Fabry-Perot interferometer with quantum well mirror for controllable dispersion compensation

TL;DR

This work addresses the challenge of achieving tunable second-order dispersion control in a compact optical cavity. It proposes a monolithic Fabry-Perot interferometer in which a quantum-well mirror introduces negative GDD near the exciton resonance while maintaining high reflectivity, with dispersion that can be switched on/off by changing the exciton environment. The authors derive the compensation condition $h = \frac{m \lambda}{4 \cos \alpha}$ and define the effective quality factor $F = \frac{\Gamma}{\Gamma+\gamma}$, providing the phase function $\Phi$ that yields the negative GDT and GDD; they experimentally demonstrate compensation in an InGaAs/GaAs QW with $F \approx 0.58$, achieving a maximum $\mathrm{GDT} \approx -10$ ps and $\mathrm{GDD} \approx 3.6\times 10^{6}$ fs$^2$. The results indicate a viable route to on-demand dispersion control in integrated optics and motivate future MQW and room-temperature implementations using higher-bandgap excitons such as GaN or 2D materials, expanding the practical impact of dispersion engineering in photonic devices.

Abstract

In this work, we investigate a possibility of controlling second-order dispersion in a monolithic Fabry-Perot interferometer based on epitaxial heterostructure with quantum well (QW) serving as a bottom mirror. Careful choice of heterostructure parameters and experimental conditions makes it possible to introduce negative dispersion in a very narrow spectral region of QW excitonic resonance while maintaining a constant reflection coefficient across this region. The feasibility of the concept is demonstrated for heterostructures with InGaAs/GaAs QWs at cryogenic temperatures. We also propose an active device design that can switch the dispersion compensation on and off by controlling the exciton ensemble's environment.

Figures (4)

• Figure 1: Single (a) and multiple (b) QW heterostructures under consideration. Red lines represent light beams paths. $\lambda$ -- wavelength in the material medium, $\alpha$ -- angle of incidence, $h$ -- cap layer thickness.
• Figure 2: (a) Compensation mode polarization and incidence angles $\alpha_c$ for different quality factors $F$ for $n_1 = 1$ and $n_2 = 3.36$ (GaAs). Blue curve -- p-polarization, red -- s-polarization. Note that the compensation is always possible for any $m$ but at different polarizations and $\alpha_c$. (b) Reflectivity $K_R$ spectra for different quality factors $F$ demonstrating the same reflectivity for "on" state (compensation) and "off" state ($F=0$). (c) GDT spectrum for "on" and "off" states shown in (b). Calculation parameters for (b) and (c): $n_1 = 1$, $n_2 = 3.36$ (GaAs), p-polarization, incident angle $\alpha = \alpha_c = 55.4^\circ$, $\Gamma = 86$$\mu$eV, $\gamma$ is a variable.
• Figure 3: Calculated reflection phase $\Phi$ (blue) and its derivatives: relative group delay time GDT (red) and relative group delay dispersion GDD (orange) in reflection compensation mode. Calculation parameters: $n_1 = 1, n_2 = 3.36$, p-polarization, incident angle $\alpha = \alpha_c = 55.4^\circ$, $F = 0.58$.
• Figure 4: Experimental reflectivity spectra $K_R(E)$ (a,b) and dependence of the area of the heavy-hole exciton peak (c,d) on additional illumination at $T=10$ K (a,c) and on sample temperature (b,d). Black curves in (a,b) denote the reflectivity when the compensation condition is met at dashed lines position in (c,d).