Self-written Waveguide Research Articles

Near-Infrared Self-Written Optical Waveguides for Fiber-to-Chip Self-Coupling

The light-induced self-written (LISW) waveguide technique is a promising candidate for the practical realization of a passive alignment between telecommunication and silicon photonic devices. While silicon is transparent to wavelengths above 1100 nm, the one-photon polymerization wavelength range is limited below 1100 nm. In this study, LISW waveguide fabrication at telecommunication wavelengths was demonstrated using a single-photon photopolymerizing resin. The LISW waveguide fabrication threshold values are lower than that of the two-photon photopolymerization system by six to seven orders of magnitude. LISW waveguides are fabricated from a single-mode fiber, a vertical-cavity surface-emitting laser, and a silicon waveguide. Using this technique, fiber-to-chip self-coupling between silicon photonic devices at telecommunication wavelengths is demonstrated. The results demonstrate the potential of the LISW technique for optical self-coupling of telecommunication and silicon photonic devices.

Investigation of Near-Infrared Light Induced Photopolymerization and Its Application for Self-Written Optical Waveguide

Investigation of Near-Infrared Light Induced Photopolymerization and Its Application for Self-Written Optical Waveguide

Optical and mechanical properties of self-written polymer waveguide between single mode optical fibers using UV photocurable monomer system

Self-written polymer waveguides have been constructed between two single mode fibers by single photon polymerization. Norland Optical Adhesives (NOA) were used as photopolymerizable system. A droplet of the monomer was deposited between two aligned fibers, the liquid drop then cured by broadband laser driven xenon lamp to form a polymer channel between the cores of the aligned fibers. Optical transmission, mechanical, and nonlinear optical properties of the waveguide were investigated. Polymer waveguide with 100 µm long showed insertion loss about 1.25 dB at 1550 nm. Then, the polymer bridges were put under longitudinal and transverse mechanical stress. The optimum strain of 75% was achieved. Finally, optical nonlinearity of coefficient of 0.8 mm long polymer waveguide was calculated which is about 1300 W−1 km−1, this value is about 1000 times greater than that of silica fiber.

Optical Trajectory Manipulations Using the Self-Written Waveguide Technique.

This study is novel for several reasons: We used a thin drop cast layer of dry photosensitive materials to study the behaviors of wet photopolymer media using microscopic distances during the Self-Written Waveguide (SWW) process; then, we examined the self-trajectories formed inside the solid material. The results provide a framework for theoretical and experimental examinations by handling the effects of manipulating the alignment of fibers. The other main advantage of these techniques is their lightweight, easy to process, highly flexible, and ultimately low-cost nature. First, the SWW process in wet photopolymer media (liquid solutions) was examined under three cases: single-, counter-, and co-fiber exposure. Then, the SWWs formed inside the solid material were examined along with the effects of manipulating the alignment of the fibers. In all cases, high precision measurements were used to position the fiber optic cables (FOCs) before exposure using a microscope. The self-writing process was indirectly monitored by observing (imaging) the light emerging from the side of the material sample during SWW formation. In this way, we examined the optical waveguide trajectories formed in Acrylamide/Polyvinyl Alcohol (AA/PVA), a photopolymer material (sensitized at 532 nm). First, the transmission of light by this material is characterized. Then, the bending and merging of the waveguides that occur are investigated. The predictions of our model are shown to qualitatively agree with the observed trajectories. The largest index changes taking place at any time during exposure, i.e., during SWW formation, are shown to take place at the positions where the largest exposure light intensity is present. Typically, such maxima exist close to the input face. The first maximum is referred to as the location of the Primary Eye. Other local maxima also appear further along the SWW and are referred to as Secondary Eyes, i.e., eyes deeper within the material.

Polymer Microlens on Pillar Grown From Single-Mode Fiber Core for Silicon Photonics

A novel coupling device composed of a combination of microlens and pillar having an approximately $8~\mu \text{m}$ diameter and $20~\mu \text{m}$ height and grown from single-mode fiber (SMF) core end is proposed. This device was successfully fabricated by using a self-written waveguide and dipping method with UV-curable resin. Theoretical and experimental studies were done. A high coupling efficiency of more than −0.97dB was obtained for coupling to an ultrahigh numerical aperture (0.41) SMF with a spot diameter of $3.7~\mu \text{m}$ at a $1.55~\mu \text{m}$ wavelength in place of a silicon chip with an integrated spot-size converter. In contrast, it is only −4.0dB by a conventional SMF.

Experimental and theoretical study of the formation process of photopolymer based self-written waveguides.

The realization of optical interconnects between multimode (MM) optical fibers and waveguides based on a self-writing process in photopolymer media represents an efficient approach for fast and easy-to-implement connection of light-guiding elements. When light propagates through photopolymer media, it modulates the material properties of the media and confines the spreading of the light beam to create a waveguide along the beam propagation direction. This self-writing process can be realized with a single photopolymer medium and is also suited to connect optical fibers or waveguides with active elements such as light sources and detectors. Numerical simulations of the underlying light-induced polymerization process is carried out by using a diffusion based material model which takes account both monomer diffusion and its conversion to polymer chains in regions exposed to light fields. In this work experimental results obtained from a one-polymer approach are validated with theoretical predictions from the diffusion model. The study involved the demonstration of temporal dynamics and transmittance from self-written waveguide (SWW) couplers during the self-writing process. The measured attenuation coefficient from experiment αexperiment = (8.43 ± 0.3) × 10-5 dB/µm showed good agreement with the theoretically predicted attenuation coefficient αsimulation = 7.93 × 10-5 dB/µm, thus demonstrating a successful application of the diffusion model to epoxy based acrylate SWWs. For comparison, attenuation measurements between optical fibers with SWWs as interconnects and one without SWW, i.e. with an air gap in between, were performed. The obtained results reveal that the theoretical approach correctly describes the waveguide formation process so that in the next step the studies can be extended towards including further relevant parameters such as temperature.

An optical fiber-waveguide-fiber platform for ppt level evanescent field-based sensing

Photonic sensing has always encountered problems such as enhancements of light-analyte interaction and signal collection efficiency. In this study, we propose an optical fiber-waveguide-fiber (OFWF) sensing platform, which comprises a non-cladded polymer waveguide sandwiched by two multimode optical fibers coaxially fabricated by laser-induced self-written waveguide (LISW) technique. The sensing platform not only provides a highly effective and versatile evanescent field (EF) based probe, but also possesses three orders of magnitude higher sensing signal collection ability than that of microscopic systems. A typical chromophore rhodamine B (Rh B) was used to verify the capability of the sensing platform, and a limit of detection of 10−12 g/ml level in fluorescent measurement was demonstrated without using any enhancement approaches. The sensing platform is compact and low cost, which can be utilised for various highly sensitive photonic sensing applications.

UV-curable resin microlenses on optical pillars for optical interconnect

A unique combination of pillar and microlens is demonstrated to enable easy coupling between VCSEL layers and a multi-layer/channel optical printed wiring board. A number of uniform pillars having a microlens on the top were fabricated on a substrate using UV-curable resin by mask-transfer self-written waveguide and dipping methods. Ray-trace analysis indicated that the focusing characteristics could be controlled by adjusting the pillar height and the microlens radius of curvature. Tolerance coupling efficiency between pillar height and microlens radius of curvature is acceptable. Light propagation measurements showed that uniform power was obtained from all top microlenses of the 3 × 4 pillar array on a slide glass. Studies of the reproducibility of microlens-on-pillar fabrication using the dipping method show a positive outcome. As a result, optical coupling efficiency is expected to be improved in optical interconnect applications.

Improvement of optical and mechanical properties of self-written polymer waveguides attached to optical fibers

Polymer waveguide bridges with high reproducibility up to 750 μm in length were optically written between two single-mode optical fibers. Fiber ends were treated by adhesion promoter to covalently bond to both the silica fiber and the photopolymer waveguide, the mechanical properties of both long and short bridges were improved. The optical insertion loss was 0.5 dB for the longest waveguide. The mechanical properties and optical transmission of polymer waveguides were investigated under shear and tensile stress. Bi-directionally cured 500 μm polymer bridges showed average lateral misalignment of 175 μm before breakage. Fibers treatment also improved adhesion bonding at both polymer/fiber interfaces such that 300 μm polymer waveguide could endure average longitudinal strain of 23% for photobleached and 32% for unbleached polymer bridges.

Polymer-Based Transmission Path for Communication and Sensing Applications

Optical transmission paths consisting of waveguides, light sources, and detectors form basic components in a large variety of applications ranging from photonic sensors to short distance communication. We demonstrate the design and fabrication of a polymer transmission path, which incorporates standard semiconductor light sources. In this paper, we especially focus on low-cost fabrication of such systems including easy-to-fabricate and optically efficient coupling structures. Our concept relies on self-written waveguide interconnects, which can be created without complex equipment and compensates for misalignment of the components to be connected automatically. Out-coupling toward a photodiode is achieved using a grating coupler. In addition, we present optical characterization results of the components regarding losses and demonstrate signal propagation.

Simultaneous detection of humidity and temperature through an adhesive based Fabry–Pérot cavity combined with polymer fiber Bragg grating

In this work we report the fabrication of a dual fiber sensor composed of an adhesive based Fabry–Pérot cavity combined with a polymer fiber Bragg grating (PFBG), for the simultaneous detection of humidity and temperature. The Fabry–Pérot structure was fabricated through a modified version of the self-written waveguide technology, by employing a no-core fiber, while the PFBG was inscribed in a flat-sides microstructured polymer fiber (mPOF) using the phase mask technology through the 248 nm UV laser. The combination of these two polymer based technologies allow an easy fabrication and provide an efficient route for the simultaneous detection of humidity and temperature with high resolution.

Self-phase modulation and spectral broadening in millimeter long self-written polymer waveguide integrated with single mode fibers

Polymer waveguide bridges up to 1.2 mm in length were optically written between two single-mode optical fibres. Optical Nonlinearity of polymer waveguide was measured by coupling a high power ultra-short pulsed laser. Before waveguide fabrication fiber ends were treated by adhesion promoter which covalently bond to both the silica fibre and the photopolymer, also photopolymerization was conducted from both fibres. The new techniques improve both the mechanical properties and optical transmission of polymer bridges. The optical insertion loss was 1.1 dB for the longest waveguides. A considerably long interaction length of polymer waveguide allows spectral broadening and self-phase modulation features to occur in response to the high power laser propagation through the polymer bridges. The spectral broadening in polymer waveguide was much broader than that of 1.5 m plain fibre. The ultrafast nonlinearity of the polymer waveguides was determined to be of the order of 103 times the nonlinearity of silica.

Controlling the trajectories of self-written waveguides in photopolymer

The diffraction of a light beam as it propagates through a medium can be effectively compensated by self-trapping. A laser beam propagating through a nonlinear medium can generate a waveguiding action, i.e., a higher refractive index, along the direction of the light propagation. Experiments involving light beams illuminating the front surface of a solid bulk photopolymer sample are reported. The self-bending of parallel beams (input simultaneously but separated in space) during the resulting self-writing process is studied. It is shown that there is strong correlation between the initial beam input separation distance and the resulting waveguide trajectories taken during channel formation. Finite element-based simulations are performed, which predict the self-writing waveguide formation process, e.g., beam focusing, trapping, and the deviations of the waveguide trajectories caused by adjacent beams. The model is shown to be in good qualitative agreement with observed experimental results.

Numerical investigations on polymer-based bent couplers

A diffusion-based material model is implemented and linked to the Crank–Nicholson beam propagation method to carry out numerical investigations on self-written bent waveguide couplers on a polymer basis. Such couplers are established in a photopolymer mixture when two opposing Gaussian laser beams with an offset or gap along their propagation axes traverse through a medium and the beams, eventually, get self-trapped. In this work, numerical investigations of the processes involved with respect to the temporal dynamics of refractive index modulation and the corresponding intensity profiles are presented. We also show that compensation for misalignments or gaps is possible as the coupling length of the structure increases. Furthermore, we report and analyze the curing time and curvature of the bent couplers, which are regulated by control of model parameters such as propagation distance between opposing beams, component concentrations, and the value of the rate constant during the simulation process.

Self-written waveguides in photopolymer.

Self-written waveguide (SWW) trajectories fabricated inside a dry photopolymer bulk material, acrylamide/polyvinyl alcohol (AA/PVA), are studied. Their production using both Gaussian and Laguerre-Gauss exposing (writing) light beams, output from optical fibers, is explored. The formation of the primary and secondary eyes is also discussed. Furthermore, the interactions that take place when two counterpropagating beams pass through the photopolymer material (both Gaussian and Laguerre-Gauss) are examined. In all cases experimental and theoretical results are presented. Good agreement between the predictions of the proposed model and experimental observations are demonstrated.

Two-Photon Absorption Light-Induced Self-Written Waveguide for Single-Mode Optical Interconnection

We propose two-photon absorption light-induced self-written (LISW) waveguide formation using short-wavelength infrared pulse laser light. It is suitable and efficient for single-mode optical interconnection, and also promising for small-core single-mode optical interconnection. The approach offers the possibility of not only decreasing the insertion loss, but also reducing the interconnection task time. We assessed this approach for single-mode optical interconnection. We obtained an LISW waveguide loss of about 0.06 dB for an LISW waveguide length of 100 μ m and a connection loss per facet of about 0.37 dB. We also presented the results on the interconnection between high-numerical-aperture small-core thermally-diffused expanded-core single-mode fibers having the mode field diameters of about 3 μ m by using the same approach. The results showed the present approach to be a promising alternative route for efficient interconnection of small-core single-mode optical devices, such as silicon nanowires with appropriate configurations.

Low-Loss Connection of Embedded Optical Fiber Sensors Using a Self-Written Waveguide

This letter reports on a new concept for making a low-loss connection to an optical fiber sensor, which is embedded in a fiber reinforced composite material for structural health monitoring. First, a cross section of the composite is made to reveal the end-face of the embedded optical fiber. Then, an external fiber is aligned and an intermediate polymer-based self-written waveguide (SWW) is fabricated between both fibers. This SWW bridges the gap and serves as mode size converter ensuring a low-loss optical connection even if both fibers have dissimilar mode field diameters. The advantage of this approach is that no special care needs to be taken during the composite production cycle not to damage the sensor fiber in- or egress points, since it will be reconnected afterward.

A Review of Hologram Storage and Self-Written Waveguides Formation in Photopolymer Media.

Photopolymer materials have received a great deal of attention because they are inexpensive, self-processing materials that are extremely versatile, offering many advantages over more traditional materials. To achieve their full potential, there is significant value in understanding the photophysical and photochemical processes taking place within such materials. This paper includes a brief review of recent attempts to more fully understand what is needed to optimize the performance of photopolymer materials for Holographic Data Storage (HDS) and Self-Written Waveguides (SWWs) applications. Specifically, we aim to discuss the evolution of our understanding of what takes place inside these materials and what happens during photopolymerization process, with the objective of further improving the performance of such materials. Starting with a review of the photosensitizer absorptivity, a dye model combining the associated electromagnetics and photochemical kinetics is presented. Thereafter, the optimization of photopolymer materials for HDS and SWWs applications is reviewed. It is clear that many promising materials are being developed for the next generation optical applications media.

Light-induced self-written waveguide fabrication using 1550 nm laser light.

Light-induced self-written (LISW) optical waveguides were fabricated for the first time, to the best of our knowledge, using a photopolymerizable resin system formed by 1550nm pulse laser light. A two-photon absorption (TPA) chromophore with a TPA cross section of several hundred Goeppert-Mayer (GM) at 1550nm was used. Furthermore, the optical interconnection between a single-mode fiber and a fiber Bragg grating was demonstrated by the present technique, using one-way irradiation of 1550nm laser light through the single-mode fiber. The LISW waveguide formation using 1550nm laser light offers a new and promising alternative route for optical interconnection in silicon photonics technology.

Automated Misalignment Compensating Interconnects Based on Self-Written Waveguides

Optical interconnects are the key components for integrated optics to link photonic integrated circuits or to connect external elements such as light sources and detectors. However, misalignment of the optical elements contained and its compensation is a remaining challenge for integrated optical devices. We present a novel method to establish rigid interconnects based on a 2-wavelength self-written waveguide process which automatically compensates for misalignment. We exemplarily demonstrate the capability of our process by writing interconnects between two multimode fibers as well as hot-embossed integrated polymer waveguides and a bare laser diode chip. The coupling efficiency of the interconnects obtained is analyzed with respect to misalignment. We found that coupling losses are as low as 1.3dB if a lateral misalignment lies within a 10 μ m interval, which is achieved by commercially available pick-and-place machines. Our approach is easily combined with high-throughput techniques such as hot embossing and enables low-cost production of interconnects even for mass fabrication in future applications.