In this work, we demonstrated lossy mode resonance (LMR) generation in optical fiber structures based on multimode fibers coated with aluminum-doped zinc oxide (AZO) films. AZO thin films were deposited by using radio frequency magnetron sputtering. In order to exhibit the usefulness of the LMR effect for sensing applications in optical fiber based systems, the deposition conditions of the AZO film coatings were set to obtain the second LMR order within the 1.55 µm wavelength range. An optical transmission configuration setup was used to investigate the LMR effect on fiber structures based on the use of no-core and cladding-removed multimode fibers coated with AZO films synthesized from metallic sputtering targets with different proportions of Zn:Al, 92:8% and 98:2%, at atomic concentrations. The optical and electrical/chemical features of the AZO films were characterized with UV–vis and XPS spectroscopy, respectively. The optical response of the proposed sensing configuration to refractive index (RI) variations was experimentally demonstrated. For the best approach, the sensitivity of wavelength displacement to RI variations on the liquid surrounding media was found to be 1214.7 nm/RIU.

Tunable dual-wavelength emission of a Tm-doped fiber laser based on two fiber Bragg gratings (FBGs) is experimentally demonstrated. By using two FBGs with central wavelengths at 2069.30 and 2069.44 nm, stable dual-wavelength laser generation in the 2 μm wavelength region is achieved by adjusting the differential loss of the two wavelengths in the laser cavity. Strain applied on the FBG allows independent tuning of the simultaneously generated wavelengths with separation between the laser lines in a range from 0.54 to 9 nm. The laser has output power fluctuations less than 0.093% for an output power of 77.3 mW.

The use of titanium oxynitride (TiOxNy) thin films as a saturable absorber (SA) element for generation of passive Q-switched (PQS) laser pulses, from a linear cavity Er-Yb double-clad fiber (EYDCF) laser, is demonstrated. Additionally, the deposition of the material as a thin film covering a fiber micro-ball lens (MBL) structure is reported for the first time. The TiOxNy coating is deposited by a direct current (DC) magnetron-sputtering technique. The MBL is inserted within the laser cavity in a reflection configuration, alongside a reflecting mirror. As a result, the coated fiber MBL simultaneously acts as a SA element for PQS laser pulses generation and as an interference filter for wavelength selection and tuning of the generated laser line. Tunable single-laser emission in a wavelength range limited by dual-wavelength laser generation at 1541.96 and 1547.04 nm is obtained. PQS laser pulses with a repetition rate from 18.67 to 124.04 kHz, minimum pulse duration of 3.57 µs, maximum peak power of 0.359 W, and pulse energy of 1.28 µJ were obtained in a pump power range from 1 to 1.712 W.

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The passive Q-switched operation of a ring cavity Er/Yb-doped double clad fiber laser by using an Al-doped ZnO (AZO) thin film as saturable absorber is experimentally demonstrated. In order to improve the absorbance in the C-band wavelength region, a thin film of AZO containing Zn and Al metal precursors in a proportion of 98:2 wt% was developed by an radio-frequency (RF) magnetron sputtering process. Then the AZO film was used as a saturable absorber (SA) in a ring cavity Er/Yb double clad fiber laser. The AZO-SA exhibits a modulation depth of 11.3% and a saturation intensity of 0.057 MW cm −2 in the 1.55 µm waveband. In a pump power range from 0.475 to 1.356 W, stable Q-switched pulse trains with repetition rates of 70.1-161.3 kHz were observed. With a maximum pump power of 1.356 W, a minimum pulse width of 1.12 µs and a maximum pulse energy of 1.32 µJ are obtained. To the best of our knowledge, we present the first demonstration of a passive Q-switching laser operation using an RF sputtered AZO thin film as a saturable absorber. The reliability of the RF magnetron sputtered AZO thin films used as an SA for 1.55 µm Q-switched laser applications is experimentally demonstrated.