Compact Optical Key Based on a Two-Dimensional Photonic Crystal with 120 Degree Folding

Abstract

The present invention is based on a two-dimensional photonic crystal where are inserted defects that originate two waveguides and one resonant cavity. An electromagnetic signal that crosses the device is confined in the interior of the defects, due to the photonic band gap associated with the periodic structure that surrounds it. Its main function is the control of the flux of an electromagnetic signal over a communication channel, blocking (state off) or allowing (state on) the passage of the signal. It also promotes the change in the propagation direction of an electromagnetic signal by an angle of 120 degrees, providing greater flexibility in the design of integrated optical systems. The working principle of the device is based on the excitation of dipole modes in its resonant cavity, accordingly to the application of an external DC magnetic field on the magneto-optical material that constitutes it. In states on and off the magneto-optical material is magnetized and nonmagnetized, respectively.

Claims

1. Compact optical switch based on a two-dimensional photonic crystal with 120 degree bending, based on a two-dimensional photonic crystal in which defects are inserted, in a controlled way, originating two waveguides and one resonant cavity in a magneto-optical material, characterized by controlling the flow of an electromagnetic signal along a optical communications channel, interrupting or allowing the passage of the signal in accordance with the application of applied external DC magnetic field.

2. Compact optical switch based on a two-dimensional photonic crystal with 120 degree bending in accordance with claim 1, characterized by promoting the change of the propagation direction of an electromagnetic signal by an angle of 120 degrees in state on, providing greater flexibility in the development of integrated optical systems.

3. Compact optical switch based on a two-dimensional photonic crystal with 120 degree bending in accordance with claims 1 and 2, characterized by operating, in state off (nonmagnetized case), with stationary dipole modes whose the 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 120 degree bending in accordance with claims 1 to 3, characterized by presenting, in the normalized central frequency a/2c=0.30235, insertion losses (transmission coefficient in state on) equal to 1.5 dB and isolation between the input and output ports (transmission coefficient in off state) equal to 53 dB. The operating bandwidth is equal to 146 GHz, considering the levels 2 dB and 15 dB of the insertion losses curve and isolation curve, respectively.

Description

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

[0042] FIGS. 1a and 1b present, in a simplified way, the switch operating in states on and off, respectively.

[0043] FIGS. 2a and 2b show the eigenvectors V.sub.1 and V.sub.2, respectively, which are associated with two of the six existing dipole modes in the nonmagnetized resonator, with resonant frequency .sub.0. FIG. 2c presents the 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 the 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 in which the device is based, the rectilinear waveguides 301 and 302 (input and output, respectively), the resonant cavity in which the dipole modes are excited and the H.sub.z component of the electromagnetic signal, transferred from input to output, are shown, in the normalized central frequency a/2c=0.30235, where: 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 shows a top view of the device operating in state off. The photonic crystal in which are inserted the resonant cavity and the waveguides 401 (input) and 402 (output) are shown, as well as the H.sub.z component of the electromagnetic signal, which is reflected back to the input, in the normalized central frequency a/2c=0.30235.

[0046] FIG. 5 presents the transmission curves of the switch operating in states on and off.

[0047] When the switch is under the influence of an external DC magnetic field H.sub.0 (FIG. 1a), an electromagnetic signal in the input waveguide 101 excites, in the resonant cavity, a rotating dipole mode 103. This mode makes the incident signal to be transferred to the output waveguide 102. This is the state on and, in this case, the value of the parameter g is equal to 0.26.

[0048] On the other hand, considering the case in which an external DC magnetic field is not applied to the switch (FIG. 1b), an electromagnetic signal incident at the input waveguide 104 excites, in the resonant cavity, a stationary dipole mode 106, whose nodes are aligned with the output waveguide 105. In this case, the incident signal is totally reflected back to the input and there is no transmission of the signal. This is the state off and the value of the parameter g is equal to 0.

[0049] The analysis of the behavior of the magneto-optical resonator without loads, i.e., without the connection of input and output waveguides, allows the understanding of the behavior of the device in the two states of operation. In the nonmagnetized case, there are six stationary dipole modes V.sub.i(i=1, 2, . . . , 6), with resonant frequency .sub.0. Both V.sub.1 and V.sub.2 modes are shown in FIGS. 2a and 2b, respectively. Others V.sub.i modes can be obtained by rotating the first and the second modes by 60 and 120 degrees, respectively, in relation to z axis.

[0050] V.sub.i modes can be combined in a way that degenerate rotating dipole modes V.sup. and V.sup.+ can be produced, with resonant frequency .sub.0 and rotating in opposite directions (FIG. 2c).

[0051] Application of an external DC magnetic field H.sub.0 on the magneto-optical material in which is based the resonant cavity, oriented along the z axis, causes the removal of degeneracy of the modes V and i.e., they now have distinct resonance frequencies .sup. and .sup.+. This situation is illustrated in FIG. 2d, where the V.sub.m.sup. and V.sub.m.sup.+ modes, originated from V.sup. and V.sup.+, are nondegenerated.

[0052] The connection of the two waveguides to the resonant cavity, in both non magnetized and magnetized cases, is also responsible for removing the degeneracy of dipole modes. The higher the coupling between the cavity and the waveguides the higher the difference between the resonance frequencies of the previously degenerate modes.

[0053] The state on is obtained when an external DC magnetic field H.sub.0 (FIG. 3) is applied on the device. In this situation, one of two rotating dipole modes V.sub.m.sup. or V.sub.m.sup.+ is excited in the resonant cavity, making possible the transfer of the input signal to the output.

[0054] The state off is obtained when an external DC magnetic field is not applied on the device (FIG. 4). In this case, a stationary dipole mode, derived from the combination between the V.sub.i modes, is excited in the resonant cavity. The resulting mode has the nodes aligned with the outgoing waveguide of the device, preventing the transfer of the input signal to the output.

[0055] Transmission curves in the two operating states are shown in FIG. 5. The operating bandwidth, considering the levels 2 dB of the insertion losses curve (transmission coefficient in state on) and 15 dB of the isolation curve (transmission coefficient in state off), is 146 GHz. In the normalized central frequency a/2c=0.30235, the insertion losses are 1.5 dB and the isolation between the input and output ports is 53 dB.