Microjet printing of high-precision microlens array for packaging of fiber optic components

Abstract

We describe high-precision microlenses with excellent optical characteristics. The lenses are formed precisely at desired locations on a wafer using a polymer-jet system in which hydrophobic effects define the lens diameter and surface tension creates a high-quality optical surface. To make the lenses, we defined hydrophilic circular regions at desired locations using photolithography to pattern a 0.2-pm thick Teflon (hydrophobic) layer on a quartz substrate, as shown in Figures 1 and 2. Then, using a polymer-microjet printing system (Figure 3), we dispense an exact amount of UV-curable polymer within hydrophilic circles to obtain microlenses having desired optical properties [ 13. Figure 4 shows that adjusting the volume of the W-curable optical epoxy within a hydrophilic circle of a given diameter changes the curvature of the microlens. The step resolution of the microlens volume is determined by the average droplet size (-25pL) of the polymer-jet print head. This hybrid method enables us to define the locations and diameters of microlenses with a 21 pm precision as well as to control the curvatures of the microlenses accurately. We measured the quality of our lenses using several precise optical-characterization systems. Figures 5 and 6 are scanning-electron microscope pictures showing several of our microlenses. AFM measurements show that the surface roughnesses of our microlenses are lower than 5nm. We used a WYKO NT3300 to measure the curvature and volume of the microlenses. The maximum deviation of the surface profile from an ideal circle was approximately 0.15pm for most cases (range-0.05-0.23pm). The effective focal lengths measured are shown in Figure 7. Thef-numbers range from 1.5-2.1, 2.0-5.5, 3.4-6.3, and 2.9-7.4 for 200pm-, 400 pm-, 600 pm-, and 1 mm-diameter microlenses, respectively. The Seidel aberrations, root-mean-square wavefront errors (rms WFE), peak-to-valley optical-path differences (p-v OPD) of the microlenses were measured at h = 635 nm using a commercial Shack-Hartmann system with an accuracy of AI100 [2], [3]. The rms WFE values of our microlenses were between U5 and 2/80, depending on the aperture size, diameter, and volume of the microlenses. The average p-v OPD values were 0.14,0.25,0.33, and 0.46 p m for 200 pm-, 400 pm-, 600 pm-, and lmm-diameter microlenses, respectively. Decreasing the aperture size of the microlenses produced much smaller rms WFE and p-v OPD values, as shown in Figure 8. These values were sometimes as low as 2/80. The fabrication process showed good repeatability as well; twenty 400-pm-diameter microlenses showed-1.43% variations in measured volumes and effective focal lengths. The fabrication of microlenses using surface tension and/or hydrophobic effects has attracted considerable research because of this method's potential applicability to micro-optical systems. A previously reported dipping method produced lenses, but did not provide a reliable means to vary or control optical properties if, for example, several lenses at differing locations on a wafer wer...

Comparing glass and plastic refractive microlenses fabricated with different technologies

“…The materials best suited for DOD microlens fabrication are UV curing optical epoxies because of their thermal and chemical durability as compared to other optical-grade plastics such as photoresists, acrylics and thermoplastics [50]. Microlenses ranging in diameter from 20 µm to 5 mm have been fabricated with this method [51].…”

Fabricating optical fiber imaging sensors using inkjet printing technology: A pH sensor proof-of-concept

“…The process for inkjet printing indicator chemistries on an optical substrate is similar to that used to produce micro-optical components (Cox et al, 1995;Cox et al, 1996;Chen et al, 2002). This technology, known as Drop-on-Demand microjet printing, is a process that utilizes a piezo driven orifice, which emits a highly reproducible droplet (i.e.…”

Devices, structures, and processes for optical MEMS

“…A number of researchers have described methods for fabricating microlenses that may possibly be suitable for SH systems. Some techniques that have been reported include: microprinting technology, a gray-scale mask/RIE etch followed by photoresist reflow and selective liquid polymer deposition using hydrophobic effects [2,3,[19][20][21][22][23]. The optical qualities of the lenses produced by these techniques have, in most cases, not been sufficiently characterized to evaluate them for use in the SH system.…”