Study On The Interference-type Optical Current Sensor

To meet the challenge of global warming, various technologies which are energy saving have emerged all around the world. Developing high-tech industries becomes an inevitable trend of world economy. Under this background, many countries focus their eyes on the development of smart grid to seize the commanding heights of future low-carbon economy. The core feature of the smart grid is that the operating voltage/current level of the power system is ultra-high. Thus, the current sensing device used in the smart must have the ability to measure large current. As traditional electromagnetic induction current transformers have shortcomings such as saturation, poor transient response, insulation difficulties and high operating cost disadvantages, they cannot fit the requirements of smart grid construction. Comparing with the traditional electromagnetic induction current transformers, the optical current sensors have many great advantages, such as inherent insulation, immunity to electromagnetic interference, wide dynamic range, safety, small size and light weight, thus they are the best choice of the next generation current sensor. This paper mainly studies the interference-type optical current sensors. High-performance optical current sensors are proposed and demonstrated in this paper to detect the large/small current in the power system with high sensitivity and accuracy. The main contribution and specialty of this paper is manifested in the following areas:1. All fiber current sensors based on Faraday Effect was proposed and demonstrated. (1) The basic theory of the reflective fiber-optic current sensor was studied comprehensively. The error model of the current sensor was established to determine the optimal parameters of the devices used in the sensing system. (2) The optical current sensing system which was based on the backward used Y waveguide was propped and demonstrated. Meanwhile, the four-channel lock-in amplifier was developed to demodulate the output signal of the sensor accurately. The test results show that the accuracy of the proposed current sensor meet the requirement of IEC 0.2S. (3) The mode-lock fiber laser current sensor was proposed to simplify the demodulation method of the reflective fiber-optic current sensor. On the other hand, the structure of the reflective fiber-optic current sensor was modified and a new magnetic sensor which can detect magnetic field in any direction of the plane was proposed.2. An ultra-sensitive integrated photonic current sensor which incorporates a silicon-based single mode-multimode-single mode waveguide (SMSW) structure was proposed and experimentally investigated. This kind of SMSW structure is placed over a direct current carrying power resistor, which produces the Joule’s heat to change the temperature of the SMSW and further result in the change of the effective refractive index between different propagating modes. Interference occurs when the modes recombined at the second single mode waveguide. Finally, the current variation was measured by monitoring the shift in the output spectrum of the multimode interferometer. This effect can be used as a current sensor with a slope efficiency of 4.24nm/A in the range of 0-200mA.3. Optical current sensors based on silicon ring resonator were proposed and experimentally investigated. The TiN heater was integrated with the ring. The sensitivity of the current sensor based on single-ring resonator reaches up to. Last but not least, a compact silicon photonic current sensor based on dual-ring resonator was proposed and demonstrated. This senor don’t need the wavelength demodulation device. The output power of the designed dual-ring resonator is highly sensitive to the effective refractive index of the propagating TE mode. The current flowing through the integrated resistive TiN heater produces Joule’s heat and changes the temperature, which results in the change of refractive index of the TE mode. Finally, the output power of the dual-ring resonator is changed. A photoelectric detector is used to measure the change of the output power. Our experiments show that the proposed sensor achieves a sensitivity of (1575dbm/A) and good linearity in the test range of 0-6mA.