Saied Shojaeddin - Academia.edu (original) (raw)
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Massachusetts Institute of Technology (MIT)
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Papers by Saied Shojaeddin
Optics Communications, 2018
Signal-to-noise power ratio (SNR) and capture effect of intensity-modulation direct-detection (IM... more Signal-to-noise power ratio (SNR) and capture effect of intensity-modulation direct-detection (IMDD) microwave photonic links (MWPLs) operating under small-and large-signal modulation in noise have been studied. Arbitrary N sinusoidal signals in random noise are applied at radio frequency (RF) input port of the IMDD MWPL and the output spectrum is derived using a nonlinear analytical approach. General expressions for signal and noise powers at output of the IMDD MWPL are derived. From these expressions SNR and capture effect for all values of input signal power ratios can be determined. It is shown that a) the output noise and signal power for strong and weak input signals can severely be affected by the interaction of input signals with themselves, input signals with noise and input noise with itself due to the effects of nonlinearity of the MWPL combined with sum of several input signals in noise, b) the capture effect of the IMDD MWPL in noise depends on the link input back-off, the power ratio of input signals and on the number of input signals and this dependence is severe in the large-signal regime, c) the capture effect does not depend on the noise and in the presence and absence of noise are the same, d) output SNR for strong and weak input signals depend on input SNR, power ratio of input signals and input back-off. We have shown that when MWPLs are operating in the absence of noise, our theoretical predictions for the capture effect approach the already published results on this case. Besides, we have shown that the general behavior of the ratio of the input SNR to that of the output in small-and large-signal regime, is the same as the case of one input signal in random noise (or noise figure) that have been previously published.
Journal of the Optical Society of America B, 2018
Resonator Q-factor and amplifier flicker noise are the most important parameters that determine t... more Resonator Q-factor and amplifier flicker noise are the most important parameters that determine the phase noise of microwave oscillators. The Q-factor of intermediate frequency (IF) crystal resonators at IF frequencies can be larger than that of microwave resonators at microwave frequencies. In addition, flicker noise of IF amplifiers can be less than that of microwave amplifiers. One of the well-known usual ways to implement low phase noise microwave oscillators is to use ultra-low phase noise IF crystal oscillators and frequency multipliers. In this paper a new method to implement such oscillators based on IF crystal resonators and amplifiers, called a transposedfrequency microwave oscillator, is proposed. In the proposed structure, a microwave photonic frequency transposer is used to downconvert RF to IF followed by a high-Q IF crystal filter and low flicker noise IF amplifier and then upconverting IF to RF frequency. This novel method in comparison to the well-known multiplier-based microwave oscillators presents significant advantages. In this paper, the proposed new structure is introduced, and a theoretical model is developed to study its performance. Oscillation frequency and amplitude, equivalent Q-factor, phase noise, etc., are theoretically studied and compared with the performances of the well-known microwave oscillators based on frequency multipliers and optoelectronic oscillators. It is shown that the phase noise of the proposed microwave oscillator can be less than −130 dBc∕Hz at 100 Hz from a 10 GHz carrier with a noise floor less than −165 dBc∕Hz.
Optics Communications, 2018
Signal-to-noise power ratio (SNR) and capture effect of intensity-modulation direct-detection (IM... more Signal-to-noise power ratio (SNR) and capture effect of intensity-modulation direct-detection (IMDD) microwave photonic links (MWPLs) operating under small-and large-signal modulation in noise have been studied. Arbitrary N sinusoidal signals in random noise are applied at radio frequency (RF) input port of the IMDD MWPL and the output spectrum is derived using a nonlinear analytical approach. General expressions for signal and noise powers at output of the IMDD MWPL are derived. From these expressions SNR and capture effect for all values of input signal power ratios can be determined. It is shown that a) the output noise and signal power for strong and weak input signals can severely be affected by the interaction of input signals with themselves, input signals with noise and input noise with itself due to the effects of nonlinearity of the MWPL combined with sum of several input signals in noise, b) the capture effect of the IMDD MWPL in noise depends on the link input back-off, the power ratio of input signals and on the number of input signals and this dependence is severe in the large-signal regime, c) the capture effect does not depend on the noise and in the presence and absence of noise are the same, d) output SNR for strong and weak input signals depend on input SNR, power ratio of input signals and input back-off. We have shown that when MWPLs are operating in the absence of noise, our theoretical predictions for the capture effect approach the already published results on this case. Besides, we have shown that the general behavior of the ratio of the input SNR to that of the output in small-and large-signal regime, is the same as the case of one input signal in random noise (or noise figure) that have been previously published.
Journal of the Optical Society of America B, 2018
Resonator Q-factor and amplifier flicker noise are the most important parameters that determine t... more Resonator Q-factor and amplifier flicker noise are the most important parameters that determine the phase noise of microwave oscillators. The Q-factor of intermediate frequency (IF) crystal resonators at IF frequencies can be larger than that of microwave resonators at microwave frequencies. In addition, flicker noise of IF amplifiers can be less than that of microwave amplifiers. One of the well-known usual ways to implement low phase noise microwave oscillators is to use ultra-low phase noise IF crystal oscillators and frequency multipliers. In this paper a new method to implement such oscillators based on IF crystal resonators and amplifiers, called a transposedfrequency microwave oscillator, is proposed. In the proposed structure, a microwave photonic frequency transposer is used to downconvert RF to IF followed by a high-Q IF crystal filter and low flicker noise IF amplifier and then upconverting IF to RF frequency. This novel method in comparison to the well-known multiplier-based microwave oscillators presents significant advantages. In this paper, the proposed new structure is introduced, and a theoretical model is developed to study its performance. Oscillation frequency and amplitude, equivalent Q-factor, phase noise, etc., are theoretically studied and compared with the performances of the well-known microwave oscillators based on frequency multipliers and optoelectronic oscillators. It is shown that the phase noise of the proposed microwave oscillator can be less than −130 dBc∕Hz at 100 Hz from a 10 GHz carrier with a noise floor less than −165 dBc∕Hz.