OPTICAL THREE-PORT FORK-LIKE CIRCULATOR BASED ON A TWO-DIMENSIONAL PHOTONIC CRYSTAL WITH A TRIANGULAR LATTICE

Abstract

Provided a two-dimensional photonic crystal device in which are inserted three waveguides and one resonant cavity by the creation of linear and local defects. Due to the photonic band gap related to the photonic crystal, electromagnetic signals are confined to the interior of waveguides and resonant cavity. By exciting dipole modes in the resonant cavity, with orientation that depends on the intensity of the applied DC magnetic field, the present circulator device can provide the nonreciprocal transmission of signals in the clockwise and counterclockwise directions. It can fulfill the isolation function and it is fork-shaped, providing greater flexibility in the design of integrated optical communication systems.

Claims

1: An optical three-port fork-like circulator device based on a two-dimensional photonic crystal with triangular lattice, wherein the device comprises a photonic crystal in which are inserted three waveguides and one resonant cavity, adapted to isolate signal sources against parasitic reflections in a communication system with high integration density of components.

2: An optical three-port fork-like circulator device based on a two-dimensional photonic crystal with triangular lattice, wherein the device is adapted to provide nonreciprocal transmission of electromagnetic signals in clockwise and counterclockwise directions, depending on a direction of a DC magnetic field applied to the device.

3: An optical three-port fork-like circulator device based on a two-dimensional photonic crystal with triangular lattice, wherein a dipole mode excited in a resonant cavity of the device is oriented such that its field distribution is almost the same between its input and output ports, with its nodes aligned with the isolated waveguide.

4: An optical three-port fork-like circulator device based on a two-dimensional photonic crystal with triangular lattice, wherein when the device is subjected to a DC magnetic field at the operating normalized central frequency a/2c=0.30467, insertion losses are lower than 0.45 dB, while the bandwidth, defined at the level 15 dB of the isolation curves, is equal to 173 GHz for ports 1 and 3, and equal to 133 GHz for port 2, considering =1.55 m.

Description

[0036] In the following, the performance characteristics and the operating principle of the device will be presented with the support of several figures.

[0037] FIG. 1 shows, in a simplified manner, the structure of the developed circulator.

[0038] FIG. 2 presents, in a simplified manner, the operation of the circulator when a DC magnetic field +H.sub.0 is applied. In FIGS. 2a, 2b and 2c, the cases in which the excitation is applied to ports 1, 2 and 3 are presented, respectively.

[0039] FIG. 3 shows, in a simplified manner, the case in which the circulator is operating and subjected to the application of a DC magnetic field H.sub.0. FIGS. 3a, 3b and 3c correspond to the cases in which the excitation is applied to ports 1, 2 and 3, respectively.

[0040] FIG. 4 presents, in a schematic manner, the proposed circulator operating as an isolator.

[0041] FIG. 5 shows a top view of the device when it is subjected to a DC magnetic field +H.sub.0, with excitation applied to port 1, in which it is possible to see the photonic crystal, the three waveguides and the resonant cavity that comprise the device, as well as the electromagnetic field component H.sub.z, at the normalized central frequency a/2c=0.30467, 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).

[0042] FIG. 6 shows a top view of the circulator when it is subjected to the application of a DC magnetic field +H.sub.0, with excitation applied to port 3, in which it is possible to see the photonic crystal, the three waveguides and the resonant cavity that comprise the device, as well as the electromagnetic field component H.sub.z, at the normalized central frequency a/2c=0.30467.

[0043] FIG. 7 shows a top view of the developed circulator when the excitation is applied to port 2, with application of a DC magnetic field +H.sub.0, in which it is possible to see the photonic crystal, the three waveguides and the resonant cavity that comprise the device, as well as the electromagnetic field component H.sub.z, at the normalized central frequency a/2c=0.30467.

[0044] FIG. 8 presents the frequency response of the circulator when it is subjected to a DC magnetic field +H.sub.0.

[0045] The developed circulator is comprised by the waveguides 1 (101), 2 (102) and 3 (103), connected to a resonant cavity 104 such that the final design resembles the format of a fork (FIG. 1).

[0046] In the case where a DC magnetic field +H.sub.0 is applied to the circulator, it occurs the nonreciprocal transmission of signals in counterclockwise direction, as can be seen, in a schematic manner, in FIG. 2. In this case, the value of the parameter g is equal to 0.3. Electromagnetic signals applied to the waveguides 201 (FIG. 2a), 203 (FIG. 2b) and 202 (FIG. 2c) excite dipole modes 204, inside the resonant cavity, whose orientations allow the transmission of the signals, with low insertion losses, to the waveguides 203, 202 e 201, respectively. In these cases, waveguides 202, 201 and 203 are isolated, respectively.

[0047] On the other hand, in the case where the circulator is subjected to the application of a DC magnetic field H.sub.0, the nonreciprocal transmission of signals occurs in the clockwise direction, as can be seen, in a schematic manner, in FIG. 3. In this case, the parameter g is 0.3. The application of electromagnetic signals to the waveguides 301 (FIG. 3a), 302 (FIG. 3b) and 303 (FIG. 3c) excites, inside the resonant cavity, dipole modes 304, whose orientations allow the transmission of these signal, with low insertion losses, to the waveguides 302, 303 and 301, respectively. In these cases, waveguides 303, 301 and 302 are isolated, respectively.

[0048] Due to the fact that they promote the nonreciprocal transmission of electromagnetic signals, circulators are mainly employed as isolators (FIG. 4). The utilization of the developed circulator as an isolator can be analyzed, for example, by considering that: a DC magnetic field +H.sub.0 is applied to the resonant cavity 404; a signal source 405 is connected to the waveguide 401; an output load 407 is connected to the waveguide 403; an ideally matched load 406 is connected to the waveguide 402.

[0049] In this case, an electromagnetic signal 408, coming from the signal source 405, is transmitted to the output load 407. However, if the output load is not ideally matched, parasitic reflections 409 will arise from it. As the circulator promotes the nonreciprocal transmission of signals in the counterclockwise direction, these reflections will not return to the signal source 405, being absorbed by the ideally matched load 406. Thus, the signal source 405 is protected against the instabilities usually provoked by these reflections.

[0050] The designed circulator can also be used as isolator in the cases where the signal source is connected to the other waveguides or in the case where a DC magnetic field H.sub.0 is applied to the device. In these cases, the positions of the output load and of the ideally matched load must be changed, accordingly to the analysis performed before.

[0051] The electromagnetic field profile, considering the excitation being applied to the port 501 and the application of a DC magnetic field +H.sub.0 to the device, is shown in FIG. 5. In this figure, it is shown the electromagnetic field component H.sub.z, at the normalized central frequency a/2c=0.30467. In this case, one can see, in a detailed manner, that a dipole mode with nodes aligned to the waveguide 502 is excited inside the resonant cavity of the device, with almost equal field distribution between the waveguides 501 and 503. Thus, the input signal is transferred, with low losses, to the waveguide 503, with the isolation of waveguide 502.

[0052] When the excitation is applied to the waveguide 603 and a DC magnetic field +H.sub.0 is applied to the device, as shown, in a detailed manner, in FIG. 6, one can see that the dipole mode excited inside the resonant cavity has its nodes aligned with the waveguide 601, with almost equal field distribution between the waveguides 602 and 603. It is represented, in this figure, the electromagnetic field component H.sub.z, at the normalized central frequency a/2c=0.30467, and it is possible to see the transmission of the input signal from waveguide 603 to waveguide 602, while the waveguide 601 remains isolated.

[0053] The operation of the circulator as an isolator, shown in a schematic manner in FIG. 4, can be verified in a detailed manner in FIGS. 5 and 6. By means of an analogy between FIG. 4 and FIGS. 5 and 6, one can say that, in FIG. 5, it is represented the transmission of signals between the signal source and the output load, while in FIG. 6 it is represented the absorption of the parasitic reflections, coming from the output load, in the ideally matched load, with protection of the signal source.

[0054] The electromagnetic field component H.sub.z at the normalized central frequency a/2c=0.30467, in the case where the excitation is applied to the waveguide 702 and the DC magnetic field +H.sub.0 is applied to the circulator, is shown in FIG. 7. In this case, there is an almost equal field distribution of the excited dipole mode between waveguides 702 and 701, while waveguide 703 is aligned with the dipole nodes. Thus, it takes place the transmission of signals from waveguide 702 to waveguide 701, with isolation of waveguide 703.

[0055] The frequency response of the circulator, in the case where a DC magnetic field +H.sub.0 is applied to the device, is shown in FIG. 8. At the normalized central frequency a/2c=0.30467, the insertion losses are lower than 0.45 dB. The bandwidth, defined at the level 15 dB of the isolation curves, is equal to 173 GHz for ports 1 and 3, and equal to 133 GHz for port 2, considering that the circulator operates with operating wavelength equal to 1.55 m.