2F and 2G illustrate alternative groove patterns which may be used for the periodic grating. [0143]FIGS. 3A and 3B are a graphs which plot light intensity as a function of wavelength output by one embodiment of the present invention. [0144]FIGS. 4A and 4B illustrate cross-sectional views of a tunable apparatus used in one embodiment of the present invention. [0145]FIGS. 5A and 5B illustrate use o