Modulation device with adjustable splitting ratio

Abstract

The invention discloses a modulation device with an adjustable splitting ratio. The modulation device comprises a polarization controller, two Mach-Zehnder interferometers, a polarization rotation beam combiner and an end face coupler, wherein the two output ends of the polarization controller are respectively connected with the input ends of the two Mach-Zehnder interferometers; one output end of each Mach-Zehnder interferometer is connected with the input end of the polarization rotation beam combiner; the output end of the polarization rotation beam combiner is connected with the input end of the end face coupler. The embodiment of the invention can realize any splitting ratio adjustment in a large range, and can be widely applied to the technical field of optical devices.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to an adjustable splitting ratio modulation device. Background Art

[0002] In optical communication systems, optical splitters are important devices used to split a single optical signal into multiple optical path optical signals. In polarization control systems, optical splitters that can achieve arbitrarily adjustable splitting ratios are essential for flexible optical path management. Currently, optical splitters tend to have fixed splitting ratios, making it difficult to achieve arbitrary splitting ratio adjustment over a wide range. Summary of the invention

[0003] In view of this, in order to solve one of the above problems, an object of an embodiment of the present invention is to provide an adjustable splitting ratio modulation device, which can achieve arbitrary splitting ratio adjustment in a wide range.

[0004] The embodiment of the present invention provides an adjustable splitting ratio modulation device, including a polarization controller, two Mach-Zehnder interferometers, a polarization rotation combiner and an end coupler; wherein:

[0005] The two output ends of the polarization controller are respectively connected to the input ends of the two Mach-Zehnder interferometers;

[0006] One of the output ends of each of the Mach-Zehnder interferometers is connected to the input end of the polarization rotation beam combiner;

[0007] The output end of the polarization rotation beam combiner is connected to the input end of the end face coupler.

[0008] Optionally, the polarization controller comprises a thermo-optical dynamic polarization controller or an electro-optical dynamic polarization controller.

[0009] Optionally, the Mach-Zehnder interferometer includes a beam splitter, a 2×2 multimode interference coupler, two optical waveguide phase shift arms and modulation devices on both sides of the phase shift arms.

[0010] Optionally, the beam splitter includes any one of a 1×2 multimode interference coupler, a directional coupler or a Y-type beam splitter.

[0011] Optionally, the modulation device includes a traveling wave electrode or a heating resistor.

[0012] Optionally, the heating resistor includes a symmetrical on-chip resistor, and the structure of the on-chip resistor includes a serpentine structure or a linear structure.

[0013] Optionally, the adjustment mode of the traveling wave electrode includes single-arm modulation or double-arm push-pull modulation.

[0014] Optionally, the adjustable splitting ratio modulation device further includes two photodetectors, and one of the output ends of each Mach-Zehnder interferometer is connected to one of the photodetectors.

[0015] Optionally, the adjustable splitting ratio modulation device includes a substrate layer, a buried oxide layer, a thin film layer, an upper cladding layer and a metal layer.

[0016] Optionally, the material of the thin film layer includes any one or more of silicon on insulator, silicon nitride, lithium niobate, lithium tantalate, indium phosphide, gallium arsenide, aluminum nitride or silicon carbide.

[0017] The implementation of the embodiment of the present invention includes the following beneficial effects: in this embodiment, the adjustable splitting ratio modulation device includes a polarization controller, two Mach-Zehnder interferometers, a polarization rotation combiner and an end coupler. The two polarization states of light waves output by the polarization controller are input to the Mach-Zehnder interferometer. By changing the phase difference of the transmitted light waves in the phase shift arm of the Mach-Zehnder interferometer, the interference intensity of the output light signal is controlled, so that the splitting ratio of the output light path can be dynamically adjusted in the range of 0% to 100%, thereby achieving precise control of the output signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a structural block diagram of an adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0019] Figure 2 is a structural block diagram of another adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0020] Figure 3 is a structural block diagram of another adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0021] Figure 4 is a cross-sectional view of an adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0022] Figure 5 is a connection diagram of a polarization rotation beam splitter and a polarization controller provided by an embodiment of the present invention;

[0023] Figure 6 is a three-dimensional view of an adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0024] Figure 7 is a top view of an adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0025] Figure 8 is a three-dimensional view of another adjustable splitting ratio modulation device provided by an embodiment of the present invention;

[0026] Fig. 9It is a top view of another adjustable splitting ratio modulation device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0028] See also Figure 1 The embodiment of the present invention provides an adjustable splitting ratio modulation device, including a polarization controller, two Mach-Zehnder interferometers, a polarization rotation combiner and an end coupler; wherein,

[0029] Two output ends of the polarization controller are respectively connected to input ends of two Mach-Zehnder interferometers;

[0030] One of the output ends of each Mach-Zehnder interferometer is connected to the input end of the polarization rotation beam combiner;

[0031] The output end of the polarization rotation beam combiner is connected to the input end of the end face coupler.

[0032] It should be noted that two Mach-Zehnder interferometers are used in parallel, and the end face coupler is a polarization-independent end face coupler.

[0033] The two output ends of the polarization controller output light waves in two polarization states, which enter two Mach-Zehnder interferometers for phase modulation respectively. The modulated light waves are output after passing through the polarization rotation combiner and the end coupler in sequence.

[0034] Optionally, the adjustable splitting ratio modulation device further includes two photodetectors, and one output end of each Mach-Zehnder interferometer is respectively connected to a photodetector.

[0035] See also Figure 2 In a specific embodiment, the end coupler 1 is used as the input end. After any polarized light passes through the end coupler 1, the polarization rotation beam splitter and the polarization controller, the X and Y polarization state component light waves of the transverse electric mode TE mode are output respectively, corresponding to the optical path 1 and the optical path 2; the optical path 1 passes through one of the Mach-Zehnder interferometers (MZM1) to separate the optical path 3 and the optical path 4; similarly, the light wave in the optical path 2 is separated into the optical path 5 and the optical path 6 by another Mach-Zehnder interferometer (MZM2); the optical path 4 and the optical path 5 are connected to the polarization rotation beam combiner and then output from the end coupler 2; the optical path 3 and the optical path 6 are respectively used as the polarization control feedback optical path 1 and the feedback optical path 2, and are respectively connected to two photodetectors to convert the optical signal into an electrical signal for monitoring.

[0036] Optionally, the polarization controller comprises a thermo-optical dynamic polarization controller or an electro-optical dynamic polarization controller.

[0037] It should be noted that the thermo-optical dynamic polarization controller or the electro-optical dynamic polarization controller can be cascaded in multiple stages (N≥2).

[0038] By using the thermo-optical effect, Joule heat is generated by applying voltage or current to the heating resistor integrated on the chip, thereby heating the optical waveguide. By adjusting the voltage or current, different heat can be generated, causing the refractive index of the optical waveguide to change, causing the phase of the light wave transmitted in the phase shift arm of the Mach-Zehnder modulator to change, thereby adjusting the output light intensity, so that the splitting ratio of the output optical path can be dynamically adjusted within the range of 0% to 100%, thereby achieving precise control of the output signal.

[0039] By utilizing the electro-optic effect, a voltage is applied to the traveling wave electrode integrated on the chip to generate an electric field. By adjusting the voltage, the refractive index of the optical waveguide can be changed, resulting in a change in the phase of the optical signal transmitted in the phase shift arm of the Mach-Zehnder modulator, thereby adjusting the output light intensity. The splitting ratio of the output optical path can be dynamically adjusted in the range of 0% to 100%, thereby achieving precise control of the output signal.

[0040] Optionally, the Mach-Zehnder interferometer includes a beam splitter, a 2×2 multimode interference coupler, two optical waveguide phase shift arms and modulation devices on both sides of the phase shift arms.

[0041] It should be noted that the Mach-Zehnder interferometer is based on a symmetrical Mach-Zehnder interferometer structure. The function of the beam splitter is to split the input light wave into two light waves. The waveguide area between the beam splitter and the 2×2 multimode interference coupler is a modulated area, which is modulated by the electro-optical effect or thermo-optical effect of the thin film material. The refractive index of the optical waveguide is changed by the traveling wave electrode or the heating resistor to achieve the control of the optical path phase, thereby achieving any splitting ratio.

[0042] See also Figure 3 The Mach-Zehnder interferometer is arranged on the thin film layer (1), and comprises a beam splitter (2), a 2×2 multi-mode interference coupler (4), and modulation devices (3) on both sides of the phase shift arm.

[0043] Optionally, the beam splitter includes any one of a 1×2 multimode interference coupler, a directional coupler or a Y-type beam splitter.

[0044] The splitting ratio of the beam splitter is determined according to the actual application, and this embodiment does not impose any specific restrictions. In a specific embodiment, the beam splitter performs 3dB beam splitting on the incident light wave, that is, the light wave is split in half. The beam splitter includes but is not limited to a 1×2 multimode interference coupler, a directional coupler, or a Y-type beam splitter.

[0045] Optionally, the modulation device comprises a traveling wave electrode or a heating resistor.

[0046] By adjusting the voltage applied to the traveling wave electrode, the refractive index of the optical waveguide changes, which causes the phase of the optical signal transmitted in the phase shift arm of the Mach-Zehnder modulator to change, thereby adjusting the output light intensity, so that the splitting ratio of the output optical path can be dynamically adjusted within the range of 0% to 100%. By adjusting the voltage or current applied to the heating resistor, different heat is generated, the refractive index of the optical waveguide changes, causing the phase of the light wave transmitted in the phase shift arm of the Mach-Zehnder modulator to change, thereby adjusting the output light intensity, so that the splitting ratio of the output optical path can be dynamically adjusted within the range of 0% to 100%.

[0047] Optionally, the heating resistor includes a symmetrical on-chip resistor, and the structure of the on-chip resistor includes a serpentine structure or a straight line structure.

[0048] It should be noted that the specific structures of the heating resistor and the on-chip resistor are determined according to actual applications and are not specifically limited in this embodiment.

[0049] Optionally, the adjustment method of the traveling wave electrode includes single-arm modulation or double-arm push-pull modulation.

[0050] In addition to single-arm modulation, the traveling wave electrodes at both ends of the phase shift arm can also realize double-arm push-pull modulation through a shared electrode structure, which can not only reduce the number of independent electrodes, but also realize synchronous adjustment of the modulator. The push-pull structure design can not only simplify the control circuit, but also reduce the modulation delay and power consumption, further simplifying the complexity of the electronic control system.

[0051] Optionally, the adjustable splitting ratio modulation device includes a substrate layer, a buried oxide layer, a thin film layer, an upper cladding layer and a metal layer.

[0052] It should be noted that the specific materials of the substrate layer, the buried oxide layer, the thin film layer, the upper cladding layer and the metal layer are determined according to the actual application, and this embodiment does not impose any specific limitation.

[0053] See also Figure 4 In a specific embodiment, the material of the substrate layer is silicon, the material of the buried oxide layer is silicon dioxide, the material of the thin film layer is lithium niobate, and the material of the upper cladding layer is silicon dioxide. Various optical devices are formed on the thin film layer by etching and other techniques, including a polarization controller, two symmetrical Mach-Zehnder interferometers, a polarization rotation combiner and an end coupler. The beam splitter, 2×2 multimode interference coupler, and optical waveguide phase shift arm of the Mach-Zehnder interferometer are all arranged in the thin film layer. In addition, a traveling wave electrode or a heating resistor is deposited on the surface of the silicon dioxide upper cladding layer to form a Mach-Zehnder modulator structure; two photodetectors are flip-chip soldered on the surface of the silicon dioxide upper cladding layer.

[0054] Optionally, the material of the thin film layer includes any one or more of silicon on insulator, silicon nitride, lithium niobate, lithium tantalate, indium phosphide, gallium arsenide, aluminum nitride or silicon carbide.

[0055] It should be noted that the material of the thin film layer is determined according to the actual application and is not specifically limited in this embodiment, including silicon on insulator, silicon nitride, lithium niobate, lithium tantalate, indium phosphide, gallium arsenide, aluminum nitride or silicon carbide.

[0056] The present application is described below with reference to several specific embodiments.

[0057] Embodiment 1: A parallel dual-path Mach-Zehnder modulator based on thermo-optical effect.

[0058] See also Figure 5-7 In this embodiment, x-cut lithium niobate on insulator (LNOI) is used, and a heating resistor is arranged in the modulation area, and the refractive index of the lithium niobate optical waveguide is changed by using the thermo-optical effect of lithium niobate. The resistance of the heating resistor is generally large, up to thousands of ohms. By applying voltage or current, the resistor can be heated, thereby heating the lithium niobate optical waveguide and changing its refractive index. The amount of applied voltage or current can be adjusted to adjust the heat.

[0059] According to the principle of wave optics, the light wave (U 0 ) can be described in the following plural form:

[0060]

[0061] A represents the amplitude of the light wave, is the initial phase of the light wave, and ω is the angular frequency of the light wave. The relationship between ω and frequency f can be expressed as ω=2πf. The relationship between phase and refractive index is:

[0062]

[0063] Where L is the transmission distance, n is the refractive index of the material, and λ is the wavelength of the light wave. Combined with the refractive index change of lithium niobate material, the phase can be expressed as:

[0064]

[0065] Where α represents the thermo-optic coefficient of lithium niobate in a specific direction, and ΔT represents the temperature change under different applied voltages or currents. Assume that the phase change value of the modulation arm is Then the modulated light wave (U 1 ) and the lower arm unmodulated light wave (U 2 ) can be expressed as

[0066]

[0067] U 2 =U 0 (t) / 2

[0068] The two beams of light interfere with each other through the 2×2 multimode interference coupler, and the phase difference is converted into two beams of light with varying light intensities, which are output from the output port. When the phase difference between the two arms is 0, the power of the two output ports is equivalent, both -3dB, that is, the output light is equally divided; when the phase difference between the two input beams is π / 2, output port 2 is in an interference enhancement state, and the other output port 1 is in an interference destructive state; when the phase difference between the two input beams is 3π / 2, contrary to the situation when the phase difference is π / 2, output port 1 is in an interference enhancement state and output port 2 is in an extinction state. The relationship curves between the output light intensity and the phase difference of the two ports are both periodic curves with a period of 2π. For any output port, when it changes from an extinction state to an interference enhancement state, or from an interference enhancement state to an extinction state, the change in the phase difference at the input port should be π.

[0069] In this embodiment, the working process is as follows: any polarized light is input from the end coupler 1, and after passing through the polarization rotation beam splitter and the polarization controller, it is divided into the X polarization state component light wave and the Y polarization state component light wave of the transverse electric mode TE. The X polarization state component light wave enters the 1×2 multimode interference coupler in the symmetrical Mach-Zehnder modulator to achieve 3dB beam splitting, and is input into two phase shift arms respectively; the phase of the X polarization state component light wave transmitted in the phase shift arm is changed by the heating resistor. Then it enters the 2×2 multimode interference coupler, and according to the different phases of the light waves incident on the two input ports of the 2×2 multimode interference coupler, the intensities of the two output ports of the 2×2 multimode interference coupler are different, one of which is connected to the photodetector 1 to convert the optical signal into an electrical signal for monitoring; the other output port is connected to the polarization rotation combiner, and finally the transverse electric mode TE is output and output at the end coupler 2. Similarly, the optical path and modulation experienced by the Y polarization state component light wave are similar to those experienced by the X polarization state component light wave, and finally the transverse electric mode TE is output and outputted at the end face coupler 2.

[0070] Embodiment 2: A parallel dual-path Mach-Zehnder modulator based on electro-optic effect.

[0071] See also Figure 8-9 , using x-cut lithium niobate on insulator (LNOI), arranging traveling wave electrodes on both sides of the phase shift arm, and using the electro-optic effect of lithium niobate to change the refractive index of the lithium niobate optical waveguide. The traveling wave electrodes are arranged on both sides of the phase shift arm so that the direction of the applied electric field is perpendicular to the direction of light wave transmission to utilize the maximum electro-optic coefficient of lithium niobate. By adjusting the magnitude of the applied voltage, the refractive index of the lithium niobate optical waveguide can be linearly changed.

[0072] According to the principle of wave optics, the light wave (U 0) can be described in the following plural form:

[0073]

[0074] A represents the amplitude of the light wave, is the phase of the light wave, and ω is the angular frequency of the light wave. The relationship between ω and frequency f can be expressed as ω=2πf. The relationship between the phase and the refractive index is:

[0075]

[0076] Where L is the transmission distance, n is the refractive index of the material, and λ is the wavelength of the light wave. Combined with the refractive index change of lithium niobate material, the phase can be expressed as:

[0077]

[0078] Among them, n e represents the extraordinary refractive index of lithium niobate, r 33 represents the electro-optic coefficient of lithium niobate, E z represents the electric field along the z-axis of lithium niobate. Assume that the phase change value of the modulation arm is Then the modulated light wave (U 1 ) and the lower arm unmodulated light wave (U 2 ) can be expressed as:

[0079]

[0080] U 2 =U 0 (t) / 2

[0081] The two beams of light interfere with each other through the 2×2 multimode interference coupler, and the phase difference is converted into two beams of light with varying light intensities, which are output from the output port. When the phase difference between the two arms is 0, the power of the two output ports is equivalent, both -3dB, that is, the output light is equally divided; when the phase difference between the two input beams is π / 2, output port 2 is in an interference enhancement state, and the other output port 1 is in an interference destructive state; when the phase difference between the two input beams is 3π / 2, contrary to the situation when the phase difference is π / 2, output port 1 is in an interference enhancement state and output port 2 is in an extinction state. The relationship curves between the output light intensity and the phase difference of the two ports are both periodic curves with a period of 2π. For any output port, when it changes from an extinction state to an interference enhancement state, or from an interference enhancement state to an extinction state, the change in the phase difference at the input port should be π.

[0082] In this embodiment, the working process is as follows: any polarized light is input from the end coupler 1, and after passing through the polarization rotation beam splitter 1 and the polarization controller, it is divided into the X polarization state component light wave and the Y polarization state component light wave of the transverse electric mode TE. The X polarization state component light wave enters the 1×2 multimode interference coupler in the symmetrical Mach-Zehnder modulator to achieve 3dB beam splitting, and is input into two phase shift arms respectively. The phase of the X polarization state component light wave transmitted in the phase shift arm is changed by the heating resistor; then it enters the 2×2 multimode interference coupler, and according to the different phases of the light waves incident on the two input ports of the 2×2 multimode interference coupler, the intensities of the two output ports of the 2×2 multimode interference coupler are different, one of which is connected to the photodetector 1 to convert the optical signal into an electrical signal for monitoring; the other output port is connected to the polarization rotation combiner, and finally the transverse electric mode TE is output and output at the end coupler 2. Similarly, the optical path and modulation experienced by the Y polarization state component light wave are similar to those experienced by the X polarization state component light wave, and finally the transverse electric mode TE is output and outputted at the end face coupler 2.

[0083] The implementation of the embodiments of the present invention includes the following beneficial effects: (1) Dynamically adjustable splitting ratio: By using the electro-optic effect or the thermo-optic effect to change the refractive index of the optical waveguide, the splitting ratio control in the range of 0% to 100% can be flexibly achieved by adjusting the phase difference of the transmitted light in the two arms of the Mach-Zehnder interferometer; (2) Dual-path control: By operating two Mach-Zehnder modulators in parallel, the X and Y polarization state optical signals can be processed simultaneously; (3) On-chip integration: The device is fully integrated on the photonic chip, has a high degree of integration and a compact design, and is suitable for application scenarios of high-density integrated photonic circuits. It has the advantages of low driving voltage, low power consumption, and integration; in addition, it can be manufactured using micro-nano processing technology, so that the system is compatible with the existing CMOS process, and realizes low-cost, high-integration photonic circuit mass production; (4) Wide application: The device can be used in adjustable optical branching, optical signal modulation and highly flexible optical communication network design.

[0084] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. An adjustable splitting ratio modulation device, characterized in that: It includes a polarization controller, two Mach-Zehnder interferometers, a polarization rotation beam combiner and an end coupler; wherein, The two output ends of the polarization controller are respectively connected to the input ends of the two Mach-Zehnder interferometers; One of the output ends of each of the Mach-Zehnder interferometers is connected to the input end of the polarization rotation beam combiner; The output end of the polarization rotation beam combiner is connected to the input end of the end face coupler.

2. The adjustable splitting ratio modulation device according to claim 1, characterized in that: The polarization controller includes a thermo-optical dynamic polarization controller or an electro-optical dynamic polarization controller.

3. The adjustable splitting ratio modulation device according to claim 1, characterized in that: The Mach-Zehnder interferometer comprises a beam splitter, a 2×2 multimode interference coupler, two optical waveguide phase shift arms and modulation devices on both sides of the phase shift arms.

4. The adjustable splitting ratio modulation device according to claim 3, characterized in that: The beam splitter includes any one of a 1×2 multimode interference coupler, a directional coupler or a Y-type beam splitter.

5. The adjustable splitting ratio modulation device according to claim 3, characterized in that: The modulation device includes a traveling wave electrode or a heating resistor.

6. The adjustable splitting ratio modulation device according to claim 5, characterized in that: The heating resistor includes a symmetrical on-chip resistor, and the structure of the on-chip resistor includes a serpentine structure or a linear structure.

7. The adjustable splitting ratio modulation device according to claim 5, characterized in that: The adjustment method of the traveling wave electrode includes single-arm modulation or double-arm push-pull modulation.

8. The adjustable splitting ratio modulation device according to claim 1, characterized in that: The adjustable splitting ratio modulation device also includes two photoelectric detectors, and one output end of each Mach-Zehnder interferometer is connected to one of the photoelectric detectors.

9. The adjustable splitting ratio modulation device according to claim 1, characterized in that: The adjustable splitting ratio modulation device comprises a substrate layer, a buried oxide layer, a thin film layer, an upper cladding layer and a metal layer.

10. The adjustable splitting ratio modulation device according to claim 9, characterized in that: The material of the thin film layer includes any one or more of silicon on insulator, silicon nitride, lithium niobate, lithium tantalate, indium phosphide, gallium arsenide, aluminum nitride or silicon carbide.

Images