Effect Of Phase Mismatch Research Articles

Modelling second harmonic generation at mid-infrared frequencies in waveguide integrated Ge/SiGe quantum wells.

A promising alternative to bulk materials for the nonlinear coupling of optical fields is provided by photonic integrated circuits based on heterostructures made of asymmetric-coupled quantum wells. These devices achieve a huge nonlinear susceptivity but are affected by strong absorption. Here, driven by the technological relevance of the SiGe material system, we focus on Second-Harmonic Generation in the mid-infrared spectral region, realized by means of Ge-rich waveguides hosting p-type Ge/SiGe asymmetric coupled quantum wells. We present a theoretical investigation of the generation efficiency in terms of phase mismatch effects and trade-off between nonlinear coupling and absorption. To maximize the SHG efficiency at feasible propagation distances, we also individuate the optimal density of quantum wells. Our results indicate that conversion efficiencies of ≈ 0.6%/W can be achieved in WGs featuring lengths of few hundreds µm only.

Extension of high-order harmonic generation cutoff from laser-ablated tin plasma plumes.

The high-order harmonic spectra from laser-ablated tin plasma plumes are investigated experimentally and theoretically at different laser wavelengths. It is found that the harmonic cutoff is extended to ∼84 eV and the harmonic yield is greatly improved by decreasing the driving laser wavelength from 800 nm to 400 nm. Appling the Perelomov-Popov-Terent'ev theory with the semiclassical cutoff law and one-dimensional time-dependent Schrödinger equation, the contribution of the Sn3+ ion to harmonic generation accounts for the cutoff extension at 400 nm. With the qualitative analysis of the phase mismatching effect, we reveal the phase matching caused by the dispersion of free electrons is greatly optimized in the 400 nm driving field relative to the 800 nm driving field. The high-order harmonic generated from laser-ablated tin plasma plumes driven by the short laser wavelength provides a promising way to extend cutoff energy and generate intensely coherent extreme ultraviolet radiation.

Some Features of the Formation of Quantum Ghost Imaging Considering the Effects of Self-Phase Modulation, Cross-Phase Modulation, and Phase-Mismatch

Some Features of the Formation of Quantum Ghost Imaging Considering the Effects of Self-Phase Modulation, Cross-Phase Modulation, and Phase-Mismatch

Generation of entangled photons via parametric down-conversion in semiconductor lasers and integrated quantum photonic systems

We propose and design a high-brightness, ultra-compact electrically pumped GaSb-based laser source of entangled photons generated by mode-matched intracavity parametric down-conversion of lasing modes. To describe the nonlinear mixing in highly dispersive and dissipative waveguides, we develop a nonperturbative quantum theory of parametric down-conversion of waveguide modes which takes into account the effects of modal dispersion, group and phase mismatch, propagation, dissipation, and coupling to noisy reservoirs. We extend our theory to the regime of quantized pump fields with a new approach based on the propagation equation for the state vector which solves the nonperturbative boundary-value problem of the parametric decay of a quantized single-photon pump mode and can be generalized to include the effects of dissipation and noise. Our formalism is applicable to a wide variety of three-wave mixing propagation problems. It provides convenient analytic expressions for interpreting experimental results and predicting the performance of monolithic quantum photonic systems.

Experimental study of the effect of phase mismatch on a CW-pumped cascaded quadratic nonlinear frequency comb

Optical frequency comb generation by continuous-wave-pumped cascaded quadratic nonlinearities (CQN) appears a promising alternative to well-established modelocked lasers, especially if access to the mid-infrared spectral region is needed. We report an experimental investigation of spectral properties of a CQN frequency comb, which is based on second-harmonic generation (SHG) and is pumped internally by a continuous-wave optical parametric oscillator. Our study focuses on SHG phase mismatch, which has drawn little attention in the previously reported CQN frequency comb research. The main observation of our study is that it is possible to improve spectral purity of the CQN frequency comb by adjusting the phase mismatch. In addition to the CQN process that generates a frequency comb in the near-infrared region, our experimental setup involves several other nonlinear processes. These processes lead to a composite comb, which extends from visible to mid-infrared.

Common-mode interference and power conversion efficiency of differential rectifiers in RF energy harvesters

This paper studies the effect of amplitude and phase mismatch on the power conversion efficiency of differentially-drive rectifiers employing cross-coupled MOSFETs. The analysis begins by defining the different operational regions of the differential rectifier and how the common-mode interference resulting from amplitude and phase mismatches affects the symmetrical operation of the rectifier. A mathematical model is developed to estimate the output voltage and the power conversion efficiency under such mismatching conditions. Simulation and measurement results are provided to validate the mathematical model through the design of a three-stage differential rectifier in $$0.13\,{\upmu }\hbox {m}$$ CMOS technology. Modification to the original rectifier design using a tail load topology is also proposed to reduce the effect of mismatches.

Spatially structured transparency and transfer of optical vortices via four-wave mixing in a quantum-dot nanostructure

We propose a scheme to generate structured light using a medium consisting of semiconductor quantum dots via four-wave mixing (FWM). We consider a four-level quantum-dot structure where two strong electromagnetic fields couple upper-level biexciton transitions, whereas a weak field is applied to one of the ground-level exciton transitions. A weak signal field is generated, corresponding to a second ground-level exciton transition; thus the overall configuration transforms into a closed-loop diamond-type shape. To realize a spatially dependent modulating quantum-dot medium, we consider strong coupling fields as structured lights and investigate different regions of spatially structured electromagnetically induced transparency via absorption of the generated signal field. The azimuthal phase-dependent modulation of the absorption profile of the generated signal field is the key factor behind the creation of structured light. In addition, we also demonstrate transfer of orbital angular momentum (OAM) of the control beam to the generated beam through the FWM process and study the effect of phase mismatch on efficiency of the OAM transfer.

Influence of co- and counter-propagating light on the phase-mismatch effect in semiconductor optical amplifiers

The phase-mismatch effect, caused by the difference in confinement factor between transverse electric (TE) and transverse magnetic (TM) modes, has not been observed in semiconductor optical amplifiers (SOAs) and is not typically accounted for. In this work, we investigate the characteristics of the phase-mismatch four wave mixing (FWM) effect, which occurs in SOA devices. Our results reveal a sinc-like response in the intensity of co- and counter-FWM conjugates as a function of the detuning shift between interacting beams. It is demonstrated that the coherence lengths between the phase match/mismatch cycles differ between co- and counter-propagating nondegenerate FWM experiments and depend on the amplified TE/TM polarizations of interacting waves aligned with respect to the birefringent axes of SOAs. The coherence lengths between each phase match/mismatch cycle in co-propagation experiments are found to be 1600 and infinite GHz, respectively, compared to 800 and 400 GHz found in counter-propagation experiments.

Phase-mismatch dependence of the four-wave mixing effect in semiconductor optical amplifiers.

The phase-mismatch effect due to polarization-dependent mode confinement factor has been shown to be not a crucial problem in semiconductor optical amplifiers (SOAs) and is usually not accounted for. The phase-mismatch four-wave mixing (FWM) process in SOA devices is experimentally reported. The results reveal a sinc-like behavior in the intensity of FWM conjugate as a function of wavelength separation between transverse electric (TE)/transverse magnetic (TM) pumps due to induced confinement factors difference. Efficient FWM occurred for a detuning shift of about 500 GHz, limited by phase-mismatch conditions and determined by coherence length required for low and high frequencies to complete a full phase-match cycle. Phase-match FWM with an infinity coherence length can be fulfilled by proper alignments of co-polarized TE/TM modes of input waves with respect to the birefringent axes of the device structure.

A 64-Element 28-GHz Phased-Array Transceiver With 52-dBm EIRP and 8–12-Gb/s 5G Link at 300 Meters Without Any Calibration

This paper presents a 64-element 28-GHz phased-array transceiver for 5G communications based on $2\times 2$ transmit/ receive (TRX) beamformer chips. Sixteen of the $2\times 2$ TRX chips are assembled on a 12-layer printed circuit board (PCB) together with a Wilkinson combiner/divider network and 28–32-GHz stacked-patch antennas. The 64-element array results in 1.1 dB and 8.9° rms amplitude and phase error, respectively, with no calibration due to the symmetric design of the $2\times 2$ beamformer chips and the PCB Wilkinson network. The effect of phase and amplitude mismatch between the 64 elements is analyzed and shown to have little impact on the 64-element array performance due to the averaging effects of phased arrays. Detailed pattern, effective isotropic radiated power (EIRP), and link measurements performed without any array calibration are presented and show the robustness of the symmetrical design technique. The phased array can scan to ±50° in azimuth ( $H$ -plane) and ±25° in elevation ( $E$ -plane) with low sidelobes and achieves a saturated EIRP of 52 dBm with 4-GHz 3-dB bandwidth. A 300-m wireless link is demonstrated with a record-setting data rate of 8–12 Gb/s over all scan angles using two 64-element TRX arrays and 16-/64-QAM waveforms.

A 6.7–11.2 Gb/s, 2.25 pJ/bit, Single-Loop Referenceless CDR With Multi-Phase, Oversampling PFD in 65-nm CMOS

A single-loop referenceless clock and data recovery (CDR) with a compact frequency acquisition scheme is presented. A bang–bang phase–frequency detector (BBPFD) is proposed that tracks the frequency difference by detecting the drift direction of the non-return to zero bit stream with respect to the multi-phase clock and generates UP/DN output signals accordingly. When frequency locked, the BBPFD is degenerated into the conventional bang–bang phase detector (BBPD). The UP/DN output signals from the BBPFD are thus connected directly to the loop filter, thereby reducing the acquisition time without any loss of cycles. The effect of sampling phase mismatch is analyzed, and the capture range is calculated. In addition, the frequency acquisition time is analytically derived and verified by simulation. The proposed CDR has been implemented in a 65-nm CMOS process and occupies an active area of 0.047 mm2. The measured capture range is 6.7–11.2 Gb/s, and the frequency acquisition time is less than 2.19 $\mu \text{s}$ . The proposed CDR achieves error-free operation (BER < 10−12) for PRBS31 pattern and consumes 22.5 mW at 10 Gb/s.

Interference and phase mismatch effects in coherent triple sum frequency spectroscopy

Triply resonant sum frequency is a fully coherent method for multidimensional vibrational/electronic spectroscopy that creates cross-peaks between fundamental, overtone, and combination band vibrational states and electronic/vibronic states if they are coupled. It is also a methodology that cannot be phase matched. This paper explores the consequences of coherent interference and phase matching on the multidimensional spectra obtained in experiments performed in sample cells. Fringes appear in the multidimensional spectra and simulations show the character of the fringes depend on the refractive index dispersion, the thickness of different parts of the sample cell, the volume of the excitation region, and the relative third order susceptibility of the sample and the windows. It is suggested that the fringes provide a mechanism for determining the third order susceptibility and its multidimensional dispersion.

Terahertz Electro-Optic Sampling in Thick ZnTe Crystals Below the Reststrahlen Band With a Broadband Femtosecond Laser

The method of electro-optic (EO) sampling of terahertz (THz) pulses in thick EO crystals leads to waveform distortions due to effects of phase mismatch, dispersive propagation, and absorption. In this paper, we demonstrate theoretically and experimentally that EO sampling with a broadband femtosecond (fs) laser could significantly eliminate these distortions below the Reststrahlen band. Our simulation results show that the oscillations and dips in the signals of EO response function of thick crystals are smoothed out by the broadband spectrum of the femtosecond laser. In the experiment, we use a laser with a bandwidth of 100 nm and a low temperature GaAs photoconductive antenna to generate typical THz pulses (0.1–3 THz). The measurement results confirm that a $\langle {110} \rangle $ -oriented 3-mm-thick ZnTe crystal is an attractive EO material for sampling THz pulse below 3 THz and agree with simulation results. This technique is particularly useful in areas where a large time window is needed, for example in the THz time-domain spectroscopy system.

High-efficiency backward four-wave mixing by quantum interference

Electromagnetically-induced-transparency-based four-wave mixing (FWM) in a resonant four-level double-Λ system has a maximum conversion efficiency (CE) of 25% due to spontaneous emission. Herein, we demonstrate that spontaneous emission can be considerably suppressed by arranging the applied laser beams in a backward configuration. With the backward double-Λ FWM scheme, we observe a CE of 63% in cold rubidium atoms with an optical depth (OD) of 48. To the best of our knowledge, this is the first observation of a CE exceeding the conversion limit in resonant FWM processes. Furthermore, we present a theoretical model that includes the phase-mismatch effect in the backward double-Λ FWM system. According to the theoretical model, the present scheme can achieve 96% CE using a medium with a large OD of 200 under ideal conditions. Such an efficient frequency conversion scheme has potential applications in optical quantum information technology.

Planar light bullets under conditions of second-harmonic generation.

We study solutions to second-harmonic-generation equations in two-dimensional media with anomalous dispersion. The analytical solution is obtained in an approximate form of the planar spatiotemporal two-component soliton by means of the averaged Lagrangian method. It is shown that a decrease in the amplitudes of both soliton components and an increase in the value of the transverse coordinate are accompanied by an increase in their temporal duration. Within this variational approach, we have managed to find a stability criterion for the light bullet and a period of oscillations of soliton parameters. Then, we use the obtained form as an initial configuration to carry out the direct numerical simulation of soliton dynamics. We demonstrate stable propagation of spatiotemporal solitons undergoing small oscillations predicted analytically for a long distance. The formation of a two-component light bullet is shown when we launch a pulse only at the fundamental frequency. In addition, we investigate the phase and group-velocity mismatch effects on the propagation of pulses.

Slow light enhanced atomic frequency comb quantum memories in photonic crystal waveguides

In this paper, we propose a slow light-enhanced quantum memory with high efficiency based on atomic frequency comb (AFC) in ion-doped photonic crystal waveguide (PCW). The performance of the quantum memory is investigated theoretically, considering the impact of the signal bandwidth. Both the forward and backward retrieval schemes are analyzed. In the forward retrieval scheme, the analysis shows that a moderate slow light effect can improve the retrieval efficiency to above 50% with very high fidelity, even when the intrinsic optical depth is very low and the signal bandwidth is comparable with the AFC bandwidth. In the backward retrieval scheme, retrieval efficiency larger than 90% can be obtained and fidelity can remain above 90% for signal with bandwidth much narrower than AFC bandwidth, when moderate slow light is introduced into waveguide with low intrinsic optical depth. Although the phase mismatching effect limits the slow light enhancement on retrieval efficiency and decreases the fidelity for signal with bandwidth approaching AFC bandwidth, we design a modified atomic frequency comb structure (MAFC) based on which a moderate slow light can make the retrieval efficiency larger than 85% and keep the fidelity above 80%. Our calculations show that the proposed scheme provides a promising way to realize high efficiency on-chip quantum memory.

Spectral broadening due to intra-cavity four-wave mixing at low pump powers in erbium-doped fiber ring laser

In this paper, we present the experimental results of multi-pump-induced four-wave mixing (FWM) in erbium-doped fiber ring laser (EDFRL) in the wavelength range of 1560–1600 nm. The required multiple pumps are generated within the ring cavity by an appropriate choice of the wavelength range of operation with a suitable length of erbium-doped fiber. By introducing the optical nonlinearity with specialty fibers such as the highly nonlinear fiber (HNLF) and dispersion shifted fiber (DSF), FWM processes occurring in the laser are studied at low powers of the pump laser at 980 nm. The prevalent FWM theory is improved to interpret the two-pump and four-pump-induced side band generation in the first- and second-orders, after including the effect of phase mismatch at the wavelengths used in the experiments.

Simultaneous high-speed planar imaging of mixture fraction and velocity using a burst-mode laser

Simultaneous high-speed quantitative imaging of mixture fraction and velocity is demonstrated using the fourth- and second-harmonic outputs, respectively, of a burst-mode Nd:YAG laser. A tenfold increase in the record length and 16-fold increase in per-pulse energy are achieved compared with previous measurements of mixture fraction using burst-mode and continuously pulsed diode-pumped solid-state lasers, respectively. The high output energy is used for quantitative, high-speed mixture-fraction imaging with acetone planar laser-induced fluorescence, which also enables simultaneous particle-based velocimetry without interference from particle scattering. A semiquantitative model is used to determine the limitations on fourth-harmonic output energy due to the effects of transient absorption and thermal phase mismatch over a range of repetition rates. Data are presented for mixing within a turbulent jet (Reynolds number of 15,000) and are validated by comparisons with known turbulent mixing laws and previously published data.

Effect of phase mismatch on second-harmonic generation in negative-index materials

Second-harmonic generation in negative-index metamaterials is considered. Theoretical analysis of the corresponding model demonstrates a significant difference of this phenomenon in conventional and negative-index materials. For example, and in contrast to conventional materials, there is nonzero critical phase mismatch. The behavior of interacting waves is dramatically different when phase mismatch is smaller or greater than a critical value.

Frequency‐tunable terahertz electromagnetic‐pulses generation based on an optical Fabry–Perot microresonator with variable birefringence material

AbstractA frequency‐tunable terahertz (THz)‐frequency electromagnetic‐pulses generation method is proposed based on an optical Fabry–Perot (FP) microresonator with variable birefringence materials. At the output FP microcavity, polarization mode beat with high‐frequency can be achieved due to the phase mismatch effect of the two polarization modes in the birefringence materials in the FP cavity. One can generate frequency‐tunable electromagnetic pulse radiation through changing the birefringence of the materials. When the birefringence changed from 3.7355 × 10−4 to 7.4710 × 10−2, electromagnetic‐pulses with frequencies from 0.05 to 10.0 THz can be obtained. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2879–2882, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26422