Towards optical fiber synthesis of millimeter and submillimeter - PowerPoint PPT Presentation

Towards optical fiber synthesis of millimeter and submillimeter waves European Microwave Conference from 3 rd to 7 th October Presentation 06/10/2016 By Ayman HALLAL Steve Bouhier, Simon Le Méhauté and François Bondu

Outline  Introduction  Design Schematic • Electronic control circuit  Experimental results • Optical carrier: Frequency noise and Relative intensity noise • Beat note : Phase noise measurements 2 to 92 GHz Electrical power spectrum  Conclusion 2 • Outlook

Introduction Goal : Generation of millimeter and sub-millimeter low phase noise and widely tunable optical waves • 1 GHz to 500 GHz with steps of 1 GHz • Compact, Robust and Low cost system Applications:  THz spectroscopy of molecules  Modern communications using high frequency bands: • Radio Over Fiber • Wireless communications 3  Radar and radio-astronomy applications

Introduction Waves provided by an optical beat note of two optical carriers • Two commercial DFB laser diodes (1.5 µm telecom components) • Stabilization of two optical carriers on a single commercial fibered cavity • Electronic control circuits for frequency noise correction of each optical carrier ∆ 𝜉 = RF frequency = multiple of the Free Spectral Range 𝜉 1 𝜉 2 P( 𝜉 ) 𝜉 4

DFB laser and Fibered cavity DFB: Wavelength tunable over 4 nm (500 GHz) • Linewidth: 110 kHz • Optical power: 4 mW (Max) • Wavelength: around 1550 nm EBLANA Cavity: Linewidth: 1 MHz • Free Spectral Range: 1 GHz • Finesse 1000 (Q = 2.10 8 ) Fibered cavity advantages: • Vibration and shock resistant • Low loss FSR = 1GHz Q = 2.10 8 • No alignment required 5

Outline  Introduction  Design Schematic • Electronic control circuit  Experimental results • Optical carrier: Frequency noise and Relative intensity noise • Beat note : Phase noise measurements 2 to 92 GHz Electrical power spectrum  Conclusion 6 • Outlook

Design Schematic  Error signal generation: Pound-Drever-Hall technique Cavity Laser carrier Laser carrier Side bands generated Input of the second laser 45 ° PC Feedback of the second laser 7 Main Challenge:  High level frequency noise of free running laser : 150 Hz/√Hz white noise over 100’s MHz bandwidth  Avoiding saturations of error and correction signals

Design Schematic Solutions:  Servo loop design  Fast servo Loop 7 MHz bandwidth (length of 3.5 m)  Fast loop : Compensation of the phase laser with an Electro-optic phase modulator with low V π = 3.2 V, 150 MHz bandwidth  Slow loop : Modulation of the Laser injection current (350 kHz bandwidth)  LTspice simulation model  Fast Electronic circuit design (Unity Frequency Gain ~40 MHz)  Very high gain under 200 kHz with Proportional multiple integrators P+I 5 (DC gain ~ 6.10 12 ) 8  High bandwidth Operational Amplifiers (450 MHz)  LTspice model

Electronic control circuit Zeros at 200 kHz Error signal G1 I 3 Zeros for cavity and EO pole compensation G2 Fast correction K = 1 P+I 2 Zero at 4 KHz G3 G4 Slow correction G3 P+I Fast corrector transfer function I: integrator P: proportional G: Loop Gain control 9

Outline  Introduction  Design Schematic • Electronic control circuit  Experimental results • Optical carrier: Frequency noise and Relative intensity noise • Beat note : Phase noise measurements 2 to 92 GHz Electrical power spectrum  Conclusion 10 • Outlook

Experimental results Single optical carrier Frequency noise Relative Intensity noise RIN High phase to amplitude couplings 100 kHz RMS frequency excursion -93 dBc/Hz at 1 kHz 11 -106 dBc/Hz at 1 MHz

Experimental results 2, 10 18 GHz G: 26 dB Beat note ESA BW: 22 GHz Orthogonal LO: 39.5 GHz polarizations 40 GHz G: 36 dB 45 ° DFB 1 servo ESA loops PC DFB 2 BW: 40 GHz Fibered cavity Phase noise measurements LO: 11.25 GHz 92 GHz G: 30 dB G: 26 dB Optical shot noise ESA Electronic noise BW: 108 GHz Sub-harmonic Mixer N = 8 Electrical thermal noise limit -60 dBc/Hz at 1 kHz 12 -90 dBc/Hz at 1 MHz

Experimental results Beat note Electrical power spectrum at 10 GHz Beat note linewidth: 30 Hz Same linewidth measurement at 92 GHz 13 Span : 10 kHz

Outline  Introduction  Design Schematic • Electronic control circuit  Experimental results • Optical carrier: Frequency noise and Relative intensity noise • Beat note : Phase noise measurements 2 to 92 GHz Electrical power spectrum  Conclusion 14 • Outlook

Phase noise measurements Conclusions Optical shot noise Electronic noise  Beat note wave tunable 1 GHz to 500 GHz 1GHz step  2 to 92 GHz beat note phase noise measurements : -60 dBc/Hz at 1 kHz -90 dBc/Hz at 1 MHz  30 Hz beat note linewidth has been measured at 10 and 92 GHz frequencies  6 Hz/s frequency drift (170 kHz over 7 hours)  7 MHz servo bandwidth with electronic corrections of widely tunable DFB lasers stabilized on a fibered cavity demonstrated for the first time: 100 kHz RMS residual frequency noise excursion  Home made electronic correction circuits, reliable and robust feedback loops, 15 no error and correction signal saturations

DFB lasers Fibered Electronic Outlook EO- cavity control 2 circuits  Phase noise measurements from 92 GHz to 500 GHz  Submillimeter wave phase and amplitude noise improvements: 22 MHz servo bandwidth ( Integrated electro-optical components, 30 cm) • 18 dB further reduction on the phase noise at 1 MHz • 10 dB further reduction on the relative intensity noise  Submillimeter wave frequency accuracy with thermal control of the cavity 100 kHz  0.12 °C  Continuous frequency tunability with Phase Locked Loop 5-10 GHz with third DFB laser 16

Thanks For your attention 17

Real Complex envelope 𝐭𝐭𝐭 ( 𝟑𝟑𝝃 𝒑𝒑𝒖 𝒖 + 𝒋 φ ( 𝒖 )) 𝐟𝐟𝐟 ( 𝒋 φ ( 𝒖 )) 𝒕 𝒖 = 𝒕 𝟏 𝟐 + 𝒃 𝒖 𝒇 𝒖 = 𝒇 𝟏 𝟐 + 𝒏 𝒖 Signal 𝜉 𝑝𝑝𝑝 optical carrier frequency 𝑏 𝑢 amlitude noise φ 𝑢 phase noise Second order filter (resonator) 2 / 𝑅 𝜉 𝑠 𝐼 𝜉 = 2 − 𝜉 2 + 𝑗𝜉𝜉 𝑠 / 𝑅 Real signal in Real signal out 𝜉 𝑠 𝜉 𝑠 resonance frequency 𝑅 quality factor First order filter 1 ℎ 𝑔 = 𝜉 − 𝜉 𝑝𝑝𝑝 ≅ 𝑑 1+𝑗𝑗 / 𝑗 Complex envelope in Complex envelope out if 𝜉 𝑠 = 𝜉 𝑝𝑝𝑝 𝜉 𝑠 Quadrature signal modeling 𝑔 𝑑 = 2𝑅 Cut frequency p(t) and q(t) = resonance half linewidth 𝒇 𝒖 = 𝒇 𝟏 𝟐 + 𝒑 𝒖 + 𝒋𝒋 ( 𝒖 )

Electronic control circuit I: integrator Zeros at 200 kHz P: proportional Ɛ G1 I 3 G: Gain Zeros for cavity and EO pole compensation G2 Fast correction K = 1 P+I 2 Zero at 4 KHz G3 G4 Low correction G3 P+I THS30001 in proportional mode • Current feedback, Supply to ± 16 V • BW: 450 MHz (G=1), Slew rate = 6500 V/ μs • Instability DC gain > 100, not recommended in integrator mode Fast corrector transfer function THS46311 in integrator mode • Voltage feedback, Supply to ± 15 V • BW: 325 MHz (G=1), Slew rate = 900 V/ μs • Instability DC gain > 100 • Voltage noise at input 7 nV/sqrt(Hz) 19 OPA827 in proportional and integrator mode • Voltage feedback, Supply to ± 18 V • BW: 22 MHz (G=1), Slew rate = 28 V/ μs • Open loop gain stability, high DC gain

Experimental results Beat note Frequency drift at 10 GHz 170 kHz over 7.5 hours of lock Average: 6.3 Hz/s 20

Phase noise measurements G: 26 dB (a) ESA BW: 22 GHz Orthogonal LO: 39.5 GHz (b) polarizations G: 36 dB 45 ° DFB 1 servo ESA loops PC DFB 2 BW: 40 GHz Fibered FP cavity LO: 11.25 GHz (c) G: 30 dB G: 26 dB ESA BW: 108 GHz Sub-harmonic Mixer N = 8

Non-linear effect on the PDH signal 𝜉 𝑝 2 Non linear function 𝜉 ( 𝑢 )/(1 + 2 ) 𝑗 𝑑 where 𝑔 𝑑 = half linewidth of the cavity 22

New designs  Loop length 30 cm → 22 MHz unity gain frequency RMS reduction to 30 kHz  + High finesse cavity RMS reduction to 640 Hz Filter effect of the cavity • Non linear effect reduction • Phase to amplitude couplings reduction 23

Beat note: Electrical power spectrums at 10 GHz Span : 1 MHz Span : 10 kHz 24 Beat note linewidth: 30 Hz

Some types of noises in a fequency servo loop Frequency noise of the laser (dominant noise) Read noise of the error signal detector • Electronic noise • Shot noise • Obscurity Noise of the photodiode Some noise in a FP cavity • Thermal noise • Seismic noise • Acoustic noise 25 • Alignment (negligible in a fibered cavity)

Design constraints and solutions Solutions constraints • Wide servo bandwidth 7 MHz • White noise of DFB laser  Fast electronic control circuit 150 Hz/√Hz over 100 MHz  LTspice Model : Servo loop and control circuit • Avoiding saturation :  High bandwidth and frequency  Error signal excursion correction actuators:  Correction signal Low Vπ (3.5 V) EO phase modulator (BW: 150 MHz) • Narrow linewidth cavity:  Frequency filter effect 26

Résultats expérimentaux Bruit de fréquence d’une diode laser DFB Bande passante d’asservissement 7 MHz Bande passante de la voie lente 350 KHz Plancher de bruit de fréquence en mode verrouillé dans le signal d’erreur 10 Hz/ Hz 27