Alleviation of DC drift in a thin-film lithium niobate modulator utilizing Ar⁺ ion milling

The thin-film lithium niobate (TFLN) modulator is among the most critical devices in photonic integrated circuits (PICs), owing to its large modulation bandwidth, low optical loss, and high extinction ratio. However, it suffers from DC drift issues at low frequencies or long timescales. Here, we have successfully alleviated the DC drift effect of the electro-optical phase shifter (EOPS) at low frequencies by employing a high-energy Ar ⁺ ion milling preprocessing. This EOPS can stably output square wave modulation signals at a frequency of 1 Hz, and the output signal exhibits no DC drift under DC voltage modulation within 1 h. Compared with the thermo-optical phase shifter (TOPS), the optimized EOPS not only has higher modulation rate but also exhibits the same stability at low frequency. Furthermore, we applied this ion milling technique to produce a TFLN modulator. At a DC bias voltage of 4.5 V, the bandwidth of the modulator is above 40 GHz and remained a stable output within 30 min.