Dual frequency laser principle

48 / Dual frequency laser principle linear birefringence inside a solid state laser cavity : L Two linearly polarized eigenstates : a single cavity : stable frequency difference the two frequencies are separable by polarization after a 45 polarizer, the beam is 1% modulated c 2L 2 1 stable source of optically carried microwave signals c 4L G. W. Baxter et al, IEEE PTL 8, 1996 (Macquarie University) M. Brunel et al, Opt. Lett. 22, 1997 (University of Rennes) 49 / Diode-pumped solid-state dual-frequency laser prelim demo. simultaneous oscillation of the laser on two crossed polarizations with a frequency offset in the microwave range 25 mw, 1% modulation depth tuneable beat note from 2 to 13 GHz high speed tuneability: 1 GHz / 1µs long term linewidth of the beat-note : 2 µhz @ 2 GHz (comparison of the optically carried RF signal with the RF ref.) compatible with requirements for radar L.O distribution pump diode: 976 nm active medium: Er:Yb: glass

5 / Dual frequency laser source (DFL) experimental demos. -6-14 1 2 1 3 1 4 1 5 1 6 Frequency (Hz) optical links based on dual frequency laser permit L.O distribution very low additive phase noise measured demonstration of optical mixing, Doppler generation DFL combined with a frequency shifter provides up- / down-converted microwave signals tunable in the range.5-23 GHz extension to radar echo synthesis extension to millimeter-wave and THz range (up to 2.5 THz) Phase noise level (dbc/hz) -8-1 -12 3.9 GHz 12.34 GHz 9.6 GHz see also A. Rolland, paper 2192, Wednesday 15. 51 / Compact dual-frequency laser Er Yb doped glass electro optical ceramic Etalon laser beam fiber coupling pump beam tuning

52 / Compact dual-frequency laser >6 mw output power with 1 W pump power optical spectrum Level (dbm) Level (db) -2-3 -4-5 -6-7 -8-9 -1-2 -3-4 -5-6 -7 1535.8 1535.9 1536 1536.1 1536.2 Wavelength (nm) free running beatnote -1-1 -.5.5 1 Frequency (MHz) around 3.25 GHz 53 / 14 12 Compact dual-frequency laser voltage tuning range Phase noise DSP (dbc/hz) Beatnote frequency (GHz) 6 4 2-2 -4-6 -8-1 -12-14 1 8 6 4 2 1 2 3 4 5 6 7 Voltage (V) -3 db/ dec -4 db/dec -4 db/dec Laser optical phase noise (+3 db) Beatnote phase noise -27,5 db/ dec -2 db/ dec 1 1 1 2 1 3 1 4 1 5 1 6 1 7 Frequency (Hz) free-running phase noise Altaïr Custom Solid-State DFL Series

54 / Optical Phase-Locked Loop (OPLL) stabilization Optically carried version of the RF L.O <1 Hz BW for drift compensation HV amp. + slow fast Loop filters MHz BW high speed photodiode LNA RF Local Oscillator -12 dbrad²/hz @1 khz over the complete tunabilty range phase-noise PSD (dbrad 2 /Hz) 4 2-2 -4-6 -8-1 -12 Phase noise of the stabilized beatnote 1.6 GHz Free-running phase noise 1 1 1 2 1 3 1 4 1 5 1 6 frequency (Hz) 1 7 55 / Optical Phase-Locked-Loop (OPLL) stabilization Phase noise of the stabilized beatnote phase-noise PSD (dbrad 2 /Hz) 4 2-2 -4-6 -8-1 -12 Free-running phase noise 1 1 1 2 1 3 1 4 1 5 1 6 Frequency (Hz) 1.6 GHz 1 7-117 dbrad²/hz @1 khz

56 / Optical Phase-Locked-Loop (OPLL) stabilization Phase noise of the stabilized beatnote : limiting noises phase-noise PSD (dbrad 2 /Hz) 4 2-2 -4-6 -8-1 -12 Free-running noise 1 1 1 2 1 3 1 4 1 5 1 6 Frequency (Hz) 1 7 Loop electronics noise and laser intensity noise 57 / Optical Phase-Locked-Loop (OPLL) stabilization Phase noise of the stabilized beatnote : limiting noises phase-noise PSD (dbrad 2 /Hz) 4 2-2 -4-6 -8-1 -12 Free-running noise 1 1 1 2 1 3 1 4 1 5 1 6 1 7 Frequency (Hz) RF reference noise

58 / In collab with Quantel Dual-Frequency DFB Fiber Laser doped optical fiber with a Bragg grating (6kHz linewidth laser emission) birefringence induced when engraving the Bragg grating same grating period on the two axis (n 1, 1 ) (n 2, 2 ) Bragg Grating phase shift grating phase matching dual frequency operation Fiber Doped core (v 1,n 1 ) (v 2,n 2 ) c c 1 ; 2 2n 2n 1 c 1 1 2 n2 n1 4 cm long Er doped fiber laser similar results when pumped at 148 nm and 98 nm.2 mw @ 1.5 µm 2 RIN (db/hz) 59 / electrical spectrum of the beatnote (resolution bandwidth = 1 khz) Relative Power (db) -2-4 -1-11 -12-13 -14-15 -16-6 1.1775 1.178 1.1785 Frequency (GHz) RIN (db/hz) -1-11 -12 short-term linewidth <1 Hz -13 5.1 5 1.1 6 Frequency (Hz) -17 2.1 6 4.1 6 6.1 6 8.1 6 1.1 6 Frequency (Hz) Dual-Frequency DFB Fiber Laser Phase Noise Power Spectral Density (dbc/hz) shot noise limited low fiber anisotropy ~9.1-6 microwave beatnote ~ 1.2 GHz 4 2-2 -4-6 -8-1 -29dB/dec pump = 98nm -12 1 1 1 2 1 3 1 4 1 5 1 6 Frequency offset (Hz) pump =148 nm Foster Measurements [7] * S. Foster and al., Phys. Rev. A, 79,5382 (29)

6 / Dual wavelength DFB lasers 7 tilted waveguide DFB sections With phase-shift -3 db coupler Tilted output active two DFB lasers integrated on the same chip: with different lengths and similar KLs optical linewidth of optical linewidth : 7 khz with.8mm long DFBs 3 khz with 2.5 mm long DFBs -3dB optical linewidth (MHz) 2.5 2 1.5 1.5 passive 52 µm 78 µm 25 µm F. van Dijk, et al paper, Thursday session S5, 9: - 9:15 1 2 3 4 5 bias current (ma) 61 / Dual wavelength DFB lasers electrical power (dbm) -3-35 -4-45 -5-55 -6-65 can be tuned either thermally or by carrier injection: thermal tuning range of 2 GHz beat note linewidth <1 MHz (over the whole range) tuning speed up to 1 GHz/ns I2=22 ma I2=44 ma -7 5 1 15 2 Frequency (GHz) heteordyne signal frequency (GHz) 25 2 15 1 5 Frequency (GHz) heterodyne beating -3dB linewidth (MHz) 2 25 3 35 4 45 section 2 bias current (ma) 2.5 2 1.5 1.5 heterodyne signal -3 db linewidth (MHz)

62 / High-Speed and High-Power UTC Photodiodes GaInAs/InP Uni-Traveling-Carrier Photodiodes back-side illuminated mesa-structure CPW RF access reduced saturation effects compared to classical PIN photodiodes for surface radars for airborne systems 6 GHz bandwidth 2 GHz.9 A/W responsivity.7 A/W > 8 ma saturation current > 5 ma linearity OIP3 > 3 dbm high efficiency opto-links with an RF «gain» >-7dB 63 / Low noise / high linearity optical amplification Raman based fibre amplifier RIN (db/hz) signal laser @157 nm MZM -12-13 -14-15 -16-17 EDFA RF excitation mux Pin = -5 dbm Pin = 5 dbm 3 6 9 12 15 18 Frequency (GHz) 5 km single mode fiber -12-13 -14-15 -16-17 lower RIN with Raman amplifier for 5dBm input power well adapted to optical distribution of analog signals RIN (db/hz) RAMAN mux pump 4 W @1481 nm to optical spectrum analyzer Pin = -5 dbm Pin = 5 dbm 3 6 9 12 15 18 Frequency (GHz)

64 / Low noise / high linearity optical amplification Raman based fibre amplifier signal laser @157 nm MZM pulse-to-pulse phase stability tested in on a representative radar chain lower degradation of phase stability (1 db for Raman / 27 db for EDFA) especially for long pulses / complex waveforms correlation coefficient RF excitation 1.8.6.4.2 mux EDFA RAman RAMAN 5 km single mode fiber.99.98.97.96.95 2 4 6 Time (a.u.) 2 4 6 8 1 Time (a.u.) correlation coefficient 1 mux pump 4 W @1481 nm to optical spectrum analyzer 65 / Classical Opto Electronic Oscillator (OEO) operating principle resonant microwave photonic loop long low loss delay line based on a fiber loop high quality factor (Q 1GHz ~5.1 5 for 4 km) : high spectral purity can oscillate every 1/ (4km 5 khz ): narrow RF filter required X.S. Yao et al. Optoelectronic microwave oscillator, J. Opt. Soc. Amer. B, vol. 13, p. 1725, 1996.

66 / Classical Opto Electronic Oscillator (OEO) basic implementation in Thales 4 km delay line MW output CW LASE R Amplitude Modulator (MZM) 1 db coupler HPA resonant cavity 1 GHz RF filter standard 1.5 µm components 4 km fiber length : trade-off in between spectral purity and stability operation at 1 GHz Photodiode LNA 67 / Classical Opto Electronic Oscillator (OEO) basic implementation in Thales Phase noise PSD (dbc/hz) -2-4 -6-8 -1-12 -14-16 Bench noise floor S 1/ 5 khz low frequency phase noise results from both amplifiers phase noise and fiber length :, OEO fibre S, amp f 2 2 offset fibre 1 1 1 1 2 1 3 1 4 1 5 1 6 1 7 Frequency offset (Hz) Carrier frequency ~1 GHz

68 / Optical resonator based OEOs fiber based delay line replaced by an optical resonator: need for absolute wavelength stabilization PDH loop more sensitive to non-linear effects limitation of injected power CW tunable LASER MW output PDH loop Amplitude Modulator (MZM) Coupler Optical resonator Main loop RF-Filter (fiber ring case) Photodiode HPA Fiber rings: developped in LAAS easy to realize 2 m long Q 1GHz ~2.1 5 WGM resonators: developed in CNR-IFAC coupled with fiber tapers CaF 2 5.36 mm disks Q 1GHz ~5.1 3 69 / Optical resonator based OEOs Limited by laser optical frequency noise and by quality factor Indicative : Classical OEO 2 m fiber ring (Q 1GHz ~2.1 5 ) 5 mm CaF 2 disk resonator (Q 1GHz ~ 5.1 3 ) Limited by injected power

7 / OEOs based on dual frequency lasers as VCOs RF splitter dual frequency optical source ampli. filter RF output photodiode optical output to take advantage of the use of dual-frequency beams for: fiber loop(s) or µ-sphere(s) or µ-disk(s) improved efficiency ( 1% modulation depth, combined with high sat. PDs) already resonant operation ( relax the requirement on the RF filter in the loop) reduction of the influence of chromatic dispersion in the long delay lines ( implementation of high Q oscillators) 71 / Dual frequency laser based OEO DFL in a frequency locked loop scheme G. Pillet et al., JLT, 28 G. Pillet et al., CLEO Europe 211 Phase noise PSD (dbc/hz) 4 2-2 -4-6 -8-1 -12 RF mixer -14 1 1 1 2 1 3 1 4 1 5 1 6 1 7 Frequency offset (Hz) Carrier frequency ~5 GHz Analog LF Filter Standard Ampl. Dual frequency laser PhotoD. 1 m fiber stable frequencies : 1/ = 2MHz for1 m LF phase noise still limited by detection noise (amplifiers?) HF phase noise limited by the DFL intensity noise Q 1GHz ~1 4 highly tunable MW output same principle with DFL laser diodes and 1 loop

72 / Optoelectronic processing of microwave signals laser availability of analog optoelectronic links: large time delay up to 2-4 GHz bandwidth optical wavelength multiplexing free space propagation 1µs delay, 1 GHz BW high speed modulator S(t) 1 ns delay, 1 channels, 1 GHz BW processing architecture parallel processing high speed photodiode(s) (time x frequency) : 1 4 possible implementation of channelized optoelectronic architectures with (time.frequency) products up to 1 3-1 4 S(t-) 73 / Optical control of phased array antennas Time delay switching through: fibre delay line switching (e.g. Northrop-Grumann (prev. Westinghouse, Univ. Lille) components (laser and photodiodes) switching (e.g. HRL.) wavelength switching/tuning (e.g. NRL, TRW, NTU, Univ. Valencia, UCLA..) polarization switching (e.g. Thales, CREOL)

74 / Phased array antenna Far field pattern controlled through amplitude and phase distributions of the microwave signals accross the aperture Phase plane Radiating elements Main Lobe Microwave technology: side-lobes In-phase radiation electronic phase shifter (phase increment constant with frequency) dispersive aperture (similar to a diffraction grating in optic) beam squint when the antenna operates over a large frequency bandwidth Main Lobe side-lobes Electronic phase shifter 75 / Phased array antenna For large instantaneous bandwidth: time delay control is necessary («phase» increment proportional to frequency) no beam squint (similar to a prism in optic with a constant refractive index) Main Lobe side-lobes time delays Optical implementation of the necessary time delays max delay: up to 2 ns (for a 3m antenna) time resolution: few ps (equivalent to few deg. of phase at 1 GHz)

76 / Optically controlled phased array antennas Transmit mode 77 / Optically controlled phased array antennas M : SLM used in electrically controlled birefringent mode heterodyne generation for simultaneous control of the phase of RF signals: SLM i : rotate by or 9 the light polarization on pxp pixels

78 / Implementation of the phase control Electrically controlled birefringent mode p x p pixels on channel k: i(k)=i cos(2 f t + 2 e n(v k )/) with n(v k )=n(v k )-n 79 / Implementation of the time delays N Spatial light modulators 2 N delays each SLM i : pxp pixels on channel k: i k (t)=i cos(2 f t + 2f kj 2 j-1 ) if reflection on PBSj kj = 1 if not kj =

8 / Démonstration d une antenne à balayage électronique en bande S contrôlée optiquement retards: 5 bits contrôle de la phase : 6 bits 16 canaux, 16 elts. rayonnants diagrame de rayonnement de l antenne: angle balayé: ± 2 bande passante : 27-31 MHz pas de dépointage 81 / Optically controlled phased array antennas Transmit mode

82 / output fibres Compact True Time Delay module for transmit and receive modes input fibres 2 cm BW = 2-2GHz 8 channels, 8 radiating elts unit delay =6.5ps 5 SLMs 32 delays/ch. t on =2ms, t off =1ms main limitation measured far field pattern for: scan angle : ± 2 frequency : 6 18 GHz no beam squint 83 / EO ceramic based polarization switch Incident polarization V-groove array Gnd V V V 1 2 3 V 4 45 PM fibers EO ceramic (PLZT) Output polarization Vi=V Vi= to PBS for free space or fiber based architectures Input Lensed fibers Output Polarization Switches array Fibered Polarization splitters Block of delays Fibered Polarization combiners

84 / 4 channels EO ceramic polarization switch Incident polarization V-groove array Gnd V V V 1 2 3 V 4 3 µs response time < 2 db insertion loss > 2 db extinction ratio 45 PM fibers EO ceramic (PLZT) Output polarization Vi=V Vi= to PBS 85 / Rx Dispersive OBFN principle 4 lines Sub-arrays Antenna Optical summation of RF signals LNA LNA LNA LNA 1 2 3 4 Elevation Laser 1 Laser 2 Laser i Laser 4 W D M Optical rotary joint 1 2 LNA : Low Noise Amplifier WDM : Wavelength Division Multiplexing Splitter : standard balanced optical power splitter True time delay laws are applied 1 through the set of dispersive fibers 2 j i i 4 S P L I T T E R Dispersive fiber Dispersive fiber Dispersive fiber ODEON Pd Pd Pd Pd n Beam 1 Beam2 Beam 3 Beam 4

-1.E+2-8.E+1-6.E+1-4.E+1-2.E+1.E+ 2.E+1 4.E+1 6.E+1 8.E+1 1.E+2.E+ -5.E+ -1.E+1-1.5E+1-2.E+1-2.5E+1-3.E+1-3.5E+1-4.E+1-1.E+2-8.E+1-6.E+1-4.E+1-2.E+1.E+ 2.E+1 4.E+1 6.E+1 8.E+1 1.E+2.E+ -5.E+ -1.E+1-1.5E+1-2.E+1-2.5E+1-3.E+1-3.5E+1-4.E+1-1.E+2-8.E+1-6.E+1-4.E+1-2.E+1.E+ 2.E+1 4.E+1 6.E+1 8.E+1 1.E+2.E+ -5.E+ -1.E+1-1.5E+1-2.E+1-2.5E+1-3.E+1-3.5E+1-4.E+1 86 / Dispersive OBFN principle has been validated with a 4 channel mock-up Radiating patterns without beam squint No temperature sensitivity 3 GHz 3.3 GHz 2.7 GHz Dispersive OBFN MOCK-UP Lasers WDM 12 m Fibers Several OBFN architectures have reached TRL 4 mainly depending on operating bandwidth L1 L2 L3 L4 C W D M Pd Climatic chamber -4 C -> +65 C Pd 87 / Analog processing of the receive mode microwave signals spread over a large dynamic range (up to 1 db) frequency bandwidth from 1% (radar) up to 2-18 GHz (E.W) in-phase addition over a large frequency BW of the received signals with a precision of few degrees need of pxp analog microwave / optical links with large dynamic range and low noise figure limited dynamic range of opto-links (typ. 9-95 db in 1 MHz BW) architecture with matched local oscillator (time-delayed and optically carried)

88 / Time reversal vs matched L.O transmitted j received direct transposition time reversal matched LO transmitted j receive d matched L.O phase conjugation 89 / Matched L.O Implementation of the delays f t f lo SLM 1 SLM 2 optical carriers of the transmitted signal and of the L.O - with crossed polarizations - at different wavelengths complementary time delays on each channel i : - max - i for the matched L.O - i for the transmitted signal

9 / Matched L.O architecture f tr f LO max - i f LO network 2:1 2D time delay PD i PD n f tr, i Radar Processing f LO -f r f r in phase I.F signals T/R module f tr f r 91 / Matched Local Oscillator Architecture single mixing on channel j : transmitted signal : cos [ 2f tr ( t - j ) ] local oscillator : cos [ 2f LO ( t - ( max - j ) ) ] received signal : cos [ 2f r ( t - T + j ) ] intermediate frequency f I signal : LO cos [ 2( f LO -f r ) t + 2( f LO -f r ) j -2f LO max + 2f r T ] in-phase addition of the signals at f I when 2p ( f LO -f r ) t j << phase quantization tr. j rec.

92 / Experimental results double mixing Two channel architecture with: f = 2.8 GHz I.F= 7 MHz in phase I.F signals residual errors < 1 ps, ~ 5 o I.F signal for no delay between the channels I.F signal for time delay = 45 ps between the channels