Idler-efficiency-enhanced long-wave infrared beam generation using aperiodic orientation-patterned GaAs gratings

Abstract

In this paper, we design aperiodic gratings based on orientation-patterned gallium arsenide (OP-GaAs) for converting 2.1 μm pump laser radiation into long-wave infrared (8-12 μm) in an idler-efficiency-enhanced scheme. These single OP-GaAs gratings placed in an optical parametric oscillator (OPO) or an optical parametric generator (OPG) can simultaneously phase match two optical parametric amplification (OPA) processes, OPA 1 and OPA 2. We use two design methods that allow simultaneous phase matching of two arbitrary χ⁽²⁾ processes and also free adjustment of their relative strength. The first aperiodic grating design method (Method 1) relies on generating a grating structure that has domain walls located at the zeros of the summation of two cosine functions, each of which has a spatial frequency that equals one of the phase-mismatch terms of the two processes. Some of the domain walls are discarded considering the minimum domain length that is achievable in the production process. In this paper, we propose a second design method (Method 2) that relies on discretizing the crystal length with sample lengths that are much smaller than the minimum domain length and testing each sample's contribution in such a way that the sign of the nonlinearity maximizes the magnitude sum of the real and imaginary parts of the Fourier transform of the grating function at the relevant phase mismatches. Method 2 produces a similar performance as Method 1 in terms of the maximization of the height of either Fourier peak located at the relevant phase mismatch while allowing an adjustable relative height for the two peaks. To our knowledge, this is the first time that aperiodic OP-GaAs gratings have been proposed for efficient long-wave infrared beam generation based on simultaneous phase matching.

Photonic crystals based on aperiodic dielectric multilayers for optical filtering

“…In recent years, quasi-periodic and aperiodic gratings have gathered the great interest of researchers, since they exhibit more advantageous properties compared to periodic gratings or bulk materials for manipulating electromagnetic waves for various purposes in both linear and nonlinear optics [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53]. In linear optics where gratings are formed by creating regions in the material whose linear properties, such as the refractive index, are varied from one region to another, numerous important applications of aperiodic grating designs have been introduced to the literature, including narrow-and broad-band optical filters [15], distributed feedback lasers [16,17], omni-directional reflection [18,19], perfect transmission resonance [20], and solar-cell reflectors [21].…”

“…It becomes possible to employ quasi-phase matching [38][39][40] in such gratings, hence three-wave interactions such as difference frequency generation or sum-frequency generation, which may not be phase-matchable using birefringent phase-matching, can efficiently take place in these gratings. Although periodic gratings are usually adequate for phase matching a given three-wave process, quasi-periodic [41][42][43][44][45] or aperiodic [46][47][48][49][50][51][52][53] gratings are required for phase matching multiple processes, hence generation of multiple frequencies, by employing simultaneous phase-matching. Here, the term 'quasi-periodic' defines the property of being irregular periodic, which shows a long-range order.…”

“…This method was later employed by several other research teams for wavelength generation by simultaneous phase-matching (see, for instance [48,49]). Recently, Figen et al proposed another aperiodic grating design method relying on the maximization of the magnitude of the Fourier transform of the grating function at the spatial frequency locations corresponding to the phase mismatches of the nonlinear processes [47]. In [47], this method was employed for designing orientation-patterned GaAs gratings for efficient long-wave infrared beam generation and its performance was compared with the method given in [46].…”

“…Recently, Figen et al proposed another aperiodic grating design method relying on the maximization of the magnitude of the Fourier transform of the grating function at the spatial frequency locations corresponding to the phase mismatches of the nonlinear processes [47]. In [47], this method was employed for designing orientation-patterned GaAs gratings for efficient long-wave infrared beam generation and its performance was compared with the method given in [46]. These methods and also other aperiodic grating design methods proposed in [51][52][53] offer the advantage of the free adjustment of the relative strength of the simultaneously phase-matched nonlinear processes.…”

“…In this paper, we employ the two aperiodic multilayer design methods that are given in [47] but rather than generating gratings for nonlinear interactions, we employ these methods for the purpose of generating one-dimensional PCs with aperiodic distributions of refractive indices similar to what is mentioned above and investigate their optical filtering characteristics. In the first grating design approach (Method-1) a grating function is generated using the summation of cosine functions that has different spatial frequencies corresponding to predefined RLVs and the refractive index layer boundaries are placed at the zero-crossing locations of this function.…”