Microring Optical Phase-Shifters With Low Driving-Voltage, Low Insertion Loss, and Small Residual Amplitude Modulation

Novel microring based optical phase-shifters on Si-photonic platforms for microwave photonic applications are demonstrated. By using an add-drop microring structure in combination with an additional multimode interferometer (MMI), pure phase modulation with an ultrahigh modulation efficiency can be realized. Comparison is made to the reference all-pass ring design with both the same radius (5 μm) and coupling coefficient (κ: ∼0.2). The demonstrated structure minimizes the residual amplitude modulation (0.9 vs. 1.8 dB) for nearly 2π phase shifting over a wide optical window (1520 to 1570 nm) at the expense of a larger insertion loss (0.06 dB) due to the additional MMI. The demonstrated phase shifter structure is implemented in a Mach-Zehnder interferometer (MZI) for further study of its dynamic and linearity performance. Under forward bias, it exhibits a low V
_π
/I
_π
(0.4 V/12.7 mA), fast rise-time (3 ns), low insertion loss (0.2 dB), low residue-amplitude-modulations (<0.9 dB), and can cover wide optical windows (1560–1568 nm) with a small footprint (37
$ \times $
37 μm
²
). The measured spurious-free dynamic range (SFDR: 70–75 dB) of our novel phase shifter-based MZI is comparable to that of the traditional traveling-wave MZI (∼75 dB) under reverse bias and tested using the same setup.