16:15 〜 16:30
▲ [17p-F204-10] A novel method to tune the operating point of silicon Mach-Zehnder modulator
キーワード：optical modulator, silicon photonics, photonic integrated circuits
Operating point control is very important for Mach-Zehnder modulators (MZM) that convert phase modulation to intensity modulation because it determines the maximum phase-intensity conversion efficiency, i.e., modulation depth. This operating point control can be achieved by adjusting the phase difference between two arms of MZM. To realize the phase tuning for the high-speed silicon MZM, the usual way is fabricating an individual heater on one arm together with the phase shifter to utilize thermo-optic phase tuning [1]. In this report, we propose a novel method to tune the operating point without utilizing a heater; instead, we intend to employ the finite resistance of the RF signal electrode of coplanar waveguide (CPW) for thermal phase tuning without utilizing the individual heater. The CPW used for RF wave propagation usually takes the GS or GSG configuration and a reverse DC bias must be applied to the PN diode through G and S electrodes for the depletion-type silicon modulator. In this case, there is no voltage drop along the S electrode which undergoes a uniform bias. However, in this novel proposal, we intend to apply a non-uniform bias to the S electrode. The bias difference along the S electrode and its finite resistance can be utilized to realize phase tuning. The S electrode is shared by both high-speed modulation driving and by operating point tuning. This method has two advantages: (1) Decreasing the process cost and shortening the fabrication cycle because the photomasks and process for fabricating heaters are removed. In addition, the device layout of modulator becomes simple and compact. (2) The non-uniform bias applied to the S electrode could enhance the phase modulation efficiency by gradually reducing the reverse bias when RF signal attenuates along the CPW. Here we verify the feasibility of this principle for tuning the operating point of silicon modulator without using an individual heater.