High concentration factor diffractive microlenses integrated with CMOS single-photon avalanche diode detector arrays...

Area of Science:

• Photonics and Optical Engineering
• Semiconductor Device Physics
• Detector Array Technology

Background:

• Large-format single-photon avalanche diode (SPAD) arrays typically have low fill-factors, limiting detection efficiency.
• Microlens arrays can enhance detection efficiency by concentrating light onto active areas.
• Diffractive optical elements (DOEs) offer advantages for pixel coverage and fast lens capabilities in microscale detector arrays.

Purpose of the Study:

• To fabricate and characterize fast diffractive microlenses for large-format SPAD detector arrays.
• To evaluate the performance of these microlenses under various illumination conditions.
• To demonstrate the benefits of DOEs for improving light collection in SPAD arrays.

Main Methods:

• Fabrication of diffractive microlenses using binary-mask-based photolithography for 32x32 SPAD arrays.
• Spectral characterization of the fabricated microlenses.
• Performance analysis under a range of illumination angles (f/2 to f/22).

Main Results:

• Achieved concentration factors exceeding 33x with short focal lengths (190µm), corresponding to f-number 3.8.
• Produced focal spot diameters less than 4µm.
• Demonstrated high performance uniformity across 1024 devices for each SPAD array design.

Conclusions:

• Fast diffractive microlenses significantly enhance light collection efficiency in SPAD arrays.
• DOEs provide a versatile and effective solution for improving sparse photon applications.
• Implementation of DOEs offers substantial benefits for integrated detector systems with small active area SPADs.