Nonreciprocal three-way divider based on a magneto-optical resonator

Abstract

The present invention is based on a two-dimensional photonic crystal in which defects are inserted in a controlled manner, has the main function of division of the power of an input signal, excited in one of its six waveguides, among other three waveguides (output ones), while keeping isolation of the input port by means of two other waveguides. The operating principle of the device is based on the alignment of a dipole mode excited in the resonant cavity, in such a way that the nodes of this mode are oriented in the direction of two waveguides, so that these waveguides are not excited. Due to this alignment, each of the three output waveguides receive about one third of the power of input signal. The orientation of dipole mode is controlled by the applied DC magnetic field and the physical and geometrical parameters of the resonator.

Claims

1. A nonreciprocal three-way divider based on a magneto-optical resonator, comprising a two-dimensional photonic crystal in which six waveguides and a resonant cavity are inserted, wherein dividing a signal present in an input port between three output ports, with high isolation of the former in relation to the latter, wherein the transmission level for the isolated ports is about −29 dB, the transmission level for the output ports is in the range (−6.4±0.4) dB and the bandwidth, for the isolation level −20 dB, is 219 GHz.

2. The nonreciprocal three-way divider based on a magneto-optical resonator in accordance with claim 1, wherein a dipole mode excited in the resonator cavity has its nodes aligned with two waveguides where matched loads are situated.

3. The nonreciprocal three-way divider based on a magneto-optical resonator in accordance with claim 1, wherein two waveguides, whose orientations are aligned with the nodes of the dipole mode, receive the most part of the parasite reflections originated due to unmatched elements in the output ports of the device.

4. The nonreciprocal three-way divider based on a magneto-optical resonator in accordance with claim 1, wherein due to the alignment of nodes of dipole mode with two waveguides, the three remaining waveguides (output ones) receive approximately one third of the power of input signal.

5. The nonreciprocal three-way divider based on a magneto-optical resonator in accordance with claim 2, wherein two waveguides, whose orientations are aligned with the nodes of the dipole mode, receive the most part of the parasite reflections originated due to unmatched elements in the output ports of the device.

6. The nonreciprocal three-way divider based on a magneto-optical resonator in accordance with claim 3, wherein due to the alignment of nodes of dipole mode with two waveguides, the three remaining waveguides (output ones) receive approximately one third of the power of input signal.

7. The nonreciprocal three-way divider based on a magneto-optical resonator in accordance with claim 6, wherein due to the alignment of nodes of dipole mode with two waveguides, the three remaining waveguides (output ones) receive approximately one third of the power of input signal.

Description

(1) Below the invention is described in detail as well as the figures are shown, in order to illustrate its operation. It is expected, therefore, that the operation of the device as well as its potential applications can be well understood.

(2) FIG. 1 schematically shows the configuration with six ports and dipole mode in the resonator. Item (a) schematically shows the proposed divider and an operation of rotation by 60° (which is among the elements of the symmetry group that characterizes the device). Item (b) shows the dipole mode without the application of magnetization. Item (c) shows the dipole mode rotated by the angle 30° clockwise, due to application of an external DC magnetic field. H.sub.0. Item (d) shows the dipole mode rotated by the angle 30° in a counterclockwise direction, due to application of the external DC magnetic field −H.sub.0.

(3) FIG. 2 shows details of the divider of FIG. 1(c) with two matched loads (7) and (8). The arrows inside the resonator show the division of the incident wave.

(4) FIG. 3 shows the divider of FIG. 2 being excited through ports (2), (4) and (5)—items (a), (b) and (c), respectively.

(5) FIG. 4 shows the frequency response of the divider considering the application of excitation on port (1).

(6) FIG. 5 is the top view of the device that shows the periodic structure of the photonic crystal, the six straight waveguides, the resonant cavity and the H.sub.z component of the electromagnetic field inside the divider, for excitation at port (1), at the central normalized frequency ωa/2πc=0.3035, where ω is the angular frequency (in radians per second); a is the lattice constant of the photonic crystal (in meters); c is the speed of light in free space (about 300,000,000 meters per second).

(7) Considering the case in which a DC magnetic field H.sub.0 is not applied and the excitation is in one of the six waveguides (1), the resonator of the divider supports two degenerate modes, which rotate in opposite directions. By the superposition of these two degenerate modes, a stationary dipole mode is created, as shown in FIG. 1(b). The electromagnetic field of this mode excites electromagnetic waves in all the remaining waveguides (2), (3), (4), (5) and (6). In this case, the division is not equal and the divider is reciprocal.

(8) By applying a DC magnetic field H.sub.0, the stationary dipole mode is rotated by the angle 30° around the z axis, in a clockwise way. In this case, the off-diagonal parameter of the electric permittivity tensor related to the magneto-optical material is equal to 0.3. As can be seen in FIG. 1(c), the nodes of the dipole are aligned with waveguides (3) and (6). Therefore, these two waveguides are not excited. From FIG. 2 it can be seen that in waveguides (2), (4) and (5) the field intensity is equal, in the proportion ⅓:⅓:⅓. The rotation of the dipole mode occurs due to magneto-optical properties of the resonator and it can be adjusted by modifying the geometric parameters of the resonator and the magnetic field DC H.sub.0.

(9) In the case where the DC magnetic field is applied in the opposite direction, i.e., −H.sub.0, as shown in FIG. 1(d), the field pattern is also rotated by the angle 30°, but in the opposite direction (counter-clockwise). Thus, waveguides (2) and (5) are isolated and the power division of the electromagnetic wave occurs between waveguides (3), (4) and (6).

(10) The isolation properties of the structure can be observed by exciting output ports (ports (2), (4) and (5) in FIG. 2). The excitation of these ports is related to signal reflection caused by unmatched elements connected to these ports. Due to the symmetry of rotation by 60° of this structure, applying excitation in only one of the six ports, e.g., port (1), is sufficient, in order to obtain the characteristics of the divider. For the other ports, the characteristics in question can be obtained by cyclic permutation of the ports (ports renumbering). These three cases are shown in FIGS. 3(a), 3(b) and 3(c), which are obtained by a simple rotation of the dipole mode of FIG. 2 by 30°, 180° and 210°, respectively.

(11) In all cases of FIG. 3, two ports, where the nodes of the stationary wave are located, are decoupled in relation to the excitation port. The reflected power to port (1), originated from ports (2), (4) and (5), is very small (only one third of the reflected power at port (4)), i.e., most of the reflected power originated at output ports is absorbed by ideally matched loads (7) and (8) connected in ports (3) and (6). Therefore, there is a significant reduction of the influence of parasite reflections originated from unmatched loads, which corresponds to the main idea of the invention in question.

(12) The application of a DC magnetic field H.sub.0 promotes the separation of frequencies ω.sup.+e ω.sup.− of the two degenerated modes that rotate in opposite directions. These two modes comprise the dipole mode of the resonator. The intensity of this separation depends on parameter g (off-diagonal term of the electric permittivity tensor of the magneto-optical material). The present invention is designed to operate with g=0.3.

(13) The operational frequency band of the divider is proportional to the separation of frequencies ω.sup.+ and ω.sup.−, associated with the two dipole modes which rotate in opposite directions. The higher the g value, the wider the operational frequency band of the divider. The parameter g is proportional to magnetization M of the magnetic material.

(14) The waveguide losses are discounted from the transmission coefficients between the ports of the device. These losses, on the order of −2 dB, are discounted in order to make evident only the losses related to the divider itself.

(15) The frequency response of the divider, considering port (1) as input and ports (2) to (6) as output ones, is shown in FIG. 4. At the normalized central frequency ωa/2πc=0.3035, the power division between output ports (2), (4) and (5) is about −6.4 dB. Ports (3) and (6), where ideally matched loads (7) and (8) are connected, are isolated from the input port for approximately −29 dB, i.e., there are minimal power losses in these ports.

(16) The divider bandwidth, at the isolation level −20 dB, is equal to 219 GHz and, in this band, the variation of division levels is equal to (−6.4±0.4) dB. FIG. 5 shows the distribution of H.sub.z field component, at the central frequency. The nodes of the dipole mode are oriented in the directions of ports (3) and (6).