M. Ebrahimzadeh

Characteristics of a noncritically phasematched Ti: sapphire pumped femtosecond optical parametric oscillator

Abstract The operating characteristics of a singly-resonant famtosecond optical parametric oscillator (OPO) based on a noncritically phasematched geometry in KTP are described. The parametric oscillator is synchronously pumped by a self-modelocked Ti: sapphire laser and is operated in a standing-wave cavity configuration. With extracavity dispersion compensation, chirped pulses of 90 fs are generated, whilst shorter transform-limited pulses of 40 fs are generated with intracavity dispersion compensation. A numerical model of the effects of self-phase-modulation in the OPO has been developed and gives results which are in good qualitative agreement with experiment. Experimental results are presented relating to non-phasematched processes in the OPO, and the implications for the development of a tunable femtosecond source in the blue spectral region are discussed. A characterisation of the amplitude and phase noise of the OPO has also been performed, and provides insight into the important physical processes governing the stability of OPO operation.

Quasi phase matching in GaAs--AlAs superlattice waveguides through bandgap tuning by use of quantum-well intermixing.

We report the observation of second-harmonic generation by type I quasi phase matching in a GaAs-AlAs superlattice waveguide. Quasi phase matching was achieved through modulation of the nonlinear coefficient chi((2))(zxy), which we realized by periodically tuning the superlattice bandgap. Second-harmonic generation was demonstrated for fundamental wavelengths from 1480 to 1520 nm, from the third-order gratings with periods from 10.5 to 12.4microm . The second-harmonic signal spectra demonstrated narrowing owing to the finite bandwidth of the quasi-phase-matching grating. An average power of ~110 nW was obtained for the second harmonic by use of an average launched pump power of ?2.3mW .

Low-pump-threshold continuous-wave singly resonant optical parametric oscillator

We describe a compact all-solid-state continuous-wave singly resonant optical parametric oscillator (SRO) with a minimal pump-power requirement. The SRO is based on periodically poled LiNbO(3) as the nonlinear material and is pumped by a 1-W diode-pumped Nd:YVO(4) minilaser at 1.064 microm . By exploiting the intracavity pumping technique in a 50-mm crystal, we have achieved SRO operation threshold at a diode pump power of only 310 mW.At 1 W of input diode power, the SRO delivers 70 mW of output power in the nonresonant idler at 3.66 microm , at a photon conversion efficiency of 55%. Multiparameter tuning of the SRO yields a signal wavelength range from 1.45 to 1.60 microm and an idler wavelength range from 3.16 to 4.02 microm in the mid infrared. The device is characterized by robust turnkey operation and long-term amplitude-stable performance.

Second-harmonic generation through optimized modal phase matching in semiconductor waveguides

We report optical second-harmonic generation (SHG) through modal phase matching in GaAs/AlGaAs semiconductor waveguides. Using femtosecond pulses, both type-I and type-II SHG is demonstrated for fundamental wavelengths near 1.55 μm.

Nonlinear frequency conversion in semiconductor optical waveguides using birefringent, modal and quasi-phase-matching techniques

We describe the use of GaAs-based semiconductor optical waveguides for nonlinear frequency conversion of femtosecond pulses in the infrared. Different techniques for the realization of phase matching, including artificial birefringence, quasi-phase-matching and modal dispersion, are reported and analysed and key issues relating to efficiency, practicality and applicability are discussed. Using the data obtained from these experiments, an overall comparison is made with other prominent techniques in order to identify the most promising and viable route to the development of efficient semiconductor waveguide frequency conversion devices for incorporation in the future generation of integrated photonic networks.

Femtosecond optical parametric oscillator based on periodically poled lithium niobate

We describe a femtosecond optical parametric oscillator based on periodically poled lithium niobate and pumped by a self-mode-locked Ti:sapphire laser. Signal and idler outputs almost continuously tunable from 975 nm to 4.55 μm were generated by a combination of grating tuning and cavity-length tuning, and an explanation of the tuning properties is given in terms of the gain bandwidth. A threshold of 45 mW was measured and, in the absence of optimized output coupling, signal powers of 90 mW and idler powers of 70 mW were obtained, with 140 mW of green light at 540 nm generated by phase-matched frequency doubling of the signal. Dispersion compensation produced near-transform-limited signal pulses of duration 140 fs. Observations regarding temperature tuning and pump depletion are also presented.

Continuous-wave, singly resonant, intracavity parametric oscillator

Performance characteristics of a continuous-wave intracavity optical parametric oscillator are described by use of an experimental arrangement comprising a KTP singly resonant oscillator located within a Ti:sapphire laser cavity and analyzed by use of a steady-state model. Internal and external powers, circulating fields, tuning ranges, spectral bandwidths, and amplitude-stability levels are measured and discussed. The nonresonant idler tunes from 2.53 to 2.87 microm, delivers a maximum output power of approximately 0.4W and displays long-term amplitude-stable operation. The total downconverted power approaches the optimum power coupled out of the Ti:sapphire laser in the absence of frequency conversion.

Five-optical-cycle pulse generation in the mid infrared from an optical parametric oscillator based on aperiodically poled lithium niobate.

We describe an optical parametric oscillator based on aperiodically poled lithium niobate that generates nearly transform-limited 53-fs duration pulses at a center wavelength of 3mum, corresponding to only 5 optical cycles. Results are presented illustrating the effect of pump- and grating-period chirp on the idler pulses, and a configuration capable of producing idler bandwidths in excess of 700 nm is discussed.

Quasi-phase-matched second-harmonic generation in a GaAs/AlAs superlattice waveguide by ion-implantation-induced intermixing

We report type I second-harmonic generation by use of first-order quasi-phase matching in a GaAs/AlAs symmetric superlattice structure with femtosecond fundamental pulses at 1.55 microm. Periodic spatial modulation of the bulklike second-order susceptibility chi(zxy)(2) was achieved with quantum-well intermixing for which the group III vacancies were created by As+-ion implantation. A narrow second-harmonic bandwidth of approximately 0.9 nm (FWHM) with an average power of approximately 1.5 microW was detected, corresponding to an internal conversion efficiency of approximately 0.06%, which was considerably limited by the spectral bandwidth of the fundamental.

Broadly tunable infrared femtosecond optical parametric oscillator based on periodically poled RbTiOAsO 4

We present results from what we believe is the first reported example of an optical parametric oscillator based on periodically poled RbTiOAsO(4). The oscillator is pumped by a femtosecond self-mode-locked Ti:sapphire laser and, with a single-grating 2-mm-long crystal and one mirror set, a combination of pump and cavity-length tuning provided wavelength coverage from 1060 to 1225nm (signal) and 2.67 to 4.5 microm (idler). Average output powers were as much as 120mW in the signal and 105mW in the idler and interferometric autocorrelations recorded at signal and idler wavelengths of 1.1 and 3.26 microm, respectively, imply pulse durations of 125 and 115fs, respectively.