A dual-wavelength switchable perfect absorber, comprised of a continuous Au film, an alumina (Al2O3) spacer, an indium tin oxide (ITO) layer, double-layer Dysprosium-doped cadmium oxide (CdO:Dy) films, and a gold ring array from bottom to top, is numerically designed in this paper. The epsilon-near-zero (ENZ) properties are determined by the carrier concentration of these ENZ materials. As for ITO material, the carrier (electron) concentration can be electrically modified by applying a biasing voltage V. And different growth conditions afford significant variation of carrier concentration in CdO:Dy layers. Via changing the biasing voltage V, we can achieve broadband and multifrequency absorption in our infrared absorber. Especially, the proposed infrared absorber demonstrates excellent electrical regulation performance, enabling bidirectional switching of “ON” and “OFF” states at dual-wavelength. We also further reveal the absorption mechanism by establishing quasi-Fabry–Pérot cavity resonance model. In addition, it is shown that the infrared absorber can tolerate a wide range of incident angles as well as has polarization insensitive features by verification. This device has great potential in numerous optoelectronic applications, such as invisibility cloaking, sub-diffraction imaging, and thermal emission.
We propose an optically switchable ultra-broadband terahertz (THz) perfect absorber based on doped superlattice photonic-crystal silicon. The structure consists of a superlattice photonic crystal silicon slab capped by a SU-8 layer with no metal reflector. It achieves ultra-broadband perfect absorption due to the coupled cavity modes of superposed lattices with two different cavity radii and the enhanced diffraction assisted by the top SU-8 layer. Switchable absorption is realized by changing the carrier concentration of doped silicon controlled by pump beam. Simulation shows that proposed structure exhibits polarization-insensitive and wide-angle absorption with efficiency larger than 90% within 1.03 to 5 THz ultra-broadband, with modulation depth larger than 60% within bandwidth more than 1 THz. The all-dielectric structure uncommonly integrates optical switching, ultra-broadband absorption, polarization, and incident angle insensitivity, which may find potential applications in dynamic THz devices.
Real-time identification of frequency-hopping millimeter-wave (mm-wave) signals is a real challenge, due to the high demand for detection bandwidth and processing speed. In this paper, we propose and demonstrate a novel microwave photonic approach to identifying frequency hopping of mm-wave signals based on the concepts of photonic time stretch (PTS) and Reservoir Computing (RC). The PTS scheme allows the modulated signal to be slowed down hence reducing the required detection bandwidth. The developed RC model offers unique features such as being more efficient and time saving in temporal data pattern classification than traditional methods. According to the simulation, RC can recognize the hopping instants and give a precise hop timing estimation in real-time.
A waveform generation scheme based on complex filter and frequency-time mapping is proposed. In the experiment, a programmable processor was used for the complex filter. The shape of the spectrum is controlled by the amplitude frequency response, and the second order phase is controlled by the phase frequency response to realize frequency-time mapping. In experiment, rectangular pulse, sawtooth pulse and comb lines are realized by adjusting the complex filter. The influence of dispersion and spectral 3dB bandwidth on the time domain waveform is also analyzed. The proposed waveform generation is dynamically adjustable due to the dispersion is continuously tunable.
In this paper, we propose a push-pull type double fiber Bragg gratings liquid level sensor. It consists with two-matched fiber Bragg gratings and converts the shift of optical wavelength into output power according to the matching relationship between transmission spectrum and reflection spectrum of gratings. The output power of the optical sensor is linearly changed with liquid level by utilizing the push-pull structure. The liquid level sensor achieves self-demodulation, which greatly simplifies the sensing structure.
We consider the continuous wave propagation in a highly dispersive and nonlinear medium wherein the wave
propagation is governed by the generalized nonlinear Schrodinger equation. We demonstrate the novel flat-top
modulational instability gain for a wide range of modulation frequencies in the anomalous dispersion regime of highly
dispersive and nonlinear media. We find that the resulting MI gain is independent of input power. Besides, we compare
the analytical results with those of numerical results.
The temporal characteristics of a fiber ring laser are reported. The laser has a simple configuration, which contains
an Erbium-doped fiber amplifier (EDFA), a polarization controller (PC) and a coupler. The EDFA has a high saturation
power of 27dBm to provide the gain in the cavity. The PC is used to control the polarization state of light. A 99/1
coupler is used to extract the laser output. There is no filter in the cavity to confine the spectrum of the laser. The simple
laser configuration can operate in different temporal modes with different pump power. In the self mode locking state,
the repetition rate is equal to the inverse of the round trip time of the cavity. The repetition rate of the laser can be
increased by increasing the pump power of the EDFA. This self mode locking phenomena is due to the homogeneous
gain medium in the cavity, rather than the nonlinear effect in the cavity. The nonlinear effect can suppress the self mode
locking phenomena by inserting a short length highly nonlinear fiber in the laser cavity.
A novel filter with tunable bandwidth and wavelength is introduced. Its bandwidth can be tuned by a transverse voltage. And its wavelength can be tuned by a longitudinal voltage. The main parameters that affect its properties are synthetically analyzed. Computer simulation results show that its transmission bandwidth is changeable and the transmission spectrum with rectangular working area is close to the ideal band-pass function. Experimentally, its free spectral range is more than 50nm. The tunable range of the center wavelength is about 50nm. The full width at half maximum can be tuned from 1.2nm to 50nm.
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