查看更多>>摘要：An accurate chirp synthetic aperture lidar is proven, and the chirp laser signal is generated by an optical filter selecting specific sidebands from infinite sidebands, which are generated by laser signals passing through an electro-optic phase modulator driven by a chirp signal. And the bandwidth and chirp rate of the N-th order sideband is N times as large as the chirp signal by the signal generator. Then, a chirp signal with a modulation bandwidth of 1.2 GHz and a tuning rate of 12 THz/s is obtained by selecting the positive second-order sideband by an optical filter. Next, by adopting composite optical phase-locking processing, the random phase caused by the lidar system will be well offset, and the phase is stable within 0.1rad. Finally, Laboratory imaging results show that the azimuth resolution of synthetic aperture lidar is better than 0.04 m. In the future, by applying the higher-order sideband, higher tuning rates and bandwidths can be expected.
Lawandy, Nabil M.Smuk, Andrei Y.Lovett, JohnathanUmyskov, Alexander...
5页
查看更多>>摘要：We experimentally study non-degenerate two-wave mixing where reflection from a moving mirror is used to create frequency shifts and show that both the subwavelength motion of the mirror and periodic reversal of the intensity grating direction significantly affect the frequency dependence of the two-wave mixing signals detected both in ruby and colloidal media. It is shown that the Doppler shifts are suppressed when the reflecting moving mirror excursions are small compared to a wavelength and that the periodic reversal of the mirror motion results in a response that does not produce the expected maximum at the grating relaxation time. An approximate theoretical model agrees well with the results of the experiments and elucidates the transition from the observed response to the previously described idealized Doppler shift models.
查看更多>>摘要：During green wavelength femtosecond laser ablation, d-band electrons are excited to become free and to participate in the absorption process. The increased electron temperature also induces the density of state shift and causes the gap between the d-band and the Fermi level to expand. The d-band electron transition effect during the laser ablation process causes nonlinear absorption, therefore, it should always be considered during simulations of laser-copper interaction. This study used a single femtosecond laser pulse with a wavelength of 515 nm and a pulse duration of 300 fs to ablate copper with fluence 0.7-63 J/cm(2). The experimental results were compared with the theoretical results, where a modified Drude-critical point model was adopted to simulate the ablation depth. The modified model considered the electron transition effect and a two-temperature model that assumed both the linear and nonlinear absorption effect. Comparison of the experimental and simulated results revealed that the simulated ablation depth obtained using the nonlinear absorption model was consistent with the experimental results.
查看更多>>摘要：This paper reports an optical injection locking (OIL) assisted all-optical microwave oscillator (AOMO) scheme for the photonic generation of a microwave (MW) signal and demonstrates a 40th harmonic single-mode signal generation with an external low-frequency radio-frequency (RF) signal. In this all-optical single-loop oscillator that only depends on optical devices, the stimulated Brillouin scattering (SBS) effect of a coil of single mode fiber (SMF) and a semiconductor optical amplifier (SOA) are used to select the oscillation frequency and modulate the optical feedback signal, respectively. The OIL effect in a distributed feedback (DFB) laser multiplies the frequency of the external RF signal. Thanks to the OIL module, it only requires an optical loop to acquire a single-mode oscillation and the oscillation signal is phase-related to the low-frequency RF source. The experiment demonstrates the generation of a single-mode MW signal of 10.71 GHz with an external RF signal of 267.8 MHz, with a frequency multiplication factor of 40. Mode-hopping is not evident in the output signal, and a moderately low-quality OIL signal is acceptable since unwanted harmonics and the phase noise floor of the OIL signal have little impact on the generated MW signal.
查看更多>>摘要：Distinguished from the dynamical phase gained by optical path difference, the geometric phase (GP) is an additional phase delay produced by the variation of polarization states when light propagates in an anisotropic medium. Its modulation amount does not depend on the thickness of the medium or the wavelength of the light, therefore, it is expected to realize smaller and faster phase modulation unit. Based on the principle that the geometric phase generated by two passes through a wave plate of circularly polarized light with the same rotation direction is four times the rotation angle of optical axis of the wave plate, a reflective phase modulation structure composed of an In-plane Switching (IPS) liquid crystal (LC) cell, a mirror and two quarter wave plates is proposed in this paper. Under the action of IPS electrodes, the LC director can rotate nearly 80 degrees in-plane to realize a 320 degrees GP modulation. Finite Difference Time Domain (FDTD) method is used to simulate the GP modulation, and an optical path for interferometric measurement is built. The experimental results are in good agreement with the simulation results. This method uses only a single layer of driving electrodes and a LC cell to achieve 320 degrees GP modulation, which avoids the alignment problem and provides a new idea for the spatial light dynamic modulator.
查看更多>>摘要：Stimulated Raman scattering (SRS) of deuteroxide was investigated using a pulsed Nd:YAG laser with a wavelength of 532 nm. After the pump laser passed through the first sample cell (C-1), the output light included the transmitted pump beam and the Stokes SRS lights, and the frequency difference between the two self-matched the O-D symmetric and antisymmetric stretching vibration modes. The 1st and the 2nd -order cascaded Stokes and the anti-Stokes SRS (Coherent Anti-Stokes Raman Spectroscopy-CARS) of both two modes were observed. The 2nd -order Stokes SRS and its CARS were firstly observed at a pump energy of 14.79 mJ. The pure Stokes SRS were always collinear with the pump beam along the axial direction. Some ring-like Stokes SRS and CARS, which originated from the four-wave mixing (FWM) processes, were also observed only in the forward direction along with different angles apart from the pump beam direction, respectively. This method not only reduced the SRS threshold but also increased the SRS intensity of the weak vibration mode, resulting in an energy conversion efficiency reaching up to 54%. The technique can be used in a tunable Raman laser.
查看更多>>摘要：A visible light communication (VLC) system with intensity modulation and direct detection is considered. A channel coding scheme based on a binary low-density parity-check (LDPC) code and M-ary pulse amplitude modulation (PAM) is designed. The LDPC encoder is followed by a many-to-one mapper. This mapper induces the input distribution for the non-equally spaced M-PAM alphabet under a desired dimming target. No auxiliary coding technique for DC-balance is needed. The coded scheme using non-equally probable M-PAM levels outperforms the use of equally probable levels showing capacity-approaching performance. Moreover, the scheme is flicker-free for typical information rates of a VLC system. The main advantage of the proposed scheme is that it does not incur any coding rate loss compared to other similar schemes in the literature.
查看更多>>摘要：We demonstrate controlled-NOT (CNOT) operation of a silicon nitride photonic integrated circuit using path-entangled photon pairs from a silicon-photonic integrated circuit as logical inputs. The CNOT gate is constructed by combining several silicon-nitride Mach-Zehnder interferometers for a linear-optical quantum gate. We package each of the two photonic circuits with electrical wire bonding and optical fiber bonding for stable measurement. The logical-basis fidelity of CNOT operation is measured better than 81% for the fully packaged photonic circuits.
NSTL
Elsevier