Zhao Qida

Liquid-level sensor with a high-birefringence-fiber loop mirror

A novel liquid-level sensor with a high-birefringence-fiber loop mirror (HBFLM) based on a uniform-strength cantilever beam (UCB) is proposed and demonstrated. Part of the high-birefringence fiber is pasted onto the central surface of the UCB. A hollow suspending pole is utilized to apply force at the end of the beam. The applied force varies with the change of the liquid level, leading to a change of transmission intensity. Thus the variation of liquid level can be determined via the laser wavelength within the quasi-linear transmission range of the HBFLM filter. Its sensitivity, resolution, and linear measurement range reach 0.047/cm, 10 mm, and 140 mm, respectively. The advantages of the sensor include simple structure, high sensitivity, low cost, and good repeatability, etc. The sensing signal can be directly detected by a photodetector and does not require complicated demodulation devices.

Generation of wavelength-switched optical pulse from a fiber ring laser with an F-P semiconductor modulator and a HiBi fiber loop mirror

A simple configuration to perform wavelength switching in an actively mode-locked fiber ring laser is demonstrated. A Fabry-Perot laser diode was used as a modulator and a HiBi fiber loop mirror was used as a periodic multichannel wavelength filter in the cavity. By setting the channel spacing of nm can be achieved by tuning the fiber loop mirror filter. In the wavelength-switched process, the modulation frequency was not required to be changed.

Tunable dual-wavelength actively mode-locked fiber laser with an F-P semiconductor modulator

A novel actively mode-locked fiber laser for generating dual-wavelength picosecond pulses is proposed by using a Fabry-Perot laser diode as the modulator in the ring cavity. A linear chirped fiber grating was used as a wavelength selector and produces temporal-spectral multiplexing of the pulses in the gain medium to reduce gain cross-saturation effects. About 2-GHz stable dual-wavelength pulses with a wavelength spacing of 0.92 nm at room temperature were experimentally demonstrated and the wavelengths could be tuned in a range of about 3 nm.

Pulse-amplitude equalization in a rational harmonic mode-locked fiber ring laser by using modulator as both mode locker and equalizer

A simple method, by letting the pulses pass through an electrooptic intensity modulator twice, for the amplitude equalization of high repetition rate pulses generated from a p-order rational harmonic mode-locked fiber ring laser when p<5 was proposed. The modulator was used as both a mode locker and a pulse-amplitude equalizer in the cavity. A theoretical explanation based on time-domain analysis was used to find appropriate parameters to obtain an equalized pulse train and the experimental results agree with the theory.

Principles and realizations of FBG wavelength tuning with elastic beams

The general principles and realizations of FBG wavelength tuning with elastic beams are proposed and demonstrated. Theories and experiments show that when displacement at the center point of simple beams, deflection of cantilever beams and torsion strain of torsion beams are relatively small, Bragg wavelength shifts of sensing FBGs have linear relationship with applied external stress, lateral displacement, torque and torsional angles, respectively. The experimental results indicate that the curvature sensitivity of the simple beam is 1.65 nm/m−1, the displacement sensitivity of the equivalent-strain cantilever beam is 4.4 cm/kg and the torque and torsional angle sensitivities of the torsion beam are 6.27 nm/Nm and 0.0867 nm/degree, respectively.

Temperature-independent stress and displacement bidirectional sensing tuned by an applied bilateral cantilever beam

A novel and simple approach of temperature-independent stress and displacement bidirectional sensing tuned by an applied bilateral cantilever beam is proposed and demonstrated. The 3dB bandwidth of fibre gratings is linear with respect to the stress and displacement in the tuning range of 16 nm. The sensing sensitivities of the stress and displacement are 5.76 nm/N and 0.941 nm/mm, respectively.

The correlation setting of the optical pickup head's laser beam measuring equipment

For industrial producing, the same type of manufacturing equipment may lead to some product with different quality. In order to compare the measuring results of different machine easily and correctly we develop one kind of correlation setting method. We use a standard evaluator to evaluate 18 pieces of optical pickup head and record the data. Then we use one measuring equipment to measure the above 18 pieces of optical pickup head and record the data. Through comparing the skew R and skew T data of the above two group data, we can know the primary correlation coefficient of the skew R and skew T. If the coefficient is small or the offset is big we should set the correlation. Through modifying the correlation coefficient related terms and offset related terms, measuring and comparing again and again, we can control the correlation coefficient and offset in the range we wanted. Through correlation setting, we can compare the result of different measuring machine and we can determine the different error we can accept for different producing processes. It suggests that such kind of correlation setting is useful and necessary for industrial production.