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A unique photocurrent response of a photovoltaic cell using photosynthetic protein bacteriorhodopsin (bR) is similar to that seen in the retinal ganglion cell, therefore, there are considerable interest in utilizing bR in visual sensors.
A position sensitive detector (PSD) is a monolithic photosensor utilizing photodiode surface resistance. When a spot light strikes the PSD, an electric charge proportional to the light intensity is generated at the incident position. This electric charge is driven through the resistive layer and collected by two electrodes as photocurrents, while being divided in inverse proportion to the distance between the incident position and each electrode.
In this study, we present 1D 10-cm-long PSD based on bR instead of organic semiconducting polymers. A bR-PSD consists of a dip-coated bR film on a high-resistivity indium-tin-oxide (ITO)-PET film, and counter ITO-PET. The position sensitive output signals of the PSD are measured in response to the intensity-modulated light of a green laser. Nonlinearity, δ=2×RMS deviation/full scale, is a measure of the distortion of the sensor output. An acceptable device has nonlinearities of less than 15%. When the position was detected at a beam diameter of φ = 5 mm, 40 mW/cm2, and the measurement interval 1 mm, the nonlinearity was 3.42%. Especially within an area of position detection error of less than 1%, the nonlinearity was 0.33%. When a beam diameter of φ = 1.5 mm and a measurement interval 500 μm, the nonlinearity showed 0.81% within the range of the light receiving centre of 2 cm. It satisfies 15%, which is the allowable range of general nonlinearity. The bR-PSD showed excellent linearity for all increments measured. Notably, the low cost (3 Euro) and simplicity of fabricating bR-PSD, and no requirement for a bias supply are two of the major advantages over conventional semiconductor material.
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