Optimization design of an ultrabroadband, high-efficiency, all-dielectric grating

Abstract

More than 97% flat-top diffraction efficiency in the −1st-order TE polarization over a 110 nm wavelength range around 800 nm in an all-dielectric grating is designed by a simulated annealing algorithm and the Fourier mode method. Its band is near to the maximum bandwidth provided by a dielectric high-reflectivity mirror under the match layer. This result will provide a way for high-efficiency chirped-pulse amplification to be used in an ultrashort high-power pulse laser system based on all-dielectric gratings. Furthermore, an effective method for broadband high-efficiency all-dielectric grating design is presented in this Letter. For an ultrashort pulse laser system, the pulse compression requires more than a 100 nm high-DE bandwidth of an MDG to output a femtosecond pulse. However, as the reflection bandwidth of dielectric high-reflectivity (HR) mirror is much narrower than that of a metal HR mirror, it is a challenge to design a broadband, high-efficiency MDG. In recent years, Flury et al. have reported their works about broadband gratings and have obtained some fruitful results [6,8,9], including an all-dielectric grating with a DE close to 100% over a range of 40 nm wide and metal-dielectric grating with an average DE of 95% over a 200 nm wavelength bandwidth centered at 800 nm. Although the bandwidth has been widened in metal-dielectric gratings, the use of metal material would more or less lead to the light absorption. And the 40 nm bandwidth of an all-dielectric grating with top-hat high efficiency is the widest one that has reported in literature (to our knowledge).In this Letter, an all-dielectric grating with DE Ͼ97% over a 110 nm wavelength range is obtained, and an effective method for the design of a broadband, high-efficiency, all-dielectric grating is presented. A simulated annealing (SA) algorithm [10] is employed for MDG optimization design. The diffraction efficiency of MDG is calculated by the Fourier mode method (FMM) [11]. Figure 1 illustrates a general all-dielectric grating structure. The grating model is composed of a Bragg HR mirror and two leaky-mode propagating layers. The top high-index layer would be etched periodically, and the second layer is named as the match layer. The match layer is very important factor for this design. With this layer, there are one or more parameters to optimize, and a broadband MDG can be obtained more easily. To determine that the MDG fabrication is realizable and convenient, a quarterwave HR mirror is included in the MDG.The physical mechanism of leaky-mode resonant gratings obtaining near 100% DE in the −1st reflected diffraction order is explained as follows [7]. The amplitudes of two parts of light, which are reflected at the top of corrugation directly and leaked from the wave-guided layers (as shown in Fig. 1), are equal, and the phases of them are 180°out of phase.

Influence of geometry variations and defects on the near-field optical properties of pulsed compression gratings

“…As shown in Fig. 1, the formula of high reflection (HR) stack under the grating layer is H(2LH) 9 , where H is HfO 2 (n h =1.96) and L is SiO 2 (n l =1.46), and the optical thicknesses of H and L layer are one quarter of the reference wavelength 820nm, respectively. The thickness of the grating layer is 550nm (L material).…”

“…The highest efficiency of about 99.577% has been achieved in practice [7] , and the full size of MDGs has been scaled up to 91cm×42cm [8] . Moreover, the working spectral bandwidth of MDGs has been extended to more than 100 nm, which can fully satisfy the requirements of femtosecond laser systems [9] . However, the optical properties of MDGs with defects have been studied in few cases only [10] .…”

High-spectral-resolution characterization of broadband high-efficiency reflection gratings

“…To provide large output energy in a chirped-pulse amplification system, the pulse compression gratings should satisfy the requirements of high diffraction efficiency [3][4][5][6], high laser-induced damage threshold [7][8][9][10], and a broad diffraction band [11][12][13]. Multilayer dielectric gratings (MDGs) and metal multilayer dielectric gratings (MMDGs), which meet the above requirements, have widely replaced the traditional metal gratings in high-power laser systems.…”

“…In recent years, most research on MDGs and MMDGs mainly focused on the innovation of design and fabrication methods [11,12,[14][15][16][17][18]. To verify the effectiveness of the proposed MDG or MMDG structures, the diffraction efficiencies of the fabricated samples were only tested at a few tuning wavelengths of the illumination laser [6,[17][18][19].…”

Innovations in structured thin film design and fabrication for optical applications

“…Due to the low absorption, multilayer dielectric gratings (MDG) provide high-efficiency, high laser-induced damage threshold (LIDT) [15][16][17]. To meet the bandwidth requirements in ultrashort laser systems, the research on broadband MDG draws increasing attention [18][19][20][21]. Pulse compression gratings and broadband polarizers can be realized with a single material based on a 2D photonic crystal structure.…”