Zhichen Gu

GaInAsP/InP-based optical modulator consisting of gap-surface-plasmon-polariton waveguide: theoretical analysis

We propose a III–V-based electro-absorption plasmon modulator that can be used to construct fully monolithic plasmonic integrated circuits. Our device consists of a GaInAsP/InP gap-surface-plasmon-polariton waveguide with TiO2/ITO layers on both sides of the InGaAsP core. Using this design, the intensity of transmitted light can be modulated by controlling the carrier concentration of the ITO layer, as a positive gate voltage induces electron accumulation in the ITO layer (this is similar to the operation of FinFETs). The extinction ratio was 4.5  dB/μm with a gate voltage swing of 0–5, and the insertion loss was found to be 1.5  dB/μm. The figure of merit (ratio of extinction ratio to transmission loss) is 3, a result that is far superior to other conventional Si-based plasmonic photomodulators.

Study of a slow-light-enhanced membrane photodetector for realizing on-chip interconnection with low power consumption

Slow-light propagation can be used to enhance light–matter interactions such as material loss and gain, which enables the realization of ultracompact photonic devices toward the ultralow-power-consumption on-chip or chip-scale optical interconnection. We designed a slow-light-enhanced waveguide-type GaInAs p–i–n photodetector (PD) by using the three-dimensional finite-difference time domain method. As a result, it was found that a cut-off frequency of 19.6 GHz with moderate output voltage, which was attributed to the high impedance characteristic, can be obtained with a 5.5-μm-long PD.

Integrated Optical Link on Si Substrate Using Membrane Distributed-Feedback Laser and p-i-n Photodiode

On-chip optical interconnection is a promising technology for wiring future large-scale integrated circuits, as a means to mitigate the considerable power dissipation of traditional wiring layers. Here, we fabricate an integrated optical link using a membrane distributed-feedback (DFB) laser and a p-i-n photodiode (PD) in a butt-jointed built-in coupling geometry. The optical link is formed on a Si substrate by benzocyclobutene bonding. The integrated DFB laser shows a low-threshold current of 0.48 mA. Light transmission between the DFB laser and the p-i-n PD is confirmed with static measurements of the optical link. The optical link has a 3-dB bandwidth of 11.3 GHz at a 2.73 mA DFB laser bias current and a –3 V p-i-n PD bias voltage. A data transmission experiment of the optical link is performed, using a nonreturn to zero, pseudorandom-bit-sequence with a word length of 231-1 signals. With a DFB laser bias current of 2.5 mA, 10 Gbit/s data transmission with a bit-error-rate of 6 × 10–7 is successfully achieved.

Organic membrane photonic integrated circuits (OMPICs)

We propose the concept of organic membrane photonic integrated circuits (OMPICs), which incorporate various functions needed for optical signal processing into a flexible organic membrane. We describe the structure of several devices used within the proposed OMPICs (e.g., transmission lines, I/O couplers, phase shifters, photodetectors, modulators), and theoretically investigate their characteristics. We then present a method of fabricating the photonic devices monolithically in an organic membrane and demonstrate the operation of transmission lines and I/O couplers, the most basic elements of OMPICs.

Analysis of plasmonic phase modulator with furan–thiophene chromatophore electro-optic polymer

We analyzed two types of Mach-Zehnder plasmonic modulators on a silicon-on-insulator platform with a different furan-thiophene chromophore electro-optic polymer to compare to other reports. The metal-taper coupling structure and the metal-insulator-metal cross section in our design have been optimized based on the new material parameters. According to the simulation result, a modulator with a slot width of 50 nm and an on-off voltage of Vπ=20  V can be 21 μm long, leading to a total modulator loss of 15 dB, which is comparable to previously reported devices.

Optical interconnection between III–V chips on Si by using photonic wire bonding

We connected two III-V laser and photodiode chips on Si substrate by using three-dimensional polymeric wires based on two-photon polymerization. We achieved an enhancement of the transmitting efficiency through PWB compare to the free-space transmission.

Analysis of plasmonic Mach-Zehnder modulator with metal taper structure embedded in FTC-EO polymer

We analyzed a Mach-Zehnder plasmonic modulator with metal-insulator-metal structure embedded by the Furan-Thiophene Chromophore. π-phase shift between two Mach-Zehnder arms can be obtained with a device length of 6.5 μm and the figure of merit of 3.1.

Optical transmission between III-V chips on Si using photonic wire bonding

Photonic wire bonding (PWB) was used to achieve flexible chip-scale optical interconnection as a kind of 3D-freeform polymer waveguide based on the two-photon polymerization of SU-8. First, the fabrication conditions of PWB were determined for the two-photon absorption process, and the coupling structure between PWB and III-V optical components was numerically simulated in order to obtain high coupling efficiency. Then, using PWB, chip-to-chip optical transmission was realized between laser and detector chips located on a common Si substrate. We fabricated a 2.5-μm-wide PWB with 1:3 aspect ratio between two optical chips of 140-μm gap and achieved a connection loss of approximately 10 dB.