| In magneto-optic (MO) film waveguides, the interaction between guided-optical waves (GOWs) and magnetostatic waves (MSWs) excited by the RF signal within microstrip line under external bias magnetic field may lead to the Bragg diffraction effect and mode conversion of the GOWs. The microwave signal can be processed in optical-domain by the MO Bragg diffraction effect, which can be used as a new approach for studying microwave photonics. Similar to acoustooptic (AO) devices, the MO Bragg modulator and correlator can be realized by the MO effects induced by magnetostatic waves. Besides, the MO Bragg devices have advantages on much simpler design of the transducer, larger bandwidth, higher operating frequency (0.5~40GHz) and faster modulation speeds, which have a very attractive prospect in RoF systems, radar and spread spectrum communications.The interaction between continuous MSWs and continuous GOWs is very well researched, but MO information processing has hardly been quantitatively analyzed until now. In this article, the characteristics of the MO pulse modulation induced by magnetostatic forward volume waves (MSFVWs) pulses and the MO correlation processing are analyzed.The main contents and innovations are as follows:1. The coupled-mode equations for the GOWs modulated by MSFVW pulse is deduced through the perturbation theory and the numerical method for the equations is introduced in detail. The diffracted pulse obtained from the numerical solution is basically agreement with the experimental result. In the slow-varying envelope approximation, the complex amplitude of diffracted light pulse is given under the phase-matching conditions and a simple analytical method for analyzing the MO modulation is proposed in the small signal case. It is shown that, the diffracted pulses, respectively obtained by the two methods in the case of small phase mismatch, are in agreement with each other.2. According to the analytical method, the MO Bragg modulation by using rectangular pulses is theoretically studied in detail. It is shown that, the diffracted light pulses approximate to an isosceles trapezoid, and the duration time and the flat-top response time are equal to the sum and difference between the width and transit time of the rectangular MSFVW pulse, respectively; the rise or fall edge of diffracted light pulse is the parabolic distribution; when the MSW duty factor is less than 0.5, the modulating data rate can be improved, but the relative peak intensity of the diffracted light pulse is reduced. The conclusions are very useful for designing MO Bragg modulators.3. The operating principle of MO space-integrating correlators is described and the analytic expressions of heterodyne detection for the single and double diffracted light are given. It is shown that the detection of the single diffracted light has a larger signal to noise ratio than the double diffracted light detection, but the the former is more complicated.4. Taking barker code as an example, the output characteristics of MO space-integrating correlators and the performance influenced by the intensity of microwave RF signals are discussed. It is shown that, the output width of MO correlators is a half of that of the general; in the range of small signals, the peak value of normalized envelope is approximately proportional to the RF-driven power and the MO correlation can be strictly realized with the processing gain of 20dB or more. |
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