A.S. Sharbirin

Variable Waist-Diameter Mach–Zehnder Tapered-Fiber Interferometer as Humidity and Temperature Sensor

In-line single-mode tapered-fiber Mach-Zehnder interferometer (MZI-SMTF) with average waist diameters (davg) of 4.05 and 2.89 μm have been fabricated, and both the temperature and the humidity sensitivity of the surrounding media have been measured and compared. The humidity and the temperature were measured over the ranges from 0% to 90% and 28 °C to 40 °C, respectively. The stability of the system at 50%RH and 90%RH was investigated, while the temperature of the chamber was maintained at about 28 °C. The humidity and temperature sensitivity resolution values were 0.02 nm/%RH and 0.05 nm/0.1 °C for the MZI-SMTF-1 with an average waist diameter of 4.05 μm, while they were 0.01 nm/%RH and 0.025 nm/0.1 °C for the MZI-SMTF-2 with an average waist diameter of 2.89 μm.

Noncontact Optical Displacement Sensor Using an Adiabatic U-Shaped Tapered Fiber

A simple noncontact displacement microfiber sensor using adiabatic U-shaped tapered fiber is proposed and demonstrated. The microfiber is fabricated using a systematic fiber flame brushing technique, where the fiber waist diameter is proportional to the duration of the heating cycles. The sensor is capable of measuring a wide displacement distance up to 12 mm. A sensitivity of 0.2 dB/mm is recorded at a minimum tapered diameter of 8 μm. In comparison with the previous works of using Fresnel reflection method, the results of our proposed method show significant improvement in sensing range, which is indicated by distinct inclination of the loss slope. The microfiber probe shows a promise for a sensitive sensing at low development cost.

All-fiber multimode interferometer for the generation of a switchable multi-wavelength thulium-doped fiber laser

A compact all-fiber multimode interferometer (MMI) designed to produce a switchable multi-wavelength thulium-doped fiber laser (TDFL) is proposed and demonstrated. The TDFL fiber ring cavity employs a 60-cm-long multimode fiber into the cavity to induce multimode interference and provide intensity-dependent loss in order to generate a multi-wavelength output. The suppression of mode competition and the overall stability of the TDFL are further improved by exploiting the filtering capability of a Sagnac loop. By increasing the pump power, a switchable wavelength output is allowed with a wavelength spacing of ∼1.8  nm. At 361 mW input pump power, nine laser lines are generated, with a maximum signal-to-noise ratio value of ∼36  dB and an output power of 3.3 mW. The multi-wavelength TDFL also exhibits great stability in one-hour operation with a wavelength drift of 0.2 nm. The proposed multi-wavelength TDFL has potential to be employed in future thulium-doped fiber amplifier-based telecommunication infrastructure and also may be applicable in areas such as sensing and spectroscopy, largely associated with its 2 μm wavelength output.

Passively Q-switched thulium-doped fiber laser with silver-nanoparticle film as the saturable absorber for operation at 2.0 µm

In this work, a compact thulium-doped fiber laser with a Q-switched output is proposed and demonstrated. A thulium-doped fiber is used for the laser, with a peak absorption of 200 dB m−1 at 790 nm and a cutoff wavelength of 1350 nm as the primary gain medium, and a silver-based saturable absorber as the pulse generation mechanism. The pulses obtained from the proposed laser have repetition rates from 38.3 kHz up to 56.2 kHz, with a pulse width as low as 4.2 µs and pulse energy as high as 67.3 nJ at a maximum pump power of 228.8 mW. The generated pulses are highly stable, showing no changes or fluctuations over operation for a period of 60 min, and further validated with signal-to-noise ratios of 57.0 dB and 59.5 dB in the optical and frequency domains respectively. The proposed laser has high potential for eye-safe applications in manufacturing and medicine.