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Optical printed circuit board (OPCB) waveguide materials and fabrication methods have advanced considerably over the past 15 years, giving rise to two classes of embedded planar graded index waveguide based on polymer and glass. We consider the performance of these two emerging waveguide classes in view of the anticipated deployment in data center environments of optical transceivers based on directly modulated multimode short wavelength VCSELs against those based on longer wavelength single-mode photonic integrated circuits. We describe the fabrication of graded index polymer waveguides, using the Mosquito and photo-addressing methods, and graded index glass waveguides, using ion diffusion on thin glass foils. A comparative characterization was carried out on the waveguide classes to show a clear reciprocal dependence of the performance of different waveguide classes on wavelength. Furthermore, the different waveguide types were connected into an optically disaggregated data switch and storage system to evaluate and validate their suitability for deployment in future data center environments.

A model and the waveguide parameters of a broadband, polymer-based slab waveguide difference interferometer is presented in this paper. The parameters were determined based on knowledge of the dispersion in the structure materials used to fabricate the waveguide. The impact of the waveguide layer thickness, propagation path length, and change in the waveguide cover refractive index on the output signal from the system was determined. It has been shown that the direction of the maximum shifting is determined by the thickness of the waveguide layer. A relationship describing the shift in the signal extrema for a change in the waveguide cover refractive index was derived. The results show that the use of a propagation constant simplifies the description of the interferometer. Polymer waveguides, although they have a small contrast in refractive indices, allow for large shifts in the maxima of the signal. The determined shifts in the output signal extrema for polymer waveguides are comparable, and these shifts are larger for some waveguide thicknesses compared to waveguides based on Si3N4.

Thermal imprinting, a technique proposed more than four decades ago, is known for its cost-efficiency and high throughput in microstructuring capability. The process involves the structuring of a substrate with a patterned working stamp under certain conditions. The parameters applied in the process effectively determine the replication quality and accuracy. In many cases, there is still no comprehensive study on the effect of system parameters or technical aspects on replication quality. To address this gap, we demonstrated a systematic study of the process for fabricating functional optical structures using a home-built thermal imprinting setup. On this basis, optimization strategies (i.e., reformation of the PDMS mixing time, tuning of the curing process, and optimization of imprinting temperature) were proposed and developed in both the working stamping and the thermal imprinting processes to enhance the structuring accuracy and quality as well as reproducibility in this work. With our optimizations, improved replication accuracies with a dimension difference down to 0.14% for the pattern transfer from silicon master mold onto polydimethylsiloxane (PDMS) working stamp and 0.04% (compared to silicon master mold) for the pattern imprinted onto polymethyl methacrylate (PMMA) substrate were achieved, respectively. The replication patterns on PDMS working stamp and the imprinted structures on PMMA exhibit a roughness of 24 ± 3 nm and 101 ± 8 nm, respectively, with high structuring quality. In this work, we also demonstrated the gas sensing functionality of thermal-imprinted waveguides by integrating them with a thin metal–organic framework film, which features porous structures enabling the adsorption of gas molecules and serves as the sensing layer. In our experiments, a micro-Watt power was used for the sensing performance characterization. The integrated optical sensor device exhibits high sensibility to CO 2 , with a relative output power decrease of 2.8 µW when it was exposed to CO 2 . In addition, an adsorption time of 28 s and desorption time of 61 s were demonstrated, respectively. This work opens an attractive path for the development of low-cost, scalable, and flexible on-chip optical sensors for gas detection and industrial monitoring.

A random laser was achieved in a polymer membrane with silver nanoflowers on a flexible substrate. The strong confinement of the polymer waveguide and the localized field enhancement of silver nanoflowers were essential for the low-threshold random lasing action. The lasing wavelength can be tuned by bending the flexible substrate. The solution phase synthesis of the silver nanoflowers enables easy realization of this type of random lasers. The flexible and high-efficiency random lasers provide favorable factors for the development of imaging and sensing devices.

Minimally Invasive Surgery is often limited by the lack of tactile feedback. Indeed, surgeons have traditionally relied heavily on tactile feedback to estimate tissue stiffness - a critical factor in both diagnostics and treatment. With this in mind we present in this paper a flexible sensor foil, based on polymer optical waveguide. This sensor has been applied for real-time contact force measurement, material stiffness differentiation and surface texture reconstruction. Interrogated by a commercially available optoelectronic device, the sensor foil offers precise and reproducible feedback of contact forces up to 5 N, with a minimal detectable limit of 0.1 N. It also demonstrates distinct optical attenuation responses when indenting silicone samples of varying stiffnesses under controlled displacement. When integrated onto a 3D-printed module resembling an endoscopic camera and manipulated by a robotic arm, the sensor successfully generated spatial stiffness mapsof a phantom. Moreover, by sliding over structures with varying surface textures, the sensor foil was able to reconstruct surface profiles based on the light attenuation responses. The results demonstrate that the presented sensor foil possesses great potential for surgical applications by providing additional haptic information to surgeons.

In this work, an evanescent Bragg grating sensor inscribed in a few-mode planar polymer waveguide was integrated into microchannel structures and characterized by various chemical applications. The planar waveguide and the microchannels consisted of epoxide-based polymers. The Bragg grating structure was postprocessed by using point-by-point direct inscription technology. By monitoring the central wavelength shift of the reflected Bragg signal, the sensor showed a temperature sensitivity of −47.75 pm/K. Moreover, the functionality of the evanescent field-based measurements is demonstrated with two application examples: the refractive index sensing of different aqueous solutions and gas-phase hydrogen concentration detection. For the latter application, the sensor was additionally coated with a functional layer based on palladium nanoparticles. During the refractive index sensing measurement, the sensor achieved a sensitivity of 6.5 nm/RIU from air to 99.9% pure isopropyl alcohol. For the gas-phase hydrogen detection, the coated sensor achieved a reproducible concentration detection up to 4 vol% hydrogen. According to the reported experimental results, the integrated Bragg-grating-based waveguide sensor demonstrates high potential for applications based on the lab-on-a-chip concept.

This work presents a compact and sensitive refractive index sensor able to evaluate the concentration of an analyte in a sample. Its working principle leverages on the changes in the optical absorption features introduced by the sample itself on the evanescent waves of a light beam. The device’s high compactness is achieved by embedding the sample–light interaction site and the detector in a 1 cm2 glass substrate, thanks to microelectronics technologies. High sensitivity is obtained by employing a low-noise p-i-n hydrogenated amorphous silicon junction, whose manufacture process requires only four UV lithographic steps on a glass substrate, thus ensuring low production costs. The system’s capabilities are investigated by sensing the sugar content in three commercial beverages. Sensitivities of 32, 53 and 80 pA/% and limits of detection of 47, 29 and 18 ppm are achieved. The above performance is comparable with state-of-the-art results available in the literature, where more complex optical setups, expensive instrumentation and bulky devices are used.

This paper presents the achievements and progress made on the polymer optical fiber (POF) gratings inscription in different types of Fiber Bragg Gratings (FBGs) and long period gratings (LPGs). Since the first demonstration of POFBGs in 1999, significant progress has been made where the inscription times that were higher than 1 h have been reduced to 15 ns with the application of the krypton fluoride (KrF) pulsed laser operating at 248 nm and thermal treatments such as the pre-annealing of fibers. In addition, the application of dopants such as benzyl dimethyl ketal (BDK) has provided a significant decrease of the fiber inscription time. Furthermore, such improvements lead to the possibility of inscribing POF gratings in 850 nm and 600 nm, instead of only the 1550 nm region. The progress on the inscription of different types of polymer optical fiber Bragg gratings (POFBGs) such as chirped POFBGs and phase-shifted POFBGs are also reported in this review.

Despite the rapid developments in the field of two-photon polymerization-based direct laser writing, limited attention has been paid to the efficient design of optical waveguide-based building blocks. To fill that gap, we have numerically investigated air-clad waveguides, tapers, and S-bends, with the aim to minimize insertion losses, whilst reducing the device sizes. We have first demonstrated waveguides with square and circular cross-sections that are mode-matched with single-mode optical fibers featuring insertion losses below −0.6 dB and −1.5 dB around 1550 nm for lengths of respectively 0.2 mm and 1 mm. We have also identified parabolic tapers that allow for adiabatic transition between a wide range of input and output waveguide sizes. These shapes allow, for example, tapering down from 15 µ m to 2 µ m diameter waveguides over a length as short as 43.2 µ m. We have fabricated a series of such components and confirmed their nearly lossless performance with insertion loss measurements. Finally, we have designed and optimized S-bends with Bezier curve shapes. As a proof-of-principle demonstration, we have fabricated a 160 µ m long S-bend that offsets the waveguide axis by 50 µ m. The insertion loss of the resulting 400 µ m long component, which also included two parabolic tapers, was less than −1.7 dB. Apart from providing design rules and ready-to-use recipes for fabricating low-loss 3D-printed waveguide-based building blocks, we project that our work will spark the development of a series of efficient photonic devices that rely on these components and that can be exploited in diverse application fields.

9,9‐bis (diphenylphosphorylphenyl) fluorene (FDPO) and dibenzotetrathienoacene (DBTTA), are synthesized as the neutral and anionic ligands, respectively, to prepare the ErIII coordination polymer [Er(DBTTA)3(FDPO)]n. Based on the intramolecular energy transfer, optical gains at 1.5 µm are demonstrated in [Er(DBTTA)3(FDPO)]n‐doped polymer waveguides under excitations of low‐power light‐emitting diodes (LEDs) instead of laser pumping. A ligand‐sensitization scheme between organic ligands and Er3+ ions under an excitation of an ultraviolet (UV) LED is established. Relative gains of 10.5 and 8.5 dB cm−1 are achieved at 1.53 and 1.55 µm, respectively, on a 1‐cm‐long SU‐8 channel waveguide with a cross‐section of 2 × 3 µm2 and a 1.5‐µm‐thick [Er(DBTTA)3(FDPO)]n‐doped polymethylmethacrylate (PMMA) as upper cladding. The ErIII coordination polymer [Er(DBTTA)3(FDPO)]n can be conveniently integrated with various low‐loss inorganic waveguides to compensate for optical losses in the C‐band window. Moreover, by relying on the intramolecular energy transfer and UV LED top‐pumping technology, it is easy to achieve coupling packaging of erbium‐doped waveguide amplifiers (EDWAs) with pump sources in planar photonic integrated chips, effectively reducing the commercial costs. Based on the intramolecular energy transfer, relative gains of 10.5 and 8.5 dB cm−1 at 1535 and 1550 nm respectively are demonstrated in ErIII coordination polymer [Er(DBTTA)3(FDPO)]n‐doped waveguides under excitations of light‐emitting diode instead of laser pumping. This study is expected to achieve the application of polymer waveguide amplifiers in planar photonic integration and facilitate low‐cost packaging of the waveguide and pump sources.