Requirements for true time delay imaging systems with photonic components

Abstract

In this paper, we generalize the phase and amplitude requirements of microwave components, within true time delay imaging systems, to include photonic devices. An analytic expression for the relationship between the optical and RF transfer functions is suggested for double sideband modulation and the effect of optical phase ripple on RF transfer function is simulated for an optical component such as a chirped Bragg grating. The effect of phase ripple on the system impulse response is considered.

Small signal analysis for analogue optical links with arbitrary optical transfer function

“…Previous works assumed the optical devices to be characterised by an all-phase transfer function [1][2][3], where the optical phase, was approximated by a finite order Taylor expansion around the optical centre frequency. However, present day optical devices have more complex transfer functions, including both phase and amplitude variations, at higher RF frequencies (millimetre waves) and with ever-wider RF bandwidths [4], requiring a more generalised matrix. This Letter derives such a matrix, valid for small signal modulation.…”

Hybrid Optical Beam-Former in Receiver Mode

“…In receiving, the quality and the signal's impulse response also have a higher priority. Previous report suggested that optical beamformers using chirped grating do not perform well in reception [12]. However, the system in [12] did not use the hybrid approach.…”

“…In the worst case with additional amplitude fluctuations from all devices, the main beam gain was decreased by 2.57 dB and the sidelobe level was increased by 0.6 dB. The simulated pattern's 3dB beam width is increased by As analyzed in [11,12], the fluctuations in group delay characteristic of the grating force many limitations on the optical beamformer using chirped grating. Since the proposed beamformer uses a chirped grating, its robustness against the GDR error should be tested.…”

“…Since the proposed system use chirped grating, the effect of group delay ripples (GDR) has also been addressed. As studied in [11,12], the GDR has a strong negative impact on the performance of optical beam-former using chirped grating in transmission operation. The study in [12] also suggested that grating may not be suitable for receiving operation.…”

“…As studied in [11,12], the GDR has a strong negative impact on the performance of optical beam-former using chirped grating in transmission operation. The study in [12] also suggested that grating may not be suitable for receiving operation. However, simulations have shown that our proposed hybrid system is more robust against GDR.…”