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.
In this work, for the first time of our knowledge, we present a well-supported procedure to fabricate ridge optical waveguides onto thin films of PLZT by femtosecond laser ablation. In order to achieve smooth guiding structures to guarantee good optical performance, we have studied the ablation threshold characteristics for different kinematic conditions of fs laser machining and also we have explored the different ablation regimens for several fluencies reached. Besides, we characterize the morphology and roughness of ridge waveguides through a modal and scattering loss analysis, for waveguides made with single and multiple scan. An innovative phenomenological model that relates the sidewall roughness to process parameters is proposed in this paper. Conducting this approach it is possible to extend the fabrication method of smooth guiding structures by fs micromachining to many optical thin films in order to develop integrated photonics devices addressed to different technological applications.
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