Shenglai Zhen

Study of speckle pattern effect for self-mixing laser diodes in vertical-cavity surface-emitting lasers

We present a theoretical analysis and a comparison to experimental results on self-mixing interference. From the theoretical analysis and experiment, the error of the velocity measurement, which is caused by a speckle pattern, has been investigated and optimization of the laser diode velocity system by selecting suitable experiment parameters and proper signal processing methods has been reported. The actual measurement error is <3.1% over a wide velocity range (5.2-479 mm/s).

Controlling optical bistability of acceptor and donor quantum dots embedded in a nonlinear photonic crystal

We investigate the optical bistability and multistability in donor and acceptor quantum dots embedded in a nonlinear photonic crystal inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the corresponding parameters of the system. The effect of the dipole–dipole interaction has also been included in the formulation, which leads to interesting phenomena. Our scheme opens the possibility to control the optical bistability and multistability in photonic materials doped with nanoparticles.

Temperature-Independent Ultrasensitive Fabry–Perot All-Fiber Strain Sensor Based on a Bubble-Expanded Microcavity

A fiber Fabry-Perot interferometer (FPI) based on a bubble-expanded microcavity is investigated in this paper. Due to the expanded bubble microcavity, the FPI exhibits high strain sensitivity of 30.66 pm/με. To the best of our knowledge, such strain sensitivity is three to ten times higher than that of the fiber FPIs based on the microcavities previously reported. The strain response of the FPI with different shapes is analyzed, and the experimental results are consistent with the theoretical analysis.

A fiber micro-vibration sensor based on single-mode fiber ring laser

A new micro-vibration sensor based on single-mode fiber ring laser is put forward. The Mach-Zehnder interferometric (MZI) detection technique is presented for interrogating laser frequency shift due to the measurand (piezoelectric transducer (PZT) is used to simulate the micro-vibration) induced laser cavity strain from both single- and multi-mode lasers. In the experiment, compared with multi-mode laser sensors, the single-mode laser sensor is proved to be a sensor with high resolution. When the PZT is driven by the analog signal (0.03 rad near 2 kHz), the signal-to-noise ratio (SNR) of output signal from the single-mode laser sensor is close to 55 dB and the sensitivity of the sensor is about 5\times10^{-5} rad/Hz^{1/2}.

Remote Low-Coherence Fiber Vibrometer With Wide Dynamic Range

We present a remote low-coherence fiber vibrometer, which is composed of a hybrid configuration of Mach-Zehnder and Sagnac interferometer. In the interferometer, the signal and reference beams travel along the same path but in opposite directions. Owing to the fiber differential interferometric theory and a passive demodulation algorithm, absolute amplitude at a distance more than 1 m could be measured. The experimental results demonstrate that the vibrometer has a wide dynamic range for amplitude measurement from 4.34 pm to 2.43 mm. The deviation of measured amplitude is less than 0.8 dB, and the frequency response range is 30 Hz-11 kHz. The proposed method is potentially suitable for applications that require noncontact and high-dynamic-range measurements.

Single-mode fiber sensor based on core-offset splicing

An inter-mode interferometer based on a simple single-mode fiber by core-offset splicing is presented. Through manually adjusting the horizontal displacement and the angle of two sections of core-offset fiber, we can achieve maximum interference spectrum. Then we add a reflector at the end of the last single-mode fiber. This reflector can lead the light to propagate twice in the offset single mode fiber structure so that we can get larger interference intensity, in the experimental process we see a better extinction ratio. The proposed method can find application in strain, temperature and vibration measurements and so on. By measuring the extinction ratio (ER) variation or wavelength shift of the interference pattern in this paper, sensitivity measurement can be achieved. The sensitivity of strain and temperature without reflector is respectively 10.38 pm με and 31pm/ °C. When reflector added, it can increase the sensitivity of the strain and temperature at a certain degree.

A new fiber-optic microphone based on waveguide modulator

A new fiber-optic microphone was demonstrated theoretically and experimentally in this paper. The microphone is based on Mach-Zehnder and Sagnac interferometers, which comprise an amplified spontaneous emission (ASE) light source, a conventional single-mode fiber, a fiber reflector and two 3dB couplers. As two light paths have the same optical length but travel different sequence paths in this hybrid interferometer, the beams in different paths pass through the sensing fiber at different times and the phase signals differ from each other. Utilizing the two light paths interfered and fiber waveguide modulator replaced by piezoelectric ceramic (PZT) modulation, to implement the direct acquiring of weak voice signals. Adoption of the ASE light source and the single-mode fiber as sensing fiber decreases the system cost. The application of the fiber waveguide modulator overcomes the limitation in high frequency and nonlinear effect of PZT modulation, improves the flexibility of the system and the frequency response range. Phase shifts of the two interfered beams, which is caused by the slowly varying environmental parameter, is equal to eliminate the influence from outside effectively. In this system, the signal demodulation circuit based on weak voice signal is simpler than the PGC demodulation circuit. The experimental results of the fiber-optic microphone based on waveguide modulator have been demonstrated that the simple circuit demodulation for the weak voice signal is feasible.

An improved PGC demodulation algorithm of interferometric sensor for eliminating the intensity disturbance

A modified phase generated carrier (PGC) demodulation algorithm for interferometric sensor is presented in this letter. Compared with the differential-cross-multiplying measure (PGC-DCM algorithm), the effect of light intensity disturbance (LID) is eliminated. Additionally, the harmonic distortion of arctangent measure (PGC-arctan algorithm) is well suppressed. In the experiment, while the simulated LID frequency is settled to 50 Hz, the signal-to-noise of the improved PGC algorithm respectively receives an increase of 10.3 dB and 18.2 dB over PGC-DCM and PGC-Arctan algorithms. The system has a dynamic range of 45.9 dB at 600 Hz by employing the improved PGC demodulation algorithm.

Sensing with slow light in an active fiber Bragg grating

The phase-shifted sensitivity of an interferometer can be enhanced by increasing the group index. In this paper, we experimentally demonstrate a slow light sensor by placing an active fiber Bragg grating (FBG) in one arm of the Michelson’s interferometer. A 25 KHz AC voltage was applied to a piezoelectric (PZT) set nearby the active FBG. Once the wavelength is varied to near the FBG band edge, the maximum phase-shifted amplitude appears, which is about 1.8 rad and is 4 times greater than that when wavelength is near the center of the reflection band. The active FBG is pumped by a 980 nm laser diode, which can help us to stabilize the system works in the slow light regime to obtain the maximum phase shift. It provides a very simple approach to increase the phase-shifted sensitivity, which is likely to have important applications for strain and acoustic sensors.

Non-contact gas leakage detection of tank based on low-coherence optical fiber interferometer

In this paper, a method for non-contact detecting the acoustic signal of tank gas leakage based on low-coherence optical fiber interferometer is presented. Vibration signals which caused by acoustic field of gas leakage are detected by low-coherence interference. The experimental results show that the vibration signals are wideband signals (0 Hz~90 KHz). While increasing the internal pressure, high-frequency components of the frequency spectrum have an obvious increasing trend, the amplitude and energy of the acoustic signal will both increase. The minimum detectable internal pressure of tank is 0.12MPa. The sensor is simple and reliable, and has a good practicability.