Group Velocity Delay Research Articles

Time delay in the mixed pump two-stage cascade erbium-doped fiber

This thesis mainly focuses on the study of slow light under the mixed pump two-stage cascade erbium-doped fiber. Compared with previous studies, we adopt different pump optical fiber connections in structure and this structure can produce larger time delay. We specifically explore the relationship between modulation frequency, group velocity and time delay under different pump ratios. We find that the time delay gradually increases and the group velocity gradually decreases as the pump ratio M (M = P1480:P980) decreases. We also study length ratio and time delay at different frequencies. With the increase of length ratio N (N = L1:L2, L1 and L2 represent the length of the first and second cascaded optical fibers, respectively), the time delay all increases at different frequencies, and the time delay changes significantly at low frequencies.

High-sensitivity plasma density retrieval in a common-path second-harmonic interferometer through simultaneous group and phase velocity measurement

Precise measurements of the plasma density in ionized gas cells and discharged capillaries are critical to the design and operation of plasma-based accelerators, active plasma lenses, and plasma-based radiation sources. In this manuscript, a spectral-domain common-path second-harmonic interferometer is upgraded with the simultaneous measurement of the group and phase velocity, allowing for high-sensitivity density characterization (from the phase velocity advance) without the need for phase tracking from zero-density (enabled by the group velocity delay). The technique is applied to 1.5-cm-long plasma structures, without density ambiguity in parameter scans with >2π phase jumps. The single-shot sensitivity in phase retrieval is demonstrated at 63 mrad, equivalent to a density-length product of 1.8·1015 cm−2. This is an improvement of ×45 compared to group velocity analysis alone.

Angular dependent strong coupling between localized waveguide resonance and surface plasmon resonance in complementary metamaterials

We give direct evidence of both surface plasmon resonance (SPR) and localized waveguide resonance (LWR) contribution to the extraordinary optical transmission in complementary metamaterials. Strong coupling between SPR and LWR are also observed with clear evidence of Rabi splitting and anti-crossing phenomena. The splitting introduces sharp phase shift, which in turn enhances group velocity delay by the incident angle without geometric parameter change. The results not only clarify SPR and LWR effects in the extraordinary optical transmission, but also provide a novel route to control light-metamaterial interaction by angular modulation for on-chip slow light devices.

Pulse delay and group velocity dispersion measurement in V-type electromagnetically induced transparency of hot atom

Pulse delay with the group velocity dispersion (GVD) characteristics was studied in the V-type electromagnetically induced transparency in the hyperfine levels of atoms with a closed system configuration. The phase coherency between the pump and the probe laser beams was maintained. We studied the pulse delay and the GVD characteristics with the variation of the pump Rabi frequency taking optical density (OD) as a parameter. We observed a maximum of 268 ns pulse delay for 21.24 MHz pump Rabi frequency at OD 5.04 of the Rb vapor cell. For a better understanding of the experimental results, we have derived an analytical solution for the delay characteristics considering the thermal averaging. The analytical solution was derived for a three level V-type system. The theoretical plots of the delay and the GVD show the same characteristics as we observed in the experiment. This analytical approach can be further generalized for the higher level schemes to calculate different quantities such as susceptibility, group velocity delay or GVD characteristics.

Density characterization of discharged gas-filled capillaries through common-path two-color spectral-domain interferometry.

Electrically discharged plasma structures, typically several centimeters in length and sub-millimeter in diameter, have been applied to guide laser pulses in laser plasma accelerators and to focus ion and relativistic electron beams in compact, radially symmetric transport configurations. Knowledge of the on-axis plasma density is critical. Traditional density interferometry has been ineffective for these laser-machined structures, while group velocity delay (GVD) techniques involve combining two laser paths with corresponding alignment complexities and stability sensitivities. Here the GVD technique is advanced to a common-path two-color interferometer configuration performed in the spectral domain of a broad-bandwidth femtosecond laser. Multi-shot tracking of the phase is not required, and the common path assures improved stability. This in situ technique was validated on 15mm long plasma structures, measuring electron densities of 1017-1018 cm-3 for various fill pressures.

Simultaneous microwave photonic and phononic band gaps in piezoelectric–piezomagnetic superlattices with three types of domains in a unit cell

A novel phoxonic crystal using the piezoelectric (PMN-PT) and piezomagnetic (CoFe2O4) superlattices with three types of domains in a unit cell (PPSUC) is present, in which dual microwave photonic and phononic band gaps can be obtained simultaneously. Two categories of phononic band gaps, originating from both the Bragg scattering of acoustic waves in periodic structures at the Brillouin zone boundary and the electromagnetic wave-lattice vibration couplings near the Brillouin zone center, can be observed in the phononic band structures. The general characteristics of the microwave photonic band structures are similar to those of pure piezoelectric or piezomagnetic superlattices, with the major discrepancy being the appearance of nearly dispersionless branches within the microwave photonic band gaps, which show an extremely large group velocity delay. Thus, the properties may also be applied to compact acoustic-microwave devices.

Slow light in metal–insulator–metal waveguide by negative Goos–Hänchen shift

We demonstrated group velocity delay using a metal–insulator–metal structure for slow light that would be very simple to fabricate. A negative Goos–Hänchen shift of the surface plasmon resonance can be caused by incident radiation while reflecting, resulting in a general group delay. Using this phenomenon, we induced a group delay of 70fs using a very simple 20-μm-long waveguide.

Generation of multicolor vacuum ultraviolet pulses through four-wave sum-frequency mixing in argon

We demonstrate efficient generation of multicolor vacuum ultraviolet pulses with excellent mode quality through ${\ensuremath{\chi}}^{(3)}$-based four-wave sum-frequency mixing and third-order harmonic generation of 400- and 267-nm femtosecond laser pulses in argon gas. The ${\ensuremath{\chi}}^{(3)}$-based nonlinear optical processes were optimized with appropriate control of gas pressure and group velocity delay between the driving pulses. Furthermore, the pulse breakup effects were observed for tightly focused ultraviolet pulses.

Single-photon transport properties in an optical waveguide coupled with a Λ-type three-level atom

We investigate the single-photon transport properties in an optical waveguide coupled with a Λ-type three-level atom (ΛTLA) based on symmetric and asymmetric couplings between the photon and ΛTLA. The transmission and reflection coefficients of the single photon in such a hybrid system are deduced using the real-space approach. Symmetric and asymmetric bifrequency photon attenuators are realized by tuning the atom–photon couplings. The phase shift and group velocity delay of the transmitted single photon are also analyzed.

Slow Light in One-Dimensional Coupled-Resonator Waveguide Controlling by an Electric Field

The photon transport properties in one-dimensional coupled-resonator waveguide embedded with a quantum dot molecule are investigated. The calculations reveal that one can control the photon transport by using a gate electric field. The phase shift and group velocity delay of the transmitted single photon are discussed. This research may be found applications in integrated optoelectronic devices and solid quantum devices.

Photonic generation of arbitrary waveforms based on incoherent wavelength-to-time mapping

We demonstrate experimentally a radio frequency arbitrary waveform generator using the incoherent wavelength-to-time mapping technique. The system is implemented by amplitude modulation of a broadband optical resource whose spectrum is reshaped by a programmable optical pulse shaper and transmitted over a single mode fiber link. The shape of the generated waveform is controlled by the optical pulse shaper, and the fiber link introduces a certain group velocity delay to implement wavelength-to-time mapping. Assisted by the flexible optical pulse shaper, we obtain different shapes of optical waveforms, such as rectangle, triangle, and sawtooth waveforms. Furthermore, we also demonstrate ultra-wideband generation, such as Gaussian monocycle, doublet, and triplet waveforms, using the incoherent technique.

The connection between electromagnetically induced transparency in the Zeeman configuration and slow light in hot rubidium vapor

We experimentally studied Zeeman electromagnetically induced transparency (EIT) resonances and slow light propagation in hot Rb vapor. Propagation of weak σ− polarized light pulses in the presence of stronger σ+ polarized background through Rb vapor was realized using a single laser beam and the Pockels cell. The dependences of slow light group velocity and fractional pulse delay on the overall laser beam intensity and temporal pulse length showed that lower optical power and longer light pulses lead to improved EIT and slow light features. The connection between EIT and slow light was also investigated showing that narrower and more contrasted EIT resonances are necessary for further decreasing a group velocity.

Role of group velocity delay in Faraday rotation in a multilayer polymer lattice

We measure and model the spectral dependence of Faraday rotation in one-dimensional lattice structures composed of co-extruded alternating polymer layers of polymethylmethacrylate and polystyrene. We develop a theory that shows that the net Faraday rotation in a symmetric multilayer system is determined not by the total thickness of the constituent materials but by the time spent in each constituent material as measured by the overall group velocity delay of the structure and the relative energy distribution per material. We compare measured and computed Faraday rotation spectra for these films to theoretical predictions, taking into account ellipticity as well as layer thickness variations and finite spectral width detection. To measure rotations of these thin, non-magnetic, weak Faraday rotators, we constructed and optimized an apparatus capable of measuring broadband Faraday rotation spectra at 0.001° resolution for rotation angles as small as 0.002°.

Fano resonance analysis in a pair of semiconductor quantum dots coupling to a metal nanowire

We investigate theoretically a surface plasmon transport in the metal nanowire coupling to a pair of quantum dots. The Fano-type transmission spectrum is analyzed. The phase shift and group velocity delay of the transmitted surface plasmon are explored. The electromagnetically-induced-transparency-type transmission spectrum is also discussed.

The tunable dispersion based on side‐polished fiber bragg gratings

AbstractThe tunable‐dispersion characteristics of a side‐polished fiber Bragg grating (FBG) encapsulated in a polymer‐half‐filled metal cylinder are investigated at different pressures exerted on polymer.The related group velocity delay, chromatic dispersion, and polarization dispersion of the reflection bandwidth of side‐polished FBG are measured and analyzed for applications in optical communication systems. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:681–684, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26655

Effect of Dimple Potential on Ultraslow Light in a Bose-Einstein Condensate

We investigate the propagation of ultraslow optical pulse in atomic Bose-Einstein condensate in a harmonic trap decorated with a dimple potential. The role of dimple potential on the group velocity and time delay is studied. Since we consider the interatomic scattering interactions nonlinear Schrodinger equation or Gross-Pitaevskii equation is used in order to get the density profile of the atomic system. We find large group delays of order 1 msec in an atomic Bose-Einstein condensate in a harmonic trap with a deep dimple potential.

Amplified dispersive delay generator using angular dispersion amplification

Angular dispersion amplification can be used to design compact dispersive delay generators with delay amplification. A specific design is presented that can be used to generate 1 ns delay for two wavelengths separated by 1 nm. The delay generator can be easily switched from a positive to a negative group velocity delay and can be used as a pulse compressor, a pulse stretcher, or a pulse shaper in chirped pulse amplification, high-resolution time-gated spectroscopy as well as other applications.

Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay

This paper demonstrates an approach that negative uniaxial crystal has a relative anomalous dispersion effect which can compensate group velocity delay, and applies this approach to nonlinear frequency conversion of an ultrafast laser field. High efficiency of the third harmonic generation is experimentally fulfilled by adopting a collinear configuration of doubing-compensation-tripling system. Through finely adjusting the incident angle and optical axis direction of the compensation plate, it obtains ultraviolet (UV) output energy of 0.32 mJ centered at 270 nm with spectral bandwidth of 2 nm when input beam at 800 nm was 70 fs pulse duration and 6 mJ pulse energy which was extracted from Ti:sapphire laser system by a diaphragm, corresponding to an 800-to-270 nm conversion efficiency of 5.3% and a factor-of-1.6 improvement in the third harmonic generation of UV band in comparison with a general conventional configuration. Furthermore, when the full energy of 18 mJ from a Ti:sapphire laser system was used and optimized, the UV emission could reach 0.83 mJ.

Group velocity delay in coupled-cavity waveguides based on ultrahigh-Qcavities with Bragg reflectors

Optical waveguides formed by coupled ultrahigh-Q cavities have been investigated by finite-difference time-domain (FDTD) simulation. The flexible control of group velocity and bandwidth are demonstrated by adjusting the coupling strength. An ultrahigh group velocity dispersion (GVD) of 3 ? 106?ps??m?1??m?1 together with a group velocity as low as 3 ? 10?5c (c is the speed of light in vacuum) is obtained at the band edge, creating a potential application in dispersion compensation. In a coupled-cavity waveguide (CCW) consisting of cavities with quality factor (Q) of 106, slow light at c/100 with a useful bandwidth as wide as 230?GHz is demonstrated, in which the calculated propagation loss is only 1.3?dB?cm?1. A design for a cascaded CCW with inverse dispersion is proposed for the further improvement of bandwidth.

Laser pulse shaping for generating uniform three-dimensional ellipsoidal electron beams

A scheme of generating a uniform ellipsoidal laser pulse for high-brightness photoinjectors is discussed. The scheme is based on the chromatic aberration of a dispersive lens. Fourier optics simulation reveals the interplay of group velocity delay and dispersion in the scheme, as well as diffractions. Particle tracking simulation shows that the beam generated by such a laser pulse approaches the performance of that by an ideal ellipsoidal laser pulse and represents a significant improvement from the traditionally proposed cylindrical beam geometry. The scheme is tested in an 800-nm, optical proof-of-principle experiment at lower peak power with excellent agreement between the measurement and simulation.