Integrated optical isolator based on dual-arm phase modulator and optical isolation method

Abstract

The present disclosure provides an integrated optical isolator based on a dual-arm phase modulator and an optical isolation method, which can be applied to the technical field of optical isolators. The integrated optical isolator comprises: a micro-ring resonator for screening input optical signals to retain optical signals of a specific frequency domain; a dual-arm phase modulator for phase modulation of optical signals output by the micro-ring resonator or reflected optical signals; an optical delay waveguide for introducing a delay in the transmission process of the optical signals; and a cross waveguide for realizing cross transmission of the optical signals. The integrated optical isolator provided by the present disclosure can effectively reduce the half-wave voltage under the same chip length, significantly reduce the device power consumption, and is simple to operate and stable in performance.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of optical isolators, and particularly relates to an integrated optical isolator based on a dual-arm phase modulator and an optical isolating method. BACKGROUND

[0002] An optical isolator is a key component widely used in optical systems such as lasers and amplifiers, which is used to block reflected light from entering the resonant cavity and suppress signal noise. With the continuous development of integrated microwave photonics technology, the on-chip integration of optical isolators has become a key technology to realize efficient and complex functional photonic integrated circuits (PICs). There are currently three methods to achieve on-chip integration of optical isolators, including magnetic bias, optical nonlinearity and space-time modulation. However, the method based on magnetic bias usually faces challenges in material integration and has high optical loss. The method based on nonlinear optics either requires an additional pump laser and filter or relies on the input optical power of the light source. In contrast, the method based on electro-optic modulation does not require the integration of heterogeneous materials and is not affected by the optical power, which is an attractive choice for realizing on-chip isolators.

[0003] The method based on electro-optic modulation breaks the optical reciprocity by utilizing the different modulation effects of forward and backward light passing through the phase modulator to obtain the isolation degree. In order to achieve complete suppression of reflected light, the phase modulator needs to reach a certain modulation depth, so the half-wave voltage of the phase modulator needs to be low enough to reduce the additional power consumption in this process. In order to reduce the half-wave voltage of the phase modulator, it is usually necessary to increase the length of the modulation region electrode or to accumulate the phase change through the cascade of two phase modulators, but both of the above ways will sacrifice the footprint of the device, which is not conducive to large-scale integration. SUMMARY

[0004] (I) Technical problems to be solved

[0005] The present disclosure provides an integrated optical isolator based on a dual-arm phase modulator and an optical isolating method, which is used to at least partially solve one of the above technical problems.

[0006] (II) Technical solutions

[0007] According to a first aspect of the present disclosure, an integrated optical isolator based on a dual-arm phase modulator is provided, comprising: a micro-ring resonator for filtering an input optical signal to retain an optical signal in a specific frequency domain; a dual-arm phase modulator for phase modulating an optical signal or a reflected optical signal output by the micro-ring resonator; an optical delay waveguide for connecting the optical waveguides in the dual-arm phase modulator; and a cross waveguide for realizing cross transmission of the optical signal.

[0008] According to an embodiment of the present disclosure, the micro-ring resonator comprises: a first straight waveguide for inputting a received optical signal into a ring waveguide through a first coupling region; the ring waveguide is used for constituting a resonant cavity of the micro-ring resonator and performing frequency domain filtering on the input optical signal; a second straight waveguide is used for outputting the resonated optical signal into a dual-arm phase modulator through a second coupling region; a metal hot electrode is arranged above the ring waveguide and used for regulating the resonant wavelength of the micro-ring resonator; and a semi-circular waveguide is used for avoiding end face reflection.

[0009] According to an embodiment of the present disclosure, the dual-arm phase modulator comprises: an optical waveguide group for transmitting an optical signal; and a traveling wave electrode group for modulating the optical signal transmitted in the optical waveguide group.

[0010] According to an embodiment of the present disclosure, the traveling wave electrode group comprises: a signal electrode for transmitting a radio frequency signal; and a ground electrode group for terminating the electric field lines emitted from the signal electrode.

[0011] According to an embodiment of the present disclosure, the optical waveguide group comprises a first optical waveguide and a second optical waveguide, and the ground electrode group comprises a first ground electrode and a second ground electrode, the first optical waveguide is located between the signal electrode and the first ground electrode, and the second optical waveguide is located between the signal electrode and the second ground electrode.

[0012] According to an embodiment of the present disclosure, the optical delay waveguide comprises: a curved optical waveguide for transmitting an optical signal, and the two ends of the curved optical waveguide are connected with the first optical waveguide and the second optical waveguide respectively.

[0013] According to an embodiment of the present disclosure, the cross waveguide comprises: a multi-mode interference coupler for avoiding transverse divergence of the optical field at the intersection point through the self-mapping principle; and a wedge waveguide for connecting the waveguide and the multi-mode interference coupler.

[0014] According to a second aspect of the present disclosure, an optical isolation method based on the above integrated optical isolator is provided, comprising: inputting an optical signal based on the first straight waveguide and inputting a radio frequency signal based on the signal electrode; adjusting the parameters of the dual-arm phase modulator and the frequency of the radio frequency signal in the case of reverse transmission of the optical signal and the radio frequency signal, so that the optical signal is completely transmitted; in the case of co-directional transmission of the optical signal and the radio frequency signal, the energy of the optical signal is converted to the sideband through phase modulation and frequency conversion, and the sideband is filtered through the micro-ring resonator.

[0015] According to an embodiment of the present disclosure, in the case of reverse transmission of the optical signal and the radio frequency signal, the phase accumulation of the optical signal after passing through the dual-arm phase modulator is a periodic function of the propagation distance in the dual-arm phase modulator, and when the frequency of the radio frequency signal satisfies a specific value, the phase accumulation is 0, and the complete transmission of the optical signal in the transmission direction is realized.

[0016] According to the embodiment of the present disclosure, in the case of co-directional transmission of the optical signal and the radio frequency signal, the phase accumulation of the optical signal after the double-arm phase modulator is a linear function of the propagation distance in the double-arm phase modulator, and when the power of the radio frequency signal satisfies a certain value, the modulation depth reaches 0.765π, and the reflected optical signal is completely suppressed at the center frequency.

[0017] (Three) beneficial effects

[0018] The integrated optical isolator and the optical isolation method based on the double-arm phase modulator provided by the present disclosure at least have the following beneficial effects:

[0019] The half-wave voltage of the phase modulator is reduced by one half while ensuring that the length of the chip remains unchanged, significantly reducing the additional power consumption of the integrated optical isolator, and the operation is simple and the performance is stable. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure taken with reference to the accompanying drawings, in which:

[0021] Figure 1 The structure diagram of the integrated optical isolator based on the double-arm phase modulator provided by the embodiment of the present disclosure is schematically shown;

[0022] Figure 2 The structure diagram of the micro-ring resonator provided by the embodiment of the present disclosure is schematically shown;

[0023] Figure 3 The structure diagram of the cross waveguide provided by the embodiment of the present disclosure is schematically shown;

[0024] Figure 4 The numerical simulation diagram of the optical isolation method provided by the embodiment of the present disclosure is schematically shown, in which the Bessel function (up to the fourth order) is used as the modulation index.

[0025]

REFERENCE NUMERALS

[0026] 110-micro-ring resonator; 1101-first straight waveguide; 1102-ring waveguide; 1103-second straight waveguide; 1104-metal hot electrode; 1105-semi-circular waveguide; 120-double-arm modulator; 1201a-first optical waveguide; 1201b-second optical waveguide; 1202-signal electrode; 1203a-first ground electrode; 1203b-second ground electrode; 130-optical delay waveguide; 140-cross waveguide; 1401-multimode interference coupler; 1402-wedge waveguide; 001-first coupling region; 002-second coupling region. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application with reference to the specific embodiments and accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0028] The terms used herein are only used to describe specific embodiments, and are not intended to limit the present application. The terms "comprise", "include", and the like used herein indicate the presence of the stated features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0029] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection or can communicate with each other; can be direct connection, or indirect connection through intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0030] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "length", "circumferential", "front", "back", "left", "right", "top", "bottom", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the subsystems or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0031] Throughout the drawings, the same elements are denoted by the same or similar reference numerals. When it may cause confusion in understanding the present application, the conventional structure or configuration will be omitted. And the shape, size, positional relationship of each component in the drawing does not reflect the true size, proportion and actual positional relationship. In addition, in the claims, any reference symbol located between parentheses should not be construed as a limitation on the claims.

[0032] Similarly, to the extent that the foregoing description contains specificities, those specifics have been presented for the purposes of illustration and description. They are not intended to be exhaustive or to be unduly restrictive of the teachings of the present application. Obviously, many modifications and variations are possible in view of the above teachings. Thus, it is contemplated to cover the modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

[0033] In addition, the terms "first", "second", etc. are used herein only to describe various elements, and do not connote an ordering, unless otherwise indicated by the context. Thus, these terms are used interchangeably to distinguish between different elements, and do not connote any ordering or sequence. Furthermore, the terms "comprise", "include", "have", and any variations thereof are used synonymously to denote the inclusion of a stated element or step, but not to the exclusion of any additional element or step.

[0034] Figure 1 A structural diagram of an integrated optical isolator based on a dual-arm phase modulator is illustratively shown.

[0035] As shown in Figure 1 The integrated optical isolator based on a dual-arm phase modulator includes a micro-ring resonator 110, a dual-arm modulator 120, an optical delay waveguide 130, and a cross waveguide 140.

[0036] The micro-ring resonator 110 is configured to filter an input optical signal to retain an optical signal in a specific frequency domain. The micro-ring resonator 110 can act as a filter to suppress the sidebands of the reflected light.

[0037] Figure 2 A structural diagram of a micro-ring resonator is illustratively shown.

[0038] As shown in Figure 2 In some embodiments, the micro-ring resonator includes a first straight waveguide 1101, a ring waveguide 1102, a second straight waveguide 1103, a metal hot electrode 1104, and a semi-circular waveguide 1105.

[0039] The first straight waveguide 1101 is configured to input a received optical signal into the ring waveguide 1102 through a first coupling region 001.

[0040] The ring waveguide 1102 is used to form a resonant cavity of a micro-ring resonator, and to perform frequency domain filtering on an input optical signal. When the optical signal is input to the ring waveguide, only the light waves of a certain wavelength that meet certain conditions can form effective propagation and interference in the ring waveguide, and then form a stable standing wave mode in the ring waveguide, to produce a resonance phenomenon and achieve frequency domain filtering.

[0041] The second straight waveguide 1103 is used to output the optical signal after the resonant processing to the dual-arm phase modulator through the second coupling area 002.

[0042] The metal hot electrode 1104 is arranged above the ring waveguide, and is used to regulate the resonant wavelength of the micro-ring resonator. When the metal hot electrode is powered and heated, heat is transferred to the ring waveguide, causing a change in the refractive index of the ring waveguide, thereby regulating the resonant wavelength of the micro-ring resonator. The semi-circular waveguide 1105 is used to avoid end reflection.

[0043] The dual-arm phase modulator 120 is used to perform phase modulation on the optical signal output by the micro-ring resonator and / or the reflected optical signal. The reflected optical signal is an optical signal formed by reflection of the optical signal output by the integrated optical isolator through other devices. By performing phase modulation on the optical signal and / or the reflected optical signal through the dual-arm phase modulator, the transmission of the reflected light can be effectively suppressed while ensuring the transmission of the forward light.

[0044] In some embodiments, the dual-arm phase modulator includes an optical waveguide group and a traveling wave electrode group. The optical waveguide group includes a first optical waveguide 1201a and a second optical waveguide 1201b, and is used to transmit an optical signal. The traveling wave electrode group includes a signal electrode 1202 and a ground electrode group, and is used to modulate the optical signal transmitted in the optical waveguide group. The signal electrode 1202 is used to transmit a radio frequency signal, and the ground electrode group is used to terminate the electric field lines emitted from the signal electrode. The ground electrode group includes a first ground electrode 1203a and a second ground electrode 1203b, the first optical waveguide 1201a is located between the signal electrode 1202 and the first ground electrode 1203a, and the second optical waveguide 1201b is located between the signal electrode 1202 and the second ground electrode 1203b.

[0045] The optical delay waveguide 130 is used to connect the optical waveguides in the dual-arm phase modulator.

[0046] In some embodiments, the optical delay waveguide includes a curved optical waveguide, the curved optical waveguide is used to transmit an optical signal, one end of the curved optical waveguide is connected to the first optical waveguide 1201a, and the other end of the curved optical waveguide is connected to the second optical waveguide 1201b. The waveguide used in the integrated optical isolator provided in the embodiments of the present disclosure is a ridge waveguide.

[0047] The cross waveguide 140 is used to realize cross transmission of the optical signal, so as to ensure cross transmission of the optical signal with minimum interference and loss.

[0048] Figure 3 A structural diagram of a cross waveguide is shown schematically.

[0049] As shown in Figure 3 some embodiments, the cross waveguide includes a multimode interference coupler 1401 and a tapered waveguide 1402. The multimode interference coupler 1401 is used to avoid the transverse divergence of the light field at the intersection point by the principle of self-mapping. The tapered waveguide 1402 is used to connect the waveguide and the multimode interference coupler.

[0050] Based on the above-mentioned integrated optical isolator based on a two-arm phase modulator, the present disclosure further provides an optical isolation method.

[0051] The optical isolation method includes: based on a first straight waveguide input optical signal, inputting a radio frequency signal based on a signal electrode; in the case of reverse transmission of the optical signal and the radio frequency signal, adjusting the parameters of the two-arm phase modulator and the frequency of the radio frequency signal to make the optical signal completely transmit; in the case of co-directional transmission of the optical signal and the radio frequency signal, converting the energy of the optical signal to the sideband by phase modulation and frequency conversion and filtering the sideband by a micro-ring resonator.

[0052] The method will be described in detail below in combination with Figure 1 the integrated optical isolator based on a two-arm phase modulator shown in

[0053] As shown in Figure 1 , the light source inputs an optical signal with a wavelength of from the first straight waveguide, and the optical signal is transmitted to the ring waveguide through the first coupling area 001. When the wavelength of the optical signal overlaps with the resonant wavelength of the micro-ring resonator, the optical signal with the wavelength can form a stable standing wave mode in the ring waveguide, and a resonance phenomenon is generated. The expression of the resonant wavelength is:

[0054]

[0055] wherein, is the resonant wavelength, L r is the circumference of the ring waveguide, n eff is the effective refractive index of the ring waveguide, and m is an integer.

[0056] By changing the voltage applied to the metal hot electrode, the effective refractive index of the ring waveguide can be changed, so as to regulate the resonant wavelength of the micro-ring resonator. When the wavelength of the optical signal overlaps with the resonant wavelength of the micro-ring resonator , the optical signal can be output to the first optical waveguide of the two-arm phase modulator through the second coupling area.

[0057] When the optical signal is input from left to right into the first optical waveguide, the radio frequency signal is input into the signal electrode and is transmitted from right to left through the signal electrode, forming electric fields in opposite directions on the cross sections of the first optical waveguide and the second optical waveguide. The frequency of the radio frequency signal is f s , and the peak voltage is A. At this time, the optical signal and the radio frequency signal are transmitted in opposite directions.

[0058] Since the input optical signal and the electric signal (i.e., the radio frequency signal) are transmitted in opposite directions, the total phase accumulation of the optical signal after being transmitted through the first optical waveguide can be expressed as:

[0059]

[0060] wherein R f π is a modulation index when the optical signal and the electric signal are transmitted in opposite directions, L is an electrode length of the dual-arm phase modulator, α is a microwave power attenuation coefficient, n opt is an optical group refractive index, n RF is a microwave refractive index. According to the expression of the total phase accumulation, when the optical signal and the electric signal are transmitted in opposite directions, the phase accumulation is a periodic function of the propagation distance in the dual-arm phase modulator. Assuming that the microwave power attenuation coefficient is 0, when the frequency f s of the radio frequency signal satisfies , the phase accumulation is 0. Then, the optical signal enters the second optical waveguide through the optical delay waveguide, wherein the modulation process of the optical signal in the second optical waveguide is completely the same as that in the first optical waveguide, and thus the phase accumulation of the optical signal in the second optical waveguide is still 0 (i.e., the optical signal is not modulated), realizing complete transmission of the optical signal in the current transmission direction and outputting the optical signal after the cross waveguide.

[0061] When the optical signal is output, a reflected optical signal is formed by reflection through other devices. The reflected optical signal is reflected back into the dual-arm phase modulator through the cross waveguide, at this time, the transmission directions of the reflected optical signal and the radio frequency signal are the same, i.e., the optical signal and the radio frequency signal are transmitted in the same direction.

[0062] The output optical field of the reflected light after passing through the second optical waveguide, the optical delay waveguide and the first optical waveguide can be expressed as:

[0063]

[0064] wherein E0 is an amplitude of an optical carrier, ω0 is an angular frequency of the optical carrier, is a time delay between the first optical waveguide and the second optical waveguide, wherein is a length of the optical waveguide between the input ends of the first ground electrode and the second ground electrode, and the length is equal to the sum of the length of the optical delay waveguide and the length of the signal electrode, Where A is the peak voltage of the microwave signal. f is the half-wave voltage during forward modulation of a single-arm phase modulator. s The frequency of the radio frequency signal.

[0065] At that time, the delay ΔT satisfies In this embodiment, the modulation index of the output optical signal of the dual-arm phase modulator is twice that of the single-arm modulation, i.e., β = 2πR. b Where k is an integer.

[0066] In summary, when the amplitude A of the radio frequency signal satisfies Frequency f s satisfy Where m is an integer; the length L of the time-delay waveguide s satisfy Where k is an integer, the integrated optical isolator provided in this embodiment achieves the optical isolation effect with the maximum isolation degree under the minimum power consumption.

[0067] Figure 4 The illustration shows a numerical simulation diagram of the optical isolation method provided according to an embodiment of the present disclosure using a Bessel function (up to the fourth order) as the modulation index.

[0068] like Figure 4 As shown in the figure, the dots represent the operating points of the integrated optical isolator provided in this embodiment. According to the Bessel function expansion, when the modulation index β is approximately 0.765π, that is, A is approximately 0.3825. At that time, f c The reflected light at that point can be completely depleted, and the power can be allocated to a frequency of f. c +nf s At the edge of the band, n is an integer.

[0069] Subsequently, the modulated reflected light enters the second straight waveguide. Since the wavelength corresponding to the sideband is the same as the resonant wavelength λ of the micro-ring resonator... m Since there is no overlap, only a small amount of reflected light at f0 after suppression is coupled into the first waveguide before entering the light source.

[0070] Therefore, a high degree of isolation can be achieved using the integrated optical isolator and optical isolation method based on a dual-arm phase modulator proposed in this disclosure. In summary, the integrated optical isolator and optical isolation method based on a dual-arm phase modulator provided in this disclosure reduces the half-wave voltage of the phase modulator by half while maintaining the same chip length, significantly reducing the additional power consumption of the integrated optical isolator, and is simple to operate and has stable performance.

[0071] The embodiments of the application have been described. However, these embodiments are merely for illustration and are not intended to limit the scope of the application. Although each embodiment is described above separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Various alternatives and modifications to the embodiments described herein will be apparent to those skilled in the art in view of the foregoing without departing from the scope of the application.

Claims

1. An integrated optical isolator based on a two-arm phase modulator, characterized in that, The integrated optical isolator comprises: a micro-ring resonator for screening input optical signals to retain optical signals of a specific frequency domain; a dual-arm phase modulator for phase modulating forward optical signals output by the micro-ring resonator or reflected optical signals input from the other side of the modulator; the dual-arm phase modulator comprises an optical waveguide group and a traveling wave electrode group, the optical waveguide group is used for transmitting optical signals and comprises a first optical waveguide and a second optical waveguide; the traveling wave electrode group is used for modulating optical signals transmitted in the optical waveguide group, the traveling wave electrode group comprises a signal electrode for transmitting radio frequency signals and a ground electrode group for terminating electric field lines emitted from the signal electrode, the ground electrode group comprises a first ground electrode and a second ground electrode; the first optical waveguide is located between the signal electrode and the first ground electrode, and the second optical waveguide is located between the signal electrode and the second ground electrode; an optical delay waveguide for connecting the first optical waveguide and the second optical waveguide to make the transmission directions of the forward optical signals or the reflected optical signals in the first optical waveguide and the second optical waveguide the same; a cross waveguide having four ports connected with the first optical waveguide, the second optical waveguide, the optical delay waveguide and an output waveguide respectively, and used for realizing cross transmission of optical signals at the first optical waveguide, the second optical waveguide, the optical delay waveguide and the output waveguide.

2. The integrated optical isolator of claim 1, wherein, The micro-ring resonator comprises: a first straight waveguide for inputting received optical signals into a ring waveguide through a first coupling area; a ring waveguide for constituting a resonant cavity of the micro-ring resonator and performing frequency domain filtering on input optical signals; a second straight waveguide for outputting optical signals processed by resonance to the dual-arm phase modulator through a second coupling area; a metal hot electrode arranged above the ring waveguide and used for regulating a resonant wavelength of the micro-ring resonator; a semicircular waveguide arranged at the end of the straight waveguide and used for avoiding end face reflection.

3. The integrated optical isolator of claim 1, wherein, The optical delay waveguide comprises: a curved optical waveguide for transmitting optical signals, two ends of the curved optical waveguide being connected with the first optical waveguide and the second optical waveguide respectively.

4. The integrated optical isolator of claim 1, wherein, The cross waveguide comprises: a multimode interference coupler used for avoiding transverse divergence of an optical field at a cross point through a self-mirroring principle; a wedge-shaped waveguide used for connecting the waveguide and the multimode interference coupler.

5. An optical isolation method based on the integrated optical isolator according to any one of claims 1 to 4, characterized by, The optical isolation method comprises: inputting optical signals based on the first straight waveguide and inputting radio frequency signals based on the signal electrode; adjusting parameters of the dual-arm phase modulator and a frequency of the radio frequency signals in the case of reverse transmission of the optical signals and the radio frequency signals to make the optical signals completely transmitted; in the case of same direction transmission of the optical signals and the radio frequency signals, converting energy of the optical signals to a sideband through phase modulation and frequency conversion and filtering the sideband through the micro-ring resonator.

6. The optical isolation method of claim 5, wherein, In the case of reverse transmission of the optical signals and the radio frequency signals, phase accumulation of the optical signals after passing through the dual-arm phase modulator is a periodic function of a propagation distance in the dual-arm phase modulator, and when the frequency of the radio frequency signals satisfies a specific value, the phase accumulation is 0, and complete transmission of the optical signals in the transmission direction is realized.

7. The optical isolation method of claim 5, wherein, The phase accumulation of the optical signal after passing through the dual-arm phase modulator is a linear function of the propagation distance in the dual-arm phase modulator in the case of co-transmission of the optical signal and the radio frequency signal, and when the power of the radio frequency signal satisfies a specific value, the modulation depth reaches 0.765π, and the reflected optical signal is completely suppressed at the center frequency.

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