We have previously demonstrated that indirect excitons (IXs) in GaAs quantum well structures can be efficiently transported by SAWs. Here, we combine a network of SAW with electrostatic gates to realize an acoustic exciton multiplexer (EXAM) for the interconnection of IX systems separated by millimeter distances on a chip. Figure 1(a) shows the structure of an EXAM with 8 input/output ports (I/Oi, labeled by the port index i=1,...,8). Each I/O port contains an interdigital transducer (IDT, not shown) to generate an outgoing SAW beam as well as an IX acoustic transistor (EXAT). In the EXAT, the voltage applied to the gate electrode (Gi) is used to separate the port electrode (Si) from the common drain electrode, where multiplexing takes place. In each I/O port, IXs can be stored or reconverted to photons by selecting an appropriate source voltage to control their recombination lifetime.
The IXs are optically generated at one of the ports (e.g. S1). IX transfer between two facing I/O ports (e.g., ports 1 and 4 in Fig. 1(a)) can be carried out by simply turning on the SAW beam connecting them. Multiplexing function relies on the transfer of IXs between two orthogonal acoustic beams (e.g., from SAW1 to SAW2 or SAW3) at their intersection. Here, a moving array of potential dots created by the interference of the two SAW beams captures the IXs from one beam and transfers them to the other.
The transfer of IXs from SAW1 to either SAW2 or SAW3 is demonstrated by the photoluminescence (PL) images of Fig. 1(b) and 1(c), respectively. When SAW2 (SAW3) is switched ON, IXs transported by SAW1 to the intersection area are captured by the moving potential dots and transferred to SAW2 (SAW3). IXs can then be reversibly transferred between any two ports by appropriately switching on at most three SAW beams.
The EXAM combines IX storage, inter-conversion to photons, long-range transport, and multiplexing. It not only delivers a proof-of-concept for all-exciton optoelectronic device but also offers a platform to investigate non-linear interactions as well as collective phenomena involving IXs.