Glass Waveguides Research Articles

Ultra-high-power-confinement-factor integrated mid-infrared gas sensor based on the suspended slot chalcogenide glass waveguide

In this paper, we propose, design, and analyze a suspended slot chalcogenide glass waveguide gas sensor in detail. Within a bandwidth from 3.0 μm to 4.4 μm, a power confinement factor of larger than 90 % can be achieved by rationally optimizing structural parameters of the proposed waveguide sensor. When the methane is considered as the target gas, the power confinement factor, sensitivity, and limit of detection of the proposed waveguide sensor are respectively 93.81 %, 0.4578, and 18.17 ppm at a wavelength of 3.67 μm. If the operating wavelength is selected to be 3.291 μm, the power confinement factor, sensitivity, and limit of detection will be 91.98 %, 7.151, and 1.139 ppm, respectively.

42.4: Compact Stereo Waveguide Display Using a Polarization‐Multiplexed In‐coupling Metagrating

Three‐dimensional (3D) vision in augmented reality (AR) displays can enable highly immersive and realistic viewer experience, hence attracts much attention. Most current approaches create 3D visions by projecting stereoscopic images to different eyes using two separate projection systems, which are inevitably bulky for wearable devices. Here, we propose a compact stereo waveguide AR display system using a single piece of thin flat glass integrated with a polarization‐multiplexed metagrating in‐coupler and two diffractive grating out‐couplers. Incident light of opposite circular polarization states carrying stereoscopic images are first steered by the metagrating to opposite propagation directions in the flat glass waveguide, subsequently extracted by the diffractive gratings and finally received by different eyes, forming 3D stereo vision. Experimentally we fabricated a display prototype and demonstrated independent projection of two polarization‐multiplexed stereoscopic images. This work paves a novel path towards the implementation of high‐performance stereo displays with compact size, light weight, and multi‐color compatibility.

Photonic implementation of artificial synapses in ultrafast laser inscribed waveguides in chalcogenide glass

Simple and direct prototyping methods are ideal for large-scale delivery of cognitive photonic hardware. Here, we choose ultrafast laser writing as a direct fabrication technique to later demonstrate all-optical synaptic-like performance along the laser-written waveguides in a chalcogenide glass. Neuronal communication protocols, such as excitatory and inhibitory responses, temporal summations, and spike-timing-dependent plasticity, are shown in the glass chip. This work manifests the potential for large-scale delivery of fully integrated photonic chips based on cognitive principles by single-step fabrication procedures.

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Active and Quantum Integrated Photonic Elements by Ion Exchange in Glass

Ion exchange in glass has a long history as a simple and effective technology to produce gradient-index structures and has been largely exploited in industry and in research laboratories. In particular, ion-exchanged waveguide technology has served as an excellent platform for theoretical and experimental studies on integrated optical circuits, with successful applications in optical communications, optical processing and optical sensing. It should not be forgotten that the ion-exchange process can be exploited in crystalline materials, too, and several crucial devices, such as optical modulators and frequency doublers, have been fabricated by ion exchange in lithium niobate. Here, however, we are concerned only with glass material, and a brief review is presented of the main aspects of optical waveguides and passive and active integrated optical elements, as directional couplers, waveguide gratings, integrated optical amplifiers and lasers, all fabricated by ion exchange in glass. Then, some promising research activities on ion-exchanged glass integrated photonic devices, and in particular quantum devices (quantum circuits), are analyzed. An emerging type of passive and/or reconfigurable devices for quantum cryptography or even for specific quantum processing tasks are presently gaining an increasing interest in integrated photonics; accordingly, we propose their implementation by using ion-exchanged glass waveguides, also foreseeing their integration with ion-exchanged glass lasers.

Femtosecond laser induced low propagation loss waveguides in a lead-germanate glass for efficient lasing in near to mid-IR

To support the growing landscape of near to mid-IR laser applications we demonstrate a range of low propagation loss femtosecond laser (FSL) written waveguides (WGs) that have achieved guided-mode laser operation in a rare earth (RE) doped lead-germanate glass. The WGs are fabricated in both the athermal and thermal FSL writing regimes using three different pulse repetition frequencies (PRF): 100 kHz (athermal); 1 MHz; and 5 MHz (thermal). The lasing capability of Yb3+ doped lead-germanate waveguides is verified in the near-IR. The refractive index contrast (∆n) for 100 kHz WGs is ~ 1 × 10–4, while for 5 MHz, ∆n increases to ~ 5 × 10–4. The WGs in the thermal regime are less effected by self-focusing and are larger in dimensions with reduced propagation losses. For the 1 MHz repetition rate thermal writing regime we report a low propagation loss WG (0.2 dB/cm) and demonstrate laser operation with slope efficiencies of up to ~ 28%.

Two-dimensional waveguides in magneto-optical glasses fabricated by carbon ion implantation and femtosecond laser ablation

The exploration of 2D waveguide structures on optoelectronic materials is important for applications in integrated optics devices. In this work, 2D waveguides on the magneto-optical glass were fabricated via combining the carbon ion implantation and the femtosecond laser ablation. Firstly, the 1D waveguide was formed by the double energy (6.0+5.5) MeV carbon ion implantation with fluences of (8.0+4.0)×1013 ions/cm2. Subsequently, the femtosecond laser ablation with 800-nm central wavelength and 1.0-kHz repetition rate was conducted on the 1D waveguide surface to manufacture 2D guiding structures. The end-facet images were captured by an optical microscope. The near-field modal profiles of the 2D waveguides were recorded by an end-face coupling system at near-infrared (976 nm) and visible (532 nm) bands. The research results provide the feasibility and the experimental basis for the preparation of a magneto-optical waveguide isolator.

Femtosecond laser induced thermophoretic writing of waveguides in silicate glass

Here in, the fs-laser induced thermophoretic writing of microstructures in ad-hoc compositionally designed silicate glasses and their application as infrared optical waveguides is reported. The glass modification mechanism mimics the elemental thermal diffusion occurring in basaltic liquids at the Earth’s mantle, but in a much shorter time scale (108 times faster) and over a well-defined micrometric volume. The precise addition of BaO, Na2O and K2O to the silicate glass enables the creation of positive refractive index contrast upon fs-laser irradiation. The influence of the focal volume and the induced temperature gradient is thoroughly analyzed, leading to a variety of structures with refractive index contrasts as high as 2.5 × 10–2. Two independent methods, namely near field measurements and electronic polarizability analysis, confirm the magnitude of the refractive index on the modified regions. Additionally, the functionality of the microstructures as waveguides is further optimized by lowering their propagation losses, enabling their implementation in a wide range of photonic devices.

Vibration monitoring based on optical sensing of mechanical nonlinearities in glass suspended waveguides.

Vibration monitoring plays a key role in numerous applications, including machinery predictive maintenance, shock detection, space applications, packaging-integrity monitoring and mining. Here, we investigate mechanical nonlinearities inherently present in suspended glass waveguides as a means for optically retrieving key vibration pattern information. The principle is to use optical phase changes in a coherent light signal travelling through the suspended glass waveguide to measure both optical path elongation and stress build-up caused by a given vibration state. Due to the intrinsic non-linear mechanical properties of double-clamped beams, we show that this information not only offers a means for detecting excessive vibrations but also allows for identifying specific vibration patterns, such as positive or negative chirp, without the need for any additional signal processing. In addition, the manufacturing process based on femtosecond laser exposure and chemical etching makes this sensing principle not only simple, compact and robust to harsh environments but also scalable to a broad frequency range.

Photonic circuits written by femtosecond laser in glass: improved fabrication and recent progress in photonic devices

Integrated photonics is attracting considerable attention and has found many applications in both classical and quantum optics, fulfilling the requirements for the ever-growing complexity in modern optical experiments and big data communication. Femtosecond (fs) laser direct writing (FLDW) is an acknowledged technique for producing waveguides (WGs) in transparent glass that have been used to construct complex integrated photonic devices. FLDW possesses unique features, such as three-dimensional fabrication geometry, rapid prototyping, and single step fabrication, which are important for integrated communication devices and quantum photonic and astrophotonic technologies. To fully take advantage of FLDW, considerable efforts have been made to produce WGs over a large depth with low propagation loss, coupling loss, bend loss, and highly symmetrical mode field. We summarize the improved techniques as well as the mechanisms for writing high-performance WGs with controllable morphology of cross-section, highly symmetrical mode field, low loss, and high processing uniformity and efficiency, and discuss the recent progress of WGs in photonic integrated devices for communication, topological physics, quantum information processing, and astrophotonics. Prospective challenges and future research directions in this field are also pointed out.

Femtosecond laser writing low-loss waveguides in silica glass: highly symmetrical mode field and mechanism of refractive index change

Here, single-mode waveguides are written in silica glass by femtosecond (fs) laser. The waveguides exhibit a low propagation loss of 0.15 dB/cm and a symmetrical mode field. The loss performance and the mode field symmetry are demonstrated to strongly depend on the pulse repetition and polarization of fs laser, respectively. Raman and photoluminescence properties indicate that an increase of refractive index originates from an increment in the total density of glass networks consisting of small and large rings, but only increasing the number of small rings does not necessarily lead to an increase in refractive index. The long working distance of the objective lens promises to fabricate low-loss waveguides in a large depth of glass, which would inspire manufacturing integrated photonic devices by fs laser writing. Clarifying the mechanism of refractive index change offers a new perspective to understand the fs laser-matter interaction.

Optical properties and annealing effects of planar waveguides on fluoride lead silicate glass formed by proton and helium-ion implantation

The optical planar waveguides were fabricated by proton implantation with an energy of 400 keV and a dose of 8 × 1016 ions / cm2 or 400-keV helium-ion implantation with a fluence of 6 × 1016 ions / cm2 in the fluoride lead silicate glass. The morphologies were studied by a Zeiss microscope to estimate the thickness of the waveguides. The annealing effects on the fluoride lead silicate glass waveguides were investigated by 60 min annealing cycles at different temperatures ranging from 260°C to 310°C in air atmosphere. The dark-mode spectra and corresponding effective refractive indices before and after the thermal treatments were measured by the prism coupling system. The Stopping and Range of Ions in Matter 2013 code was used to simulate the irradiation process and calculate the energy losses. The refractive index distributions were reconstructed by the reflectivity calculation method. The near-field light intensity profiles of the proton and helium-ion implanted fluoride lead silicate glass waveguides were measured by the end-face coupling system. The comparison of optical properties between the proton-implanted waveguide and helium-ion implanted one was carried out. The experimental results show that the helium-ion implantation is more suitable for the fabrication of the fluoride lead silicate glass optical waveguides and the He + -implanted waveguide has better optical propagation performances.

Tunable thermal diffusion and heat accumulation in transparent materials based on varying the scanning speed of a femtosecond laser

Based on heat accumulation effects, symmetric optical waveguides in glass can be obtained via femtosecond laser irradiation. Such modification inside glass is interesting in terms of developing integrated mini-optical devices with 3-D structures and micro channels for biosensors. This work experimentally investigated the formation of micro-channels inside porous glass irradiated with an 800 nm, 100 fs, and 250 kHz femtosecond laser with scanning speeds ranging from 250 μm/s to 1000 μm/s at a fixed power of 300 mW. Strong heat accumulation effects were thus observed at laser scanning at 250μm/s, which offered significant variations in structure morphology.

Coupled localized surface plasmon resonances in periodic arrays of gold nanowires on ion-exchange waveguide technology

Coupled localized surface plasmon resonances (LSPRs) in periodic arrays of metallic nanowires are attractive for use in sensing applications due to their light enhancement and their sensitivity to the surrounding environment. Due to the interwire coupling, they behave as plasmonic waveguides with high wavevector modes that require bulky methods for efficient excitation. In this contribution, we demonstrate the excitation of coupled LSPRs in gold nanowires with photonic modes supported by an optical waveguide made with ion exchange technology. Currently, although weakly-coupled LSPRs are experimentally demonstrated, strongly-coupled LSPRs are only demonstrated numerically due to the challenge represented by the fabrication of a high density nanowire array with current electron beam lithography. Due to their operation across the visible spectrum and its low-loss coupling to standard optical fibers, integrated nanowires on glass waveguides open new perspectives for the development of hybrid photonic-plasmonic integrated optical devices.

Optical Sensitivity of Waveguides Inscribed in Nanoporous Silicate Framework

Laser direct writing technique in glass is a powerful tool for various waveguides’ fabrication that highly develop the element base for designing photonic devices. We apply this technique to fabricate waveguides in porous glass (PG). Nanoporous optical materials for the inscription can elevate the sensing ability of such waveguides to higher standards. The waveguides were fabricated by a single-scan approach with femtosecond laser pulses in the densification mode, which resulted in the formation of a core and cladding. Experimental studies revealed three types of waveguides and quantified the refractive index contrast (up to Δn = 1.2·10−2) accompanied with ~1.2 dB/cm insertion losses. The waveguides demonstrated the sensitivity to small objects captured by the nanoporous framework. We noticed that the deposited ethanol molecules (3 µL) on the PG surface influence the waveguide optical properties indicating the penetration of the molecule to its cladding. Continuous monitoring of the output near field intensity distribution allowed us to determine the response time (6 s) of the waveguide buried at 400 µm below the glass surface. We found that the minimum distinguishable change of the refractive index contrast is 2 × 10−4. The results obtained pave the way to consider the waveguides inscribed into PG as primary transducers for sensor applications.

Externally Pumped Photonic Chip‐Based Ultrafast Raman Soliton Source

AbstractThe advantages of low cost, compact size, and reduced power consumption makes a photonic chip‐based ultrafast laser source an appealing technology for diverse applications such as all‐optical signal processing, frequency metrology, spectroscopy, and sensing. To date, on‐chip ultrafast sources are typically generated by microresonator‐based Kerr‐comb solitons, which require precise phase tuning and frequency agile lasers to access the soliton state. Here, this work reports the first experimental demonstration of an externally pumped on‐chip ultrafast soliton laser source based on Raman soliton self‐frequency shift. By capitalizing on strong optical nonlinearity and versatile dispersion control in Ge28Sb12Se60 chalcogenide glass waveguides, 185 fs duration Raman soliton generation has been demonstrated, possessing continuous wavelength tunability from 1589 to 1807 nm with signal‐to‐noise ratios consistently exceeding 65 dB. The source operates with pump pulse energies as low as 1.08 pJ, representing over three orders of magnitude improvement compared to fiber‐based Raman soliton sources. In addition, the generated solitons exhibit excellent spectral purity and stability free from parasitic sidebands. These experimental results are further validated by theoretical analysis, revealing insights into the soliton dynamics and critical device design guidelines. This work therefore enables a new class of broadly tunable, energy‐efficient, compact, and potentially cost‐effective on‐chip ultrafast laser sources.

Optical properties of He+-implanted fused silica glass waveguides

An optical waveguide is an important dielectric device that guides the propagation of light waves. Ion implantation is a competitive waveguide preparation technique with advantages including reliance, simpleness and flexibility. In this work, a 400-keV helium ion implantation with a fluence of [Formula: see text] ions/cm2 was carried out to manufacture a planar waveguide on the surface of the fused silica glass. The formation mechanism of the waveguide was analyzed by the nuclear energy deposition based on the SRIM 2013 and the refractive index distribution with the help of the reflectivity calculation method (RCM). The geometry structure and the guiding performance of the waveguide were studied by the metallographic microscope and the end-face coupling system, respectively. The investigation on the fabrication and characteristics of fused silica glass optical waveguides is of great significance for the development of passive devices in the field of optical communications.

On-Chip Detector Based on Supercontinuum Generation in Chalcogenide Waveguide

We present the design, preparation, and performance optimization of strip waveguide in chalcogenide glass (ChG) for broadband supercontinuum (SC) generation. Ternary Ge-Sb-S systems possess large band-gap, high refractive index, and strong laser damage resistance. The characterization of strip waveguide in Ge-Sb-S glass for SC source generation with 1300 nm bandwidth is experimentally demonstrated. Sensing capability of the device is validated for optical absorption of β-phenylethylamine solutions near 1551 nm in various concentrations, revealing the repeatability and consistency of the generated SC spectrum in test. The advantages of high specificity detection scheme, scalable integration and ease of miniaturization might make the device a promising platform for biochemical monitoring.

Er3+/Yb3+ co-doped phosphate glass waveguides formed by the H+ ion implantation

The 400 keV proton implantation with a fluence of [Formula: see text] ions/cm2 was applied on the [Formula: see text] co-doped phosphate glass to fabricate a planar waveguide structure. The mode profile at the end face of the waveguide was measured by the end-face coupling technique. The energy loss profile of the energetic protons was calculated by the SRIM 2013. The refractive index distribution was simulated by the reflectivity calculation method. Based on these results, the formation theory of the planar waveguides was discussed through simulating the energy loss distribution and analyzing the reconstructed refractive index profile, which could be used for applications in the future integrated optical systems.

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels.

SummaryIn this work, we introduce HI-Light, a surface-engineered glass-waveguide-based “shell-and-tube” type photothermal reactor which is both scalable in diameter and length. We examine the effect of temperature, light irradiation, and residence time on its photo-thermocatalytic performance for CO2 hydrogenation to form CO, with a cubic phase defect-laden indium oxide, In2O3-x(OH)y, catalyst. We demonstrate the light enhancement effect under a variety of reaction conditions. Notably, the light-on performance for the cubic nanocrystal photocatalyst exhibits a CO evolution rate at 15.40 mmol gcat−1 hr−1 at 300°C and atmospheric pressure. This is 20 times higher conversion rate per unit catalyst mass per unit time beyond previously reported In2O3-x(OH)y catalyst in the cubic form under comparable operation conditions and more than 5 times higher than that of its rhombohedral polymorph. This result underscores that improvement in photo-thermocatalytic reactor design enables uniform light distribution and better reactant/catalyst mixing, thus significantly improving catalyst utilization.