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

Abstract

High-speed, tunable integrated silicon photonic delay lines are demonstrated by cascading complementary apodized silicon grating waveguides. The cascaded grating waveguides, with inward and outward super-Gaussian apodization profiles, compensate each other's dispersion and allow high-speed operation. Characterization of the compact delay lines shows that they have low loss, offer true time delays of 82 ps and a tuning range of 32 ps, and can potentially operate at bit rates as high as 107 Gb/s.

Silicon Photonics for Microwave Photonics Applications

“…For example, while SWG waveguides can support both large as well as small total or incremental delays, continuous tuning will be more challenging to achieve. On the other hand, wavelength variable ODLs, including the use of resonance enhancements based on coupled resonators [7,50,51,53] or slow light effects in photonic crystal waveguides [52,57] or the dispersive properties of grating structures [55,56] (all in SOI) allow readily for continuous tuning. The tuning range, however, is typically limited from tens to ~ 200 ps.…”

“…There are a number of ways to implement an optical delay passively, i.e., without gain, and these can be broken down in two broad approaches: (1) variation of the propagation length (L) of the delay element (i.e., the delay Δt is given by L/v g where v g is the propagation group velocity), also known as a length variable delay line [43][44][45][46][47][48][49] and (2) variation of the propagation group velocity (v g ), also referred to as a variable propagation velocity line and for some implementations, a wavelength variable delay line [50][51][52][53][54][55][56][57][58][59]. These two approaches encompass employing a fixed length of waveguide, fiber, or free space as the delay medium, as well as resonance enhancements, whereby the physical length of the delay medium is enhanced, e.g., through a cavity or exploiting a material resonance where dispersion can be large.…”

Integrated optical delay lines: a review and perspective [Invited]

“…In a uniform grating, the group delay at the bandgap edge increases considerably, as shown in Fig. 8(a) [74] . The tuning of delay is obtained by shifting the grating stopband by heating or free-carrier injection.…”

“…The BG has a stopband width of 1 nm and an extinction ratio (ER) of 35 dB. The group delay can be continuously tuned [74] . by an integrated heater.…”

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].…”