Optical Intensity Research Articles

Large wavelength bandwidth Mach-Zehnder modulator based on optical intensity equalization structure

In this paper, we propose a large wavelength bandwidth Mach-Zehnder modulator based on light intensity equalization structure. The modulator is designed into a symmetric structure to increase the optical operating bandwidth. Besides, two auxiliary MZIs are connected to the respective phase shifters of the main modulator to balance the optical intensity in them. Compared with a conventional Mach-Zehnder modulator, this design has a larger optical operating bandwidth over 56.1 nm. Besides, the maximum extinction ratio of this modulator is 26.2dB, which is 12 dB higher than that of a conventional one. The dynamic extinction ratios at speed of 40Gbps are 4.10 dB in the wavelength of 1530nm and 4.02 dB in the wavelength of 1560 nm respectively. The 3 dB electro-optical bandwidth of this modulator under different voltages are almost consistent with the performance of the conventional one. All of these prove that this structural design can effectively increases the performance of Mach-Zehnder modulators.

Complexity curtailed MLSE equalizer based on a compact look-up-table for C-band DSB IM/DD transmission.

Chromatic dispersion appears to be a major performance limiting problem in optical intensity modulation direct detection (IM/DD) transmission systems, especially for a double-sideband (DSB) signal. We propose a complexity-reduced look-up-table based maximum likelihood sequence estimation (LUT-MLSE) for DSB C-band IM/DD transmission based on pre-decision-assisted trellis compression and a path-decision-assisted Viterbi algorithm. To further compress the size of the LUT and reduce the length of the training sequence, we proposed a finite impulse response (FIR) and LUT hybrid channel model for the LUT-MLSE. For PAM-6 and PAM-4, the proposed methods can compress the size of the LUT into 1/6 and 1/4, and reduce the number of multipliers by 98.1% and 86.6% with slight performance degradation. We successfully demonstrate a 20-km 100-Gb/s PAM-6 and a 30-km 80-Gb/s PAM-4 C-band transmission over dispersion-uncompensated links.

A Stacked Multi-Sensor Platform for Real-Time MRI Guided Interventions

We present a stacked temperature, pressure, and localization platform, targeted for minimally invasive surgical and diagnostic applications under Magnetic Resonance Imaging. The platform comprises a micro-fabricated three-layer (Titanium-Parylene-Titanium) membrane pressure sensor, a Gallium Arsenide band-gap temperature sensor, and a magnetic material on double prism retro-reflector that benefits from Magneto-Optic Kerr effect as a magnetic field sensor, to provide localization feedback under Magnetic Resonance Imaging. All sensors can be addressed with a single fiber optic cable, where the collected light is directed to a spectrometer and a polarimeter. For the three-layer microfabricated membrane sensor, an analytical formulation is derived, linking the pressure to optical intensity. Moreover, finite-element simulation results are provided, verifying analytical findings. Wavelength division multiplexing is exploited to address the sensors simultaneously. We measured sensitivities of 0.025 millidegree/Gauss rotation of polarization, 1.5 nm/mmHg displacement (in agreement with simulation results and analytical findings), 0.36 nm/°C bandgap wavelength shift for magnetic field, pressure, and temperature sensors; respectively. With further development, the proposed device can be adapted to a clinical setting for use in Magnetic Resonance assisted surgical procedures.

Loss-induced suppression, revival, and switch of photon blockade

Loss-induced transparency (LIT), featuring the revival of optical intensity by adding loss, has been demonstrated in classical optics. However, a fundamental question has remained unexplored, i.e., during the process of LIT, whether quantum correlations of the photons can also be revived or even tuned by increasing the loss. Here we find that, accompanying classical LIT in a nonlinear optical-molecule system, a purely quantum effect as photon blockade (PB) indeed can be revived with the help of loss. In particular, a quantum critical point emerges in the system: below the point, adding loss leads to the suppression of optical intensity and its correlations; in contrast, by surpassing the point, PB is revived and enhanced with more losses. Also, a quantum switch between single-PB and two-PB can be realized by simply tuning the loss. Our work provides a counterintuitive strategy to engineer quantum devices in a practical lossy environment.

Experimental study of dynamics and soft X-ray emission of laser produced plasma from low-density foam Ti targets

Low-density foam targets are expected to be good candidates for efficient laser produced plasma (LPP) and soft X-ray (SXR) sources due to the less energetic debris compared with solid targets. Three Ti targets with different densities were irradiated by a pulsed Nd:YAG laser in vacuum. The average ion energy and the time-of-flight (TOF) peak voltage decreased as the Ti target density decreased. Furthermore, the differences among the three Ti targets increased with increasing laser intensity. The average ion energy of low-density foam Ti targets had a slightly weaker angular dependence compared with solid Ti targets. The plasma plume optical images illustrated that solid Ti plasma expanded faster in the direction of laser incidence with stronger anisotropy compared to foam Ti plasma. In addition, the optical radiation intensity integrated from a wavelength region of 200–850 nm of plasma plume increased with decreasing initial target density, which indicated that more absorbed laser energy was converted to plasma optical radiation energy (internal energy) instead of ion kinetic energy for targets with lower initial densities. The SXR radiation had no significant difference among the three Ti targets. These results demonstrate that appropriately reducing the initial target density can significantly reduce kinetic energy of ion debris without affecting the SXR radiation output.

Effect of Chitosan and Amphiphilic Polymers on the Photosensitizing and Spectral Properties of Rose Bengal.

The influence of chitosan (CS) and amphiphilic polymers (AP: pluronic F108 and polyvinylpyrrolidone (PVP)) on the photocatalytic activity of rose bengal (RB) in a model reaction of tryptophan photo-oxidation in phosphate-buffered saline (PBS) was studied. It was shown that in the presence of CS, the effective rate constant keff of tryptophan photo-oxidation catalyzed by RB in PBS solution decreases by a factor of two. This is due to the ionic interaction of the RB with the chitosan. Rose bengal in a slightly acidic environment (pH 4.5) passes into a neutral lactone form, which sharply reduces the photosensitizing properties of the dye. It was demonstrated that the introduction of AP into a solution containing RB and CS prevents direct interaction between RB and CS. This is evidenced by the presence of photocatalytic activity of the dye in the RB-AP-CS systems, as well as bathochromic shifts of the main absorption bands of the dye, and an increase in the optical density and luminescence intensity of the RB when AP is introduced into a buffer solution containing RB and chitosan. The presence of RB-CS and RB-AP interaction in aqueous and PBS media is confirmed by the increase in the degree of fluorescence anisotropy (r) of these binary systems. In an aqueous solution, the value of r for the RB-F108-CS system decreases by a factor of 3.5 (compared to the value of r for the RB-CS system), which is associated with the localization of the dye in pluronic micelles. In PBS, the fluorescence anisotropy is practically the same for all systems, which is related to the stability of the dye structure in this medium. The presence of interaction between RB and AP in aqueous solutions was confirmed by the proton NMR method. In addition, the formation of RB-F108 macromolecular complexes, which form associates during solution concentration (in particular, during evaporation), was shown by AFM. Such RB-AP-CS systems may be promising for practical application in the treatment of local foci of infections by aPDT.

Mitigating end-to-end nonlinearity in LED-based VLC transceivers via optical intensity feedback: erratum.

We present an erratum to our Letter [Opt. Lett.47, 3688 (2022)10.1364/OL.463637]. This erratum corrects subscript errors in Eq. (1), H1 and H2. These errors could confuse readers when they perform the derivation processes, but the errors do not affect our experimental results. Therefore, these corrections do not affect the results and conclusions of the original Letter.

Subwavelength Quasi-Periodic Array for Infrared Antireflection.

Infrared antireflection of a zinc sulfide (ZnS) surface is important to improve performance of infrared detector systems. In this paper, double-pulse femtosecond laser micro-machining is proposed to fabricate a subwavelength quasi-periodic array (SQA) on ZnS substrate for infrared antireflection. The SQA consisting of approximately 30 million holes within a 2 × 2 cm2 area is uniformly formed in a short time. The double-pulse beam can effectively suppress the surface plasma shielding effect, resulting in obtaining a larger array depth. Further, the SQA depth is tunable by changing pulse energy and pulse delay, and can be used to readily regulate the infrared transmittance spectra as well as hydrophobicity. Additionally, the optical field intensity distributions of the SQA simulated by the rigorous coupled-wave analysis method indicate the modulation effect by the array depth. Finally, the infrared imaging quality captured through an infrared window embedded SQA is evaluated by a self-built infrared detection system.

Programmable Parallel Optical Logic Gates on a Multimode Waveguide Engine

Optical logic gates have been proposed and demonstrated on a function programmable waveguide engine constructed using buried silicon nitride waveguides in polymer and a set of thermal electrodes. The device can perform logic AND or OR operations for the input signals A and B, each containing two bits of information, in parallel. The input signals, in the form of binary current values in the electronic domain, are applied to a subset of thermal electrodes, while the computed logic states are converted to optical intensity variations at the single-mode waveguide outputs. The rest of the electrodes work as weights to define the device function, either AND or OR, by adjusting the light interference in the multimode waveguide through thermo-optic effect. Simulations were first performed to reveal the nonlinear response of the received light intensity with respect to the applied current, thus allowing complex and effective manipulation of the light field on the waveguide engine. After chip fabrication and system integration, 65,536 experiments were performed automatically. The data are fed into a sorting program to find the valid settings that satisfy the respective truth table out of the 283,852,800 possible input/weight/output combinations. Four cases of operations for the AND and OR gates are presented in the end, with different bar and contrast values. This simple, low-cost yet powerful engine may be further developed for applications in on-chip photonic computing and signal switching.

Metallic support films reduce optical heating in cryogenic correlative light and electron tomography

Super-resolved cryogenic correlative light and electron tomography is an emerging method that provides both the single-molecule sensitivity and specificity of fluorescence imaging, and the molecular scale resolution and detailed cellular context of tomography, all in vitrified cells preserved in their native hydrated state. Technical hurdles that limit these correlative experiments need to be overcome for the full potential of this approach to be realized. Chief among these is sample heating due to optical excitation which leads to devitrification, a phase transition from amorphous to crystalline ice. Here we show that much of this heating is due to the material properties of the support film of the electron microscopy grid, specifically the absorptivity and thermal conductivity. We demonstrate through experiment and simulation that the properties of the standard holey carbon electron microscopy grid lead to substantial heating under optical excitation. In order to avoid devitrification, optical excitation intensities must be kept orders of magnitude lower than the intensities commonly employed in room temperature super-resolution experiments. We further show that the use of metallic films, either holey gold grids, or custom made holey silver grids, alleviate much of this heating. For example, the holey silver grids permit 20× the optical intensities used on the standard holey carbon grids. Super-resolution correlative experiments conducted on holey silver grids under these increased optical excitation intensities have a corresponding increase in the rate of single-molecule fluorescence localizations. This results in an increased density of localizations and improved correlative imaging without deleterious effects from sample heating.

Power dependent nonlinear optical characteristics and two-photon absorption of NiO/PVA thin film

The NiO/PVA thin film was prepared by drop-casting the nickel oxide nanoparticles synthesized by the chemical precipitation method. The structural and optical characteristics of the film were investigated using XRD and UV-VIS absorption. The nonlinear optical property of the Nickel oxide thin film was studied by the open aperture Z-scan method at 532 nm. The two-photon absorption coefficient of the film was calculated with different optical intensities. With increasing input intensity, the value of the two-photon absorption coefficient has decreased. This is attributed to the saturation of two-photon absorption mechanism. The NiO/PVA film can be used for optical limiting applications.

(INVITED)Judd-Ofelt analysis, visible to NIR photoluminescence emission under 450 nm and 976 nm excitations and energy transfer of barium fluorotellurite glasses doping with Ho3+, Yb3+, Ho3+:Yb3+

Barium fluorotellurite glasses doping with Ho3+, Yb3+, and Ho3+:Yb3 were fabricated using the conventional melt and quenching method, and their optical properties were studied using different optical spectroscopic techniques. The FITR absorption band at 3000 cm−1 was used to investigate OH- concentrations of the prepared glasses, which increased with Yb3+ content. However, it decreased by substituting a portion of BaF2 content with Ba2CO3 concentration. The electric dipole line strengths and Judd-Ofelt parameters were estimated using UV–visible near-infrared (NIR) optical absorption spectra to gain information on the rare earth ions doped glasses for laser applications. The various radiative parameters such as line strengths, optical intensity, and radiative rates from the higher energy levels, including 5F4+5S2, 5F5, 5I4,5I5,5I6 and 5I7, to the ground state, 5I8 have been reported and discussed. The influence of the Yb3+ and Ba2CO3 concentrations on the upconversion and downconversion photoluminescence emission intensities of the glasses prepared have been investigated by pumping with 450 nm and 976 nm excitation sources. Under 450 nm and 976 nm, the NIR photoluminescence emissions reveal a band ranging from 980 nm to 1220 nm attributing to an overlap between Yb3+ and Ho3+ transitions. The influence of Yb3+ concentration on photoluminescence lifetime at the 2F5/2→2F7/2, 5F4+5S2 →5I8 and 5I6 →5I8 transitions under 976 nm laser excitation has been studied and reported. The results indicate that lifetime decreases with increasing Yb3+ concentration attributing to an efficient energy transfer from Yb3+ to Ho3+ ions. The energy transfer efficiency from Yb3+ → Ho3+ has been examined, which rises from 30% to 47% upon increasing Yb3+ content. Nevertheless, it decreases with the mixing of BaF2 and Ba2CO3 lattice modifier contents. The results demonstrated that the 1200 nm (5I6 →5I8 transition) has remarkable potential for developing fiber lasers.

11.2: Invited Paper: Study of Green LED Growth for Advanced Display Applications

Advanced display technology has various potential applications with a huge potential market. Recently, mini‐LEDs and micro‐LEDs are attracting great attentions for advanced display applications because of the high dynamic range, high ambient contrast ratio, thin profile, and low power consumption [1]. Due to higher indium composition in the active layers, green LEDs' wavelength is more sensitive to temperature variation. Higher indium content InGaN layers also make green LEDs seriously suffer from quantum confined stark effect (QCSE). So it is much more difficult to get good wavelength uniformity and high efficiency for green LEDs. In this work, several factors including local temperature tuning, stress control during epitaxy growth, substrate pattern size and substrate orientation have been studied to improve green mini‐LED's wavelength uniformity and optical intensity.

Application of additional high-frequency modulation to reduce influence of residual amplitude modulation LiNbO3 phase modulator on fiber optical gyroscope signal

Residual amplitude modulation in LiNbO3 phase modulator is one of the key factors that limit the accuracy of high-sensitive fiber-optical sensors. A fiber-optical gyroscope is an angular velocity sensor whose sensitivity is better than 0.001 °/h. Optical light intensity changes after phase modulator is a reason for wrong phase difference that introduces an error in the angular velocity signal. Most existing residual amplitude modulation suppression methods are based on reduction of back reflections between an optical fiber and integrated optical waveguide, absorbing groove to suppress or reduce reflection on the bottom face, and algorithmic compensation. In this paper, new approach to reduce residual amplitude modulation in LiNbO3 for fiber optical gyroscope application is presented. Method feature is an application of additional differential signal modulation with uniform amplitude distribution in the input signal voltage range of the phase modulator. The proposed method allows to suppress residual amplitude modulation of the multifunctional integrated optical circuit phase modulator more than 3 times using additional triangle signal modulation with the frequency f = 200.09 MHz and power P = 36 dBm. This method is suitable for improving fiber optical gyroscope accuracy. Moreover, it could be applied for any fiber-optic sensors based on LiNbO3 phase modulator. The paper will be of interest to specialists in the field of highly sensitive fiber optical sensors, fiber, and integrated optics.

Multiwavelength observations of Swift J0243.6+6124 from 2017 to 2022

Context.Swift J0243.6+6124 is a high-mass X-ray binary that went into a giant X-ray outburst in 2017. During this event, the X-ray luminosity reached the highest value ever measured in a galactic Be/X-ray binary. Aims. Our aim is to study the long-term variability of Swift J0243.6+6124 after the 2017 major X-ray outburst. Methods. We have obtained optical spectroscopy and photometry data during four years after the event. The long-term photometric light curve and the equivalent widths of the Hα and He I λ6678 lines were used to monitor the state of the Be star’s circumstellar disk. The Hα line profiles show evidence for V/R variability that was accounted for by fitting the Hα spectral line profile with two Gaussian functions. We divided our data into three phases according to the intensity of the X-ray, optical, and infrared emission. Results. Phase I covers the rise and decay of the giant X-ray outburst that took place in October–November 2017. We interpret phase II as the dissipation of the Be star’s equatorial disk and phase III as its recovery. The timescale of a complete formation and dissipation process is about 1250 days. The epoch when the dissipation process stopped and the reformation period began is estimated to be around MJD 58530. We find a delay of ∼100–200 days between the minimum of the optical or infrared intensity and the strength of the Hα line after the X-ray outburst, which may indicate that the dissipation of the disk begins from the inner parts. The motion of the density perturbation inside the disk is prograde, with a V/R quasi-period of about four years. The source shows a positive correlation in the (B − V) color index versus V-band magnitude diagram, which implies that the system is seen at a small or moderate inclination angle. Conclusions. Despite the super-Eddington X-ray luminosity during the outburst, the subsequent pattern of long-term optical and IR variability of Swift J0243.6+6124 is typical of Be/X-ray binaries.

High-SNR Capacity of MIMO Optical Intensity Channels: A Sphere-Packing Perspective

This letter investigates the capacity for the multiple-input multiple-output (MIMO) optical intensity channels in the high signal-to-noise ratio (SNR) regime from a sphere-packing (SP) perspective. In such a channel, the inputs represent optical intensities, hence are nonnegative. Considering the peak- and average-power constraints for the inputs, the high-SNR capacity can be expressed in terms of the volume of an image signal space through an SP argument. When the number of transmit antennas <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n_{\mathrm{T}} $ </tex-math></inline-formula> and receive antennas <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n_{\mathrm{R}} $ </tex-math></inline-formula> satisfies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n_{\mathrm{T}} \leq n_{\mathrm{R}} $ </tex-math></inline-formula> , the image-space volume is derived in terms of singular values of the channel matrix. While for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n_{\mathrm{T}} &gt; n_{\mathrm{R}} $ </tex-math></inline-formula> , the image-space volume is derived by decomposing the image space into multiple non-overlapping subpolytopes, whose volumes can be conveniently calculated.

On the General Error Event Probability Evaluation of Optical Intensity Modulation Schemes

Wireless intensity-modulated optical channels feature some very specific differences compared to wireless radio channels. These properties have a strong impact on the performance of digital modulation techniques. This paper discusses basics to consider when designing optical intensity modulation schemes. We introduce an error event probability expression for such modulation schemes that is generally applicable for all non-negative waveforms. We indicate the importance of amplitude fluctuations and the influence of pulse shaping on the power efficiency in the optical domain. In numerical examples, we apply the error event probability expression to modifications of orthogonal frequency-division multiplexing and to Hadamard coded modulation.

Study on 1.9 [formula omitted]m structured lasers based on Ince–Gaussian modes superposition with multi-modulation by different directions off-axis dual-end-pump

The double IGp,pe modes multi-modulation superposition evolution structured lasers output is realized, based on the proposed different directions off-axis dual-end-pumping Tm:YLF laser method. Under the modes orthogonal superposition, the theoretical simulation and experimental measurement results have a high degree of agreement, and the orthogonal superposition of double IGp,pe modes within 5 orders is realized, which proves that different order modes and optical field intensity ratio have the capability to modulate the formation of vortex array structured beams. When the low-order IGp,pe modes of the same order are orthogonally superimposed, the phenomenon of superposition of different phase differences occurs, which proves the possibility of modulating the superposition of IGp,pe modes by the phase difference. At the same time, it is found that the regular pattern output of high-order IGp,m modes (odd mode m ≤ 3 or even mode m ≤ 2) can be realized at different angles, which proves the ability of rotation angle to modulate the superposition of double IGp,pe modes. Finally, the 1.9μm Tm:YLF structure laser output with double IGp,pe modes multi-factor composite modulation superposition evolution within 10 orders is realized. When the 10-order double IG10,10e modes are superimposed, the output power exceeds 5.7 W, and the conversion efficiency is higher than 17.5%.

Self-parametric amplification of a bound-state dissipative soliton assisted by spectral filtering effect in the negative dispersion regime

Various striking nonlinear dynamics have been obtained from an ultrafast fiber laser. Herein, we first numerically demonstrate the self-parametric amplification of the bound-state dissipative soliton induced by the spectral filtering effect in the negative dispersion regime. The self-parametric amplification in our work manifests itself as optical spectrum intensity enhancement in the absence of extra pump light injection, which is resulted by the energy flowing within the laser field. Comparing the ultrafast fiber laser system without bandwidth filter and those with 8-nm or 10-nm bandwidth filters respectively, a stable spectrum and two spectral periodic evolutions can be observed, which demonstrates that the spectral filtering effect plays a key role in the self-parametric amplification process. These findings can provide new insights into the complex nonlinear behavior of bound-state dissipative solitons in the ultrafast fiber lasers.

Self-powered, ultraviolet-to-near infrared broadband photodetector based on Ag-doped CsPbI3/PEDOT:PSS heterojunction.

Metal halide perovskites are studied for photodetection applications because of their outstanding optical and electrical properties. A self-powered ultraviolet-to-near infrared broadband photodetector based on a Ag-doped CsPbI3/PEDOT:PSS heterojunction was investigated. The photodetector using a CsPbI3:Ag/PEDOT:PSS heterostructure with a planar photoconductive structure operated over a broad 355-1560 nm wavelength range in self-powered mode. A terahertz signal was modulated with the CsPbI3:Ag/PEDOT:PSS structure at low optical excitation intensity to investigate its photodetection mechanism. The experimentally designed detector can present images of the letters "C", "N" and "U" in the visible and near-infrared wavelengths, indicating a potential broadband imaging application.