Optical companding

Christmas came and gone, and I am still trying to keep up with some papers I’ve read in the last months.

The guys at UCLA keep doing impressive stuff. First time I saw something from them was their work on Nature about ultrafast optical imaging (woah!).

This time they have proposed a way to improve the digitization of an electrical signal. Living in the time of the ‘great convergence’, every time we are more aware than Optics, Electronics, and Computer Science are closely related. Nowadays, in order to acquire optical information, one has almost always to deal with electrical signals in the analog domain, which need to be digitized before working with them in a computer. To do so, the most used tools are analog-to-digital converters (ADC). These instruments receive an electrical signal (analog), and convert it to a digital signal (a number representing the voltage or the current you are working with). This quantification sometimes results problematic, given that the full dynamic range of the signal (from the maximum to the minimum value) has to be divided in a finite number of steps (bins). If the signal presents very low variations, the bins might be not small enough to see the full details. One can try to see those details by amplifying the signal, but then the bigger values of the signal might be larger than the maximum value measurable by the ADC, provoking saturation.

Jalali’s group proposes to use Optical Companding to overcome this issue. The fundamental idea is to use optical processes that are not linear to compress the high amplitude signal parts, while amplifying the small amplitude signal values at the same time. After that, a traditional ADC digitizes the signal, and the knowledge about the optical compressor makes it possible to restore the original signal with great accuracy.

Optical Companding,

Yunshan Jiang, Bahram Jalali, submitted on 29 Dec 2017, https://arxiv.org/abs/1801.00007

(featured image exctracted from Fig. 1 of the manuscript)

We introduce a new nonlinear analog optical computing concept that compresses the signal’s dynamic range and realizes non-uniform quantization that reshapes and improves the signal-to-noise ratio in the digital domain.