Electronically tunable silicon photonic delay lines

Abstract

Electronically tunable optical true-time delay lines are proposed. The devices utilize the combination of apodised gratings and the free-carrier plasma effect to tune the enhanced delay of silicon waveguides at a fixed wavelength. Three variations of the proposed scheme are studied and compared. The compact and integrable devices can achieve tuning ranges as high as ~660 ps with a loss of < 2.2 dB when operated in the reflection mode of the gratings. A delay of ~40 ps with a loss of < 10 dB and an estimated operation bit rate of ~20 Gb/s can be achieved.

Demonstration of complementary apodized cascaded grating waveguides for tunable optical delay lines

“…For either apodization, the time delay can be tuned by changing the refractive index of the core waveguide material (silicon) by changing its temperature, through the thermo-optic effect as demonstrated here or through the electro-optic effect, as we have proposed elsewhere [2]. As the refractive index of silicon increases with temperature, the delay spectra of both grating devices are redshifted.…”

“…Continuously tunable, true-time optical delay lines are important components for a host of photonic systems applications [1][2][3]. Historically, delay lines based on fiber Bragg gratings (FBGs) have been used.…”

“…cavity formed by the sharp ends of the grating, prevent using the device as an optical delay line in the transmission mode. This problem can be solved by apodizing the grating profile [2], and the performance can be enhanced if two complementary apodized grating waveguides are cascaded [3]. Figure 1(b) schematically depicts such cascaded waveguides and their individual and combined dispersioncompensating delay spectra for transmission-mode operation.…”

“…Transmission coefficients of the structures were calculated and optimized by using the standard transfer matrix method [2,3]. The commercial simulation software COMSOL is used to determine the effective refractive index of each corrugated section of the gratings.…”

Silicon Quantum Photonics

“…This can be achieved, for example, using nonlinear interactions [123], [124] but such memories are, for now, difficult to manufacture and integrate, and have a significant control overhead. Plasma dispersion based tunable delay lines have been demonstrated on silicon [125], but they have inherent losses and their single-photon operation has not yet been tested. Discrete programmable delay lines can be made from several different optical structures [126]: CROWs [127], photonic crystals [128], or sequences of unbalanced MZIs [129].…”