Inline fiber optic power sensor featuring a variable tap ratio based on a tightly focused femtosecond laser inscription.

We propose and demonstrate an inline fiber optic power sensor (IFPS) resorting to an embedded waveguide tap, which is formed to traverse across the cladding and core of a standard single-mode fiber. The tap was produced via a single-step inscription based on the femtosecond laser direct-writing method. A tightly focused pulsed laser beam has been particularly exploited to suppress the elongation along the laser propagation direction, thereby improving the cross-sectional symmetry of the created tap waveguide. The fabricated fiber optic tap has been stably combined with a photodiode via a compact package. The achieved tap ratio could be tuned from 1.0% to 5.9% at the wavelength of 1550 nm by adjusting the applied laser power, while the induced excess loss was kept below 0.6 dB. The proposed IFPS will be highly suitable for real-time power monitoring in a variety of applications, including optical communication networks and systems.

Highly sensitive electro-optic probe incorporating an ultra-high Q-factor LiNbO3 etalon.

A highly sensitive electro-optic (EO) probe has been proposed and realized by tethering an ultra-high-quality (Q)-factor LiNbO3 etalon to a single-mode fiber operating at around a 1550-nm wavelength. For the adopted EO etalon, the electric-field-induced refractive index modification is deemed to shift its own spectral response. An electrical modulation signal is anticipated to be produced when a probe light beam with a fixed bias wavelength impinges upon the EO etalon. The EO etalon is particularly required to exhibit a remarkably steep spectral response and thus facilitate modulation efficiency. In aiming to scrutinize the performance in terms of sensitivity, two EO probes involving profoundly different Q-factors were prepared and applied to detect the electric field emitted from a microstrip device. It was confirmed that the sensitivity could be efficiently enhanced by as much as 28 dB by boosting the Q-factor 18 times when a probe light beam operating at =∼1550 nm was properly collimated and polarized. Accordingly, the minimum detectable signal was successfully diminished.