Dual frequency laser principle

Transcription

1 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 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

2 5 / Dual frequency laser source (DFL) experimental demos 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) GHz GHz 9.6 GHz see also A. Rolland, paper 2192, Wednesday / Compact dual-frequency laser Er Yb doped glass electro optical ceramic Etalon laser beam fiber coupling pump beam tuning

3 52 / Compact dual-frequency laser >6 mw output power with 1 W pump power optical spectrum Level (dbm) Level (db) Wavelength (nm) free running beatnote Frequency (MHz) around 3.25 GHz 53 / Compact dual-frequency laser voltage tuning range Phase noise DSP (dbc/hz) Beatnote frequency (GHz) 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 Frequency (Hz) free-running phase noise Altaïr Custom Solid-State DFL Series

4 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 khz over the complete tunabilty range phase-noise PSD (dbrad 2 /Hz) Phase noise of the stabilized beatnote 1.6 GHz Free-running phase noise frequency (Hz) / Optical Phase-Locked-Loop (OPLL) stabilization Phase noise of the stabilized beatnote phase-noise PSD (dbrad 2 /Hz) Free-running phase noise Frequency (Hz) 1.6 GHz khz

5 56 / Optical Phase-Locked-Loop (OPLL) stabilization Phase noise of the stabilized beatnote : limiting noises phase-noise PSD (dbrad 2 /Hz) Free-running noise 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) Free-running noise Frequency (Hz) RF reference noise

6 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 n2 n1 4 cm long Er doped fiber laser similar results when pumped at 148 nm and 98 nm µm 2 RIN (db/hz) 59 / electrical spectrum of the beatnote (resolution bandwidth = 1 khz) Relative Power (db) Frequency (GHz) RIN (db/hz) short-term linewidth <1 Hz Frequency (Hz) 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 dB/dec pump = 98nm Frequency offset (Hz) pump =148 nm Foster Measurements [7] * S. Foster and al., Phys. Rev. A, 79,5382 (29)

7 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) passive 52 µm 78 µm 25 µm F. van Dijk, et al paper, Thursday session S5, 9: - 9: bias current (ma) 61 / Dual wavelength DFB lasers electrical power (dbm) 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 Frequency (GHz) heteordyne signal frequency (GHz) Frequency (GHz) heterodyne beating -3dB linewidth (MHz) section 2 bias current (ma) heterodyne signal -3 db linewidth (MHz)

8 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 nm MZM EDFA RF excitation mux Pin = -5 dbm Pin = 5 dbm Frequency (GHz) 5 km single mode fiber lower RIN with Raman amplifier for 5dBm input power well adapted to optical distribution of analog signals RIN (db/hz) RAMAN mux pump 4 nm to optical spectrum analyzer Pin = -5 dbm Pin = 5 dbm Frequency (GHz)

9 64 / Low noise / high linearity optical amplification Raman based fibre amplifier signal 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 mux EDFA RAman RAMAN 5 km single mode fiber Time (a.u.) Time (a.u.) correlation coefficient 1 mux pump 4 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.

10 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) 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 Frequency offset (Hz) Carrier frequency ~1 GHz

11 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 mm disks Q 1GHz ~ / 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 ~ ) Limited by injected power

12 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) RF mixer 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

13 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 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)

14 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)

15 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

16 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 =

17 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 : MHz pas de dépointage 81 / Optically controlled phased array antennas Transmit mode

18 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 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

19 84 / 4 channels EO ceramic polarization switch Incident polarization V-groove array Gnd V V V 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 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

20 -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 db in 1 MHz BW) architecture with matched local oscillator (time-delayed and optically carried)

21 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

22 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.

23 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