Single-photon avalanche diode (SPAD) sensors are versatile candidates for applications in low-light imaging and scenarios where high temporal resolution is crucial, like quantum imaging, fluorescence lifetime imaging, and (direct) time-of-flight methods. We demonstrate the improvement in light sensitivity by a factor of 7x for LiDAR (Light Detection and Ranging) by molding application-specific filling factor enhancing microlenses directly onto backside-illuminated SPADs. An 8"-wafer-level process is presented utilizing a mask aligner device for selective UV-curing of highly transparent polymer lenslets only in areas where SPADs are located and rinse uncured material from areas being compatible with postprocessing steps like chip dicing and electrical bonding. In addition to the optical benefits of chip-integrated lenslets, advantages arise from less system integration efforts of separately realized microlenses, especially with respect to tolerance conditions.

The increased use of light detection and ranging (LiDAR) systems for distance determination requires the investigation of mutual interference. In this article, we describe the conditions for the occurrence of LiDAR interference. We outline suppression methods for different LiDAR types identifying pulse-position modulation (PPM) as a solution for time-of-flight LiDAR with time-correlated single photon counting (TCSPC) histograms. Based on PPM, we present a suppression method, which randomly varies the laser pulse emission times. For optimal suppression, we switch on the suppression only when interference is present. To recognize the occurrence of LiDAR interference, we develop a multipulse detection algorithm that can also extract all pulse positions. Simulations show that the algorithm can be applied for a signal-to-noise ratio greater than 3. Determining the heights of all recognized pulse signatures, an appropriate suppression level can be chosen. We successfully show the optimized interference suppression for an example LiDAR measurement. For safe use by multiple systems, we suggest random numbers. We reuse the TCSPC histograms to generate random numbers, whose generation probability is calculated theoretically and confirmed by simulation and measurement data. For nearly all histogram distributions consisting of background- and laser-generated data, a sufficient amount of random numbers is produced.

We have developed a 32x24 pixel sensor array based on single-photon avalanche diodes (SPADs). Beside conventional 2- dimensional imaging, this sensor allows for precise timing of single-photon arrival times which can be exploited in a variety of technical and scientific approaches like 3D image acquisition, quantum imaging and quantum random number generation. Thus, such a sensor is eligible for many fields of application such as autonomous driving, remote and non-lineof- sight sensing, safety, robotics and more recently random number generation for statistical applications or data encryption. The novel sensor contains CMOS integrated backside illuminated SPADs which are connected to an underlying read-out IC by wafer-to-wafer bonding. Their single-photon sensitivity (quantum efficiency QE=60 % @ 580 nm) and high-speed performance (readout frequency 𝑓 = 25 kHz, temporal resolution 𝑡TDC = 312.5 ps) make the sensor a promising choice for, e.g. quantum imaging with photon-pairs where a 2-dimensional spatial and temporal resolution are as crucial as a low noise level. SPADs also offer exciting opportunities for random number generation by using the randomness of photon generation paired with time-resolved detection and post-processing. Another potential application of the sensor is light detection and ranging for which we integrated the sensor into a demonstrator system for direct time-of-flight measurements. It is capable of coincidence detection using 4 SPADs in each pixel, which allows for background light suppression in outdoor situations. This combination of single-photon sensitivity, precise photon arrival timing and our recent developments in wafer-to-wafer bonding technology gives access to a new generation of optical sensors for a variety of applications.

We present first results of a novel type of setup for quantum ghost imaging based on asynchronous single photon timing using single photon avalanche diode (SPAD) detectors. This scheme enables photon pairing with arbitrary path length difference and does, therefore, obviate the dependence on optical delay lines of current quantum ghost imaging setups [Nat. Commun.6, 5913 (2015)NCAOBW2041-172310.1038/ncomms6913]. It is also, to our knowledge, the first quantum ghost imaging setup to allow three-dimensional imaging.