Flexible Polymer Waveguides Research Articles

Bend- and Twist-Insensitive Flexible Multimode Polymer Optical Interconnects

Polymer multimode optical waveguides can enable high-speed short-reach optical interconnection at low cost within high performance electronic systems. The formation of such waveguides on flexible substrates can offer important additional advantages such as light weight, ability to be tightly bent, and reconfigurability which are particularly important in environments where space, weight, and shape conformity are critical, for instance in vehicles and aircraft. The ability of such flexible optical interconnects to be tightly bent and twisted with low excess loss is crucial in enabling their use in systems with limited space and with movable parts. As a result, in this work, we present a new design of such flexible polymer multimode waveguides that achieves improved bending loss performance over the conventional waveguide design. It is experimentally shown that the proposed design achieves a very low excess loss of 0.5 dB for a 3 mm radius bend under a 50 μm MMF launch. In comparison, flexible waveguides with the conventional design exhibit a 2 dB excess loss under the same launch and bend conditions. Additionally, useful rules that associate the twisting loss performance of flexible polymer waveguide samples with their geometric characteristics are derived. It is shown that negligible twisting losses (<0.1 dB for a 50 μm MMF input) can be achieved when the dimensions of the waveguide samples are appropriately selected. The results demonstrate the strong potential of such bend- and twist-insensitive flexible polymer waveguides for use in next-generation vehicles and aircraft.

Selective Equatorial Sclera Crosslinking in the Orbit Using a Metal-Coated Polymer Waveguide.

PurposePhotochemical crosslinking of the sclera is an emerging technique that may prevent excessive eye elongation in pathologic myopia by stiffening the scleral tissue. To overcome the challenge of uniform light delivery in an anatomically restricted space, we previously introduced the use of flexible polymer waveguides. We presently demonstrate advanced waveguides that are optimized to deliver light selectively to equatorial sclera in the intact orbit.MethodsOur waveguides consist of a polydimethylsiloxane cladding and a polyurethane core, coupled to an optical fiber. A reflective silver coating deposited on the top and side surfaces of the waveguide prevents light leakage to nontarget, periorbital tissue. Postmortem rabbits were used to test the feasibility of in situ equatorial sclera crosslinking. Tensometry measurements were performed on ex vivo rabbit eyes to confirm a biomechanical stiffening effect.ResultsMetal-coated waveguides enabled efficient light delivery to the entire circumference of the equatorial sclera with minimal light leakage to the periorbital tissues. Blue light was delivered to the intact orbit with a coefficient of variation in intensity of 22%, resulting in a 45 ± 11% bleaching of riboflavin fluorescence. A 2-fold increase in the Young's modulus at 5% strain (increase of 92% P < 0.05, at 25 J/cm2) was achieved for ex vivo crosslinked eyes.ConclusionsFlexible polymer waveguides with reflective, biocompatible surfaces are useful for sclera crosslinking to achieve targeted light delivery. We anticipate that our demonstrated procedure will be applicable to sclera crosslinking in live animal models and, potentially, humans in vivo.

Optical coupling with flexible polymer waveguides for chip-to-chip interconnects in electronic systems

This contribution discusses technology development for the realization of chip-to-chip interconnection based on flexible optical waveguides. Two approaches for optical coupling between waveguides and active devices are presented. Both approaches built on the planar polymeric optical multimode waveguides integrated on flexible substrates (PEN-foil). This waveguides structured using UV-photolithography and Ormocere-materials feature low optical attenuation below 0.05 dB/cm. The first approach for coupling between optical waveguides uses a bidirectional interruption-free waveguide coupler. The principle bases on directional core-core-coupling and allows for adjustable coupling ratio by tuning the overlap area. In addition, an asymmetric coupling behavior depending on the coupling direction due to a bending of one of the coupling waveguides is achieved. This coupling method shows supremacy for optical bus systems where tunable, asymmetric coupling ratios are desired. The second optical coupling approach for waveguide-to-chip coupling bases on out-of-plane optics. Direct integration of 45° micro-mirrors into polymer waveguides using dicing process is investigated. Two approaches for optoelectronic (OE) subassembly with flexible optical waveguides are considered one with flip-chip bonded and one with embedded OE-devices. Using optical characterization the influence of fabrication parameters on the optical performance of diced mirrors with insertion power loss measurement is derived and presented.

Polymer thermal optical switch for a flexible photonic circuit.

Flexible and wearable optoelectronic devices are the new trend for an active lifestyle. These devices are polymer-based for flexibility. We demonstrated flexible polymer waveguide optical switches for a flexible photonic integrated circuit. The optical switches are composed of a single-mode inverted waveguide with dimensions of 5μm waveguide width, 3μm ridge height, and 3μm slab height. A Mach-Zehnder structure was used in the device, with the Y-branch horizontal length of 0.1cm, the distance between two heating branches of 30μm, and the heating branch length of 1cm. The optical field of the device was simulated by beam propagation to optimize the electrode position. The switching properties of the flexible optical switch with different working conditions, such as contact to the polymer, silicon, and skin, were simulated. The device was prepared based on the photo curved polymer and lithography method. The end faces of the flexible film device were processed using an excimer laser with optimized parameters of 28 mJ/cm2 and 15Hz. The response rise time and fall time on the PMMA substrate were measured as 1.98ms and 2.71ms, respectively. The power consumption was 16mW and the extinction ratio was 11dB. The response rise and fall times on the Si substrate were measured as 1.08ms and 1.62ms, respectively. The power consumption was 17mW and the extinction ratio was 11dB. The demonstrated properties indicate that this flexible optical waveguide structure can be used in the light control area of a wearable device.

Development of Versatile Polymer Waveguide Flex Technology for Use in Optical Interconnects

We report on the implementation of novel flexible polymer waveguide interconnects. They are based on newly developed mechanically flexible low-loss silicone waveguides. In addition to meeting the generic requirements of rigid waveguide interconnects, several flex-material challenges were mastered: a) mechanical flexibility permitting waveguide flexing down to radii of 1.0 mm without cracking; b) minimization of waveguide curling induced by the CTE mismatch between flex substrates and polymer layers to enable assembly and connectorization; c) greatly improved cladding adhesion on standard PCB flex substrates, such as polyimide; and d) high environmental stability despite the reduced polymer cross-linking required for better mechanical flexibility. The new waveguides exhibit excellent stability in damp heat (2000 h in 85°C/85% rH) and under thermal shock (500 cycles from -40° to +120°C), and lead-free solder reflow up to 260°C. Using the newly engineered “Dow Corning WG-1017 Optical Waveguide Clad Dev Sample” and the established “Dow Corning WG-1010 Optical Waveguide Core”, we were able to develop a manufacturing process suitable for large areas and offering high process control and stability to produce waveguides having optical loss values of less than 0.05 dB/cm at 850 nm VCSEL wavelength and fulfilling requirements (a) to (d) above. We describe this manufacturing process and how we have overcome the material challenges mentioned. Furthermore, we present characterization and manufacturing results, show demonstrators, and outline the potential of flexible waveguides as versatile electro-optic assembly platform.

12.5‐Gb/s Highly Flexible 180° Polymer Waveguide on Optical and Electronic Printed Circuit Board

ABSTRACTThe optical interconnection using polymer waveguides on the optical and electronic printed circuit board was designed and fabricated for low optical propagation loss and high speed data rate. The ray tracing simulation for the tolerance study of optical interconnection and fabrication was carried by the LightTools commercial software. In order for the easy fabrication and high position accuracy, the polymer waveguides were forming 45° reflective mirrors using dicing approach and followed by the e‐beam deposition for silver coated 90° beam turning. The interface coupling loss was discussed in different polishing grit sizes and dicing approaches. Upto 12.5 Gb/s transmission rate and 0.1 dB/cm optical propagation loss were demonstrated in the board‐embedded flexible polymer waveguide. The Q factor of 7.4 at 12.5 Gb/s and additional optical loss of 0.3 dB were experimentally shown on the 2‐mm bending radius and 180° curvature angle. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1999–2003, 2013

Flexible thin-film polymer waveguides fabricated in an industrial roll-to-roll process

The fabrication of flexible low-loss, thin-film, foil-based polymer waveguides with grating couplers employing a high-volume industrial roll-to-roll process is demonstrated. The embossed waveguides feature propagation losses of less than 1 dB/cm (633 nm, TE polarization), bending losses of 0.4-0.8 dB/360° for bending radii as small as 2 mm, and grating coupling efficiencies of up to 25%. In addition, the waveguides possess a thermo-optic coefficient of -1.58×10(-4) 1/°C. The fabricated waveguides are promising candidates for short-distance data communication as well as for sensing applications.

Flexible Polymer Waveguides With Integrated Mirrors Fabricated by Soft Lithography for Optical Interconnection

Flexible polymer waveguides with integrated 45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> mirrors to support surface normal optical coupling for optical interconnection were fabricated using a vacuum assisted microfluidic (VAM) soft lithographic technique. Waveguide array structures with slanted surfaces of the SU-8 master were realized by prism-assisted inclined UV lithography. The internal surface reflected UV light was utilized to eliminate undercut structures and to form the inclined surfaces on both ends of the straight waveguide structure via one-step UV exposure. Varying the inclined surface depth can result in different needed light coupling efficiency. A polydimethylsiloxane (PDMS) mold was subsequently created. The use of UV curable resins in the VAM fabrication resulted in the polymer waveguides with 45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> integrated mirrors, demonstrating a coupling efficiency of 75% for full mirrors and 38% for half mirrors.

Strain-imposed External Cavity Tunable Lasers Operating for NIR Wavelength

For demonstrating widely tunable external cavity lasers operating for near-infrared (NIR) wavelength, a flexible polymer waveguide with an imbedded Bragg grating is incorporated. Due to the superior flexibility of the polymer material, the reflection wavelength of the Bragg grating is widely tunable by imposing tensile and compressive strains on the flexible Bragg grating. A third-order Bragg grating is formed on the device for facilitating the fabrication method. With a superluminescent laser diode as a gain medium of ECL, the tunable laser exhibited output power of -3 dBm and a tuning range of 32 nm.

Flexible Polymeric Tunable Lasers for WDM Passive Optical Networks

Flexible polymer waveguide with a Bragg reflection grating is incorporated to form an external cavity laser with a wide tuning range, and it is evaluated as a tunable light source for wavelength division multiplexing optical communication systems. The highly elastic property of polymer materials makes them suitable for producing a tunable Bragg reflector controlled by an imposed strain. The flexible tunable Bragg reflector is installed on a compact moving stage 6 connected to a piezoelectric motor. By applying a total strain of 60680 μe (6.07%), wavelength tuning of 82 nm is achieved with a side-mode suppression ratio of 43 dB and a linewidth less than 0.1 nm. The tunable laser controlled by a microactuator exhibits long-term stability with a wavelength fluctuation of less than 0.1 nm. In the optical transmission experiment, various wavelengths are used to transmit the 2.5 Gb/s signal over 50 km, excellent performance was observed with a power penalty of 1 dB compared to the DFB laser.

Optical Pressure Sensors Based on Vertical Directional Coupling With Flexible Polymer Waveguides

An optical pressure sensor based on the radiation coupling in vertical direction between a channel waveguide and a flexible polymer waveguide is proposed. The flexible waveguide is bent by an applied pressure to reduce the separation distance between the two waveguides so that the light propagating in the channel waveguide is radiated into the flexible planar waveguide. By applying a pressure ranging from 100 to 500 kPa, the output intensity modulation of 20 dB is obtained by virtue of the efficient phase matched coupling between the waveguides made of the same polymer material. The large extinction ratio is useful to measure the pressure precisely for a wide range.

Strain induced tunable wavelength filters based on flexible polymer waveguide Bragg reflector

A tunable wavelength filter is demonstrated by imposing a strain on a polymeric Bragg reflection waveguide fabricated on a flexible substrate. The highly elastic property of flexible polymer device enables much wider tuning than the silica fiber. To produce a uniform grating pattern on a flexible plastic substrate, a post lift-off process along with an absorbing layer is incorporated. The flexible Bragg reflector shows narrow bandwidth, which is convincing the uniformity of the grating structure fabricated on plastic film. By stretching the flexible polymer device, the Bragg reflection wavelength is tuned continuously up to 45 nm for the maximum strain of 31,690 muepsilon, which is determined by the elastic expansion limit of waveguide polymer. From the linear wavelength shift proportional to the strain, the photoelastic coefficient of the ZPU polymer is found.