Abstract
We demonstrate for the first time a waveguide-based frequency shifter on the silicon photonic platform using single-sideband modulation. The device is based on silicon-organic hybrid (SOH) electro-optic modulators, which combine conventional silicon-on-insulator waveguides with highly efficient electro-optic cladding materials. Using small-signal modulation, we demonstrate frequency shifts of up to 10 GHz. We further show large-signal modulation with optimized waveforms, enabling a conversion efficiency of -5.8 dB while suppressing spurious side-modes by more than 23dB. In contrast to conventional acousto-optic frequency shifters, our devices lend themselves to large-scale integration on silicon substrates, while enabling frequency shifts that are several orders of magnitude larger than those demonstrated with all-silicon serrodyne devices.
Highlights
Frequency shifters are key elements for a wide range of applications, comprising, e.g., heterodyne interferometry, vibrometry, distance metrology, or optical data transmission [1,2,3,4]
The device is based on silicon-organic hybrid (SOH) electro-optic modulators, which combine conventional silicon-on-insulator waveguides with highly efficient electro-optic cladding materials
Such devices have been demonstrated on the silicon photonic platform, providing a remarkable side-mode suppression ratio (SMSR) of 39 dB [11,12], but the achievable frequency shift is limited by fundamental properties of silicon-based phase shifters: To avoid unwanted spurious lines in the output spectrum, pure serrodyne phase modulation must be achieved without any residual amplitude modulation
Summary
Frequency shifters are key elements for a wide range of applications, comprising, e.g., heterodyne interferometry, vibrometry, distance metrology, or optical data transmission [1,2,3,4]. This results in a phase shift that is piecewise linear in time and leads to a frequency shift that corresponds to the fundamental frequency of the sawtooth drive signal Such devices have been demonstrated on the silicon photonic platform, providing a remarkable SMSR of 39 dB [11,12], but the achievable frequency shift is limited by fundamental properties of silicon-based phase shifters: To avoid unwanted spurious lines in the output spectrum, pure serrodyne phase modulation must be achieved without any residual amplitude modulation. As for the serrodyne method, a good SMSR requires a pure frequency shift without any spurious amplitude-phase coupling, making it challenging to realize high-performance single-sideband modulators based on the standard silicon photonic device portfolio. A rigorous mathematical description of frequency shifters based on single-sideband modulation is given in the Appendix
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