High-speed tunable light wave plate chip

Abstract

The invention discloses a high-speed tunable light wave plate chip, and the chip comprises a first end face coupler which is used for coupling an optical signal to be regulated and controlled; the polarization beam splitting rotator is used for splitting the optical signal to be regulated and controlled into two paths of optical signals with orthogonal polarization states, and rotating the polarization state of one path to enable the polarization states of the two paths of optical signals to be consistent; the radio frequency driving phase delay unit is used for loading a radio frequency signal to the two paths of optical signals and carrying out reverse phase delay regulation and control on the two paths of optical signals; the direct-current driving phase compensation unit is used for introducing a fixed phase difference to the two paths of optical signals through direct-current signals; the polarization rotation beam combiner is used for rotating the polarization state of one of the two paths of optical signals and combining the two paths of optical signals into one path of modulated optical signal; and the second end face coupler is used for coupling the modulated optical signal. Input of any linearly polarized light is supported, regulation and control efficiency is improved through the maximum electro-optical coefficient r33 of lithium niobate, and the device has the advantages of being large in bandwidth, small in size, low in half-wave voltage and low in power consumption.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optoelectronic technology and optical communication technology, and particularly relates to a high-speed tunable optical waveplate chip based on thin film lithium niobate electro-optic effect. BACKGROUND

[0002] As a core device for light polarization state regulation, the tunable optical waveplate can change the phase delay of incident light through external control means (such as electric field, temperature, etc.), so as to realize flexible conversion between linearly polarized light, circularly polarized light and elliptically polarized light. According to the different regulation principles, the tunable optical waveplate can be divided into electro-optically tunable, thermo-optically tunable, liquid crystal tunable and other types, among which the electro-optically tunable optical waveplate has irreplaceable advantages in the field of high-speed optical information processing due to its fast response speed and high regulation precision.

[0003] In the prior art, the preparation of the tunable optical waveplate mainly relies on liquid crystal and silicon light process platforms. However, these platforms have obvious shortcomings: the response speed of the liquid crystal tunable optical waveplate is slow (usually in the order of milliseconds), which is difficult to meet the requirements of high-speed optical systems; the silicon light process is based on thermal-optic effect regulation, and it is difficult to balance the response speed and stability, and lacks an efficient polarization state matching mechanism.

[0004] Therefore, it is urgent to propose a high-speed tunable optical waveplate chip to solve the pain points of the prior art, so as to achieve the purpose of "flexible input polarization state, fast regulation speed, high integration, stable performance". SUMMARY

[0005] In order to solve the technical problems existing in the prior art, according to the embodiments of the present application, a high-speed tunable optical waveplate chip with simple internal structure, strong input light polarization state compatibility and high regulation efficiency is provided. Moreover, the high-speed tunable optical waveplate chip has the characteristics of large bandwidth, small size, low half-wave voltage and low power consumption, and can meet the integration requirements of high-speed optical systems.

[0006] According to an aspect of the embodiment of the present application, a high-speed tunable optical wave chip comprises: a first end face coupler for coupling in a to-be-regulated optical signal; a polarization beam splitting rotator for splitting the to-be-regulated optical signal into two optical signals with orthogonal polarization states, and rotating the polarization state of one of the two optical signals to make the polarization state of the other one of the two optical signals consistent with that of the optical signal after polarization state rotation; a radio frequency driving phase delay unit for loading a radio frequency signal on the other one of the two optical signals and the optical signal after polarization state rotation, and performing reverse phase delay regulation on the other one of the two optical signals and the optical signal after polarization state rotation loaded with the radio frequency signal, thereby outputting two modulated optical signals; a direct current driving phase compensation unit for introducing a fixed phase difference into the two modulated optical signals through a direct current signal to compensate for the phase difference between the two modulated optical signals; a polarization rotation combiner for rotating the polarization state of one of the two modulated optical signals after phase difference compensation, and combining the one of the two modulated optical signals after polarization state rotation with the other one of the two modulated optical signals after phase difference compensation to form a modulated optical signal with a target polarization state; and a second end face coupler for coupling out the modulated optical signal with the target polarization state.

[0007] In one example of the high-speed tunable optical wave chip provided in the above aspect, the polarization state of the other one of the two optical signals output by the polarization beam splitting rotator and the polarization state of the optical signal after polarization state rotation are both consistent with the direction of the optical axis with r33 electro-optic coefficient in the lithium niobate crystal.

[0008] In one example of the high-speed tunable optical wave chip provided in the above aspect, the optical wave chip is based on an X-cut or Y-cut thin film lithium niobate wafer, which comprises a substrate layer and, sequentially arranged on the substrate layer, an optical isolation layer, a lithium niobate thin film substrate, a lithium niobate ridge waveguide, a buffer layer, an electrode and an upper cladding layer.

[0009] In one example of the high-speed tunable optical wave chip provided in the above aspect, the first end face coupler and the second end face coupler are both further used for connecting a single mode fiber or a polarization maintaining fiber outside the optical wave chip to couple in or out the optical signal from the optical wave chip, and the first end face coupler is further used for coupling in an arbitrary linearly polarized optical signal.

[0010] Preferably, the optical signal is split into two orthogonal polarization states (such as TE mode and TM mode) according to the polarization state or mode difference of the input optical carrier, the polarization state of one of the two optical signals is rotated by 90° through geometric structure design (such as asymmetric grating or mode converter), and finally two optical signals with consistent polarization states (both aligned with the r33 optical axis direction of lithium niobate) are output, to ensure that the subsequent electro-optic regulation efficiency is maximized.

[0011] In an example of the high-speed tunable optical waveplate chip provided in the above aspect, the radio frequency driving phase delay unit comprises an optical link and a radio frequency link; the optical link comprises two identical and parallel lithium niobate ridge waveguides, thereby having two optical input / output ports for transmitting two optical signals output by the polarization beam splitting rotator; the radio frequency link comprises a push-pull coplanar waveguide and a 50-ohm radio frequency load; the push-pull coplanar waveguide comprises two ground electrodes respectively located on both sides of the two lithium niobate ridge waveguides and a signal electrode located between the two lithium niobate ridge waveguides, the signal electrode is connected to one end of the 50-ohm radio frequency load, the two ground electrodes are connected to each other and connected to the other end of the 50-ohm radio frequency load, and the signal electrode introduces a radio frequency signal, thereby performing reverse phase delay control on the optical signals in the two identical and parallel lithium niobate ridge waveguides in the optical link.

[0012] Preferably, the high-speed reverse phase delay of the two optical signals is realized by using the r33 electro-optic effect of lithium niobate; the 50-ohm radio frequency load is connected to the output end of the push-pull coplanar waveguide, thereby avoiding the control noise caused by the reflection of the radio frequency signal.

[0013] In an example of the high-speed tunable optical waveplate chip provided in the above aspect, the radio frequency driving phase delay unit comprises an optical link and a radio frequency link; the optical link comprises two identical and parallel lithium niobate ridge waveguides, thereby having two optical input / output ports for transmitting two optical signals output by the polarization beam splitting rotator; the radio frequency link comprises a push-pull coplanar waveguide, the push-pull coplanar waveguide comprises two ground electrodes respectively located on both sides of the two lithium niobate ridge waveguides and a signal electrode located between the two lithium niobate ridge waveguides, the signal electrode introduces a radio frequency signal, thereby introducing a fixed phase difference to the two optical signals in the two lithium niobate ridge waveguides by using the electro-optic effect of the lithium niobate crystal.

[0014] In another example of the high-speed tunable optical waveplate chip provided in the above aspect, the direct current driving phase compensation unit comprises an optical link and a thermal-optic link; the optical link comprises two identical and parallel lithium niobate ridge waveguides, thereby having two optical input / output ports for transmitting two optical signals output by the radio frequency driving phase delay unit; the thermal-optic link comprises a heating resistor, the heating resistor is located outside one of the two lithium niobate ridge waveguides, and the heating resistor generates heat after being connected to a direct current signal, thereby introducing a fixed phase difference to the two optical signals in the two lithium niobate ridge waveguides by using the thermal-optic effect of the lithium niobate crystal.

[0015] Preferably, when the push-pull coplanar waveguide is used, a fixed phase difference is introduced by an external direct current voltage, which is suitable for high-precision compensation scenarios; when the thermal resistor is used, a fixed phase difference is introduced by the thermo-optic effect, which is suitable for low-voltage start scenarios; and the core function is to calibrate the phase offset in the radio frequency regulation process, and to ensure that the total delay accurately matches the target value (such as λ / 4, λ / 2, λ, etc.).

[0016] In an example of the high-speed tunable optical waveplate chip provided in the above aspect, the transmission direction of the radio frequency signal transmitted by the push-pull coplanar waveguide is consistent with the transmission direction of the optical signal in the optical waveplate chip.

[0017] In an example of the high-speed tunable optical waveplate chip provided in the above aspect, the characteristic impedance of the push-pull coplanar waveguide is greater than or equal to 47.5 ohms and less than or equal to 52.5 ohms; and / or, the effective refractive index of the push-pull coplanar waveguide deviates from the effective refractive index of the lithium niobate ridge optical waveguide by no more than 3%.

[0018] In an example of the high-speed tunable optical waveplate chip provided in the above aspect, the positions of the radio frequency driving phase delay unit and the direct current driving phase compensation unit in the optical path can be interchanged.

[0019] Preferably, the polarization rotation combiner geometry is completely consistent with the polarization beam splitting rotator (because the polarization beam splitting rotator is a reversible device), the two optical signals output by the direct current driving phase compensation unit are taken as inputs, the polarization state of one of the optical signals is reversed (the orthogonal polarization state is restored), and then the two optical signals are combined into one optical signal through mode coupling, so as to ensure that the polarization state of the output light meets the design requirements (such as converting linearly polarized light into circularly polarized light).

[0020] Preferably, the first end face coupler and the second end face coupler are used to connect external optical fibers (single-mode optical fibers or polarization maintaining optical fibers), to realize low-loss coupling (coupling loss ≤1.5 dB) of optical signals between the optical fibers and the optical waveplate, and to support any linearly polarized light input without additional polarization preprocessing.

[0021] Preferably, in order to improve the regulation bandwidth (target bandwidth ≥40 GHz) of the optical waveplate chip, the push-pull coplanar waveguide of the radio frequency driving phase delay unit needs to meet the following conditions:

[0022] The transmission direction of the radio frequency signal is consistent with the transmission direction of the optical signal, realizing electrical-optical synchronous regulation;

[0023] The characteristic impedance of the push-pull coplanar waveguide is accurately matched with 50Ω (deviation ≤5%), reducing signal attenuation caused by impedance mismatch;

[0024] - Effective refractive index matching (deviation ≤ 3%) between push-pull coplanar waveguide and lithium niobate ridge waveguide, avoiding bandwidth limitation caused by the difference in optical-electrical signal transmission speed.

[0025] Beneficial effects: The high-speed tunable optical wave chip according to an aspect of the embodiment of the present application has the following advantages:

[0026] (1) Strong input polarization state compatibility: supporting arbitrary linearly polarized light input, without additional polarization preprocessing modules, and can be directly connected to complex optical systems, reducing system integration difficulty; at the same time, it can apply reverse phase delay to a pair of orthogonal polarization state optical signals, and is suitable for dual polarization optical control scenarios;

[0027] (2) Excellent control efficiency and speed: using the maximum electro-optic coefficient r33 of lithium niobate crystal for control, with low half-wave voltage and low power consumption, and the response speed of the radio frequency driving module is fast, with a control bandwidth of ≥ 40 GHz, meeting the needs of high-speed optical systems;

[0028] (3) Simple structure and high integration: using an integrated structure of "splitting-control-combining", without additional load resistors or Bias-T circuits, with small size (typical chip area ≤ 1 mm x 5 mm);

[0029] (4) High control precision and good stability: the radio frequency control deviation is calibrated by the direct current driving phase compensation unit, with a phase delay precision of ≤ 0.1 rad, and the thin film lithium niobate material has excellent thermal stability (temperature coefficient ≤ 10 ppm / ℃), ensuring long-term working reliability. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and other aspects, features and advantages of the embodiments of the present application will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0031] Figure 1 is a structural top view of a high-speed tunable optical wave chip according to an embodiment of the present application;

[0032] Figure 2 is a structural top view of a radio frequency driving phase delay unit according to an embodiment of the present application;

[0033] Figure 3 is a structural top view of a direct current driving phase compensation unit according to an embodiment of the present application;

[0034] Figure 4 is a structural top view of a direct current driving phase compensation unit according to another embodiment of the present application. DETAILED DESCRIPTION

[0035] Hereinafter, specific embodiments of the present application will be described in detail with reference to the accompanying drawings. The present application can, however, be implemented in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. Like reference numerals refer to like elements throughout the specification.

[0036] As used herein, the terms "including", "includes", "comprising", "comprises", "has", "have", "having", "contains", "containing", or variants thereof, mean "including but not limited to". The terms "based on", "according to", and the like, mean "based at least in part on", "according to at least part on". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "a first", "a second", etc., mean "at least one", "at least one", and the like. The following can include other definitions, whether explicit or implicit. Unless the context clearly indicates otherwise, the definition of a term is consistent throughout the specification.

[0037] Figure 1 is a structure top view of a high-speed tunable optical waveplate chip according to an embodiment of the present application.

[0038] Referring to Figure 1 A high-speed tunable optical waveplate chip according to an embodiment of the present application includes a first end face coupler 1, a polarization beam splitting rotator 2, a radio frequency driving phase delay unit 3, a direct current driving phase compensation unit 4, a polarization rotating combiner 5, and a second end face coupler 6; wherein the first end face coupler 1, the polarization beam splitting rotator 2, the radio frequency driving phase delay unit 3, the direct current driving phase compensation unit 4, the polarization rotating combiner 5, and the second end face coupler 6 are connected in sequence.

[0039] The first end face coupler 1 is used for coupling in the optical signal to be modulated. The polarization beam splitting and rotating device 2 is used for splitting the optical signal to be modulated into two optical signals with orthogonal polarization states, and rotating the polarization state of one of the two optical signals, so that the polarization state of the other of the two optical signals is consistent with that of the optical signal after polarization state rotation. The radio frequency driven phase delay unit 3 is used for loading a radio frequency signal on the other of the two optical signals and the optical signal after polarization state rotation, and performing reverse phase delay modulation on the two optical signals loaded with the radio frequency signal, so as to output two modulated optical signals. The direct current driven phase compensation unit 4 is used for introducing a fixed phase difference into the two modulated optical signals through a direct current signal, so as to compensate for the phase difference between the two modulated optical signals. The polarization rotating and combining device 5 is used for rotating the polarization state of one of the two modulated optical signals after phase difference compensation, and combining the one of the two modulated optical signals after polarization state rotation with the other of the two modulated optical signals after phase difference compensation, so as to form one modulated optical signal with a target polarization state. The second end face coupler 6 is used for coupling out the one modulated optical signal with the target polarization state.

[0040] In the embodiment, the optical wave chip according to the embodiment of the application is based on an X-cut or Y-cut lithium niobate wafer, which comprises a substrate layer and, sequentially arranged on the substrate layer, an optical isolation layer, a lithium niobate thin film substrate, a lithium niobate ridge waveguide, a buffer layer, an electrode and an upper cladding layer. The substrate layer is a silicon or lithium niobate crystal layer, the optical isolation layer is a silicon dioxide layer, the buffer layer is a silicon dioxide layer, and the upper cladding layer is a silicon dioxide or silicon oxynitride layer.

[0041] Since the optical isolation layer is a silicon dioxide layer, optical crosstalk between the substrate layer and the lithium niobate thin film can be isolated. In addition, since the buffer layer is a silicon dioxide layer, the waveguide structure can be protected and the parasitic capacitance between the electrode and the waveguide can be reduced. Further, since the upper cladding layer is a silicon dioxide or silicon oxynitride layer, the propagation loss of the optical signal can be reduced.

[0042] Specifically, the first end face coupler 1 is used for connecting an optical fiber outside the optical wave chip, so as to couple an optical signal into the optical wave chip, thereby realizing low-loss coupling (coupling loss ≤1.5 dB) between the optical fiber and the optical wave chip. It should be understood that, in this case, the polarization state of the optical signal is linear polarization, and the optical fiber outside can be a single-mode optical fiber or a polarization maintaining optical fiber.

[0043] The polarization beam splitting and rotating device 2 splits the optical signal to be modulated into two optical signals with orthogonal polarization states according to the polarization state or mode of the input optical signal to be modulated, and then rotates the polarization state of one of the two optical signals. Finally, the polarization beam splitting and rotating device 2 outputs the two optical signals, which not only have consistent polarization states but also are consistent with the direction of the optical axis with r33 electro-optic coefficient in the lithium niobate crystal.

[0044] When the input of the polarization beam splitting rotator 2 satisfies the optical field of the light signal to be regulated, the optical field of the two light signals outputted by the two outputs of the polarization beam splitting rotator 2 satisfies the following formula:

[0045]

[0046] wherein, and represent a pair of orthogonal optical polarization states, and the direction of the polarization state is consistent with the direction of the optical axis of lithium niobate with r33 electro-optic coefficient, E1 and E2 respectively represent the optical field intensity of the optical field of the input light signal to be regulated of the polarization beam splitting rotator 2 on and polarization states, E PSR,out1 represents the optical field of the light signal outputted by the first output of the polarization beam splitting rotator 2, E PSR,out2 represents the optical field of the light signal outputted by the second output of the polarization beam splitting rotator 2, α PSR1 and α PSR2 respectively represent the loss from the input end to the first output end and from the input end to the second output end of the polarization beam splitting rotator 2, and ω is the angular frequency of the light signal.

[0047] Figure 2 is a structure top view of a radio frequency driven phase delay unit according to an embodiment of the present application. Referring to Figure 2 , the radio frequency driven phase delay unit 3 comprises an optical link and a radio frequency link; wherein the optical link comprises two identical and parallel lithium niobate ridge optical waveguides 7, thereby having two light input ports and two light output ports, the two light input ports input the two light signals outputted by the polarization beam splitting rotator 2 into the radio frequency driven phase delay unit 3, that is, the radio frequency driven phase delay unit 3 is used for receiving the two light signals split by the polarization beam splitting rotator 2 and applying reverse phase modulation.

[0048] The radio frequency link comprises a push-pull coplanar waveguide 8 and a 50-ohm radio frequency load 9; wherein the push-pull coplanar waveguide 8 comprises two ground electrodes respectively located on both sides of the two lithium niobate ridge optical waveguides 7 and a signal electrode located in the middle of the two lithium niobate ridge optical waveguides 7, the input end (i.e. the signal electrode) of the push-pull coplanar waveguide 8 is connected to one end of the 50-ohm radio frequency load 9, so as to avoid the reflection of the radio frequency signal at the output end of the push-pull coplanar waveguide 8, the input end of the push-pull coplanar waveguide 8 guides the radio frequency signal into the optical link, thereby performing reverse phase modulation on the light signal in the two identical and parallel lithium niobate ridge optical waveguides 7. In addition, the output end (i.e. the two ground electrodes connected to each other) of the push-pull coplanar waveguide 8 is connected to the other end of the 50-ohm radio frequency load 9.

[0049] In addition, the transmission direction of the RF signal driving the transmission of the push-pull coplanar waveguide 8 in the RF-driven phase delay unit 3 is consistent with the transmission direction of the optical signal in the optical wave chip, so as to increase the bandwidth of the optical wave chip. Further, the characteristic impedance of the push-pull coplanar waveguide 8 in the RF-driven phase delay unit 3 is greater than or equal to 47.5 ohms and less than or equal to 52.5 ohms, and preferably 50 ohms, so as to increase the bandwidth of the optical wave chip. Still further, the effective refractive index of the push-pull coplanar waveguide 8 in the RF-driven phase delay unit 3 is greater than or equal to 97% of the effective refractive index of the lithium niobate ridge optical waveguide 7 and less than or equal to 103% of the effective refractive index of the lithium niobate ridge optical waveguide 7, and preferably, the effective refractive index of the push-pull coplanar waveguide 8 is the same as the effective refractive index of the lithium niobate ridge optical waveguide 7, so as to increase the bandwidth of the optical wave chip.

[0050] When the optical signals output by the two output ports of the polarization beam splitting rotator 2 are input to the input ports of the two ridge optical waveguides 7 of the RF-driven phase delay unit 3, the optical fields of the two modulated optical signals output by the output ports of the two ridge optical waveguides 7 of the RF-driven phase delay unit 3 satisfy the following formula:

[0051]

[0052] wherein α RFOPS and V π respectively represent the loss and half-wave voltage of the ridge optical waveguide 7 of the RF-driven phase delay unit 3, s(t) represents the RF control signal introduced by the push-pull coplanar waveguide 8 in the RF-driven phase delay unit 3, E RFOPS,out1 represents the optical field of the modulated optical signal output by one of the output ports of the two ridge optical waveguides 7 of the RF-driven phase delay unit 3, and E RFOPS,out2 represents the optical field of the modulated optical signal output by the other of the output ports of the two ridge optical waveguides 7 of the RF-driven phase delay unit 3.

[0053] The DC-driven phase compensation unit 4 is configured to receive the two optical modulation signals output by the RF-driven phase delay unit 3 and apply an optical phase difference introduced by a DC signal (i.e., a DC voltage signal). Figure 3 is a structure top view of a DC-driven phase compensation unit according to an embodiment of the present application.

[0054] Referring to Figure 3The direct-current driving phase compensation unit 4 according to the embodiment of the present application comprises: an optical link and a radio frequency link, wherein the optical link is composed of two identical and parallel lithium niobate ridge optical waveguides 10, so as to have two optical input ports and two optical output ports, and the two optical input ports input two modulated optical signals output by the radio frequency driving phase delay unit 3 into the direct-current driving phase compensation unit 4. The radio frequency link comprises a push-pull coplanar waveguide 11, which comprises two ground electrodes respectively located on two sides of the two lithium niobate ridge optical waveguides 10 and a signal electrode located between the two lithium niobate ridge optical waveguides 10. The input end (i.e. the signal electrode) of the push-pull coplanar waveguide 11 guides a direct-current signal, so as to introduce a fixed optical phase difference into the two modulated optical signals in the two identical and parallel lithium niobate ridge optical waveguides 10 in the optical link by using the electro-optic effect of the lithium niobate crystal.

[0055] Figure 4 The structure top view of the direct-current driving phase compensation unit according to another embodiment of the present application is shown in FIG. 4. Referring to FIG. 4, Figure 4 The direct-current driving phase compensation unit 4 according to another embodiment of the present application comprises: an optical link and a thermo-optic link, wherein the optical link is composed of two identical and parallel lithium niobate ridge optical waveguides 12, so as to have two optical input ports and two optical output ports, and the two optical input ports input two modulated optical signals output by the radio frequency driving phase delay unit 3 into the direct-current driving phase compensation unit 4. The thermo-optic link comprises a thermal resistor 13 located outside one of the two lithium niobate ridge optical waveguides 12. The thermal resistor 13 generates heat after being connected to an external direct-current signal, so as to introduce a fixed optical phase difference into the two modulated optical signals in the two identical and parallel lithium niobate ridge optical waveguides 12 in the optical link by using the thermo-optic effect of the lithium niobate crystal.

[0056] When the optical fields of the two modulated optical signals output by the two output ports of the two lithium niobate ridge optical waveguides 7 of the radio frequency driving phase delay unit 3 are input into the input ports of the two lithium niobate ridge optical waveguides 10, 12 of the direct-current driving phase compensation unit 4, the optical fields of the two modulated optical signals output by the two output ports of the two lithium niobate ridge optical waveguides 10, 12 of the direct-current driving phase compensation unit 4 satisfy the following formula:

[0057]

[0058] wherein α DCOPS represents the loss of the lithium niobate ridge optical waveguide 10, 12 of the direct-current driving phase compensation unit 4, represents the fixed optical phase difference introduced between the two lithium niobate ridge optical waveguides 10 (12) of the direct-current driving phase compensation unit 4 due to the direct-current signal (i.e. the direct-current voltage) V DC represents the fixed optical phase difference introduced between the two lithium niobate ridge optical waveguides 10 (12) of the direct-current driving phase compensation unit 4 due to the direct-current signal (i.e. the direct-current voltage) V DCOPS,out1E DCOPS,out2 represents the optical field of the modulated light signal output from the other of the output ports of the two ridge optical waveguides 10(12) of the DC-driven phase compensation unit 4.

[0059] With continued reference to Figure 1 , the geometry of the polarization-rotating combiner 5 is consistent with that of the polarization beam-splitting rotator 2. The polarization beam-splitting rotator 2 is a reversible device, and the polarization-rotating combiner 5 takes the two outputs of the polarization beam-splitting rotator 2 as inputs, and the polarization-rotating combiner 5 takes the inputs of the polarization beam-splitting rotator 2 as outputs.

[0060] Specifically, the two optical input ports of the polarization-rotating combiner 5 take one of the two modulated light signals output from the DC-driven phase compensation unit 4, and after polarization state rotation, the one of the two modulated light signals and the other of the two modulated light signals output from the DC-driven phase compensation unit 4 are combined into one modulated light signal, and the combined one modulated light signal is input into the second end-face coupler 6 from the output port of the polarization-rotating combiner 5, that is, the polarization-rotating combiner 5 is used to receive the modulated light signals output from the DC-driven phase compensation unit 4 and combine the light, specifically, the polarization-rotating combiner 5 orthogonally rotates one of the two modulated light signals output from the DC-driven phase compensation unit 4, for example, rotates one of the two modulated light signals from TE mode to TM mode, at this time, the two modulated light signals become a pair of orthogonal light, and then are combined into one and output from the output port of the polarization-rotating combiner 5.

[0061] When the optical fields of the two modulated light signals output from the two output ports of the two ridge optical waveguides 10(12) of the DC-driven phase compensation unit 4 are input into the two input ports of the polarization-rotating combiner 5, the optical field of the modulated light signal output from the output port of the polarization-rotating combiner 5 satisfies the following formula:

[0062]

[0063] wherein E PRC,out represents the optical field of the modulated light signal output from the output port of the polarization-rotating combiner 5, α PRC1 and α PRC2 respectively represent the losses of the first input port to the output port and the second input port to the output port of the polarization-rotating combiner 5. The polarization state of the modulated light signal output from the output port is jointly determined by the radio frequency control signal s(t) and the direct current voltage V DC , so that the fast conversion between linearly polarized light, circularly polarized light and elliptically polarized light can be realized.

[0064] It is worth noting that the second end face coupler 6 is used for receiving the optical signal output by the polarization rotation combiner 5, and connecting the optical fiber outside the optical wave chip to couple the optical signal inside the optical wave chip into the optical fiber outside.

[0065] In addition, it should be noted that in Figure 1 In the structure shown, the positions of the radio frequency driving phase delay unit 3 and the direct current driving phase compensation unit 4 can be interchanged, that is, the two optical signals output by the polarization beam splitting rotator 2 are first input to the radio frequency driving phase delay unit 3 and then input to the direct current driving phase compensation unit 4, or first input to the direct current driving phase compensation unit 4 and then input to the radio frequency driving phase delay unit 3, which has the same effect and function, and does not affect the effect and function of the entire optical wave chip.

[0066] Further, the transmission efficiency loss of the two optical signals output by the polarization beam splitting rotator 2 after splitting the input optical signal is not more than 0.5dB; the transmission efficiency loss of the radio frequency driving phase delay unit 3 is not more than 0.8dB; the transmission efficiency loss of the direct current driving phase compensation unit 4 is not more than 0.5dB; and the transmission efficiency loss of the polarization rotation combiner 5 is not more than 0.5dB.

[0067] In summary, the high-speed tunable optical wave chip has the following advantages:

[0068] (1) Strong input polarization state compatibility: supports arbitrary linearly polarized light input, does not require additional polarization preprocessing modules, can be directly connected to complex optical systems, and reduces system integration difficulty; at the same time, it can apply reverse phase delay to a pair of orthogonal polarization state optical signals, and is suitable for dual polarization optical control scenarios;

[0069] (2) Excellent control efficiency and speed: using lithium niobate crystal with maximum electro-optic coefficient r33 for control, low half-wave voltage and low power consumption, and fast response speed of radio frequency driving module, control bandwidth ≥40GHz, meeting the needs of high-speed optical systems;

[0070] (3) Simple structure and high integration: using an integrated structure of "splitting-control-combining", without additional load resistance or Bias-T circuit, small size (typical chip area ≤1mm×5mm);

[0071] (4) High control precision and good stability: the radio frequency control deviation is calibrated by the direct current driving phase compensation unit, the phase delay precision is ≤0.1 rad, and the thin film lithium niobate material has excellent thermal stability (temperature coefficient ≤10ppm / ℃), ensuring long-term working reliability.

[0072] The optional implementation of the embodiments of the present application is described in detail above in combination with the drawings, but the embodiments of the present application are not limited to the specific details in the above implementation, and various simple modifications can be made to the technical solutions of the embodiments of the present application within the technical concept scope of the embodiments of the present application, and these simple modifications all belong to the protection scope of the embodiments of the present application.

Claims

1. A high-speed tunable optical waveplate chip, characterized in that, The high-speed tunable optical waveplate chip includes: The first end-face coupler is used to couple in the optical signal to be modulated. A polarization beam splitter is used to split the optical signal to be controlled into two optical signals with orthogonal polarization states, and to rotate the polarization state of one of the two optical signals so that the polarization state of the other optical signal is consistent with the polarization state of the optical signal after the polarization state is rotated. The radio frequency (RF) driven phase delay unit is used to load an RF signal onto the other of two optical signals and the optical signal after polarization state rotation, and to perform reverse phase delay modulation on the other of the two optical signals loaded with the RF signal and the optical signal after polarization state rotation, thereby outputting two modulated optical signals. A DC-driven phase compensation unit is used to introduce a fixed phase difference between two modulated optical signals using a DC signal to compensate for the phase difference between the two modulated optical signals. A polarization rotation beam combiner is used to rotate the polarization state of one of two modulated optical signals after phase difference compensation, and to combine one of the two modulated optical signals after polarization state rotation with the other of the two modulated optical signals after phase difference compensation to form a modulated optical signal with a target polarization state. The second end-face coupler is used to couple out the modulated optical signal with the target polarization state.

2. The high-speed tunable optical waveplate chip according to claim 1, characterized in that, The polarization state of the other of the two optical signals output by the polarization beam splitter, as well as the polarization state of the optical signal after the polarization state is rotated, are consistent with the optical axis direction of the lithium niobate crystal with an electro-optic coefficient of r33.

3. The high-speed tunable optical waveplate chip according to claim 1 or 2, characterized in that, The optical waveplate chip is based on an X-cut or Y-cut thin-film lithium niobate wafer, and includes: a substrate layer and an optical isolation layer, a lithium niobate thin-film substrate, a lithium niobate ridge waveguide, a buffer layer, an electrode, and an upper cladding layer sequentially disposed on the substrate layer.

4. The high-speed tunable optical waveplate chip according to claim 1, characterized in that, Both the first end-face coupler and the second end-face coupler are also used to connect to a single-mode fiber or polarization-maintaining fiber outside the optical waveplate chip to couple optical signals into or out of the optical waveplate chip. The first end-face coupler is also used to couple in arbitrary linearly polarized optical signals.

5. The high-speed tunable optical waveplate chip according to claim 1, characterized in that, The radio frequency driven phase delay unit includes an optical link and a radio frequency link; The optical link includes two identical and parallel lithium niobate ridge waveguides, thus providing two optical input / output ports for transmitting the two optical signals output by the polarization beam splitter. The radio frequency link includes a push-pull coplanar traveling waveguide and a 50-ohm radio frequency load. The push-pull coplanar traveling waveguide includes two ground electrodes located on both sides of two lithium niobate ridge optical waveguides and a signal electrode located between the two lithium niobate ridge optical waveguides. The signal electrode is connected to one end of the 50-ohm radio frequency load, and the two ground electrodes are connected to each other and connected to the other end of the 50-ohm radio frequency load. The signal electrode introduces a radio frequency signal, thereby performing reverse phase delay modulation on the optical signals in the two identical and parallel lithium niobate ridge optical waveguides in the optical link.

6. The high-speed tunable optical waveplate chip according to claim 1, characterized in that, The DC-driven phase compensation unit includes an optical link and a radio frequency link; The optical link includes two identical and parallel lithium niobate ridge optical waveguides, thus providing two optical input / output ports for transmitting the two modulated optical signals output by the radio frequency drive phase delay unit. The radio frequency link includes a push-pull coplanar traveling waveguide, which includes two ground electrodes located on both sides of two lithium niobate ridge waveguides and a signal electrode located between the two lithium niobate ridge waveguides. The signal electrode introduces a DC signal, thereby using the electro-optic effect of the lithium niobate crystal to introduce a fixed phase difference between the two modulated optical signals in the two lithium niobate ridge waveguides.

7. The high-speed tunable optical waveplate chip according to claim 1, characterized in that, The DC-driven phase compensation unit includes an optical link and a thermo-optical link; The optical link includes two identical and parallel lithium niobate ridge optical waveguides, thus providing two optical input / output ports for transmitting two modulated optical signals output by the radio frequency drive phase delay unit. The thermo-optical link includes a thermal resistor located on the outside of one of the two lithium niobate ridge optical waveguides. The thermal resistor generates heat when a DC signal is applied to it, thereby using the thermo-optical effect of the lithium niobate crystal to introduce a fixed phase difference between the two modulated optical signals in the two lithium niobate ridge optical waveguides.

8. The high-speed tunable optical waveplate chip according to claim 5, characterized in that, The transmission direction of the radio frequency signal transmitted by the push-pull coplanar traveling wave waveguide is consistent with the transmission direction of the optical signal in the optical waveplate chip.

9. The high-speed tunable optical waveplate chip according to claim 5 or 8, characterized in that, The characteristic impedance of the push-pull coplanar traveling waveguide is greater than or equal to 47.5 ohms and less than or equal to 52.5 ohms. And / or, the effective refractive index of the push-pull coplanar traveling waveguide deviates from the effective refractive index of the lithium niobate ridge waveguide by no more than 3%.

10. The high-speed tunable optical waveplate chip according to claim 1, characterized in that, The positions of the radio frequency driven phase delay unit and the DC driven phase compensation unit in the optical path can be interchanged.

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