Optical circulator

Abstract

The application belongs to the field of optoelectronic technology and relates to an optical circulator, which comprises a ring resonant cavity containing an input-output waveguide and a traveling wave modulator arranged in the ring resonant cavity; the traveling wave modulator is used for dynamically modulating the refractive index of the ring resonant cavity by transmitting a traveling wave modulation signal; if the propagation direction of signal light transmitted in the ring resonant cavity is the same as the propagation direction of the traveling wave modulation signal propagating in the modulator, the modulation signal produces effective modulation on the refractive index of the ring resonant cavity, and the signal light is output from the through port corresponding to the incident end; if the propagation direction of the signal light transmitted in the ring resonant cavity is opposite to the propagation direction of the modulation signal propagating in the modulator, the wave vector of the signal light is not matched with the wave vector of the traveling wave modulation signal, the modulation efficiency of the modulation signal on the refractive index of the ring resonant cavity is low, and the signal light is output from the download port corresponding to the incident end, thereby realizing the function of the optical circulator, and the optical circulator is conducive to on-chip integration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optoelectronics, and more particularly relates to an optical circulator. BACKGROUND

[0002] The optical circulator is one of the important elements in optical communication systems and photonic chips, and its function is to realize the bidirectional transmission of optical signals in a photonic path, and can avoid the crosstalk between different signals, and has a very important role in the field of optical communication and integrated optics.

[0003] The design and manufacture of the optical circulator depend on the non-reciprocity of optical transmission, so as to realize the isolation of the output and input of optical signals in different propagation directions and avoid the crosstalk between signals. The non-reciprocity in the traditional optical circulator is mainly generated through the magneto-optical effect or the nonlinear optical effect. Since the magneto-optical material is not compatible with the existing CMOS process, it is complex and difficult to realize its on-chip integration process, and the generation of the third-order nonlinear optical effect requires a strong laser signal. The above characteristics limit the development and application of the optical circulator, especially in the field of on-chip integration.

[0004] Therefore, it is of great research significance and application value to develop a new type of optical circulator. SUMMARY

[0005] In view of the defects and improvement needs of the prior art, the present application provides an optical circulator, which aims to solve the problem that the traditional optical circulator is not conducive to on-chip integration.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, an optical circulator is provided, which is an add-drop structure containing at least three ports, comprising: a ring resonator containing input and output waveguides, and a traveling wave modulator arranged in the ring resonator;

[0007] The traveling wave modulator is used to dynamically modulate the refractive index of the ring resonator by transmitting a traveling wave modulation signal; if the propagation direction of the signal light transmitted in the ring resonator is the same as the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, the traveling wave modulation signal produces effective modulation of the refractive index of the ring resonator, and the signal light is output from the through port corresponding to the incident end; if the propagation direction of the signal light transmitted in the ring resonator is opposite to the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, the wave vector of the signal light does not match the wave vector of the traveling wave modulation signal, the modulation efficiency of the traveling wave modulation signal on the refractive index of the ring resonator is low, and the signal light is output from the download port corresponding to the incident end, thereby realizing the function of the optical circulator.

[0008] Further, the traveling wave modulator can dynamically modulate the refractive index of the ring resonator when the traveling wave modulation signal is loaded.

[0009] Further, the traveling wave modulation signal and the structural parameters of the ring resonator cavity satisfy:

[0010] The modulation frequency Ω of the traveling wave modulation signal is greater than the linewidth γ of the ring resonator cavity and less than the free spectral range FSR of the ring resonator cavity, and A0 / Ω>(γ / Ω) 2 ; the modulation depth m φ of the traveling wave modulation signal is such that J0(A0 / Ω)=0, realizing the transmittance T drop (Δω=0)=0 of the signal light at the drop end.

[0011] Wherein, A0 is the amplitude of the change of the resonant frequency of the ring resonator cavity with time when the dynamic modulation is loaded, J0 is the zero-order Bessel function, A0 and m φ form a linear relationship, and Δω is the detuning of the resonant frequency of the ring resonator cavity.

[0012] Further, the traveling wave modulation signal and the structural parameters of the ring resonator cavity are determined through simulation optimization aiming at maximizing the isolation of the optical circulator and minimizing the insertion loss of the optical circulator.

[0013] Further, the implementation of the simulation optimization is as follows:

[0014] Determine the structural parameters of the ring resonator cavity, including the electrode length and electrode spacing of the traveling wave modulator, the spacing between the input / output waveguide and the ring resonator cavity, the center ring length of the ring resonator cavity, and the effective refractive index of the ring resonator cavity;

[0015] According to the structural parameters, simulate and calculate the power coupling strength α between the input / output waveguide and the micro-ring resonator cavity, the modulation depth m φ of the traveling wave modulation signal, and the propagation loss in the ring resonator cavity;

[0016] According to the power coupling strength α, the modulation depth m φ , the propagation loss in the ring resonator cavity, and the structural parameters, simulate and calculate the insertion loss and the isolation of the optical circulator;

[0017] Optimize the structural parameters according to the insertion loss and the isolation, so that the insertion loss and the isolation are optimal.

[0018] Further, the power coupling strength α between the input / output waveguide and the micro-ring resonator cavity is 0.15, the center ring length L of the ring resonator cavity is 0.6 cm, the effective refractive index n is 2.5, the modulation depth m φ of the traveling wave modulation signal is 1.5438π, and the propagation loss in the ring resonator cavity is 30 dB / m.

[0019] Further, the ring resonator is composed of a fiber loop or a micro-ring and a waveguide integrated on a chip.

[0020] Further, the modulation of the traveling wave modulator is implemented by electro-optic modulation, acousto-optic modulation or thermo-optic modulation.

[0021] In general, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0022] (1) The present application introduces a traveling wave modulator in a ring resonator, and realizes dynamic modulation of the refractive index of the ring resonator by loading a traveling wave modulation signal thereto; the optical non-reciprocity generated based on the dynamic modulation is: if the propagation direction of the signal light transmitted in the ring resonator is the same as the propagation direction of the traveling wave modulation signal propagated in the traveling wave modulator, the signal light is output from the through port corresponding to the incident end; if the propagation direction of the signal light transmitted in the ring resonator is opposite to the propagation direction of the traveling wave modulation signal propagated in the traveling wave modulator, the signal light is output from the drop port corresponding to the incident end, thereby realizing the function of the optical circulator. Therefore, the optical circulator of the present application realizes its function depending on the optical non-reciprocity derived from the traveling wave modulation, and does not depend on magneto-optical materials or high-order nonlinear optical effects, which is easy to integrate on a chip, and at the same time, the intensity of the signal light transmitted in the ring resonator is not limited, thereby breaking through the limitations of the above traditional methods, greatly widening the intensity range of the signal light of the optical circulator, and facilitating large-scale manufacturing and integration on a chip.

[0023] (2) The present application gives the structure parameters of the traveling wave modulation signal and the ring resonator, which satisfy: the modulation frequency Ω of the traveling wave modulation signal is greater than the linewidth γ of the ring resonator and less than the free spectral range FSR of the ring resonator, and A0 / Ω>(γ / Ω) 2 ; the modulation depth m φ of the traveling wave modulation signal makes J0(A0 / Ω)=0, realizes the transmittance T drop (Δω=0) of the signal light at the drop port=0, thereby more effectively realizing the function of the optical circulator.

[0024] (3) The present application also proposes that on the basis of satisfying the transmittance T drop (Δω=0) of the signal light at the drop port=0, the structure parameters of the ring resonator can be further optimized to realize the optimization of the isolation and insertion loss of the optical circulator. That is, the parameters such as the optical loss of the material and structure, the modulation efficiency of the traveling wave modulator, etc. are optimized, which can further reduce the device loss, improve the overall performance such as modulation bandwidth and efficiency, and isolation ratio. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1A schematic diagram illustrating the principle of generating non-reciprocal optical transmission and optical ring routing based on in-ring traveling wave modulation, provided for an embodiment of the present invention;

[0026] Figure 2 The diagram illustrates the structure and working principle of an optical circulator according to an embodiment of the present invention; wherein, (a) shows the signal light input at port 1; (b) shows the signal light input at port 2; (c) shows the signal light input at port 3; and (d) shows the signal light input at port 4.

[0027] Figure 3 The following are simulation results of the optical circulator performance without a traveling wave modulation signal provided in the embodiments of the present invention; wherein, (a) is the relationship between the transmittance and detuning of the ring resonator without dynamic modulation; (b) is the relationship between the transmittance and loss of the ring resonator without dynamic modulation; and (c) is the relationship between the transmittance and power coupling strength of the ring resonator without dynamic modulation.

[0028] Figure 4 for Figure 3 The corresponding performance relationship of the optical circulator after loading a traveling wave modulated signal is shown in the figure; where (a) represents A0 and the modulation depth m. φ (a) shows the linear relationship between the two; (b) shows the relationship between the transmittance at the drop end and the frequency detuning when A0 / Ω = 0 and A0 / Ω = 2.4; (c) shows the transmittance of the 0th-order peak at the drop end as a function of modulation depth m. φ The changing relationship.

[0029] Figure 5 The following diagram shows the performance simulation results of an optical circulator provided in an embodiment of the present invention; wherein, (a) and (b) are the transmission spectra of the input signal light from port 1 and the output signals from ports 2 and 3, respectively; (c) and (d) are the transmission spectra of the input signal light from port 2 and the output signals from ports 4 and 1, respectively; (e) and (f) are the transmission spectra of the input signal light from port 4 and the output signals from ports 3 and 2, respectively; and (g) and (h) are the transmission spectra of the input signal light from port 3 and the output signals from ports 1 and 4, respectively. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Example 1

[0032] An optical circulator, for an add-drop structure containing at least three ports, comprising: a ring resonant cavity containing an input-output waveguide, and a traveling wave modulator arranged in the ring resonant cavity;

[0033] The traveling wave modulator is used to dynamically modulate the refractive index of the ring resonant cavity by transmitting a traveling wave modulation signal; if the propagation direction of the signal light transmitted in the ring resonant cavity is the same as the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, the traveling wave modulation signal effectively modulates the refractive index of the ring resonant cavity, and the signal light is output from the through port corresponding to the incident port; if the propagation direction of the signal light transmitted in the ring resonant cavity is opposite to the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, the wave vector of the signal light does not match the wave vector of the traveling wave modulation signal, the modulation efficiency of the traveling wave modulation signal on the refractive index of the ring resonant cavity is low, and the signal light is output from the drop port corresponding to the incident port, thereby realizing the function of the optical circulator.

[0034] It should be noted that there are often two directions of signal light propagating in the optical circulator, so the propagation direction of one direction of signal light is the same as the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, and the propagation direction of the other direction of signal light is opposite to the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator.

[0035] Now the principle is explained according to Figure 1 . The principle is shown in Figure 1 , in which the refractive index of the ring resonant cavity is dynamically modulated by loading a traveling wave modulation signal in the traveling wave modulator in the add-drop type ring resonant cavity. Assuming that a single-frequency signal light s=p0exp[i(ω0+Δω)t] is input from the port of the ring resonant cavity waveguide, where ω0 is a resonant frequency of the ring resonant cavity, and is an inherent property of the ring resonant cavity. When the detuning amount Δω=0 (i.e. the frequency spectrum of the signal light satisfies the resonant frequency), the input signal light (single-frequency light) can be coupled to the ring resonant cavity and stably transmitted in the cavity. When the traveling wave modulation signal is applied in the traveling wave modulator, two cases are analyzed: (1) as shown in the left part of Figure 1 , if the propagation direction of the signal light transmitted in the ring resonant cavity is opposite to the propagation direction of the traveling wave modulation signal in the traveling wave modulator, there is a phase mismatch between the signal light and the traveling wave modulation signal, resulting in low modulation efficiency. The signal light can be regarded as propagating in the ring resonant cavity without being modulated, and at this time the signal light satisfying the resonant frequency in the cavity can be directly output from the drop port. (2) as shown in the right part of Figure 1As shown in the right figure, if the propagation direction of light in the ring resonator is the same as the propagation direction of the traveling wave modulation signal in the traveling wave modulator, the optical signal and the traveling wave modulation signal satisfy phase matching. Therefore, traveling wave modulation can generate a time-varying additional optical path ΔnLcos(Ωt+φ) (i.e., it is modulated), where Δn is the effective refractive index change caused by traveling wave modulation, L is the central ring length of the ring resonator, resulting in the instantaneous resonant frequency of the cavity being ω(t)=ω0+A0cos(Ωt+φ), where ω0 is a resonant frequency of the ring resonator without modulation, and A0 is the amplitude of the resonant frequency of the ring resonator changing with time when dynamic modulation is applied. The change in refractive index will cause a change in the resonant frequency, which is related to the modulation depth m of the traveling wave modulation. φ There is a linear relationship between them, where Ω is the frequency of the modulation signal, φ is the phase of the modulation signal, and γ is the linewidth of the ring resonator. This relationship is satisfied when A0 / Ω > (γ / Ω). 2 Especially when γ << Ω, the transmittance of the dynamically modulated ring resonator is approximately independent of time, and the transmittance at the drop end (i.e., the download end) is... J k It is a k-th order Bessel function.

[0036] Therefore, when the incident signal light satisfies the ring resonant cavity resonance condition Δω=0, the modulation depth m can be changed. φ Make J0(A0 / Ω) = 0, thus realizing T drop (Δω=0)=0, meaning the transmittance of the signal light (0th order peak) at the drop end is zero. At this time, although the incident signal light frequency ω0 is the resonant frequency of the ring resonant cavity, photons with frequency ω0 are isolated by the dynamically modulated ring resonant cavity. Therefore, when signal light with frequency ω0 is input along the traveling wave modulation direction, the signal light is only transmitted from the through end.

[0037] Therefore, as a preferred embodiment, the structural parameters of the traveling wave modulation signal and the ring resonator satisfy the following: the modulation frequency Ω of the traveling wave modulation signal is greater than the linewidth γ of the ring resonator and less than the free spectral range FSR of the ring resonator, and A0 / Ω>(γ / Ω). 2 The modulation depth m of the traveling wave modulated signal φ To achieve J0(A0 / Ω) = 0, the transmittance T of the signal light at the drop end is realized. drop (Δω=0)=0; where A0 is the amplitude of the resonant frequency of the ring resonant cavity changing with time under dynamic modulation, J0 is the zero-order Bessel function, and A0 and m φ The relationship is linear, where Δω is the detuning of the resonant frequency of the ring resonant cavity.

[0038] According to the principle, the ω0signal light can be output at the through port and the drop port respectively by applying (loading the traveling wave modulation signal in the same direction as the signal light propagates) and turning off (not loading the traveling wave modulation signal or loading the traveling wave modulation signal in the opposite direction of the signal light propagation) the traveling wave modulation signal, so as to realize the optical switch. Further, when the traveling wave modulation signal in a certain direction is applied, considering two ports on the same waveguide, the signal light incident from one of the ports propagates in the same direction as the traveling wave modulation signal, at this time, the signal light can be transmitted from the other port; and conversely, the signal light incident from the other port propagates in the opposite direction of the traveling wave modulation signal, at this time, the signal light cannot be output from the through port corresponding to the other port, that is, the function of optical isolation between two signal lights incident from different ports in the same waveguide is realized.

[0039] For example, an optical circulator is designed and implemented according to the structure and principle as shown in Figure 2 Two straight waveguides and a ring resonant cavity are coupled to form a four-port add-drop structure, a traveling wave modulation signal is introduced into the ring to dynamically modulate the refractive index of the ring, the structural parameters such as the electrode length and the electrode spacing of the traveling wave modulator can be determined according to the required half-wave voltage and other parameters, and the modulation depth can be further improved by using a push-pull structure. For the convenience of analysis, the input port, the through port, the add port and the drop port in Figure 1 are marked as port 1, port 2, port 3 and port 4 respectively, and it is assumed that the direction of the traveling wave modulation signal is clockwise. As shown in Figure 2 (a) in , the signal light (the frequency is represented by ω0) satisfying the resonant frequency of the ring resonant cavity is incident from the port 1, and the working principle of the optical circulator can be analyzed according to the same process as shown in Figure 1 (b): when the single-frequency optical signal s=p0exp(iω0t) is input from the port 1, the signal will be coupled into the ring and propagate in the same direction as the traveling wave signal, and will be modulated by the traveling wave signal. When the modulation signal satisfies: (1) the modulation frequency Ω is greater than the line width γ, but less than the FSR, and satisfies A0 / Ω>(γ / Ω) 2 ; (2) the modulation depth is just enough to satisfy J0(A0 / Ω)=0, the transmittance T drop (Δω=0) of the light at the drop port is 0, that is, zero transmission, at this time, the signal light will be output from the port 2. As shown in Figure 2 (b) in , the single-frequency light satisfying the resonant frequency of the ring resonant cavity is incident from the port 2, and the analysis process is similar to that in Figure 1 (a): since the signal light propagates in the opposite direction of the traveling wave modulation in the ring, the signal light is equivalent to being input into a static add-drop type micro-ring, and the optical signal will be output from the port 3. As shown in Figure 2As shown in (c), when the signal light is incident from port 3, it travels in the same direction as the traveling wave in the ring resonant cavity, and the process is the same as described above. Figure 1 The process shown in (b) is similar, enabling the output of signal light from port 3 to port 4. For example... Figure 2 As shown in (d), when the signal light is incident from port 4, its propagation direction in the ring resonant cavity is opposite to that of the traveling wave, and the process is the same as described above. Figure 1 The process in (a) is similar, enabling the output of signal light from port 4 to port 1. Based on the principles described above, an optical circulator function can be implemented to transmit signals from 1 to 2, 2 to 3, 3 to 4, and 4 to 1.

[0040] Furthermore, based on the above principles, the specific structure and performance parameters of the optical circulator are analyzed and designed. Assume the power coupling strength between the two straight waveguides and the ring resonator is 0.15, the central ring length of the ring resonator is L = 0.6 cm, the effective refractive index is n = 2.5, the corresponding free spectral range is FSR = 2π × 20 GHz, and the propagation loss within the ring resonator is 30 dB / m. The simulation results of the optical circulator's performance without a traveling wave modulation signal are as follows: Figure 3 As shown, Figure 3 In diagram (a), the relationship between transmittance and detuning (Δω) is shown when the input signal light is output at both the through and drop ends of the structure. According to... Figure 3 The transmittance curve shown in (a) indicates that when the incident signal light satisfies the resonance condition Δω=0, most of the light (~78.4%, -1.05dB) will be output from the drop end, while only a small amount of light (~1.3%, -18.86dB) will be output through the through end, corresponding to an isolation of 17.8dB. Figure 3 Figure (b) shows the relationship between the drop end transmittance and the propagation loss of the ring resonator when other parameters remain unchanged. As the propagation loss increases, the drop end transmittance gradually decreases, while the through end transmittance gradually increases. That is, the device isolation decreases as the propagation loss increases. Therefore, the device performance can be improved by reducing the propagation loss. Figure 3 Figure (c) shows the relationship between the power coupling strength of the two waveguides and the ring resonator, with other parameters remaining constant. As the power coupling strength increases, the transmittance at the drop end continuously increases and eventually approaches 1, while the transmittance at the through end continuously decreases and approaches 0. Although increasing the power coupling strength can improve the isolation, it also correspondingly increases the linewidth of the resonant peak. The modulation frequency Ω needs to satisfy FSR>Ω>γ, that is, the modulation period is less than the photon lifetime. Therefore, choosing a propagation loss α=30dB / m and a power coupling strength α=0.15 is more appropriate.

[0041] Figure 4(a) in the figure shows A0(the amplitude of the resonant frequency of the ring resonator varying with time when the dynamic modulation is loaded, the change of the refractive index causes the change of the resonant frequency) and the modulation depth m between the linear relationship. φ Figure 4 (b) in the figure shows the transmittance of the drop end and the frequency detuning amount when A0 / Ω = 0 (no modulation, solid line) and A0 / Ω = 2.4 [J0(A0 / Ω) = 0] (with modulation, dotted line), where γ = 2π×1.16GHz, Ω = 2π×6GHz, A0 / Ω = 2.4>(γ / Ω) 2 = 0.0374, as shown by the shaded part, the dynamic traveling wave modulation realizes the zero transmission of the 0-order peak at the drop end, which is contrary to the high transmission behavior of the drop end without modulation, indicating that the effect of optical non-reciprocal transmission can be achieved by using traveling wave modulation. Figure 4 (c) in the figure shows the change relationship of the transmittance of the 0-order peak at the drop end with the modulation depth m φ , which shows that when m φ = 1.5438π, the transmittance of the drop end is the lowest, that is, the non-reciprocal transmission effect is the best.

[0042] Therefore, as a preferred embodiment, the traveling wave modulation signal and the structural parameters of the ring resonator are determined by simulation optimization aiming at maximizing the isolation of the optical circulator and minimizing the insertion loss of the optical circulator.

[0043] In this embodiment, a traveling wave modulation is introduced into an add-drop type ring resonator to obtain a four-port structure with the effect of an optical circulator. The ring resonator structure is theoretically applicable to all resonant wavelengths and can be used for wavelength division multiplexing, and the single-wavelength communication bandwidth is only limited by the operating wavelength of the traveling wave modulator. Moreover, the optical circulator realized by the structure has the advantages of low insertion loss and high isolation. Compared with the traditional optical circulator, the technical scheme of the present application is based on traveling wave modulation and does not rely on magneto-optical materials or high-order nonlinear optical effects. It can be constructed by using existing optical fiber systems and traveling wave modulators, and can also be prepared as an integrated device on a chip platform, effectively solving the problem of difficulty in integrating an optical circulator on a chip.

[0044] The simulation optimization can be implemented in the following way:

[0045] (1) Determine the structural parameters of the ring resonator, including the electrode length and electrode spacing of the traveling wave modulator, the spacing between the input / output waveguide and the ring resonator, the center ring length of the ring resonator, and the effective refractive index of the ring resonator.

[0046] ​Traveling wave modulators are added to both sides of the waveguide inside the ring resonant cavity, and a straight waveguide is added to each of the two coupling sections of the ring structure for optical signal coupling input and output. The power coupling coefficients of the two waveguides and the ring resonant cavity are consistent, forming a symmetrical add-drop type four-port micro-ring structure.

[0047] (2) Based on the structural parameters, the power coupling strength α between the input and output waveguides and the micro-ring resonator, and the modulation depth m of the traveling wave modulation signal are simulated and calculated. φ And the propagation loss within the ring resonant cavity; based on the power coupling strength α and the modulation depth m φ Based on the propagation loss within the ring resonator and structural parameters, the insertion loss and isolation of the optical circulator are simulated and calculated. The structural parameters are then optimized based on the insertion loss and isolation to achieve the optimal insertion loss and isolation.

[0048] To calculate the performance parameters of the optical circulator, simulation calculations were performed according to the steps outlined above. In the simulation, the circulator structure was configured according to the design steps described above, with a power coupling coefficient of 0.15, a central ring length L of 0.6 cm, a refractive index n = 2.5, and a ring FSR of approximately 20 GHz. First, a traveling wave modulation signal was loaded into the traveling wave modulator. Second, a single-frequency signal light was selected as input from port 1, with a power of 0 dBm and a resonant frequency ω0 = 193.0863 THz. The modulation depth m of the inner electrode was also specified. φ =1.5438π, the spectrum of the output light is detected at ports 2 and 3. For example... Figure 5 (a) and Figure 5 As shown in (b), at the 0th-order peak at the same frequency as the input optical signal, the output power of port 2 is approximately -0.7 dBm, and the output power of port 3 is approximately -62 dBm, indicating that the optical signal is mainly output from port 2, with an insertion loss of approximately -0.7 dB and an isolation of approximately 62 dB. Then, a single-frequency signal light is selected as the input from port 2, and the spectrum of the output light is detected at ports 1 and 4. Figure 5 (c) and Figure 5 As shown in (d), at the 0th-order peak at the same frequency as the input optical signal, the output power of port 4 is approximately -1.1 dBm, and the output power of port 1 is approximately -18.54 dBm. This indicates that the optical signal is mainly output from port 4, with an insertion loss of approximately -1.1 dB and an isolation of approximately 17.4 dB. Furthermore, selecting single-frequency light input from port 4 follows a similar process to inputting from port 1. The spectrum of the output light is probed at ports 3 and 2, as shown... Figure 5 (e) and Figure 5As shown in (f) of FIG. 6, the output power of the 0th order peak at port 3 is about -0.7 dBm, and the output power at port 2 is about -63 dBm, which indicates that the optical signal is mainly output from port 3, the insertion loss is about -0.7 dB, and the isolation is about 62 dB. Figure 5 As shown in (g) of FIG. 6 and Figure 5 As shown in (h) of FIG. 6, the output power of the 0th order peak at port 1 is about -1.1 dBm, and the output power at port 3 is about -18.54 dBm, which indicates that the optical signal is mainly output from port 1, the insertion loss is about -1.1 dB, and the isolation is about 17.4 dB. In summary, the optical non-reciprocal effect generated by the traveling wave modulator can realize an optical circulator, the insertion loss of which is about -1 dB, and the signal isolation is greater than 17 dB.

[0049] As a preferred embodiment, the ring resonator is composed of a fiber loop or a micro-ring and a waveguide integrated on a chip.

[0050] As a preferred embodiment, the modulation of the traveling wave modulator is implemented by electro-optic modulation, acousto-optic modulation or thermo-optic modulation. For example, if the electro-optic modulation is used, the light-transmitting material of the traveling wave modulator is an electro-optic material, such as lithium niobate, lithium tantalate or liquid crystal.

[0051] In summary, the present application aims at the problems of the conventional optical circulator which relies on magneto-optic material and high-order nonlinear optical effect in terms of on-chip integration and applicable power, and designs an optical circulator with simple structure, easy on-chip integration, low loss and high isolation, which has important application value for solving the optical circulator routing in optical communication, especially on-chip integration.

[0052] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An optical circulator, characterized by, The add-drop structure containing at least three ports comprises a ring resonator containing input and output waveguides, and a traveling wave modulator arranged in the ring resonator; The traveling wave modulator is used to dynamically modulate the refractive index of the ring resonator by transmitting a traveling wave modulation signal; if the propagation direction of the signal light transmitted in the ring resonator is the same as the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, the traveling wave modulation signal effectively modulates the refractive index of the ring resonator, and the signal light is output from the through port corresponding to the incident end; if the propagation direction of the signal light transmitted in the ring resonator is opposite to the propagation direction of the traveling wave modulation signal propagating in the traveling wave modulator, the wave vector of the signal light and the wave vector of the traveling wave modulation signal do not match, the modulation efficiency of the traveling wave modulation signal on the refractive index of the ring resonator is low, and the signal light is output from the download port corresponding to the incident end, thereby realizing the function of an optical circulator. The traveling wave modulation signal and the structural parameters of the ring resonator satisfy: the modulation frequency Ω of the traveling wave modulation signal is greater than the linewidth γ of the ring resonator and less than the free spectral range FSR of the ring resonator, and A0 / Ω > (γ / Ω) 2 ; the modulation depth m of the traveling wave modulation signal φ such that J0(A0 / Ω) = 0, achieving a signal light transmittance T drop (Δω = 0) = 0 at the drop port. wherein A0 is the amplitude of the variation of the resonance frequency of the ring resonator with time when dynamic modulation is applied, J0 is the zeroth order Bessel function, A0 and m φ are linearly related, and Δω is the detuning of the resonance frequency of the ring resonator.

2. The optical circulator of claim 1, wherein, The traveling wave modulator can apply a modulation electric field to the ring resonator when the traveling wave modulation signal is loaded, so as to dynamically modulate the refractive index of the ring resonator.

3. The optical circulator of claim 1, wherein, The traveling wave modulation signal and the structural parameters of the ring resonator are further determined by simulation optimization with the goal of maximizing the isolation of the optical circulator and minimizing the insertion loss of the optical circulator.

4. The optical circulator of claim 3, wherein, The implementation of the simulation optimization is: The structural parameters of the ring resonator are determined, including the electrode length and electrode spacing of the traveling wave modulator, the spacing between the input and output waveguides and the ring resonator, the center ring length of the ring resonator, and the effective refractive index of the ring resonator; Based on the structural parameters, the power coupling strength α between the input / output waveguides and the micro-ring resonator, and the modulation depth m of the traveling wave modulation signal are calculated through simulation. φ And propagation loss within the ring resonant cavity; According to the power coupling strength α, the modulation depth m φ And the ring resonator propagation loss and the structure parameters, the simulation calculation of the optical circulator insertion loss and isolation; The structural parameters are optimized according to the insertion loss and the isolation, so that the insertion loss and the isolation are optimal.

5. The optical circulator of claim 4, wherein, The power coupling strength α between the input and output waveguides and the microring resonator is 0.

15. The central ring length of the ring resonator is L = 0.6 cm, the effective refractive index is n = 2.5, and the modulation depth m of the traveling wave modulation signal is... φ The value is 1.5438π, and the propagation loss within the ring resonator is 30 dB / m.

6. The optical circulator of claim 1, wherein, The ring resonator is composed of a fiber loop or a micro-ring and a waveguide integrated on a chip.

7. The optical circulator of claim 1, wherein, The modulation of the traveling wave modulator is electro-optic modulation or acousto-optic modulation.

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