High-speed Optical Devices Research Articles

Reversible Ultrafast Chiroptical Responses in Planar Plasmonic Nano-Oligomer.

Ultracompact chiral plasmonic nanostructures with unique chiral light-matter interactions are vital for future photonic technologies. However, previous studies are limited to reporting their steady-state performance, presenting a fundamental obstacle to the development of high-speed optical devices with polarization sensitivity. Here, a comprehensive analysis of ultrafast chiroptical response of chiral gold nano-oligomers using time-resolved polarimetric measurements is provided. Significant differences are observed in terms of the absorption intensity, thus hot electron generation, and hot carrier decay time upon polarized photopumping, which are explained by a phenomenological model of the helicity-resolved optical transitions. Moreover, the chiroptical signal is switchable by reversing the direction of the pump pulse, demonstrating the versatile modulation of polarization selection in a single device. The results offer fundamental insights into the helicity-resolved optical transitions in photoexcited chiral plasmonics and can facilitate the development of high-speed polarization-sensitive flat optics with potential applications in nanophotonics and quantum optics.

Optical Set-Reset Flip-Flop based on Dielectric-Loaded Graphene-Plasmonic waveguides

In this paper, an optical Set-Reset (SR) flip-flop based on dielectric-loaded graphene-plasmonic waveguides (DLGPWs) working in the mid-infrared region is presented. The design is based on using an additional signal called Bias and the interference effect between the input signals. The graphene sheet is modeled using the Kubo formula, and the performance of the flip-flop is numerically evaluated utilizing the finite-difference time-domain method (FDTD). Various situations that may occur for the proposed flip-flop as well as the effects of possible imperfections including lack of synchronization between switches and fabrication errors are examined in detail. The minimum extinction ratio (ER) obtained from the time response is equal to 9.95 dB at λ = 10.8 µm which can also be enhanced by increasing the amplitude of the Bias signal. The proposed structure with features such as a footprint of 13.52 μm2, maximum frequency of 886 GHz, and high ER value could pave the way for the design and use of high-speed and efficient optical sequential devices instead of electronic counterparts.

Efficient and Broadband Trident Spot-Size Convertor for Thin-Film Lithium Niobate Integrated Device

Thin-film lithium niobate on insulator (LNOI) has recently emerged as a promising platform for high-speed optical communication devices. For practical applications, an efficient, polarization-insensitive, misalignment-tolerant and broadband fiber-to-chip optical coupler is necessary. In this letter, we present a fiber-to-chip edge coupler based on trident spot-size convertor (SSC). Experiment shows 1.18/1.10 dB per facet low loss at 1550 nm for TE/TM polarization respectively. A relatively large alignment tolerance (AT) has also been demonstrated. Over a broadband wavelength range from 1490 nm ~ 1640 nm, the edge coupler exhibits a maximum loss of 1.30 dB, a wavelength dependent loss (WDL) of 0.23 dB for TE mode and a polarization dependent loss (PDL) of 0.33 dB when coupled to a single mode fiber (SMF) with a mode field diameter (MFD) of ~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6~\mu \text{m}$ </tex-math></inline-formula> .

Effects of Atypical Hydrogen Bonds and π-π Interactions on Nonlinear Optical Properties: Dimers of Triangular Structures Based on Perylene, Naphthalene, and Pyromellitic Diimides.

Nonlinear optical (NLO) materials have become important materials in the field of high-speed optical devices due to the changes in light absorption and refraction caused by the photoelectric field. Compounds tend to exist as aggregates rather than single molecules, so intermolecular interactions are crucial to the nature of aggregates. Therefore, to study the effects of intermolecular interactions on nonlinear optical properties, we use a dimer simplified model and adopt the methods of controlling variables, which are the different intermolecular interactions resulting from the different stacking patterns of dimers based on the same monomer structures (2PMDI-1NDI and 2NDI-1PDI). It is found that compared with dimers involving π-π interactions, dimers involving C-H···O interactions have shorter intermolecular distances, larger intermolecular interaction energies, and smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps. Moreover, the C-H···O interactions are more conducive to the intermolecular charge transfers and more beneficial for increasing the nonlinear optical response values of aggregates with respect to π-π interactions. This work provides an important basis for the influence of intermolecular interactions on nonlinear optical properties.

Single-step etched grating couplers for silicon nitride loaded lithium niobate on insulator platform

Dielectrically loaded thin-film lithium niobate (LiNbO3) on insulator (LNOI) platforms have enabled a range of photonic integrated circuit components, such as high-speed optical modulators, switches, and nonlinear devices, while avoiding the direct etching of the LiNbO3 thin film. Silicon nitride (Si3N4) is one of the most attractive dielectric loading materials as it has a similar refractive index and transparency window to LiNbO3 and can be deposited and patterned by mature fabrication processes. The patterning of Si3N4 opens the opportunity to fabricate grating couplers in the same fabrication step, providing efficient optical interfaces for wafer-scale testing. In this paper, we investigate and demonstrate single-step etched grating couplers on a Si3N4-LNOI (X-cut) platform. The grating couplers (straight and curved) are designed and fabricated for TE-polarized modes along the Y and Z crystallographic directions, considering the LiNbO3 crystal’s birefringence. The experimentally demonstrated coupling losses are as low as 4.02 and 4.24 dB along the crystallographic Y and Z directions, respectively. The corresponding peak wavelengths are 1609 and 1615 nm, respectively. The measured 3-dB bandwidths are wider than 70 nm for both crystallographic directions. We also numerically investigated the influence of fabrication variations and the fiber angle on the transmission. To the best of our knowledge, this work is the first demonstration of grating couplers with different light propagation directions on the Si3N4 loaded LNOI platform.

Precise Optical Modulation and Its Application to Optoelectronic Device Measurement

Optoelectronic devices which play important roles in high-speed optical fiber networks can offer effective measurement methods for optoelectronic devices including optical modulators and photodetectors. Precise optical signal modulation is required for measurement applications. This paper focuses on high-speed and precise optical modulation devices and their application to device measurement. Optical modulators using electro-optic effect offers precise control of lightwaves for wideband signals. As examples, this paper describes frequency response measurement of photodetectors using high-precision amplitude modulation and wavelength domain measurement of optical filters using fast optical frequency sweep. Precise and high-speed modulation can be achieved by active trimming which compensates device structure imbalance due to fabrication error, where preciseness can be described by on-off extinction ratio. A Mach-Zehnder modulator with sub Mach-Zehnder interferometors can offer high extinction-ratio optical intensity modulation, which can be used for precise optoelectronic frequency response measurement. Precise modulation would be also useful for multi-level modulation schemes. To investigate impact of finite extinction ratio on optical modulation, duobinary modulation with small signal operation was demonstrated. For optical frequency domain analysis, single sideband modulation, which shifts optical frequency, can be used for generation of stimulus signals. Rapid measurement of optical filters was performed by using an optical sweeper consisting of an integrated Mach-Zehnder modulator for optical frequency control and an arbitrary waveform generator for generation of a source frequency chirp signal.

An all optical photonic crystal half adder suitable for optical processing applications

Abstract Increasing the speed of operation in all optical signal processing is very important. For reaching this goal one needs high speed optical devices. Optical half adders are one of the important building blocks required in optical processing. In this paper an optical half adder was proposed by combining nonlinear photonic crystal ring resonators with optical waveguides. Finite difference time domain method wase used for simulating the final structure. The simulation results confirmed that the rise time for the proposed structure is about 1 ps.

Tungsten-doped Ge2Sb2Te5 phase change material for high-speed optical switching devices

The large impedance mismatch between the highly resistive amorphous state and the highly conductive crystalline state of Ge2Sb2Te5 is an impediment for the realization of high-speed electrically switched optical devices. In this paper, we demonstrate that tungsten doping can reduce this resistivity contrast and also results in a lower amorphous state resistivity. Additionally, it lowers the contact resistance, improves the optical contrast, and extends the face-centered-cubic state up to 350 °C, with a minimal impact on thermal conductivity.

Optical properties of nanopatch antennas based on plasmonic nanoparticles and ruthenium complex

In this work, a significant reduction (up to 7 ns) of the excited states lifetime of the Ru dye (with a decay time of 850 ns) in an inhomogeneous «aluminium – silver nano-prism system (nano-patch antenna, NPA)», as well as an increase in the photoluminescence emitter to 2-3 times. The increase in the spontaneous emission rate of this substance is caused by the Purcell effect. The Purcell coefficient for the emitter in the cavity with hexagonal silver particles was 120. This decrease in the spontaneous emission decay time in the nano-patch antenna configuration is associated with an increase in the local density of photon states in the plasmon resonator, which increases the probability of a spontaneous transition from the excited state of the emitter. The results obtained by shortening the spontaneous emission time and increasing the intensity of the emitter radiation in a nano-patch antenna show possible prospects for using quantum dots and individual molecules with shorter luminescence times in nano-patch antennas. Such nano-patch antennas can form the basis for creating compact high-speed optical devices. Modeling in the mathematical package Comsol Multiphysics showed that the maximum values of the Purcell factors can exceed 104 in the NPA.

Self-driven visible-near infrared photodetector with vertical CsPbBr3/PbS quantum dots heterojunction structure

Self-driven photodetectors are widely used in communication and imaging. As a newly developed semiconductor material, perovskite quantum dots (QDs) are not only bandgap tunable, but also easily combined with other materials. In this paper, a vertical structure self-driven photodetector based on heterojunction of CsPbBr3 QDs and PbS QDs is proposed, and the device is prepared by solution spin coating method. The device can work in visible and near infrared (400–1130 nm) regions, and has excellent performance, such as ultrafast response speed (rise and decay time are 0.4 μs/0.73 μs under 532 nm laser irradiation in self-driven mode, the estimated response time under 1064 nm laser irradiation is about 11.5 μs), more than 100 dB linear dynamic range for both visible and infrared regions, and good stability. Similarly, the responsivity of the photodetector can also reach an average of 10 mA W−1, and the detectivity is 1.13 × 1010 Jones at 0 V bias for 1064 nm laser irradiation. The device combines two kinds of QDs revealing its good prospects and great advantages in self-driven photodetectors and high-speed optical communication devices.

Optical Fiber Transfer Delay Measurement Based on Phase-Derived Ranging

High-accuracy optical fiber transfer delay (OFTD) measurement with a broad measurement range is essential for the development of high-speed or parallel optical devices and systems. In this letter, we propose a system for OFTD measurement using the phase-derived ranging. A microwave signal is converted into an optical signal, which is transmitted through a fiber under test. After photodetection, the OFTD is converted into the phase shift of the microwave signal, which can be detected using a microwave phase detector. When calculating the OFTD, the phase error is divided by the highest microwave frequency, which ensures the high measurement accuracy. The integer ambiguity caused by the phase detection can be removed by sweeping the microwave frequency in a range of 1 MHz. An experiment is performed. The measurement of a motorized variable optical delay line and a long fiber shows that a dynamic range of more than 20 km and an accuracy of ±0.1 ps can be achieved with no dead zone.

Ultra-contrast ratio optical encoder using photonic crystal waveguide

In recent year, ultra-compact and high-speed optical logic devices are extremely attractive for the scientific community and optical computing. In this paper, 2 × 1 encoder is proposed and designed using two-dimensional photonic crystal based microstructure. This logic device is constructed by point and line defects in a triangular lattice with silicon rod embedded in air host. The encoder performances are analyzed by using Finite Difference Time Domain method. The numerical results reveal that the designed micro device is capable of working accurately for different logic states. The proposed device is operated at 1520 nm, and it provides a high contrast ratio of 25.82 dB, the excellent response time of 0.2833 ps and a bit rate of around 3.52 Tbps. Hence, it is highly suitable for an optical signal processor and photonic integrated circuits.

High-Frequency and Integrated Design Based on Flip-Chip Interconnection Technique (Hi-FIT) for High-Speed (&gt;100 Gbaud) Optical Devices

High-Frequency and Integrated Design Based on Flip-Chip Interconnection Technique (Hi-FIT) for High-Speed (&gt;100 Gbaud) Optical Devices

Propagation properties of optical soliton in an erbium-doped tapered parabolic index nonlinear fiber: soliton control

In this paper, with the aid of symbolic computation, we investigate the generalized nonlinear Schrodinger Maxwell–Bloch equation, which describes the propagation of the optical soliton through an inhomogeneous two-level dielectric tapered fiber medium. By virtue of the Darboux transformation method, two-soliton solutions are generated based on the constructed Lax pair and figures are plotted to illustrate the properties of the obtained solutions. Moreover, through manipulating the dispersion and nonlinearity profiles, various soliton control systems are investigated which is promising for potential applications in the design of soliton compressor, soliton amplification and high-speed optical devices in ultralarge capacity transmission systems. This means that we are able to control the soliton types with suitably selected values of the parameters. Additionally more soliton control techniques are proposed and investigated. We expect that the above analysis could be observed in future experiments.

Study of all-optical logic XNOR gate based on XGM in linear optical amplifier

Future digital optical communication cannot develop without all-optical high-speed optical devices, especially in the field of high speed large capacity optical transmission, all-optical packet switching and optical computing, and thus optical logic devices are becoming a hotter spot of research. Based on the cross-gain modulation (XGM), a novel scheme of all-optical logic XNOR gate using linear optical amplifier (LOA) is presented in this paper. LOA results show a good gain characteristic, which can get better output logic operation than traditional semiconductor optical amplifier (SOA). Choosing suitable injection current, wavelength scope of the input signal and CW power can achieve better logic operation effect.

Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces

Strong interaction of graphene with light accounts for one of its most remarkable properties: the ability to absorb 2.3% of the incident light's energy within a single atomic layer. Free carrier injection via field-effect gating can dramatically vary the optical properties of graphene, thereby enabling fast graphene-based modulators of the light intensity. However, the very thinness of graphene makes it difficult to modulate the other fundamental property of the light wave: its optical phase. Here we demonstrate that considerable phase control can be achieved by integrating a single-layer graphene (SLG) with a resonant plasmonic metasurface that contains nanoscale gaps. By concentrating the light intensity inside of the nanogaps, the metasurface dramatically increases the coupling of light to the SLG and enables control of the phase of the reflected mid-infrared light by as much as 55° via field-effect gating. We experimentally demonstrate graphene-based phase modulators that maintain the amplitude of the reflected light essentially constant over most of the phase tuning range. Rapid nonmechanical phase modulation enables a new experimental technique, graphene-based laser interferometry, which we use to demonstrate motion detection with nanoscale precision. We also demonstrate that by the judicious choice of a strongly anisotropic metasurface the graphene-controlled phase shift of light can be rendered polarization-dependent. Using the experimentally measured phases for the two orthogonal polarizations, we demonstrate that the polarization state of the reflected light can be by modulated by carrier injection into the SLG. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.

Multi-structural optical devices modeling using graphene tri-layer sheets

In this paper, multi-structural optical devices are designed based on graphene tri-layer sheets using finite deference time domain (FDTD) method with surface boundary condition (SBC). The perfectly matched layer (PML) absorbing boundary condition is also used with FDTD SBC to terminate the computational space. Numerical demonstration of plasmon polaritons (SPPs) wave propagating along variety shaped tri-layer graphene sheets is presented of the proposed method by means of utilizing the gate voltage dependent property of graphene. Finally, the theoretical fabrication of a straight line interferometer, L-shaped optical waveguide and T-shaped optical splitter based on the proposed model is presented. The paper provides an effective technique in modeling multi-layer graphene based high-speed and ultra-compact optical devices.

Enhanced performance configuration for fast-switching deformed helix ferroelectric liquid crystal continuous tunable Lyot filter.

In this paper, we present a novel design configuration of double DHFLC wave plate continuous tunable Lyot filter, which exhibits a rapid response time of 185 μs, while the high-contrast ratio between the passband and stop band is maintained throughout a wide tunable range. A DHFLC tunable filter with a high-contrast ratio is attractive for realizing high-speed optical processing devices, such as multispectral and hyperspectral imaging systems, real-time remote sensing, field sequential color display, and wavelength demultiplexing in the metro network. In this work, an experimental prototype for a single-stage DHFLC Lyot filter of this design has been fabricated using photoalignment technology. We have demonstrated that the filter has a continuous tunable range of 30 nm for a blue wavelength, 45 nm for a green wavelength, and more than 50 nm for a red wavelength when the applied voltage gradually increases from 0 to 8 V. Within this tunable range, the contrast ratio of the proposed double wave plate configuration is maintained above 20 with small deviation in the transmittance level. Simulation and experimental results showed the proposed double DHFLC wave plate configuration enhances the contrast ratio of the tunable filter and, thus, increases the tunable range of the filter when compared with the Lyot filter using a single DHFLC wave plate. Moreover, we have proposed a polarization insensitive configuration for which the efficiency of the existing prototype can theoretically be doubled by the use of polarization beam splitters.

Picosecond Carrier Spin Relaxation in In0.8Ga0.2As/AlAs/AlAs0.56Sb0.44 Coupled Double Quantum Wells

The carrier spin relaxation of In0.8Ga0.2As/AlAs/AlAs0.56Sb0.44 coupled double quantum wells is investigated by spin-dependent pump and probe reflectance measurements with a high time resolution of 200 fs. The observed fast spin relaxation time of 9 ps at room temperature indicates high potential for applications to high-speed optical devices. A negative temperature dependence of spin relaxation time is observed between 100 K and room temperature. The spin relaxation is found to be governed by the Bir–Aronov–Pikus process between 10 and 100 K and by the D'yakonov–Perel' and Elliott–Yafet processes between 100 K and room temperature.

Exciton spin relaxation in In0.53Ga0.47As/AlAs0.56Sb0.44 quantum wells

The spin relaxation process of In0.53Ga0.47As/AlAs0.56Sb0.44 quantum wells is investigated by spin-dependent pump and probe reflectance measurements with a high time resolution of 200 fs. The observed spin relaxation time of 17.5 ps at 20 K indicates high potential for applications to high-speed optical devices. A positive temperature dependence of the spin relaxation time due to the unique band structure is observed at 30–100 K. The spin relaxation is found to be mainly governed by the Bir-Aronov-Pikus process [Sov. Phys. JETP 42, 705 (1976)] below 100 K and by the D’yakonov-Perel’ process above 100 K.