Application of the optical fiber to generation and measurement of low phase noise microwaves

International audienceThe optical delay line proved to be a method to measure the phase noise of microwave oscillators with high sensitivity. The delay, inherently, turns frequency fluctuations into phase fluctuations. Hence, a mixer is used to compare the phase of the oscillator signal to a delayed copy, from which we measure the oscillator phase noise. This article reports on the progress in this type of instruments in our laboratory. For practical reasons, the delay is implemented with an optical-fiber channel, either at 1.3 or 1.55 µm wavelength, modulated in intensity. The laser Relative Intensity Noise (RIN) turns out to be a critical parameter because it converts the RIN into near DC noise through the mixer offset sensitivity to power. The best semiconductor lasers we can find show a RIN of about -155 dB/Hz. Additionally, in our experience the simple microwave photodiodes are to be preferred to the photodiodes with integrated transconductance amplifier because of the lower noise. This seems to be a technical issue, rather than a general property. Thus, we used a separate amplifier, based on SiGe technology for lowest flicker. The optical fiber is temperature stabilized by an Aluminum mass and a sub-milliKelvin electronic control. Other components, like the Mach Zehnder intensity modulator, seem to be less critical for noise. A single channel version was realized and tested with a microwave synthesizer and with a sapphire whispering gallery oscillator at 10 GHz carrier frequency. Using a 2 km delay line (Τ=10 µs) the measured 1/f3 noise is b-3 = -12 dB.rad²/Hz, which matches the a-priori knowledge of the oscillator 1/f3 noise. This means that the instrument sensitivity is higher than this value, thus it is sufficient to measure a room-temperature sapphire oscillator without need of correlation. At higher Fourier frequencies, the instrument background noise is of -145 dBrad²/Hz at 10 kHz off the carrier. Unfortunately, with other source types (eg, a synthesizer) the background noise can be higher because of the effect of am noise. Another test of the noise floor consists of shortening the optical delay to a negligible value. In this way, the oscillator noise is rejected. Unfortunately, this is only a qualitative test because it hides the noise of the optical fiber, due to Rayleigh scattering and other optical phenomena. The background noise is reduced proportionally to 1/√m, where m is the number of averaged spectra, by correlation and averaging on two fully independent channels that measure the same oscillator. Using 2 km optical fibers and averaging on 200 spectra, the background noise is of -110 dBrad²/Hz at 100 Hz off the carrier, and of -160 dBrad²/Hz at 10 kHz. Re-using the parts of the two-channel system, we assemble single-channel system with matched 10 µs optical delays at the two inputs of the mixer, which rejects the noise of the oscillator. The 1/f noise measured in this condition, b-1 = -113 dBrad²/Hz referred to one channel, is the background noise of the system without correlation, which includes amplifiers, detector and optical fiber

Applications of the optical fiber to the generation and to the measurement of low-phase-noise microwave signals

The optical fiber used as a microwave delay line exhibits high stability and low noise and makes accessible a long delay (>100 microseconds) in a wide bandwidth (about 40 GHz, limited by the optronic components). Hence, it finds applications as the frequency reference in microwave oscillators and as the reference discriminator for the measurement of phase noise. The fiber is suitable to measure the oscillator stability with a sensitivity of parts in 1E-12. Enhanced sensitivity is obtained with two independent delay lines, after correlating and averaging. Short-term stability of parts in 1E-12 is achieved inserting the delay line in an oscillator. The frequency can be set in steps multiple of the inverse delay, which is in the 10-100 kHz region. This article adds to the available references a considerable amount of engineering and practical knowledge, the understanding of 1/f noise, calibration, the analysis of the cross-spectrum technique to reduce the instrument background, the phase-noise model of the oscillator, and the experimental test of the oscillator model.Comment: 23 pages, 13 figures, 41 reference

Implementing two-photon interference in the frequency domain with electro-optic phase modulators

Frequency-entangled photons can be readily produced using parametric down-conversion. We have recently shown how such entanglement could be manipulated and measured using electro-optic phase modulators and narrow-band frequency filters, thereby leading to two-photon interference patterns in the frequency domain. Here we introduce new theoretical and experimental developments showing that this method is potentially a competitive platform for the realization of quantum communication protocols in standard telecommunication fibres. We derive a simple theoretical expression for the coincidence probabilities and use it to optimize a Bell inequality. Furthermore, we establish an equivalence between the entangled- photon scheme and a classical interference scheme. Our measurements of two-photon interference in the frequency domain yield raw visibilities in excess of 99%. We use our high quality setup to experimentally validate the theoretical predictions, and in particular we report a violation of the CH74 inequality by more than 18 standard deviations.Comment: 19 pages, 3 figure

Applications of the optical fiber to the generation and to the measurement of low-phase-noise microwave signal

International audienceThe optical fiber used as a microwave delay line exhibits high stability and low noise and makes accessible a long delay (≳100 μs) in a wide bandwidth (≈40 GHz, limited by the optronic components). Hence, it finds applications as the frequency reference in microwave oscillators and as the reference discriminator for the measurement of phase noise. The fiber is suitable to measure the oscillator stability with a sensitivity of parts in 10−12. Enhanced sensitivity is obtained with two independent delay lines, after correlating and averaging. Short-term stability of parts in 10−12 is achieved inserting the delay line in an oscillator. The frequency can be set in steps multiple of the inverse delay, which is in the 10-100 kHz region. We add to the available references a considerable amount of engineering and practical knowledge, the understanding of 1/f noise, calibration, the analysis of the cross-spectrum technique to reduce the instrument background, the phase-noise model of the oscillator, and the experimental test of the oscillator model

High-performance 1560 nm Entangled Photon Source for high secure key rates QKD satellite-based communications

International audienceIn the frame of the Secure And cryptoGrAphic (SAGA) project under ESA ARTES 4.0 program we, report the design and the test of a high-performance entangled photon source (HP-EPS) dedicated to QKD satellite-based communication by using C-band fibered telecom components. We developed an asynchronous time binning higher than 10 bits/sec and 5 bits/sec for respectively a 60 dB (LEO) and 65 dB (GEO) transmission loss budget (both downlinks combined). The compactness and simplicity of the optical design, the low electrical consumption and the low mass combined with the robustness of the all-fibered design to the space environment (mechanical vibrations, shock, and radiation)s make the HP-EPS a new challenger to the satellite-based QKD quest

Realization of a phase noise measurement bench using cross correlation and double optical delay line

International audienceIn this paper are presented first results obtained with a phase noise measurement bench system operating in X-band, realized in our laboratory, using double optical delay line and cross correlation. Phase noise floor using a microwave sapphire oscillator is better than -160 dB.rad²/Hz at 10 kHz from the 10 GHz carrier, using a 2 km optical delay line

Frequency-Bin Entanglement using Cross-Polarized Twin-Photon Frequency Comb Source

International audience&nbsp;&nbsp; We report a frequency fin entanglement experiment using a commercial cross-polarized of high brightness frequency entangles source combining with inline Fabry Perot etalon at 1550 nm allowing the generation of cross-polarized frequency comb entangled photons.<br&g

Manipulating Frequency Entanglement with Phase Modulators

info:eu-repo/semantics/publishe

Enchevêtrement de paires de photons dans le domaine fréquentiel

info:eu-repo/semantics/publishe

Two-photon interference using frequency-bin entanglement

info:eu-repo/semantics/publishe