# The Quantum Well of One-Dimensional Photonic Crystals

Authors: Xiao-Jing Liu; Ji Ma; Xiang-Dong Meng; Hai-Bo Li; Jing-Bin Lu; Hong Li; Wan-Jin Chen; Xiang-Yao Wu; Si-Qi Zhang; Yi-Heng Wu
Journal: Advances in Condensed Matter Physics
 (2015)

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## 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(BA)6(BBABB)n(AB)6, and the numbers of the bound states are equal to n+1. 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.


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## Body

## 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 (BA)6(BBABB)n(AB)6, 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(BA)6(AB)6 and (BBABB)n, respectively, where n are the numbers of the second PCs layers. The two 1D PCs can consist of 1D PCs of QW structure, which is (BA)6(BBABB)n(AB)6.In quantum theory approach [26, 27], we consider the photon travels along with the x-axis, and the QW structure and quantum wave functions distribution are shown in Figure 1. The thicknesses and refractive indexes of layers A and B are a, b, na, and nb, respectively. The ψB1 and ψA1 are the photon wave functions of the first period media B and A. The photon wave functions of incident, reflection, and transmission are [26, 27] (1)ψI=FeiKx,ψR=F′e-iKx,ψD=DeikAPa+ikBQb+Kx-Pa-Qb,where K=ω/c, kA=(ω/c)na, and kB=(ω/c)nb are the wave vector of photon in vacuum, mediums A and B. The constants F, F′, and D 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 A and B. For medium A (B) of the (Pi+1)th ((Qj+1)th) layer, the photon wave function can be written as (2)ψAPi+1x=AeikAPia+kBQib+kAx-Pia-Qib+A′eikAPi+1a+kBQib+kAPi+1a+Qib-x,ψBQj+1x=BeikAPja+kBQjb+kBx-Pja-Qjb+B′eikAPja+kBQj+1b+kBPja+Qj+1b-x;before the (Pi+1)th layer medium A, there are Pi layers medium A and Qi layers medium B, and before the (Qj+1)th layer medium B, there are Pj layers medium A and Qj layers medium B. The constants A, A′, B, and B′ 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 jth medium layer; it is(3)Mj=121+kj-1kj1-kj-1kj1-kj-1kje-2ikjdj1+kj-1kje-2ikjdj,where kj (kj-1) is the wave vector of photon in the jth ((j-1)th) layer medium and dj is the thickness of jth layer medium. For the QW structure (BA)6(BBABB)n(AB)6, its total quantum transfer matrix is (4)M=MBMA6MBMBMAMBMBnMAMB6=m1m2m3m4,and the quantum transmissivity T is [26, 27] (5)T=DF2=2kAm2m3-m1m4m2kA-K-m4kA+K2.Figure 1
The QW structure of 1D PCs.


## 3. Numerical Result

In this section, we report our numerical results of the QW quantum transmissivity. The refractive indexes and the thicknesses of mediumA and medium B are as follows: na=1.35, nb=2.45 and a=890 nm, b=469 nm. The quantum transmissivity of (BBABB)12 and (BA)6(AB)6 is shown in Figures 2(a) and 2(b). In Figures 3 and 4, we only change the refractive index of medium B in relation to Figure 2; they are nb=2.45-i0.0001 (active medium) and nb=2.45+i0.0001 (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 ω/ω0=1.0, the quantum transmission peaks are T=1.0, T>1.5, and T<1.0 for the 1D PCs (BA)6(AB)6; that is, the quantum transmission peaks are gained and attenuated when the medium B is active medium (nb=2.45-i0.0001) and absorbing medium (nb=2.45+i0.0001). (2) The forbidden band of 1D PCs (BA)6(AB)6 is in the range of ω/ω0=0.8~1.2, and the conduction band of 1D PCs (BBABB)12 is inside the forbidden band. So, the PCs (BA)6(AB)6 play a role similar to a barrier to PCs (BBABB)12, and the PCs (BBABB)12 act as a well in the forbidden band. We put the 1D PCs (BBABB)n and (BA)6(AB)6 together to constitute the 1D PCs of QW structure (BA)6(BBABB)n(AB)6, which are shown in Figure 1. In Figures 5, 6, and 7, we should study the quantum transmissivity of the QW structure (BA)6(BBABB)n(AB)6. As mentioned above, the conduction band of PCs (BBABB)n is inside the forbidden band of PCs (BA)6(AB)6; that is, the PCs (BA)6(AB)6 prohibit the propagation of photon in its forbidden band; then the photon will be confined in the PCs (BBABB)n. 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 (AB)6(BA)6, which are shown in Figures 5, 6, and 7. In Figures 5, 6, and 7, (a), (b), and (c) are corresponding to n=1, n=2, and n=3 for the QW structure (BA)6(BBABB)n(AB)6. In Figures 5, 6, and 7 refractive indexes of medium B are real number, nb=2.45 (convention medium), and complex numbers nb=2.45-i0.0001 (active medium) and nb=2.45+i0.0001 (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 n+1; that is, when n=1, n=2, and n=3, the numbers of the sharp peaks are 2, 3, and 4. (2) In Figure 5, the quantum transmissivity of the sharp peaks T=1 for n=1, n=2, and n=3, which can be designed optic filter of multiple channel. (3) In Figure 6, the quantum transmissivity of the sharp peaks T>1 for n=1, n=2, and n=3. When n increase, the sharp peaks value T 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 T<1 for n=1, n=2, and n=3; when n increase, the sharp peaks value T decrease, which can be used to design optic attenuator.Figure 2
The quantum transmissivity of 1D PCs withnb=2.45. (a) The structure is (BBABB)12; (b) the structure is (BA)6(AB)6.
(a)
(b)Figure 3
The quantum transmissivity of 1D PCs withnb=2.45-i0.0001. (a) The structure is (BBABB)12; (b) the structure is (BA)6(AB)6.
(a)
(b)Figure 4
The quantum transmissivity of 1D PCs withnb=2.45+i0.0001. (a) The structure is (BBABB)12; (b) the structure is (BA)6(AB)6.
(a)
(b)Figure 5
The quantum transmissivity for QW structure(BA)6(BBABB)n(AB)6 with nb=2.45. (a) n=1, (b) n=2, and (c) n=3.
(a)
(b)
(c)Figure 6
The quantum transmissivity for QW structure(BA)6(BBABB)n(AB)6 with nb=2.45-i0.0001. (a) n=1, (b) n=2, and (c) n=3.
(a)
(b)
(c)Figure 7
The quantum transmissivity for QW structure(BA)6(BBABB)n(AB)6 with nb=2.45+i0.0001. (a) n=1, (b) n=2, and (c) n=3.
(a)
(b)
(c)


## 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(BA)6(BBABB)n(AB)6, and the numbers of the bound states are equal to n+1, which are formed by the quantum effect of photon in QW. We also find that the QW (BA)6(BBABB)n(AB)6 can be used to design optic amplifier, attenuator, and optic filter of multiple channel.



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