A new automatic feedback potometer for physiological studies of water uptake by root systems is described. A dual-optical-fibre amplitude-modulating displacement transducer of improved sensitivity is employed to detect the changes in liquid level. The merits of optimal double-cut fibres, which make full use of the critical angle and improve coupling between the emitter and the receiver, have resulted in a sensor that is 64 times more responsive than the simple emitter-detector probe. Positioning the optical fibre transducer in a narrow capillary and using feedback to control the liquid level allows continuous measurement of volumes in the nanolitre range. The optical sensor used does not need re-calibration for the different salt solutions used in such studies.

Highly efficient surface normal spatial light modulators (SLMs) using ultrahigh purity GaAs layers (30 μm thick) grown on (100) -oriented n + -GaAs substrate by liquid phase epitaxy (LPE) method have been realized. The extinction ratio of 25 dB has been demonstrated with a low -driving voltage (32 V) at 895 nm, based on electroabsorption (EA) effect. Very large depletion length over 150 μm is confirmed by analyzing the extinction ratio and capacitance-voltage (C-V) measurements. The calculated value of impurity concentration is low (≈10 12 cm -3 ) and indicates donor and accepter in the device are highly compensated.