Fig. 2: Characterization of the photoinduced second-harmonic frequency offset.
From: Self-organized spatiotemporal quasi-phase-matching in microresonators
a Experimental setup for measuring the frequency offset between second-harmonics generated in a Si3N4 microresonator and a standard frequency doubler. ECDL: external-cavity diode laser; MWG: microwave generator; AOM: acousto-optic modulator; EDFA: erbium-doped fiber amplifier; PPKTP: periodically poled KTiOPO4 crystal; SF: spectral filter; FPC: fiber polarization controller; DM: dichroic mirror; PD: photodetector; BS: beam splitter; ESA: electrical spectrum analyzer; OSC: oscilloscope. Both self-homodyne measurements of temporal oscillations using an OSC (excluding dashed boxes) and self-heterodyne measurements of frequency spectra using an ESA are performed. The inset showcases a χ(2) nonlinear grating obtained using the two-photon microscopy after the microresonator is poled near the pump resonance at 1549.0 nm. The participating SH mode is TE30 inferred from the measured grating period. b Left: measured frequency offsets (blue dot-lines: self-heterodyne; black dots: self-homodyne) as functions of the pump wavelength when tuning the laser wavelength across the resonance at 1549.0 nm from blue to red side. The inset shows the spectral map on a logarithmic scale obtained from the self-heterodyne measurement with a 1 Hz resolution bandwidth (RBW) in ESA. Right: temporal oscillation traces measured by the self-homodyne technique for the data points indicated on the left panel (i-vii).
