Compact Optical Key Based on a Two-Dimensional Photonic Crystal with 60 Degree Folding

Abstract

The present invention is based on a two-dimensional photonic crystal in which are inserted, in a controlled manner, defects that originate the waveguides and the resonant cavity that integrate the device. Its main function is to provide the control of the passage of an electromagnetic signal over a communications channel, blocking (state off) or allowing (state on) the passage of the signal. It also has the function of changing the propagation direction of an electromagnetic signal by an angle of 60 degrees, offering greater flexibility in the design of integrated optical systems. The operating principle of the device is associated with the excitation of dipole modes in the resonant cavity, which is based on a magneto-optical material. When the switch is under the influence of an external DC magnetic field H.sub.0, a rotating dipole mode excited in the cavity allows the passage of the input signal to the output (state on), whereas without the application of H.sub.0, a stationary dipole mode excited in the cavity, with the nodes aligned to the output waveguide, prevents the passage of the input signal to the output (state off).

Claims

1. Compact optical switch based on a two-dimensional photonic crystal with 60 degree bending, consisting of a two-dimensional photonic crystal in which two waveguides and one resonant cavity are inserted, characterized by blocking or allowing the passage of an electromagnetic signal from the input to the output accordingly to the intensity of applied external DC magnetic field.

2. Compact optical switch based on a two-dimensional photonic crystal with 60 degree bending in accordance with claim 1, characterized by the fact that it promotes the change of propagation direction of electromagnetic signals by an angle of 60 degrees, providing greater flexibility in the development of integrated optical systems.

3. Compact optical switch based on a two-dimensional photonic crystal with 60 degree bending in accordance with claims 1 and 2, characterized by operating, in state off (nonmagnetized case), with stationary dipole modes whose nodes are aligned with the output waveguide and, in state on (magnetized case), with rotating dipole modes.

4. Compact optical switch based on a two-dimensional photonic crystal with 60 degree bending in accordance with claims 1 to 3, characterized by the fact that, in the normalized central frequency a/2c=0.30308, the insertion losses in state on are 0.9 dB and the isolation between the ports in state off is 54 dB, while the bandwidth, considering the levels 2 dB of the insertion losses curve and 15 dB of the isolation curve, is 186 GHz.

Description

[0041] In the following, the figures that illustrate the operation of the device are presented, as well as is described, in details, the developed invention.

[0042] FIGS. 1a and 1b illustrate, schematically, the switch operating in states on and off, respectively.

[0043] FIGS. 2a and 2b show the eigenvectors V.sub.1 and V.sub.2, which correspond to two of the six dipole modes that exist in the nonmagnetized resonator, with resonant frequency .sub.0. FIG. 2c shows two rotating modes V.sup. and V.sup.+ of the nonmagnetized resonator, rotating in opposite directions and having the same resonant frequency .sub.0. FIG. 2d shows two rotating modes V.sub.m.sup.+ and V.sub.m.sup. of the magnetized resonator, rotating in opposite directions and having resonance frequencies .sup.+ and .sup., respectively.

[0044] FIG. 3 shows a top view of the device operating in state on. The photonic crystal, the two rectilinear waveguides 301 (input) and 302 (output), the resonant cavity and the H.sub.Z component of electromagnetic signal, transferred from input to output, are shown, in the normalized frequency a/2c=0.30308, where w is the angular frequency (in radians per second); a is the lattice constant of the crystal (in meters); c is the speed of light in free space (approximately equal to 300.000.000 meters per second).

[0045] FIG. 4 presents a top view of the device operating in state off. The photonic crystal is shown, as well as the two rectilinear waveguides 401 (input) and 402 (output), the resonant cavity and the H.sub.Z component of the electromagnetic signal reflected back to the input, in the normalized frequency a/2c=0.30308.

[0046] FIG. 5 shows the frequency response of the switch operating in states on and off.

[0047] When the device is under the influence of an external DC magnetic field H.sub.0 (FIG. 1a), an electromagnetic signal applied to the input waveguide 101 excites, in the magneto-optical resonator, a rotating dipole mode 103. In turn, this fact promotes the transference of the signal present on the input to the output waveguide 102, with low insertion losses, corresponding to the state on of the device. The value of the parameter g, which is proportional to the magnitude of H.sub.0, is equal to 0.3.

[0048] On the other hand, when the external DC magnetic field is equal to 0 (FIG. 1b), an electromagnetic signal applied to the input waveguide 104 excites, in the resonant cavity, a stationary dipole mode 106. The nodes of the mode are aligned with the output guide 105, in a way that electromagnetic waves are not excited on that. The incident signal is fully reflected, with high isolation between input and output. This situation corresponds to the state off and, in this case, the value of the parameter g is equal to 0.

[0049] This behavior can be explained by the analysis of modes excited in the magneto-optical resonator without loads connected to it, i.e., without the connection of the input and output waveguides. In the nonmagnetized case, there are six stationary dipole modes V.sub.i (i=1, 2, . . . , 6) with resonant frequency .sub.0, and two of them are represented in FIGS. 2a (V.sub.1 mode) and 2b (V.sub.2 mode). Other modes can be obtained from rotations per 60 or 120 degrees of V.sub.1 and V.sub.2 modes around the z-axis.

[0050] These modes can be combined in order to produce degenerate rotating modes V.sup. and V.sup.+, with resonant frequency .sub.0 and rotating in opposite directions (FIG. 2c).

[0051] Application of an external DC magnetic field H.sub.0, oriented along the z direction, removes the degeneracy of V.sup. and V.sup., so that now they possess different resonance frequencies .sup. and .sup.+ (V.sub.m.sup. and V.sub.m.sup.+ modes, respectively, represented in FIG. 2d).

[0052] The insertion of waveguides in the structure, both in the nonmagnetized and magnetized cases, also removes the degeneracy of the excited modes in the resonant cavity. The higher the coupling between the cavity and the waveguides the higher the difference between the frequencies of the previously degenerate modes.

[0053] The state on (FIG. 3) is obtained when the device is magnetized. In this case, a rotating mode (V.sub.m.sup. or V.sub.m.sup.+) is used, represented by the arched arrow located in the center of the figure.

[0054] On the other hand, the state off (FIG. 4) is obtained when the device is nonmagnetized. In this situation, it is used a mode that results from the combination between the stationary dipole modes V.sub.i. The resulting mode has its nodes aligned with the output waveguide.

[0055] The frequency response of the device is presented in FIG. 5. Considering the excitation of port 1 (associated with the waveguides 301 and 401), the bandwidth of the device is equal to 186 GHz, considering the levels 2 dB and 15 dB of the curves associated with states on and off, respectively. In the normalized central frequency a/2c=0.30308, the insertion losses in state on are 0.9 dB and the isolation between the waveguides in the state off is 54 dB.