All-Optical Differentiators

Year: 2006

Radan Slavík, Ph.D., DSc.

Optics-based signal processing systems and devices with operation speeds inaccessible to electronics (hundreds GHz and more) are required for a wide variety of applications, including ultrafast computing, ultrahigh-bit-rate telecommunications, ultrafast pulse shaping, and analysis of ultrashort optical pulses. In collaboration with EMT-INRS, Université du Québec, Montréal, we realized one of the basic signal processing devices – a universal all-optical temporal differentiator. Our devices calculate the time derivative of an envelope of an arbitrary optical field with temporal features as short as a few hundreds of femtoseconds. This corresponds to a processing speed of several terahertz, which is about three orders of magnitude faster than with the current state-of-the-art electronics-based systems and computers.

We demonstrated two devices [1-3], the first one based on an all-fiber implementation [1,2] and the second one based on bulk-optics components [3]. The first implementation is low-loss, low-cost, robust, and compatible with fiber optic technology; the other can be implemented using off-the-shelf components and thus is widely accessible for research laboratories.

In the fiber implementation, a special in-fiber-made filter based on a long-period fiber grating (LPFG) was made and tested [1,2]. Further, we developed a tuning technique [4] to get the desired performance. In the bulk-optics-based implementation, the device consists of an imbalanced, symmetric Michelson interferometer. This technique is also straightforward to be extended for higher-order temporal derivatives – as a ‘proof of concept’ we have successfully demonstrated the second-order temporal differentiation [3].

1. R. Slavík, M. Kulishov, Y. Park, J. Azaña, and R. Morandotti, Temporal differentiation of sub-picosecond optical pulses using a single long period fiber grating, Conference on Lasers and Electro-Optics (CLEO/IQEC and PhAST), Long Beach, CA, USA, článek CTuBB5, květen 2006.
2. R. Slavík, Y. Park, M. Kulishov, R. Morandotti, and J. Azaña, Ultrafast all-optical differentiators, Optics Express, 14: 10699-10707, (2006).
3. Y. Park, J. Azana, and R. Slavík, Ultrafast all-optical first and higher-order differentiators based on interferometers, Optics Letters Vol. 32, No. 6 (v tisku), k dispozici on-line, 2007.
4. R. Slavík, Extremely deep long-period fiber grating made with CO2 laser, IEEE Photonics Technology Letters, 18: 1705-1707, (2006).