An Analog VLSI Chip Emulating Polarization Vision of Octopus Retina

Abstract

Biological systems provide a wealth of information which form the basis for human-made artificial systems. In this work, the visual system of Octopus is investigated and its polarization sensitivity mimicked. While in actual Octopus retina, polarization vision is mainly based on the orthogonal arrangement of its photoreceptors, our implementation uses a birefringent micropolarizer made of YVO4 and mounted on a CMOS chip with neuromorphic circuitry to process linearly polarized light. Arranged in an 8 x 5 array with two photodiodes per pixel, each consuming typically 10 microW, this circuitry mimics both the functionality of individual Octopus retina cells by computing the state of polarization and the interconnection of these cells through a bias-controllable resistive network.

Fabrication of a dual-tier thin film micropolarization array

“…Carbon monoxide (CO) and carbon dioxide (CO 2 ) are released during the etching procedure (equation 5). (5) In order to increase the etching rate of the PVA, the concentration of oxygen atoms must be increased. This is achieved with the addition of fluorine gases, such as CF 4 , CF 3 , C 2 F 6 , SF 6 and others.…”

“…This sensory system integrates an array of imaging elements, a micro-polarization array and analog processing circuitry for polarimetric computation at the focal plane in order to achieve a compact, low power polarization sensitive system. Biologically inspired, polarization difference (contrast) imaging (PDI) sensors have been one of the dominant research topics in developing polarization sensitive systems [4][5][6]. Several imaging systems have been made where polarization-contrast information has been computed at the focal plane [4,5] or with bulky, power hungry set-ups composed of CMOS/CCD imaging sensors, electro/mechanically controlled polarization filters and DSPs/CPUs [6,7].…”

“…Biologically inspired, polarization difference (contrast) imaging (PDI) sensors have been one of the dominant research topics in developing polarization sensitive systems [4][5][6]. Several imaging systems have been made where polarization-contrast information has been computed at the focal plane [4,5] or with bulky, power hungry set-ups composed of CMOS/CCD imaging sensors, electro/mechanically controlled polarization filters and DSPs/CPUs [6,7]. These systems sample the environment via two orthogonal polarization filters and compute contrast information at the focal plane with translinear circuits or in the digital domain with a DSP/CPU.…”

“…The large pixel pitch was limited by the wet isotropic etching technique employed for patterning the thin-film polarization filter and by the in-pixel circuit processing for extracting polarization contrast information in the birefringence imaging system. An 8 by 5 birefringent micro-polarization element array with pixel-pitch size of 128μm was reported in [5]. The large pixel pitch in these polarimetric imaging systems limits the fidelity of the imaged environment, which is a major shortcoming for high resolution imaging applications.…”

“…The previously reported PDI systems, which have been directly inspired from biological systems, compute polarimetric information in simplified and compact form [4,5]. In contrast, the complete polarimetric information tends to be far more complex and its computational demands usually prevent real time extraction [10].…”