On-chip Nonreciprocal Light Storage

We demonstrate non-reciprocal light storage based on stimulated Brillouin scattering in a planar highly nonlinear waveguide. The bandwidth of this scheme approaches a GHz, has wide frequency tunability and scales linearly with data power

Uni-directional optical signal processing is of key interest for integrated photonic circuits as it allows to suppress distortions from spurious reflections. Storing light as coherent sound waves is an intriguing and powerful concept for delaying optical signals. It was shown that optical data pulses can be transferred to acoustic waves in optical fiber [1] and, more recently, in integrated circuits [2]. The coupling between the optical and acoustic waves has to fulfill a strict phase matching condition, which was exploited in silica fiber-tip resonators to realize non-reciprocal signal delays [3,4].

Here, we demonstrate that breaking time-reversal symmetry in the Brillouin interaction can be used for uni-directional light storage in a waveguide. Data that travels in one direction is stored and delayed while data propagating in the opposite direction is not delayed and does affect the storage process. Furthermore, we show that this storage scheme scales linearly with data power, is tunable over a wide frequency range, and has an extinction of more than 10 dB. At the same time, it has a wide bandwidth of almost a GHz, exceeding the intrinsic acoustic linewidth by more than an order of magnitude.

The dispersion diagram of the backward SBS process that is applied in the Brillouin light storage is shown in Fig. 1a). It shows that the acoustic wave generated from the interaction of optical data pulses and counter-propagating “write” pulses is not phase-matched for data pulses that propagate in the opposite direction. Figure 1b) shows experimental measurements of a data signal that is delayed by 4 ns when traveling in one direction, while a data stream simultaneously propagating in the opposite direction at the same optical frequency is not interacting with the Brillouin storage process or the acoustic wave present in the waveguide.

Fig. 1. a) Phase matching diagram for backward stimulated Brillouin scattering. b) Non-reciprocal light storage: data traveling in one direction is delayed by 4 ns while the simultaneously counter-propagating data is not affected (inset).

Email: moritz.merklein@sydney.edu.au