Fig. 1. (a) Schematic of the on-chip group delay measurement system using low-bandwidth electronics. RF modulated optical signal experiences ring delay and subsequently, is detected and measured by PD and VNA, respectively. (b) RF phase-to-delay transformation illustration. CW, continuous-wave; EO modulator, electro-optic modulator; PC, polarization controller; Ring, ring resonator; PD, photodetector; RF Amp., RF amplifier; EVNA, electrical vector network analyzer; ∠ϕ21, phase response of S21; τ(λ), delay, and (ϕ21T−ϕ21S), phase shift due to the MRR only.

Fig. 2. Measured MRR characteristics. (a) Prototype of the fabricated MRR; (b) ring resonance tuning by adjusting integrated heater power supply.

Fig. 3. Measured MRR characteristics. (a) Ring coupling k tuning by integrated heater and (b) ring–bus coupling (k) variation for different heater powers.

Fig. 4. Cross-sectional view of the (a) Si APD, (b) Ge SACM APD, and (c) Ge PIN PD, respectively. Light enters these waveguide PDs normal to the plane of the page.

Fig. 5. Characterization of the avalanche PDs. (a), (d) Si and Ge APD photocurrent versus bias; (b), (e) photocurrent versus optical power; and (c), (f) small-signal bandwidth of the Si APD and Ge SACM APD for different bias configurations. Popt indicates input optical power at fiber tip.

Fig. 6. Characterization of Ge PIN PD. (a) Ge PD I-V response operating at PIN mode, and (b) small-signal response of the Ge PIN detector under different reverse bias voltages. Popt represents input optical power at fiber tip.

Fig. 7. Measured RF phase and delay responses (after compensating for static components) using (a) Si APD, (b) Ge SACM APD, and (c) Ge PIN PDs for different ring–bus coupling configurations, respectively.

Fig. 8. Comparison of measured delay results with simulations for (a) Si APD (k=0.62) and (b) Ge SACM APD (k=0.73) PD. Black represents simulation, whereas orange and blue are for measured results.

Fig. 9. Measured delay responses for a constant ring–bus coupling using (a) Si APD and (b) Ge SACM APD PDs with different bias voltages.

Fig. 10. Minimum required optical power measurement for different bias voltages of the Si APD.

Fig. 11. RF signal phase responses for different input optical powers to the (a) Si APD and (b) Ge SACM APD.

Fig. 12. (a) RF spectra for different integrated PDs and (b) broader frequency range for harmonic analysis. The inset shows zoomed-in view of the RF signals far away from the fundamental component.

Table 1. Comparison of Different Delay Measurement Approaches^a