We present a light-by-light photonic crystal configuration consisting of a bend waveguide with three embedded Kerr-type nonlinear rods and a T-branch waveguide. We show that such a configuration can also demonstrate all-optical AND gate operation with extremely high-contrast between the OFF state and ON state in its transmission. Because the presented photonic crystal configuration of all-optical light-by-light switching is simple, this facilitates fabricating practical all-optical devices and further large-scale optical integration.

In this Letter, we suggest an on-chip integrated isolator based on an add-drop filter with unidirectional Raman-induced gain (or loss). For the steady state, complete one-way propagation for monochromatic signals is realized in the bus waveguide. For transient transmission, the burr is suppressed. And the power consumption is reduced by enhancing the Q factor of the resonator at the control frequency.

Employing the small-signal analysis, we study the bidirectional operating characteristics in a Raman ring laser. Bidirectional operation is found not stable in a silicon ring because of the existence of two-photon absorption. Using polar crystals which have different forward and backward Raman gain or introducing external optical injections helps to establish stable bidirectional operation in a Raman ring laser.

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