In this paper, generation of soliton molecules by a self-mode-locked Er/Yb double clad fiber laser is experimentally demonstrated. The optical spectrum of the bound solitons exhibits eight well defined peaks at ~1563 nm with high modulation depth. The corresponding autocorrelation measurement shows a fundamental trace with several narrow peaks, suggesting the presence of bound solitons. The obtained results demonstrate the reliability of our simple laser configuration for the formation of more robust soliton molecules as the pump power is increased. The soliton molecules exhibit repetition rate of 19.54 MHz and average power of 1.2 W, achieved with a pump power of ~4.8 W.

A polymer optical Sagnac interferometer is proposed as a compact and low-cost refractive index sensor for the first time to our best knowledge. The Sagnac interferometer is fabricated by only one piece of fiber to facilitate its fabrication and to avoid losses due to misalignment or fusion. The coupler was developed based on chemical and twisting techniques of ∼ 5 c m of fiber. We modified the coupling ratio by varying the refractive index of media surrounding the coupler and consequently modified the transmission. For several values of mass percent concentration of sugar solutions surrounding the coupler, we found that transmittance decreases as the mass concentration increases. However, the decay is faster for the low concentration, while the decay is slower for higher concentrations. Two sets of experiments were carried out, at high ( ≥ 1 gm/100 ml) and low ( < 1 g m / 100 m l ) mass concentration of sugar solutions. The calibration of the sensor was done at 733 nm, where the response of the interferometer displays larger transmission variations for different solutions. The refractive index estimation was possible by correlation of the transmittance function (calculated by fitting the experimental data) with a linear refractive index model. The estimated resolution of the system is 0.057 weight percent of sugar solution, determined by the noise of the system.

The Rotational Shearing Interforometer has been proposed for direct detection of extra-solar planets. This interferometer cancels the star radiation using destructive interference. However, the resulting signal is too small (few photons/s for each m²). We propose a novel method to enhance the signal magnitude by means of the star–planet interference when the star radiation is not cancelled. We use interferograms computationally simulated to confirm the viability of the technique.

In this work, we study a double-sense twisted low-birefringence Sagnac loop structure as a sound/vibration sensing device. We study the relation between the adjustments of a wave retarder inside the loop (which allows controlling the transmission characteristic to deliver 10, 100, and 300 $\mathsf{\mu }\mathrm{W}$ average power at the output of the system) and the response of the Sagnac sensor to vibration frequencies ranging from 0 to 22 kHz. For a 300 m loop Sagnac, two sets of experiments were carried out, playing at the same time all the sound frequencies mixed for ∼1 s, and playing a sweep of frequencies for 30 s. In both cases, the time- and frequency-domain transmission amplitudes are larger for an average power of 10 $\mathsf{\mu }\mathrm{W}$, and smaller for an average power of 300 $\mathsf{\mu }\mathrm{W}$. For mixed frequencies, the Fourier analysis shows that the Sagnac response is larger for low frequencies (from 0 to ∼5 kHz) than for high frequencies (from ∼5 kHz to ∼22 kHz). For a sweep of frequencies, the results reveal that the interferometer perceives all frequencies. However, beyond ∼2.5 kHz, harmonics are present each ∼50 Hz, revealing that some resonances are present. The results about the influence of the power transmission through the polarizer and power emission of laser diode (LD) on the Sagnac interferometer response at high frequencies reveal that our system is robust, and the results are highly reproducible, and harmonics do not depend on the state of polarization at the input of the Sagnac interferometer. Furthermore, increasing the LD output power from 5 mW to 67.5 mW allows us to eliminate noisy signals at the system output. in our setup, the minimum sound level detected was 56 dB. On the other hand, the experimental results of a 10 m loop OFSI reveal that the response at low frequencies (1.5 kHz to 5 kHz) is minor compared with the 300 m loop OFSI. However, the response at high frequencies is low but still enables the detection of these frequencies, yielding the possibility of tuning the response of the vibration sensor by varying the length of the Sagnac loop.

We propose a spectral filter based on a plastic optical fiber with micro-holes as a low-cost, robust, and highly reproducible spectral filter. The spectral filter is explored for two configurations: a fiber extended in a straight line and a fiber optic loop mirror scheme configuration. The transmission traces indicate a spectral blue shift in peak transmission, at 587 nm, 567 nm, 556 nm, and 536 nm for zero, one, two, and three holes in the fiber, respectively. The filter exhibits a bandpass period of approximately 120 nm. Additionally, we conduct a comparison of the transmission with holes separated by distances of 1 cm and 500 μm. The results demonstrate that the distance between holes does not alter the spectral transmission of the filter. In the case of the fiber loop mirror configuration, we observe that the bandpass can be adjusted, suggesting the presence of multimode interference. Exploring variations in the refractive index within the holes by filling them with glucose solutions at various concentrations, we determine that the filtering band and spectral shape remain unaltered, ensuring the stable and robust operation of our spectral filter.

In this work, we present an experimental investigation of the temperature-dependent transmission characteristics of a low-birefringence Sagnac interferometer incorporating a double-sense twisted fiber loop. The study focuses on the influence of wave retarder adjustments within the loop on the interferometric response over a temperature range of 25°C to 50°C. A 10-meter fiber loop, optimized for maximum transmission, exhibited an approximately linear transmission profile, achieving a sensitivity of 10.62µW/°C within the 35–50°C interval. In contrast, the 300-meter loop demonstrated a sinusoidal transmission behavior, with a sensitivity of approximately 140.03µW/°C observed between 30°C and 35°C. The comparative analysis reveals that the short-loop configuration offers stable and predictable linear response characteristics. In contrast, the higher sensitivity of the longer loop restricts its utility to narrower temperature windows. Hysteresis effects were consistently recorded in both configurations, suggesting dynamic thermal responses attributable to coil-induced birefringence. These results underscore the significant influence of temperature on the performance of Sagnac interferometers across a variety of industrial and scientific scenarios.