All-optical Bit Memory Based on Photonic Crystal Nanocavity
Akihiko Shinya1, Shinji Matsuo2, Yosia1, Takasumi Tanabe1, Eiichi Kuramochi1,
Tomonari Sato2, Takaaki Kakitsuka2, and Masaya Notomi1
1Optical Science Laboratory, 2NTT Photonics Laboratories
We have focused on a resonant tunneling filter on a Si based photonic crystal (PhC) platform where single-mode waveguides (WGs) are effectively coupled with an ultrasmall cavity with a high Q factor. The photon density in the cavity is extremely high owing to its small size and effective coupling with PhC-WGs, and this results in a large optical nonlinearity that enables us to realize all-optical memories with very low operating power . However, it is very difficult to achieve a long memory time for a Si based PhC because of its small optical nonlinearity. In this work, we developed an InGaAsP based PhC nanocavity and realized an all-optical bit memory that can operate at very low power and achieve a long memory time.
Figure 1 shows the bit memory operation of the InGaAsP based PhC nanocavity . The initial state of the memory is OFF and it outputs a low level signal (gray line). When a set pulse with a width of 100 ps is input from the waveguide to write one bit of information, the memory turns ON and outputs a high level signal (black line). The memory remains in the ON state after the set pulse has been applied, which means that the bit information is stored. The longest memory time is 150 ns, which is much longer than that of a Si-PhC memory (2.5 ns). The minimum bias power for the memory operation is 40 µW, which is ten times lower than for a Si-PhC and around 100 times lower than that of a conventional optical memory based on bistable lasers. This technology is expected to eliminate certain photonic device bottlenecks such as the difficulty of dense integration on a chip and the difficulty of achieving low power consumption in all-optical memories.
This work was supported by the National Institute of Information and Communications Technology (NICT).
 T. Tanabe, et al., Opt. Lett., 30 (2005) 2575.
 A. Shinya, et al., CLEO/QELS2008, San Jose, U.S.A., May 2007.
Fig. 1. Bit memory operation of InGaAsP based PhC.
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