No abstract

In this work we design, fabricate and characterize a 1  ×  2 Y-branch power splitter based on simplified coherent coupling. This device was constructed by type II waveguide structures inscribed by a direct femtosecond laser writing technique in x-cut lithium niobate crystal. First of all, a theoretical study that links the kinematic and writing fluence of the process is developed, which allows us to establish the design trade-off and justify the best geometry chosen. Then, the design was optimized and tested by using commercial software, resulting in a compact and low-loss photonic circuit. The efficiency of the proposed device is compared with two others: a curved and a straight splitter. Finally, the experimental results were compared with simulations and then a statistical analysis of multiple comparisons was also conducted, obtaining 3.7 dB  ±  0.1 dB insertion losses and 4.5% of the unbalanced coupling ratio.

This work describes a setup to characterize the effective diffusivity of barrier membranes to mass transport. Membranes with controlled and well‐defined barrier microstructures are produced from an elastomeric polydimethylsiloxane (PDMS) matrix. Physical obstacles to mass transport are generated by carving in the matrix microscopic holes with well‐defined shapes and in specific positions. Lateral Raman mapping is used to follow mass transport of a penetrant molecule, hexadecanol (HDOL), in the carved matrix. The influence of circular and elongated holes over mass transport is examined by monitoring the HDOL Raman intensity over time, after it passes the barrier microstructure. Results are compared with computer simulations of mass transport and excellent agreement is found. It is shown that holes act as bidimensional barriers to HDOL and that the effective diffusion coefficient of HDOL in the barrier membrane is reduced with respect to that of the homogenous material. Overall, Raman measurements provide a valuable base of data generation to contrast theoretical models of mass transport in heterogeneous barrier membranes.