Electro-optic comb based real time ultra-high sensitivity phase noise measurement system for high frequency microwaves

Abstract

Recent progress in ultra low phase noise microwave generation indispensably depends on ultra low phase noise characterization systems. However, achieving high sensitivity currently relies on time consuming averaging via cross correlation, which sometimes even underestimates phase noise because of residual correlations. Moreover, extending high sensitivity phase noise measurements to microwaves beyond 10 GHz is very difficult because of the lack of suitable high frequency microwave components. In this work, we introduce a delayed self-heterodyne method in conjunction with sensitivity enhancement via the use of higher order comb modes from an electro-optic comb for ultra-high sensitivity phase noise measurements. The method obviates the need for any high frequency RF components and has a frequency measurement range limited only by the bandwidth (100 GHz) of current electro-optic modulators. The estimated noise floor is as low as −133 dBc/Hz, −155 dBc/Hz, −170 dBc/Hz and −171 dBc/Hz without cross correlation at 1 kHz, 10 kHz, 100 kHz and 1 MHz Fourier offset frequency for a 10 GHz carrier, respectively. Moreover, since no cross correlation is necessary, RF oscillator phase noise can be directly suppressed via feedback up to 100 kHz frequency offset.

A photonic frequency discriminator based on a two wavelength delayed self-heterodyne interferometer for low phase noise tunable micro/mm wave synthesis

“…The PFD is based on a two wavelength delayed self-heterodyne interferometer (TWDI) 24 – 26 as shown in Fig. 1a .…”

“…From these relations, L mix (f) is Here, L OEO (f) is phase noise PSD of the OEO, respectively. Note that phase noise of the cw laser is cancelled out in the mixing process 26 . By feeding back to a modulator in the OEO, using L mix (f) as an error signal, phase noise of the OEO is reduced.…”

High-sensitivity optical to microwave comparison with dual-output Mach-Zehnder modulators

“…This suggests that a direct comparison between an optical reference pulse train and a microwave signal could greatly improve the achievable sensitivity and the dynamic range of microwave phase noise measurements. Recently, optical delay lines 14 – 17 , Sagnac loop fiber interferometers 9 , 18 , and dual-output Mach-Zehnder modulator (DO-MZM)-based phase detectors 19 have been demonstrated. When used as phase detectors, DO-MZMs are simple to calibrate, provide a direct link between optical and microwave oscillators and offer a high sensitivity.…”

Self-calibrating and high-sensitivity microwave phase noise analyzer applying an optical frequency comb generator and an optical-hybrid-based I/Q detector

“…Compared with the work in Ref. [10], the proposed PNA is free from complex calibration and interferences from the amplitude noises of the SUT and the laser. Compared with our previous work using an I ∕Q mixer for phase noise measurement [7], the proposed PNA is free from additional procedures to deal with the dc component that is undesirable in zero-intermediate-frequency signal processing.…”

“…In Ref. [10], a cost-effective real-time ultra-high-sensitivity PNA based on an optical frequency comb (OFC) generator is proposed. By processing the selected nth order comb lines, which carry the n-times magnified phase noise of the signal under test (SUT), the measurement sensitivity of the PNA can be significantly improved.…”