Self-written Waveguide Research Articles

Light-matter interaction during and post polymerization in self-written polymer waveguide integrated with optical fibers

Self-written polymer waveguide is a polymer interconnection structure often integrated with optical fibers. The structure is fabricated by photopolymerization, through which a photon beam initiates a polymerization reaction to change liquid monomer into a solid polymer. During light-matter interaction photoinitiator molecules are excited to the singlet and then to the third state to form free radicals by attaching to the adjacent monomer molecules. The free radicals in turn form polymer chains and cross-linked structures. Photo-induced polymerization leads to a raised refractive index of the monomer and forms an optical waveguide. The change is permanent to allow the process of self-focusing and self-trapping of the propagation light beam and hence guide it to the aligned optical fiber. In this article, light matter interaction during polymer waveguide fabrication and post polymerization has been investigated. A photopolymer system of acrylate-based monomer, co-initiator amine and photo initiator is used to study the absorption of the monomer mixture at the spectral range of 450–550 nm. Then photobleaching was investigated after waveguide fabrication. The optical transmission efficiency of the polymer bridge increases as absorption ceases within the polymer structure such that optical loss reduces from 1.1 dB to about 0.65 dB.

Multimode near-infrared light-induced self-written optical waveguides for optical soldering

Connecting optical components in a highly precisely aligned manner that avoids significant losses due to misalignment is an important objective for future light-based high-speed data transmission technologies. We fabricated multimode light-induced self-written (LISW) optical waveguides using near-infrared (NIR) light for multimode optical component self-coupling. Multimode optical fibers were optically soldered with NIR light (≤ 1 mW) using this waveguide, with an insertion loss of only 0.69 dB observed when soldered at 0.6 mW.

Flexible light-induced self-written optical waveguide with 50 μm core size

We demonstrate a NIR light-induced self-written (LISW) optical waveguide between graded-index (GI) glass optical fibers with a 50 μm core size (50GIFs) using gel material. We describe the optical properties of the LISW optical solder in terms of its flexibility, adhesiveness, and loss. The results demonstrate that the two 50GIFs were self-coupled through the LISW optical waveguide, and the connection maintained adhesiveness against displacement. A low loss and relaxation of alignment tolerance were demonstrated for the optical interconnection between two 50GIFs using flexible LISW optical soldering. This technology is applicable to future autonomous driving systems using high-speed optical data transmission.

Simultaneous Multi-Core Fiber-to-Fiber Self-Coupling With Near-Infrared Light-Induced Self-Written Optical Waveguide

Simultaneous Multi-Core Fiber-to-Fiber Self-Coupling With Near-Infrared Light-Induced Self-Written Optical Waveguide

Integration of knee-shaped self-written waveguides between optical fibers by direct illumination and tip to tip coupling

Optical transmission efficiency of self-written polymer waveguide has been investigated. The polymer couplers were fabricated from a photopolymerizable monomer system by direct illumination from two pre-aligned single mode fibers, and by butt coupling of two extended long polymer tips at the end of fibers. Regarding direct illumination, the writing beams exhibit quasi-solitonic behavior and both show a tendency to attract each other to be merged at the middle point where the droplet deposited between the aligned fiber. Optical transmission gives insertion loss of 4.3 dB and 5.7 dB with total knee angles of (5° and 10°) respectively. Polymer bridges with larger deviation angles were not formed, since the induced beams were not merged properly to form a decent waveguide. Therefore, long polymer tips were fabricated separately and then they were butt coupled at different knee-angles. Optical transmission efficiency was measured over broadband from Ultraviolet to Infrared (UV-IR). In the butt-coupling approach average loss of 1.7 dB, 5.4 dB, 8.6 dB, 10.4 dB and 14.6 dB at measured wavelength 1550 nm were obtained for 300 μm- 300 μm coupling tips corresponding to knee-angles of (0°,5°,10°,15°, and 20°) respectively.

Miniaturized thin-film filters to connect multiple self-written waveguides

Self-written waveguides (SWWs) have been well investigated within the last decades. In most cases, they are used as low-loss coupling structures, i.e., to connect buried optical structures in photonic integrated circuits. In this work, we extend the field of possible applications for SWWs by embedding a novel thin-film filter to split the beam and connect multiple output ports simultaneously. The multilayer design of the dielectric filter can be customized to enable its application as a dichroic beamsplitter for photonic networks. The embedded thin-film filter was characterized in detail and used to connect an additional optical sensing element, which is also based on SWWs, to demonstrate its usability for measurement of physical quantities.

Near Infrared Light-Induced Self-Written Optical Waveguide and Its Application for Multi-Channel Waveguides

Near Infrared Light-Induced Self-Written Optical Waveguide and Its Application for Multi-Channel Waveguides

Polymer spot size converter on silicon photonics chip for enabling high coupling to single-mode fiber.

Silicon photonics (SiPh) technology has gained considerable attention as a result of the growing demand for high-bit-rate optical interconnections. Low coupling efficiencies, resulting from the difference in spot size between silicon photonic chips and single-mode fibers (SMFs), remains a challenging issue. To solve this problem, we fabricated a novel, to the best of our knowledge, polymer spot size expander (SSE) device on the end face of a silicon chip. The fabrication of SSEs using self-written waveguide technology and a dipping method using UV-curable resin was highly reproducible. The spot size of the original 3.83 µm of the SiPh chip was expanded to approximately 7.82 µm at a wavelength of 1.55 µm, and the maximum coupling efficiency achieved with the SMF was -0.88 dB. In addition, the -3 dB tolerance of the coupling efficiency along the vertical optical axis was ±4.4 µm.

Cost-effective fiber-to-lithium niobate chip coupling using a double-side irradiation self-written waveguide.

In recent years, integrated lithium niobate (LN) chips have been widely used for developing a variety of photonic devices, such as high-speed electro-optical (EO) modulators and frequency comb generators. A major challenge for their practical applications is the high coupling loss between micrometer-scale LN waveguides and optical fibers. Lensed fibers and special taper structures are commonly used to tackle the coupling issue. However, in some situations, these approaches may increase the overall complexity and cost of design, fabrication, and alignment. Here, we propose using the self-written waveguide (SWW), an optical waveguide induced by light irradiation, to cope with this coupling issue. The approach can apply in connecting a single-mode fiber (SMF) to any waveguide surface in principle, even with a large mode-field mismatch, significantly alleviating the tight alignment requirements typically needed for end-fire coupling into integrated waveguides. Our study demonstrates that the coupling loss between a SMF with a mode-field diameter (MFD) of 4.4 µm and a sub-micrometer LN rib waveguide could be dramatically reduced from an initial value of -14.27 dB to -5.61 dB, after double-side irradiated SWW formation. Our proposed approach offers a potential solution for achieving a cost-effective and flexible fiber-to-LN chip optical interconnect.

Polymer tapered pillar on a fiber end fabricated by UV irradiation using a high-NA fiber

The increasing need for single-mode fibers (SMFs) and advances in silicon photonics (SiPh) devices have led to the need for an efficient method of optical coupling between them. To achieve a higher coupling between them, a polymer tapered pillar was fabricated on the end face of the SMF by applying the optical diffraction effect and a self-written waveguide technology using a high numerical aperture (HiNA) fiber. The initial 10.4 µm spot size was reduced to 4.17 µm at 1.55 µm wavelength, and the greatest coupling efficiency of –1.01 dB was reached between an SMF with a tapered pillar and uncured resin cladding and a HiNA fiber. Full Text: PDF ReferencesR. Marchetti, C. Lacava, L. Carroll, K. Gradkowski, P. Minzioni, "Coupling strategies for silicon photonics integrated chips [Invited]", Photonics Res. 7, 201 (2019). CrossRef R. Bachelot, C. Ecoffet, D. Deloeil, P. Royer, D.-J. Lougnot, "Integration of micrometer-sized polymer elements at the end of optical fibers by free-radical photopolymerization", Appl. Opt. 40, 5860 (2001). CrossRef P. Pura, M. Szymanski, M. Dudek, L.R. Jaroszewicz, P. Marc, M. Kujawinska, "Polymer Microtips at Different Types of Optical Fibers as Functional Elements for Sensing Applications", J. Lightwave Techn. 33, 2398 (2015). CrossRef O. Mikami, R. Sato, S. Suzuki, C. Fujikawa, "Polymer Microlens on Pillar Grown From Single-Mode Fiber Core for Silicon Photonics", IEEE Photonics. Technol. Lett. 32, 399 (2020). CrossRef Y. Kamiura, T. Kurisawa, C. Fujikawa, O. Mikami, "High optical coupling efficiency of polymer microlens and pillar on single mode fiber for silicon photonics", Jpn. J. Appl. Phys. 61, SK1009 (2022). CrossRef F. Tan, H. Terasawa, O. Sugihara, A. Kawasaki, T. Yamashita, D. Inoue, M. Kagami, C. Andraud, "Two-Photon Absorption Light-Induced Self-Written Waveguide for Single-Mode Optical Interconnection", J. Lightwave Tech. 36, 2478 (2018). CrossRef H. Terasawa, O. Sugihara, "Near-Infrared Self-Written Optical Waveguides for Fiber-to-Chip Self-Coupling", J. Lightwave Technol. 39, 7472 (2021). CrossRef K. Vanmol, K. Saurav, V. Panapakkam, H. Thienpont, N. Vermeulen, J. Watté, J. Van Erps, "Mode-field Matching Down-Tapers on Single-Mode Optical Fibers for Edge Coupling Towards Generic Photonic Integrated Circuit Platforms", J. Lightwave Tech. 38, 4834 (2020). CrossRef Y. Saito, K. Shikama, T. Tsuchizawa, H. Nishi, A. Aratake, N. Sato, "Tapered Self-Written Waveguide between Silicon Photonics Chip and Standard Single-Mode Fiber", Opt. Fiber Communication Conference (OFC2020), paper W1A.2, (2020). CrossRef Y. Saito, K. Shikama, T. Tsuchizawa, N. Sato, "Tapered self-written waveguide for a silicon photonic chip I/O", Opt. Lett. 47(12), 2971 (2022). CrossRef N.A. Baharudin, C. Fujikawa, O. Mitomi, A. Suzuki, S. Taguchi, O. Mikami, S. Ambran, "Tapered Spot Size Converter by Mask-Transfer Self-Written Technology for Optical Interconnection", Photon. Technol. Lett. 29, 949 (2017). CrossRef H. Nawata, K. Ohmori, Proc. International Conference on Electronics Packaging (ICEP), paper 23 (2014) DirectLink S. J. Frisken, "Light-induced optical waveguide uptapers", Opt. Lett. 18, 1035 (1993). CrossRef Y. Obata, Y. Oyama, H. Ozawa, T. Ito, O. Mikami, T. Uchida, "Multi-array Self-written Waveguides using Photo-mask for Optical Surface Mount Technology", International Conference on Electronics Packaging (ICEP), paper 225 (2005). DirectLink P. Yin, J.R. Serafini, Z. Su, R. Shiue, E. Timurdogan, M.L. Fanto, S. Preble, "Low connector-to-connector loss through silicon photonic chips using ultra-low loss splicing of SMF-28 to high numerical aperture fibers", Opt. Expr. 27, 24188 (2019). CrossRef https://coherentinc.force.com/Coherent/UHNA3?cclcl=en_US, (18/09/2022). DirectLink

Tapered self-written waveguide for a silicon photonic chip I/O.

An optical coupling method with high alignment tolerance by self-written waveguide (SWW) formation is a promising candidate for co-packaged optics (CPO) by silicon photonics (SiPh). However, conventional SWWs cannot be used with Si waveguides because visible light for SWW formation cannot radiate from the waveguide facet. Here, we devised a new, to the best of our knowledge, optical circuit with SiOxNy waveguides for SWW formation from an SiPh chip. With our circuit, we achieved optical coupling between an SiPh chip and a standard single-mode fiber (SSMF) with a tapered SWW (TSWW). The lowest excess coupling loss compared to butt coupling with a high-numerical aperture (NA) fiber is approximately 0.6 dB over the C-band with the TSWW. In addition, our coupling method has higher alignment tolerances than butt coupling with a high-NA fiber (HNF).

Flexible Light-Induced Self-Written Optical Waveguide Using Gel Material

For in-vehicle optical communication systems, an air gap exists between two plastic optical fibers (POFs) to avoid damage to the POF end due to vibrations. There exists the disadvantage that a loss occurs in air gaps. To solve the issue of high-loss optical coupling, in this study, we designed a light-induced self-written (LISW) optical waveguide between POFs using gel material. It was demonstrated that the two optical fibers were automatically interconnected through the LISW optical waveguide, and the connection maintained the adhesiveness against mechanical displacement.

Self-Written Waveguide for Optical Connection between Silicon Photonics Chips and Standard Single-Mode Fibers

Self-Written Waveguide for Optical Connection between Silicon Photonics Chips and Standard Single-Mode Fibers

Coupling Device by Self-Written Waveguide Technology for Optical Interconnection between Silicon Photonics Chip and Fiber

Coupling Device by Self-Written Waveguide Technology for Optical Interconnection between Silicon Photonics Chip and Fiber

Latent image volumetric additive manufacturing.

Volumetric additive manufacturing (VAM) enables rapid printing into a wide range of materials, offering significant advantages over other printing technologies, with a lack of inherent layering of particular note. However, VAM suffers from striations, similar in appearance to layers, and similarly limiting applications due to mechanical and refractive index inhomogeneity, surface roughness, etc. We hypothesize that these striations are caused by a self-written waveguide effect, driven by the gelation material nonlinearity upon which VAM relies, and that they are not a direct recording of non-uniform patterning beams. We demonstrate a simple and effective method of mitigating striations via a uniform optical exposure added to the end of any VAM printing process. We show this step to additionally shorten the period from initial gelation to print completion, mitigating the problem of partially gelled parts sinking before print completion, and expanding the range of resins printable in any VAM printer.

Intermixed Time-Dependent Self-Focusing and Defocusing Nonlinearities in Polymer Solutions.

Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.

Self-supported light induced polymer waveguide for thin optical fiber interconnection

Self-written polymer waveguides were integrated by single photon photopolymerization between two single mode fibers with a diameter of 80 µm. The fiber size and photopolymerizable liquid sample allowed bridge length only up to 200 µm long. The optical transmission characteristics of polymer waveguides were investigated in the spectral range of (350 to 1750 nm). The polymer channels showed an average insertion loss value of about 3.5 dB, with bright optical modes on the surface of polymer bridges, making these polymeric photonic structures useful in sensing applications.

Optically formed rubbery waveguide interconnects.

Light induced self-written waveguides (LISWs) with unique elongation characteristics and low optical loss are formed in a monodispersed polyisoprene solution using a low-power laser photopolymerization process, while their light transmission characteristics are exemplified in the flexible interconnection of two single-mode optical fibers operating in the visible/near infrared wavelengths. The LISWs formed exhibit rubbery properties, allowing extensibilities upon cases from 400% to 800%, while still retaining significant optical transmission. The rubber elasticity enables sustaining LISWs at stressed lengths longer than 500 µm propagation losses from 1.0 to 2.9 dB/mm.

Quantitative study in coupling loss reduction under a large mode-field mismatch using a self-written waveguide.

The coupling loss between optical devices is a critical factor affecting the performance of optical interconnect. This paper quantitatively studies the effectiveness of using a dye-doped-epoxy-based self-written waveguide (SWW) to reduce the coupling loss in optical interconnect caused by large mode-field mismatch and lateral offset. We formed SWW between single-mode fiber (SMF) with different mode-field diameters (MFD) and a 5 × 2 µm rectangular channel waveguide-under-test (WUT). For the case between a SMF with a mode-field diameter of 9.4 μm and the WUT, the coupling loss is -11 dB. After forming the SWW, the coupling loss is reduced by 8.34 dB. Using SWW, the lateral tolerance length between a SMF with a mode-field diameter of 4.5 μm and the WUT increases by 2.5 times. Under the above-mentioned situation, the coupling loss falls less than 0.20 dB over ± 2 μm lateral offset range. Our findings offer insights quantitatively for coupling loss reduction and relaxing the lateral tolerance under significant mode-field mismatch conditions.

Simulation and Experimental Verification of the Thermal Behaviour of Self-Written Waveguides

In this work, we investigated the optical response of a self-written waveguide (SWW) in detail by heating the structure from room temperature up to 60 °C. Previous results indicated a decrease in the optical transmission with increasing temperature for certain waveguide parameters. Based on new experimental measurements, we have identified material parameters resulting in opposite behaviour. An experimental setup was conceived to verify these results. Hereby, we were able to show that we can adjust material parameters such as refractive index and the corresponding density of the material by adapting the curing time applied during the fabrication of the waveguides. This, in turn, affects the material’s response during the heating process. We showed that a limitation of the external curing time changes the internal conditions of the SWW and the cladding in a manner that the numerical aperture increases with the temperature, which subsequently also results in an increase in the optical transmission. In this study, we explain this unexpected behavior of the SWW and point towards possible future applications.