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Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR)

Experimental demonstration of photon number squeezing with a noisy fiber amplifier source by balanced detection technique

Shota Sawai, Hikaru Kawauchi, Kenichi Hirosawa, Fumihiko Kannari

Published Jun 1, 2013• 0 citations
Publisher

Abstract

We demonstrated photon number squeezing at 1.55 μm using a noisy erbium-doped fiber laser, making use of collinear balanced detection technique, where intensity noise at a specific radio-frequency is canceled between two pulses.
DOI
10.1109/cleopr.2013.6600355

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Photon-number squeezing with a noisy femtosecond fiber laser amplifier source using a collinear balanced detection technique

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We experimentally demonstrate photon-number squeezing at 1.55 μm using a noisy erbium-doped fiber amplifier (EDFA). We employ a collinear balanced detection (CBD) technique, where the intensity noise at a specific radio frequency is canceled between two pulse trains. In spite of substantially large excess noise (>10 dB) in an EDFA due to amplified spontaneous emission, we successfully cancel the intensity noise and achieve a shot noise limit at a specific radio frequency with the CBD technique. We exploit two sets of fiber polarization interferometers to generate squeezed light and observe a maximal photon-number squeezing of -2.6 dB.

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Photon number squeezing with a noisy fiber amplifier source by balanced detection technique

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Summary form only given. Squeezed light at telecommunication wavelength is important source in the field of quantum information and communication technology, especially for realization of entanglement state with continuous variables. However, erbium-doped fiber amplifier (EDFA) used in classical communication systems contains substantially high intensity noise which is much higher than the shot noise level (SNL) due to beat noise of amplified spontaneous emission. Therefore, alternatively, optical parametric oscillators and Cr:YAG lasers have been employed for generation of squeezed light. In this work, we achieved photon number squeezing at 1.55 μm using a noisy EDFA laser as a light source, making use of collinear balanced detection technique, demonstrated by Nose et al.[1]. This technique compensates intensity noise at a specific radio-frequency by means of pulse splitting and recombination with a relative time delay τ. The photocurrent contributed by pulse trains is given by I(t) = I1(t) + I2(t) = I1(t) + I1(t-τ), where I1(t) and I2(t) is the photocurrent contributed by the first and second pules, respectively. The equation does not contain an interference term because any pulse does not temporally overlap each other. In the Fourier domain,we can obtain I(ω) = I1(ω) + I2(ω) = I1(ω) + I1(ω)exp(iωτ) and confirm the photocurrents are added up destructively at ω = π/τ. In our experiment, laser pulses, of which intensity noise is higher than 10dB from SNL, were divided into two parts and each of them experienced self-phase modulation during propagation through two different single-mode optical fibers. We detected the two pulse trains with a relative time delay and observed photon number squeezing a specific frequency. We used a femtosecond fiber laser (Femtolite, IMRA) as a light source. The center wavelength was 1560 nm and the repetition rate was 47.5 MHz. Figure 1 shows the experimental setup. We added time delay τ=1/frep, where frep is the repetition frequency, to one of the two pulse trains and added another delay deltaτ for preventing optical interference. We confirmed that intensity noise of the two pulse trains colineared at a polarization beam splitter (PBS) was coincident to the SNL both before and after fiber propagation at 22MHz. SNL was measured by balanced homodyne detection. We employed nonlinear polarization interferometer to generate squeezed light[2]. For measuring photon number squeezing, a branch ratio at PBS1 and PBS3,4 was adjusted to 90:10 and 95:5, respectively. We constructed another Michelson interferometer after a beam splitter to compensate the difference of fiber length. As a result, a maximum photon-number squeezing of 2.6 dB was obtained when average power was 4mW.

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Intensity squeezing-i.e., photon number fluctuations below the shot-noise limit-is a fundamental aspect of quantum optics and has wide applications in quantum metrology. It was predicted in 1979 that intensity squeezing could be observed in resonance fluorescence from a two-level quantum system. However, its experimental observation in solid states was hindered by inefficiencies in generating, collecting, and detecting resonance fluorescence. Here, we report the intensity squeezing in a single-mode fiber-coupled resonance fluorescence single-photon source based on a quantum dot-micropillar system. We detect pulsed single-photon streams with 22.6% system efficiency, which show sub-shot-noise intensity fluctuation with an intensity squeezing of 0.59 dB. We estimate a corrected squeezing of 3.29 dB at the first lens. The observed intensity squeezing provides the last piece of the fundamental picture of resonance fluorescence, which can be used as a new standard for optical radiation and in scalable quantum metrology with indistinguishable single photons.

arXiv:2009.06164•Physical Review Letters•Oct 7, 2020•24 citations
We experimentally demonstrate photon-number squeezing at 1.55 μm using a noisy erbium-doped fiber amplifier (EDFA). We employ a collinear balanced detection (CBD) technique, where the intensity noise at a specific radio frequency is canceled between two pulse trains. In spite of substantially large excess noise (>10 dB) in an EDFA due to amplified spontaneous emission, we successfully cancel the intensity noise and achieve a shot noise limit at a specific radio frequency with the CBD technique. We exploit two sets of fiber polarization interferometers to generate squeezed light and observe a maximal photon-number squeezing of -2.6 dB.
Summary form only given. Squeezed light at telecommunication wavelength is important source in the field of quantum information and communication technology, especially for realization of entanglement state with continuous variables. However, erbium-doped fiber amplifier (EDFA) used in classical communication systems contains substantially high intensity noise which is much higher than the shot noise level (SNL) due to beat noise of amplified spontaneous emission. Therefore, alternatively, optical parametric oscillators and Cr:YAG lasers have been employed for generation of squeezed light. In this work, we achieved photon number squeezing at 1.55 μm using a noisy EDFA laser as a light source, making use of collinear balanced detection technique, demonstrated by Nose et al.[1]. This technique compensates intensity noise at a specific radio-frequency by means of pulse splitting and recombination with a relative time delay τ. The photocurrent contributed by pulse trains is given by I(t) = I1(t) + I2(t) = I1(t) + I1(t-τ), where I1(t) and I2(t) is the photocurrent contributed by the first and second pules, respectively. The equation does not contain an interference term because any pulse does not temporally overlap each other. In the Fourier domain,we can obtain I(ω) = I1(ω) + I2(ω) = I1(ω) + I1(ω)exp(iωτ) and confirm the photocurrents are added up destructively at ω = π/τ. In our experiment, laser pulses, of which intensity noise is higher than 10dB from SNL, were divided into two parts and each of them experienced self-phase modulation during propagation through two different single-mode optical fibers. We detected the two pulse trains with a relative time delay and observed photon number squeezing a specific frequency. We used a femtosecond fiber laser (Femtolite, IMRA) as a light source. The center wavelength was 1560 nm and the repetition rate was 47.5 MHz. Figure 1 shows the experimental setup. We added time delay τ=1/frep, where frep is the repetition frequency, to one of the two pulse trains and added another delay deltaτ for preventing optical interference. We confirmed that intensity noise of the two pulse trains colineared at a polarization beam splitter (PBS) was coincident to the SNL both before and after fiber propagation at 22MHz. SNL was measured by balanced homodyne detection. We employed nonlinear polarization interferometer to generate squeezed light[2]. For measuring photon number squeezing, a branch ratio at PBS1 and PBS3,4 was adjusted to 90:10 and 95:5, respectively. We constructed another Michelson interferometer after a beam splitter to compensate the difference of fiber length. As a result, a maximum photon-number squeezing of 2.6 dB was obtained when average power was 4mW.
Photon-number squeezing and quadrature squeezing were studied using ultrafast fibre nonlinear optics pumped by 1.5 µm femtosecond laser pulses. To obtain quadrature squeezing using an Erbium doped fibre amplifiers (EDFA) light source, we developed temporal homodyne technology to exclude the excess noise of an EDFA light source. We also performed a quadrature squeezing experiment using an optical parametric oscillator light source in stead of an EDFA light source exhibiting substantially high excess noise. Although the photon-number squeezing of -3dB was obtained from an asymmetric Sagnac fibre loop, the quadrature noise could not decrease to less than the Shot noise level without cooling the fibre, which is presumably due to GAWBS. To suppress guided acoustic wave Brillouin scattering, we refrigerated the fibre loop by liquid nitrogen, and squeezing at -0.7 dB was obtained by cooling the fiber at liquid nitrogen temperature.
We numerically and experimentally demonstrate photon-number squeezed state generation with a symmetric fiber interferometer in an 800-nm wavelength and compared with an asymmetric fiber interferometer, although photon-number squeezed pulses have been generated only with asymmetric interferometers. Even though we obtain -1.0dB squeezing with an asymmetric fiber interferometer, since perfect spectral phase and intensity matching between displacement and signal pulses are achieved with a symmetric fiber interferometer, we obtain better squeezing of -3.1dB. We also numerically calculate and clarify this scheme's usefulness at a 1.55-μm wavelength.
Intensity squeezing-i.e., photon number fluctuations below the shot-noise limit-is a fundamental aspect of quantum optics and has wide applications in quantum metrology. It was predicted in 1979 that intensity squeezing could be observed in resonance fluorescence from a two-level quantum system. However, its experimental observation in solid states was hindered by inefficiencies in generating, collecting, and detecting resonance fluorescence. Here, we report the intensity squeezing in a single-mode fiber-coupled resonance fluorescence single-photon source based on a quantum dot-micropillar system. We detect pulsed single-photon streams with 22.6% system efficiency, which show sub-shot-noise intensity fluctuation with an intensity squeezing of 0.59 dB. We estimate a corrected squeezing of 3.29 dB at the first lens. The observed intensity squeezing provides the last piece of the fundamental picture of resonance fluorescence, which can be used as a new standard for optical radiation and in scalable quantum metrology with indistinguishable single photons.