High speed optical modulator is a key device for contemporary optical communication networks, which plays an important role in the constructions of optical cross-connect and inter-connect systems. Thanks to the rapid development of photonics integration, the research on integrated optical modulators has obtained great attention. As optical modulator based on SOI platform has the advantages of small size, low power consumption, high integration, and fast response, it has gradually become a research hotspot at home and abroad. However, SOI compatible optical modulator still needs further improvements and optimizations in the loss, size, power consumption, modulation depth and so on. Addressing the problems above, many practical solutions and design ideas were presented in this paper. Moreover, SOI optical waveguide modulators based on different physical effects (thermo-optic, carrier-dispersion, electro-optic, and all-optic) were also investigated theoretically and experimentally.
A MZI-type 1×2 thermo-optic switch based on photonics-SPP hybrid integration is proposed in this paper. The phase modulation arms are composed of dielectric-loaded SPP waveguides, while other parts of MZI structure consist of Si waveguides. Compared with the conventional Si-based thermo-optic modulators, this switch has combined low propagation loss of Si waveguide with small size and high thermo-optic modulation efficiency of dielectric-loaded SPP waveguide. The length of modulation arm is only 70 μm, the power consumption is 7 mW, the response time is 6.7 μs, and the insertion loss of device is limited below 10 dB.
An n-p-n type and carrier-dispersion based plasmonic electro-absorption modulator taking advantage of highly doped Si waveguide is presented. Making Si to acquire metal-like properties by heavy doping can help to support the propagation of SPP waves, which is utilized to decrease the size of device due to its strong mode confinement capacity. Compared to the most p-i-n type Si-based modulators, the modulation extinction ratio of our device is improved with extreme high doping carrier concentration. Multiphysics simulation results have revealed that although the footprint of modulation area of device is only 1 μm2, its modulation depth could reach 25 dB, which also owns a modulation frequency of 2 GHz.
Addressing the weak electro-optical properties of Si, a heterogeneous electro-optic ring modulator that combines Si waveguides with PLZT thin film is proposed in this paper. The size of device is reduced effectively with the adoption of high refractive index Si as core layer, and an obvious electro-optic effect can be achieved through selecting PLZT film with large electro-optic coefficient as cladding layer. Besides, a large modulation depth of 32 dB and a high modulation frequency of 14 GHz are obtained by optimizing the configurations of integrated electrodes. Meanwhile, an asymmetric Au-PLZT-Au electro-optic ring modulator based on SPP waveguides is also designed here, which shows both excellent electro-optical properties of PLZT and strong optical mode confinement capacities of SPP waveguide. The size of this modulator is only 20 μm2, and the modulation depth is larger than 25 dB.
A power efficient and high integration all-optic modulator based on Si-SPP hybrid structure is presented here. And the plasmonic Fano waveguide modulation device is fabricated experimentally, which is the core part of the proposed all-optic modulator. The Au plasmonic nanocavity with compact structure is used as modulation unit, while Si waveguides with low propagation loss are utilized to transmit optical signals. Adopting signal light that is parallel to the chip surface to excite plasmonic modes in the nanocavity ‘horizontally’ is realized so that the pump light can incident perpendicular to the chip. The experimental results confirm that the plasmonic nanocavity could exhibit highlighted Fano resonance within the wavelength range of 1514 ~ 1600 nm, and the transmission spectrum varied with the change of structural parameters of nanocavity. Besides, the simulation result reveals that the device owns a high refractive index sensitivity of 1600 nm/RIU.