**8. Design of two-input photonic logic gates**

The dramatic reduction and enhancement in the reflectance and transmittance close to 0.5 **p 3** is of special interest since the two-photon resonance ( **p c** ) can give rise to the effect of sensitive optical switching control, which would lead to promising applications to new photonic device design. We shall suggest the working mechanism of two photonic logic gates (e.g., OR and NAND gates), which can be fabricated based on such an EIT-based periodic structure. The fine structure of the reflectance and transmittance for showing extraordinary sensitivity to the frequency of the probe field is demonstrated in Fig. 19(a). Here we plot only the reflectance and transmittance of two cases ( 4 *N* and 6 *N* ) as an illustrative example. It can be seen that some oscillations in the curves are exhibited in the narrow resonant frequency range [0.2 ,0.7 ] **Δp 33** .

One can see from Fig. 18 (a) that there is a minimum (i.e., 0.19) and a maximum (i.e., 0.99) in the transmittance *T* at 0.53 **p 3** and 0.46**<sup>3</sup>** , respectively, for the 6-layer periodic structure. For the 4-layer periodic structure, however, the transmittance *T* has a maximum (i.e., 0.99) and a minimum (i.e., 0.34) close to 0.53 **p 3** and 0.46**<sup>3</sup>** , respectively. Two structures of layer number 4 *N* and 6 are sketched in Fig. 18(b). Two probe beams with 0.46 **p 3** and 0.53**<sup>3</sup>** , which can act as the two input signals, are applied. We suppose that the output signal 0 *Y* if neither of the two incident probe beams propagates through the periodic layered medium (i.e., the reflection dominates in the wave propagation of the probe field), and the output signal *Y* 1 if at least one of the probe beams can be transmitted through the structure (i.e., the reflection and absorption can be ignored). Let the probe beams of 0.46 **p 3** and 0.53**3** represent the input signals 0 and 1, respectively. Then the logic operations of two-input OR gate and NAND gate can be implemented with the 4 -layer and 6 layer structures, respectively. The truth table of the OR and NAND gates are given as follows:

Fig. 17. (a) The schematic diagram of a photonic transistor designed based on the LHM-EIT layered structure. The probe field is incident on the structure, and the giant reflected wave with higher-than-unity reflectance and the transmitted wave with negative transmittance will be produced via the intriguing Klein tunneling effect. The incident probe wave, the reflected wave, and the transmitted wave correspond to the terminals of base, collector and

(b) The schematic diagram of a two-input photonic logic gate designed based on the EITbased layered structure. The two incident probe beams at different frequencies represent the

The dramatic reduction and enhancement in the reflectance and transmittance close to 0.5 **p 3** is of special interest since the two-photon resonance ( **p c** ) can give rise to the effect of sensitive optical switching control, which would lead to promising applications to new photonic device design. We shall suggest the working mechanism of two photonic logic gates (e.g., OR and NAND gates), which can be fabricated based on such an EIT-based periodic structure. The fine structure of the reflectance and transmittance for showing extraordinary sensitivity to the frequency of the probe field is demonstrated in Fig. 19(a). Here we plot only the reflectance and transmittance of two cases ( 4 *N* and 6 *N* ) as an illustrative example. It can be seen that some oscillations in the curves are exhibited in the

One can see from Fig. 18 (a) that there is a minimum (i.e., 0.19) and a maximum (i.e., 0.99) in the transmittance *T* at 0.53 **p 3** and 0.46**<sup>3</sup>** , respectively, for the 6-layer periodic structure. For the 4-layer periodic structure, however, the transmittance *T* has a maximum (i.e., 0.99) and a minimum (i.e., 0.34) close to 0.53 **p 3** and 0.46**<sup>3</sup>** , respectively. Two structures of layer number 4 *N* and 6 are sketched in Fig. 18(b). Two probe beams with 0.46 **p 3** and 0.53**<sup>3</sup>** , which can act as the two input signals, are applied. We suppose that the output signal 0 *Y* if neither of the two incident probe beams propagates through the periodic layered medium (i.e., the reflection dominates in the wave propagation of the probe field), and the output signal *Y* 1 if at least one of the probe beams can be transmitted through the structure (i.e., the reflection and absorption can be ignored). Let the probe beams of 0.46 **p 3** and 0.53**3** represent the input signals 0 and 1, respectively. Then the logic operations of two-input OR gate and NAND gate can be implemented with the 4 -layer and 6 layer structures, respectively. The truth table of the OR and NAND gates are given as follows:

(a) (b)

**8. Design of two-input photonic logic gates** 

narrow resonant frequency range [0.2 ,0.7 ] **Δp 33** .

emitter, respectively.

two input signals.


Table 1. The truth table of two-input OR gate (fabricated based on the 4-layer periodic structure) and two-input NAND gate (fabricated based on the 6-layer periodic structure).

Fig. 18. The fine structure of the reflectance and transmittance of the 4-layer and 6-layer periodic (D|E) cells in a narrow probe frequency band (a), and the schematic diagram of photonic logic gates (b). The Rabi frequency of the control field is <sup>7</sup> 4.0 10 <sup>c</sup> s <sup>1</sup> .
