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Gain-enhanced chiral sensing

Sotiris Droulias

DOI: 10.1364/JOSAB.430588 Received 03 May 2021; Accepted 02 Aug 2021; Posted 02 Aug 2021  View: PDF

Abstract: The inherent weak nature of chiroptical signals provided by typical polarimetric measurements of natural optically active media has led to the development of different techniques to achieve enhanced chiral sensing. Intuitively, the introduction of gain could provide the desired enhancement, however this requires gain media that can couple directly to the chiral medium. Here we show that nanophotonic systems that generate collinear electric and magnetic dipole moments can mediate the coupling between the gain and chiral medium, leading to signals stronger than those achieved by the chiral medium alone or when combined with the same nanophotonic system without gain. Because, depending on how strongly gain couples with the nanophotonic system, both background amplification and loss compensation are possible, we show that the enhancement occurs within the regime of loss compensation, as background amplification may as well result in amplified transmitted fields, but does not guarantee the enhancement of chiroptical signals.

Ultrafast all optical metamaterial THz switch by exploiting nanoparticle-enriched substrate nonlinearity and graphene resonator

Nasrollah Karampour and Najmeh Nozhat

DOI: 10.1364/JOSAB.432096 Received 21 May 2021; Accepted 02 Aug 2021; Posted 02 Aug 2021  View: PDF

Abstract: Emergence of graphene as a new material with a bunch of extraordinary optical properties paves a way to introduce new electromagnetic devices in the terahertz (THz) band. In this paper, we have exploited the unique qualities of graphene in combination with optical Kerr effect in order to propose a new THz switch. In the proposed structure, two graphene layers with circular and notch ring patterns are stacked to obtain two narrowband absorption peaks at the frequencies of 3.65 and 6.5 THz with high absorption values of 92% and 97%, respectively. The imposed pump power in interaction with the nano-composite substrate provides a controlling mechanism that makes this structure an ideal candidate for all optical devices in THz regime. The obtained switching time of the proposed structure is 2 ps and the maximum extinction ratio of 83% is achieved for the pump power of 273 mW. Moreover, the absorption spectrum of the switch can be manipulated by the chemical potential of graphene layers, which is useful for electro-optical modulation application. The application of the THz switch as an all optical demultiplexer is also studied in this paper.

Full 3D+ 1 modeling of tilted-pulse-front setups for single-cycle terahertz generation: reply

Lu Wang, Tobias Kroh, Nicholas Matlis, and Franz Kaertner

DOI: 10.1364/JOSAB.424203 Received 15 Mar 2021; Accepted 02 Aug 2021; Posted 03 Aug 2021  View: PDF

Abstract: This document serves as a reply to the comments published by M. Bakunov et. al. in order to clarify the claims related to our previous work "Full 3D+ 1 modeling of tilted-pulse-front setups for single-cycle terahertz generation" [J. Opt. Soc. Am. B 37, 1000 (2020)] [1] . Bakunov et. al., claim that formulas used in our work do not correspond to the conventional configuration for tilted-pulse-front terahertz generation, and that we do not include the angular dispersion along the z' dimension. Here, we clarify in detail how our numerical model was set up and show that it does correctly capture the physics of the conventional tilted-pulse-front configuration where the image of the grating is aligned with the tilted pulse front of the pump pulse. We show that angular dispersion both in x' and z' dimensions are fully covered via conversation of momentum instead of a Taylor expansion along the z'. Our numerical model correctly captures the crucial physics and can be readily extended to other cases.

Comprehensive characterization of terahertz generation with the organic crystal BNA

Isaac Tangen, Gabriel Valdivia-Berroeta, Larry Heki, Zachary Zaccardi, Erika Jackson, Charles Bahr, David Michaelis, and Jeremy Johnson

DOI: 10.1364/JOSAB.420597 Received 25 Jan 2021; Accepted 02 Aug 2021; Posted 03 Aug 2021  View: PDF

Abstract: We characterize the terahertz (THz) generation of N-benzyl-2-methyl-4-nitroaniline (BNA), with crystals ranging in thickness from 1 -700 μm. We compare excitation using 800-nm and 1250 to 1500-nm wavelengths. Pumping BNA with 800-nm wavelengths and longer near-infrared wavelengths results in a broad spectrum, producing out to 6 THz using a 100-fs pump, provided the BNA crystal is thin enough. ~200 μm or thinner crystals are required to produce a broad spectrum with an 800-nm pump, whereas ~300 μm thick crystals are optimal for broadband THz generation using the longer wavelengths. We report the favorable THz generation and optical characteristics of our BNA crystals that make them attractive for broadband, high-field THz generation, and we also compare differences in THz properties relative to BNA characteristics reported in other works.

Closed aperture CW Z-scan of L-tryptophan for determination of optical nonlinearity in the thermal regime

Sarfuddin Tarek, Syed Faruque, Sharif Sharafuddin, Khan Hasan, A K M Hossain, Hosne Ara, Manash Biswas, and Yasmeen Haque

DOI: 10.1364/JOSAB.432845 Received 11 Jun 2021; Accepted 01 Aug 2021; Posted 02 Aug 2021  View: PDF

Abstract: The closed aperture (CA) continuous wave (CW) Z-scan of L-tryptophan at 661 nm was performed to investigate the variation of on axis nonlinear phase shift(ΔΦ_0) with the change of optical field strength. ΔΦ_0 was found to vary nonlinearly with irradiance (I_0) in the range from 150 MW/m2 to 290 MW/m2. This nonlinear variation is explained by considering the effect of linear and nonlinear absorption of radiation on the thermo-optical refractive index. Using the quadratic fitting of ΔΦ_0 with I_0 we have found the temperature coefficient of refractive index dn/dT , thermal coefficient of nonlinear refractive index n_2^Tand the nonlinear absorption coefficient β in the observed power regime.

Broadening, nonlinear filtering and compression of microjoule energy laser pulses at 1 um wavelength

Joel Edouard NKECK, Léo Guiramand, xavier ropagnol, and Francois Blanchard

DOI: 10.1364/JOSAB.435905 Received 06 Jul 2021; Accepted 31 Jul 2021; Posted 02 Aug 2021  View: PDF

Abstract: In this work, we experimentally demonstrate the generation of 30 nm of spectral broadening in a bulk cadmium sulfide (CdS) semiconductor generated by a 280-fs long pulse at 1.024 µm wavelength and with a microjoule energy level. Using 2nd-harmonic generation in a barium borate, the complex ring pattern induced by self-focusing due to the strong nonlinear interaction of the laser pulse in the pair of CdS crystals is filtered out using second harmonic nonlinear crystal to recover a Gaussian shape spatial profile. We also present the temporal compression of the resulting 512 nm laser pulse up to 45 fs by using a pair of standard transmissive gratings, leading to a pulse compression factor of 6.13. This technique is compact, inexpensive, robust, and produces ultrafast optical pulses from an input laser pulses whose duration and energy range are generally incompatible with a straightforward compression method in nonlinear optical fibers.

Comprehensive Numerical Evaluation of Amplified Spontaneous Emission in a Multi-slab Nd:glass Laser Amplifier

Xiaoqin Wang, Xuechun Li, Jiangfeng Wang, Jiangtao Guo, Xinghua Lu, Qi Xiao, and Wei Fan

DOI: 10.1364/JOSAB.433131 Received 02 Jun 2021; Accepted 29 Jul 2021; Posted 29 Jul 2021  View: PDF

Abstract: A systematic design of a 100 J/10 Hz multi-slab Nd:glass laser amplifier was proposed. A four-dimensional (4-D) numerical model was developed for exploring the influence of amplified spontaneous emission (ASE) on the stored energy of the laser amplifier. The influences of different parameters, including the doping concentration of the gain slab, pump pulse duration ( ), and pump energy density ( ) absorbed in the gain slab, on the stored energy and storage efficiency were studied in detail. Furthermore, the uniform distribution of the stored energy for a larger aperture of the gain slab and a higher pump energy density of the laser amplifier was determined. In addition, the effects of the slab-to-slab transfer of ASE rays on the stored energy were explored. The results show that the distributions of the stored energy for the 100 J/10 Hz laser amplifier were uniform; furthermore, an average storage efficiency of 60.87% was obtained when the pump energy density absorbed in each slab was 0.9 J/cm2 and the pump duration was 300 µs.

Continuous variable quantum secret sharing using directly modulated lasers

Yingbin Zhu, Ling Zhang, and Duan Huang

DOI: 10.1364/JOSAB.433326 Received 10 Jun 2021; Accepted 28 Jul 2021; Posted 29 Jul 2021  View: PDF

Abstract: Quantum secret sharing (QSS) allows multiple players to achieve unconditional secure communication through a unsecure quantum channel, but the actual implementation requires modulator with high extinction ratio, which means high system expense and difficulty of miniaturization and commercialization. We propose a continuous variable QSS scheme that can replace the traditional lasers and modulators with directly modulated lasers (DML). Each player prepares quantum states through a DML, and sends the signal light to the dealer through a beam splitter into quantum channel. It provides a new way for realizing secret key sharing. Moreover, we introduce the chirp estimation algorithm to realize the phase modulation, which can achieve a two dimensional modulation scheme under a single laser.

Nonlinear optical fullerene and graphene based polymeric 1D photonic crystals: perspectives for slow and fast optical bistability

Ivan Kislyakov, Pavel Ivanov, Jean-Michel Nunzi, Andrey Vlasov, Anton Ryzhov, Anastasia Venediktova, Hongqiang Wang, Zixin Wang, Tianju Zhang, Ningning Dong, and Jun Wang

DOI: 10.1364/JOSAB.428088 Received 19 Apr 2021; Accepted 28 Jul 2021; Posted 28 Jul 2021  View: PDF

Abstract: Nonlinear optical (NLO) properties of materials can be enhanced by assembling them as thin polymer composite films alternating with other polymers and forming dielectric mirrors, one-dimensional photonic crystals (1DPCs), wherein the input light intensity is increased. Based on poly(vinyl carbazole) (PVK) and poly(vinyl alcohol) (PVA) contrasting polymer pair, variants of such structures, with graphene and fullerene in their high-index layers have been produced. Their optical switching characteristics has been studied with ns, cw, and quasi-cw fs laser sources in the IR, and with a fs laser in the visible range. We have demonstrated slow optical bistability in the polymeric 1DPCs determined by the thermal expansion of polymer composites at intensities over 100 W/cm², fast and ultra-fast optical switching due to the thermooptic and Kerr nonlinearities, respectively, in Gr@PVK and C60@PVK composites. Characteristic nonlinear refractive coefficients responsible for these processes were found to be n₂to ~ 10-¹ cm²/GW and n₂Kerr ~ 10-⁴ cm²/GW. A sub-picosecond-fast spectral shift of the 1DPC bandgap has been found. Our results and analysis provide a clear picture of the NLO-behavior of 1DPCs at different time scales. The results simulate the subsequent design of ultra-fast switches and bistable memory cells based on polymeric 1DPCs whose micrometer thickness and flexibility give promises for implementation into fiber and microchip configurations.

Design of highly sensitive interferometric sensors based on subwavelength grating waveguides operating at dispersion turning point

Tianye Huang, Guizhen Xu, Xin Tu, GANGSHUN ZHANG, RongRong Lei, Yiheng Wu, jianxing pan, Liyang Shao, and Perry Shum

DOI: 10.1364/JOSAB.430736 Received 05 May 2021; Accepted 28 Jul 2021; Posted 28 Jul 2021  View: PDF

Abstract: In this paper, a dual-mode interferometric sensor based on a sub-wavelength grating (SWG) waveguide is proposed. The design operates at the dispersion turning point (DTP) of the two dispersive TE modes in the periodic structure, exhibiting a group velocity difference of almost zero, to improve the performance of refractive index (RI) sensors. The necessary conditions for realizing DTP in SWG are analyzed. Moreover, the interference spectrum characteristics and the influence of structural parameters on gas RI sensing performance are further studied. The results show that the sensitivity value of the proposed sensor can reach ~38000 nm/RIU. The proposed structure can also achieve a gas pressure sensitivity of ~105 nm/MPa. The proposed sensors provide a potential platform for highly sensitive RI sensors.

Vision vibration measurement based on coded illumination in a single-frame

Yuanjun Zhang, XingHua Qu, Xiaobo Liang, Lianyin Xu, Jindong Wang, and FuMin Zhang

DOI: 10.1364/JOSAB.430949 Received 07 May 2021; Accepted 28 Jul 2021; Posted 28 Jul 2021  View: PDF

Abstract: A vision-based mechanical vibration measurement is presented and verified by experiments in this paper. The coded illumination is projected on the objects by a DLP projector with a Digital Micromirror Device in it. The projection patterns are designed to be concentric. In one integration time of the camera, the projector is exposed several times, which embeds temporal information in the images. A single-frame can be divided into sub-frames by separating the coded concentric patterns. Fit the centroids of the coded concentric patterns and treat the centroids as virtual feature points with vibration information. The acquisition devices are common low-speed cameras and they record the vibration whose frequency exceeds the camera frame rate. The temporal resolution is increased by 10 times, corresponding to the 400Hz sampling frequency in the experiment. We can measure the vibration of multiple points with different sampling frequencies. The frequency measurement accuracy is in the sub Hertz level, and the amplitude resolution is greater than 100 microns.

T Grating on Nano-Cavity Array based Refractive Index Sensor

Yasir Abed, Md Asif Bhuiyan, and Sajid Choudhury

DOI: 10.1364/JOSAB.426526 Received 31 Mar 2021; Accepted 28 Jul 2021; Posted 29 Jul 2021  View: PDF

Abstract: We report a refractive index sensor comprising of unique T grating on top of periodic nano-cavities. The sensor has two resonant modes sensitive to different regions of the structure with low inter-region interference, hence allows simultaneous detection of two different analytes or more accurate detection of a single analyte. The sensor also provides a self-referencing feature for a broad range of refractive index, from 1.3 to 1.5. Using the FDTD method, the sensitivities of 801.7 nm/RIU and 1386.8 nm/RIU have been recorded for the two modes respectively. The versatility of the structure makes the sensor a prominent candidate for biochemical and other sensing applications.

Small difference between the nonlinear refractions of normal and deuterated solvents measureable by nonlinear ellipse rotation

Julia de Fernandes, Emerson Barbano, JONATHAS SIQUEIRA, and Lino Misoguti

DOI: 10.1364/JOSAB.423211 Received 19 Feb 2021; Accepted 27 Jul 2021; Posted 27 Jul 2021  View: PDF

Abstract: In this work, we have measured the nonlinear refractions of six different normal and deuterated solvents: water, DMSO, methanol, acetone, toluene and, chloroform; by nonlinear ellipse rotation (NER) signal using femtosecond laser pulses. High-precision self-referenced NER measurements could detect small differences between the refractive nonlinearities of normal and deuterated solvents. We observed that the replacement of hydrogen with deuterium atoms slightly reduces the magnitude of the nonlinearity. Basically, the reduction is related to the number of hydrogen and its replacement by deuterium atoms in the molecules, and in this way, toluene (chloroform) presents the major (minor) difference. Also, by measuring the nonlinear refraction as a function of the pulse width, we could observe that the refractive nonlinearity increases as the pulse gets longer. Using a simple empirical model, we could discriminate the ultrafast electronic and delayed orientational refractive nonlinearities of these six pairs of solvents.

Developing an Optimized Metasurface for Light Trapping in Thin Film Solar Cells using a Deep Neural Network and Genetic Algorithm

Mohammad Shameli, Amirhossein Fallah, and Leila Yousefi

DOI: 10.1364/JOSAB.432989 Received 07 Jun 2021; Accepted 27 Jul 2021; Posted 02 Aug 2021  View: PDF

Abstract: In this paper, using a deep neural network and genetic algorithm, an optimized digital metasurface is designed to trap sunlight in thin film solar cells. The deep neural network is trained using full wave numerical simulation results as dataset, and is designed to predict the electromagnetic response of thin film solar cells whose active layers are shaped as a digital metasurface. The developed neural network can predict the results much faster than full wave solvers, and therefore can be used for optimization purposes. Using the results generated by the trained neural network, an evolutionary procedure based on the genetic algorithm is developed to find the optimum structure for the digital metasurface which provides the highest short circuit current inside the thin film solar cell. The performance of the resultant optimum design is validated using full-wave numerical simulation, illustrating a short circuit current of 15.39 mA/cm2 and 13.30 mA/cm2 for TE and TM polarization of the incident light, respectively. The resultant short circuit current is 3.97 and 3.43 times higher than a simple thin film solar cell with the same amount of silicon inside, for TE and TM polarization of the incident light, respectively. To have a more comprehensive comparison, the designed optimum structure is compared with several standard shapes for the metasurface such as star and plus sign. This comparison showed that the optimum structure provides a short circuit current which is much higher than the current achieved by standard shapes.

SU(1,1) interferometry with parity measurement

Shuai Wang and Jiandong Zhang

DOI: 10.1364/JOSAB.430759 Received 05 May 2021; Accepted 27 Jul 2021; Posted 02 Aug 2021  View: PDF

Abstract: We present a new operator method in the Heisenberg representation to obtain the signal of parity measurement within a lossless SU(1,1) interferometer. Based on this method, it is convenient to derive the parity signal directly in terms of input states, including general Gaussian or non-Gaussian state. As applications, we revisit the signal of parity measurement within an SU(1,1) interferometer when a coherent or thermal state and a squeezed vacuum state are considered as input states. In addition, we also obtain the parity signal of a Fock state when it passes through an SU(1,1)interferometer, which is also a new result. Therefore, the operator methodproposed in this work may bring convenience to the study of quantummetrology, particularly the phase estimation based on an SU(1,1)interferometer.

Readout of quantum information spreading using disordered quantum walk

Farzam Nosrati, Alessandro Laneve, Mahshid Khazaei Shadfar, Andrea Geraldi, Kobra Mahdavipour, Federico Pegoraro, Paolo Mataloni, and Rosario Lo Franco

DOI: 10.1364/JOSAB.431752 Received 19 May 2021; Accepted 26 Jul 2021; Posted 26 Jul 2021  View: PDF

Abstract: We design a quantum probing protocol using Quantum Walks to investigate the Quantum Information spreading pattern. We employ Quantum Fisher Information, as a figure of merit, to quantify extractable information about an unknown parameter encoded within the Quantum Walk evolution. Although the approach is universal, we focus on the coherent static and dynamic disorder to investigate anomalous and classical transport as well as Anderson localization. We provide a feasible experimental strategy to implement, in principle, the quantum probing protocol based on the quantum Fisher information using a Mach-Zehnder-like interferometric setup.Our results show that a Quantum Walk can be considered as a readout device of information about defects and perturbations occurring in complex networks, both classical and quantum.

Dual-Broadband and Single Ultra-Wideband Absorbers from Terahertz to Infrared Regimes

Saeedeh Barzegar-Parizi, Amir Ebrahimi, and Kamran Ghorbani

DOI: 10.1364/JOSAB.432329 Received 24 May 2021; Accepted 25 Jul 2021; Posted 26 Jul 2021  View: PDF

Abstract: This article presents the design and analysis of broadband metamaterial absorbers with single and dual absorption bands from terahertz to infrared frequencies. The absorbers are made of a composite graphene/metallic structure. A metallic patch array is printed on a ground plane backed dielectric slab. A graphene patch array is stacked on the top of the metallic array, whereas a dielectric spacer separates the graphene and patch spacer from each other. The tunable property of the graphene surface conductivity at terahertz frequencies together with the complex permittivity of metal at infrared regime are used to design broadband absorbers from terahertz to infrared regime. The design is based on the combination and excitation of the Plasmon Polaritons of graphene and metallic patterned arrays at terahertz and infrared frequency bands, respectively. Two broad absorption bands occur from 4.56 – 9.02 THz and 16.95 – 60. THz with the fractional bandwidths of 67% and 112%, respectively. Furthermore, by a proper design of the parameters, a single ultra-wide absorption spectra from 6.6 – 58.13 THz can be achieved with a fractional bandwidth 160%. In order to validate the simulation results, a circuit model-based analysis is developed, where the patterned arrays are modeled as the surface admittances and the dielectric spacers are modeled by transmission line stubs. The results obtained by the full-wave simulations in the HFSS are in good agreement with the circuit model results. The absorbers show great stability with respect to the incidence angle for both of the Transverse Electric (TE) and Transverse Magnetic (TM) waves.

Performance improvement of the feedback-based wave front shaping in second harmonic generation

Saeed Ghavami Sabouri and Somayeh Sadat Hashemi

DOI: 10.1364/JOSAB.425215 Received 15 Mar 2021; Accepted 23 Jul 2021; Posted 23 Jul 2021  View: PDF

Abstract: The fundamental beam wave front shaping method is developed to increase the nonlinear frequency convention efficiency and control of the nonlinear beam profile. In this work, a method is presented to accelerate the procedure of optimizing the wave front phase of the fundamental beam to approach the maximum second harmonic generation efficiency. Furthermore, this method allows using high resolution spatial phase modulators for wave front shaping while the number of the phase optimization variables remains limited. The obtained results show that the presented method reduces the number of the needed feedback by three orders of magnitudes while the SHG efficiency is improved twice.

Simultaneous detection of complex refractive index and temperature using a compact side-coupled photonic crystal nanobeam cavity

Zhe Han, Chao Wang, Yuanyuan Liu, and Huiping Tian

DOI: 10.1364/JOSAB.428815 Received 23 Apr 2021; Accepted 22 Jul 2021; Posted 23 Jul 2021  View: PDF

Abstract: In this paper, we theoretically propose a compact photonic crystal nanobeam cavity (PCNC) side coupled with a waveguide for sensing complex refractive index (CRI) and temperature (T). Two Fano resonances are achieved by coupling two discrete states (0th-order mode and 1st-order mode) in PCNC and the continuous state in the waveguide with a partial transmitting element (PTE). The transmission expression is derived based on the temporal coupled-mode theory (TCMT). By measuring the wavelength shifts and shape changes of two Fano resonances in the transmission spectrum, not only the real part of refractive index (RRI) and imaginary part of refractive index (IRI) can be sensed simultaneously, but also the effect of T on CRI is considered. The relationship between structural parameters and coupling effect is studied and the effect of T on detection accuracy is discussed. To the best of our knowledge, this is the first geometry to simultaneously sense CRI and T. Moreover, the total footprint of the device is only 11 × 1.45 × 0.22 (length × width × high) um³, which will contribute to the large-scale integrated sensor array on chip.

High-speed wide-angle interleaved scanning technique for a 3D imaging lidar

Narasimha Prasad and Anand Mylapore

DOI: 10.1364/JOSAB.430553 Received 04 May 2021; Accepted 22 Jul 2021; Posted 23 Jul 2021  View: PDF

Abstract: In this paper, we describe a novel interleaved scanner for an eye-safe 3D scanning lidar system to measure aerodynamic phenomena in a wind tunnel using elastic backscatter from seeding particles. The scanner assembly consists of a rotating polygon scanner for line scanning along the fast axis, a galvanometer (galvo) scanner for scanning along the slow axis, angular position sensors and motor controllers. The polygon scanner sweeps the lidar beam at up to 10,000 lines/s across a 27 deg angular field-of-regard in the fast axis, while the galvo scanner covers an angular range of 20 deg in the slow axis. Using this scanner, the lidar can perform non-intrusive flow visualization, velocimetry, and hard target mapping at mm-scale spatial resolution to a standoff range of 5 m at an update rate of 50 Hz for the full field-of-regard. An interleaved scanning methodology for the acquisition of two snapshots of 3D lidar intensity data with a 100 μs time offset is discussed. The design of the control and data acquisition electronics is described. The effects of rapid scanning on the response of a narrow field-of-view lidar are addressed. The design of the scanner is scalable and can be tailored to meet the requirements of other applications by increasing or decreasing the standoff range, angular field-of-regard and scan rate.

Effect of surface morphology on macro- and micro-scale optical properties of layered InSe grown by molecular beam epitaxy

Pavel Avdienko, Irina Sedova, Dmitrii Firsov, Oleg Komkov, Maxim Rakhlin, Aydar Galimov, Valery Davydov, and Sergey Sorokin

DOI: 10.1364/JOSAB.433061 Received 02 Jun 2021; Accepted 22 Jul 2021; Posted 26 Jul 2021  View: PDF

Abstract: This paper reports the results on the micro-photoluminescence (µPL) and photoreflectance (PR) spectroscopy studies of InSe thin film grown by molecular beam epitaxy (MBE) on GaAs(001) substrate. The specific surface morphology of the InSe/GaAs(001) layer consisting of a number of randomly oriented nanoplatelets with the average thickness of 40–200 nm leads to a difference in optical properties measured on the macro- (PR) and micro- (µPL) scales. The highest energy peak at 1.348 eV observed in the µPL spectra at low excitation densities was attributed to the recombination of localized excitons in ε-InSe.

Tunable terahertz dual-band perfect absorber based on the combined InSb resonator structures for temperature sensing

Hao Luo, Xi Wang, and Hang Qian

DOI: 10.1364/JOSAB.433122 Received 02 Jun 2021; Accepted 22 Jul 2021; Posted 26 Jul 2021  View: PDF

Abstract: In this paper, a tunable perfect absorber (PA) based on a combined InSb resonator structure was proposed and investigated numerically in terahertz (THz) region, which can be served as a dual-band temperature sensor. The unit-cell of the proposed PA is only consisted of the combined InSb ring-disk-shaped (RDS) resonator structures adhered on a continuous gold film and dielectric substrate. The permittivity of the InSb material is highly dependent on the variation of temperature. Numerical simulation results indicate that the proposed PA can achieve absorbance of 99.4% and 98.7% at 1.598 THz and 1.926 THz, respectively, when surrounding temperature 290K. The two absorption peaks are mainly attributed to the excitation of fundamental dipolar resonance modes caused by the ring-shaped and disk-shaped structure, separately. The absorption properties of the proposed PA can be adjusted by varying the structure parameters. Furthermore, the proposed dual-band PA can be functioned as a temperature sensor with sensitivities of about 8.54 GHz/K and 16.25 GHz/K. Due to its excellent performance, the proposed dual-band PA could be found many potential applications of thermal emitting, sensing, and detecting in THz regime.

Strong Faraday rotation in a topological insulator single layer using dielectric multilayered structures

Abbas Ghasempour Ardakani and Zahra Zare

DOI: 10.1364/JOSAB.431370 Received 13 May 2021; Accepted 21 Jul 2021; Posted 21 Jul 2021  View: PDF

Abstract: Topological insulators act as axionic materials in the presence of an external magnetic field or ferromagnetic dopants. We use a single topological insulator layer as a defect in a periodic multi-layered structure to enhance the Faraday rotation. By adjusting the structure parameters, a Faraday rotation of 709 mrad is obtained at the defect mode. The transmission in wavelength with extreme values of Faraday rotation is higher than 95%. The high transmission and giant Faraday rotation result from the electromagnetic field localization at the topological insulator defect layer and strong interaction at the interfaces of defect layer owing to the excitation of defect mode. We consider here the anti-parallel configuration in which the layers surrounding the topological insulator layer have the same zero axion coupling. It was previously shown that for this configuration multilayered structures consisting of alternating topological insulator layers demonstrated no significant Faraday rotation [17]. However, this structure showed a Faraday rotation of 2 mrad with transmission of 94% for the parallel configuration in the presence of 8 topological insulator layers [17]. Therefore, the structure proposed here is an ideal system to observe strong Faraday rotation with high transmission in a single topological insulator layer. Furthermore, the effects of different parameters such as incident angle, thickness of topological insulator defect layer, width of dielectric layers and number of unit cells on the Faraday rotation peak and its transmission are investigated.

Active THz metasurfaces for compact isolation

Evangelos Almpanis, Grigorios Zouros, and Kosmas Tsakmakidis

DOI: 10.1364/JOSAB.430160 Received 27 Apr 2021; Accepted 21 Jul 2021; Posted 21 Jul 2021  View: PDF

Abstract: Metasurfaces constitute an emerging technology, allowing for compact manipulation of all degrees of freedom of an incident lightwave. A key ongoing challenge in the design of these structures is how to allow for energy-efficient dynamic (active) operation, particularly for the polarization of incident light, which other standard devices typically cannot efficiently act upon. Here, we present a quasi-two-dimensional magneto-optic metasurface capable of, simultaneously, high-contrast on/off operation as well as rotation of the polarization angle of a linearly polarized wave - that is, without converting the incident linear polarization to elliptical, which is normally particularly challenging. Furthermore, the device's operation is broadband, with a bandwidth of around 5 microns, and can be conveniently manipulated using an external magnetic bias. Our findings, corroborated using two different full-wave simulation approaches, may allow for functional metasurfaces operating in the THz regime, giving rise to robust, energy-efficient and high-dynamic-range broadband isolation, to be used for a wealth of optoelectronic and communication applications.

Structure of low-frequency fields generated by ponderomotive force arising at the interaction of ultrashort focused laser pulse with conductor

Sergey Uryupin and Egor Danilov

DOI: 10.1364/JOSAB.430743 Received 06 May 2021; Accepted 20 Jul 2021; Posted 21 Jul 2021  View: PDF

Abstract: The spatial structure of the Fourier image of the quasi-cylindrical wave field excited at the effect of a femtosecond laser pulse focused into a strip on the conductor has been studied. In all space areas above the conductor surface, except for the near zone, analytical dependencies of the Fourier image of the field on the coordinates and physical characteristics of the conductor and laser pulse are established. The space areas in which the quasi-cylindrical wave field dominates over the surface wave field are found. For the typical metal, the comparison of the quasi-cylindrical and surface waves magnetic field shapes generated on the conductor surface is performed.

Infrared diffraction radiation from twin circular dielectric rods covered with graphene: plasmon resonances and beam position sensing

Dariia Herasymova, Sergii Dukhopelnykov, and Alexander Nosich

DOI: 10.1364/JOSAB.428037 Received 19 Apr 2021; Accepted 18 Jul 2021; Posted 20 Jul 2021  View: PDF

Abstract: This work considers the terahertz (THz) range diffraction radiation (DR) from a modulated beam of particles passing between two identical dielectric circular microwires covered with graphene. The resistive boundary conditions are set on the zero-thickness graphene covers with the electron conductivity determined from the Kubo formalism. Assuming that the beam velocity is fixed, we use the separation of variables in local coordinates and the addition theorems for cylindrical functions and cast the DR problem to a Fredholm second-kind matrix equation. This allows us to compute both near and far-field characteristics with controlled accuracy. The analysis reveals that a shift of the beam trajectory from the central-symmetric position enables the excitation of additional resonances on the modes, which remain “dark” otherwise. Ignition of these resonances can be considered as a tool for the non-invasive beam position monitoring with microscale devices.

Duty cycle variation methods for Bragg gratings: comparative study and optimal design

Anatole Lupu

DOI: 10.1364/JOSAB.428746 Received 03 May 2021; Accepted 18 Jul 2021; Posted 20 Jul 2021  View: PDF

Abstract: An analysis of spectral response apodization by duty cycle methods for grating-assisted optical filters is presented. The study is performed for the case of co-directional couplers, Bragg reflectors and mirrors. The modeling results show that the supersymmetric duty cycle (SDC) modulation method, initially considered for Parity-Time symmetric gratings [JSTQE 22(5), 35-41 (2016)], performs better than the other methods. An analytical approach to the transfer matrix of the modulated grating explains the better performance of the SDC method.

High-performance terahertz refractive index sensor based on bybrid graphene Tamm structure

Jinlei Hu, Zhengda Hu, Jicheng Wang, Sergei Khakhomov, Igor Semchenko, Zexiang Wang, and Menghan Li

DOI: 10.1364/JOSAB.431912 Received 19 May 2021; Accepted 15 Jul 2021; Posted 19 Jul 2021  View: PDF

Abstract: In recent years, the researches on tunable and high-performance terahertz devices have attracted widespread attention. In this paper, we propose a novel refractive index sensor consisting of monolayer graphene and multilayer photonic crystal (PC) with a defect layer. It is found that Tamm plasmon polariton (TPP) can be excited at the top graphene interface, which can strongly interact with defect mode in this coupled structure. The results of numerical simulation demonstrate that the coupling can be either tuned by adjusting the geometric parameters or actively controlled by the chemical potential in graphene as well as the incident angle of light, allowing for tunable dual-band perfect absorption with strong interaction. Moreover, the resonance frequency of defect mode is sensitive to the changes of the ambient refractive index. The sensitivity and quality factor of this device as a sensor can reach 1.01 THz per refractive index unit (THz/RIU) and 145 RIU-1, respectively. In addition to high performance, the sensor does not require phase or polarization matching devices, paving the way for the research of optical devices.

Spectroscopic Mueller Matrix ellipsometry of gap surface plasmon array at conical incidences

Per Magnus Walmsness, Nathan Hale, and Morten Kildemo

DOI: 10.1364/JOSAB.432466 Received 26 May 2021; Accepted 14 Jul 2021; Posted 15 Jul 2021  View: PDF

Abstract: Spectroscopic Mueller matrix ellipsometry is used to study an array of rectangular Au patches on a SiO2 film backed by optically thick Au. The array supports resonances related to gap surface plasmons and Rayleigh anomalies, and these are mapped out by full rotation of the azimuthal angle of incidence. The finite element method is used to model the system, and it is found that the Ti adhesion layers at SiO2/Au interfaces used in the manufacture process must be included in the model for accurate results. We show how oxidation of the Ti layer beneath the Au patch causes the optical response to drift in time, and we demonstrate an extreme sensitivity of the Mueller matrix to the dimensions of the patch.

High-performance surface plasmon resonance refractometer based on no-core fiber coated with silver film

Yundong Liu, Hailiang Chen, HongYu Li, song zhang, Zhigang Gao, Yuhui Feng, Yingyue Zhang, and Shuguang Li

DOI: 10.1364/JOSAB.433055 Received 01 Jun 2021; Accepted 14 Jul 2021; Posted 15 Jul 2021  View: PDF

Abstract: Owing to their high sensitivity, surface plasmon resonance (SPR)-based sensors depicted broad application prospects in biochemical detection, environmental monitoring, and food safety. In this paper, an optical fiber-based SPR sensor was proposed and demonstrated for the refractive index (RI) detection of liquid samples. This sensor was composed of a multi-mode fiber (MMF), a no-core fiber (NCF), and another MMF which connected in sequence. The length of NCF was 2 cm. A thin silver film was deposited on the NCF surface in order to stimulate the SPR effect. Experimental results indicated that the shift amount of resonance dip wavelength was as high as 303.6 nm as RI increased from 1.333 to 1.4107. A sensitivity of 2507.58 nm/RIU with a fitting linearity R2 of 0.9931 was obtained in the lower RI region of 1.333-1.37 , while the sensitivity and R2 reached 5228.21 nm/RIU and 0.97395 respectively in the higher RI region of 1.37 -1.4107. Compared with previous reported RI sensors, the proposed fiber optic SPR sensor exhibits the advantages of simple structure, small volume, low cost, high sensitivity, and wide detection range.

Tripartite entropic uncertainty in an open system under classical environmental noise

Saeed Haddadi, Mohammad Pourkarimi, and Dong Wang

DOI: 10.1364/JOSAB.431554 Received 18 May 2021; Accepted 13 Jul 2021; Posted 20 Jul 2021  View: PDF

Abstract: The uncertainty principle is a remarkable and fundamental feature in quantum mechanics that suggests a significant lower bound to predict the results of arbitrary incompatible observables measured on a particle. In this work, we study the dynamics of tripartite entropic uncertainty bound and quantum fidelity in a three non-interacting qubits model which initially prepared in a maximally entangled pure GHZ state and then subjected to classical environmental noise in different and common environments. Interestingly, we find that the dynamics of tripartite uncertainty bound and fidelity are strongly affected by the type of system-environment interaction and the growth speed of uncertainty bound is strongly influenced by the disorder of the environment. Explicitly, our results show that the uncertainty bound and fidelity can be improved when the qubits are coupled to the noise in a common environment.

Quantum dynamics of mixed polarization states: Effects of environment-mediated intermode coupling

Andrei Gaidash, Anton Kozubov, George Miroshnichenko, and Alexei Kiselev

DOI: 10.1364/JOSAB.425226 Received 15 Mar 2021; Accepted 13 Jul 2021; Posted 19 Jul 2021  View: PDF

Abstract: We study quantum dynamics of mixed polarization states represented by the two-mode boson system interacting with an environment. Using the form of general dynamical equations for averaged operators that preserves normal ordering, we show that the dynamical regimes of the averaged Stokes operators crucially depend on anisotropy of the relaxation operator resulted from the intermode coupling induced by the anisotropic environment. We analyze how this coupling impacts on the quantum bit error rate in the well known single-photon polarization-coding quantum key distribution protocol BB84.

Optical Kerr nonlinearity and multi-photon absorption of DSTMS measured by Z-scan method

Jiang Li, Rakesh Rana, Li-Guo Zhu, cangli Liu, Harald Schneider, and Alexej Pashkin

DOI: 10.1364/JOSAB.431986 Received 24 May 2021; Accepted 12 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: We investigate the optical Kerr nonlinearity and multi-photon absorption (MPA) properties of DSTMS excited by femtosecond pulses at a wavelength of 1.43 μm, which is optimal for terahertz generation via difference frequency mixing. The MPA and the optical Kerr coefficients of DSTMS at 1.43 μm are strongly anisotropic indicating a dominating contribution from cascaded 2nd-order nonlinearity.

Scheme for sub-shot-noise transmission measurement using a time multiplexed single-photon source

Agustina Magnoni, Laura Knoll, and Miguel Larotonda

DOI: 10.1364/JOSAB.428105 Received 16 Apr 2021; Accepted 12 Jul 2021; Posted 15 Jul 2021  View: PDF

Abstract: Sub-shot-noise performance in transmission measurements can be achieved in optical quantum metrology due to the significantly lower uncertainty in light intensity of quantum beams compared to their classical counterparts. In this work, we simulate the outcome of an experiment that uses a multiplexed single-photon source, considering several types of experimental losses, where we show that the sub-Poissonian statistics of the output is key for achieving sub-shot-noise performance. We compare the numerical results with the shot-noise limit achieved using coherent sources and the quantum limit, obtained with an ideal photon-number Fock state. We also investigate conditions in which threshold detectors can be used, and the effect of input light fluctuations. Our results show that sub-shot-noise performance can be achieved, even without using number-resolving detectors, with improvement factors that range from 1.5 to 2.

A scanning planar Yagi-Uda antenna for fluorescence detection

navid soltani, Elham Rabbany, Sergey Druzhinin, Gregor Schulte, Julian Müller, Florian Sledz, Assegid Flatae, Benjamin Butz, Holger Schönherr, Nemanja Markesevic, and Mario Agio

DOI: 10.1364/JOSAB.434980 Received 25 Jun 2021; Accepted 11 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: An effective approach to improve the detection efficiency of nanoscale light sources relies on a planar antenna configuration, which beams the emitted light into a narrow cone. Planar antennas operate like optical Yagi-Uda antennas, where reflector and director elements are made of metal films.Here we introduce and investigate, both theoretically and experimentally, a scanning implementation of a planar antenna. Using a small ensemble of molecules contained in fluorescent nanobeads placed in the antenna, we independently address the intensity, the radiation pattern and the decay rate as a function of distance between a flat-tip scanning gold wire (reflector) and a thin gold film coated on a glass coverslip (director).The scanning planar antenna changes the radiation pattern of a single fluorescent bead and it beams light into a narrow cone down to angles of 45º (full width at half maximum). Moreover, the collected signal compared to the case of a glass coverslip is larger than a factor of 3, which is mainly due to the excitation enhancement. These results offer a better understanding of the modification of light-matter interaction by planar antennas and they hold promise for applications, such as sensing, imaging and diagnostics.

Effect of Loss on Linear Optical Quantum Logic Gates

Durdu Guney and James Davis

DOI: 10.1364/JOSAB.430603 Received 03 May 2021; Accepted 11 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: Linear optical quantum gates have been proposed as a possible implementation for quantum computers. Most experimental linear optical quantum gates are constructed with free space optical components with negligible loss. In this work we analyse a symmetric and asymmetric partially polarizing lossy beam splitters. Using the generalized beam splitter equations we study the effects of loss on two linear optical quantum gates. The first is a commonly used CNOT gate. The second is a W state expansion gate. Envisioning inherent loss in plasmonics and metamaterials as a new degree of freedom and those materials systems a route for miniaturization, we reconsider the requirements of the lossy CNOT gate and show it is possible to simplify the three beam splitter design to a single beam splitter without sacrificing success probability.

Study of dissipative soliton in distributed mathematical model of ultra-long mode-locked fiber lasers

Olga Shtyrina, Evgeny Podivilov, Anton Skidin, Irina Yarutkina, Roman Lobasenko, and Mikhail Fedoruk

DOI: 10.1364/JOSAB.430329 Received 03 May 2021; Accepted 10 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: We propose the new distributed mathematical model of dissipative soliton evolution in ultra-long fiber lasers. The model is based on a modified Ginzburg-Landau equation, has a stable analytical solution and takes into account the saturated gain and saturable absorption. The analytical results show a good accordance with the results of numerical simulation of ultra-long ring cavity fiber lasers. The results may be applied to the analysis of a wide range of fiber laser systems.

Simulation of enhanced light extraction from periodic, disordered and quasi-periodic OLED structures

R. Biswas, Yu Zhang, Ruth Shinar, and Joseph Shinar

DOI: 10.1364/JOSAB.430593 Received 04 May 2021; Accepted 09 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: We have developed a rigorous scattering matrix theory of light emission from periodically structured media, using a Green’s function approach. We computationally simulate the spectral power inside the structure, incorporating Purcell factor enhancements, and find internal waveguiding modes and plasmonic losses. We simulate the light-outcoupling factor ηout and describe how corrugations and structured media can enhance ηout. We have extended our framework to describe non-periodic disordered arrays, as well as aperiodic quasi-crystalline arrays. Flat organic light emitting diodes (OLEDs) have low outcoupling with ηout ~20% since most of the light is trapped in waveguided modes in higher index layers or lost to plasmonic excitations at the metal cathode. Periodically corrugated OLEDs can achieve highly enhanced ηout~ 65-70% for pitch values between 1000-2000 nm, representing an enhancement factor exceeding 3 over planar structures. Periodic corrugations strongly diffract trapped waveguided and plasmonic modes to the emissive air-cone. Disordered templates also can cause significant enhanced outcoupling with ηout ~ 50-55% for smaller nearest-neighbor separations of 300-400 nm. Quasi-crystalline tilings can also lead to enhancements of ηout ~ 50-55%. This framework can be utilized to design novel structured media that can generate high light extraction.

Parity-time Symmetric gratings in 1550 nm Distributed-Feedback lasers diodes: insight on device design rules

Henri Benisty, Vincent Brac de la Perrière, Abderrahim Ramdane, and Anatole Lupu

DOI: 10.1364/JOSAB.428638 Received 29 Apr 2021; Accepted 09 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: We build up on former results from our work on parity-time symmetric gratings implemented in 1550 nm distributed feedback laser diodes to address the design issues raised by the first observed trends. These laser diodes are of “complex-coupled” nature, with modulations of both real and imaginary part of effective index, with relative phase π/2 related to the parity-time symmetry. The unidirectionality of the photonic behavior in reflection mode is dependent on the level of extra losses incurred by the metallic grating used to implement fixed loss modulation onto a nearly uniform gain, either as a first order or as a third order grating. The observed behavior suggests that facets play a large role in setting the desired “unidirectional” lasing operation points, with preferential emission on one side. We explore this issue, of generic interest for the coupling of parity-time symmetric structures to open space.

Phase Retrieval and Design with Automatic Differentiation

Alison Wong, Benjamin Pope, Louis Desdoigts, Peter Tuthill, Christopher Betters, and Barnaby Norris

DOI: 10.1364/JOSAB.432723 Received 31 May 2021; Accepted 09 Jul 2021; Posted 12 Jul 2021  View: PDF

Abstract: The principal limitation in many areas of astronomy, especially for directly imaging exoplanets, arises from instability of the point spread function (PSF) of a telescope. To understand the transfer function, it is often necessary to infer a set of optical aberrations given only the intensity PSF — the problem of phase retrieval. This can be important for post-processing of existing data, or for the design of optical phase masks to engineer PSFs optimized to achieve high contrast, angular resolution, or astrometric stability. By exploiting newly efficient and flexible technology for automatic differentiation, which in recent years has undergone rapid development driven by machine learning, we can perform both phase retrieval and design in a way that is systematic, user-friendly, fast, and effective. By using modern gradient descent techniques, this converges efficiently and is easily extended to incorporate constraints and regularization. We show in simulations that our new package, morphine, can perform phase retrieval even from heavily-saturated sensor data, and with regularization can robustly recover both discrete and smooth phase distributions. We also show that the same code can optimize continuous or binary phase masks that are competitive with existing best solutions for two example problems: an apodizing phase plane coronagraph for exoplanet direct imaging, and a diffractive pupil for astrometry. The MORPHINE source code and examples are available open-source, with a similar interface to the popular physical optics package POPPY.

Nano shell impact on Huygens’ metasurface dipolar resonances and optical response

Hasan Kocer, Halil Isik, Yilmaz Durna, Bahram Khalichi, Hamza Kurt, and Ekmel Ozbay

DOI: 10.1364/JOSAB.424589 Received 10 Mar 2021; Accepted 08 Jul 2021; Posted 08 Jul 2021  View: PDF

Abstract: Due to several advantages over conventional devices for the control of electromagnetic (EM) radiation, the demand for metasurface utilization based on artificially engineered micro and nano structures is boosted, especially in new generation devices. Among the metasurfaces family, there has been a growing interest in Huygens' metasurfaces that are easy to fabricate due to their lower aspect ratio compared to their counterparts and also provide alternative electromagnetic radiation control by tuning the dipolar electric and magnetic resonances. In this study, an all dielectric Huygens' metasurface consisting of the high refractive index nano shells embedded in the low refractive index environment is designed and extensively investigated numerically and analytically in the near infrared spectrum. By simply tuning the nano shell inner radius, the effects on the dipolar resonances are unveiled specific to the proposed design. To assess the EM wave interactions in the designed Huygens' metasurface, an analytical model based on the coupled discrete dipole approach is applied for selected distinct cases of the designed metasurface. It is shown that the spectral position of the dipolar resonances can be detuned or tuned simultaneously depending on the structural parameter of the meta-atoms arranged in a periodic array. This study sheds light on the physics and abilities of the nano shell structure as a Huygens’ metasurface for the potential applications of metasurface based light-matter interaction including imaging and sensing.

A novel graphene-based metasurface absorber for the active and broadband manipulation of terahertz radiation

Ekin Bosdurmaz, Hodjat Hajian, Veysel Ercaglar, and Ekmel Ozbay

DOI: 10.1364/JOSAB.427975 Received 14 Apr 2021; Accepted 08 Jul 2021; Posted 08 Jul 2021  View: PDF

Abstract: Graphene-based metasurface nearly perfect absorbers (MPAs) can provide an efficient tool for the active control and manipulation of waves in the terahertz (THz) gap. Here, we propose a novel graphene-based MPA that is designed based on a simple configuration and is capable of absorbing THz radiation within a broad bandwidth of almost 3 THz with polarization insensitive and omnidirectional characteristics. The MPA is composed of a periodic array of graphene patches with two different dimensions that are separated from a gold bottom reflector with an SiO2 spacer layer. The broadband spectral response of the MPA, which is also verified by analytical calculations, is due to the support of propagating surface plasmon excitations and can be either actively tuned via changes in the chemical potential of graphene or passively adjusted by the modification of geometrical parameters of the patches and thickness of the spacer layer. As a complement to the previous studies in the literature, due to its simplicity of the design and broad spectral response, it is believed that the suggested graphene-based MPA finds potential applications in THz spectroscopy and communications.

Vector magnetic field sensor based on orthogonal off-set spliced optical fiber cladded with magnetic fluid

Zijian Hao, Shengli Pu, Yongxi Li, and Dihui Li

DOI: 10.1364/JOSAB.423839 Received 03 Mar 2021; Accepted 08 Jul 2021; Posted 09 Jul 2021  View: PDF

Abstract: Based on the anisotropic distribution of magnetic nanoparticles within magnetic fluid under external magnetic field, a novel vector magnetic field sensor based on orthogonal off-set spliced optical fiber structure cascaded with fiber taper has been proposed. The expression of interference dip wavelength with respect to external magnetic field is formulated and the dual parameter sensing matrix is established. Simultaneous measurement of magnetic field intensity and direction is realized. The corresponding physical principle is clarified. The sensing properties are experimentally investigated and theoretically verified. The theoretical results are in good agreement with the experimental ones.

Predicting instabilities of a tuneable ring laser with an iterative map model

Brady Metherall and C. Bohun

DOI: 10.1364/JOSAB.424346 Received 15 Mar 2021; Accepted 17 Jun 2021; Posted 18 Jun 2021  View: PDF

Abstract: Simple mathematical models have been unable to predict the conditions leading to instabilities in a tuneable ring laser. Here, we propose a nonlinear iterative map model for tuneable ring lasers. Solving a reduced nonlinear Schrödinger equation for each component in the laser cavity, we obtain an algebraic map for each component. Iterating through the maps gives the total effect of one round trip. By neglecting the nonlinearity, we find a linearly chirped Gaussian to be the analytic fixed point solution, which we analyze asymptotically. We then numerically solve the full nonlinear model, allowing us to probe the underlying interplay of dispersion, modulation, and nonlinearity as the pulse evolves over hundreds of round trips of the cavity. In the nonlinear case, we find the chirp saturates, and the Fourier transform of the pulse becomes more rectangular in shape. Finally, for a nominal plane in the parameter space, we uncover a rich, sharp boundary separating the stable region and the unstable region where modulation instability degrades the pulse into an unsustainable state.

On-sky results for the novel integrated micro-lens ring tip-tilt sensor

Phillip Hottinger, Robert Harris, Jonathan Crass, Philipp Dietrich, Matthias Blaicher, Andrew Bechter, Brian Sands, Timothy Morris, ALASTAIR BASDEN, Nazim Bharmal, Jochen Heidt, Theodoros Anagnos, Philip Neureuther, Martin Glueck, Jennifer Power, Jörg Pott, Christian Koos, Oliver Sawodny, and Andreas Quirrenbach

DOI: 10.1364/JOSAB.421459 Received 03 Feb 2021; Accepted 16 Jun 2021; Posted 16 Jun 2021  View: PDF

Abstract: We present on-sky results of our novel 3D-printed, fiber-based tip-tilt sensor that was used on the iLocater acquisition camera at the \acl{LBT}. This sensor utilizes a \acl{MLR} and six \aclp{MMF} surrounding a central \acl{SMF}. The surrounding fibers are used to couple misaligned light and thus reconstruct the centroid position, while the central fiber is connected to a science instrument. The limit on the maximum achieved \acl{RMS} reconstruction accuracy is $0.19\,\lambdaD$ (wavelength $\uplambda$, primary mirror diameter D) in both tip and tilt, of which approximately 50\% originates at frequencies below 10\,Hz. This limit is largely due to evolving speckles and depends highly on the observed \acl{SR}. Further optimization can be achieved by redesigning the lens and fiber, tuning the correction algorithm and using the sensor for near diffraction-limited applications.

Second-Order Nonlinear Optical Response of Graphene Irradiated by Two-Color Lights: Ellipticity and Phase Modulation

Sen Pei, Suqing Duan, Ning Yang, and Wei Zhang

DOI: 10.1364/JOSAB.424447 Received 08 Mar 2021; Accepted 21 May 2021; Posted 09 Jul 2021  View: PDF

Abstract: We investigate the second order optical response of graphene irradiated by two-color lights with frequencies ω and 3ω, focusing on the modulation by ellipticity and phase of the incident fields. Based on the analytical perturbation theory, it is found that the interplay between second harmonic generation (ω+ω) (SHG) and the difference frequency generation (3ω-ω) (DFG) processes lead to nontrivial nonlinear optical properties. The quantum interference between the two processes (SHG and DFG) results in different dependence of the second order response intensity I(2ω) on the ellipticity, including monotonic, nonmonotonic change of I(2ω) with the ellipticity, or even nearly independent on the ellipticity under suitable conditions.The optimal incident angles for the highest I(2ω) are found, which can be tuned by changing the ellipticity, relative phase or field strength of the incident light. In particular, a large output enhancement with respect to small increment of the incident field can be achieved. We have found effective methods of modulating the nonlinear optical processes, which may have applications in optical devices based on two dimensional materials.

Full 3D+1 modeling of tilted-pulse-front setups for single-cycle terahertz generation: comment

Michael Bakunov and Sergey Bodrov

DOI: 10.1364/JOSAB.404387 Received 31 Jul 2020; Accepted 01 Feb 2021; Posted 02 Feb 2021  View: PDF

Abstract: Wang et al. [J. Opt. Soc. Am. B 37, 1000 (2020)] simulated terahertz generation by tilted-pulse-front optical excitation of a lithium niobate crystal and made predictions about the optimal generation conditions and spatial distribution of the generated terahertz beam. We point out that formulas used by Wang et al. for the tilted-pulse-front optical pulse and optically induced nonlinear polarization are irrelevant to the conventional tilted-pulse-front configuration. Therefore, the predictions made by Wang et al. are incorrect and cannot be used for optimizing experiments.

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