Abstract
High-fidelity photodetection enables the transfer of the low noise inherent to optical oscillators to the microwave domain. However, when photodetecting optical signals of the highest timing stability, photodiode flicker (1/f) noise can dominate the resulting timing jitter at timescales longer than ~1 ms. With the goal of improving femtosecond-level timing fidelity when transferring from the optical to microwave domain, we vary the duty cycle of a train of optical pulses and show that the photodetector flicker phase noise on a photonically generated 1 GHz microwave signal can be reduced by ~10 dB under ultrashort pulse illumination, reaching as low as -140/f dBc/Hz. In addition, a strong correlation between amplitude and phase flicker noise is found, implying a single baseband noise source can modulate both quadratures of the microwave carrier. These findings expand the limits of the ultimate timing stability that can be transferred from optics to electronics.
Highlights
Photonic systems offer a compelling solution for microwave signal generation, processing, and dissemination thanks to the low noise of optical sources, the broad bandwidth supported by optical fiber and components, and the ability to transmit over large distances with extremely low loss [1]
As stated above, the model only predicts the ratio of A√M and phase modulation (PM) values and not the absolute level, the center of the shaded region was chosen to lie on LAMLPM for each pulse width
Flicker noise in photonically generated 1 GHz microwave signals resulting from the detection of optical pulse trains has been shown to be unequally distributed between amplitude and phase quadratures
Summary
Photonic systems offer a compelling solution for microwave signal generation, processing, and dissemination thanks to the low noise of optical sources, the broad bandwidth supported by optical fiber and components, and the ability to transmit over large distances with extremely low loss [1]. Photonics can outperform traditional microwave techniques in areas such as low noise signal generation [2]–[6], timing synchronization [7], [8], arbitrary waveform generation [9], and high-speed signal processing [10], [11]. In such applications, high-fidelity optical-to-electrical conversion is nearly always required such that the microwave signal that has been generated or processed optically can be delivered to the end user. Generating ultrastable microwaves with instability below 10−15 at 1 second derived
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