Design and analysis of a fiber-optic sensing system for shape reconstruction of a minimally invasive surgical needle

This paper presents the performance analysis of the system for real-time reconstruction of the shape of the rigid medical needle used for minimally invasive surgeries. The system is based on four optical fibers glued along the needle at 90 degrees from each other to measure distributed strain along the needle from four different sides. The distributed measurement is achieved by the interrogator which detects the light scattered from each section of the fiber connected to it and calculates the strain exposed to the fiber from the spectral shift of that backscattered light. This working principle has a limitation of discriminating only a single fiber because of the overlap of backscattering light from several fibers. In order to use four sensing fibers, the Scattering-Level Multiplexing (SLMux) methodology is applied. SLMux is based on fibers with different scattering levels: standard single-mode fibers (SMF) and MgO-nanoparticles doped fibers with a 35–40 dB higher scattering power. Doped fibers are used as sensing fibers and SMFs are used to spatially separate one sensing fiber from another by selecting appropriate lengths of SMFs. The system with four fibers allows obtaining two pairs of opposite fibers used to reconstruct the needle shape along two perpendicular axes. The performance analysis is conducted by moving the needle tip from 0 to 1 cm by 0.1 cm to four main directions (corresponding to the locations of fibers) and to four intermediate directions (between neighboring fibers). The system accuracy for small bending (0.1–0.5 cm) is 90$$\%$$ % and for large bending (0.6–1 cm) is approximately 92$$\%$$ % .

Application of WGM Resonances to the Measurement of the Temperature Increment of Ho and Ho-Yb Doped Optical Fibers Pumped at 1125 and 975 nm

Optical fiber characterization using whispering gallery mode resonances of the fiber itself has been demonstrated to be a powerful technique. In this work, we exploit the thermal sensitivity of whispering gallery mode resonances to characterize the pump-induced temperature increment in holmium doped and holmium-ytterbium codoped optical fibers. The technique relies on the measurement of the resonances’ wavelength shift due to temperature variation as a function of the pump power. Holmium doped fibers were pumped to the second excited level 5I6 of the Ho3+ ion using a laser diode at 1125 nm and ytterbium-holmium codoped fibers to the 2F5/2 level of the Yb3+ ion by a laser diode at 975 nm. Our results demonstrate that pumping ytterbium-holmium codoped fibers at 975 nm results in dramatic thermal effects, producing a temperature increment two orders higher than that observed in holmium doped fibers pumped with a 1125 nm laser diode.

Estimation and Management of Performance Limiting Factors in the Development of 1 kW Peak Power Pulsed Fiber MOPA at 1550 nm

An all-fiber three-stage master oscillator power amplifier (MOPA), based on Erbium and Erbium-Ytterbium co-doped fibers, has been designed and developed. The performance of such a laser is primarily limited by amplified spontaneous emission (ASE), Yb bottlenecking, and non-linear effects. Other important factors, that need to be considered towards performance improvement, are fiber bend diameter and heat generated in the fiber. This paper describes the methodology for the estimation and management of these limiting factors for each amplifier stage. The work presented here is limited to the fibers which are commercially easily available, unlike customised Yb- free large mode area (LMA) Erbium-doped fibers, where very high peak and average powers are being reported due to the absence of Yb ASE. Presented experimental results and discussion shall be beneficial for the fiber laser amplifier designers. With suitable management, 1 kW peak power pulses of 30 ns duration at 200 kHz repetition rate have been achieved with 30 % optical efficiency. The collimated output of 6 W average power (limited by Yb ASE) with high beam quality (M2 ≈ 1.6) at 1550 nm can be employed for a variety of applications. By adding additional amplifier stages, power can be scaled further.