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Two passive plasmonic demultiplexers with multimode interferometer (MMI) based rectangular and bow-tie designs are demonstrated for 1.31- and 1.55-μm-band wavelength division multiplexing system operation in plasmonic circuits. These demultiplexers are designed using the finite-difference time-domain (FDTD) method and fabricated using complementary metal–oxide–semiconductor compatible processes. SiO2 films deposited on metal films are etched to form mesa structures by focused ion beam milling, and single-mode waveguides, MMIs, and bow-tie structures are then formed on the metal films. In the plasmonic circuits, 1.31- or 1.55-μm-wavelength surface plasmon polariton (SPP) signals can be distributed to each of the different demultiplexer outputs without any change in signal propagation speed. The SPP intensity distributions that are measured using a scanning near-field optical microscope agree well with the distributions that were calculated using the FDTD method. The insertion loss and crosstalk are then calculated for each demultiplexer. In the rectangular-type demultiplexer, the calculated values were less than 9.5 dB and –2.4 dB, and in the bow-tie-type demultiplexer, the corresponding values were 8.9 dB and less than –2.3 dB, respectively. These results demonstrate the applicability of the developed plasmonic demultiplexers to plasmonic circuits when monolithically integrated on a silicon substrate.

We have analyzed the propagation behavior of 1.31-and 1.55-μm-wavelength-band surface plasmon polaritons (SPPs) for three simple Si-based plasmonic waveguides: the Au stripe waveguide, the SiO2 stripe waveguide, and the Au/SiO2 stripe waveguide on a Si substrate. The SPP propagation length in the waveguide varied depending on the waveguide structure and propagation lengths for waveguides with different structural parameters are summarized. The energy that was required for SPP detection after propagation along the waveguides for the 1.31- and 1.55-μm-wavelength bands was calculated for intensity-modulation direct-detection and heterodyne frequency-shift keying systems. The results demonstrate that SPPs can propagate with lower energy consumption than conventional electric wiring below a specific interconnect length. A wavelength-selective structure for SPPs that comprised nano-slits in an Au film on an Si substrate was fabricated. The device can selectively detect 1.31-μm-wavelength SPPs as electrical signals and transmit 1.55-μm-wavelength SPPs. Experimental photoresponses and transmittances were measured and compared with calculated results. Magnitude correlation of the measured and calculated photoresponses and transmittances showed good agreement. Evaluation of the SPP propagation behavior and the wavelength-selective structure are important considerations for the development of optoelectronic integrated circuits that use SPPs and electrons as signal carriers.

This paper presents a feasibility study of optical interconnections using surface plasmon polaritons (SPPs) as coherent carrier waves in a silicon-based electrical circuit. A gold film plasmonic waveguide and a gold/silicon Schottky-type plasmonic detector were monolithically integrated with an electrical circuit based on metal–oxide–semiconductor field-effect transistors on a silicon substrate. A 1550-nm-band laser source was used for SPP excitation, and the photocurrent generated by the plasmonic detector was amplified 16 000 times by the monolithically integrated electrical circuit after SPPs carrying the optical intensity signal propagated over the gold film surface for a distance of 100 μm. The integrated circuit detected an optical beat signal by using a delayed self-homodyne technique, thus demonstrating that SPPs can be used as coherent carrier waves in the circuit. Additionally, optical amplitude- and frequency-modulated signal transmission in a gold film plasmonic waveguide and optical heterodyne detection by amplification of the signal intensity in a gold/silicon Schottky-type plasmonic detector were also demonstrated.

Using metal plasmonic waveguides as transmission lines for optical signals and an electrical bias is shown to be feasible in Si-based devices with a separation gap formed between the waveguide and Au/Si Schottky-barrier diode (SBD). Optical signal transmission is confirmed by calculating the radiation pattern from the waveguide edge and measuring the photocurrent detected at the SBD. From a finite-difference time-domain simulation, the radiation pattern from the waveguide edge is represented as an interference fringe. The simulation result for the separation-length dependence of the detected photocurrent at the SBD corresponds well with experiment. Moreover, the intensity-modulated optical signal at 10 MHz is also observed across the 3-μm-length separation gap. The electrical bias separation is confirmed by applying a bias voltage between the waveguide and the Si substrate and generating a bias current through the waveguide. The detected photocurrent at the SBD barely increased with changing bias voltage and was clearly smaller than that under changes in optical intensity. In addition, electrical current produced no influence on the surface-plasmon signal on the waveguide.