#### Abstract

We have studied the transmissivity of one-dimensional photonic crystals quantum well (QW) with quantum theory approach. By calculation, we find that there are photon bound states in the QW structure , and the numbers of the bound states are equal to . We have found that there are some new features in the QW, which can be used to design optic amplifier, attenuator, and optic filter of multiple channel.

#### 1. Introduction

Photonic crystals (PCs) are artificial structures with a periodic dielectric constant in one, two, or three dimensions [1, 2]. They are characterized by photonic band structures owing to the multiple Bragg scatterings [3, 4]. Between photonic bands there may exist a photonic band gap (PBG), in which the propagation of electromagnetic waves or photons is strongly inhibited [5]. This facilitates the manipulation and control of the flow of electromagnetic waves or photons as well as the design of high-performance optoelectric devices [6, 7].

The concept of super lattice and quantum well (QW) stemmed from the pioneering work of Shimuzu and Ishihara [8]. It is well known that there are many interesting and new phenomena for electrons in semiconductor QW structures [9]. The QW structures and super lattices can be used to tailor the electronic band structures of semiconductors [9–13]. Similar to the idea of semiconductor QW structures, one can use different PCs to construct photonic QW structures, provided that the PBG of the constituent PCs are aligned properly. The constituents can be one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D) PCs. It has been shown by the authors [14] that the transmission properties of the 1D and 2D PCs can be tailored by using QW structures. The nontransmission frequency range can be enlarged as desired by using QW. The use of QW exciton embedded in high-finesse semiconductor microcavities of the Fabry-Perot type has allowed observing a modification of spontaneous emission (weak coupling regime) [15–21] as well as the occurrence of a vacuum Rabi splitting (strong coupling regime) [22–25]. The latter effect arises when the radiation-matter coupling energy overcomes the damping rates of QW exciton and microcavities photons.

In [26, 27], we have studied the quantum transmission characteristic of 1D PCs with quantum theory approach and given the quantum transform matrix, quantum transmissivity, and reflectivity. In this paper, we use the quantum method to research the QW transmissivity of 1D PCs. It is found that there are some new features in the QW structure , which can be used to design optic amplifier, attenuator, and optic filter of multiple channel.

#### 2. Quantum Transform Matrix and Transmissivity of QW

The QW structures consisted of two different 1D PCs. The first and second 1D PCs structures are and , respectively, where are the numbers of the second PCs layers. The two 1D PCs can consist of 1D PCs of QW structure, which is .

In quantum theory approach [26, 27], we consider the photon travels along with the -axis, and the QW structure and quantum wave functions distribution are shown in Figure 1. The thicknesses and refractive indexes of layers and are , , , and , respectively. The and are the photon wave functions of the first period media and . The photon wave functions of incident, reflection, and transmission are [26, 27] where , , and are the wave vector of photon in vacuum, mediums and . The constants , , and are the wave function amplitudes of incident, reflection, and transmission wave. By calculation, similarly as [26, 27], we can directly give the wave functions of photon in arbitrary layers and . For medium () of the th (th) layer, the photon wave function can be written as before the th layer medium , there are layers medium and layers medium , and before the th layer medium , there are layers medium and layers medium . The constants , , , and are the wave function amplitudes. By the condition of wave function and its derivative continuation at the interface of two mediums, we can obtain the quantum transfer matrix of th medium layer; it iswhere () is the wave vector of photon in the th (th) layer medium and is the thickness of th layer medium. For the QW structure , its total quantum transfer matrix is and the quantum transmissivity is [26, 27]

#### 3. Numerical Result

In this section, we report our numerical results of the QW quantum transmissivity. The refractive indexes and the thicknesses of medium and medium are as follows: , and nm, nm. The quantum transmissivity of and is shown in Figures 2(a) and 2(b). In Figures 3 and 4, we only change the refractive index of medium in relation to Figure 2; they are (active medium) and (absorbing medium). From Figures 2 to 4, we can obtain results as follows. (1) In Figures 2(b), 3(b), and 4(b), when the ratio , the quantum transmission peaks are , , and for the 1D PCs ; that is, the quantum transmission peaks are gained and attenuated when the medium is active medium and absorbing medium . (2) The forbidden band of 1D PCs is in the range of , and the conduction band of 1D PCs is inside the forbidden band. So, the PCs play a role similar to a barrier to PCs , and the PCs act as a well in the forbidden band. We put the 1D PCs and together to constitute the 1D PCs of QW structure , which are shown in Figure 1. In Figures 5, 6, and 7, we should study the quantum transmissivity of the QW structure . As mentioned above, the conduction band of PCs is inside the forbidden band of PCs ; that is, the PCs prohibit the propagation of photon in its forbidden band; then the photon will be confined in the PCs . Because of the quantum effect of photon in QW of 1D PCs, the photon should form the bound state in the QW, which is analogous to the bound state of electron in semiconductor QW. The photon can pass the QW by the resonance perforation way and form the very sharp peaks of quantum transmissivity within the forbidden band of the PCs , which are shown in Figures 5, 6, and 7. In Figures 5, 6, and 7, (a), (b), and (c) are corresponding to , , and for the QW structure . In Figures 5, 6, and 7 refractive indexes of medium are real number, (convention medium), and complex numbers (active medium) and (absorbing medium), respectively. From Figures 5 to 7, we can obtain some results. (1) The numbers of the sharp peaks (bound states) are equal to ; that is, when , , and , the numbers of the sharp peaks are , , and . (2) In Figure 5, the quantum transmissivity of the sharp peaks for , , and , which can be designed optic filter of multiple channel. (3) In Figure 6, the quantum transmissivity of the sharp peaks for , , and . When increase, the sharp peaks value increase, which can be used to design optic amplifier and optic filter of multiple channel. (4) In Figure 7, the quantum transmissivity of the sharp peaks for , , and ; when increase, the sharp peaks value decrease, which can be used to design optic attenuator.

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#### 4. Conclusion

In summary, we have studied the quantum transmissivity of the QW of 1D PCs with quantum theory approach. By calculation, we find that there are photon bound states in QW structure , and the numbers of the bound states are equal to , which are formed by the quantum effect of photon in QW. We also find that the QW can be used to design optic amplifier, attenuator, and optic filter of multiple channel.

#### Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

#### Acknowledgments

This work was supported by the National Natural Science Foundation of China (no. 61275047), the Research Project of Chinese Ministry of Education (no. 213009A), and Scientific and Technological Development Foundation of Jilin Province (no. 20130101031JC).