Heterogeneously integrated ITO plasmonic Mach\u2013Zehnder interferometric modulator on SOI

Rubab Amin,Ray T. Chen,Jacob B. Khurgin,Elham Heidari,Volker J. Sorger,Hamed Dalir,Mario Miscuglio,Yaliang Gui,Can Suer,Rishi Maiti

doi:10.1038/s41598-020-80381-3

Abstract

Densely integrated active photonics is key for next generation on-chip networks for addressing both footprint and energy budget concerns. However, the weak light-matter interaction in traditional active Silicon optoelectronics mandates rather sizable device lengths. The ideal active material choice should avail high index modulation while being easily integrated into Silicon photonics platforms. Indium tin oxide (ITO) offers such functionalities and has shown promising modulation capacity recently. Interestingly, the nanometer-thin unity-strong index modulation of ITO synergistically combines the high group-index in hybrid plasmonic with nanoscale optical modes. Following this design paradigm, here, we demonstrate a spectrally broadband, GHz-fast Mach–Zehnder interferometric modulator, exhibiting a high efficiency signified by a miniscule VπL of 95 V μm, deploying a one-micrometer compact electrostatically tunable plasmonic phase-shifter, based on heterogeneously integrated ITO thin films into silicon photonics. Furthermore we show, that this device paradigm enables spectrally broadband operation across the entire telecommunication near infrared C-band. Such sub-wavelength short efficient and fast modulators monolithically integrated into Silicon platform open up new possibilities for high-density photonic circuitry, which is critical for high interconnect density of photonic neural networks or applications in GHz-fast optical phased-arrays, for example.

Highlights

Indium tin oxide (ITO), belonging to the class of transparent conductive oxides, is a material extensively adopted in high-tech industry such as in touchscreen displays of smartphones or contacts for solar cells
We have recently demonstrated an Mach–Zehnder interferometer (MZI) based modulator using photonic-modal ITO-oxide-Si characterized by a VπL = 0.52 V∙mm[3], and a plasmonic version deploying a lateral gate exhibiting a VπL = 0.063 V∙mm[7] each deploying a different ITO process either for a photonic[3] or plasmonic m ode[7]
The lurking and fundamental challenges with LN modulators rest in their large footprint and weak electrostatics, which are both geometry related; electrostatically inefficient confinement of the RF field with both electrodes on opposite sides of waveguide necessarily widens the gap; whereas for the ITO case one of the electrodes is the active layer itself tightening the gap for efficient manipulations

Summary

Introduction

Indium tin oxide (ITO), belonging to the class of transparent conductive oxides, is a material extensively adopted in high-tech industry such as in touchscreen displays of smartphones or contacts for solar cells. We have recently demonstrated an MZI based modulator using photonic-modal ITO-oxide-Si characterized by a VπL = 0.52 V∙mm[3], and a plasmonic version deploying a lateral gate exhibiting a VπL = 0.063 V∙mm[7] each deploying a different ITO process either for a photonic[3] or plasmonic m ode[7] The latter enables strong light-matter-interactions i.e. extrinsic slow-light effects, coupled with the intrinsic slow-light effect of the ITO material, i.e. epsilon-near-zero (ENZ) effect allowing high mode confinement which is synergistic with the MOS capacitor approach of free-carrier modulation in I TO8. Continuous efforts to minimize V πL in MZI schemes have succeeded in realizing miniscule FOMs (10′s of V μm) over the years (Table 1)

Methods

Results

Conclusion