For various values of x, given an input wavelength of 1500 nm (0.827 eV) , the calculated values of y (given a lattice match to InP), the direct bandgap energy Eo, and the index of Al(x)Ga(y)In(1-x-y)As are as follows:
Acknowledgement: Luxpop would like to thank Professor Piprek of UCSB and Professor Montrosset of Politecnico di Torino for their assistance.
References (note that different references may have different notations for subscripts etc):
 M. Guden and J. Piprek, "Material parameters of quaternary III-V semiconductors for multilayer mirrors at 1.55 micron wavelength," Modeling Simul Mater. Sci. Eng. vol 4, (1996) pp. 349-357,
 D. Olego, T. Y. Chang, E. Silberg, E. A. Caridi, and A. Pinczuk, "Compositional dependence of band-gap energy and conduction-band effective mass of In1-x-yGaxAlyAs lattice matched to InP," Appl. Phys. Lett.Vol. 41, No.5, 1 September 1982 p. 478,
Professor Piprek, personnal communication to G. Boisset.
n for AlGaInAs