Photonic Crystal Demultiplexer with Square Defect Scatterers

Azliza J. M. Adnan1, Shahbudin Shaari2 , R. Mohamed1, Imran Tengku1

1TM Research & Development (Malaysia) Sdn. Bhd. 1TM Innovation Centre, LingkaranTeknokrat Timur, 63000 Cyberjaya, Selangor, Malaysia

2Institute of Micro-Engineering and Nanoelectronics Universiti Kebangsaan Malaysia, 43600 UKM Bangi, MALAYSIA

E-mail: azliza@tmrnd.com.my

Abstract: A 1310/1490/1550 nm wavelength demultiplexer consiss of two-dimensional photonic crystal is proposed. The system consists of three filters to separate the three wavelength into three different output channels. Filter 1 and 3 use circular defect scatterer and filter 2 use square defect scatterers. Square defect scatterers can increase the power transfer inside filter 2 when wavelength 1310 nm propagates inside it.

Keywords: Photonic crystals, wavelength demultiplexer, resonant cavities, defect scatterer.

1. INTRODUCTION

Photonic crystals (PhC) have inspired a lot of research recently due to the ability to control the propagation of light in more drastic way compared to conventional planar waveguide. The periodic variation of the permittivity in photonic crystals can resort in photonic band gap, ie. a range of frequencies with no allowed electromagnetic mode. By creating a defect in these structures, the periodicity and consequently the completeness of the band gap are broken and the propagation of light can be localized in the defect region. Its frequency is corresponding to the defect frequency inside the gap.

2. PHOTONIC CRYSTAL DEMULTIPLEXER The aim of this paper is to design 1310/1490/1550 nm demultiplexer (DEMUX) based on photonic crystal (PhC). The device consist of Silicon (refractive index of 3.4) circular pillar scatterers in rectangular lattice sorrounded by air with lattice period 570 nm and circular scatterers diameter of 206 nm. In this device, the mechanism to demultiplex the wavelength is by introduce resonant cavities inside PhC. The wavelength demultiplexing in this device is carried out by the three filter channels, channel 1, channel 2 and channel 3, to filter wavelength 1310 nm, 1490 nm and 1550 nm as shown in Figure 1 The device consists of input channel produced by

the waveguide that is form by removing one row of pillar scatterers. This waveguide connects to the three output channel waveguides. In each output channel waveguides, the resonant cavities is place along the waveguides to filter the appropriate wavelengths.

FIGURE 1 Schematic diagram of the three-port channel filter for photonic crystal demultiplexer [1]

3. RESULT AND DISCUSSION

Figure 2 shows the performance of DEMUX PhC with circular defect pillar scatterer inside each filters across wavelengths at three different output channels. The diameter of circular defect scatterer inside filter 1 is 34 nm, 262 nm for filter 2 and 68 nm for filter 3. The device is successfully demultiplexing three wavelengths into three different output channels. It is clearly shown from Figure 2, channel 3 only allow wavelength 1550 nm to propagates inside filter 3, channel 2 only permit wavelength 1310 nm to propagates inside filter 2 and channel 1 allow wavelength 1490 nm to penetrate into filter 1.

The performance of channel 2 is very weak where only 10% of wavelength 1310 nm propagates inside filter 2. The device need to be modified in order to increase the gain at filter 2. Hence, the square defect pillar scatterers is introduced at the filter 2.

FIGURE 2 The performance of device with circular defect scatterer across the wavelength at different output channels.

FIGURE 3 Transmission propagation at (a) = 1310 nm, (b) = 1490 nm and (c) = 1550 nm respectively. Noted that inside the filter 2, two square defect pillar are placed inside it.

The propagation of wavelength 1310 nm, 1550 nm and 1550 nm inside the device with square defect scatterers at filter 2 is shown in Figure 3. Noted that in filter 2 (the right arm) two square defect scatterers with diameter 420 nm is place inside it. All three wavelengths are successfully filter into three different filters. When wavelength 1310 nm propagates inside the device, the light change the direction towards 90° and enter filter 2 which has square defect pillar inside it and wavelength 1490 nm is allow to propagates inside filter 1. Wavelength 1550 nm can propagates through the filter 3 and not allow to propagates inside filter 1 and 2.

Figure 4 shows the performance of the device across wavelengths at three different output channels when the shape of defect pillar is changed to square defect pillar in filter 2. This device is successfully demultiplexing three wavelengths into three different output channels. It is clearly shown from Figure 4, channel 3 only allow wavelength 1550 nm to propagates inside filter 3, channel 2 only permit wavelength

1310 nm to propagates inside filter 2 and channel 1 only allows wavelength 1490 nm to penetrate into filter 1.

FIGURE 4 The performance of the device across the wavelength at different output channels when the circular pillar is replace with square defect pillar at filter 2.

Wavelength (nm)

Powertransfer at Channel

1(%)

Powertransfer at Channel 2

(%)

Powertransfer at Channel 3

(%) 1310 0.2 0.4 9.8 47 1.2 0.61490 65 63 0.16 1.4 0.8 0.71550 0.28 3 0.12 0.4 68 66

TABLE 1 The power transfer at each channel. The shaded boxes are power when the circular defect scatterers in filter 2 is change to square defect scatterers

Table 1 shows the power transfer achieve at each channels when wavelength 1490 nm, 1310 nm and 1550 nm propagates inside the device. The shaded boxes are values when the circular defect scatterers is change to square defect scatterers inside filter 2. It shown clearly that at channel 2, when wavelength 1310 nm propagates inside filter 2 the power is increase from 9.8% to 47% when the shape of defect scatterers is change to square defect pillars.

4 CONLUSION In this work, we have successfully design and model wavelength demultiplexer for 1310 nm, 1490 nm and 1550 nm wavelengths, using circular Silicon scatterers in rectangular lattice sorrounded by air. Filter 1 and 3 use circular defect scatterers to filter wavelength 1490 nm and 1550 nm. Meanwhile in filter 2, square defect scatterers are place inside filter 2 to filter wavelength 1310 nm. The function of square defect scatterers inside filter 2 is to increase the power transfer inside filter 2 when wavelength 1310 nm propagates inside it.

REFERENCES

[1] Azliza J. M. Adnan, S. Shaari, R. Mohamad, Z. Lambak, and W.Y. Chan, “Photonic Crystal 1310/1490/1550 nm Demultiplexer,” Conference on Lasers and Electro-Optics/Pacific Rim (CLEOPR), 2007.

[2] J.D. Joannopoulos, R. D. Meade, J. N. Winn, Photonic Crystals, Princeton Univ. Press, 1995.