Communication Wavelength Research Articles

Direct visualization of phase-matched efficient second harmonic and broadband sum frequency generation in hybrid plasmonic nanostructures

Second harmonic generation and sum frequency generation (SHG and SFG) provide effective means to realize coherent light at desired frequencies when lasing is not easily achievable. They have found applications from sensing to quantum optics and are of particular interest for integrated photonics at communication wavelengths. Decreasing the footprints of nonlinear components while maintaining their high up-conversion efficiency remains a challenge in the miniaturization of integrated photonics. Here we explore lithographically defined AlGaInP nano(micro)structures/Al2O3/Ag as a versatile platform to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both narrow- and broadband infrared (IR) wavelength regimes (1300–1600 nm). The effective excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113 nm × 250 nm, with a mode area on the deep subwavelength scale (λ2/135) at fundamental wavelengths. Remarkably, we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides. This together with mode analysis highlights the origin of the improved SHG/SFG efficiency. We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1 µm diameter AlGaInP disks/Al2O3/Ag with a conversion efficiency of 14.8% MW−1 which is five times the SHG value using the narrowband IR source. In both configurations, the hybrid plasmonic structures exhibit >1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts. Our results manifest the potential of developing such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.

Mode coupling enhancement from dielectric to plasmonic waveguides

Efficient dielectric–plasmonic interconnect is significant in the design of future electronic–photonic integrated circuits that deal with large data transfer. We propose three designs and analysis of small-footprint couplers that are located at the interface between dielectric and plasmonic waveguides. To the best of our knowledge, our proposed couplers outperform all the works reported in the literature in several aspects including size and coupling efficiency (CE). Our results indicate that the optimum dimensions of the proposed couplers are determined based on whether the coupler is located in the metal side or dielectric side, or the coupler extends equally in both types of materials. The proposed couplers work over a broad frequency range achieving a CE above 88% at the optical communications wavelength 1550 nm. In addition, our results indicate that the CE can be further increased to above 93% by increasing the width of the dielectric waveguide before it is connected to the coupler. Moreover, our proposed designs provide a considerable alignment tolerance, which is needed when aligning the dielectric waveguide to the metal–dielectric–metal waveguide. Our proposed couplers have an impact on the design and miniaturization of nanoscale all-optical devices.

Portable Automatic Microring Resonator System Using a Subwavelength Grating Metamaterial Waveguide for High-Sensitivity Real-Time Optical-Biosensing Applications

The slow light sensor techniques have been applied to bio-related detection in the past decades. However, similar testing-systems are too large to carry to a remote area for diagnosis or point-of-care testing. This study demonstrated a fully automatic portable biosensing system based on the microring resonator. An optical-fiber array mounted on a controller based micro-positioning system, which can be interfaced with MATLAB to locate a tentative position for light source and waveguide coupling alignment. Chip adapter and microfluidic channel could be packaged as a product such that it is cheap to be manufactured and can be disposed of after every test conducted. Thus, the platform can be more easily operated via an ordinary user without expertise in photonics. It is designed based on conventional optical communication wavelength range. The C-band superluminescent-light-emitting-diode light source couples in/out the microring sensor to obtain quasi-TE mode by grating coupler techniques. For keeping a stable chemical binding reaction, the cost-effective microfluidic pump was developed to offer a specific flow rate of 20 μL/min by using a servo-motor, an Arduino board, and a motor driver. The subwavelength grating metamaterial ring resonator shows highly sensitive sensing performance via surface index changes due to biomarker adhered on the sensor. The real-time peak-shift monitoring shows 10μg/mL streptavidin detection of limit based on the biotin-streptavidin binding reaction. Through the different specific receptors immobilized on the sensor surface, the system can be utilized on the open applications such as heavy metal detection, gas sensing, virus examination, and cancer marker diagnosis.

GALYUM KATKILI ÇİNKO OKSİT NANOANTEN İLE MİKROLENS

Alternative plasmonics based fractal microlens are investigated. In this context, lensing performance of gallium-doped zinc oxide Sierpinski carpet-based fractal construction functionalized by conformal Talbot effect is analyzed for communication wavelength 1550 nm. Focusing via diffraction from these 2D finite-sized and two-iterated fractal lattice system is computationally demonstrated. In this regard, focusing performance parameters are computationally examined on the basis of geometrical parameter sweep and fractal generation via finite difference time-domain numerical simulations. Focusing efficiency > 50%, absolute 
 efficiency > 18%, and focal depth larger than primary spot size are introduced by all computational samples. Moreover, a conformal Talbot effect is exhibited by this novel alternative plasmonics construction. A novel perspective based on alternative plasmonics by a newly adapted fractal design to optics is proposed. Thus, this fractal microlens is presented as a new planarized focusing platform, acting a conformal transformation optics device for light capturing tolerance and low-cost.

Photonic crystal add–drop filter: a review on principles and applications

Add–drop filter (ADF) is a key component in optical integrated circuits that can be used in all-optical communication networks and wavelength division multiplexing (WDM) systems. The quality factor, coupling efficiency, transmission efficiency and coupling length are important parameters in add–drop filters. Photonic crystal (PC) optical devices have become popular among researchers because their structure is suitable to embed into optical circuits. This paper covers a comprehensive review of the principle structure of ADF, coupled mode theory (CMT), types and recent applications in WDMs, accelerometer and bio/chemical sensors. Although there are some different categories of photonic crystal ring resonator-based ADF in general, all of them can be divided into photonic to two class of non-circular and circular. This article is reported a comprehensive study about ADF and improvement of these ADF.

High-performance infrared Ge-based plasmonic photodetector enhanced by dual absorption mechanism

A sub-wavelength plasmonic Au–Ge grating was used to enhance the responsivity of Ge-based metal–semiconductor–metal photodetectors at infrared communication wavelengths. Furthermore, a finite-difference time-domain simulation was performed to optimize absorption of light by the detectors. Characterizations of the photoelectronic properties of the optimized device revealed high-performance photodetection with a responsivity of 0.38 A/W and an external quantum efficiency of 30% for 1.55 μm wavelength incident light. Moreover, an enhancement peak across three infrared telecommunication bands (C-band, L-band, and U-band) was achieved in the plasmon-enhanced photodetector. According to the simulation results of the optical absorption spectra, the distributions of electric field, and absorbed power, the enhancements of responsivity and quantum efficiency could be ascribed to the surface plasmons at the Au/Ge interface. These plasmons boosted inter-band transition and internal photoemission effect simultaneously, enabling high efficient photodetection around the C-band. The results of the fabricated devices demonstrated the potential of this approach for achieving high-performance Ge-based photodetectors.

Conformal Talbot-effect-focusing performance of nested gallium-doped zinc oxide nanorings at communication wavelength

Metasurfaces, artificial micro- and nano-photonic structures can modify wavefront of electromagnetic waves to the desired form. Metalenses are the metasurfaces assuming the role of focusing light. The focusing performance of nested gallium-doped zinc oxide nanoring-arrangements functionalized by conformal Talbot effect is investigated for communication wavelength 1550 nm. The Talbot-effect-focusing performance of the 2D finite-sized structures are computationally demonstrated in a systematically manner. The impact of geometrical parameters on the primary focal spot and focusing performance parameters such as numerical aperture, full-width half-maximum, focal depth, efficiency, and fill-factor is examined and summarized via finite difference time-domain numerical simulations. All samples presenting an alternative plasmonic option in this work yield a good focusing efficiency of >50%, absolute efficiency of >19%, numerical aperture up to 0.67, focal depth up to 1.4 times of focal length, and a wide focal spot size up to 6.0654 times of operating wavelength. As a result of finite-sized construction, conformal Talbot effect is examined from a novel alternative plasmonics perspective. Thus, a new planarized focusing platform is employed by using a nanostructured microlens, acting conformal transformation optics devices with low-cost and light capturing tolerance.

A Three-Core Hybrid Plasmonic Polarization Splitter Designing Based on the Hybrid Plasmonic Waveguide for Utilizing in Optical Integrated Circuits

In this research, by using the theory of the surface plasmon polaritons and the plasmonic hybrid components, a new symmetric three-core hybrid plasmonic splitter is proposed at the communication wavelength range. The design consists of two silicon external waveguides with the same dimensions and features, and a centered hybrid waveguide. The centered hybrid waveguide simulated with two silver metal layers and a core silicon waveguide. The plasmonic hybrid coupler supports three supermodes and directly couples the transverse magnetic (TM) mode to the second external waveguide. In contrast, the transverse electric (TE) mode passes through the first external waveguide without coupling. The essential features of the proposed design were studied thoroughly. The most significant parameters of the structure, including propagated modes in the waveguides, extinction ratio (ER), insertion loss (IL), and power transfers, were evaluated using the finite-difference eigenmode (FDE) and eigenmode expansion (EME) methods. The results show that the ERs for the external waveguides are greater than 38 dB for the first external waveguide and 40 dB for the second external waveguide. The ILs of the TE and TM modes are less than 0.1 dB and 0.5 dB at the 1550 nm telecommunication wavelength, respectively.

Comparison of probability density functions for aperture-averaged irradiance fluctuations of a Gaussian beam with beam wander.

Over the years, there has been much interest in the use of optical wavelengths for communication because of the potential for high data rates. However, the performance of these systems can become significantly degraded due to turbulence-induced signal fluctuations. These fluctuations can be minimized by enlarging the receiving aperture, thereby averaging the fluctuations. There is extensive interest in developing probability density functions (PDFs) describing these intensity fluctuations so as to accurately predict system performance. This work examines several PDF models that have been suggested to represent fluctuations by comparing them to simulations of realistic propagation scenarios of a collimated Gaussian beam with centroid wander. Unlike with an infinite plane or spherical wave, the empirical PDF shape in these simulations changed significantly with increased aperture, going from a positively skewed to a negatively skewed distribution; therefore, the PDF model that describes it also must change. This change in skew can have serious consequences on the metrics of an optical communication system, e.g., number of fades and bit-error rate. In this work, we examine the evolution of the empirical PDF with aperture size and the fit of potential PDF models under various strengths of turbulence. We show that the change in skew with increasing aperture size occurred for all strengths of turbulence and that the currently used PDF models do not adequately characterize this for realistically sized apertures where beam wander is present.

Efficient Er/O‐Doped Silicon Light‐Emitting Diodes at Communication Wavelength by Deep Cooling

AbstractA silicon light source at the communication wavelength is the bottleneck for developing monolithically integrated silicon photonics. Doping silicon with erbium and oxygen ions is considered one of the most promising approaches to produce silicon light sources. However, this method suffers from a high concentration of defects in the form of nonradiative recombination centers at the interface between the crystalline silicon and large Er2O3/ErSi1.7 precipitates during the standard rapid thermal treatment. Here, a deep cooling process is applied to suppress the growth of these precipitates by flushing the high‐temperature Er/O‐doped silicon substrates with helium gas cooled in liquid nitrogen. The resultant light‐emitting efficiency at room temperature is enhanced by two orders of magnitude in comparison with that of the sample treated via standard rapid thermal annealing. The deep‐cooling‐processed Si samples are further processed into light‐emitting diodes. Bright electroluminescence with a main spectral peak at 1536 nm is also observed from the silicon‐based diodes with the external quantum efficiency reaching ≈0.8% at room temperature. Based on these results, the development of electrically driven silicon optical amplifiers or even lasers at communication wavelengths is promising for monolithically integrated silicon photonics.

Hybrid Plasmonic Ring-Resonator Uni-Traveling Carrier Pin-Photodetector on InGaAsP/InP Layer Stack

In this article, for the first time, a hybrid plasmonic (HP) ring resonator uni-traveling carrier pin-photodetector was numerically presented that offers a high responsivity of 0.68 A/W, a high bandwidth of over 125 GHz, and low footprint. This device has the capability of monolithic integration with HP-passive devices on the InP platform at an optical communication wavelength of 1550 nm.

Hot-Electron Photodetection Based on Graphene Transparent Conductive Electrode

Excited in metal nanoantennas by surface plasmons, the hot electrons with high energy can pass through the Schottky barrier between metal and semiconductor to form photocurrent. Because the energy required to excite hot-electrons is lower than the bandgap of the semiconductor of silicon, the photodetectors can obtain a wider detection spectrum, including the communication wavelengths. In recent years, the two-dimensional material of graphene has attracted wide attention due to its excellent optical transmissivity and electrical conductivity. In this paper, hot-electron photodetectors based on graphene transparent conductive electrode are proposed. Compared with the device utilizing Indium Tin Oxide (ITO) as transparent conductive electrode, the responsivity of the proposed device is greatly enhanced, which achieves 27.5 nA/mW and 17.4 nA/mW for wavelength of 1520 nm and 1550 nm respectively. This study shows that the proposed hot-electron photodetector with graphene transparent conductive electrode possesses great potential in optical communication.

Fast optimal design of optical components using the cultural algorithm.

Design of the guided-mode resonance (GMR) grating filter, as one of the most important optical components, using the cultural algorithm (CA) is presented, for the first time. CA is an evolutionary algorithm (EA) which is easy-to-implement, flexible, inspired by the human cultural evolution, upon using the domain knowledge for reducing the search space as a metaheuristic optimization method. Reflection spectra of the designed GMR filter based on the CA is in good agreement with the previous simulation results. CA has both acceptable accuracy and enough high speed to optimize the complicated structures; therefore, a novel double-line asymmetrical transmitter (DLAT) is introduced and optimized as a complex grating-based optical component using the mentioned algorithm. The results show the transmittance at two different communication wavelengths (1.5039 and 1.6113 µm) using the combination of binary diffraction grating and customized photonic crystal (PhC) structure. Also, the DLAT shows the characteristics of a perfect transverse magnetic (TM) polarizer. Furthermore, we demonstrated the Talbot effect at the DLAT output which is so applicable in the optical usage, especially for the integrated optics.

Theoretical investigation of optical intersubband transitions and infrared photodetection in β-(AlxGa1 − x)2O3/Ga2O3 quantum well structures

We provide theoretical consideration of intersubband transitions designed in the ultra-wide bandgap aluminum gallium oxide [(AlxGa1 − x)2O3]/gallium oxide (Ga2O3) quantum well system. Conventional material systems have matured into successful intersubband device applications such as large-area quantum well infrared photodetector (QWIP) focal plane arrays for reproducible imaging systems but are fundamentally limited via maximum conduction band offsets to mid- and long-wavelength infrared applications. Short- and near-infrared devices are technologically important to optical communication systems and biomedical imaging applications but are difficult to realize in intersubband designs for this reason. In this work, we use a first-principles approach to estimate the expansive design space of monoclinic β-(AlxGa1 − x)2O3/Ga2O3 material system, which reaches from short-wavelength infrared (1–3 μm) to far infrared (>30 μm) transition wavelengths. We estimate the performance metrics of two QWIPs operating in the long- and short-wavelength regimes, including an estimation of high room temperature detectivity (∼1011 Jones) at the optical communication wavelength λp = 1.55 μm. Our findings demonstrate the potential of the rapidly maturing (AlxGa1 − x)2O3/Ga2O3 material system to open the door for intersubband device applications.

Broadband Plasmonic Polarization Filter Based on Photonic Crystal Fiber with Dual-Ring Gold Layer.

Polarization filter is a very important optical device with extinction characteristics. Due to the design flexibility of photonic crystal fibers and the high excitation losses of the gold layer, the polarization filter based on the photonic crystal fiber and surface plasmonic resonance effect is widely studied. Considering these, we present a simple and high-performance polarization filter using the finite element method. Numerical simulations show that there is a large difference in energy between the two polarization directions by reasonable adjustment of the structural parameters, the confinement loss in the x-pol direction is less than that in the y-pol direction, which is suitable to realize a broadband polarization filter. When the fiber length is 2 mm, the extinction ratio peak can reach −478 dB, and the bandwidth with the extinction ratio better than −20 dB is 750 nm, which covers communication wavelengths of 1.31 μm and 1.55 μm (1.05–1.8 μm). It also has a low insertion loss of 0.11 dB at 1.31 μm and 0.04 dB at 1.55 μm. In addition, our design has high feasibility in fabrication and better tolerance. The proposed filter with compactness, high extinction ratio, broad bandwidth, and low insertion loss would play an important role in the sensing detection, bio-medical, and telecommunication field.

Vanadium-Oxide-Based Thin Films with Ultra-High Thermo-Optic Coefficients at 1550 nm and 2000 nm Wavelengths.

In this paper, the temperature-dependent dielectric properties of vanadium-sesquioxide-based thin films are studied to assess their suitability for thermally tunable filters at optical communication wavelengths. Spectroscopic ellipsometry is utilized to measure the optical constants of vanadium oxide thin films at temperatures ranging from 25 °C to 65 °C. High thermo-optic coefficients (dn/dTs) were observed. The highest dn/dTs, measured at approximately 40 °C, were −8.4 × 10−3/°C and −1.05 × 10−2/°C at 1550 nm and 2000 nm, respectively.

Photonic engineering of superbroadband near-infrared emission in nanoglass composites containing hybrid metal and dielectric nanocrystals

Photonic media containing hybrid noble metal–dielectric nanocrystals (NCs) represent a wonderland of nanophotonics, with a myriad of uncharted optical functions yet to be explored. Capitalizing on the unique phase separation and spontaneous formation of Au-metal NCs in a gallosilicate glass, we fabricated Ni 2 + -doped transparent nanoglass composites (GCs) containing Au - metal / γ - Ga 2 O 3 -dielectric NCs. Compared with GCs free of Au-metal NCs, the superbroadband near-infrared emission of Ni 2 + with a full width at half-maximum over 280 nm is enhanced twice in the Au - metal / γ - Ga 2 O 3 dual-phase GCs. A comparison is given as to the spontaneous emission (SPE) properties of Ni 2 + in the dual-phase GCs when pumped resonantly and off-resonantly with the localized surface plasmon resonance band of the Au-metal NCs. The important role of the Au-metal NCs in the SPE enhancement is revealed by theoretical simulation based on the finite-element method. Combining the photonic engineering effect of hybrid Au - metal / γ - Ga 2 O 3 NCs and the sensitization effect of Yb 3 + on Ni 2 + , a record-high enhancement factor of over 10 of the Ni 2 + NIR emission is achieved, and optical gain is demonstrated in the GCs at the fiber communication wavelength.

Compact, high-performance, and fabrication friendly two-mode division multiplexer based on a silicon bent directional coupler.

In response to the increasing demands of the capacity enhancement of optical communication, a compact and high-performance silicon mode division multiplexer is proposed that multiplexes the fundamental and first-order transverse magnetic modes. The device structure is based on an asymmetric bent directional coupler with an ultrasmall coupling length of 3.67 µm. Utilizing single-layer silicon waveguides with the same heights allows the proposed device to be fabricated using a single-step CMOS-compatible fabrication process, which provides a cost-effective design in comparison with the previously reported structures. The three-dimensional finite-difference time-domain simulation results confirm that the device has a low loss of 0.87 dB, low crosstalk of ${-}{21.8}\;{\rm dB}$-21.8dB, and high mode conversion efficiency of 98.3% at the communication wavelength of 1.55 µm. Furthermore, the device shows a broad bandwidth of about 110 nm, completely covering the C and L bands with crosstalk less than ${-}{10}\;{\rm dB}$-10dB. Moreover, it is shown that the proposed mode (de)multiplexer is fabrication tolerant for the coupling gap variation of ${-}{40}\;{\rm nm} \lt \Delta {g} \lt {23}\;{\rm nm}$-40nm<Δg<23nm and the waveguide width variation of ${-}{25}\;{\rm nm} \lt \Delta {W} \lt {25}\;{\rm nm}$-25nm<ΔW<25nm for a low loss of ${ \lt }- {1.67}\;{\rm dB}$<-1.67dB and low crosstalk of ${ \lt }- {10}\;{\rm dB}$<-10dB.

Photothermal switch of sub-microsecond response: a monolithic-integrated ring resonator and a metasurface absorber in silicon photonic crystals.

Here, we demonstrate an all-silicon photonic switch, working at an infrared communication wavelength and pumped by spatial light, where a ring resonator and a metasurface absorber are both designed in photonic crystals and monolithically integrated on a silicon-on-insulator wafer. Through selective doping, the absorber gets a pump absorption completely different from near zero of the resonator. Based on the thermo-optical effect, the device is capable of tuning the wavelength of the guided mode by $\sim{341}\;{\rm pm/mW}$∼341pm/mW and switching in time $ {\lt} {1.0}\;\unicode{x00B5} {\rm s}$<1.0µs to the pump response. The high responsivity and switching speed as well as all-silicon processing techniques make the design potentially for free-space optical communication and detection.

Characterization of off-axis phase singular optical vortex and its nonlinear wave-mixing to generate control broad OAM spectra

We theoretically and numerically studied the off-axis Gaussian vortex beam (GVB) characteristics. The off-axis GVB scheme is utilized to generate tunable broad OAM modes using a single helical phase. The single helical phase can be easily created in the high peak power lasers using a spiral phase plate (SPP). The high peak power GVBs greatly enhances the efficiency of nonlinear wave-mixing to tune the wavelength as well as OAM modes of laser beams. Further, we propose type-II second harmonic generation (SHG) of off-axis GVB to tune the wavelength and to increase the number of OAM modes of vortex beam. Polarization-controlled broad OAM spectra is generated at SHG wavelength. This scheme is effective for control generation of a broad range of OAM spectra in the required wavelength for high-capacity and multi-channel optical communication.