Gain-enabled optical delay readout unit using CMOS-compatible avalanche photodetectors

Ranjan Das; Yanran Xie; Henry Frankis; Keru Chen; Hermann Rufenacht; Guillaume Lamontagne; Jonathan D. B. Bradley; Andrew P. Knights

doi:10.1364/PRJ.463832

Journals >Photonics Research >Volume 10 >Issue 10 >Page 2422 > Article

Photonics Research
Vol. 10, Issue 10, 2422 (2022)

Gain-enabled optical delay readout unit using CMOS-compatible avalanche photodetectors

Ranjan Das^1、†,*, Yanran Xie^1、†, Henry Frankis¹, Keru Chen¹, Hermann Rufenacht², Guillaume Lamontagne², Jonathan D. B. Bradley¹, and Andrew P. Knights¹

Author Affiliations

¹Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4L7, Canada

²McDonald Detwiler Associates, Sainte-Anne-de-Bellevue, Quebec H9X 3R2, Canada

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DOI: 10.1364/PRJ.463832 Cite this Article Set citation alerts

Ranjan Das, Yanran Xie, Henry Frankis, Keru Chen, Hermann Rufenacht, Guillaume Lamontagne, Jonathan D. B. Bradley, Andrew P. Knights. Gain-enabled optical delay readout unit using CMOS-compatible avalanche photodetectors[J]. Photonics Research, 2022, 10(10): 2422 Copy Citation Text

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(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. 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.

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

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

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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.

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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.

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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.

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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.

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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.

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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.

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

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

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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.

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Measurement Method	Delay Element and Detector	Error	Resolution	On-Chip RF Amplification	Remarks	Reference
Optical vector analyzer	Si waveguide spiral (6.56 cm long) with maximum delay range of 0–320 ps, detector not on-chip	$< 0.5 %$	$< 1 ps$	No	High accuracy, expensive infrastructure	[34]
Optical vector analyzer	Cascaded Si MRR ( $600 μm \times 300 μm$ ) with maximum tunable delay range of 0–1700 ps, detector not on-chip	$< 0.5 %$	$< 1 ps$	No	High accuracy, expensive infrastructure	[35]
Optical time-domain reflectometry	External single-mode fibers with differential delay of 0.4 ps, detector type not mentioned	$> 12 %$	N.A.	No	Requiring high power optical pulses	[36]
Optical frequency-domain reflectometry	Fiber Bragg grating with maximum tunable delay range of 0–253 ns, external detector	$\sim 25 %$	15 ps	No	Requiring complex signal processing	[39]
Frequency-shifted self-heterodyne	Single-mode fiber with maximum delay range of 50.13 ns, external detector	N.A.	N.A.	No	Requiring narrow linewidth laser source	[44]
VNA	Single Si MRR ( $500 μm \times 100 μm$ ) with tunable delay range of 0–300 ps, integrated on-chip detectors	$< 2 %$	$< 10 ps$	10 dB^b	Low BW electronics without RF amplifiers TLS, Max. optical power: −2 dBm	This work