Extensible, Low-Chromatic-Sensitivity, All-diffractive-Optics Relay for Interconnecting Optoelectronic Device Arrays

For free-space optical interconnections between optoelectronic chips to reach commercial realization, the technology must provide high-density optical channels in a simple, inexpensive, and easily aligned package. Although point-to-point connections with microlens pairs can provide densities of several thousand channels per square centimeter, the Gaussian nature of the beams limits the connection range to a few millimeters. We propose an arrangement of microlens pairs with an intermediate relay lens that significantly increases the connection distance. This basic setup can be tiled laterally across large chips to form extensible arrays. The optical design is constructed entirely with diffractive elements because of the low chromatic sensitivity over a range of approximately ?10% around the design wavelength. We derive the lateral positioning error at the image by using a simple ray trace, and we show the effect of Gaussian beams. We experimentally demonstrate the low chromatic sensitivity for a system with an interconnection distance of 64 mm. Finally, we demonstrate the interconnection of two linear arrays of multimode fibers with two adjacent channels operating at data rates of hundreds of megabits per second.