A frequency swept source optical coherence tomography (OCT) imaging system is proposed. The frequency swept source used in the system is a Fourier-domain mode-locked (FDML) laser which has a narrow instantaneous linewidth due to the nonlinear spectrum narrowing effect generated by the nonlinear semiconductor optical amplifier (SOA) used in the FDML laser ring cavity. Therefore, the OCT imaging system has the ability to achieve a large imaging depth. The concept is verified in the experiment, which demonstrates a clear two-dimensional target image and a large imaging depth up to 14 mm.
We propose and demonstrate a high-resolution and high-sensitivity tunable liquid refractive index (RI) sensor interrogated using a microwave photonic filter (MPF) with two taps implemented based on optical polarization orthogonality. In the structure, a fiber laser with its wavelength determined by a microfiber Bragg grating (mFBG) is employed as a light source. A chirped fiber Bragg grating (CFBG) is incorporated in one tap, and an optical tunable delay line (TDL) is included in the other tap. The sensing information is encoded in the laser wavelength caused by the RI change, which will cause a change in the time delay difference between the two taps due to the wavelength-dependent group delay of the CFBG, which would result in a change in the MPF frequency response. By monitoring the spectral response, the sensing information is detected. The spectral response of the MPF is tuned by controlling the length of the TDL, which would lead to a change in the sensor sensitivity. An experiment is performed. The results show, for three TDL time delays of 300 ps, 400 ps and 500 ps, the liquid RI sensitivities are 50.621 GHz/ RIU, 37.293 GHz/RIU and 26.015 GHz/RIU, respectively, and the corresponding resolutions are 8.0253×10-5 RIU, 1.0893×10-4 RIU and 1.5616×10-4 RIU.
A real-time gas vacuum sensor interrogated based on a microwave photonic method at high speed and high resolution is proposed and demonstrated. The sensor is a microfiber Mach-Zehnder interferometer (mMZI) with its wavelength sensitive to the gas concentration. Instead of detecting the wavelength shift of the mMZI spectrum in the optical domain, we convert the mMZI spectrum to the time domain by spectral shaping and wavelength-to-time (SS-WTT) mapping and apply a digital signal processor (DSP) to realize the cross-correlation to estimate the wavelength shift of the mMZI. The sensitivity and resolution of the proposed gas vacuum sensor are -0.586 ps/ppm and 34.13 ppm with a concentration range from 0 to 1.4×104 ppm, respectively.
Microwave signal with high frequency and low phase noise is generated based on a parity-time (PT) symmetric optoelectronic oscillator (OEO). The PT-symmetric OEO based on normal and reversed traveling-wave modulation is formed by normal and reversed modulation in a travelling-wave intensity modulator (IM) using the radio-fiber (RF) input and termination ports. Gain and loss balance can be realized to achieve PT symmetry thanks to the different modulation efficiencies for microwave signals applied via different RF ports. The operation of the proposed OEO has been experimentally verified. A microwave signal is generated at 10 GHz with a phase noise of -110.7 dBc/Hz at an offset frequency of 10 kHz and a sideband suppression ratio of 46.46 dB. The approach has potential applications in high-quality microwave signal generation and simplify the structure of PT-symmetric OEO system.
As a typical tumor suppressor and transcription factor in cancer biology, p53 protein is involved in DNA repair, the cell cycle regulation and programmed cell death. The p53 protein in human blood can be linked with tissue alterations for more than 50% human cancer, and its concentration can be used for early-stage cancer diagnostics and related risk assessments. In this work, we demonstrated a high resolution biomedical sensor. It is based on a micro Bragg fiber grating (mFBG) as a sensing probe to form lasing in a fiber laser ring resonant cavity. It is able to detect the p53 protein by measuring the fiber laser wavelength via the optical wavelength meter (OWM). Compared with the traditional sensing system based on the full-spectrum measurement, a higher signal-to-noise ratio and more stable output can be obtained, which improves the wavelength resolution and measurement speed. The optical fiber biomedical sensor successfully maintains its specificity for p53 protein, and has a promising application in clinical oncology diagnosis.
A high speed TFBG-SPR sensing demodulation system based on microwave photonics interrogation is proposed theoretically. The wavelength shifting of the SPR envelope in optical domain is converted to the microwave pulse shifting in time domain. The RI resolution is improved by one order of magnitude compared with wavelength demodulation, and the sensing speed is as high as 40 KHz.
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