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Crow Delay Lines on a Silicon Platform

Slow light is emerging as a promising approach for applications where the dynamic control of the delay is required, such as data synchronization, time multiplexing, and data storage [1]. Coupled-resonator optical waveguides (CROWs) [2] have exhibited advantageous features like on-chip integration, delay tunable, large bandwidth, and transparency to modulation format, and so on. The numerical simulation for CROWs from the device level requires too much simulation resource and is not realistic. It is mainly done with circuit-level tools, such as OptSim, based on analytical or measurement coupling coefficients. Using the S-Matrix utility combined with OptSim Circuit, the design and optimization of CROWs can be realized with a device-level numerical approach.

Figure 1 shows a top view of fabricated CROWs [2]. It consists of eight ring resonators with a radius of 20µm. The silicon waveguide has a 480x220nm^2 cross-section and is buried in a silica cladding. Note that the yellow parts depict the heating wire for modulation (not modeled in this simulation).

Fig. 1: Top View of 8 ring CROW | Synopsys

Fig. 1: Top View of 8 ring CROW [2]

Figure 2 shows the waveguide-to-ring and ring-to-ring coupling geometries and spectra calculated with the S-Matrix Utility. Due to symmetry, we only need to calculate two input ports for the waveguide-to-ring coupling (Fig. 2a) and only one input port for the ring-to-ring coupling (Fig. 2b).

Two input ports for the waveguide-to-ring coupling | Synopsys

(a)

The ring-to-ring coupling | Synopsys

(b)

Fig. 2: (a) Waveguide-to-ring coupling geometry and corresponding spectra for input at Port 1 and Port 2;   (b) ring-to-ring coupling geometry and the spectra for input at Port 1

We use OptSim Circuit to build the CROW device as shown in Figure 3. 

Fig. 3: The compound component of 8 ring CROW created in OptSim Circuit | Synopsys

Fig. 3: The compound component of 8 ring CROW created in OptSim Circuit

The power spectrum and the group delay plots obtained from OptSim Circuit simulations are shown in Figure 4. In this way, by combing system circuit tool and device tools, we have realized a device-level simulation for a CROW system. The simulation includes the effect of material dispersion, bending waveguide loss, and so on. The custom PDK model approach helps model larger, passive photonic devices as photonic circuits in OptSim Circuit, thereby bringing computational efficiency as compared to rigorous, device level simulations. As an example, the FDTD simulation of one of the rings in the CROW device of Figure 1 took around 16 hours to converge, while the entire PIC of Figure 4 took a few seconds to simulate in OptSim Circuit. 

Fig. 4: The power spectrum and group delays for 8 ring CROWs | Synopsys

Fig. 4: The power spectrum and group delays for 8 ring CROWs

For more information, please contact photonics_support@synopsys.com. 

Download Design Files

References: 

  1. A. Melloni, F. Morichetti, C. Ferrari, and M. Martinelli, "Continuously tunable 1 byte delay in coupled-resonator optical waveguides," Opt. Lett. 33, 2389-2391 (2008).
  2. A. Canciasmilla, C. Ferrari, “Reconfigurable CROW Delay Lines on a Silicon Platform” Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference.