Glass Waveguides Research Articles

Ultrafast laser processing of glass waveguide substrates for multi-fiber connectivity in co-packaged optics

High bandwidth demanding applications such as high-performance computing and hyperscale datacenters are drivers for co-packaged optics, which aims to bring optical signals as close as possible to the electrical computing chips by integrating the electro-optic transceivers and ASICs on the same package substrate. These next-generation switches require advanced fiber-to-chip connectivity and novel packaging concepts to enable sufficient power and cost savings. As such, low-loss, high bandwidth, and high fiber-counts are required at the photonic chip interface. In this work, these challenges are addressed by enabling the multi-fiber push-on (MPO) interface at the edge of integrated glass waveguide substrates and thus leverages the existing fiber connector eco-system. An ultrafast laser process is used to singulate glass wafers into individual photonic chips leaving optical-quality end-facets with <1 μm flatness over the 6.5 mm wide connector region thereby directly enabling low-loss fiber-to-chip edge-coupling. To overcome the high-costs and complex photonic packaging associated with active alignment of the fiber connectors to the glass waveguide interfaces, ultrafast laser-ablated features are accurately positioned on the glass substrate to enable self-alignment of the MPO connector guide-pins resulting in a passive alignment approach. Subsequent mating and de-mating of the MPO connector to the glass waveguide interface yields on average a 0.19 dB increase in the coupling loss compared to using active alignment.

Supercontinuum generation in As2S3 chalcogenide waveguide pumped by all-fiber structured dual-femtosecond solitons.

Supercontinuum sources with high compactness are essential for applications such as optical sensing, airborne detection and communication systems. In the past decades, the adoption of bulky optical parametric amplifier to pump various chalcogenide glass waveguides are widely reported for on-chip mid-infrared supercontinuum generation, but this usually leads to a large volume of the whole system, and is not practical. Therefore, integrating advanced femtosecond fiber lasers with optical waveguides using nano-fabrication technology are highly desired. However, the scarcity of compact pump sources and the dispersion-matched high-nonlinearity waveguide in short wavelength regions have hindered the advancement of integrated supercontinuum source performances in the near and mid-infrared region. In this study, we demonstrate a broadband supercontinuum source from As2S3 waveguide pumped by a compact dual-femtosecond solitons pulse source. The laser is completely fiber structured, and its wavelength can be readily tuned from 2 to 2.3 µm using Raman soliton self-frequency shift technology in a Tm3+-doped fiber amplifier. Furthermore, the As2S3 waveguide is designed with controllable dispersion and high nonlinearity for a broadband supercontinuum generation. These results will advance the development of on-chip supercontinuum sources based on chalcogenide waveguides.

In situ ultrasonic interface tracking for photovoltaic silicon directional solidification

This paper presents an experimental validation of an in situ ultrasound technique for tracking the solid–liquid interface during directional solidification of photovoltaic silicon. Ultrasound bursts are introduced from the top into the melt via the tip of a carbon glass waveguide directly plunged into the liquid. Several runs of solidification have been conducted using the same waveguide thus demonstrating its reusability, its mechanical resilience and its appropriate acoustical and chemical compatibility with the melt. We present the times of flight analysis to track the location of the solid–liquid interface. As part of the signal crosses the solidifying ingot, we also measure cs, the average celerity of sound waves in the solid. Since cs exhibits a significant dependance on crystal orientation, we consider the possibility to use the echoes to extract some information on the crystalline orientation in the ingot. By quantifying the uncertainties and their dependence with the duration of the experiment in particular, we outline the conditions necessary to detect accurately the average orientation in the solid.

Glass Substrate for Co-Packaged Optics

Co-packaged optics leads to significant power reduction by placing the electronic and photonic chiplets in a single package. An integrated electro-optical substrate made of glass with optical waveguides, through vias and electrical redistribution layers inside a single-sided cavity enables fine-line electrical routing and low-cost assembly. Existing glass and thin film technologies were evaluated and combined into a single process stream including photonic assembly. Photonic chips with silicon nitride waveguides were optically coupled to integrated low-loss (<0.1 dB/cm) glass waveguides with minimum loss of 0.65 dB achieved by fiducial alignment and pick-and-place assembly.

High-density optical interconnects based on self-imaging in coupled waveguide arrays

Rapidly increasing demand for higher data bandwidths has motivated exploration of new communication channels based on spatially multiplexed in-fibre and on-chip coupled light guides. However, the conventionally used periodically arranged coupled waveguides display complicated light propagation patterns, ranging from quasiperiodic to nearly chaotic. Taking a different approach, we spectrally engineer interwaveguide coupling to instigate self-imaging of the input light state at the array output and thus enable construction of novel high-fidelity interconnects. Simple implementation via modulation of the interwaveguide separations makes these interconnects realizable in all fabrication platforms. Their competitive advantages are negligible crosstalk-induced information loss, high density that exceeds the current standards by an order of magnitude, and compatibility with both classical and quantum information encoding schemes. Moreover, the wavelength-dependent self-imaging opens up new possibilities for wavelength and spatial division demultiplexing. The proposed analytical designs are supported by extensive numerical simulations of silicon-on-insulator, silicon nitride and silica glass waveguide arrays, and a statistical feasibility study.

Low-loss fiber-to-chip edge coupler for silicon nitride integrated circuits.

Silicon nitride (SiN) integrated optical waveguides have found a wide range of applications due to their low loss, broad wavelength transmission band and high nonlinearity. However, the large mode mismatch between the single-mode fiber and the SiN waveguide creates a challenge of fiber coupling to these waveguides. Here, we propose a coupling approach between fiber and SiN waveguides by utilizing the high-index doped silica glass (HDSG) waveguide as the intermediary to smooth out the mode transition. We achieved fiber-to-SiN waveguide coupling efficiency of lower than 0.8 dB/facet across the full C and L bands with high fabrication and alignment tolerances.

Anomalous transport in periodic photonic chains with designed loss

Here we show that a coherent random walk in a perfectly periodic chain of bosonic modes with designed loss can exhibit a variety of different anomalous transfer regimes in dependence on the initial state of the chain. In particular, for any given finite initial time-interval there is a set of initial states leading to a hyperballistic transport regime. Also, there are initial states allowing one to achieve a subdiffusive regime or even localization for a given time-interval, or change an asymptotic long-time diffusion rate. We show how these anomalous transport regimes can be practically realized in a laser-written network of single-mode waveguides in balk glass or how a planar system of coupled single-mode waveguides can be realized with an integrated photonic platform.

MicroLED biosensor with colloidal quantum dots and smartphone detection.

A fluorescence sensor with the capability for spatially multiplexed measurements utilizing smartphone detection is presented. Bioconjugated quantum dots are used as the fluorescent tag and are excited using a blue-emitting microLED (µLED). The 1-dimensional GaN µLED array is butt-coupled to one edge of the glass slide to take advantage of total internal reflection fluorescence (TIRF) principles. The bioassays on the top surface of the glass waveguide are excited and the resultant fluorescence is detected with the smartphone. The red, green, and blue channels of the digital image are utilized to spectrally separate the excitation light from the fluorescence for analysis. Using a biotin-functionalized glass slide as proof of principle, we have shown that streptavidin conjugated quantum dots can be detected down to a concentration of 8 nM.

High-order mode waveguide amplifier with high mode extinction ratio written in an Er3+-doped phosphate glass.

Inscription of fiber-compatible active waveguides in high-gain glass, followed by direct interconnection with few-mode fibers, is one of the most promising solutions for all-optical mode-division multiplexing. In this work, based on the femtosecond laser writing technique, we propose a general fabrication scheme for inscribing high-order mode waveguides in glass, by carefully tailoring the cross-section of the waveguides to match the mode intensity distribution via an improved multi-scan approach. Specifically, we design and fabricate two kinds of waveguides, namely, LP01-mode waveguide and LP11-mode waveguide in a highly Er3+-doped phosphate glass, enabling the insertion loss of the waveguides to be as low as 1.88 dB, and the mode extraction factor of the LP11-mode waveguide up to ∼24 dB. Importantly, we have successfully achieved optical amplification of the waveguides, with an on-off gain as high as 3.52 dB. This novel high-order mode waveguide amplifier has broad application prospects in monolithic on-chip integrated photonic light sources and optical interconnection with few-mode fiber and/or silicon-based waveguide.

Ultralow birefringent glass waveguide fabricated by femtosecond laser direct writing.

Optical waveguides prepared by femtosecond laser direct writing have birefringent properties, which can affect polarization encoding and entanglement on chips. Here, we first propose a shape-stress dual compensation fabrication scheme to decrease birefringence. Ultralow birefringent waveguides (1 × 10-9) were obtained by controlling the cross sectional shape of the main waveguide and adjusting the position of the auxiliary lines. In addition, we prepared polarization-independent directional coupler and demonstrated the evolution of polarization-independent waveguide array with different polarized light. In the future, ultralow birefringent waveguides will be widely applied in polarization encoding and entangled quantum photonic integrated circuits.

High density vertical optical interconnects for passive assembly.

The co-packaging of optics and electronics provides a potential path forward to achieving beyond 50 Tbps top of rack switch packages. In a co-packaged design, the scaling of bandwidth, cost, and energy is governed by the number of optical transceivers (TxRx) per package as opposed to transistor shrink. Due to the large footprint of optical components relative to their electronic counterparts, the vertical stacking of optical TxRx chips in a co-packaged optics design will become a necessity. As a result, development of efficient, dense, and wide alignment tolerance chip-to-chip optical couplers will be an enabling technology for continued TxRx scaling. In this paper, we propose a novel scheme to vertically couple into standard 220 nm silicon on insulator waveguides from 220 nm silicon nitride on glass waveguides using overlapping, inverse double tapers. Simulation results using Lumerical's 3D Finite Difference Time Domain solver are presented, demonstrating insertion losses below -0.13 dB for an inter-chip spacing of 1 µm; 1 dB vertical and lateral alignment tolerances of approximately 2.6 µm and ± 2.8 µm, respectively; a greater than 300 nm 1 dB bandwidth; and 1 dB twist and tilt tolerances of approximately ± 2.3 degrees and 0.4 degrees, respectively. These results demonstrate the potential of our coupler for use in co-packaged designs requiring high performance, high density, CMOS compatible out of plane optical connections.

Direct Detection of Antibodies to <i>Yersinia pestis</i> Using Glass Microstructural Waveguides as an Express Method for Assessing Seroconversion in Individuals Vaccinated against Plague

Relevance. As part of ensuring sanitary and epidemiological well­-being, in the territory of natural plague foci of the Russian Federation, according to epidemiological indications, the population is vaccinated against this infection. The lack of a unified scheme for evaluating the effectiveness of vaccination dictates the need to develop universal express methods that allow screening studies of anti­-plague immunity, including in the field.Aims. To evaluate the effectiveness of the express method for the direct detection of antibodies to Yersinia pestis in biological material using microstructural glass waveguides with a hollow core (MGW HC) as immunosensors in studying the dynamics of seroconversion in people vaccinated with the plague live people.Materials and methods. In the study, blood serum samples were taken from 30 individuals vaccinated according to epidemic indications with the live plague vaccine (PLV) and 30 volunteers who were not vaccinated and did not have a history of contact with the plague agent.Results. An assessment was made of the possibility of using the method of direct detection of antibodies using MGW HC at different time intervals according to the receipt of blood sera in the framework of monitoring vaccinated individuals from among the inhabitants of the Caspian sandy natural plague focus. The presence of specific antibodies to the F1 protein in the blood serum of vaccinated volunteers was revealed both with the help of ELISA and with the use of MGW HC. The speed of the method of direct detection of antibodies (maximum 2 minutes per test), the absence of the need to use species­specific secondary antibodies, enzymes and substrates and additional costs for laborious sample preparation were noted.Conclusions. The method of direct detection of antibodies using glass microstructural waveguides is promising for introduction into the list of express methods for assessing the immunological effectiveness of anti­plague vaccination.

Glass Platform for Co-Packaged Optics

Placing the electrical and photonic chiplets in a single package leads to significant power reduction. Chiplets are connected by fine-line electrical routing over a length of a few millimeters and optical interconnects in the package connect photonic chips with optical fibers for off-package communication. A packaging substrate made of glass with optical waveguides, through glass vias and electrical redistribution layers inside a single-sided cavity enables lower-cost assembly. A single-sided 50 µm deep cavity was etched in glass, and electrical copper lines with 5 µm in height and width were deposited on the floor of the cavity. Ion-exchange (IOX) waveguides with propagation loss of <0.1 dB/cm were fabricated below the glass surface. For flip-chip assembly of photonic chips and optical coupling with the IOX waveguides at the top surface of the glass, all electrical interconnects were located inside the cavity. Photonic chips with silicon nitride waveguides were optically coupled to glass waveguides with a minimum loss of 0.5 dB, achieved by fiducial-aligned flip-chip photonic assembly. A low-profile fiber connector with height of 4.4 mm connects the integrated ion-exchanged waveguides with the optical fibers. Average connector loss of 0.83 dB was demonstrated with physical contact between fibers and IOX glass waveguides.

LD Side Pumped Er3+,Yb3+∶Glass Waveguide Passively Q-Switched Laser

LD Side Pumped Er3+,Yb3+∶Glass Waveguide Passively Q-Switched Laser

Fabrication of an erbium–ytterbium-doped waveguide amplifier at communication wavelengths for integrated optics applications

Erbium–ytterbium-doped waveguide amplifiers provide a considerable gain at telecom wavelengths, low noise, nonlinearity, and compatibility with optical networks, making it an outstanding amplification module for telecommunication systems. This study reports on the fabrication of an optical waveguide amplifier for integrated optics. The signal can be amplified by using rare-earth dopings such as erbium (Er), which works at telecommunication wavelengths, i.e., 1.55 μm. Er-doped phosphate glass waveguides can be deposited using the sol–gel method, which is convenient for preparing active films on several substrates. The Er concentration was 1–2 × 1020/cm3. The confinement and the gain of the waveguide can be increased by reducing the width of the waveguide to 0.5 μm. In such a case, more than 1dB net gain can be achieved without additional pump power. The other material used as a dopant in optical amplifiers is ytterbium (Yb). For Er energy levels, a more significant pump intensity is necessary for inversion due to the limited absorption cross-section. This issue is solved by including a substance with a large absorption cross-section that transfers energy to Er. The Ag–Na ion exchange process is then used to fabricate the buried waveguide. In such a process, ions trade between the core material and the molten salt. Then, the waveguide is immersed in the molten salt. The fabricated waveguide has low loss, and a net gain of around 2 dB at a wavelength of approximately 1.55 μm in Er:Yb:Al: phospho silicate glass is achieved. The focus of the research is on the fabrication procedure (materials and methods) of the waveguide.

Recent advancements in femtosecond laser inscribed waveguides in germanate glass for ∼ 2.1 µm laser applications

The realization and integration of high-power and high-speed microscale functionalities on a single chip have been made possible through the revolutionizing field of Photonics. This next generation monolithic technology emphasizes on efficient and cost-effective fabrication of the miniaturized photonic devices with high degree of accuracy. For such monolithic devices small cavity, single frequency laser sources (waveguide lasers) are of immense importance. Multiple techniques have been utilized for the inscription of waveguides in the laser gain media. Femtosecond laser direct writing (FLDW) is an emerging technique for rapid inscription of highly symmetrical and high-quality 3D guiding structures in substrates with low propagation loss. In this article, we present a review on the latest developments around femtosecond laser inscribed waveguides in an emerging germanate glass (in contrast to the commercially available and exotic transparent media) for short to mid-IR laser applications.

A Surface-Scattering-Based Composite Optical Waveguide Sensor for Aerosol Deposition Detection

Aerosol is a suspension of fine chemical or biological particles in the air, and it is harmful, easily causing air pollution, respiratory diseases, infrastructure corrosion, and poor visibility. Therefore, the development of advanced optical sensors for real-time detection of aerosol deposition is of great significance. In this work, a prism-coupled composite optical waveguide (COWG) sensor for aerosol deposition detection based on surface scattering is proposed and demonstrated theoretically and experimentally. The COWG consists of a single-mode slab glass waveguide locally covered with a tapered thin film of high-index metal oxide. The tapered film can greatly enhance the evanescent field through the adiabatic transition of the fundamental transverse electric (TE0) mode between the uncovered and film-covered regions, thereby enabling the COWG to serve as a simple yet highly sensitive evanescent-wave scattering sensor for sensitive detection of aerosol deposition. The COWG with a tapered layer of Ta2O5 was prepared by masked sputtering, aerosol salt particle deposition on the COWG was successfully detected, and the influence of surface water droplets on the COWG sensor performance was analyzed. The experimental results indicate that the sensitivity of the COWG is 30 times higher than that of the bare glass waveguide.

One-dimensional and two-dimensional Er3+-doped germanate glass waveguides by combination of He+ ion implantation and precise diamond blade dicing

Compact and miniaturized Er3+-doped waveguide structure is an important research direction in integrated optics. In this work, the Er3+-doped germanate glass was bombarded by a 400-keV He+ ion beam with a fluence of 6.0 × 1016 ions/cm2 for the formation of the one-dimensional waveguide in a vacuum. Subsequently, the precise diamond blade with a rotating velocity of 20,000 rpm and a cutting speed of 0.1 mm/s was applied to dice the surface of the one-dimensional waveguide for the fabrication of the two-dimensional structure. The formation mechanism and the refractive index profile of the one-dimensional waveguide were studied by the SRIM 2013 and the RCM, respectively. The electromagnetic field profiles for the fundamental modes of both one-dimensional and two-dimensional waveguides were measured by the end-face coupling method. It presents some useful information in the field of fabrication and characterization of optical waveguides for active photonic applications.

Improvement in measuring losses by interferometric technique for glass waveguides produced by femtosecond laser writing

This study describes a straightforward and non-destructive interferometric technique for measuring the propagation loss in single-mode optical glass waveguides by exploiting a Fabry–Perot cavity effect. The experiment involves coupling a powerful tunable laser source to a single-mode waveguide that is being tested, then using a detector to analyze the transmission fringes of that source after coating the glass end facets with highly reflective coating. Our first experiment, which used a 22.4-mm-long fabricated waveguide on Non-Iox Gorilla glass to demonstrate the technique, resulted in a propagation loss of 0.49 dB/cm at a transmitting wavelength of about 1575 nm, which is completely consistent with the value obtained by a conventional characterization method. The measurement procedure is also independent from the coupling losses, making the characterization easier and reliable after the manufacturing just with a reversible deposition process on the sample under testing.

Broadband differential interference in a waveguide with a gradient refractive index distribution

The paper presents a model of a planar broadband differential waveguide interferometer with a gradient refractive index distribution. Its response to the change in the refractive index of the waveguide cover layer is presented. The analysis was performed for the wavelength range from 0.5um to 0.7um. The orthogonal TE0 and TM0 modes propagating in this wavelength range are considered. The influence of the coverage refractive index change on the output characteristics of the system is shown. Full Text: PDF ReferencesP. Kozma, F. Kehl, E.Ehrentreich-Forster, C. Stamm and F.F. Bier, "Integrated planar optical waveguide interferometer biosensors: A comparative review", Biosens. Bioelectron. 58, 287 (2014), CrossRef M. Kitsara, K. Misiakos, I. Raptis, and E. Makarona, "Integrated optical frequency-resolved Mach-Zehnder interferometers for label-free affinity sensing", Opt. Express 18, 8193 (2010). CrossRef K. Misiakos, I. Raptis, A. Salapatas, E. Makarona, A. Bostials, et al., "Broad-band Mach-Zehnder interferometers as high performance refractive index sensors: Theory and monolithic implementation", Opt. Express 22, 8856 (2014). CrossRef K. Misiakos, I. Raptis, E. Makarona, A. Botsialas, A. Salapatas, et al, "All-silicon monolithic Mach-Zehnder interferometer as a refractive index and bio-chemical sensor", Opt. Express 22, 26803 (2014) CrossRef K. Misiakos, E. Makarona, M. Hoekman, R. Fyrogenis, K. Tukkiniemi, et al., "All-Silicon Spectrally Resolved Interferometric Circuit for Multiplexed Diagnostics: A Monolithic Lab-on-a-Chip Integrating All Active and Passive Components", ACS Photonics 6, 1694 (2019). CrossRef E. Makarona, A. Salapatas, I. Raptis, P. Petrou, S. Kakabakos, et al., "Broadband Young interferometry for simultaneous dual polarization bioanalytics", J Opt Soc Am B 34, 1691 (2017). CrossRef K. Gut, "Broad-band difference interferometer as a refractive index sensor", Opt. Express 25, 3111 (2017), CrossRef K. Gut, "Study of a Broadband Difference Interferometer Based on Low-Cost Polymer Slab Waveguides", Nanomaterials 9, 729 (2019), CrossRef T. Pustelny, J. Ignac-Nowacka and Z. Opilski, "Optical investigations on layered metalphthalocyanine nanostructures affected by NO2 applying the surface plasmon resonance method", Opt. Appl. 34, 563 (2004). CrossRef W. Lukosz, Sensor Actuat. B-Chem. "Integrated optical chemical and direct biochemical sensors", 29, 37 (1995). CrossRef Z. Qi, S. Xia and N. Matsuda, "Spectropolarimetric interferometer based on single-mode glass waveguides", Opt. Express, 16, 2245 (2008). CrossRef K. Gut, A. Zakrzewski, T. Pustelny, "Sensitivity of Polarimetric Waveguide Interferometer for Different Wavelengths", Acta Phys. Pol. 118, 1140 (2010). CrossRef J.E. Broquin, S. Honkanen, "Integrated Photonics on Glass: A Review of the Ion-Exchange Technology Achievements", Appl.Sci. 11, 4472 (2021). CrossRef G.C. Righini, J. Linares, "Active and Quantum Integrated Photonic Elements by Ion Exchange in Glass", Appl.Sci. 11, 5222 (2021). CrossRef