Photonic radio frequency phase-shift amplification by radio frequency interferometry

Abstract

We present a new technique for radio frequency (RF) phase-shift amplification based on RF interferometry and demonstrate it in an optical system. A striking feature of this amplifier is that the input phase noise is not amplified together with the input phase signal, so the phase sensitivity improves with higher phase amplification. We also predict that in the case of correlated amplitude noise, the sensitivity is not affected by the amplitude noise. With 600 MHz of modulated light and a phase amplification of 100, we demonstrate a phase resolution of 0.2 mrad, giving a distance resolution of 8 μm. We postulate that nanometric distance resolution can be achieved with sub-gigahertz modulation.

High-resolution, on-chip RF photonic signal processor using Brillouin gain shaping and RF interference

“…Constructive interference may be achieved if the two signals are in phase; alternatively destructive interference is achieved if the phase offset between the two signals is ±π. The vector sum can also result in the change of the phase of the RF signal resulting in phase amplification 54–56 . In practice, we achieved RF interference by encoding the RF signals into the optical domain using a modulation format with arbitrary amplitudes and phase in each sideband (achieved by using a phase modulator and a programmable optical filter) and mixing the processed signals through photodetection.…”

“…Similar to an EIT resonance, a corresponding sharp phase slope resulting in an analogous slow-light effect 59 is also expected in this case. This is due to a vector-sum between two RF signals resulting in phase amplification 54 . The zeroes placed adjacent to the passband can increase the slope at the edges even further.…”

“…Next, on switching on the lower sideband, RF interference resulted in the introduction of zeroes at the edge of the passband, causing phase amplification by more than an order of magnitude within the passband of the filter. This can be explained through a vector sum addition of two RF signals: the upper sideband and the lower sideband which can be represented by two vectors 54 . In previous approaches, phase amplification has been achieved in a notch filter, where the signal experiences loss 55 .…”

Brillouin-based phase shifter in a silicon waveguide

“…It has previously been shown that a phase shift can be enhanced using interferometry [27][28][29]. However, so far these schemes have only been applied over a relative narrow bandwidth [27][28][29]. Here, on the other hand, we propose and demonstrate a phase enhancement scheme that has a broad bandwidth of sev-eral GHz through acting on the carrier.…”

“…So by applying a narrowband phase shift to the carrier, a broadband RF phase shifter can be achieved. It has previously been shown that a phase shift can be enhanced using interferometry [27][28][29]. However, so far these schemes have only been applied over a relative narrow bandwidth [27][28][29].…”