We propose and demonstrate a photonic approach to instantaneous frequency measurement with an extended range based on phase modulation.In the measurement system,two optical wavelengths and two dispersion fiber segments are used to construct the frequency-dependent amplitude comparison functions(ACFs).Several ACFs can be utilized jointly to determine the microwave frequency without ambiguities beyond a monotonic region of the lone conventional ACF.The measurable range of microwave frequency can be extended and the accuracy can be improved by selecting an ACF with a large slope.The experimental results show that the errors are limited within ±140 MHz of a frequency measuremental range from 8 to 20 GHz.
A theoretical model of the erbium-doped waveguide ring laser is established according to the theory of erbium-doped waveguide amplifier and the transmission matrix of waveguide directional coupler. The influence of bend radius, coupling coefficient and doped erbium ion concentration on the characteristics of waveguide ring laser is investigated. It is shown that due to the co-action of waveguide bend loss and other relevant loss there is an optimal bend radius which can provide simultaneously low threshold pumping power and high laser light output power. As one part of the resonator's loss, the laser light coupling coefficient of directional coupler has an impact on the laser property. The analysis indicates that the laser achieves the high output power when the coupling coefficient is about 0.2. The threshold pumping power is the minimum when the doped erbium ion concentration is 0.85×1026 m-3. Increasing the concentration of doped erbium ions will enhance the output power of laser light as long as the concentration doesn't introduce remarkable up-conversion effect. The results give a good theoretical basis for the design and fabrication of erbium-doped waveguide ring laser devices.
A photonic approach for measuring microwave frequency over a wide bandwidth is proposed.An optic group delay line composed of several magneto-optical switches and a 1.6-km single-mode fiber is used as a tunable dispersive medium in the measurement setup.A minimum frequency accuracy of 80 MHz in the range of 1-20 GHz is achieved experimentally.
