Multi-Path Interferometer Structures with Cleaved Silica Microspheres

in: SPIE Proceedings (2018)
Gomes, André D.; Silveira, Beatriz; Karami, Fatemeh; Zibaii, Mohammad I.; Latifi, Hamid; Dellith, Jan; Becker, Martin; Rothhardt, Manfred; Bartelt, Hartmut; Frazão, Orlando
Two multi-path interferometers were developed using cleaved silica microspheres. A microsphere on top of a singlemode fiber tip was cleaved with a focused ion beam. The asymmetry introduced in the structure generates a new set of optical paths due to random reflections inside the microsphere. The obtained reflection spectrum presents a random-like interferometric behavior with strong spectral modulation of around 3 dB amplitude. Two distinct regions can be observed when a fast Fourier transform is applied. The first involves two cavities at a lower frequency and the second region involves a band of frequencies that is originated by the random interferometric reflections. These two spectral characteristics can be separated using low-pass and high-pass filters, respectively. A correlation method was used to obtain a temperature response from the two-cavity component. A similar structure was also created in a microsphere of multimode fiber. The microsphere was cleaved by polishing the structure with a certain angle. The interference between the different optical paths can be seen as the superposition of several two-wave interferometers, which can be discriminated through signal processing. Temperature sensing was also explored with this structure. The sensitivity to temperature is more than 3-fold for smaller cavities. Moreover, a sensitivity enhancement is also verified if a correlation method is used.

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