Optimization of broadband semiconductor chirped mirrors with genetic algorithm

Abstract

and high damage threshold. However, the high refractive index contrast results in low number of distributed Bragg reflector (DBR) pairs and, consequently, constant value of high negative GDD can be hard to achieve over a broad band (around 10 nm near the 1-µm wavelength) with such mirrors. On the other hand, semiconductor chirped mirrors have lower refractive index contrast and, thus, require more DBR pairs, which allows to provide better separation of reflection of different wavelengths and makes it easier to tune constant negative GDD over a broader band. In our previous works [4][5][6] we have demonstrated tunable semiconductor double-chirped mirrors with negative dispersion for applications in femtosecond lasers operating near 1 µm. We have fabricated them using arsenide-based molecular beam epitaxy (MBE), and with intentionally introduced layer thickness spatial gradient, we were able to make the mirror properties (reflectivity and dispersion) tunable over an 80-nm range across the mirror surface. We demonstrated tunable mode-locked femtosecond operation of an Yb:KY(WO 4 ) 2 diode-pumped laser oscillator at the 1035-nm wavelength.We obtained negative group-delay dispersion (GDD), necessary for the femtosecond laser operation in the soliton regime, by using a double chirp of the mirror stack that resulted in different wavelengths being reflected at different depths within the semiconductor stack. In our mirror design, we followed classical approach, using an analytical formula [7]. However, to apply this formula we had to make a number of approximations [8], which resulted in a non-optimal mirror design. Hence, we have decided to focus our research on using exact numerical solutions of Maxwell equations and to perform computer optimization in order to achieve a structure with lower mean GDD spanning over a wider bandwidth with reduced oscillations. AbstractGenetic algorithm was applied for optimization of dispersion properties in semiconductor Bragg reflectors for applications in femtosecond lasers. Broadband, large negative group-delay dispersion was achieved in the optimized design: The group-delay dispersion (GDD) as large as −3500 fs 2 was theoretically obtained over a 10-nm bandwidth. The designed structure was manufactured and tested, providing GDD −3320 fs 2 over a 7-nm bandwidth. The mirror performance was verified in semiconductor structures grown with molecular beam epitaxy. The mirror was tested in a passively mode-locked Yb:KYW laser.

Reflective Spiral Phase Converter: A New Route to Ultrafast Singular Optics

“…15 (d) dashed line) due to impedance mismatch in the air/device interface. These oscillations can be reduced using computer optimization methods, such as needle optimization technique [50], genetic algorithms [51], memetic algorithms [52], simulated annealing [53]. Fig.…”

Study of Ion-Assisted E-Beam Evaporation Coating Process on Chirped Mirrors

“…This is especially cumbersome in the multilayer thin film optimization problems due to the under-constraint conditions. Many algorithms are available for the optimization of film thickness design of chirped mirrors published recently [8][9][10]; however, the most notable and conventional method is the needle optimization method proposed by Tikhonravov in 1982 to verify the capability of optimization in the number of layers in shop practice [11][12][13]; additionally, in some specific problems, the method can even directly start from a single layer without an appropriate initial number of layers. Since many mass production coater systems are customer-made with a limited number of materials crucibles and monitoring glass substrates, a fast and reliable optimization method should be selected for this study.…”

Design of a broadband reflection mirror for the water window region using a stacked multilayer with optimized structure

“…In this paper, we proposed a Cr/Sc multilayer with an optimized stacked structure, in which the bilayer number for each PM in the SM is also set to be an optimized object, together with the bilayer thickness and the thickness ratio for each PM. For enhancing the optimization efficiency of the Cr/Sc SM, we used a genetic algorithm (GA) [27,28] to optimize the bilayer number, bilayer thickness, and thickness ratio for each PM. To obtain maximum uniform reflection in the desired spectral band, a two-parametric merit function consisting of the mean value and the mean square deviation of reflectivity [29] is employed in GA.…”