T-shaped circulator based on a two-dimensional photonic crystal with a square lattice

Abstract

A two-dimensional photonic crystal formed of a square lattice of dielectric rods immersed in air, in which are inserted, in a controlled manner, defects that originate three waveguides and one resonant cavity. The cavity is formed of a ferrite cylinder with magneto-optical properties, and by two dielectric cylinders located near to the ferrite cylinder. It has the function of transmitting electromagnetic signals in a desired direction (clockwise or counterclockwise), defined by the sign of an external DC magnetic field H.sub.0.

Claims

1. A T-shaped circulator device based on a two-dimensional photonic crystal with a square lattice, the device comprising a two-dimensional photonic crystal in which are inserted three waveguides and a single resonant cavity and it performs a transmission of electromagnetic signals in a given direction (clockwise or counterclockwise), with the direction being determined by a sign of an external DC magnetic field applied to the device, wherein the resonant cavity has a simplified structure, consisting of a single ferrite cylinder and two cylinders near the dielectric ferrite with enlarged diameters when compared to other cylinders that make up the photonic crystal.

2. The T-shaped circulator device based on a two-dimensional photonic crystal with square lattice according to claim 1, wherein when operating at a normalized central frequency a/2c=0.3499, insertion losses are lower than 0.05 dB, while a bandwidth, set to 100 GHz, is equal to 620 MHz for excitation at port a first, 680 MHz for excitation at a second port, and 730 MHz for excitation at a third port, at the level 15 dB of isolation curves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the E.sub.z component of the electromagnetic field in the device when the input signal is applied to the waveguide 101.

(2) FIG. 2 shows the E.sub.z component of the electromagnetic field in the device when the input signal is applied to the waveguide 102.

(3) FIG. 3 shows the E.sub.z component of the electromagnetic field in the device when the input signal is applied to the waveguide 103.

(4) FIG. 4 shows, schematically, details of the geometry of the resonant cavity which is part of the device.

(5) FIG. 5 shows the device frequency response.

DETAILED DESCRIPTION OF THE INVENTION

(6) When the excitation is applied at port 1 (associated with the waveguide 101), it occurs the signal transmission from this port to port 3 (associated with the waveguide 103), with isolation of port 2 (associated with the waveguide 102) due to the special alignment of the dipole mode, as can be seen in FIG. 1; Similarly, when the input signal is applied in ports 2 (FIGS. 2) and 3 (FIG. 3), it is transferred to ports 1 (with isolation of port 3) and 2 (with isolation of port 1), respectively. This case corresponds to the propagation in counterclockwise direction. If the sign of the external DC magnetic field H.sub.0 is inverted, the signal propagation takes place in the clockwise direction (1.fwdarw.2, 2.fwdarw.3 and 3.fwdarw.1).

(7) In the cases illustrated in FIGS. 1 and 2, it can be seen that the stationary dipole excited in the resonant cavity mode is rotated by an angle of 45, which provides isolation of ports 2 and 3, respectively. On the other hand, in the case illustrated in FIG. 3, it is shown that the stationary dipole mode suffers no rotation, causing the transmission of the input signal (applied to port 3) to port 2, with isolation of the port 1.

(8) In order to obtain a higher bandwidth, adjustments were made in the central structure of the device, which can be seen in FIG. 4. The radius of the cylinder 401 was increased by 0.10562a and the offset relative to the axis of waveguides 102 and 103 (y1) is 0.69086a. The cylinder 402 has its radius reduced by 0.01249a and it was moved vertically, relatively to the axis of the upper cylinders (y2), by 0.2563a. The radii of the cylinders 403 and 404 were increased by 0.07439a.

(9) The device's frequency response is shown in FIG. 5. At the normalized central frequency a/2c=0.3499, the insertion losses are smaller than 0.05 dB, where: is the angular frequency (in radians per second); a is the lattice constant (in meters); c is the speed of light in free space (roughly equal to 300,000,000 meters per second). In the frequency band located around 100 GHz, the bandwidth (defined at the level 15 dB of isolation curves) is equal to 620 MHz for excitation at port 1, 680 MHz for excitation at port 2 and 730 MHz for excitation at port 3.