed based on three linear polarization images (0°, 45°, and 90°). The polarization orientation angle of the light scattered by the haze particles is introduced in the algorithm. No additional image-processing algorithm is needed in the postprocessing. It is found that the dehazed image suffers from little noise and the details of the objects close to the observer can be preserved well. In addition, this algorithm is also proved to be useful for preserving image colors. Experimental results demonstrate that such an algorithm has some universality in handling all kinds of haze. We think that this robust algorithm might be very suitable for real-time dehazing.
62 citations
TL;DR: In this paper, a blind deconvolution algorithm with modified Tikhonov regularization is introduced to improve the spectral resolution, spectral structure information is incorporated into regularization by using the adaptive term to distinguish the spectral structure from other regions.
Abstract: A blind deconvolution algorithm with modified Tikhonov regularization is introduced. To improve the spectral resolution, spectral structure information is incorporated into regularization by using the adaptive term to distinguish the spectral structure from other regions. The proposed algorithm can effectively suppress Poisson noise as well as preserve the spectral structure and detailed information. Moreover, it becomes more robust with the change of the regularization parameter. Comparative results on simulated and real degraded Raman spectra are reported. The recovered Raman spectra can easily extract the spectral features and interpret the unknown chemical mixture.
58 citations
TL;DR: In this article, a three-dimensional (3D) terahertz (THz) imaging or THz tomography has been used for nondestructive testing of industrial materials and structures.
Abstract: Three-dimensional (3D) terahertz (THz) imaging or THz tomography has recently proven to be useful for nondestructive testing of industrial materials and structures In place of previous imaging techniques such as THz pulsed/continuous-wave radar and THz computed tomography, we propose a THz optical coherence tomography using photonics- and electronics-based THz sources, and demonstrate thickness measurement and tomographic imaging in frequency regions from 400 to 800 GHz
56 citations
TL;DR: In this paper, a photonics-electronics convergence system was proposed to solve the bandwidth bottleneck in interchip interconnects, achieving 20 Gbps error-free data links and 30 Tbps/cm2 bandwidth density.
Abstract: One of the most serious challenges facing exponential performance growth in the information industry is the bandwidth bottleneck in interchip interconnects. We propose a photonics–electronics convergence system in response to this issue. To demonstrate the feasibility of the system, we fabricated a silicon optical interposer integrated with arrayed laser diodes, spot-size converters, optical splitters, optical modulators, photodetectors, and optical waveguides on a single silicon substrate. Using this system, 20 Gbps error-free data links and a 30 Tbps/cm2 bandwidth density were achieved. This bandwidth density is sufficient to meet the interchip interconnect requirements for the late 2010s.
42 citations
TL;DR: In this paper, the authors report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide, which enables a small signal amplitude <1'V with a micrometer-sized footprint for compatibility with CMOS circuit integration.
Abstract: In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide. There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as VπLπ≃0.07 V cm for straight waveguides and VπLπ≃0.0024 V cm for 12 μm radius microring resonators. This phase modulation device uniquely enables a small signal amplitude <1 V with a micrometer-sized footprint for compatibility with CMOS circuit integration. Examples of phase-induced changes are computed for straight waveguides and for microring resonators, showing the possibility of implementing several optoelectronic functionalities as modulators, tunable filters, and switches.
TL;DR: In this article, a hybrid integrated light source was developed with a configuration in which a laser diode (LD) array was mounted on a silicon optical waveguide platform for interchip optical interconnection.
Abstract: A hybrid integrated light source was developed with a configuration in which a laser diode (LD) array was mounted on a silicon optical waveguide platform for interchip optical interconnection. This integrated light source is composed of 13-channel stripes with a pitch of 20 or 30 μm. The output power of each LD in the 400 or 600-μm long LD array was over 40 mW at room temperature without cooling. An output power uniformity was 1.3 dB including an LD array power uniformity. The use of a SiON waveguide with a spot size converter resulted in an optical coupling loss of 1 dB between an LD and SiON waveguide. The integrated light source including 52 output ports demonstrated a reduction in the footprint per channel. We also demonstrated a light source with over 100 output ports in which the number of output ports is increased by using a waveguide splitter and multichip bonding. These integrated light sources are practical candidates for use with photonic integrated circuits for high-density optical interconnection.
TL;DR: In this article, a window of lattice constants that support Fano resonances in square lattices of plasmonic nanostructures was identified in a range from 500 to 900 nm.
Abstract: Fano resonances between plasmons and diffracted light offer tunable energies and locales, but attribution of Fano resonance features to geometry and physicochemistry of metal nanostructures and adjacent dielectrics has been confounded by complexity and computational expense. This work shows predictable modal shifts of Fano resonance in square lattices of plasmonic nanostructures can be attributed directly to changes in medium wavenumber, particle size, and lattice constant that alter plasmon polarizability and diffractive interference. For 45 to 80 nm radius particles, a window of lattice constants that support Fano resonances is identified in a range from 500 to 900 nm. Lattice constants that support high intensity resonances are determined by individual particle polarizability and medium wavenumber. Fano resonance wavelengths redshift from diffracted photon energies as local refractive index (RI) changes due to coupling with particle polarizability in the window. Redshift sensitivities for quadrupole, dipole, and Fano resonances are 150, 348, and 541 nm, respectively, per RI unit. Fano resonance intensity may be enhanced more than tenfold by selecting nanoparticle sizes and lattice constants. The quantitative effects of such parametric changes are rapidly and intuitively distinguished using a semi-analytic approach, consisting of an exact expression for particle polarizability, a trigonometric description of diffraction, and a semi-analytical coupled dipole approximation.
TL;DR: ErxY2−xSiO5 and ErxYbyY 2−x−y SiO5 crystalline thin films were investigated to apply to the high-gain media for silicon photonics as mentioned in this paper.
Abstract: ErxY2−xSiO5 and ErxYbyY2−x−ySiO5 crystalline thin films were investigated to apply to the high-gain media for silicon photonics. In addition to the sol–gel method, the directed self-assembly approach, using layer-by-layer deposition techniques, was also introduced to improve the crystallinity. The relaxation processes in Er ions were discussed to clarify the contribution of the energy transfer and cooperative upconversion. After optimization of the Er content, a Si photonic crystal slot ErxY2−xSiO5 waveguide amplifier was fabricated, and a 30 dB/cm modal gain was demonstrated. This achievement demonstrates the potential for compact and high optical gain devices on Si chips.
TL;DR: In this article, a scheme for spatial resolution enhancement of digital holographic microscopy (DHM) by using the structured illumination but without phase shifting is proposed, where the structured illuminations of different directions, which are generated by a spatial light modulator, illuminate the sample sequentially in the object plane.
Abstract: When structured illumination is used in digital holographic microscopy (DHM), each direction of the illumination fringe is required to be shifted at least three times to perform the phase-shifting reconstruction. In this paper, we propose a scheme for spatial resolution enhancement of DHM by using the structured illumination but without phase shifting. The structured illuminations of different directions, which are generated by a spatial light modulator, illuminate the sample sequentially in the object plane. The formed object waves interfere with a reference wave in an off-axis configuration, and a CCD camera records the generated hologram. After the object waves are reconstructed numerically, a synthetic aperture is performed by an iterative algorithm to enhance the spatial resolution. The resolution improvement of the proposed method is proved and demonstrated by both simulation and experiment.
TL;DR: In this article, the characterizations of quasi-Bessel beam (QBB) formed by the ideal axicon and oblate-tip axicon are described, and simple analytical formulas can be used to predict the required laser parameters, including the laser pulse energy, the generated fluence distributions, and the beam diameters.
Abstract: A quasi-Bessel beam (QBB) is suitable for laser ablation because it possesses a micrometer-sized focal spot and long depth of focus simultaneously. In this paper, the characterizations of QBBs formed by the ideal axicon and oblate-tip axicon are described. Strong on-axis intensity oscillations occur due to interference between the QBB and the refracted beam by the oblate tip. Using the axicon for laser ablation was theoretically investigated. Simple analytical formulas can be used to predict the required laser parameters, including the laser pulse energy, the generated fluence distributions, and the beam diameters.
TL;DR: In this paper, a novel scheme for the generation of background-free pulsed microwave signals is proposed and experimentally demonstrated based on spectral shaping, frequency-to-time mapping, and balanced photodetection.
Abstract: A novel scheme for the generation of background-free pulsed microwave signals is proposed and experimentally demonstrated based on spectral shaping, frequency-to-time mapping, and balanced photodetection. In the proposed scheme, the optical spectral shaper, which consists of a differential group delay (DGD) element, two polarization controllers, and a polarization beam splitter, has two outputs with complementary power transfer functions. By passing a short optical pulse through the spectral shaper and a dispersive element (DE), a pulsed microwave signal is obtained after balanced photodetection. Thanks to the balanced photodetection, the low-frequency components (i.e., the background signal) in the electrical spectrum is suppressed, leading to the generation of a background-free pulsed microwave signal. Meanwhile, the spectral power of the obtained microwave signal is enhanced compared to that obtained by single-end detection. Experimental results for the generation of a pulsed microwave signal centered at 12.46 GHz show that the background signal can be suppressed by more than 30 dB, and the spectral power is increased by 5.5 dB. In addition, the central frequency of the obtained background-free pulsed microwave signal can be tuned by changing the DGD introduced by the DGD element, and/or by changing the dispersion of the DE.
TL;DR: In this paper, an approach to implement optical single sideband (OSSB) polarization modulation, which is a combination of two orthogonally polarized OSSB modulations with complementary phase differences between the optical carrier and the sideband, is demonstrated based on two cascaded polarization modulators.
Abstract: An approach to implementing optical single sideband (OSSB) polarization modulation, which is a combination of two orthogonally polarized OSSB modulations with complementary phase differences between the optical carrier and the sideband, is demonstrated based on two cascaded polarization modulators (PolMs). The two PolMs are driven by two RF signals that are 90° out of phase. By properly adjusting the polarization state between the two PolMs, OSSB polarization modulation with large operation bandwidth can be realized. An experiment is performed. OSSB polarization modulation with an operation bandwidth from 2 to 35 GHz is successfully demonstrated. The spectral profile of the OSSB polarization-modulated signal is observed through an optical spectrum analyzer, and its complementary phase properties are analyzed by sending the signal to a photodetector (PD) for square-law detection. Due to the complementary phase differences between the optical carrier and the sideband along the two polarization directions, no microwave frequency component is generated after the PD. The generated OSSB polarization-modulated signal is transmitted through 25 and 50 km single-mode fiber with 50 Mbaud 16 quadrature amplitude modulation baseband data to investigate the transmission performance of the proposed system in radio-over-fiber applications, and very small error vector magnitude degradation is observed. OSSB polarization modulation is also employed to realize a microwave photonic phase shifter. A full-range tunable phase shift is obtained for 2 and 35 GHz microwave signals.
TL;DR: In this paper, the authors proposed a two-dimensional effective index approximation for 2×2 electro-optical switching in the 1.3-12-μm wavelength range, and showed that three or four side-coupled Si or Ge channel waveguides can provide complete crossbar broad-spectrum switching when the central waveguide are injected with electrons and holes to modify the waveguide's core index by an amount Δn+iΔk.
Abstract: New designs are proposed for 2×2 electro-optical switching in the 1.3–12 μm wavelength range. Directional couplers are analyzed using a two-dimensional effective-index approximation. It is shown that three or four side-coupled Si or Ge channel waveguides can provide complete crossbar broad-spectrum switching when the central waveguides are injected with electrons and holes to modify the waveguides’ core index by an amount Δn+iΔk. The four-waveguide device is found to have a required active length L that is 50% shorter than L for the three-waveguide switch. A rule of ΔβL>28 for 3w and ΔβL>14 for 4w is deduced to promise insertion loss <1.5 dB and crosstalk <−15 dB at the bar state. At an injection of ΔNe=ΔNh=5×1017 cm−3, the predicted L decreased from ∼2 to ∼0.5 mm as λ increased from 1.32 to 12 μm. Because of Ge’s large Δk, the Ge bar loss is high in 4w but is acceptable in 3w.
TL;DR: Wang et al. as discussed by the authors presented a scheme to reconstruct sectional images in OSH with enhanced depth resolution, where a spatial light modulator (SLM) is adopted as a configurable point pupil.
Abstract: The optical scanning holography (OSH) technique can capture all the three-dimensional volume information of an object in a hologram via a single raster scan. The digital hologram can then be processed to reconstruct individual sectional images of the object. In this paper, we present a scheme to reconstruct sectional images in OSH with enhanced depth resolution, where a spatial light modulator (SLM) is adopted as a configurable point pupil. By switching the SLM between two states, different Fresnel zone plates (FZPs) are generated based on the same optical system. With extra information provided by different FZPs, a depth resolution at 0.7 μm can be achieved. © 2014 Chinese Laser Press
TL;DR: In this article, a serial line scan microscopic imaging system with 1 GHz scan rate is proposed and demonstrated, based on optical time-stretch in dispersive fiber to realize superfast scan imaging.
Abstract: A serial line scan microscopic imaging system with 1 GHz scan rate is proposed and demonstrated. This method is based on optical time-stretch in dispersive fiber to realize superfast scan imaging. Furthermore, a wavelength division technique is utilized to overcome the trade-off between high frame rate and spatial resolution caused by dispersion-induced pulse overlap. Every single frame is carved into two channels by optical filters and is detected in different wavelength bands separately. Then, both channels are combined to reconstruct the whole frame. By this method, an imaging system with spatial resolution of 28 μm at line scan rate of 1 GHz with chromatic dispersion of 1377 ps/nm is realized. It has the potential to capture fast, nonrepetitive transient phenomena with a timescale of less than one nanosecond.
TL;DR: In this article, photonics technology based on a bulk-Si substrate for cost-sensitive dynamic random access memory (DRAM) optical interface application is presented, and the feasibility of high-speed multidrop interface is demonstrated using the Mach-Zehnder interferometer modulators and commercial photodetectors.
Abstract: We present photonics technology based on a bulk-Si substrate for cost-sensitive dynamic random-access memory (DRAM) optical interface application We summarize the progress on passive and active photonic devices using a local-crystallized Si waveguide fabricated by solid phase epitaxy or laser-induced epitaxial growth on bulk-Si substrate The process of integration of a photonic integrated circuit (IC) with an electronic IC is demonstrated using a 65 nm DRAM periphery process on 300 mm wafers to prove the possibility of seamless integration with various complementary metal-oxide-semiconductor devices Using the bulk-Si photonic devices, we show the feasibility of high-speed multidrop interface: the Mach–Zehnder interferometer modulators and commercial photodetectors are used to demonstrate four-drop link operation at 10 Gb/s, and the transceiver chips with photonic die and electronic die work for the DDR3 DRAM interface at 16 Gb/s under a 1∶4 multidrop configuration
TL;DR: In this article, the authors present several laser sources dedicated to advanced microwave photonic applications, including a quantum-dash mode-locked laser delivering a high-power, ultra-stable pulse train.
Abstract: We present several laser sources dedicated to advanced microwave photonic applications. A quantum-dash mode-locked laser delivering a high-power, ultra-stable pulse train is first described. We measure a linewidth below 300 kHz at a 4.3 GHz repetition rate for an output power above 300 mW and a pulse duration of 1.1 ps after compression, making this source ideal for microwave signal sampling applications. A widely tunable (5–110 GHz), monolithic millimeter-wave transceiver based on the integration of two semiconductor distributed feedback lasers, four amplifiers, and two high-speed uni-traveling carrier photodiodes is then presented, together with its application to the wireless transmission of data at 200 Mb/s. A frequency-agile laser source dedicated to microwave signal processing is then described. It delivers arbitrary frequency sweeps over 20 GHz with high precision and high speed (above 400 GHz/ms). Finally, we report on a low-noise (below 1 kHz linewidth), solid-state, dual-frequency laser source. It allows independent tuning of the two frequencies in the perspective of the implementation of a tunable optoelectronic oscillator based on a high-Q optical resonator.
TL;DR: In this article, a photonic assisted radio frequency (RF) down-converter integrating with the optoelectronic oscillator (OEO)-based high quality local oscillator was proposed and experimentally demonstrated.
Abstract: A photonic-assisted radio frequency (RF) down-converter integrating with the optoelectronic oscillator (OEO)-based high quality local oscillator (LO) has been proposed and experimentally demonstrated. The LO and the RF input signal are mixed at the same phase modulator and photo-detector (PD) of the OEO-loop without any additional modulator or PD. The working bandwidth of the proposed RF down-converter is nearly from 2.5 to 10 GHz. The performance of the proposed down-converter is presented and the spurious frequency dynamic range at frequency of 5.5 GHz with the LO at 6.138 GHz is measured to be 98.4 dB–Hz2/3. The influences that the frequency range and power of the RF input signal bring to the system are discussed as well.
TL;DR: In this article, a vector integral differential equation to describe electromagnetic wave propagation in nanowave-guides and photonic crystals containing thin metal layers is developed and exact solution of the equation is obtained with the Galerkin method, taking into account the complex dielectric permittivity of metals in the optical range.
Abstract: A vector integral–differential equation to describe electromagnetic wave propagation in nanowaveguides and photonic crystals containing thin metal layers is developed. Exact solution of the equation is obtained with the Galerkin method, taking into account the complex dielectric permittivity of metals in the optical range. A simple method for finding complex effective refractive indices for low-loss waveguide structures is developed and proved. Surface plasmon-polariton waves are simulated in the structures under consideration.
TL;DR: This paper focuses on the latest measurement results achieved using a hybrid integrated ACP-OPLL, as well as the design and performance potential of a monolithically integrated ACp-opLL photonic integrated circuit.
Abstract: In order to achieve small size, light weight, and immunity to electromagnetic interference, it is desirable to replace bulky coaxial cables with optical fiber in advanced radar front-ends. Such applications require a large dynamic range that is beyond the reach of conventional intensity modulation–direct detection fiber-optic links. A coherent fiber-optic link employing an optical phase-locked loop (OPLL) phase demodulator has been proposed as a solution to this problem. The challenge is the practical realization of the OPLL demodulator that satisfies the stringent loop delay requirement. A novel attenuation counterpropagating (ACP) OPLL concept has been proposed and demonstrated as a solution. In this paper we review the recent progress in realizing chip-scale ACP-OPLL devices. In particular, we focus on the latest measurement results achieved using a hybrid integrated ACP-OPLL, as well as the design and performance potential of a monolithically integrated ACP-OPLL photonic integrated circuit.
TL;DR: In this article, the authors proposed an efficient and low-power second harmonic generation (SHG) process in a silicon-compatible hybrid plasmonic microring resonator.
Abstract: We propose an efficient and low-power second harmonic generation (SHG) process in a silicon-compatible hybrid plasmonic microring resonator. By making the microring resonator doubly resonant at the fundamental wavelength of 3.1 μm and second harmonic wavelength of 1.55 μm, the SHG efficiency is enhanced by almost two orders of magnitude when compared to the previous result induced in a straight plasmonic waveguide. A SHG efficiency of 13.71% is predicted for a low pump power of 20 mW in a ring with radius of 2.325 μm. This device provides a potential route for realizing efficient frequency conversion between mid-infrared and near-infrared wavebands on a chip.
TL;DR: In this article, Quadrupolar and dipolar transversal Bloch modes were obtained in an MNW chain embedded in a dielectric material, which can be coupled efficiently with the fundamental transverse magnetic (TM) mode of the waveguide.
Abstract: The eigenmodes analysis of Bloch modes in a chain of metallic nanowires (MNWs) provides a significant physical understanding about the light propagation phenomena involved in such structures. However, most of these analyses have been done above the light line in the dispersion relation, where the Bloch modes can only be excited with radiative modes. By making use of the Fourier modal method, in this paper we rigorously calculate the eigenmode and mode excitation of a chain of MNWs via the fundamental transverse magnetic (TM) mode of a dielectric waveguide. Quadrupolar and dipolar transversal Bloch modes were obtained in an MNW chain embedded in a dielectric material. These modes can be coupled efficiently with the fundamental TM mode of the waveguide. Since the eigenmodes supported by the integrated plasmonic structure exhibit strong localized surface plasmon (LSP) resonances, they could serve as a nanodevice for sensing applications. Also, the analysis opens a direction for novel nanostructures, potentially helpful for the efficient excitation of LSPs and strong field enhancement.
TL;DR: In this paper, the influence of feedback light on z-scan measurement is analyzed and the calculated formula of feedback-light-induced false nonlinear Z-scan curves is theoretically derived and experimentally verified.
Abstract: With the development of semiconductor technology, semiconductor laser devices and semiconductor laser pump solid-state laser devices have been widely applied in z-scan experiments. However, the feedback light-induced output instability of semiconductor laser devices can negatively affect the accurate testing of the nonlinear index. In this work, the influence of feedback light on z-scan measurement is analyzed. Then the calculated formula of feedback light-induced false nonlinear z-scan curves is theoretically derived and experimentally verified. Two methods are proposed to reduce or eliminate the feedback light-induced false nonlinear effect. One is the addition of an attenuator to the z-scan optical path, and the other is the addition of an opto-isolator unit to the z-scan setup. The experimental and theoretical results indicate that the feedback light-induced false nonlinear effect is markedly reduced and can even be ignored if appropriate parameters are chosen. Thus, theoretical and experimental methods of eliminating the negative effect of feedback light on z-scan measurement are useful for accurately obtaining the nonlinear index of a sample.
TL;DR: The experimental results show that ACO-OFDM can outperform DC-biased optical OFDM by BER performance of 1.5 dB at the same data rate and 4 dB in the same bandwidth, which clearly demonstrates the benefit and feasibility of ACO -OFDM.
Abstract: Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been a promising candidate in visible light communications (VLC) due to its improvement in power efficiency and reduction of nonlinearity based on previous simulation analysis. In this paper, for the first time as far as we know, we experimentally verify that ACO-OFDM would be an efficient scheme to improve the performance of a gigabit wavelength division multiplexing VLC system. Our theoretical investigations reveal that the advantages of ACO-OFDM can be attributed to the reduction of inter-carrier interference caused by signal–signal beating noise. An aggregate data rate of 1.05 Gb/s is successfully achieved over 30 cm transmission below the 7% forward-error-correction threshold of 3.8×10−3. The experimental results show that ACO-OFDM can outperform DC-biased optical OFDM by BER performance of 1.5 dB at the same data rate and 4 dB at the same bandwidth, which clearly demonstrates the benefit and feasibility of ACO-OFDM.