Optimization and Analysis of Magnesium Doping in MOCVD Grown p-GaN

p-type conductivity and crystal quality of Mg-doped GaN grown by MOCVD have been improved through opti- mization of the magnesium flow rate. The hole concentration first increased and then decreased with the magnesium flow rate while the mobility decreased monotonously. The optimum sample reached a hole concentration of 4. 1×10^17cm -3 and a resistivity of 1Ω·cm. Based on a self-compensation model involving the deep donor Mo, VN, we calculate the hole con- centration as a function of magnesium doping concentration NA ,which indicates that the self-compensation coefficient in- creases with NA;the hole concentration first increases with NA and reaches a maximum at NA≈4×10^19 ,then decreases rapidly as doping concentration increases. XRD also indicate that dislocation density decreased as magnesium flow rate decreased.

High gain fiber-solid hybrid double-passing end-pumped Nd:YVO4 picosecond amplifier with high beam quality

We propose a fiber-solid hybrid system which consists of a semiconductor saturable absorber mirror(SESAM)modelocked fiber seed with a pulse width of 10.2 ps and a repetition rate of 18.9 MHz,a two-level fiber pre-amplifier and a double-passing end-pumped Nd:YVO4 amplifier.In the solid-state amplifier,to enhance the gain and the extraction efficiency,a specially designed structure in which the seed light passes through the gain medium four times and makes full use of population inversion is used as the double-passing amplifier.Besides,the beam filling factor(the ratio of the seed light diameter to the pump light diameter)and the thermal lens effect of the double-passing amplifier are considered and its optical-to-optical conversion efficiency is further improved.To preserve the beam quality of the double-passing amplifier,a new method of spherical-aberration self-compensation based on the principles of geometrical optics is used and discussed.Our system achieves a maximum average power of 9.5Wat the pump power of 28W,corresponding to an optical-to-optical efficiency of 27%.And the beam quality factor M^2 reaches 1.3 at the maximum output power.

A New 1-V Second-Order Temperature-Compensated Current Reference

A new bipolar temperature-compensated current reference is proposed. The first-order temperature compensation is achieved by the idea of self temperature-compensation configuration exploiting the temperature coefficient of a combined resistor. The second-order compensation employs a VBE-tracking thermal-startup technique to obtain improved temperature performance. The proposed circuit can operate down to a 1-V supply. A temperature coefficient of 46.6×10?6/℃ [0, 100℃] at a 1-V supply and a supply regulation of 0.036%/V at 25℃ are achieved. Compared with present works, the proposed circuit shows better results of the temperature coefficient and supply regulation. The current matching issue frequently encountered in current references is also discussed in detail.

One Novel Type of Miniaturization FBG Rotation Angle Sensor With High Measurement Precision and Temperature Self-Compensation

In order to achieve rotation angle measurement, one novel type of miniaturization fiber Bragg grating （FBG） rotation angle sensor with high measurement precision and temperature self-compensation is proposed and studied in this paper. The FBG rotation angle sensor mainly contains two core sensitivity elements （FBG1 and FBG2）, triangular cantilever beam, and rotation angle transfer element. In theory, the proposed sensor can achieve temperature self-compensation by complementation of the two core sensitivity elements （FBG1 and FBG2）, and it has a boundless angel measurement range with 2π rad period duo to the function of the rotation angle transfer element. Based on introducing the joint working processes, the theory calculation model of the FBG rotation angel sensor is established, and the calibration experiment on one prototype is also carried out to obtain its measurement performance. After experimental data analyses, the measurement precision of the FBG rotation angle sensor prototype is 0.2° with excellent linearity, and the temperature sensitivities of FBG1 and FBG2 are 10 pro2℃ and 10.1 pm/℃, correspondingly. All these experimental results confirm that the FBG rotation angle sensor can achieve large-range angle measurement with high precision and temperature self-compensation.

Design and Investigation of a High-Sensitivity Tilt Sensor Based on FBG

In this paper,a high-sensitivity fiber Bragg grating(FBG)tilt sensor using a cantilever-based structure is introduced.Two FBGs are fixed on a specially designed elastomer.One end of the elastomer is connected to the mass block,and the other end is connected to the shell.The principle of the tilt sensor is introduced in detail,and the mathematical model is established.The performance of the sensor is studied.The results show that there is a good linear relationship between the central wavelength difference of the two FBGs and the tilt angle in the range of-5°to 5°.The repeatability of the sensor is good,and the tilt sensitivity can reach 231.7 pm/°.The influence of the silicone oil on the damping capacity of the sensor is studied.The results show that the damping capacity of the sensor has been improved by sealing the silicone oil inside the shell of the sensor.The field test is carried out on a pier of an elevated bridge,and the result is good,which verifies the practicability of the sensor.