Ultraprecision micromilling for the fabrication of monolithically integrated refractive microoptical systems

Planar microoptical systems integration is a powerful approach for the fabrication of compact optical systems which has been demonstrated for a large variety of applications. The folded optical axis in combination with planar fabrication technologies enables highly integrated and rugged optical systems. In this geometry, however, specific care is necessary to avoid aberrations resulting from the oblique optical axis. Diffraction limited performance has been demonstrated by exploiting the design freedom of diffractive optical elements. In this case however, the overall systems efficiency drops down to a few percent and strongly depends on the spectral range of the incident light. The refractive implementation on the other hand has been suffering from the lack of fabrication technologies for freeform microoptical elements, so far. We present the results of the first fabrication of a monolithically integrated planar microoptical system by ultraprecision micromilling including a freeform reflective element and refractive coupling prisms. Details and limitations of the fabrication process as well as the experimental results demonstrating the optical performance are presented.