Focus-Induced Photoresponse: a novel way to measure distances with photodetectors

Abstract

We present the Focus-Induced Photoresponse (FIP) technique, a novel approach to optical distance measurement. It takes advantage of a universally-observed phenomenon in photodetector devices, an irradiance-dependent responsivity. This means that the output from a sensor is not only dependent on the total flux of incident photons, but also on the size of the area in which they fall. If probe light from an object is cast on the detector through a lens, the sensor response depends on how far in or out of focus the object is. We call this the FIP effect. Here we demonstrate how to use the FIP effect to measure the distance to that object. We show that the FIP technique works with different sensor types and materials, as well as visible and near infrared light. The FIP technique operates on a working principle, which is fundamentally different from all established distance measurement methods and hence offers a way to overcome some of their limitations. FIP enables fast optical distance measurements with a simple single-pixel detector layout and minimal computational power. It allows for measurements that are robust to ambient light even outside the wavelength range accessible with silicon.

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“…a novel way to measure distances with photodetectors. 860 The technology was invented and commercialized by the company Trinamix in Germany, a wholly owned subsidiary of BASF.…”

High‐speed focus‐induced photoresponse in amorphous silicon photodetectors for optical distance measurements

“…Results and discussion: The z-scan technique is used to precisely determine and quantify the irradiance dependent non-linear a-Si:H detector response by moving a focused laser cone vertically along the structure. Z-scan measurements have been conducted to quantify the FIP in a Si:H photodiodes enabling high-sensitive optical distance measurements [5]. At 488 nm, a non-linear current breakdown occurs at 380 nW corresponding to irradiances down to at least 1.3 μW/mm 2 far out of focus as seen in Figure 1b.…”

“…Although alternative light detection and ranging (LIDAR) sensors enable distance measurements exceeding 10 m, this concept has significant drawbacks with respect to achievable depth resolutions and most importantly on scalability, even in miniaturized designs [4]. The focused-induced photoresponse (FIP) is a novel, ultra-sensitive 3D-imaging technique in defective materials based on irradiance dependent responsivity changes [5] waiving subsequent data processing for image reconstruction. Simultaneous sensor read-out at different foci enables:…”

“…(I) maximum scalability (depth information can directly be extracted from the incident light from a single viewpoint) and fill-factors of 100 % [6,7], (II) highly precise distance measurements with depth resolutions in the μm-range [5], and (III) low-light-level detection (μW/mm 2 ).…”

“…Although state-of-the-art FIP sensors combine several highly attractive advantages, comparatively low cut-off frequencies stagnate at very low bandwidths, severely restricting their widespread application. This restriction stems from photodetector technologies based on high defect densities and low charge carrier mobility materials, preventing a fast optical distance acquisition above 20 kHz [5,8,9]. Here, we present FIP detector technologies based on amorphous silicon that resolve such bandwidth limitations and expand photodetector speed by more than two orders of magnitude utilizing just one single-pixel photodetector.…”