Two-photon photoconductivity in SiC photodiodes and its application to autocorrelation measurements of femtosecond optical pulses

Received: 18 June 1997     

Measurement of ultraviolet femtosecond pulses using the optical kerr effect

We demonstrate the optical Kerr shutter technique as a simple and powerful tool for the measurement of femtosecond pulses in the ultraviolet as well as in the visible spectral region. The method provides the third-order intensity correlation function which gives information about pulse asymmetry and pulse structures.     

Measuring the temporal intensity of ultrashort laser pulses by triple correlation

Received: 13 May 1997/Revised version: 1 August 1997     

Ultra-broadband optical parametric chirped-pulse amplification by matching of both group-velocity and pulse-front

Ultra-broadband optical parametric chirped-pulse amplification is analyzed based the compensation of phase-mismatch, which is achieved by matching of both group-velocity and pulse-front between signal and idler by the combination of the noncollinear-phase-match and pulse-front-tilt. The results show exactly matching of both group-velocity and pulse-front is the important criterion for constructing an UBOPCPA. Its general model is developed, in which the group velocities, noncollinear angles, spatial walk-off angles, linear angular spectral dispersion coefficients and pulse-front tilted angles are suitably linked to each other. Finally, specific numerical calculations and simulations are presented for β-barium borate OPCPA with type-I noncollinear angularly dispersed geometry.     

Giant Kerr nonlinearities and slow optical solitons in coupled double quantum-well nanostructure

We investigate the enhancement of Kerr nonlinearities in an asymmetric coupled double quantum-well (CQW) by analyzing the nonlinear optical response. With the consideration of real parameters in AlGaAs-based CQWs, we indicate the possibility to obtain the giant Kerr nonlinearities with the cancellation of linear absorption simultaneously. We also reveal both analytically and numerically that under appropriate conditions a probe field with very low intensity can evolve into a stable shape-preserving waveform that propagates with a slow group velocity. The stability of such slow optical solitons is also demonstrated numerically.     

Optical Switching in Silicon Nanowaveguide Ring Resonators Based on Kerr Effect and TPA Effect

We analyze theoretically the 1 × 2 low-power all-optical switching in silicon nanowaveguide ring resonators （RR） based on the Kerr effect and two-photon absorption （TPA）, and give a comparison between both the all-optical switches. The calculation shows that the switching power of the TPA-RR switch is 3 orders smaller than that of the Kerr-RR switch. The switching time for both the switches is about 100ps.     

Compensation of group-velocity mismatch in the frequency-doubling modelocker

We propose a method for reducing the deteriorating effect of group-velocity mismatch on the frequency-doubling modelocker time response. A birefringent plate is used to introduce a time delay between the fundamental and the second-harmonic pulses which is opposite in sign to that accumulated in the frequency-doubling crystal. In the new arrangement the modelocker may provide pulse compression at a sub-picosecond time scale     

Passive, “self-trapped family” all-optical half adder using all-optical XOR and AND gates

The paper presents an alternative novel approach to obtain all-optical logic. We show that XOR, NOT, and AND logic could be obtained by appropriately setting parameter of all-optical passive transistor. An AND gate followed by NOT gives NAND logic (building block) that, in principle can provide complete set of passive, fiber compatible “self-trapped family” all-optical logic gates (with Boolean completeness) and may find many possibilities in the area of all-optical computing. To give one example, we propose all-optical half adder.     

Nonlinear optical laser devices using GaSe

Tunable second-harmonic generation of CO₂ laser radiation and tunable upconversion of infrared radiation from CO₂-laser radiation in a GaSe crystal are demonstrated. The capability of low infrared-signal detection in this crystal is also explored and compared with the AgGaS₂ crystal.     

Efficient generation of tunable VUV laser radiation below 205 nm by SFM in BBO

Design and performance characteristics of a tunable dye laser system for sum frequency mixing (SFM) in a BBO crystal are presented. The system is composed of two tunable pulsed dye lasers pumped synchronously by the second harmonic of a commercial Nd:YAG laser. The radiation produced by the first dye laser is frequency doubled by second-harmonic generation (SHG) in KDP and subsequently mixed by SFM in BBO with the light of the second dye laser. The interest was focussed on generation of tunable laser radiation below 205 nm with high output power and long-time wavelength stability. High conversion efficiencies enable output energies of 100 J (20 kW) at 196 nm using only moderate Nd:YAG pump energies of 67 mJ. Altogether, a laser system with very good specifications for analytical application in the near VUV spectral region is reported.     

A Sensor-on-Chip Based on Second-Order Optical Effect of ZnO Nanowires

Strong second-order nonlinear effect of ZnO nanowires on a silicon wafer are demonstrated by using the hyper- Rayleigh scattering （FIRS） measurement. The large nonlinear effect can be attributed to the following two factors： （1） the large total dipole moment caused by high surface defect density and electrostatic potential gradient, （2） coherent effect due to high crystal quality of single nanowire. Moreover, the second-order nonlinear effect is found to become weaker when the chip is put into organic solvent due to modification of surface defect caused by organic molecules. The variation of second-order signal in the solvent indicated the potential applications of ZnO nanowires as a sensor-on-chip （SoC）.     

Cross-phase modulation in one-dimensional photonic crystals: applications to all-optical devices

We present a numerical study of a finite photonic band gap structure with a χ⁽³⁾ nonlinearity that couples two input pump beams at frequencies ω₁ and ω₂. We show that in this configuration a variety of all-optical devices can be obtained: an optical transistor, a double switch, and a dynamical switch.     

Experimental study on wave-mixing in semiconductor optical amplifiers

By coupling two travelling optical waves slightly detuned in a semiconductor optical amplifier, the wave-mixing effect generates a comb of new optical frequencies, which is experimentally studied as a function of detuning from 2 pm (250 MHz) to 2 nm (250 GHz). Dependences of generated powers on detuning are empirically found and theoretically justified by means of an easy deduction based on the temporal modulation of the population difference. Empirical equations allow one to determine time constants of the semiconductor optical amplifier. Moreover, while detuning is sufficiently low, exceptionally high powers are generated up to the eighth order, which could be of use to improve recent applications based on wave-mixing.     

Dye laser pumped, continuous-wave KTP optical parametric oscillators

4 (KTP) optical parametric oscillators (OPOs) with pump and idler resonant cavities. With a linear two-mirror cavity the pump power at threshold was 70 mW. The single-frequency signal and idler output wavelengths were tuned in the range of 1025 to 1040 nm and 1250 to 1380 nm by tuning the dye laser in the range of 565 to 588 nm. With a dual three-mirror cavity the threshold was 135 mW. Pumped by 500 mW of 578 nm radiation the 1040 nm single-frequency signal wave output power was 84 mW. Power and frequency stable operation with a spectral bandwidth of less than 9 MHz was obtained by piezo-electrically locking the length of the pump resonant cavity to the dye laser wavelength. Similar performance was achieved by placing the idler resonant OPO inside the resonator of the dye laser. With this system power stable and single-frequency operation was achieved with a spectral bandwidth of less than 11 MHz for the idler wave. Received: 3 February 1998/Revised version: 9 March 1998     

Anti-Stokes Line in an Index-Guiding Photonic Crystal Fibre with Two Zero-Dispersion Wavelengths

An index-guiding photonic crystal fibre with a small hole in the core is fabricated. The simulated results show that the first higher order mode possesses two zero-dispersion wavelengths, and the phase-matching is possible in the anomalous dispersion regime between the two zero-dispersion wavelengths. Using 200 fs Ti： sapphire laser of 820, 830 and 840nm, the anti-Stokes line around 530nm can be generated efficiently. The maximum ratio of the anti-Stokes signal energy to the pump component in the output spectrum is estimated to be 1.03 and the conversion efficiency is above 50%.     

AOPDF-shaped optical parametric amplifier output in the visible

Time shaping of ultra-short visible pulses has been performed using a specially designed acousto-optic programmable dispersive filter of 50% efficiency at the output of a two-stage non-collinear optical parametric amplifier. The set-up is compact and reliable. It provides a tunable shaped source in the visible with unique features: a 4-ps shaping window with preserved tunability over 500–650 nm, and pulses as short as 30 fs. Several-μJ output energy is easily obtained.     

Influence of Kerr nonlinearity on the band structures of two-dimensional photonic crystals

Dynamic modifications of the band structures of two-dimensional photonic crystals composed of Kerr-nonlinear dielectric rods in air forming hexagonal, square and honeycomb lattices are investigated. Calculations are carried out by the method based on the finite-difference time-domain (FDTD) technique for both TM and TE polarizations. The bands in all cases are observed to red-shift with the introduction of nonlinearity. Inspection of the variation of the mid-gap frequencies with source intensity reveals that the red-shift increases as gap number increases, in a manner proportional to the mid-gap frequency in linear regime. The red-shift of mid-gap frequencies is also found to follow the adopted saturable model for the change of relative permittivity with source intensity. Either the so-called dielectric or the air band edges of the gaps are found to be more sensitive to nonlinearity resulting in broadening or shrinking of the gaps. Possible utilizations of the present observations for all-optical device applications, such as wavelength multiplexing, are discussed.     

Passively mode-locked Nd:YVO4 laser using semiconductor saturable absorption mirrors of interface states relaxation region

Semiconductor saturable absorber mirrors (SESAMs) with GaAs/air interface relaxation region have less non-saturable loss than those with low temperature grown In_0.25Ga_0.75As relaxation region. A thin layer of SiO₂ and a high reflectivity film of Si/(SiO₂/Si)₄ were coated on the SESAMs, respectively in order to improve the SESAM's threshold for damage. The passively continuous wave mode-locked lasers with two such SESAMs were demonstrated, and the SESAM with high reflectivity film of Si/(SiO₂/Si)₄ is proved to be helpful for high output power.     

A dispersionless Michelson interferometer for the characterization of attosecond pulses

A novel application of a free-standing transmission grating as a beam splitter in a Michelson-type interferometer is described. The arrangement can operate in the XUV and soft X-ray spectral region and, therefore, it is well suited for the characterization of attosecond pulses. Using ray-tracing codes, we have analyzed three different setups in which spherical mirrors are employed in conjunction with the transmission grating and have investigated in detail their dispersive characteristics. It is shown that such an arrangement can be made to exhibit group-delay dispersion of ∼1 as² while it provides two co-propagating and converging beams. Received: 12 October 2001 / Revised version: 17 December 2001 / Published online: 7 February 2002