Diffractive optics for photonic packaging of laser diodes and fiber optics

Diffractive optical elements (DOEs) have many advantages over refractive optical elements including the ability to implement exotic function (such as flat-tops, line generators and splitting and combining functions), the ability to easily incorporate a variety of functions in to one element, lower volume and less weight. In addition to these advantages, diffractives offer 3 potential positive characteristics which are sometimes cited as drawbacks. These are: diffraction efficiency, dispersion and cost. In some applications, such as wavelength division multiplexing (WDM) or other applications in which it is desirable for different wavelengths of light to be affected in different manners, the highly dispersive nature of diffractives is an advantage. In other applications when the spectral width of the illumination is large (e.g. laser diodes when the case temperature varies over a wide range), the dispersion of DOEs can be a disadvantage. Diffraction efficiency, defined as the power diffracted into the desired diffraction order divided by the power incident on the DOE, can be very high or low depending on the application and design procedure. This paper focuses on these 3 potential advantages of diffractives. In the remainder of this paper each characteristic is discussed individually in order to show how the negative effects of each can be minimized and the positive effects enhanced.