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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 19 — Sep. 14, 2009
  • pp: 16947–16956

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Proposal of a grating-based optical reflection switch using phase change materials

Xiaomin Wang, Masashi Kuwahara, Koichi Awazu, Paul Fons, Junji Tominaga, and Yoshimichi Ohki  »View Author Affiliations


Optics Express, Vol. 17, Issue 19, pp. 16947-16956 (2009)
http://dx.doi.org/10.1364/OE.17.016947


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Abstract

We have proposed a novel grating-based optical reflection switch using a phase change material (PCM). The device switches on/off light or shifts the light propagation direction by switching the PCM grating between its amorphous and crystalline states. Thus, the switching status is non-volatile and the device is promising for realizing low power consumption. The device structure was designed and optimized by numerical simulations to obtain high switching efficiency. It is shown that there exists a parameter window where high efficiency is achievable. The static switching characteristics were confirmed by finite-difference time-domain (FDTD) simulations. The design scheme can also be applied to other planar dielectric gratings.

© 2009 Optical Society of America

1. Introduction

As communication traffic on the internet increases drastically, the world-wide photonic network is expanding steadily. To unleash the huge potential power of ultra-fast optical transmissions, an all-optical routing or transparent optical network is indispensable. One of the key devices of such a network is the optical router, which enables the switching of optical signal paths directly and swiftly but consumes as little energy as possible. On the other hand, chalcogenide-type phase change materials have been widely used in rewritable optical disks because they offer a large contrast in refractive index between the amorphous and crystalline phases. The phase change process can be quite fast. For example, a recrystallization speed of a few nanoseconds has been reported in [1

M. Chen, K. A. Rubin, and R. W. Barton, “Compound materials for reversible, phase-change optical data storage,” Appl. Phys. Lett. 49, 502 (1986). [CrossRef]

]. More importantly, each state is non-volatile and reversible. This implies that phase change alloys can be potentially used in an optical switch to realize very low power consumption, since there is no need for a continuous power supplying to maintain their phase states. These two features make the PCM switch an unique category when compared with the wide variety of other optical switches that have been proposed and developed till now. For example, its sub-100 nanosecond latency is orders or magnitude faster than the millisecond speeds achievable by thermo-optic switches, liquid crystal switches or micro electro mechanical system (MEMS) switches. On the other hand, while the various electro-optic switches based on acoustic-optic modulator or GaAs or LiNbO3 can operate at nanosecond or sub-nanosecond, they usually need a continuous supply of electric power to maintain the working bias points. The more advanced optic-optic switches such as Mach-Zehnder interferometer semiconductor switches [8

S. Nakamura, Y. Ueno, and K. Tajima, “Femtosecond switching with semiconductor-optical-amplifier-based Symmetric Mach-Zehnder-type all-optical switch,” Appl. Phys. Lett. 78, 3929–3931 (2001). [CrossRef]

] or intersubband transitions quantum well switches [9

T. Akiyama, N. Georgiev, T. Mozume, H. Yoshida, A. V. Gopal, and O. Wada, “1.55 um picosecond all-optical switching by using absorption in InGaAs-AlAs-AlAsSb coupled quantum wells,” IEEE Photon. Tech. Lett. 14, 495–497 (2002). [CrossRef]

] can even operate at sub-picosecond speeds. But they are mainly aimed as optical packet switches. If they were to be tried in optical path routines, in addition to the need for electrical power, again a continuous optical power source would be necessary as a bias. Therefore, PCM switches will supply the best option in these applications, as they are basically “cold” devices most of times between switching actions. In addition, thanks to the large refractive index changes between phases, PCM switches are not as bulky as most other optical switches with small nonlinearity coefficients.

To date, few prototypes optical switches using PCM have been proposed and numerically investigated [2

D. Strand, D. V. Tsu, R. Miller, M. Hennessey, and D. Jablonski, “Optical routers based on Ovonic phase change materials,” E/PCOS2006 (European Phase Change and Ovonics Symposium), Grenoble, May 29–31, 2006, http://www.epcos.org/library/papers/pdf 2006/pdf contributed/Strand.pdf.

, 3

H. Tsuda, “Proposal of an optical switch using phase-change material for future photonic network nodes,” PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39–42, Atami, Nov. 29–30, 2007.

], where a photonic crystal structure or a directional coupler structure has been utilized to realize switching action. A big challenge remains in how to obtain low loss and crosstalk while keep good compatibility with the phase change mechanisms, because the resonance characteristic of the switching cavity in photonic crystal or the long PCM waveguide in the directional coupler makes the absorption effect of PCM significant. In this paper, we propose a new grating-based optical reflection switch using a PCM, which greatly improves the loss and crosstalk performance in the amorphous state. The structure is simple and easy to fabricate. Possible ways of changing the phase state include switching by electric current as in phase change random-access memory (PCRAM) [4

H. Horii, J. H. Yi, J. H. Park, Y. H. Ha, I. G. Baek, S. O. Park, Y. N. Hwang, S. H. Lee, Y. T. Kim, K. H. Lee, U-In Chung, and J. T. Moon, “A novel cell technology using N-doped GeSbTe films for phase change RAM,” Proceedings of International Symposium on VLSI Technology , pp.177–178, Kyoto, June 10–12, 2003.

, 6

M. Wuttig and N. Yamada, “Phase-change materials for rewritable data storage,” Nature Mater. 6, 824–832 (2007). [CrossRef]

] or optically as in optical disks.

2. General design principles for a PCM grating-based optical switch

As mentioned in the introduction, phase change material offers large change in refractive index during the phase change process [5

A. V. Kolobov, P. Fons, A. I. Frenkel, A. L. Ankudinov, J. Tominaga, and T. Uruga, “Understanding the phase-change mechanism of rewritable optical medium,” Nature Mater. 3, 703 (2004). [CrossRef]

, 6

M. Wuttig and N. Yamada, “Phase-change materials for rewritable data storage,” Nature Mater. 6, 824–832 (2007). [CrossRef]

, 7

K. Shportko, S. Kremers, M. Woda, D. Lencer, J. Robertson, and M. Wuttig, “Resonant bonding in crystalline phase-change materials,” Nature Mater. 7, 653–658 (2008). [CrossRef]

]. This change is considered to originate from the significant variation in bonding between the crystalline phases and the amorphous phases. In the crystalline phases, the optical dielectric constant is strongly enhanced by resonant bonding effects, while that of the amorphous phases is more like a covalent semiconductor. In this paper, we focus on the prototypical chalcogenide-type phase change material, Ge2Sb2Te5 (GST), which has been widely used in optical disks and more recently in PCRAM. We chose this material because it has relatively small optical absorption at 1.55 µm, the C-band optical fiber communication wavelength. Using a spectroscopic ellipsometer, we have measured the refractive index of amorphous state GST to be 3.8+i 0.05 (Fig. 1); a value effectively transparent at 1.55 µm. By heating the amorphous sample to 400 °C for 5 minutes, the GST can be transformed to the crystalline state, for which a refractive index value of 7.0+i 2.3 was measured. Based on these measurements, a suitable grating structure that can utilize this large refractive index changes was designed.

Fig. 1. The measured refractive index of Ge2Sb2Te5 PCMin the amorphous and crystalline states.
Fig. 2. The schematic structure of a PCM grating device. The grating is implemented at the interface between two media with refractive indices n 1 and n 2. The light is incident from medium n 1.

Figure 2 shows schematic light paths on a cross section of a generalized PCMgrating device. Typically the incident beam will be diffracted into many characteristic directions by the grating. From the conservation of tangential wavenumber, the diffracted beams in medium n 1 obey Eq. (1), while those in medium n 2 obey Eq. (2),

sin θ 1,m= sin θi+m λ n1d, m=0,±1,±2, ⋯,
(1)
sin θ 2,m= n1 n2 sin θi+m λ n2d, m=0,±,1±2, ⋯,
(2)

where θi is the angle between the direction of incident light and the direction normal to the grating surface, while θ 1,m and θ 2,m are the corresponding angles of the diffracted lights in medium n 1 and n 2, respectively. Furthermore, λ is the vacuum wavelength and d is the grating period (see Fig. 2), while m is an integer indicating the diffraction order and m=0 represents the specular reflection.

Because we are aiming to design a switching device, to achieve high efficiency and low insertion loss, we need to consider carefully the grating parameters to converge most of the diffracted optical power into a single diffraction order. First, the possible diffraction orders should be limited to a minimum. By observing Eq. (1), it is apparent that if the grating period d is taken to be slightly smaller than the optical wavelength in medium n 1, i.e. d<λ/n 1, then only m=0 with θ 1,0=θi and m=-1 with θ 1,-1<0 can satisfy Eq. (1), which implies that only two diffraction orders will occur in medium n 1. When d becomes yet smaller and satisfies d< λ n1+ n1sin θi,, the m=-1 diffraction order is no longer allowed either and only the m=0 diffraction appears. In other words, the incident light cannot resolve the sub-wavelength grating structure. On the other hand, in Eq. (2) for medium n 2, if we choose n 1 > n 2 and take the grating period d to be shorter than λ n2+ n1sin θi,, for incidence angles larger than the total internal reflection angle sin-1(n 2/n 1), there is no integer m that can satisfy Eq. (2). Namely, all diffraction orders including m=0 will be suppressed in medium n 2.

In order to verify the above observations, in the following sections we employ numerical computations to simulate the light diffracting behavior of a GST grating for a variety of grating parameters.

More importantly, besides the above existence conditions for the diffraction orders, the final diffraction efficiency depends strongly on the grating material itself. Two other degrees of freedom in the design parameters, the grating profile and its thickness, can be used to further favor the diffraction intensity in medium n 1 between the m=0 and m=-1 diffraction orders. Here, to facilitate the device fabrication, we limit ourselves to a simple step-shape grating, and tune only the thickness and filling ratio (i.e. the width of GST over the grating period). The optimization of these parameters as well as the final diffraction efficiencies are generally only obtainable by numerical methods.

3. Optimization of a GST grating structure for optical switching

The rigorous coupled wave analysis (RCWA) method [10

M. G. Moharam and T. K. Gaylord, “Diffraction analysis of dielectric surface-relief gratings,” J. Opt. Soc. Am. , 72, 1385–1392 (1982). [CrossRef]

, 11

L. Li, “New formulation of the Fourier modal method for crossed surface-relief gratings,” J. Opt. Soc. Am. A 14, 2758–2767 (1997). [CrossRef]

] is used to analyze and optimize diffraction by the proposed grating structures. The RCWA method is especially suitable for simulating light scattering by a two-dimensional periodic structure such as a grating. It expands both the fields and the dielectric distributions into their respective spatial Fourier components, then constructs the coupling equations utilizing the boundary conditions at each interface. By numerically solving the equations, the amplitude and phase of each diffraction order can be obtained. In our simulation, the PCM grating is assumed to be fabricated from GST which has two well-defined refractive indices for its two phase states. Medium n 1 is assumed to be a common optical glass or quartz material with a refractive index of 1.46, while the medium n 2 is taken to be air. In addition, due to the inherent anisotropic character of a grating, we consider only the s-polarization in this paper.

Considering the practical power required for switching the phase states of PCM, the GST layer should be kept as thin as possible. Here we assume a thickness of 50 nm as a starting point. We first analyze the diffraction characteristics when GST is in amorphous state. Figures 3 summarizes the simulated diffraction efficiencies for the m=0 and m=-1 orders plotted as the contour maps versus the incidence angle and grating periods from 0.5 to 1.0 µm. It should be noted that we have set the RCWA code to compute the diffraction orders up to ±5. Nevertheless, in this grating period range of 0.5 to 1.0 µm, all diffraction orders other than 0 and -1 vanish. More importantly, by tuning the grating period down to a value of ~600 nm, in medium n 1 (SiO2), there exists a very low specular reflection region for incidence angles larger than the total internal reflection angle, of about 50 to 80° (see Fig. 3(a)).

Fig. 3. Contour maps showing the diffraction efficiency of s-polarized light as a function of light incidence angle and grating period, simulated for an amorphous GST grating of 50 nm thick. The grating is sandwiched between SiO2 and air. Other diffraction orders vanish unless d becomes larger.

Correspondingly, the m=-1 diffraction order reaches a peak for this grating period with an optimized efficiency approaching 92% as shown in Fig. 3(b). A further decrease in the grating period d moves the m=-1 diffraction intensity back to the m=0 specular reflection, with exactly the predicated curve d= λ n1 ( 1+sin θi) forming the boundary between red and blue regions, as is also visible in the contour map. For the case of medium n 2 (air), Fig. 3(c) shows that for incidence angles larger than the total internal reflection angle of 43°, there is no m=0 transmission. Furthermore, when the grating period is shorter than 600 nm, i.e. d< λ n2+ n1sin θi,, the m=-1 diffraction order also vanishes as expected (Fig. 3(d)). All of these facts contribute to the high efficiency window of the m=-1 diffraction order for a grating period of 600 nm. The reason that the peak efficiency does not reach 100% is due to the small amount absorption that GST has at this wavelength.

Fig. 4. Contour maps showing the diffraction efficiency of s-polarized light as a function of light incidence angle and grating period for a crystalline GST grating. Other parameters are the same as those in Fig. 3.

The same simulations were carried out for a crystalline GST grating. As shown in Fig. 4, the expectations described in Section 2 still apply. That is, in medium n 1 (SiO2), only the m=0 and m=-1 diffraction orders are allowed, as shown in Figs. 4(a) and 4(b), while in medium n 2 (air) and at large incidence angles and short grating periods (d < 600 nm), even the m=0 and m=-1 diffraction orders are not allowed (Figs. 4(c) and 4(d)). There is, however, a big difference from the results shown in Fig. 3 in that the diffracted optical power remains in the specular reflection at m=0 while the m=-1 diffraction order approaches zero in Fig. 4. This is because the light allocation between the m=0 and m=-1 orders depends not only on the grating geometric parameter, but also on the material of grating itself, i.e. its refractive index. The diffraction blazing condition obtained for the amorphous GST grating simply does not apply to the crystalline GST grating. This is an important property, by which we can realize switching action by the GST material. Since crystalline GST has a relatively large loss at 1.55 µm, the diffraction efficiency is lower than that of amorphous GST and is about 60% at an incidence angle of 65° as shown in Fig. 4(a). Possible ways of improving this efficiency will be discussed in Section 4.

For a clearer perspective of the grating parameter selection, the numerical results of Fig. 3 and Fig. 4 are summarized into a single graph shown in Fig. 5. Here, the white area enclosed by sin-1(n 2/n 1)<θi <90 and λ n1 ( 1+sin θi)<d< λ n2+ n1sin θi is the preferable working window, where only the m=0 and -1 diffraction orders are allowed and they are switchable by the phase state of the grating.

Fig. 5. The summarization of the existence conditions of the diffraction orders. The white area is the preferable working window.

The thickness and filling ratio of the GST grating do not influence the diffraction direction or the existence condition of a certain diffraction order, as they are not present in Eqs. (1) and (2). However, they do play an important role in the diffraction efficiency of each order. Fig. 6 investigates the relation between the maximum efficiencies of the m=-1 diffraction order and the grating thickness for three grating periods d, namely 550 nm, 600 nm and 700 nm. Although the peak position varies somewhat if d is different, the amorphous GST grating has two efficiency peaks when the thicknesses is either around 50 nm or 240 nm. In the current scenario, the thinner 50 nm structure is desirable from the viewpoint of switching energy considerations as stated earlier. In addition, the grating period of 600 nm appears optimal as it provides the highest overall efficiency. For crystalline GST, the intensity of the m=-1 diffraction order does not vary much with thickness and remains at a low value when the GST is thicker than 25 nm. On the other hand, when the filling ratio of GST is varied, the intensity of the m=-1 diffraction order for the amorphous grating attains a rather high value in the ratio range from 0.2 to 0.55 as shown in Fig. 7. This implies that this structure offers reasonable tolerance for grating width fabrication error. Since the diffraction intensity for the crystalline grating gradually rises for ratios smaller than 0.5, the ratio of 0.5 is a good choice.

4. Static performance of an optimized PCM grating switch

Based on the above numerical results, a GST grating of 50 nm thickness, 600 nm grating period and 0.5 filling ratio is proposed as an effective structure for a grating-based switch implemented on a glass surface. The static switching characteristics for s-polarized light are summarized in Fig. 8. When the grating is in the amorphous state, light incident at a large angle between 65 and 75° is almost completely diffracted back as the m=-1 order beam, and the specular reflection is negligibly small as shown in Fig. 8(a). The light absorption due to the grating itself is very small because GST is nearly transparent in the amorphous phase. When the GST grating is changed into the crystalline state, the input light is mainly coupled to the specular reflection with very little scattered light as shown in Fig. 8(b). The reflection efficiency is decreased due to increased absorption by the GST. In both cases, scatterings due to all other higher orders and unwanted transmitted beams are absent.

Fig. 6. The maximum efficiency of the m=-1 diffraction as a function of grating thickness, estimated for three grating periods, 550 nm, 600 nm and 700 nm or both amorphous and crystalline GSTs. The filling ratio of grating or the ratio of GST to air is fixed at 0.5.
Fig. 7. The maximum efficiency of the m=-1 diffraction as a function of the GST filling ratio. The grating thickness is fixed at 50 nm.
Fig. 8. Simulated diffraction efficiencies for s-polarized light by the GST grating at various diffraction orders. Note that m=0 means the specular reflection. All diffraction orders other than m=0 and -1 are computed to be zero, so not plotted in the figure. It is assumed that the GST is amorphous or crystalline, and that the grating is optimized to a structure 50 nm thick with a period of 600 nm and a filling ratio of 0.5.

This light switching behavior has also been verified by a FDTD simulation [12

A. Taflove and S. Hagness, Computational Electrodynamics: The Finite Difference Time DomainMethod . Boston (Artech House, Norwood, MA, 2nd edition, 2000).

] where the light beam with a Gaussian profile was incident upon the GST grating (Fig. 9). The beam spot size was set to be 4 µm. The incidence angle was chosen to be 62.2°, so that the m=-1 order beam would be diffracted back at exactly the same angle. As shown in the two contour maps of the electric field, the clear switching behavior was observed, which agreed well with the aforementioned RCWA results. It is concluded that light on-off functionality or light path switching functionality can be achieved by properly controlling the phase state of a GST grating. It should be noted that the above optimized structure does not work for the p-polarized light because of the anisotropy of the grating.

To evaluate the loss and crosstalk of the switch, the incidence angle was set to be 70°. When GST is in the amorphous state, the loss and crosstalk were estimated to be 0.4 dB and -27 dB, much better than the values of 1.7 dB and -15.2 dB for cross state reported in reference [3

H. Tsuda, “Proposal of an optical switch using phase-change material for future photonic network nodes,” PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39–42, Atami, Nov. 29–30, 2007.

]. When GST is in crystalline state, these values are estimated to be 1.8 dB and -17 dB, comparable or a little better than the 1.9 dB and -12.3 dB of bar state in [3

H. Tsuda, “Proposal of an optical switch using phase-change material for future photonic network nodes,” PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39–42, Atami, Nov. 29–30, 2007.

], even though [3

H. Tsuda, “Proposal of an optical switch using phase-change material for future photonic network nodes,” PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39–42, Atami, Nov. 29–30, 2007.

] used a much smaller absorption coefficient of 0.5 for the crystalline GST in their simulation. These improvements are contributed by the shorter interaction distance between light and GST in grating scheme, when compared with [3

H. Tsuda, “Proposal of an optical switch using phase-change material for future photonic network nodes,” PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39–42, Atami, Nov. 29–30, 2007.

]. The loss and crosstalk of the crystalline state can be further improved by increasing the incidence angle, but at the expense of degrading the performance of amorphous state. Other better way might be to alloy small amounts of additional elements into GST to tailor its refractive index, just as what reference [2

D. Strand, D. V. Tsu, R. Miller, M. Hennessey, and D. Jablonski, “Optical routers based on Ovonic phase change materials,” E/PCOS2006 (European Phase Change and Ovonics Symposium), Grenoble, May 29–31, 2006, http://www.epcos.org/library/papers/pdf 2006/pdf contributed/Strand.pdf.

] demonstrated in reducing the absorption coefficient of GST.

Fig. 9. FDTD simulations of the s-polarized light propagation for an incidence angle of 62.2°. The GST grating plane is indicated by the horizontal line at y=6 µm, above which is SiO2 (n=1.46).

Finally, the dependence of the maximum efficiency of the m=-1 diffraction order on the optical wavelength is shown in Fig. 10 when light is incident at an angle of 65°. The wavelength dependence of the refractive index of GST was explicitly included in the simulation. The device has very good wavelength performance for both the amorphous and crystalline states, covering nearly the whole telecommunication wavelength range. As with any other normal grating device, the PCM grating has also an angular dispersion for the m=-1 diffraction, which can be derived from Eq. (1) to be dθ 1,-1/dλ=-1/(n 1 d cosθ 1,-1). This dispersion should be carefully considered when coupling a wide-band optical signal out, or can be actively used for wavelength division and dispersion compensation.

5. Summary

We have proposed a novel grating-based optical switch using a phase change material. By taking Ge2Sb2Te5 (GST) as an example, we determined the optimal geometric parameters of the grating to obtain the blazing condition for highly efficient m=-1 order diffraction in amorphous state. Numerical simulations show that there exists a high efficiency window for the m=-1 diffraction order for a grating period around 600 nm and thickness of 50 nm. When GST is transformed into the crystalline state, this blazing condition does not hold and incident light is steered to the specular reflection direction. Therefore, the phase change between amorphous and crystalline provides an on/off switching or optical path shifting functionality.

Fig. 10. The maximum efficiency of the m=-1 diffraction as a function of the optical wavelength for the light incident at an angle of 65°. The device parameters are the same as those in Fig. 8.

The device structure is simple and easy to fabricate. In particular, the grating period of 600 nm and its insensitivity to the filling ratio imply that the grating can be fabricated by the nano-imprint lithography techniques. Devices can be fabricated on the surface of a prism to realize easy optical coupling. To control the phase state of PCM, one possibility is to utilize joule heating induced by electric pulses contained within transparent electrodes on the surface of GST, similar to what has been done in PCRAM. Further careful design regarding the thermal and electric structure is necessary to obtain optimized performance, just as has been done in [13

B. J. Choi, S. H. Oh, S. Choi, T. Eom, Y. C. Shin, K. M. Kim, K.-W. Yi, C. S. Hwang, Y. J. Kim, H. C. Park, T. S. Baek, and S. K. Hong, “Switching power reduction in phase change memory cell using CVD Ge2Sb2Te5 and ultrathin TiO2 films,” J. Electrochem. Soc. 156(1), H59–H63 (2009). [CrossRef]

]. Another method would be to utilize a pulsed focused 650 nm laser beam, in the same way that an optical disk is recorded.

The loss and crosstalk performance of the PCM grating switches are very good for the amorphous state, but relatively poor for the crystalline state, when compared with other types of optical switches. The reason is that the crystalline phase has a large absorption coefficient for our specific GST material. If the absorption could be reduced, the performance will be greatly improved. Further research of both the material and device structures is needed. Nevertheless, its non-volatile nature and relatively high switching speed as well as wide bandwidth, make the PCM grating an attractive and promising switching device for future all-optical network applications.

Acknowledgments

The authors would like to thank Dr. C. Rockstuhl of Institute of Condensed Matter Theory and Solid State Optics, Friedrich Schiller University Jena, for providing us a part of the computation codes.

References and links

1.

M. Chen, K. A. Rubin, and R. W. Barton, “Compound materials for reversible, phase-change optical data storage,” Appl. Phys. Lett. 49, 502 (1986). [CrossRef]

2.

D. Strand, D. V. Tsu, R. Miller, M. Hennessey, and D. Jablonski, “Optical routers based on Ovonic phase change materials,” E/PCOS2006 (European Phase Change and Ovonics Symposium), Grenoble, May 29–31, 2006, http://www.epcos.org/library/papers/pdf 2006/pdf contributed/Strand.pdf.

3.

H. Tsuda, “Proposal of an optical switch using phase-change material for future photonic network nodes,” PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39–42, Atami, Nov. 29–30, 2007.

4.

H. Horii, J. H. Yi, J. H. Park, Y. H. Ha, I. G. Baek, S. O. Park, Y. N. Hwang, S. H. Lee, Y. T. Kim, K. H. Lee, U-In Chung, and J. T. Moon, “A novel cell technology using N-doped GeSbTe films for phase change RAM,” Proceedings of International Symposium on VLSI Technology , pp.177–178, Kyoto, June 10–12, 2003.

5.

A. V. Kolobov, P. Fons, A. I. Frenkel, A. L. Ankudinov, J. Tominaga, and T. Uruga, “Understanding the phase-change mechanism of rewritable optical medium,” Nature Mater. 3, 703 (2004). [CrossRef]

6.

M. Wuttig and N. Yamada, “Phase-change materials for rewritable data storage,” Nature Mater. 6, 824–832 (2007). [CrossRef]

7.

K. Shportko, S. Kremers, M. Woda, D. Lencer, J. Robertson, and M. Wuttig, “Resonant bonding in crystalline phase-change materials,” Nature Mater. 7, 653–658 (2008). [CrossRef]

8.

S. Nakamura, Y. Ueno, and K. Tajima, “Femtosecond switching with semiconductor-optical-amplifier-based Symmetric Mach-Zehnder-type all-optical switch,” Appl. Phys. Lett. 78, 3929–3931 (2001). [CrossRef]

9.

T. Akiyama, N. Georgiev, T. Mozume, H. Yoshida, A. V. Gopal, and O. Wada, “1.55 um picosecond all-optical switching by using absorption in InGaAs-AlAs-AlAsSb coupled quantum wells,” IEEE Photon. Tech. Lett. 14, 495–497 (2002). [CrossRef]

10.

M. G. Moharam and T. K. Gaylord, “Diffraction analysis of dielectric surface-relief gratings,” J. Opt. Soc. Am. , 72, 1385–1392 (1982). [CrossRef]

11.

L. Li, “New formulation of the Fourier modal method for crossed surface-relief gratings,” J. Opt. Soc. Am. A 14, 2758–2767 (1997). [CrossRef]

12.

A. Taflove and S. Hagness, Computational Electrodynamics: The Finite Difference Time DomainMethod . Boston (Artech House, Norwood, MA, 2nd edition, 2000).

13.

B. J. Choi, S. H. Oh, S. Choi, T. Eom, Y. C. Shin, K. M. Kim, K.-W. Yi, C. S. Hwang, Y. J. Kim, H. C. Park, T. S. Baek, and S. K. Hong, “Switching power reduction in phase change memory cell using CVD Ge2Sb2Te5 and ultrathin TiO2 films,” J. Electrochem. Soc. 156(1), H59–H63 (2009). [CrossRef]

OCIS Codes
(210.4810) Optical data storage : Optical storage-recording materials
(230.1950) Optical devices : Diffraction gratings
(250.6715) Optoelectronics : Switching

ToC Category:
Optoelectronics

History
Original Manuscript: July 27, 2009
Revised Manuscript: August 27, 2009
Manuscript Accepted: August 31, 2009
Published: September 8, 2009

Citation
Xiaomin Wang, Masashi Kuwahara, Koichi Awazu, Paul Fons, Junji Tominaga, and Yoshimichi Ohki, "Proposal of a grating-based optical reflection switch using phase change materials," Opt. Express 17, 16947-16956 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-19-16947


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References

  1. M. Chen, K. A. Rubin, R. W. Barton, "Compound materials for reversible, phase-change optical data storage," Appl. Phys. Lett. 49, 502 (1986). [CrossRef]
  2. D. Strand, D. V. Tsu, R. Miller, M. Hennessey and D. Jablonski, "Optical routers based on Ovonic phase change materials," E/PCOS2006 (European Phase Change and Ovonics Symposium), Grenoble, May 29-31, 2006, http://www.epcos.org/library/papers/pdf 2006/pdf contributed/Strand.pdf.
  3. H. Tsuda, "Proposal of an optical switch using phase-change material for future photonic network nodes," PCOS2007 (The 19th Symposium on Phase Change Optical Information Storage), pp. 39-42, Atami, Nov. 29-30, 2007.
  4. H. Horii, J. H. Yi, J. H. Park, Y. H. Ha, I. G. Baek, S. O. Park, Y. N. Hwang, S. H. Lee, Y. T. Kim, K. H. Lee, U-In Chung, and J. T. Moon, "A novel cell technology using N-doped GeSbTe films for phase change RAM," Proceedings of International Symposium on VLSI Technology, pp.177-178, Kyoto, June 10-12, 2003.
  5. A. V. Kolobov, P. Fons, A. I. Frenkel, A. L. Ankudinov, J. Tominaga, and T. Uruga, "Understanding the phasechange mechanism of rewritable optical medium," Nat. Mater. 3, 703 (2004). [CrossRef]
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