High-performance Ge/Si electro-absorption optical modulator up to 85°C and its highly efficient photodetector operation

We studied a high-speed Ge/Si electro-absorption optical modulator (EAM) evanescently coupled with a Si waveguide of a lateral p–n junction for a high-bandwidth optical interconnect over a wide range of temperatures from 25 °C to 85 °C. We demonstrated 56 Gbps high-speed operation at temperatures up to 85 °C. From the photoluminescence spectra, we confirmed that the bandgap energy dependence on temperature is relatively small, which is consistent with the shift in the operation wavelengths with increasing temperature for a Ge/Si EAM. We also demonstrated that the same device operates as a high-speed and high-efficiency Ge photodetector with the Franz-Keldysh (F-K) and avalanche-multiplication effects. These results demonstrate that the Ge/Si stacked structure is promising for both high-performance optical modulators and photodetectors integrated on Si platforms

Modulation bandwidth improvement of III-V/Si hybrid MOS optical modulator by reducing parasitic capacitance

In this work, we numerically and experimentally examined the impact of parasitic capacitance on the modulation bandwidth of a III-V/Si hybrid metal-oxide-semiconductor (MOS) optical modulator. The numerical analysis revealed that the parasitic capacitance between the III-V membrane and the Si slab should be considered to achieve high-speed modulation, particularly in the case of a thick gate oxide. We also fabricated a high-speed InGaAsP/Si hybrid MOS optical modulator with a low capacitance using a SiO2-embedded Si waveguide. The fabricated device exhibited a modulation efficiency of 0.245 Vcm and a 3 dB bandwidth of up to 10 GHz. Clear eye patterns with 25 Gbps non-return-to-zero (NRZ) modulation and 40 Gbps 4-level pulse amplitude modulation (PAM-4) were obtained without pre-emphasis

Graphene perfect absorber based on degenerate critical coupling of toroidal mode

Graphene is a two-dimensional material with great potential for photodetection and light modulation applications owing to its high charge mobility. However, the light absorption of graphene in the near-infrared range is only 2.3%, limiting the sensitivity of graphene-based devices. In this study, we propose a graphene perfect absorber based on degenerate critical coupling comprising monolayer graphene and a hollow silicon Mie resonator array. In particular, monolayer graphene achieves perfect absorption by controlling the periods and holes of the Mie resonators. The proposed graphene perfect absorber can significantly improve the sensitivity of graphene-based devices.Rongyang Xu, Junichi Fujikata, and Junichi Takahara, "Graphene perfect absorber based on degenerate critical coupling of toroidal mode," Opt. Lett. 48, 1490-1493 (2023

112 Gb/s PAM-4 Silicon Photonics Receiver Integrated With SiGe-BiCMOS Linear TIA

We have developed a silicon photonics receiver integrated with a SiGe-BiCMOS linear transimpedance amplifier (TIA) using the flip-chip bonding technology to assist in resolving the I/O bottleneck problem in inter-chip data communication. The proposed device demonstrated optical 112 Gb/s four-level pulse amplitude modulation (PAM-4) operations and clear eye openings without any equalization for the pseudorandom binary sequence 215 – 1 signal. The 3 dB bandwidth and transimpedance gain were designed to be 37.1 GHz and 60.1 dBΩ, respectively, at a supply voltage of 3.3 V. The consumption current of the linear TIA was 95.1 mA, and it resulted in a power consumption of 314 mW (2.8 pJ/bit). A linear TIA circuit is a key technology for PAM-4 operation; therefore, we discussed the linearity of our receiver response through eye diagrams and simulation. The measured eye diagrams agreed with the simulation results, and the proposed device maintained a linear response for up to 450 μAp-p input current. In addition, its operation rate of 112 Gb/s is the highest operation rate reported for a silicon photonics PAM-4 receiver based on flip-chip 3D integration with a germanium photodetector and a SiGe-BiCMOS linear TIA

Direct Bandgap Control by Narrowing the Germanium Strip Structure on Silicon for C+L Band Photonic Devices

This study reports the bandgap engineering of a Ge epitaxial layer on Si to tune the operating wavelength of optical intensity modulators and photodetectors in the C (1.530–1.565μm)+L (1.565–1.625 μm) band. A strip structure of elemental Ge is investigated, rather than wider-gap SiGe or narrower-gap GeSn alloy, to achieve the key property of a C band modulation and improved L band detection. By narrowing the strip to the submicron scale, a tensile lattice strain in Ge, induced by a thermal expansion mismatch with Si, is elastically relaxed by an edge-induced relaxation effect. The photoluminescence peak and photodetection spectra show a significant blue shift as the narrowed direct gap of ~0.77 eV is restored to 0.80 eV of unstrained Ge. A standard SiNx external stressor on a narrow Ge strip induces an increased blue shift or an opposite red shift, depending on the stress polarity in SiNx. The results show that it is possible to tune the operating wavelength of modulators and photodetectors of elemental Ge in the C+L band

Supplementary document for Hybrid distributed Bragg reflector laser on Si with a transfer printed InAs/GaAs quantum dot amplifier - 6826388.pdf

supplemental documen