An ultrasensitive refractive index (RI) sensor based on enhanced Vernier effect is proposed, which consists of two cascaded fiber core-offset pairs. One pair functions as a Mach-Zehnder interferometer (MZI), the other with larger core offset low-finesse Fabry-Perot (FPI). In traditional Vernier-effect sensors, an insensitive to environment change used sensing reference. Here in proposed sensor, interference fringes MZI and FPI shift opposite directions ambient RI varies, same direction...

Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection. Conventional decoherence measurement methods delayed self-heterodyne/homodyne interferometry cannot measure such narrow linewidths accurately. This because a broadening of the Gaussian spectrum, which hides laser's intrinsic Lorentzian linewidth, be avoided. Here, we introduce new method using strong coherent...

We present an amplitude difference comparison of coherent envelope method for accurately measuring the laser linewidth. The new comparing contrast second peak and trough to determine linewidth is proved be stable has little error. feasibility accuracy have been confirmed theoretically experimentally. Our based on short delayed self-heterodyne interferometer can almost ignore influence broadening spectrum induced by 1/f frequency noise. Therefore, advantage accurate detection narrow or ultra-narrow

Dual-wavelength fiber lasers with ultra-narrow linewidth find wide applications in high-speed optical communications, optic sensors, high resolution measurements and medical instruments microwave or terahertz generation systems. Based on the compression mechanism due to Rayleigh backscattering, this paper adopts a simple ring structure cooperated two Bragg gratings centered at 1550 nm 1530 respectively, achieving dual-wavelength laser linewidth, 3dB of ~700 Hz for each wavelength, SNR 60dB....

We demonstrate a cost-effective distributed fiber sensing system for the multi-parameter detection of vibration, temperature, and strain by integrating phase-sensitive optical time domain reflectometry (φ-OTDR) Brillouin (B-OTDR). Taking advantage fast changing property vibration static properties temperature strain, both width intensity laser pulses are modulated injected into single-mode proportionally, so that three concerned parameters can be extracted simultaneously only one...

We proposed and demonstrated a linewidth compression method of laser based on stimulated Brillouin scattering (SBS) Rayleigh backscattering structure (RBS). The relationship between the output SBS input pump was studied theoretically experimentally. It is shown that narrower leads to bandwidth gain and, finally, will tend its intrinsic value as than 10 kHz; then an fiber ring would 200 Hz. In order further reduce with low cost, RBS simple dual-cavity feedback were added ∼75 Hz...

The Vernier effect magnifies optical sensitivity by the superposition of two spectra with slightly shifted frequencies from a sensing interferometer (SIM) and reference (RIM). In this study, we demonstrate that can be obtained through single interferometer, which detects changed signal provides an artificial spectrum (ARS) to superposed spectrum. ARS extracted spatial frequency down-conversion one in processing is not affected environmental changes detuned at arbitrarily small amount...

Single longitudinal mode (SLM) distributed feedback (DFB) lasers with a linewidth lower than few kHz find applications in many coherent detection systems. In this paper, we proposed and experimentally demonstrated novel method to compress the of SLM DFB laser by utilizing dual-cavity structure (DCFS). The DCFS first provides optical self-injection linewidth, then two lengths are carefully optimized achieve output via Vernier principle suppression modes overlapping between cavities....

Ultra-high sensitivity can be obtained near the dispersion turning point (DTP), which is intrinsically determined by characteristics of two arms in a Mach-Zehnder interferometer (MZI) and usually far from observation window. The shift DTP towards window was previously realized physically adjusting waveguide structure MZI's arms, complex hard to control. In this paper, it proposed that an MZI conveniently shifted any specified wavelength just simply down-converting spatial frequency its...

High-quality ZnO thin films were grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. Three excitonic transitions associated with the valence bands A, B, and C clearly revealed in reflectance spectrum measured at 33K. This result indicates that have wurtzite crystalline structure. The emission spectra backscattering geometry room temperature. When excitation exceeded a certain value, linewidth narrowing, nonlinear rise of intensity, shortening carrier lifetime observed...

Ultrasensitive refractive index (RI) sensing based on novel Vernier-effect demodulation through a single fiber Fabry–Perot interferometer (FFPI) is proposed and demonstrated. A core-offset pair used as an FFPI for RI sensing. An artificial reference spectrum (ARS) obtained by modulating extracting twice The Vernier effect realized superimposing the with ARS. By optimizing cavity length of free range (FSR) ARS, ultrahigh sensitivity 133948.33 nm/refractive unit (RIU) magnification factor...

The effect of fiber laser linewidth on the optical time-domain reflectometer based vibration distributed sensing regime is studied experimentally in this paper. Lasers with multi-longitudinal modes, 5 kHz and ~800 Hz single longitudinal mode are interrogated as light source successively. Experiments show that narrower results higher repeatable stable scattering spectrum. When 800 modulated into 50 ns width pulses, signal to noise ratio ~ 6 dB spatial resolution improved 3 m, breaking...

We propose a single longitudinal mode fiber laser with ultra-narrow linewidth of ~130 Hz by combining self-injection feedback and Rayleigh backscattering, in which backscattering collected is utilized as compressor.

In recent years, significant advancements have been made in the field of computational imaging, particularly due to application deep learning methods imaging problems. However, only a few studies related examined impact diffraction distance on image restoration. this paper, effect restoration is investigated based PhysenNet neural network. A theoretical framework for images at various distances provided along with applicable propagators. experiment, network selected train different and using...

Parameter regulations of narrow-linewidth lasers in the frequency domain have attracted considerable attention for wide spread applications precise coherent detection, generation microwaves, and light quantum computing areas. The light-controllable methods assisted by novel two-dimensional materials pave access toward wavelength-tunable with high stability excellent linearity. In this paper, we propose a light-enabled tunable fiber laser based on stable graphene-coated filter dynamical...

We propose a precision measurement method of laser linewidth based on short-delay self-homodyne, using the second peak-valley difference (SPVD) feature coherent power spectrum to fit linewidth. The SPVD model self-homodyne envelope was established. One-to-one correspondence among values SPVD, delay length, and determined theoretically through simulations, while reliability stability verified experimentally. By comparing detected results, it is found that fitted obtained by system closer its...