Ultrafast Optical Gate Research Articles

Influence of Hot Carrier Cooling and Band‐Filling Effect on Linewidth of Perovskite Microlasers

AbstractIn semiconductor‐based microlasers, the generated excited carriers can affect both the optical absorption coefficient and refractive index, influencing the lasing behavior and device performance. In this study, the lasing behavior of individual MAPbBr3 microrods pumped by femtosecond laser pulses is investigated using an ultrafast optical Kerr gating technique. By analyzing the spectral and temporal evolution of the lasing behavior, it is found that the band‐filling (BF) effect can cause a significant change in the refractive index of the material, which results in an unfavorable red‐shift and broadening of the resonant modes, deteriorating the laser linewidth and quality factor. The hot carrier cooling process can provide a buffer for alteration of the energy level occupation state, resulting in a small transient refractive index change and slight red‐shift. These results offer insights into the lasing behavior driven by photogenerated carrier dynamics and provide an optimization strategy for semiconductor‐based microlasers.

An ultra fast optical reversible gate based on electromagnetic scattering in nonlinear photonic crystal resonant cavities

Optical reversible gates are required in realizing all optical digital data processing. In reversible gates, there is a one by one mapping between the input and output ports which helps us to recover the inputs from the outputs. In this paper we aim to design and propose all optical reversible XOR and XNOR gates based on electromagnetic scattering phenomenon in nonlinear photonic crystal structures. For realizing the proposed structures a special resonator was proposed which consists of two cross connected waveguides along with some linear and nonlinear defect rods. The proposed structure will be simulated using finite difference time domain method. The simulation results show that the maximum time delay for the proposed structures is about 10 ps. The truth tables for the both structures prove that there is one by one mapping between the inputs and outputs of the proposed structures.

Single femtosecond laser beam pumped transient diffraction and transient lens effects for ultrafast measurement in background-free geometry

We proposed an ultrafast optical gating configuration for ultrafast measuring the characters of a supercontinuum (SC) probe beam. Single femtosecond laser beam pumped transient diffraction (TrD) and transient lens (TrL) effects were realized at the same time, which ensured the measurement in background-free geometry. Experimental results showed that the proposed ultrafast optical gating was robust for very high signal-to-noise ratio (SNR) detecting.

Terahertz radiation from ultrahigh-speed field-effect transistors induced by ultrafast optical gate switching

We have observed terahertz radiation due to ultrafast change in drain current induced by optical gate-field modulation in high-speed field-effect transistors (FETs). This time-domain measurement is potentially applicable to the characterization of cutoff frequencies of ultrahigh-speed FETs beyond the frequency range covered by conventional swept-frequency measurements. The cutoff frequencies of sample FETs deduced by the present technique were in good agreement with those determined by a network analyzer.

InP-based ultrafast optical gate monolithically integrating uni-travelling-carrier photodiode and Mach-Zehnder modulator

A novel InP-based ultrafast optical gate that monolithically integrates a uni-travelling-carrier photodiode and a travelling-wave Mach-Zehnder modulator is proposed. Ultrafast operation with a short gate opening time of 5 ps and a high on/off ratio of 12 dB has been experimentally demonstrated.

Picosecond fluorescence lifetime imaging by parametric image amplification

We report a new method of fluorescence lifetime imaging that uses the ultra-fast optical temporal gating properties of parametric image amplification. Images with different lifetimes in the picosecond range are resolved with reliable and reproducible results.

500 Gbit/s optical gate monolithically integrating photodiode and electroabsorption modulator

Optical demultiplexing at a corresponding data rate of 500 Gbit/s has been achieved using an ultrafast monolithic optical gate integrating a photodiode and an electroabsorption modulator. The on/off ratio is 9 dB for adjacent channels and larger than 20 dB for other channels.

Ultrafast optical sampling gate monolithically integrating a PD and EAM

Optical sampling using an ultrafast monolithic optical gate integrating a photodiode (PD) and an electroabsorption modulator (EAM) has been demonstrated. Using this system, the fixed data and eye patterns of 80 Gbit/s return-to-zero signals were successfully observed.

160 Gbit/s error-free demultiplexing by ultrafast optical gate monolithically integrating photodiode and electroabsorption modulator

A 320 Gbit/s error-free demultiplexing operation with a receiver sensitivity of −18 dBm using a monolithic optical gate integrating a uni-travelling-carrier photodiode and a travelling-wave electroabsorption modulator has been demonstrated. High on/off ratios of 14 dB for adjacent channels and 28 dB for the others have also been achieved.

ULTRAFAST COHERENT TERAHERTZ SPECTROSCOPY IN HIGH MAGNETIC FIELDS

With an aim towards measuring the high-frequency complex conductivity of correlated electron materials in the regime of low temperatures and high magnetic fields, we introduce a method for performing time-domain terahertz spectroscopy directly in the cryogenic bore of existing dc and pulsed-field magnets. Miniature, fiber-coupled THz emitters and receivers are constructed and are demonstrated to work down to 5 K and up to 6 Tesla, for eventual use in higher-field magnets. Maintaining the sub-micron alignment between fiber and antenna during thermal cycling, and obtaining ultrafast (<200fs) optical gating pulses at the end of long optical fibers constitute the major technical challenges of this project. Preliminary data on YBCO superconducting thin films is shown.

Fiber-coupled antennas for ultrafast coherent terahertz spectroscopy in low temperatures and high magnetic fields

For the purposes of measuring the high-frequency complex conductivity of correlated-electron materials at low temperatures and high magnetic fields, a method is introduced for performing coherent time-domain terahertz spectroscopy directly in the cryogenic bore of existing dc and pulsed magnets. Miniature fiber-coupled THz emitters and receivers are constructed and are demonstrated to work down to 1.5 K and up to 17 T, for eventual use in higher-field magnets. Maintaining the submicron alignment between fiber and antenna during thermal cycling, obtaining ultrafast (<200 fs) optical gating pulses at the end of long optical fibers, and designing highly efficient devices that work well with low-power optical gating pulses constitute the major technical challenges of this project. Data on a YBCO superconducting thin film and a high mobility two-dimensional electron gas are shown.

Real-time two-dimensional imaging in scattering media by use of a femtosecond Cr^4+:forsterite laser

An original femtosecond Cr(4+):forsterite laser source associated with a nonlinear optical correlator was used for imaging through scattering media with 1220-nm light. The system, which operates as an ultrafast optical gate by sum-frequency generation in a nonlinear crystal, was able to detect the light reflected from a resolution chart hidden in a turbid medium, at an attenuation of as much as 15 mean free paths. When the object was illuminated with a collimated beam, real-time two-dimensional images were obtained, with a maximum transverse resolution of ~20 microm.

Gain-switched semiconductor laser amplifier as an ultrafast dynamical optical gate

A gain-switched semiconductor laser is shown to act as an optical gate with picosecond resolution and amplification for light pulses from another laser source. The amplification mechanism and the gate width change qualitatively when the gate laser undergoes a transition from a pumping rate slightly below the dynamic laser threshold to slightly above the dynamic threshold. If the gate laser is pumped below but close to its dynamical threshold, unsaturated amplification of an external signal pulse occurs over a delay time range between the external optical pulse and the electrical driving pulse of about 100–200 ps which is equivalent to the optical gate width. The signal amplification is observed to increase by two orders of magnitude and the gate width decreases by one order of magnitude if the gate laser is pumped slightly above the dynamical threshold. Amplification then occurs for input signals injected much earlier. A detailed theory of coherent, time-dependent amplification including the nonlinear dynamics of the semiconductor laser is shown to account for the observations. Both amplification regimes, below and above threshold, are reproduced in the numerical simulations. The extremely short and highly sensitive gate range above threshold is identified as being due to the gain maximum related with the first relaxation oscillation of the laser.

Ultrafast optical nonlinearity by virtual charge polarization in DC-biased quantum well structures

An optical nonlinearity due to virtual charge polarization in a quantum-well structure biased by a DC electric field is proposed and discussed. The switching time of the nonlinearity is expected to be extremely short, on the order of 100 fs. An effective degenerative four-wave chi /sup 3/ parameter is estimated to be 1.0*10/sup -9/ (esu) for a graded gap AlGaAs quantum well and a detuning energy of pump light, 35 meV. The nonlinearity is observable and quite useful for designing an all-optical and ultrafast optical gate. >

Field-induced optical nonlinearity due to virtual transitions in semiconductor quantum well structures.

A new concept on optical nonlinearity due to virtual transitions in quantum well structure with electric field, named virtual charge-induced optical nonlinearity, is proposed, with a showing of some examples of theoretical result on the nonlinearity. The switching time of the nonlinearity is expected to be extremely short, 100 fs. The nonlinearity seems to be observable and quite useful for the design of an ultrafast optical gate. A possibility of optical bistability without external optical feedback, based on the proposed nonlinearity, is pointed out.

An ultrafast all-optical gate

We present a new ultrafast optical waveguide gate based on a nonlinear optical interaction in a waveguide interferometer. A train of signal pulses is gated by control pulses which change the refractive index in only one arm of the interferometer. The principle of operation is demonstrated using a modified Mach-Zehnder interferometer, 2 cm long, fabricated in a LiNbO 3 substrate. The experiments were performed with a near-infrared dye laser which produced 5 ps pulses at \lambda = 840 nm. A maximum modulation on the order of 10-3was obtained for a peak control power of 2 W. Experimentally, we determined the appropriate nonlinear coefficient of LiNbO 3 to be n_{2} = 3 \times 10^{-9} (MW/cm2)-1. As possible applications of the structure we describe an all-optical inverter, an XOR gate, and an AND gate. We conclude with a brief description of a random number generator encoder and decoder based on a few all-optical logic gates.

Subnanosecond Time‐Resolved Spectroscopy of the Biexciton Luminescence in CuCl

AbstractThe biexciton luminescence of CuCl at 4.2 K is studied under intense UV picosecond excitation, and its time dependence is investigated in the range of 0 to 800 ps by means of an ultrafast optical sampling gate. The time‐resolved spectra of the luminescence due to the radiative recombination of biexcitons show a change in shape of this emission band during the first 100 ps, which may be due to the relaxation time of the biexcitons by means of acoustical phonons. A dynamical model, taking into account the collisions between biexcitons and excitons, is proposed, which provides an acceptable fit for the time dependence of the luminescence if a value TM= 1 ns of the spontaneous radiative decay time of the biexcitons is assumed.

Picosecond optical sampling

A 10-channel optical-sampling technique has been developed to give oscilloscope displays of picosecond laser pulses in a single shot. Pulses with durations of 10-30 ps and powers ranging down to ∼ 1 W have been displayed with this technique. An ultrafast optical gate and a 10-channel multibeam splitter are used to cut out in one laser shot ten samples centered at 4.1-ps intervals from the leading to the lagging edge of the pulse. The ten optical samples are then spaced out at 10-ns intervals by means of an optical fiber array, detected by a fast photomultiplier, and displayed on a real-time oscilloscope. The envelope of the sample pulses represents a display of the laser pulse. This technique could substitute for picosecond streak cameras in certain applications.

Picosecond optical sampling oscilloscope

Single picosecond laser pulses are displayed on a real-time oscilloscope by a multi-channel sampling technique of picosecond resolution. An ultrafast optical gate simultaneously cuts out N samples from the laser pulse. The N samples are centered at 3.9 psec intervals from the leading to the lagging edge of the pulse; they are directed to a photo-multiplier of 3 nsec response, via N fibers cut to propagation delays of 15 nsec, 25 nsec,…, (10 N + 5) nsec. The samples appear sequentially on a 0.8 nsec risetime oscilloscope and their envelope represents a display of the laser pulse.