Nanoscale on-chip all-optical logic parity checker in integrated plasmonic circuits in optical communication range

The nanoscale chip-integrated all-optical logic parity checker is an essential core component for optical computing systems and ultrahigh-speed ultrawide-band information processing chips. Unfortunately, little experimental progress has been made in development of these devices to date because of material bottleneck limitations and a lack of effective realization mechanisms. Here, we report a simple and efficient strategy for direct realization of nanoscale chip-integrated all-optical logic parity checkers in integrated plasmonic circuits in the optical communication range. The proposed parity checker consists of two-level cascaded exclusive-OR (XOR) logic gates that are realized based on the linear interference of surface plasmon polaritons propagating in the plasmonic waveguides. The parity of the number of logic 1s in the incident four-bit logic signals is determined, and the output signal is given the logic state 0 for even parity (and 1 for odd parity). Compared with previous reports, the overall device feature size is reduced by more than two orders of magnitude, while ultralow energy consumption is maintained. This work raises the possibility of realization of large-scale integrated information processing chips based on integrated plasmonic circuits, and also provides a way to overcome the intrinsic limitations of serious surface plasmon polariton losses for on-chip integration applications.

logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(b3). Strong scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "0011", we etched two coupling grating connected with triangular air grooves in the input port of plasmonic waveguide C and D, as shown in Fig. S1(c1), which makes that the SPP mode can be excited in plasmonic waveguide C and D, and no SPP mode can be excited in the plasmonic waveguides A and B. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(c2). There is a very weak signal output from the decoupling grating of the output waveguide O with an intensity of 0.005 au. Both the outputs of the two XOR gates in the first level was "0", which makes that the output of the XOR gate in the second level become "0". This indicates that the incident four-bit logic signal "0011" has an even parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(c3). No scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "0101", we etched two coupling grating connected with triangular air grooves in the input port of plasmonic waveguide B and D, as shown in Fig. S1(d1), which makes that the SPP mode can be excited in plasmonic waveguide B and D, and no SPP mode can be excited in the plasmonic waveguides A and C. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(d2). There is a very weak signal output from the decoupling grating of the output waveguide O with an intensity of 0.004 au. Both the outputs of the two XOR gates in the first level was "1", which makes that the output of the XOR gate in the second level become "0". This indicates that the incident four-bit logic signal "0101" has an even parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(d3). No scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "0110", we etched two coupling grating connected with triangular air grooves in the input port of plasmonic waveguide B and C, as shown in Fig. S1(e1), which makes that the SPP mode can be excited in plasmonic waveguide B and C, and no SPP mode can be excited in the plasmonic waveguides A and D. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(e2). There is a very weak signal output from the decoupling grating of the output waveguide O with an intensity of 0.006 au. Both the outputs of the two XOR gates in the first level was "1", which makes that the output of the XOR gate in the second level become "0". This indicates that the incident four-bit logic signal "0110" has an even parity of logic "1". The To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "1000", we etched one coupling grating connected with triangular air grooves in the input port of plasmonic waveguide A, as shown in Fig. S1(f1), which makes that the SPP mode can be excited in plasmonic waveguide A, and no SPP mode can be excited in the plasmonic waveguides B, C and D. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(f2). There is a strong signal output from the decoupling grating of the output waveguide O with an intensity of 33 au. The outputs of the two XOR gates in the first level were "0" and "1", respectively, which makes that the output of the XOR gate in the second level become "1". This indicates that the incident four-bit logic signal "1000" has an odd parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(f3). Strong scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "1010", we etched two coupling grating connected with triangular air grooves in the input port of plasmonic waveguide A and C, as shown in Fig. S1(g1), which makes that the SPP mode can be excited in plasmonic waveguide A and C, and no SPP mode can be excited in the plasmonic waveguides B and D. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(g2). There is a very weak signal output from the decoupling grating of the output waveguide O with an intensity of 0.003 au. Both the outputs of the two XOR gates in the first level was "1", which makes that the output of the XOR gate in the second level become "0". This indicates that the incident four-bit logic signal "1010" has an even parity of logic "1". The To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "1011", we etched three coupling grating connected with triangular air grooves in the input port of plasmonic waveguide A, C and D, as shown in Fig. S1(h1), which makes that the SPP mode can be excited in plasmonic waveguide A, C and D, and no SPP mode can be excited in the plasmonic waveguide B. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(h2). There is a strong signal output from the decoupling grating of the output waveguide O with an intensity of 40 au. The outputs of the two XOR gates in the first level were "1" and "0", respectively, which makes that the output of the XOR gate in the second level become "1". This indicates that the incident four-bit logic signal "0010" has an odd parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(h3). Strong scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "1100", we etched two coupling grating connected with triangular air grooves in the input port of plasmonic waveguide A and B, as shown in Fig. S1(i1), which makes that the SPP mode can be excited in plasmonic waveguide A and B, and no SPP mode can be excited in the plasmonic waveguides C and D. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(i2). There is a very weak signal output from the decoupling grating of the output waveguide O with an intensity of 0.005 au. Both the outputs of the two XOR gates in the first level was "0", which makes that the output of the XOR gate in the second level become "0". This indicates that the incident four-bit logic signal "1100" has an even parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(i3). No scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "1101", we etched three coupling grating connected with triangular air grooves in the input port of plasmonic waveguide A, B and D, as shown in Fig. S1(j1), which makes that the SPP mode can be excited in plasmonic waveguide A, B and D, and no SPP mode can be excited in the plasmonic waveguide C. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(j2). There is a strong signal output from the decoupling grating of the output waveguide O with an intensity of 38 au. The outputs of the two XOR gates in the first level were "0" and "1", respectively, which makes that the output of the XOR gate in the second level become "1". This indicates that the incident four-bit logic signal "0010" has an odd parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(j3). Strong scattering signal can be obtained from the output waveguide O, which confirms the measured results.
To discriminate the parity of the number of logic "1" for the incident four-bit logic signal "1110", we etched three coupling grating connected with triangular air grooves in the input port of plasmonic waveguide A, B and C, as shown in Fig. S1(k1), which makes that the SPP mode can be excited in plasmonic waveguide A, B and C, and no SPP mode can be excited in the plasmonic waveguide B. The measured CCD image under excitation of a 1560 nm CW laser is shown in Fig. S1(k2). There is a strong signal output from the decoupling grating of the output waveguide O with an intensity of 38 au. The outputs of the two XOR gates in the first level were "0" and "1", respectively, which makes that the output of the XOR gate in the second level become "1". This indicates that the incident four-bit logic signal "1110" has an odd parity of logic "1". The calculated electric-field distribution of the all-optical parity checker under excitation of a 1560 nm CW laser is shown in Fig. S1(k3). Strong scattering signal can be obtained from the output waveguide O, which confirms the measured results.