Scalable Frequency Generation from Single Optical Wave

Scalable Frequency Generation from Single Optical Wave S. Radic Jacobs School Of Engineering Qualcomm Institute University of California San Diego

- Motivation - Bandwidth Engineering - Noise Inhibition and Coherency Limit - Spectral Shaping - Implications: - Optical - RF/Wireless

2xN 1 RX RX 1 2 RX RX 2 3 RX AWG N Channels AWG RX 3 N RX RX N

Carrier Generation Physical Parameter ITLA F-Generation Spectral Coverage (nm) 74? Power (dbm) 7-15.5? RIN (dbc/hz) -145? OSNR.1 nm (db) >5? f(mhz).1? F-stability (GHz) ±1.5 (±3.)? Power Dissipation (W) 3.5-7.?

Main Idea: Eliminate Multiple Actives LD/TEC LD/TEC LD/TEC LD/TEC LD/TEC f Conventional LD Array dbm-level Optical Power OSNR > 4 db Multi-band Wavelength Range MHz Linewidth Individual Frequency Tracking Required kw/mw-level Power Dissipation Frequency Comb Output Power? OSNR? Emission Bandwidth and Spacing? Linewidth? Frequency Grid Locked Watt-scale Power Dissipation

Mode-Locked Lasers - Cavity-defined - Fixed grid, f, bandwidth limits - Low harmonic power - Excess noise ~ f -1 P t E/O Modulation - Grid limited by RF generator - Noise defined by front loss Resonant Generation - Noise, Power AM f1 PM AM PM f2 f3 f4 J. Pfeifle et. al. 213.

Frequency Comb Generation in Ideal Mixer Ideal Lasers (Narrow Linewidth) Mixer f f + f f f + f +2 f +3 f +n f Advantage: No cavity freely tunable. Disadvantage: No cavity means no inhibition mechanism. - Noise introduced and grown by mixer.

Kerr Index (n 2 ) Platform W -1 m -1 Mixer efficiency - ratio Waveguide Nonlinearity Mixer of newly created and input photons: Silicon Waveguide Silica Waveguide Effective Area (A eff ) m 2 ~ 2.6 e PL 2.1 1-18 3.2 1-2 8 ( =2 n 2 / A eff ) 8.3.35 Loss db/m Effective Length (m) FOM PL) Figure Of Merit (FOM) 5.35.3 >1.5 7

Pulsed vs. Continuous-Wave Generation Mode-Locked Seed P ML t Mixer f Two-Tone CW P CW f Mixer f CW-seeding is low power Requires higher mixing efficiency

CW-Seeded Frequency Generation Efficiency ω t Dispersion-less Nonlinear Medium ω t Tone order k 6 5 4 3 2 1 Highest tone order k PL 1 1 2 3 4 5 Phase rotation parameter m Modified Carson s Rule for HPM Efficiency Limit set by SBS Threshold P SBS 21A eff gl ksbs PSBS L 1 B 42 n gb 2 1.14 1 for ordinary silica fiber High-Count generation is prohibited 2.81 1 for SBS-suppressed mixer in homogeneous mixers

CW-Seeded Frequency Generation Efficiency Δω ω ω P peak t Dispersion-less Nonlinear Medium t Higher-order mixing efficiency proportional to Peak Power P peak

Shock-Wave Mixer Pulse Compression Stage Mixing Stage Nonlinear Section 1 Linear Section Nonlinear Section 2 t t t

Attempt to synthesize CW-seeded mixer using fiber fails. -1 Fiber 6-2-6 2m Fiber 6-2-7 25m Fiber 6-2-8 25m -2 Power, dbm -3-4 -5-6 145 15 155 16 165 Wavelength, nm

D(z), r(z) ~nm z 1.5 Dispersion, ps/nm/km -.5-1 -1.5-2 12 13 14 15 16 17 18 Wavelength, nm

D peak =.6 ps/nm/km D peak =.4 ps/nm/km D peak =.2 ps/nm/km D peak =. ps/nm/km D peak = -.2 ps/nm/km D peak = -.4 ps/nm/km 15

Beyond Stochastic Barrier.6.4.2 Standard Dispersion, ps/nm/km -.2 -.4 Synthetic -.6 -.8 152 154 156 158 16 162 164 Wavelength, nm 1/27/213

Stochastic Barrier -1-2 Before Synthesis Power, dbm -3-4 -5-6 -7 13 135 14 145 15 155 16 165 17 175 18-1 -2-3 -4-5 -6 After Synthesis -7 14 145 15 155 16 165 17 Walelength, nm

Relative Power (db) -2-4 15 152 154 156 158 16 162 Wavelength (nm) 1-1 -2-3 -4-5 -6-7 159 1592 1594 1596 1598 16

- Motivation - Bandwidth Engineering - Noise Inhibition and Coherency Limit - Spectral Shaping - Implications: - Optical - RF/Wireless

Carrier Generation Noise Origins Mixer Excess Mixer Noise

Finite-Linewidth Laser Seed Ideal Lasers (Narrow Linewidth) Mixer f f + f f f + f +2 f +3 f +n f Finite Linewidth Laser ( ) 2 3 n f f + Linewidth f Mixer f f + f +2 f +3 f +n f Higher-Order tone linewidth: N ~ N N ~ N 2

Carrier Generation Phase-Referencing by Injection Locking Slave Master Weak, narrow master; Strong, broad slave; Injection locking results in strong, narrow oscillator.

Carrier Generation Spectral Fidelity Amplitude 1.8.6.4.2 Normalized Span 5 MHz -2-1 1 2 Frequency (MHz) RIO C33 1st line 5th line 1th line 15th line 2th line 25th line 3th line Linewidth FWHM (khz) Linewidth broadens quadratically with comb tone order At low copy count there is also the linear contribution to linewidth scaling law 25 2 15 1 5 Measurement 2nd order polynomial fit 1 2 3 4 Comb line

Relative Power (db) -2-4 15 152 154 156 158 16 162 Wavelength (nm) Comb Quadrature COMB In Phase Quadrature ITLA In Phase

- Motivation - Bandwidth Engineering - Noise Inhibition and Coherency Limit - Spectral Shaping - Implications: - Optical - RF/Wireless

Carrier Generation Shock-Wave Parametric Mixer Uses CW, rather than pulsed seed: achieves generation efficiency by managed shock-wave formation. Tunable frequency grid: from 1 GHz to > 4 GHz. Requires precise intra-mixer waveform control. f f Dispersive stage Nonlinear stage f AM PM Nonlinear stage 2 Δf Δf t t

Carrier Generation Inter-stage Shock-wave Shaping Pedestal pulses may form at high compression ratio Introduces spectral power ripple Regenerative stage reshapes pulses into ideal form Active loop improves extinction by >1-times Dispersive element NOLM Nonlinear element f AM PM Δf Δf 2 t P out t P in

Setup Power [db] -3-4 -5-6 -7-8.4 THz 185 19 195 2 25 Frequency [THz] -3-4 -5-6 -7-8 1 THz 185 19 195 2 25 Frequency [THz] -3-4 -5-6 -7-8 2 THz 185 19 195 2 25 Frequency [THz] -3-4 -5-6 -7-8 185 19 195 2 25 Frequency [THz] 1 GHz 2 SMF 1 NOLM 1 SMF 2 NOLM 2 SMF 3 HNLF AM PM 1 1 1 1 Amplitude.5.5.5.5-4 -2 2 4 Time [ps] -4-2 2 4 Time [ps] -4-2 2 4 Time [ps] -4-2 2 4 Time [ps]

Carrier Generation Very Dense Carrier Plan (1 GHz) Power [db] -3-4 -5-6 -7-8 <2 db >15 lines 146 15 154 158 162 Wavelength [nm] Power [db] -2-4 -2-4 -2-4 -6-6 -6 192.92 192.96 193 Frequency [THz] 194.95 195 195.5 Frequency [THz] 195.95 196 196.5 Frequency [THz]

- Motivation - Bandwidth Engineering - Noise Inhibition and Coherency Limit - Spectral Shaping - Implications: - Optical - RF/Wireless

Carrier Generation

NF (db) 18 14 1 PS-Multicasting PI-Multicasting Isotropic Mixer 5.6 db NF Improvement 6 2 3-dB Quantum Limit 189 191 193 195 197 Frequency (THz)

-4-5 PI-scheme log (BER) -6-7 PS-scheme EDFA -8-9 2. db -1-42 -4-38 -36-34 -32-3 Input Power [dbm]