Broadband Wavelength Research Articles

Broadband optical parametric amplification using PPLN waveguide pumped by detuned second harmonic.

Optical parametric amplification in the range of 1.3-1.8 µm was demonstrated by using a periodically poled LiNbO3 (PPLN) waveguide as a nonlinear medium by varying the detuning of the pump wavelength. A wide range of detuning was enabled by using a multiple-quasi-phase-matched (M-QPM) LiNbO3 waveguide for pump generation through second harmonic generation (SHG) and temperature control of the PPLN waveguide. Broadband optical amplification and wavelength conversion through difference frequency generation (DFG) are considered useful for widening the bandwidth of optical communication.

Highly sensitive organic phototransistor for flexible optical detector arrays

Innovative applications in light signal sensing require flexibility, lightweight, low-cost and low temperature processability, as well as high sensitivity and quantitative photoresponse. We report on flexible organic phototransistors (OPTs) with excellent reproducibility in the detection of outstandingly low light intensities of few nW cm−2. The optical response of the phototransistor was thoroughly characterized as a function of the wavelength, the incident optical intensity and the electrical polarizations. The photodetectors work reliably under bending and pulse cycling in different environmental conditions, at low polarizations down to the range 0.1–5 V. Based on these outcomes, arrays for broadband or multiple wavelength detection were implemented and successfully tested. The proposed device structure, derived from a layered p-p heterojunction, was developed to be easily implementable in each wavelength of interest. These results show a prospect of highly sensitive flexible OPT arrays for both experimental research and innovative optoelectronic systems.

Broadband Wavelength Swept Laser With Bidirectional Photonic Resonance for High Resolution Optical Coherence Tomography

A light source with extended spectral bandwidth applied in optical coherence tomography (OCT) systems produces highly accurate micro-scale imaging structures owing to the attainable high-axial resolution. This study presents a wide tuning range of a wavelength-swept laser to improve the axial resolution. Linear cavity configuration was performed for bidirectional photonic resonance using two semiconductor optical amplifiers placed parallelly. A polygon scanner-based tunable filter produced a broad scanning range of 155 nm from 917 nm to 1072 nm and an axial resolution of 3.4 μm in air. Bench-top imaging of a phantom made of food wraps was performed with 22.6 μm transverse resolution to evaluate the performance of the swept laser for high-resolution OCT.

High-Responsivity Gate-Tunable Ultraviolet-Visible Broadband Phototransistor Based on Graphene-WS2 Mixed-Dimensional (2D-0D) Heterostructure.

Recent progress in the synthesis of highly stable, eco-friendly, cost-effective transition-metal dichalcogenide (TMDC) quantum dots (QDs) with their broadband absorption spectra and wavelength selectivity features have led to their increasing use in broadband photodetectors. With the solution-based processing, we demonstrate a superlarge (∼0.75 mm2), ultraviolet-visible (UV-vis) broadband (365-633 nm) phototransistor made of WS2 QDs-decorated chemical vapor deposited (CVD) graphene as the active channel with extraordinary stability and durability under ambient conditions (without any degradation of photocurrent until 4 months after fabrication). Here, colloidal zero-dimensional (0D) WS2 QDs are used as the photoabsorbing material, and graphene acts as the conducting channel. A high photoresponsivity (3.1 × 102 A/W), moderately high detectivity (∼8.9 × 108 Jones), and low noise equivalent power (∼9.7 × 10-11 W/Hz0.5) are obtained at a low bias voltage (Vds = 1 V) at an illumination of 365 nm with optical power as low as ∼0.8 μW/cm2, which can be further tuned by modulating the gate bias. While comparing the photocurrent between two different morphologies of WS2 [QDs and two-dimensional (2D) nanosheets], a significant enhancement of photocurrent is observed in the case of QD-based devices. Ab initio density functional theory (DFT)-based calculations further support our observation, revealing the role of quantum confinement in enhanced photoresponse. Our work reveals a strategy toward developing a scalable, cost-effective, high-performance hybrid mixed-dimensional (2D-0D) photodetector with graphene-WS2 QDs for next-generation optoelectronic applications.

A broadband optical modulator based on rib-type silicon waveguide including graphene and h-BN layers

The rapid growth of THz communication systems needed a high data transfer rate in the broadband communication range. Increasing the amount of modulation depth increases the amount of transmission and, as a result, increases the transmitted data. In this paper, a broadband optical modulator based on rib-type silicon waveguides, including graphene and h-BN layers, is designed. In this proposed structure, Hexagonal Boron Nitride (h-BN) layers are embedded between graphene layers. This structure contains a rib-type Si waveguide and operates for the broadband wavelength from 1300 nm to 1800 nm. The maximum modulation depth is 2.23 dB/µm with 2.23 dB/µm loss at 1800 nm. We achieved a high figure of merit as high as 1.3. The modulation depth at 1550 nm is 1.13 dB/µm with 1.1 dB/µm loss. The proposed modulator has a 669 GHz modulation bandwidth.

Broadband wavelength tuning of electrically stretchable chiral photonic gel

Abstract Chiral photonic-band structure provides technical benefits in the form of a self-assembled helical structure and further functional wavelength tunability that exploits helical deformation according to pitch changes. The stopband wavelength control of the chiral photonic-band structure can be obtained by individual electrical methods or mechanical stretching deformation approaches. However, research on combined electric control of stretchable chiral photonic-band wavelength control while ensuring optical stability during the tuning process has remained limited till now. In this study, using the hybrid structure of elastomeric mesogenic chiral photonic gels (CPGs) with an electrically controlled dielectric soft actuator, we report the first observation of electrically stretchable CPGs and their electro-mechano-optical behaviors. The reliable wavelength tuning of a CPG to a broadband wavelength of ∼171 nm changed with high optical stability and repeated wavelength transitions of up to 100 times. Accordingly, for the first time, electrical wavelength tuning method of stretchable chiral liquid crystal photonicband structure was investigated.

Dynamic Beam Switching by the Highly Sensitive Metasurface Composed of All‐Metallic Split‐Ring Resonators

The development of metasurfaces capable of arbitrarily manipulating electromagnetic waves has created new opportunities for various applications. However, most tunable metasurface devices via different modulation techniques exhibit large fabrication difficulties or narrow bandwidths. Here, we use the all‐metallic split‐ring resonator to design a dynamically tunable metasurface that is highly sensitive to the ambient refractive index and capable of broadband beam switching. Different from the previous optical scatters, the split‐ring resonator is put on the metal substrate. Due to the existence of metallic substrate and large interaction of corner modes, the proposed resonator has small ohmic loss and high sensitivity to the ambient refractive index. By arraying the all‐metallic split‐ring resonators with different parameters, dynamic beam switching of anomalous reflection is demonstrated numerically. In particularly, the designed metasurface exhibits the dynamic beam switching in a broadband wavelength range of Δλ≈100 nm. Such an all‐metallic metasurface with high sensitivity can greatly reduce the designing difficulty of the tunable optical devices. The dynamic metadevices may find potential applications in stealth camouflage, information encryption, and data storage.

Numerical Study of Broadband Wavelength Conversion Based on InP/In1-xGaxAsyP1-y Strip-loaded Waveguide

Numerical Study of Broadband Wavelength Conversion Based on InP/In1-xGaxAsyP1-y Strip-loaded Waveguide

Wavelength conversion of KTP crystal based Stark-chirped rapid adiabatic passage

The nonlinear wavelength conversion can generate the laser wavelengths which are not directly available, thereby broadening the laser spectrum range. However, the phase mismatch greatly limits the development and application of nonlinear optical technology. The wavelength conversion schemes in a manner analogous to population transfer in atomic rapid adiabatic passage, stimulated Raman adiabatic passage (STIRAP), and Stark chirped rapid adiabatic passage (SCRAP) provide feasible solutions for efficient and broadband wavelength conversion. The SCRAP uses the Stark shift caused by the Stark field to generate energy level crossings, therefore, the population in initial state can be efficiently converted into the target state. It does not require the two-photon resonance, and can be applied to multi-photon transition. In this paper, by approximate analogy to the adiabatic population theory, a wavelength conversion model with the KTP crystals based SCRAP is established, the influence of the coupling delay parameters, width parameters, pump intensity, temperature, and incident wavelength on the conversion process are systematically studied. The results show that the signal laser energy can be almost converted into output laser energy, while the intermediate laser energy is kept extremely low in the conversion process. The conversion process is sensitive to changes in coupling delay parameters, width parameters, and pump intensity. The farther away fromits optimal value the coupling delay parameter, the lower the conversion efficiency is. When the width parameter <inline-formula><tex-math id="M1">\begin{document}$ d_2^2 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20210887_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20210887_M1.png"/></alternatives></inline-formula> is fixed, as the width parameter <inline-formula><tex-math id="M2">\begin{document}$ d_1^2 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20210887_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20210887_M2.png"/></alternatives></inline-formula> increases, the conversion efficiency first increases to a maximum value, and then slowly decreases. At the same time, the greater the value of the width parameter <inline-formula><tex-math id="M3">\begin{document}$ d_2^2 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20210887_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20210887_M3.png"/></alternatives></inline-formula>, the greater the achievable maximum conversion efficiencies, and the greater the bandwidth that can achieve high-efficiency wavelength conversion. The conversion efficiency increases as the pump intensity increases. When the conversion efficiency value reaches a maximum value, the increase in pump intensity has almost no effect on the conversion efficiency. However, changes in temperature and incident wavelength have little effect on the conversion efficiency. The above research can provide a theoretical basis for the acquisition of ultraviolet to mid-infrared light sources and the manufacture of photonic devices.

Perovskite Capped ZnO Nanorods Ultraviolet/Visible Broadband Photodetectors

A high-performance broadband photodetector (PD) based on triple-cation perovskite (PVSK)&#x002F;ZnO nanorods (ZnO NRs) was fabricated. Multiple material analysis, including scanning electron microscope (SEM), absorption spectrum, X-ray diffractometer (XRD), and high-resolution transmission electron microscopy (HR-TEM) were conducted. The analyses indicate that a dense perovskite film was closely capped on ZnO NRs. A light source with different wavelength is applied to evaluate the photosensitive behaviors along with impulse responses of the PVSK&#x002F;ZnO NRs PDs and pure ZnO NRs PDs. Results show that the PVSK&#x002F;ZnO NRs PDs were sensitive to the ultraviolet (UV) and visible light, while pure ZnO NRs PDs were only sensitive to the UV light. Moreover, owing to the superior photoelectric properties of triple-cation perovskite than the mono-cation perovskite, the triple-cation PVSK&#x002F;ZnO NRs PDs deliver a high declivity of 7.69 <inline-formula><tex-math notation="LaTeX">$ \times {10}^{12}$</tex-math></inline-formula> , 1.49<inline-formula><tex-math notation="LaTeX">$ \times {10}^{13}$</tex-math></inline-formula> and 3.61<inline-formula><tex-math notation="LaTeX">$ \times {10}^{13}$</tex-math></inline-formula> Jones under the light illumination with a wavelength of 350, 450 and 600 nm, respectively. Triple-cation PVSK&#x002F;ZnO NRs composites are promising materials for the broadband wavelength detection from UV to visible light with high declivity.

Bidirectional nanoprinting based on bilayer metasurfaces.

Bidirectional nanoprinting, has received significant attention in image display and on-chip integration, due to its superior advantages. By manipulating the amplitude in a narrow- or broad-band wavelength range of forward and backward incident light, different spatially varied intensities or color distributions can be generated on the structure plane. However, the current scheme cannot fully decouple the bidirectional light intensity due to the limitation of design degree of freedom, and it would hinder the development of asymmetric photonic devices. In this paper, we propose and demonstrate bidirectional nanoprinting based on an all-dielectric bilayer metasurface, which can independently control the intensity of forward and backward incident light, resulting in two different continuous grayscale meta-image displaying in the visible region. This asymmetric but still bidirectional optical response is introduced by stacking two layers of nanostructures with different functionality in space, in which the first- and second-layer nanostructures act as a half-wave plate and a polarizer, respectively. Interestingly, these bidirectional nanoprinting metasurfaces have flexible working modes and may bring great convenience for practical applications. Specifically, two different meta-images generated by a bidirectional nanoprinting metasurface can be displayed not only on two sides of the metasurface (working mode in transmission or reflection), but on the same side due to the forward transmitted light and backward reflected light also having asymmetric optical properties. Similar phenomena also exist for forward reflected light and backward transmitted light. Our work extremely expands the design freedom for metasurface devices and may play a significant role in the field of optical display, information multiplexing, etc.

Leaky-mode long-period grating on a lithium-niobate-on-insulator waveguide

Lithium niobate on insulator (LNOI) is a promising platform for the construction of high-density integrated photonics circuits. In this paper, we propose compact long-period gratings (LPGs) formed on LNOI rib waveguides for achieving light coupling from the guide mode to the leaky mode. Our LPGs are polymer gratings coated on the surfaces of LNOI waveguides and can be designed to achieve strong mode coupling at specific resonance wavelengths for the TE-like and the TM-like polarization. By means of a numerical analysis, we find that the LPGs exhibit turning points in the phase-matching curves, which promises the realization of broadband wavelength filters and polarizers with such grating structures on the LNOI platform. To experimentally verify the theoretical results and demonstrate the LPG characteristics, we fabricate a number of LPG filters on LNOI rib waveguides, which include two broadband LPGs operating near the turning points: a TE-pass polarizer with a 20 dB extinction ratio over a bandwidth of 270 nm from 1430 to 1700 nm and a TM-pass polarizer with a 20 dB extinction ratio over a bandwidth of 90 nm from 1500 to 1590 nm. The insertion losses for the passing polarization are smaller than 2 dB in the C + L band. Our LPGs can serve as building blocks for the development of a wide range of integrated LNOI devices for application in on-chip signal processing.

On-chip nanophotonic broadband wavelength detector with 2D-Electron gas

Abstract Miniaturized, low-cost wavelength detectors are gaining enormous interest as we step into the new age of photonics. Incompatibility with integrated circuits or complex fabrication requirement in most of the conventionally used filters necessitates the development of a simple, on-chip platform for easy-to-use wavelength detection system. Also, intensity fluctuations hinder precise, noise free detection of spectral information. Here we propose a novel approach of utilizing wavelength sensitive photocurrent across semiconductor heterojunctions to experimentally validate broadband wavelength detection on an on-chip platform with simple fabrication process. The proposed device utilizes linear frequency response of internal photoemission via 2-D electron gas in a ZnO based heterojunction along with a reference junction for coherent common mode rejection. We report sensitivity of 0.96 μA/nm for a broad wavelength-range of 280 nm from 660 to 940 nm. Simple fabrication process, efficient intensity noise cancelation along with heat resistance and radiation hardness of ZnO makes the proposed platform simple, low-cost and efficient alternative for several applications such as optical spectrometers, sensing, and Internet of Things (IOTs).

High‐Accuracy and Broadband Wavelength Sensor with Detection Region Ranging from Deep Ultraviolet to Near Infrared Light

AbstractIn this paper, a broadband wavelength sensor which is composed of two horizontally stacked photodetectors is reported. The top part is a monolayer graphene (MLG)/thin Si/MLG heterojunction device and the bottom part is a MLG/Ge Schottky junction device. Owing to the thin thickness of the Si and the wavelength‐dependent absorption coefficients of both Si and Ge, the two photodetectors exhibit sharp contrast in photon‐generation rate when illuminated with different wavelengths of light. This distinction in photon generation leads to completely different evolution in photocurrent, and the corresponding relationship between the photocurrent ratio and wavelength can be easily expressed as a monotonic function, via which the wavelength in a broad range from deep ultraviolet (265 nm) to near infrared light (1550 nm) can be easily calculated. Notably, the average relative error and the average absolute error of the wavelength sensor are estimated to be 2.1% and 2.3 nm, respectively, which are much better than previously reported values.

Chromium nanostructures for enhancing light trapping in a thin-film solar cell

In this work, a thin-film solar cell consists of metallic nanowires, semiconductor, and antireflection layers is investigated. The absorption of the structure is obtained numerically in the broadband wavelength range of 300–1700 nm. The influences of the layer thicknesses and the cross-section shape of metallic nanowires are studied. Results indicate that the absorption of the rectangular-nanowire system is over 90% in the range of 560 − 1180 n m . Also, the absorption in the range of 300 − 1200 nm is over 90% when the cross-section of nanowires is semi-circular. This high absorption in the visible region could be helpful in designing plasmonic solar cells. • The light trapping in a thin-film plasmonic solar cell is studied. • Impacts of the layer thicknesses and the cross-section of Chromium nanowires are investigated. • The absorption of the circular-nanowire structure in the range of 300–1200 nm is over 90%. • The absorption of the rectangular-nanowire system is over 90% in the range of 560–1180 nm.

Ultrashort pulse duration and broadband dual-comb laser system based on a free-running passively mode-locked Er-fiber oscillator

We have demonstrated pulse duration compression and wavelength extension to a dual-comb free-running passively mode-locked Er-fiber oscillator. At first, the pulse duration of the dual-comb ultrashort pulses from the oscillator is nonlinearly compressed to ∼50 fs by fiber amplifiers. Then, a dual-comb supercontinuum laser source with broadband wavelength band from 1.0 to more than 1.75 µm is achieved when the compressed pulses are used to pump highly nonlinear fibers. At last, utilizing the dual-comb supercontinuum source as the seed for spectral-selected Yb-fiber amplifiers, sub-100 fs ultrashort pulses are obtained at 1.0 µm. This free-running dual-comb fiber laser system can provide ultrashort pulses with sub-100 fs pulse duration at 1.0 µm, 1.5 µm and broadband supercontinuum covering 1.0 to more than 1.75 µm, so it can be potentially deployed in dual-comb applications such as absolute distance measurement, coherent anti-stokes Raman spectroscopy, and mid-infrared differential frequency generation.

Physical Information-Embedded Deep Learning for Forward Prediction and Inverse Design of Nanophotonic Devices

Nanophotonic devices have enabled electromagnetic manipulation with unprecedented accuracy and functionalities. With the increased functionality requirements of such devices and the progress of fabrication technologies, trends toward miniaturization and multi-functionality have emerged, making forward response prediction and inverse design increasingly complicated. In this paper, a physical information-embedded deep learning model for flexible forward prediction and multifunctional inverse design is proposed. Besides the overwhelming advantage of computing efficiency over conventional iterative optimization methods, the proposed method exhibits strong generalization on different wavelengths and polarizations by embedding the corresponding physical information into the model through effective sparse parameter method (SPM). For the forward prediction, responses can be predicted among the 1300-1550 nm wavelength band and two polarizations (TM/TE) with high accuracy. For the inverse design, with the assistance of forward prediction models and broadband training methods, multi-dimensional information for the target can be considered simultaneously to retrieve the satisfactory desired designs topologies in an unsupervised way. The multi-functionality of inverse design is demonstrated by implementing wavelength demultiplexers with small crosstalk and power splitters with arbitrary splitting ratios on a 250 nm broadband wavelength in a compact footprint of 2 × 2 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> without additional heavy training of the model.

Polarization-insensitive achromatic metalens based on computational wavefront coding.

Broadband achromatic metalens imaging is of great interest in various applications, such as integrated imaging and augmented/virtual reality display. Current methods of achromatic metalenses mainly rely on the compensation of a linear phase dispersion implemented with complex nanostructures. Here, we propose and experimentally demonstrate a polarization-insensitive achromatic metalens (PIA-ML) based on computational wavefront coding. In this method, simple circular or square nanopillars are individually coded such that the focal depths at wavelengths at both ends of the achromatic bandwidth overlap at the designed focal plane, which removes the limitation of requiring a linear phase dispersion. An optimized PIA-ML that works in the full optical communication band from 1300 to 1700nm was obtained using a particle swarm optimization algorithm. Experimental results show that both focusing and imaging of the fabricated metalens are consistent with theoretical predictions within the broadband wavelength range, which provides a new methodology for ultra-broadband achromatic imaging with simple-shaped nanostructures.

Ultra-broadband Bragg concave diffraction grating designs on 220-nm SOI for wavelength demultiplexing.

The appropriate broadband design of a de/multiplexer can significantly increase the channel number and consequently the transmission capacity of a wavelength division multiplexing system. Herein, we present the first ultra-broadband Bragg concave diffraction grating (CDG) on a 220-nm silicon-on-insulator, covering most of the E, S, C, L, and U telecommunication wavebands spanning from 1.425 to 1.675 μm. A wide-band-gap Bragg mirror is employed to facilitate broadband reflection, with a low diffraction order of grating for a sufficient free spectral range. Numerical simulations show that the proposed approaching blazed concave diffraction grating (AB-CDG) for the two-material case exhibits a high integration, simple fabrication process, and promising spectral performance. We fabricate the grating for design verification with a low transmission loss of -0.6 dB and a crosstalk below -33.7 dB for the eight measured wavelength channels covering the spectral range from 1.5 to 1.61 μm that is limited by the bandwidth of the grating coupler. This design can be used for broadband wavelength demultiplexing, frontier astronomical observation, and spectroscopic imaging.

Athermal silicon photonic wavemeter for broadband and high-accuracy wavelength measurements

We propose and demonstrate an integrated wavemeter capable of accurate and broadband measurements without control or knowledge of the temperature. In our design, interferometers composed of silicon and silicon nitride waveguides enable accurate measurements of an input optical wavelength despite large and rapid temperature fluctuations of 20°C by leveraging the disparity in thermo-optic properties of the waveguides. We derive formulas which resolve the wavelength and temperature ambiguity of the interferometers. The fabricated wavemeter chip is found to have a mean accuracy of 11 pm over an 80 nm range near 1550 nm. To our knowledge, this is the first demonstration of an athermal silicon wavemeter and the lowest measurement error across such a broad wavelength range using silicon photonics. This result may reduce the cost and size of wavemeters used in combination with integrated lasers for optical communications, sensing, and other applications.