Abstract
We describe a procedure to calculate the impulse response and phase noise of high-current photodetectors using the drift-diffusion equations while avoiding computationally expensive Monte Carlo simulations. We apply this procedure to a modified uni-traveling-carrier (MUTC) photodetector. In our approach, we first use the full drift-diffusion equations to calculate the steady-state photodetector parameters. We then perturb the generation rate as a function of time to calculate the impulse response. We next calculate the fundamental shot noise limit and cut-off frequency of the device. We find the contributions of the electron, hole, and displacement currents. We calculate the phase noise of an MUTC photodetector. We find good agreement with experimental and Monte Carlo simulation results. We show that phase noise is minimized by having an impulse response with a tail that is as small as possible. Since, our approach is much faster computationally than Monte Carlo simulations, we are able to carry out a broad parameter study to optimize the device performance. We propose a new optimized structure with less phase noise and reduced nonlinearity.
Highlights
Phase noise in the photodetectors is a critical limiting factor in many RF-photonic applications [1, 2], in metrology applications in which excess phase noise inherent in the photodetection process limits the extent to which the low noise of an optical pulse train from an optical frequency comb can be transferred to the microwave domain [2]
Later experiments showed that while there is a significant reduction in the phase noise as the pulse duration decreases, this decrease in the phase noise ceases once the optical pulse duration becomes small compared to the duration of the electrical pulse that emerges from the photodetector [7]
We compare the impulse response of the modified uni-traveling-carrier (MUTC) photodetector to the results of Sun et al
Summary
Phase noise in the photodetectors is a critical limiting factor in many RF-photonic applications [1, 2], in metrology applications in which excess phase noise inherent in the photodetection process limits the extent to which the low noise of an optical pulse train from an optical frequency comb can be transferred to the microwave domain [2]. The resulting fluctuations in the timing of the impulses manifest themselves as phase noise on the microwave harmonics of the optical pulse repetition frequency [4,5,6] This approach must be modified in a high-current photodetector, in which space charge effects due to the large number of carriers in the device affect the impulse response and the carrier fluctuations. We use the drift-diffusion equations [9, 10], combined with the observation that the arrival of electrons in any time interval is Poisson-distributed, to calculate the phase noise This approach takes minutes on a desktop computer, as opposed to the many hours on a computer cluster that the Monte Carlo approach requires. This definition is consistent with the one of Quinlan et al [3] and Sun et al [8] In order to verify that our results are independent of the choice of τ and r, we ran numerical tests in which we allowed these quantities to vary
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