Figure 2

PWB-microresonator characterization in linear regime. (a) Experimental setup for testing the PWB-microresonator configuration in the linear regime, i.e., coupling ideality and Q-factor measurement. AWG arbitrary waveform generator, EOM electro-optical modulator, PC polarization controller, FA fiber, V groove array, PWB photonic wire bond, PD photodetector. (b) 3D rendering of the FA-PWB-crystal arrangement. (c) Photograph of a 4.92 mm MgF₂ crystal with microresonator protrusion. (d) Microscope image of PWB on the FA facet coupled to the crystalline microresonator. (e) Linewidth measurement of a resonance with 3 MHz calibration sidebands, wherein a Lorentzian fit (black line) has been applied to the measured transmitted light (green line) and gives a linewidth of 240 kHz, corresponding to a Q-factor of \(\sim\) 10⁹ at 1550 nm. (f) Evolution of resonance linewidth as a function of PWB-microresonator gap for a single resonance. All traces correspond to the same resonance and have been offset to better visualize the transition from undercoupled (left), to critically coupled (center), to overcoupled (right) states. Furthermore, the total displacement between undercoupled to overcoupled regimes is 1.5 \(\upmu\)m, starting from 0 \(\upmu\)m on the left.