Ultranarrow Transmission Bands Research Articles

High-Resolution Sensing System Based on Fiber Bragg Grating Fabry–Perot Interferometer and Frequency-Domain Demodulation

A high-resolution sensing system is proposed and demonstrated. The sensor head is a Fabry–Perot interferometer formed by two cascaded uniform fiber Bragg grating sensors, and the microwave scanning demodulation system consists of a frequency-stabilized laser, a microwave generator, an electro-optic modulator, a photodetector, and a data acquisition unit. Owing to the ultra-narrow transmission bands of the sensor head and the small resolution of the microwave scanning demodulation system (at the order of kHz), the system can realize a high resolution for strain, curvature, and lateral force sensing, up to $\text{n}\varepsilon $ , 10−3 m−1, and $\mu \text{g}$ , respectively, with sensitivities of −9.696 MHz/ $\mu \varepsilon $ , −4346.97 MHz/m−1, and −120.02 MHz/g, respectively. Because of the fast frequency shifts of the microwave generator, the system proposed in this paper has high potential for dynamic signal sensing.

Stable single-polarization single-longitudinal-mode linear cavity erbium-doped fiber laser based on structured chirped fiber Bragg grating

A novel linear cavity erbium-doped fiber (EDF) laser based on a structured chirped fiber Bragg grating (CFBG) filter is proposed for stable single-polarization (SP) single-longitudinal-mode (SLM) operation. For the first time, to the best of our knowledge, a structured CFBG filter with an ultranarrow transmission band which is generated by tapering directly on CFBG is used to select the laser longitudinal mode. The SLM operation is obtained by using the structured CFBG together with an unpumped EDF acting as a saturable absorber. The fluctuations of the laser peak power and center wavelength are less than 0.07dB and 1pm in 1h, respectively. The stable SP operation is achieved by using the inline broadband polarizer. The measured 20dB laser linewidth is about 27.7kHz, which indicates the laser linewidth is approximately 1.39kHz FWHM.

Tunable and switchable dual-wavelength single polarization narrow linewidth SLM erbium-doped fiber laser based on a PM-CMFBG filter.

A tunable and switchable dual-wavelength single polarization narrow linewidth single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser based on polarization-maintaining chirped moiré fiber Bragg grating (PM-CMFBG) filter is proposed and demonstrated. For the first time as we know, the CMFBG inscribed on the PM fiber is applied for the wavelength-tunable and-switchable dual-wavelength laser. The PM-CMFBG filter with ultra-narrow transmission band (0.1 pm) and a uniform polarization-maintaining fiber Bragg grating (PM-FBG) are used to select the laser longitudinal mode. The stable single polarization SLM operation is guaranteed by the PM-CMFBG filter and polarization controller. A tuning range of about 0.25 nm with about 0.075 nm step is achieved by stretching the uniform PM-FBG. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 6.5 and 7.1 kHz with a 20 dB linewidth, which indicates the laser linewidth is approximate 325 Hz and 355 Hz FWHM.

Switchable Single-Polarization Dual-Wavelength Ring Laser Based on Structured PM-CFBG

A switchable single-polarization dual-wavelength single-longitudinal mode (SLM) erbium-doped fiber (EDF) ring laser is proposed and demonstrated. For the first time, the structured polarization-maintaining chirped fiber Bragg grating (PM-CFBG) filter, which has ultranarrow transmission band is created by tapering directly on the PM-CFBG. Then, the stable SLM operation of the fiber laser is guaranteed by the structured PM-CFBG filter and 20-cm unpumped EDF acting as a saturable absorber. Meanwhile, the stable dual-wavelength fiber laser with a wavelength spacing of ~0.41 nm and stable single polarization state is experimentally realized. The measured linewidth of the fiber laser for each wavelength is <;8 kHz with a 20-dB linewidth.

Tunable single-polarization single-longitudinal-mode erbium-doped fiber ring laser employing a CMFBG filter and saturable absorber

A tunable single-polarization single-longitudinal-mode (SLM) erbium-doped fiber ring laser is proposed and demonstrated. For the first time as we know, a chirped moiré fiber Bragg grating (CMFBG) filter with ultra-narrow transmission band and a uniform fiber Bragg grating (UFBG) are used to select the laser longitudinal mode. The stable SLM operation of the fiber laser is guaranteed by the combination of the CMFBG filter and 3m unpumped erbium-doped fiber acting as a saturable absorber. The single polarization operation of the fiber laser is obtained by using an inline broadband polarizer. A tuning range of about 0.7nm with about 0.1nm step is achieved by stretching the uniform FBG.

Photonic generation of microwave signal using a dual-wavelength erbium-doped fiber ring laser with CMFBG filter and saturable absorber

A simple approach for photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser is proposed and demonstrated. For the first time as we know, a chirped moiré fiber Bragg grating (CMFBG) filter with ultra-narrow transmission band and a chirped fiber Bragg grating (FBG) are used to select the laser longitudinal mode. The stable SLM operation of the fiber laser is guaranteed by the combination of the CMFBG filter and 3m unpumped EDF acting as a saturable absorber. Stable dual-wavelength SLM fiber laser with a wavelength spacing of approximately 0.140nm is experimentally realized. By beating the dual-wavelength fiber laser at a photodetector, photonic generation of microwave signal at 17.682GHz is successfully obtained.

Tunable microwave generation based on a dual-wavelength single-longitudinal-mode fiber laser using a phase-shifted grating on a triangular cantilever

Frequency tunable microwave signal generation, based on a dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber (EDF) laser, incorporating a phase-shifted fiber Bragg grating (PS-FBG) with two π-phase shifts, is demonstrated. In the proposed configuration, the PS-FBG with two ultranarrow transmission bands is embedded in a triangular cantilever to serve as a wavelength spacing tunable filter with a fixed center wavelength by applying various strains on the cantilever. A section of unpumped EDF is employed as a saturable absorber to ensure SLM operation in each of the two lasing lines. By beating the two wavelengths at a photodiode, a tunable microwave signal ranging from 8.835 to 24.360 GHz is successfully achieved.

Dual-wavelength single-longitudinal-mode erbium-doped fiber laser based on inverse-Gaussian apodized fiber Bragg grating and its application in microwave generation

We propose a simple erbium-doped fiber ring laser. It consists of an inverse-Gaussian apodized fiber Bragg grating filter which has two ultra-narrow transmission bands, and an unpumped erbium-doped fiber as a saturable absorber. Stable dual-wavelength single-longitudinal-mode lasing with a wavelength separation of approximately 0.082 nm is achieved. A microwave signal at 10.502 GHz is demonstrated by beating the dual wavelengths at a photodetector.

Flat-top and ultranarrow bandpass filter designed by sampled fiber Bragg grating with multiple equivalent phase shifts

We propose a novel approach to designing an optical filter with a flat-top and ultranarrow transmission band by using a sampled fiber Bragg grating (SFBG) having multiple equivalent phase shifts (EPSs). In the proposed approach, multiple EPSs are fabricated by adjusting several sampling periods of the SFBG. The obtained multiple EPSs are then arranged properly to get a flat-top transmission band in the narrow -1st reflection band of the SFBG, leading to the generation of a flat and ultranarrow transmission band. Filters with two or five EPSs are designed by simulation and experiment, with low ripples and ultranarrow 1 dB bandwidths observed in transmission bands.

Optical Single Sideband Modulation Using an Ultranarrow Dual-Transmission-Band Fiber Bragg Grating

A novel and simple optical single sideband with carrier (SSB+C) modulation scheme implemented using an ultranarrow dual-transmission-band superstructured equivalent phase shift (EPS) fiber Bragg grating (FBG) is presented. The FBG with two ultranarrow transmission bands is created by introducing two EPSs in its structure during the fabrication process. The use of EPSs instead of true phase shifts allows the reduction of the stringent requirement for accurate phase shifts during the fabrication process. An experimental setup using the EPS FBG to implement SSB+C modulation is demonstrated. The performance of the SSB filter is studied by analyzing the eye diagrams and bit-error-rate measurements

Photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode fiber ring laser

A novel approach for the generation of high-frequency microwave signals using a dual-wavelength single-longitudinal-mode fiber ring laser is proposed and demonstrated. In the proposed configuration, a dual-wavelength fiber Bragg grating (FBG) with two ultranarrow transmission bands in combination with a regular FBG is used to ensure single-longitudinal-mode operation of the fiber ring laser. A semiconductor optical amplifier is employed as the gain medium in the ring cavity. Since the two lasing wavelengths share the same gain cavity, the relative phase fluctuations between the two wavelengths are low and can be used to generate a low-phase-noise microwave signal without need of a microwave reference source. Three dual-wavelength ultranarrow transmission-band FBGs with wavelength spacing of 0.148, 0.33, and 0.053 nm are respectively incorporated into the laser. Microwave signals at 18.68, 40.95, and 6.95 GHz are obtained by beating the dual wavelengths at a photodetector. The spectral width of the generated microwave signals as small as 80 kHz with a frequency stability better than 1 MHz in the free-running mode at room temperature is obtained.

Dual-wavelength erbium-doped fiber laser with a simple linear cavity and its application in microwave generation

A single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber (EDF) laser based on a simple linear cavity is proposed and demonstrated. The SLM operation is achieved by incorporating a dual-phase-shift fiber grating with two ultranarrow transmission bands. Due to the gain grating produced by spatial hole-burning in the EDF, the proposed linear cavity supports dual-wavelength oscillation at room temperature with a wavelength interval of 27 pm. The laser output is heterodyned on a photodetector and the generated microwave signal has a linewidth <20 kHz without any feedback.