ABSTRACT
Quantum-enhanced stimulated Raman scattering (QE-SRS) is a promising technique for highly sensitive molecular vibrational imaging and spectroscopy surpassing the shot noise limit. However, the previous demonstrations of QE-SRS utilized rather weak optical power which hinders from competing with the sensitivity of state-of-the-art SRS microscopy and spectroscopy using relatively high-power optical pulses. Here, we demonstrate SRS spectroscopy with quantum-enhanced balanced detection (QE-BD) scheme, which works even when using high-power optical pulses. We used 4-ps pulses to generate pulsed squeezed vacuum at a wavelength of 844 nm with a squeezing level of -3.28 ± 0.12 dB generated from a periodically-poled stoichiometric LiTaO3 waveguide. The squeezed vacuum was introduced to an SRS spectrometer employing a high-speed spectral scanner to acquire QE-SRS spectrum in the wavenumber range of 2000-2280â cm-1 within 50 ms. Using SRS pump pulses with an average power of 11.3 mW, we successfully obtained QE-SRS spectrum whose SNR was better than classical SRS with balanced-detection by 2.27 dB.
ABSTRACT
Quantum-enhanced stimulated Raman scattering (QESRS) microscopy is expected to realize molecular vibrational imaging with sub-shot-noise sensitivity, so that weak signals buried in the laser shot noise can be uncovered. Nevertheless, the sensitivity of previous QESRS did not exceed that of state-of-the-art stimulated Raman scattering (SOA-SRS) microscopes mainly because of the low optical power (3 mW) of amplitude squeezed light [Nature594, 201 (2021)10.1038/s41586-021-03528-w]. Here, we present QESRS based on quantum-enhanced balanced detection (QE-BD). This method allows us to operate QESRS in a high-power regime (>30 mW) that is comparable to SOA-SRS microscopes, at the expense of 3 dB sensitivity drawback due to balanced detection. We demonstrate QESRS imaging with 2.89 dB noise reduction compared with classical balanced detection scheme. The present demonstration confirms that QESRS with QE-BD can work in the high-power regime, and paves the way for breaking the sensitivity of SOA-SRS microscopes.
ABSTRACT
We demonstrate that excess intensity noise of soliton fiber lasers in the average power regime exceeding 10â mW can be reduced by increasing the intracavity dispersion and reducing the pump power. Based on this strategy, we present a polarization-maintaining picosecond Yb fiber laser mode-locked by a nonlinear amplifying loop mirror whose excess noise is equal to the shot noise at an optical power of >10â mW.
ABSTRACT
We describe a successful introduction of maximum-likelihood-sequence estimation (MLSE) into digital coherent receivers together with finite-impulse response (FIR) filters in order to equalize both linear and nonlinear fiber impairments. The MLSE equalizer based on the Viterbi algorithm is implemented in the offline digital signal processing (DSP) core. We transmit 20-Gbit/s quadrature phase-shift keying (QPSK) signals through a 200-km-long standard single-mode fiber. The bit-error rate performance shows that the MLSE equalizer outperforms the conventional adaptive FIR filter, especially when nonlinear impairments are predominant.
ABSTRACT
We demonstrate unrepeated 200-km transmission of 40-Gbit/s 16-QAM signals using a digital coherent receiver, where the decision-directed carrier-phase estimation is employed. The phase fluctuation is effectively eliminated in the 16-QAM system with such a phase-estimation method, when the linewidth of semiconductor lasers for the transmitter and the local oscillator is 150 kHz. Finite-impulse-response (FIR) filters at the receiver compensate for 4,000-ps/nm group-velocity dispersion (GVD) of the 200-km-long single-mode fiber and a part of self-phase modulation (SPM) in the digital domain. In spite of the launched power limitation due to SPM, the acceptable bit-error rate performance is obtained owing to high sensitivity of the digital coherent receiver.
ABSTRACT
We propose an optoelectronic time-division demultiplexing scheme based on phase modulation and spectral filtering. The frequency of phase modulation is quarter the bit rate of the optical signal. Therefore, our scheme is applicable to 160-Gbit/s systems by using only a commercially available 40-GHz LiNbO(3) phase modulator and optical filter. The power penalties are less than 2 dB for all tributaries, when a 160-Gbit/s signal is demultiplexed by our scheme.
ABSTRACT
A circular-birefringence highly nonlinear fiber (CB-HNLF) with the nonlinear coefficient of 12 /W/km is fabricated successfully by twisting a commercial silica-based highly nonlinear fiber. Using the cross-phase modulation in a 100-m-long CB-HNLF and subsequent optical filtering, we realize error-free pulsewidth-maintaining wavelength conversion of 160-Gb/s signal with only 0.7-dB polarization sensitivity. In addition to the simplicity and stability, the demonstrated scheme features an ultrafast repolarizing functionality, where the degree-of-polarization of the input signal is restored in an all-optical manner. These advantages make the scheme highly attractive to be employed in the future photonic networks.
ABSTRACT
We propose a prescaled phase-locked loop (PLL) using a simple optoelectronic phase comparator based on phase modulation and spectral filtering. Our phase comparator has a high dynamic range of over 9 dB and a high sensitivity comparable to that using an electrical mixer. A PLL composed of our phase comparator enables to extract a low-noise 10-GHz clock from a 160-Gbit/s optical-time-division multiplexed (OTDM) signal.
ABSTRACT
We show theoretically and experimentally that the polarization sensitivity of asymmetric nondegenerate fiber four-wave mixing can be eliminated by using circularly polarized pump waves in a twisted fiber. By twisting a fiber at 15 turns/m and aligning the pump waves to a circular state of polarization, we successfully reduce the polarization sensitivity from 5.8 dB to 0.9 dB. Although the polarization-mode dispersion (PMD) of the twisted fiber sets the limitation to the conversion bandwidth, its effect is relatively small owing to the small PMD of the twisted fiber. The demonstrated scheme should be a simple and efficient way of realizing all-optical tunable wavelength converters and wavelength-exchange devices without polarization dependence.