Search Results (92)

Whispering-gallery-mode (WGM) microresonators are amongst the most promising optical sensors for detecting bio-chemical targets. A number of laser interrogation methods have been proposed and demonstrated over the last decade, based on scattering and absorption losses or resonance splitting and shift, harnessing the high-quality factor and ultra-small volume of WGMs. Actually, regardless of the sensitivity enhancement, their practical sensing operation may be hampered by the complexity of coupling devices as well as the signalprocessing required to extract the WGM response. Here, we use a silica microsphere immersed in an aqueous environment and efficiently excite optical WGMs with a free-space visible laser, thus collecting the relevant information from the transmitted and back-scattered light without any optical coupler, fiber, or waveguide. We show that a 640-nm diode laser, actively frequency-locked on resonance, provides real-time, fast sensing of dielectric nanoparticles approaching the surface with direct analog readout. Thanks to our illumination scheme, the sensor can be kept in water and operate for days without degradation or loss of sensitivity. Diverse noise contributions are carefully considered and quantified in our system, showing a minimum detectable particle size below 1 nm essentially limited by the residual laser microcavity jitter. Further analysis reveals that the inherent laserfrequency instability in the short, -mid-term operation regime sets an ultimate bound of 0.3 nm. Based on this work, we envisage the possibility to extend our method in view of developing new viable approaches for detection of nanoplastics in natural water without resorting to complex chemical laboratory methods. Full article

The article discusses the design, fabrication, and experimental evaluation of a large-area vertical grating coupler (VGC) enabling simultaneous coupling of multiple input optical beams. The presented VCG was fabricated by direct nanoimprinting of a grating pattern in a non-hardened SiO_X:TiO_Y waveguide (WG) film. The WG film was deposited on a glass substrate using a combination of the sol–gel method and the dip-coating technique. The fabrication process allowed precise control of the waveguide film thickness and refractive index, as well as the VGC geometry. The relevance of the process was proved by a demonstration of optical coupling of multiple quasi-parallel input beams via the VGC to the WG layer. To make this possible, a dedicated optical coupling system was designed, including a polymer microlens array and optical fiber array positioned in a V-groove. This opens promising perspectives on using the proposed structure for the fabrication of low-cost multichannel optical sensor chips, as highlighted in the article’s final section. Full article

Microring resonators, known for their compact size, wavelength selectivity, and high-quality factor, enable efficient light manipulation, making them ideal for photonic logic applications. This paper presents the design and simulation of seven fundamental all-optical logic gates—XOR, AND, OR, NOT, NOR, NAND, and XNOR—using a seven-microring silicon-on-silica waveguide. Operating at the standard telecommunication wavelength of 1.55 µm, the proposed design exploits constructive and destructive interferences caused by phase changes in the input optical beams to perform logic operations. Numerical simulations, conducted using Lumerical FDTD Solutions, validate the performance of the logic gates, with the contrast ratio (CR) as the primary evaluation metric. The proposed design achieves CR values of 14.04 dB for XOR, 15.14 dB for AND, 15.85 dB for OR, 13.42 dB for NOT, 12.02 dB for NOR, 12.75 dB for NAND, and 14.10 dB for XNOR, significantly higher than those reported in previous works. This results in a data rate of 199.8 Gb/s, facilitated by a compact waveguide size of 1.30 × 1.35 μm². These results highlight the potential of silicon photonics and microring resonators in enabling high-performance, energy-efficient, and densely integrated optical computing and communication systems. Full article

Molecularly imprinted polymers (MIPs) can be combined with optical fibers (OFs) to create various sensor configurations, yielding low-cost and highly sensitive extrinsic and intrinsic sensors. In this work, an MIP-based extrinsic optical fiber sensor is obtained by two silica OFs connected via an optical waveguide using an MIP as a core of micrometer size (micro OF-MIP-OF sensor). The proposed sensing approach can be used only with MIP receptors and implements an intensity-based sensor configuration. MIPs present several advantages over bio-receptors and can be exploited to realize novel sensing methods. The MIP used in this work is specifically designed for 2-furaldehyde (2-FAL) detection, and the experimental results demonstrate that the micro-probe performs well in terms of sensitivity and selectivity, with capabilities applicable to several application fields. In particular, a nanomolar detection range, from 1.5 nM to 150 nM, has been achieved. Moreover, the results are comparable to or better than those of other previously proposed MIP optical fiber sensors for 2-FAL, which employ more complex sensing principles or fabrication steps. Full article

Many current 1 × 2 splitter couplers based on multimode interference (MMI) face difficulties such as significant back reflection and limited flexibility in waveguide segmentation at the output, which necessitate the addition of transitional structures like tapered waveguides or S-Bends. These limitations reduce their effectiveness as photonic data-center applications, where precise waveguide configurations are crucial. To address these challenges, we propose a novel nanoscale 1 × 2 angled multimode interference (AMMI) power splitter with silicon nitride (SiN) buried core and silica cladding. The innovative angled light path design improved performance by minimizing back reflections back to the source and by providing greater flexibility of waveguide interconnections, making the splitter more adaptable for data-center applications. The SiN core was selected due to its lower refractive index contrast with silica compared to silicon, which helps further reduce back reflection. The dimensions of the splitter were optimized using full vectorial beam propagation method (FV-BPM), finite-difference time domain (FDTD), and multivariable optimization scanning tool (MOST) simulations to support transmission across the O-band. Our proposed device demonstrated excellent performance, achieving an excess loss of 0.22 dB and an imbalance of <0.01 dB at the output ports at an operational wavelength of 1.31 µm. The total device length is 101 µm with a thickness of 0.4 µm. Across the entire O-band range (1260–1360 nm), the performance of the splitter presented excess loss of up to 1.57 dB and an imbalance of up to 0.05 dB. Additionally, back reflections at the operational wavelength were measured at −40.96 dB and up to −39.67 dB over the O-band. This silicon-on-insulator (SOI) complementary metal-oxide semiconductor (CMOS) compatible AMMI splitter demonstrates high tolerance for manufacturing deviations due to its geometric layout, dimensions, and material selection. Furthermore, the proposed splitter is well-suited for use in O-band transceiver systems and can enhance data-center optical networks by supporting high-speed, low-loss data transmission. The compact design and CMOS compatibility make this device ideal for integrating into dense, high-performance computing environments, ensuring reliable signal distribution and minimal power loss. The splitter can support multiple communication channels, thus enhancing bandwidth and scalability for next-generation data-center infrastructures. Full article

We propose a simple and innovative configuration consisting of a quantum dot and micro-optical resonator that emits single photons with good directionality in a plane parallel to the substrate. In this device, a single quantum dot is placed as a light source between the slits of a triangular split-ring micro-optical resonator (SRR) supported in an optical polymer film with an air-bridge structure. Although most of the previous single photon emitters in solid-state devices emitted photons upward from the substrate, operation simulations confirmed that this configuration realizes lateral light emission in narrow regions above, below, left, and right in the optical polymer film, despite the absence of a light confinement structure such as an optical waveguide. This device can be fabricated using silica-coated colloidal quantum dots, focused ion beam (FIB) lithography, and wet etching using an oxide layer on a silicon substrate as a sacrificial layer. The device has a large tolerance to the variation in the position of the SRR in the optical polymer film and the height of the air-bridge. We confirmed that Pt-SRRs can be formed on the optical polymer film using FIB lithography. This simple lateral photon emitter is suitable for coupling with optical fibers and for fabricating planar optical quantum solid-state circuits, and is useful for the development of quantum information processing technology. Full article

A silica waveguide thermo-optic mode switch with small radius bimodal S-bends is demonstrated in this study. The cascaded multimode interference coupler is adopted to implement the E₁₁ and E₂₁ mode selective output. The beam propagation method is used in design optimization. Standard CMOS processing of ultraviolet photolithography, chemical vapor deposition, and plasma etching are adopted in fabrication. Detailed characterizations on the prepared switch are performed to confirm the precise fabrication. The measurement results show that within the wavelength range from 1530 to 1575 nm, for the E₁₁ mode input, the switch exhibits an extinction ratio of ≥13.1 dB and a crosstalk ≤−22.8 dB at an electrical driving power of 284.8 mW, while for the E₂₁ mode input, the extinction ratio is ≥15.5 dB and the crosstalk is ≤−18.1 dB at an electrical driving power of 282.4 mW. These results prove the feasibility of multimode S-bends in mode switching. The favorable performance of the demonstrated switch promises good potential for on-chip mode routing. Full article

Photonic circuits find applications in biomedicine, manufacturing, quantum computing and communications. Photonic waveguides are crucial components, typically having cross-section orders of magnitude inferior when compared with other photonic components (e.g., optical fibers, light sources and photodetectors). Several light-coupling methods exist, consisting of either on-plane (e.g., adiabatic and end-fire coupling) or off-plane methods (e.g., grating and vertical couplers). The grating coupler is a versatile light-transference technique which can be tested at wafer level, not requiring specific fiber terminations or additional optical components, like lenses, polarizers or prisms. This study focuses on fully-etched grating couplers without a bottom reflector, made from hydrogenated amorphous silicon (a-Si:H), deposited over a silica substrate. Different coupler designs were tested, and of these we highlight two: the superimposition of two lithographic masks with different periods and an offset between them to create a random distribution and a technique based on the quadratic refractive-index variation along the device’s length. Results were obtained by 2D-FDTD simulation. The designed grating couplers achieve coupling efficiencies for the TE-like mode over −8 dB (mask overlap) and −3 dB (quadratic variation), at a wavelength of 1550 nm. The coupling scheme considers a 220 nm a-Si:H waveguide and an SMF-28 optical fiber. Full article

In this paper, a temperature sensor based on a polymer–silica heterogeneous integrated Mach–Zehnder interferometer (MZI) structure is proposed. The MZI structure consists of a polymer waveguide arm and a doped silica waveguide arm. Due to the opposite thermal optical coefficients of polymers and silica, the hybrid integrated MZI structure enhances the temperature sensing characteristics. The direct coupling method and side coupling method are introduced to reduce the coupling loss of the device. The simulation results show that the side coupling structure has lower coupling loss and greater manufacturing tolerance compared to the direct coupling structure. The side coupling loss for PMMA material-based devices, NOA material-based devices, and SU-8 material-based devices is 0.104 dB, 0.294 dB, and 0.618 dB, respectively. The sensitivity (S) values of the three hybrid devices are −6.85 nm/K, −6.48 nm/K, and −2.30 nm/K, which are an order of magnitude higher than those of an all-polymer waveguide temperature sensor. We calculated the temperature responsivity (R_T) (FSR→∞) of the three devices as 13.16 × 10⁻⁵ K, 32.20 × 10⁻⁵ K, and 20.20 × 10⁻⁵ K, suggesting that high thermo-optic coefficient polymer materials and the hybrid integration method have a promising application in the field of on-chip temperature sensing. Full article

The mimesis of biological mechanisms by artificial devices constitutes the modern, rapidly expanding, multidisciplinary biomimetics sector. In the broader bioinspiration perspective, however, bioarchitectures may perform independent functions without necessarily mimicking their biological generators. In this paper, we explore such Bioarchitectonic notions and demonstrate three-dimensional photonics by the exact replication of insect organs using ultra-porous silica aerogels. The subsequent conformal systolic transformation yields their miniaturized affine ‘clones’ having higher mass density and refractive index. Focusing on the paradigms of ommatidia, the compound eye of the hornet Vespa crabro flavofasciata and the microtrichia of the scarab Protaetia cuprea phoebe, we fabricate their aerogel replicas and derivative clones and investigate their photonic functionalities. Ultralight aerogel microlens arrays are proven to be functional photonic devices having a focal length f ~ 1000 μm and f-number f/30 in the visible spectrum. Stepwise systolic transformation yields denser and affine functional elements, ultimately fused silica clones, exhibiting strong focusing properties due to their very short focal length of f ~ 35 μm and f/3.5. The fabricated transparent aerogel and xerogel replicas of microtrichia demonstrate a remarkable optical waveguiding performance, delivering light to their sub-100 nm nanotips. Dense fused silica conical clones deliver light through sub-50 nm nanotips, enabling nanoscale light–matter interactions. Super-resolution bioarchitectonics offers new and alternative tools and promises novel developments and applications in nanophotonics and other nanotechnology sectors. Full article

Interest grows in designing silicon-on-insulator slot waveguides to trap optical fields in subwavelength-scale slots and developing their optofluidic devices. However, it is worth noting that the inherent limitations of the waveguide structures may result in high optical losses and short optical paths, which challenge the device’s performance in optofluidics. Incorporating the planar silicon-based slot waveguide concept into a silica-based hollow-core fiber can provide a perfect solution to realize an efficient optofluidic waveguide. Here, we propose a subwavelength-scale liquid-core hybrid fiber (LCHF), where the core is filled with carbon disulfide and surrounded by a silicon ring in a silica background. The waveguide properties and the Stimulated Raman Scattering (SRS) effect in the LCHF are investigated. The fraction of power inside the core of 56.3% allows for improved sensitivity in optical sensing, while the modal Raman gain of 23.60 m⁻¹·W⁻¹ is two times larger than that generated around a nanofiber with the interaction between the evanescent optical field and the surrounding Raman media benzene-methanol, which enables a significant low-threshold SRS effect. Moreover, this in-fiber structure features compactness, robustness, flexibility, ease of implementation in both trace sample consumption and reasonable liquid filling duration, as well as compatibility with optical fiber systems. The detailed analyses of the properties and utilizations of the LCHF suggest a promising in-fiber optofluidic platform, which provides a novel insight into optofluidic devices, optical sensing, nonlinear optics, etc. Full article

This paper proposes a unique configuration for an all-optical D Flip Flop (D-FF) utilizing a quasi-square ring resonator (RR) and T-Splitter, as well as NOT and OR logic gates within a 2-dimensional square lattice photonic crystal (PC) structure. The components realizing the all-optical D-FF comprise of optical waveguides in a 2D square lattice PC of 45 × 23 silicon (Si) rods in a silica (SiO₂) substrate. The utilization of these specific materials has facilitated the fabrication process of the design, diverging from alternative approaches that employ an air substrate, a method inherently unattainable in fabrication. The configuration underwent examination and simulation utilizing both plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methodologies. The simulation outcomes demonstrate that the designed waveguides and RR effectively execute the operational principles of the D-FF by guiding light as intended. The suggested configuration holds promise as a logic block within all-optical arithmetic logic units (ALUs) designed for digital computing optical circuits. The design underwent optimization for operation within the C-band spectrum, particularly at 1550 nm. The outcomes reveal a distinct differentiation between logic states ‘1’ and ‘0’, enhancing robust decision-making on the receiver side and minimizing logic errors in the photonic decision circuit. The D-FF displays a contrast ratio (CR) of 4.77 dB, a stabilization time of 0.66 psec, and a footprint of 21 μm × 12 μm. Full article

The mode rotator is an important component in a PLC-based mode-division multiplexing (MDM) system, which is used to implement high-order modes with vertical intensity peaks, such as LP_11b mode conversions from LP_11a in PLC chips. In this paper, an LP₁₁ mode rotator based on a polymer/silica hybrid inverted ridge waveguide is demonstrated. The proposed mode rotator is composed of an asymmetrical waveguide with a trench. According to the simulation results, the broadband conversion efficiency between the LP_11a and LP_11b modes is greater than 98.5%, covering the C-band after optimization. The highest mode conversion efficiency (MCE) is 99.2% at 1550 nm. The large fabrication tolerance of the proposed rotator enables its wide application in on-chip MDM systems. Full article

A variable optical attenuator (VOA) is a crucial component for optical communication, especially for a variable multiplexer (VMUX) and reconfigurable optical add-drop multiplexer (ROADM). With the capacity increasing dramatically, a large-port-count and low-power-consumption VOA array is urgent for an on-chip system. In this paper, we experimentally demonstrate a 16-channel VOA array based on a polymer/silica hybrid waveguide. The proposed array is able to work over C and L bands. The VOA array shows an average attenuation larger than 14.38 dB with a low power consumption of 15.53 mW. The low power consumption makes it possible to integrate silica-based passive devices with a large port count on-chip. Full article

Silica-on-silicon is a major optical integration platform, while the emergent class of the integrated laser-written circuits’ platform offers additionally high customizability and flexibility for rapid prototyping. However, the inherent waveguides’ low core/cladding refractive index contrast characteristic, compared to other photonic platforms in silicon or silicon nitride, sets serious limitations for on-chip efficient coupling with single photon emitters, like semiconductor nanowires with quantum dots, limiting the applications in quantum computing. A new light coupling scheme proposed here overcomes this limitation, providing means for light coupling >50%. The scheme is based on the incorporation of an optical microsphere between the nanowire and the waveguide, which is properly optimized and arranged in terms of size, refractive index, and the distance of the microsphere between the nanowire and waveguide. Upon suitable design of the optical arrangement, the photonic nanojet emitted by the illuminated microsphere excites efficiently the guided eigenmodes of the input channel waveguide, thus launching light with high-coupling efficiency. The method is tolerant in displacements, misalignments, and imperfections and is fabricationally feasible by the current state of art techniques. The proposed method enables the on-chip multiple single photon emitters’ integration, thus allowing for the development of highly customizable and scalable quantum photonic-integrated circuits for quantum computing and communications. Full article