Flicker noise of high-speed p-i-n photodiodes

Transcription

1 Jet Propulsion Laboratory California Institute of Technology Flicker noise of high-speed p-i-n photodiodes E. Rubiola #%, E. N. Yu %, L. Maleki % # FEMTO-ST Institute, Besançon, France % JPL/CALTECH, Pasadena, CA, Dept. of Physics, California State Polytechnic University, Pomona, CA, USA Outline introduction method background noise results 1 Work carried out at the JPL/CALTECH under NASA contract, with support from ARL and AOSP/DARPA

2 p-i-n InGaAs photodiode light II forbidden region i F v F i F I forward bias region (not used) p layer i depletion region n substrate bias dark light V b bright light photoconduction load line P=0 v F =0 (virtual gnd) v F photovoltaic cell P= v F i F P=P max i F = I s [ exp v ] F kt/q 1 i P III photoconductive region short current I sc = V b /R kt/q 25.6 mv at 300 K i P = ηφ = η P hν photocurrent = ρp ρ = responsivity IV photovoltaic region 2 photoconductive region => lowest C => high speed

3 Signal and noise microwave-modulated IR microwave photocurrent with AM and PM noise P λ (t) = P λ [1 + m cos 2πν 0 t] i ac (t) = ρp λ m [1 + α(t)] cos [ω 0 t + φ(t)] white noise S i = 2qı Virtually no information on AM/PM flicker is available frequency distribution systems deep space network, VLBI, inter-lab link laser metrology Motivations 3 photonic oscillators (Leeson effect) (E. Rubiola, The Leeson effect, arxiv:physics/ )

4 Experimental method (1) the photodiode output is insufficient to saturate a mixer a preliminary survey suggests that the photodiode phase flickering is lower than that of a microwave amplifier (typical amplifier flicker -105 dbrad 2 /Hz at 1 Hz) we choose some photodiodes similar to one another, with a max speed of GHz (Discovery Semiconductors, Fermionics, Lasertron) a single-photodiode interferometric (bridge) scheme can t work because the equilibrium condition is difficult laser EOM hybrid 9 Δ RF synthes. carrier suppr. adj. 9 Σ LO IF 4 (detection of α or ϕ)

5 Experimental method (2) infrared 1.32 µ m YAG laser monitor output (13dBm) 22dBm EOM 50% coupler power meter iso P! iso (!3dBm) photodiodes under test P µ (!26dBm) hybrid r(t)!9 s(t) phase & aten. (carrier suppression)!9 % & g=37db RF LO =6dB IF phase $ (detection of " or #) v(t) g =52dB FFT analyz GHz power MHz ampli PLL synth. microwave near!dc bridge (interferometric) scheme # low phase noise, limited by the noise figure of the amplifier # carrier rejection in => the amplifier does not flicker # rejection of the source noise Rev. Sci. Instr p (2002), and arxiv:physics/ the noise of the amplifier is not detected Electron. Lett p (2003)

6 Background noise (1) well understood: phase-to-voltage gain [V/rad] thermal noise shot noise k d = S φ t = 2F kt 0 P µ + = 2F kt 0 R 0 ρ 2 P 2 λm 2 + S φ s = gpµ R 0 l 4q ρm 2 P λ [ ] g power gain dissip. ( ampli) loss [ ] dissip. loss [ dissip. loss ] P µ R 0 l F kt 0 q ρ m P λ microw. pow. charact. resist. (50 Ω) ssb mixer loss noise figure ( ampli) thermal energy ( J) electron charge ( C) responsivity [A/W] modulation index optical power 6 experimentally determined or up-bounded: contamination from AM noise (RIN)

7 Background noise (2) low optical power => thermal noise >> shot noise 1. replace the detectors with microwave signals synthes. hybrid 9 Δ RF carrier suppr. adj. 9 Σ IF LO (detection of α or ϕ) 2. terminate the input of the delta amplifier laser EOM iso hybrid 9 Δ RF synthes. 50% coupler iso 9 Σ LO IF carrier suppr. adj. (detection of α or ϕ) 7... and take the worst case

8 Technical difficulties (1): crosstalk high EOM driving power (22 dbm) low photodiode output power (-26 dbm) finite isolation ( db?) 8 even small fluctuations of the environment induce noise as a consequence of the fluctuating crosstalk work nighttime, when nobody is around W: waving a hand 0.2 m/s, 3 m far from the system B: background noise P: photodiode noise

9 Technical difficulties (2): reflections back reflection causes the spectrum to be polluted flares appear at random in some spectra, as shown unexplained physical mechanism 9 S: example of single spectrum, with optical connectors and no isolators B: background noise P: photodiode noise

10 Technical difficulties (3): reflections back reflections causes spectra to be polluted at random the average spectrum is smooth wrong slope it is difficult to identify and to discard polluted spectra 10 A: average spectrum, with optical connectors and no isolators B: background noise P: photodiode noise

11 Technical difficulties (4): fibers the path of the optical fibers affects the internal stresses, and in turn the reflections unpredictable effect on noise, which is not the photodiode noise trimming the system takes patience 11 F: after bending a fiber, 1/f noise can increase unpredictably B: background noise P: photodiode noise

12 Example of photodiode noise... after patient adjustement 12

13 Some results all the pair of two different photodiodes are compared photodiode S α (1 Hz) S ϕ (1 Hz) estimate uncertainty estimate uncertainty HSD DSC30-1K QDMH unit db/hz db dbrad 2 /Hz db 13 estimated uncertainty 0.5 db random, affects the differences (amplified by the three-corner method) 1 db systematic, affects all values in the same way (non amplified by the three-corner method)

14 Conclusions the photodetectors we measured are similar in AM and PM 1/f noise the 1/f noise is about -120 db[rad 2 ]/Hz other effects are easily mistaken for the photodetector 1/f noise environment and packaging deserve attention in order to take the full benefit from the low noise of the junction read the document arxiv:physics/ v1 14