Continuously tunable delay line based on SOI tapered Bragg gratings

Abstract

The realization of an integrated delay line using tapered Bragg gratings in a drop-filter configuration is presented. The device is fabricated on silicon-on-insulator (SOI) rib waveguides using a Deep-UV 248 nm lithography. The continuous delay tunability is achieved using the thermo-optical effect, showing experimentally that a tuning range of 450 ps can be obtained with a tuning coefficient of -51 ps/°C. Furthermore the system performance is considered, showing that an operation at a bit rate of 25 Gbit/s can be achieved, and could be extended to 80 Gbit/s with the addition of a proper dispersion compensation.

Tunable optical delay line based on integrated grating-assisted contradirectional couplers

“…Compared to the parameter in Refs. [30] (9.6 dB/ns) and [31] (21 dB/ns), the device loss can be further reduced by waveguide mode optimization. In conclusion, the apodization method can improve the performance of Bragg gratings in terms of spectral flatness, delay line linearity, and optical loss.…”

“…However, these two tuning techniques are just in the theoretical design stage. Combining tapered Bragg gratings and thermo-optical effect, continuously tunable delay lines based on silicon-on-insulator (SOI) tapered Bragg gratings have also been proposed and verified experimentally [30,31]. Although tunable linear delay lines with low loss and wide band have been realized, they are still far from being ready for use in grating-assisted delay lines.…”

“…The general chirp types of Bragg gratings are index chirping and period chirping. Index chirping is chosen here because linear variation of the effective index is more robust than varying the grating period [30,31]. The grating period of Λ is kept the same along the transmission direction with duty cycle of 50%.…”

Generating UWB and Microwave Waveforms Using Silicon Photonics

“…These include delay lines based on photonic crystals, coupled ring resonators, and various Bragggrating structures such as serial grating arrays, step-chirped gratings, continuously chirped gratings, and cascaded gratings. With grating structures, delays up to several hundreds of ps spanning a few nm or tens of ps spanning broader wavelength ranges are readily accessible [19], [32]- [34].…”

“…For the uniform Bragg grating, we use a period Λ = 320 nm, a waveguide width W 1 = 500 nm, a corrugation depth ΔW = 10 nm, and 3,000 periods. The chirped Bragg grating is based on tapering the waveguide width [32]. We also use Λ = 320 nm, ΔW = 10 nm, and 10,000 periods; the waveguide width W 1 varies linearly from 500 nm to 510 nm from one end of the grating to the other (corresponding to a grating chirp of C ∼ 0.26 nm/mm).…”