Fabrication and characterization of semiconductor microlens arrays

Small fast lenslet arrays have been fabricated in GaP and lnP substrates. These semiconductors have high refractive indices (n3) and are transparent at A. 0. 55 p. m and 0. 93 jim respectively. Diffractioniimited performance has been obtained from small-diameter (''60-130 pin) f/1 refractive lenslet arrays fabricated by the mass transport process. These lenslets are ideal for use with diode laser sources and can be readily included in monolithic integration schemes. An example of each of these applications is presented. Binary diffractive lenslets fabricated in lnP are also described. The need for small fast high quality lenslets has become apparent over the last few years with the development of diode laser sources and in particular diode laser arrays. Since diode lasers typically have a beam divergence of several tens of degrees collimating the output beams generally leads to greatly improved far-field patterns. The preferred substrate for lenslet fabrication has been fused silica on which both diffractive1 and refractive2 lenslets have been investigated with good results. However the small index of refraction of quartz (n . 5) can present problems with high aspect ratio features such as the outer rings of Fresnel zone plates. In this paper we describe the fabrication and performance of f/I microlenses fabricated on semiconductors where n" 3. Binary Fresnel lenslets were fabricated in lnP by wet etching while InP and GaP were used to fabricate refractive lenslets