In this work, we study a 215-m-long figure-of-eight fiber laser including a double-clad erbium-ytterbium fiber and a nonlinear optical loop mirror based on nonlinear polarization evolution. For proper adjustments, self-starting passive mode-locking is obtained. Measurements show that the mode-locked pulses actually are noise-like pulses, by analyzing the autocorrelation, scope traces and the very broad and flat spectrum extending over a record bandwidth of more than 200 nm, beyond the 1750 nm upper wavelength limit of the optical spectrum analyzer. Noise-like pulsing was observed for moderate and high pump power preserving the same behavior, reaching pulse energies as high as 300 nJ, with pulse durations of a few tens of ns and a coherence length in the order of 1 ps. Stable fundamental mode locking as well as harmonic mode locking up to the 6th order were observed. The bandwidth was further extended to more than 450 nm when a 100-m piece of highly nonlinear fiber was inserted at the laser output. The enhanced performances obtained compared to other similar schemes could be related to the absence of a polarizer in the present setup, so that the state of polarization along the cavity is no longer restricted.

In this letter, a temperature sensor based on a fiber ring laser is presented. A fiber Bragg grating was used as a sensor head, and a Mach-Zehnder interferometer (MZI) was utilized as a wavelength selective filter to enhance the temperature sensing capability. The MZI was achieved by splicing a piece of photonic crystal fiber between two segments of single-mode fiber. Moreover, it is shown that when the laser emission wavelength is shifted as the temperature is varied, achieving a temperature sensitivity of 18.8 pm/°C at 1550 nm, within the temperature range from 20 °C to 90 °C.

In this paper, an all-fiber Mach-Zehnder interferometer (MZI) based on a non-zero dispersion-shifted fiber (NZ-DSF) is presented. The MZI was implemented by core-offset fusion splicing one section of a NZ-DSF fiber between two pieces of single mode fibers (SMFs). Here, the NZ-DSF core and cladding were used as the arms of the MZI, while the core-offset sections acted as optical fiber couplers. Thus, a MZI interference spectrum with a fringe contrast (FC) of about 20 dB was observed. Moreover, its response spectrum was experimentally characterized to the torsion parameter and a sensitivity of 0.070 nm/° was achieved. Finally, these MZIs can be implemented in a compact size and low cost.

The present manuscript focuses on reviewing the optical techniques proposed to monitor milk quality in dairy farms to increase productivity and reduce costs. As is well known, the quality is linked to the fat and protein concentration; in addition, this issue is crucial to maintaining a healthy herd and preventing illnesses such as mastitis and ketosis. Usually, the quality of the milk is carried out with invasive methods employing chemical reagents that increase the time analysis. As a solution, several spectroscopy optical methods have been proposed, here, the benefits such as non-invasive measurement, online implementation, rapid estimation, and cost-effective execution. The most attractive optical methods to estimate fat and protein in cow’s milk are compared and discussed considering their performance. The analysis is divided considering the wavelength operation (ultraviolet, visible, and infrared). Moreover, the weaknesses and strengths of the methods are fully analyzed. Finally, we provide the trends and a recent technique based on spectroscopy in the visible wavelength.