Abstract
A two-dimensional photonic crystal in which are inserted four waveguides and a resonant cavity. Owing to the existence of the photonic band gap, an electromagnetic signal propagating through the device is confined within the guides and the cavity and, through the adjustment of the orientation of a dipole mode generated within the cavity, is able to function in three distinct regimes. In regime 1, subjected to an external DC magnetic field +H0, it functions as a two-way divider, with isolation of the input relative to the two outputs, and, upon reversal of the field signal, it functions as an optical key. In regime 2, with the use of a DC magnetic field −H0, it functions as a waveguide bender, with the input isolated from the output, and, upon reversal of the field signal, functions as an optical key. In regime 3, subject to the application of an external DC magnetic field +H1, the device functions as a three-way divider.
Claims
1. A multifunctional optical device based on a two-dimensional photonic crystal and on a magneto-optical resonator, wherein the device comprises a two-dimensional photonic crystal in which are inserted four waveguides and one resonant cavity, capable of operating in three distinct regimes and performing signal switching, power division, waveguide bending, and isolation functions.
2. A multifunctional optical device based on a two-dimensional photonic crystal and on a magneto-optical resonator, wherein the device operates as a two-way divider in a first regime, with an external DC magnetic field +H.sub.0 (on state), and as an optical switch, by inverting a sign of the external DC magnetic field (off state), so that, in an “on state”, the input is isolated from the two outputs and the power division levels are −3.8 dB, while a bandwidth, defined at the level −15 dB, is equal to 178 GHz (considering the wavelength λ=1.55 μm).
3. A multifunctional optical device based on a two-dimensional photonic crystal and on a magneto-optical resonator, wherein the device operates as a waveguide bending element in a second regime, with an external DC magnetic field −H.sub.0 (on state), and as an optical switch, by inverting a sign of the external DC magnetic field (off state), so that, in an “on state”, the input is isolated from the output and the transmission level from input to output is −0.4 dB, with a 120 degrees change on the propagation direction, while a bandwidth, defined at the level −15 dB, is equal to 113 GHz (considering the wavelength λ=1.55 μm).
4. A multifunctional optical device based on a two-dimensional photonic crystal and on a magneto-optical resonator, wherein the device operates as a three-way divider in a third regime, with an external DC magnetic field +H.sub.1, so that the power division levels between the three output ports are equal to −5.2 dB, with a variation defined by the interval (−5.2±0.7) dB, and a bandwidth, defined at the level −6 dB of the transmission curves, is equal to 110 GHz (considering the wavelength λ=1.55 μm).
Description
[0035] In the following it will be presented the figures that illustrate the operating principle of the device, as well as a detailed description of the designed invention.
[0036] FIG. 1 shows, schematically, the designed device. FIG. 1a shows the four waveguides connected to the magneto-optical resonator and the angles formed by the waveguides. FIG. 1b presents the nonmagnetized device, while FIGS. 1c and 1d present the magnetized device.
[0037] FIG. 2 presents, in a schematic way, the device operating in regime 1. FIGS. 1a, 1b, and 1c show the device subjected to the application of a DC magnetic field +H.sub.0 (on state), while FIG. 1d shows the device subjected to a DC magnetic field −H.sub.0 (off state).
[0038] FIG. 3a shows the frequency response of the device operating in “on state” of regime 1 and in “off state” of regime 2. The transmission coefficients S.sub.ij—whose indices i and j can be equal to 1, 2, 3, or 4—are the entries of the scattering matrix [S]. FIG. 3b shows a top view of the device operating in both cases, in which the four waveguides 301 to 304 and the resonant cavity of the device are shown, as well as the electromagnetic field component H.sub.z at the normalized central frequency ωa/2πc=0.30318, where: ω is the angular frequency (in radians per second); a is the lattice constant (in meters); c is the speed of light in free space (approximately equal to 300,000,000 meters per second).
[0039] FIG. 4a shows the frequency response related to the parasitic reflections arising from port 402, considering operation in “on state” of regime 1. FIG. 4b shows a top view of the device when subjected to these reflections, in which are shown the four waveguides 401 to 404, the resonant cavity, and the electromagnetic field component H.sub.z associated with these reflections, at the normalized central frequency ωa/2πc=0.30318.
[0040] FIG. 5a shows the frequency response related with parasitic reflections arising from port 503, considering operation in “on state” of regime 1. FIG. 5b shows a top view of the device when subjected to these reflections, in which are shown the four waveguides 501 to 504 and the resonant cavity of the device, as well as the electromagnetic field component H.sub.z associated with these reflections, at the normalized central frequency ωa/2πc=0.30318.
[0041] FIG. 6a presents the frequency response of the device operating in “off state” of regime 1 and in “on state” of regime 2. FIG. 6b presents a top view of the device operating in both cases, in which are shown the four waveguides 601 to 604, the resonant cavity, and the electromagnetic field component H.sub.z, at the normalized central frequency ωa/2πc=0.30318.
[0042] FIG. 7 presents, schematically, the device operating in regime 2. FIGS. 7a and 7b present the device under the application of a DC magnetic field −H.sub.0 (on state), while FIG. 7c shows the device under the application of a DC magnetic field +H.sub.0 (off state).
[0043] FIG. 8a shows the frequency response of the device related to the parasitic reflections that arise from port 804, considering operation in “on state” of regime 2. FIG. 8b presents a top view of the device when subjected to these reflections, in which are shown the four waveguides 801 to 804 and the resonant cavity of the device, as well as the electromagnetic field component H.sub.z, at the normalized central frequency ωa/2πc=0.30318.
[0044] FIG. 9 presents, in a schematic way, the device operating in regime 3, subjected to the application of a DC magnetic field +H.sub.1.
[0045] FIG. 10a presents the frequency response of the device operating in regime 3. FIG. 10b shows a top view of the four waveguides 1001 to 1004 and the resonant cavity of the device, as well as the electromagnetic field component H.sub.z, at the normalized central frequency ωa/2πc=0.30309.
[0046] The presented invention consists of four waveguides 101, separated by an angle equal to 60 degrees, and one resonant cavity 102 (FIG. 1a). When the structure is not subjected to the application of a DC magnetic field (FIG. 1b), the application of an electromagnetic signal to the input waveguide 103 promotes the excitation of a stationary dipole mode 104 in the resonant cavity 105, whose axis is aligned with the axis of the input waveguide. In this case, the device divides, theoretically, the input power between the three output waveguides 106, 107, and 108, and the parameter g is equal to 0.
[0047] When the device is subjected to the application of a DC magnetic field +H.sub.0 (FIG. 1c), the application of an electromagnetic signal to the input waveguide promotes the excitation of a dipole mode 110 in the resonant cavity 111, whose orientation is changed by an angle of 30 degrees (clockwise direction), relatively to the dipole 104. In this case, the input power is equally divided between the waveguides 112 and 113, and the dipole nodes are aligned with the waveguide 114, so that no electromagnetic waves are excited in the latter waveguide. In this case, the parameter g equals 0.21.
[0048] On the other hand, when the device is subjected to the application of a DC magnetic field −H.sub.0 (FIG. 1d), an electromagnetic signal that flows through the input waveguide 115 excites, in the resonant cavity 116, a dipole mode 117 rotated by an angle of 30 degrees (counterclockwise direction), relatively to the dipole 104. In this case, the input power is directed to the output waveguide 118, while the dipole nodes are aligned with waveguides 119 and 120, so that no electromagnetic waves are excited in the latter waveguides. In this case, the parameter g equals −0.21.
[0049] In regime 1, shown in FIG. 2, the device operates as a two-way divider in the “on state”, with external DC magnetic field +H.sub.0, and as a switch, by inverting the sign of the DC magnetic field (+H.sub.0 to −H.sub.0). In the “on state”, an electromagnetic signal applied to the input waveguide 201 has its power equally divided between the output waveguides 202 and 203 (FIG. 2a). A matched load 204, connected to the waveguide 205, receives most of the parasitic reflections originated from non-ideally matched loads connected to output waveguides 202 and 203.
[0050] FIGS. 2b and 2c present the effects of the parasitic reflections, arising from non-ideally matched loads connected to the outputs, on a signal source connected to the input waveguide. In the case where the reflections arise from waveguide 206 (FIG. 2b), most of them are directed to the matched load 207, with no interferences on the functioning of the signal source connected to the input waveguide 208. The same is true for the case in which reflections arise from waveguide 209, which are directed to the matched load 210 and do not interfere on the functioning of the signal source connected to the waveguide 211. Therefore, the input is isolated from the outputs.
[0051] By inverting the sign of the DC magnetic field (FIG. 2d), the device starts to operate in the “off state” of regime 1. In this case, an electromagnetic signal applied to the input waveguide 212 is transferred to the matched load 213, connected to the waveguide 214. No electromagnetic waves are excited in output ports 215 and 216 and the device operates as a switch.
[0052] The performance characteristics of the device operating in the “on state” of regime 1 are shown in FIG. 3. The division levels between ports 302 and 303 are about −3.8 dB, while port 304, which is connected to a matched load, is isolated from the input 301 by −19 dB. The bandwidth, defined at the level −15 dB of the isolation curves, is equal to 178 GHz (considering the wavelength λ=1.55 μm). The variation on the division levels inside this band is (−3.7±0.7) dB.
[0053] The effect of reflections on a signal source connected to the input, in this case, can be verified in FIG. 4 (FIG. 5). Reflections arising from port 402 (503) do not affect the signal source connect to port 401 (501), since they are directed to a matched load connected to port 404 (504) and to the other output port 403 (502).
[0054] The performance characteristics of the “off state” of regime 1, in which the sign of the DC magnetic field is inverted, are shown in FIG. 6. It is possible to observe that most of the input power, coming from port 601, is coupled with the matched load connected to port 604. The outputs 602 and 603 are aligned with the dipole nodes and are not excited.
[0055] In regime 2, shown in FIG. 7, the device operates as a waveguide bending element in the “on state”, with external DC magnetic field −H.sub.0, and as a switch, by inverting the sign of the DC magnetic field (−H.sub.0 to +H.sub.0). In the “on state”, an electromagnetic signal applied to the input waveguide 701 is transferred to the output waveguide 702, with a bending angle (change on the propagation direction) equal to 120 degrees (FIG. 7a). Matched loads 703 and 704, connected to the waveguides 705 and 706, respectively, receive most of the parasitic reflections arising from the output waveguide 702.
[0056] The effect of these reflections is represented in FIG. 7b, in which an electromagnetic signal coming from the output waveguide 707 (representing these reflections) is totally absorbed by the matched loads 708 and 709. Thus, the signal source connected to the input waveguide 710 is isolated from the output 707.
[0057] By inverting the sign of the external DC magnetic field (−H.sub.0 to +H.sub.0), the device starts to operate in the “off state” of regime 2. In this case, the device operates as a switch and an incident signal applied to the input waveguide 711 is transferred to two matched loads 712 and 713, connected to the waveguides 714 and 715, respectively. No electromagnetic signals are excited in the output waveguide 716.
[0058] The performance characteristics of the device operating in the “on state” of regime 2 are identical to those of the device operating in the “off state” of regime 1. The differences between the cases relate to the position and quantity of ideally matched loads connected to the device (see FIGS. 2d and 7a). The transmission level from input to output is −0.4 dB, while the transmission levels to the two ports connected with ideally matched loads are −21 dB and −17 dB. The bandwidth, defined at the level −15 dB of the isolation curves, is equal to 113 GHz (considering the wavelength λ=1.55 μm).
[0059] In FIG. 8, one can observe that parasitic reflections arising from output 804 are transmitted to two ideally matched loads connected to ports 802 and 803, so that the functioning of the signal source connected to the input port 801 is not compromised by them.
[0060] The operation of the device in the “off state” of regime 2 is similar to the operation in the “on state” of regime 1 (FIG. 3). Again, the only differences between both cases are the position and quantity of ideally matched loads connected to the device (see FIGS. 2a and 7c). One can observe that all the input power is transferred to two ideally matched loads and the output is isolated from the input.
[0061] In regime 3, the device operates as a three-way divider. An electromagnetic signal applied to the input waveguide 901 has its power equally divided between the output waveguides 902, 903, and 904. Preliminarily, the device would not need to be magnetized, in order to operate in this regime (see FIG. 1b). However, through the application of a small DC magnetic field +H.sub.1, a fine adjustment on the division levels between the three output ports has been performed, in order to obtain equal division levels. In this case, parameter g equals 0.07.
[0062] The transmission coefficients of the device operating in this regime are shown in FIG. 10a. The division levels between the three output ports are about −5.2 dB. The bandwidth, defined at the level −6 dB of the power division curves, is 110 GHz (considering the wavelength λ=1.55 μm). The variation on the division levels in this band is (−5.2±0.7) dB. In FIG. 10b, one can see the electromagnetic field profile inside the device and the division of input power, coming from port 1001, between the outputs 1002, 1003, and 1004.
