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Japanese Journal of Applied Physics

Generation and Detection of Squeezed Light with Phase Tunable Fiber Loop Mirror using Polarization Beam Splitter

Norihiko Nishizawa, Masaki Hashiura Masaki Hashiura, Takeo Horio Takeo Horio, Masakazu Mori, Toshio Goto Toshio Goto, Kazuo Yamane

Published Jul 1, 1998• 5 citations
Publisher

Abstract

Squeezed light generation is demonstrated using a new scheme of nonlinear fiber loop mirror. The squeezed light can be generated stably in a compact setup and the phase difference can be changed arbitrarily. Using a 100 ps mode-locked pulse laser at 1.064 µm and 0.85 µm single-mode fiber, the quantum noise reduction of 2.0 dB below the shot noise level is observed in the frequency range of 25–35 MHz. Accounting for the detection efficiency, this corresponds to 2.9 dB squeezing.

DOI
10.1143/jjap.37.l792

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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.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•May 1, 2013•0 citations
Squeezed light generation is demonstrated using a new scheme of nonlinear fiber loop mirror. The squeezed light can be generated stably in a compact setup and the phase difference can be changed arbitrarily. Using a 100 ps mode-locked pulse laser at 1.064 µm and 0.85 µm single-mode fiber, the quantum noise reduction of 2.0 dB below the shot noise level is observed in the frequency range of 25–35 MHz. Accounting for the detection efficiency, this corresponds to 2.9 dB squeezing.
We analyze numerically the generation of photon-number squeezed light using an asymmetric fiber loop mirror. For photon-number squeezed light generation, the maximum squeezing can be obtained using this method. The evolution of the quantum noise for the optical pulse spectra is calculated using the quantized nonlinear Schrödinger equation and linearization approximation. It is shown that the squeezed light is generated by removing the increased quantum noise part of the spectrum and enhancing the decreased quantum noise part of the spectrum, by the interference of two pulses at the beam splitter. Although the mechanism of squeezing is similar to that of a spectral filter, the maximum squeezing is as large as -13 dB due to the interference.
We demonstrate the generation of squeezed vacuum using a wavelength-tunable soliton pulse and nonlinear polarization interferometer (NOPI). Since the soliton pulse is ideal for squeezed vacuum generation and the wavelength of the soliton pulse can be tuned easily, it is expected that we can demonstrate large squeezing over a wide wavelength range. Using NOPI, since it is possible to generate squeezed light by only passing the optical pulse through the optical fiber without spatial alignment, the squeezed light can be generated easily and stably. A maximum noise reduction of -2.46 dB below shot noise level was observed. Considering the effect of quantum efficiency, the corresponding magnitude of squeezing is estimated to be -4.22 dB. The squeezing was observed when the center wavelengths were 1625 nm and 1650 nm.
Squeezed vacuum generation is demonstrated using an ultrashort pulse fiber laser and a symmetric nonlinear polarization interferometer (NOPI). In this system, the squeezed vacuum can be generated only by passing the ultrashort pulse along the optical fiber. Noise reduction of -1.7 dB below shot noise level is observed. Considering the effect of quantum efficiency in this system, the corresponding magnitude of squeezing is estimated to be -2.7 dB. The system is constructed with all fiber devices and is compact, stable, and useful for practical applications.
We present the generation and detection of squeezed light in the 2 μm wavelength region. This experiment is a crucial step in realizing the quantum noise reduction techniques that will be required for future generations of gravitational-wave detectors. Squeezed vacuum is generated via degenerate optical parametric oscillation from a periodically poled potassium titanyl phosphate crystal, in a dual resonant cavity. The experiment uses a frequency stabilized 1984 nm thulium fiber laser, and squeezing is detected using balanced homodyne detection with extended InGaAs photodiodes. We have measured 4.0±0.1 dB of squeezing and 10.5±0.5 dB of antisqueezing relative to the shot noise level in the audio frequency band, limited by photodiode quantum efficiency. The inferred squeezing level directly after the optical parametric oscillator, after accounting for known losses and phase noise, is 10.7 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.