Monolithic integrated flat electro-optical frequency comb generation system

Abstract

The invention discloses a monolithic integrated flat electro-optic optical frequency comb generation system, belongs to the technical field of optical frequency combs, and can solve the problems that an existing optical frequency comb generation system is low in integration degree and poor in working stability. The system comprises: a substrate; the buried oxide layer is formed on the substrate; the electro-optical modulator comprises an optical waveguide and two modulation arms; the optical waveguide and the two modulation arms are arranged on the buried oxide layer, and the input end of the optical waveguide is connected with the light source; the oxidation insulating layer coats the surfaces of the optical waveguide and the two modulation arms; the branch line coupler is arranged on the outer surface of the oxidation insulating layer, and two output ports of the branch line coupler are electrically connected with the two modulation arms respectively; and the electro-optical modulator outputs a flat electro-optical frequency comb under the coupling action of the branch line coupler. The method is used for generating the flat electro-optical frequency comb.

Description

Technical Field

[0001] The invention relates to a monolithic integrated flat electro-optical frequency comb generating system, belonging to the technical field of optical frequency combs. Background Art

[0002] An optical frequency comb consists of a series of discrete pulsed lasers with equal frequency intervals and a stable phase relationship, and its spectrum distribution resembles a comb. Optical frequency combs are widely used in optical atomic clocks, ultra-sensitive chemical detectors, super lasers, long-distance fiber-optic communications, and high-sensitivity lidar. Among them, an optical frequency comb with a flat spectrum can ensure uniform power distribution on all comb lines, thereby maintaining the consistency of signal quality and the calibration accuracy of the signal, which is beneficial to improving the performance and reliability of high-precision applications. Compared with technologies such as mode-locked lasers and Kerr combs, electro-optical optical frequency combs excel in providing flat spectra, thanks to their excellent flexibility in modulation control. Electro-optical optical frequency combs can achieve more uniform spectral output by using various modulators to adjust the amplitude, phase, frequency, and polarization of light.

[0003] At present, the generation system of electro-optical frequency comb with flat spectrum is usually composed of multiple components, and the multiple components are discretely set, which makes the system large in size and high in cost, and therefore difficult to be applied in compact, integrated, and cost-effective application fields. At the same time, due to the large differences in the environment in which the discretely set components are located, each component is more susceptible to different environmental factors, which makes the system control and maintenance more complicated and difficult, seriously affecting the stability of system operation. Summary of the invention

[0004] The present invention provides a monolithic integrated flat electro-optical frequency comb generation system, which can solve the problems of low integration level of existing optical frequency comb generation systems and great difficulty in system control and maintenance.

[0005] The present invention provides a monolithically integrated flat electro-optical frequency comb generation system, the system comprising:

[0006] substrate;

[0007] A buried oxide layer formed on the substrate;

[0008] An electro-optic modulator comprises an optical waveguide and two modulation arms; the optical waveguide and the two modulation arms are arranged on the buried oxide layer, and an input end of the optical waveguide is connected to a light source;

[0009] An oxidized insulating layer, covering the surface of the optical waveguide and the two modulation arms;

[0010] A branch line coupler is arranged on the outer surface of the oxide insulating layer, and its two output ports are electrically connected to two modulation arms respectively; the electro-optic modulator outputs a flat electro-optical frequency comb under the coupling action of the branch line coupler.

[0011] Optionally, the system further comprises:

[0012] Two electrical transition structures correspond one to one with the two output ports of the branch line coupler; one end of the electrical transition structure is electrically connected to the corresponding output port, and the other end passes through the oxide insulating layer and is electrically connected to one end of the corresponding modulation arm.

[0013] Optionally, the modulation arm comprises a modulation ground electrode and a modulation signal electrode arranged in parallel;

[0014] One end of the electrical transition structure connected to the corresponding modulation arm has two sub-connection ends, and the two sub-connection ends respectively pass through the oxidized insulating layer and are electrically connected to one end of the corresponding modulation ground electrode and modulation signal electrode.

[0015] Optionally, four first through holes are formed on the oxidized insulating layer; the four first through holes correspond one-to-one to four sub-connection ends of the two electrical transition structures, and the sub-connection ends are inserted into the corresponding first through holes.

[0016] Optionally, the electro-optic modulator further comprises:

[0017] Two matching resistors are arranged on the outer surface of the oxidized insulating layer and correspond to the two modulation arms one by one; the two connecting ends of the matching resistors respectively pass through the oxidized insulating layer and are electrically connected to the corresponding modulation ground electrode and one end of the modulation signal electrode away from the electrical transition structure.

[0018] Optionally, four second through holes are formed on the oxidized insulating layer; the four second through holes correspond one-to-one to four connection ends of the two matching resistors, and the connection ends of the matching resistors are inserted into the corresponding second through holes.

[0019] Optionally, the light source is arranged on a surface of the buried oxide layer away from the substrate and located at a side of an input end of the electro-optic modulator; and the oxide insulating layer is coated on a surface of the light source.

[0020] Optionally, the system further comprises:

[0021] An oxide cladding is coated on the transmission line of the branch line coupler.

[0022] Optionally, the electro-optic modulator is a single-drive Mach-Zehnder modulator or an orthogonal phase modulator.

[0023] The beneficial effects that the present invention can produce include:

[0024] The present invention arranges a branch line coupler and an electro-optic modulator on a buried oxide layer, and uses an oxide insulating layer to isolate the branch line coupler from the optical waveguide and two modulation arms of the electro-optic modulator, thereby effectively avoiding mutual interference between the branch line coupler and the electro-optic modulator during operation, so that the two can be compactly arranged on a single chip, thereby realizing the monolithic integration of a flat electro-optical frequency comb generation system. This improves the integration level of the system, reduces the volume of the system, reduces the production cost of the system, makes the system suitable for compact, integrated, and cost-effective application fields, and expands the application range of the system. At the same time, integration makes the environment of each device in the system consistent, reduces the complexity and difficulty of system control and maintenance, and is conducive to improving the stability of system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of a monolithically integrated flat electro-optical frequency comb generation system provided by an embodiment of the present invention;

[0026] Figure 2 Schematic diagram of a flattened electro-optical frequency comb generated according to an embodiment of the present invention.

[0027] Reference numerals:

[0028] 1. Substrate; 2. Buried oxide layer; 3. Oxide insulating layer; 4. Transmission line; 5. Input waveguide; 6. Optical beam splitter; 7. Modulation waveguide; 8. Optical beam combiner; 9. Output waveguide; 10. Optical signal processor; 11. Matching resistor; 12. Second through hole; 13. Modulation ground electrode; 14. Modulation signal electrode; 15. First through hole; 16. Electrical transition structure; 17. Light source; 18. Ground electrode; 19. Signal electrode. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with embodiments, but the present invention is not limited to these embodiments.

[0030] The embodiment of the present invention provides a monolithic integrated flat electro-optical frequency comb generation system, such as Figure 1 As shown, the system includes:

[0031] Substrate 1;

[0032] A buried oxide layer 2 is formed on the substrate 1;

[0033] The electro-optic modulator comprises an optical waveguide and two modulation arms; the optical waveguide and the two modulation arms are arranged on the buried oxide layer 2, and the input end of the optical waveguide is connected to the light source 17;

[0034] An oxidized insulating layer 3, covering the surface of the optical waveguide and the two modulation arms;

[0035] The branch line coupler is arranged on the outer surface of the oxide insulating layer 3, and its two output ports are electrically connected to the two modulation arms respectively; the electro-optic modulator outputs a flat electro-optical frequency comb under the coupling effect of the branch line coupler.

[0036] Specifically, an electro-optic optical frequency comb is an optical frequency comb based on the electro-optic effect, and a flat electro-optic optical frequency comb is an electro-optic optical frequency comb with a flat spectrum.

[0037] Specifically, the electro-optic modulator may be a Mach-Zehnder modulator or an orthogonal phase modulator. The Mach-Zehnder modulator may be a single-drive Mach-Zehnder modulator or a multi-drive Mach-Zehnder modulator. These modulators may implement phase-based modulation techniques in different forms.

[0038] In practical applications, strategically combining multiple electro-optic modulators can optimize the degree of freedom of electro-optic modulation, which is conducive to the generation of flat electro-optic optical frequency combs. However, the use of multiple electro-optic modulators will increase the number of system components, increase the volume of the system, and increase the difficulty of system integration; at the same time, the more components there are, the more difficult it is to operate and maintain the system, and the lower the stability. Therefore, the present invention only uses a single electro-optic modulator, that is, a single-drive Mach-Zehnder modulator, which can reduce the number of system components, reduce the volume of the system, and facilitate the monolithic integration of the system, thereby greatly reducing the difficulty of system control and maintenance and improving the operational stability of the system.

[0039] A flat electro-optic frequency comb can be generated by using a branch-line coupler and an electro-optic modulator. However, when the two are monolithically integrated on an integrated circuit, their working circuits and related devices are prone to mutual interference, including the transmission line 4 of the branch-line coupler interfering with the performance of the optical waveguide. These interferences seriously affect the stable generation of the flat electro-optic frequency comb.

[0040] In order to solve the above-mentioned interference problem, the present invention arranges a branch line coupler and an electro-optic modulator on the buried oxide layer 2, and uses an oxide insulating layer 3 to isolate the branch line coupler from the optical waveguide and two modulation arms of the electro-optic modulator, which can effectively avoid mutual interference between the branch line coupler and the electro-optic modulator during operation, so that the two can be compactly arranged on a single chip, thereby realizing the monolithic integration of a flat electro-optical frequency comb generation system. This improves the integration level of the system, reduces the volume of the system, reduces the production cost of the system, makes the system suitable for compact, integrated, and cost-effective application fields, and expands the application range of the system. At the same time, integration makes the environment of each device in the system consistent, reduces the complexity and difficulty of system control and maintenance, and is conducive to improving the stability of system operation.

[0041] Specifically, the light source 17 is disposed on the surface of the buried oxide layer 2 away from the substrate 1 and located at the input end side of the electro-optic modulator; the oxide insulating layer 3 covers the surface of the light source 17. In practice, the present invention may not be provided with the light source 17, and the optical waveguide may be connected to an external light source.

[0042] Specifically, the material of the optical waveguide may be silicon, lithium niobate, aluminum nitride, silicon carbide, lithium tantalate or barium titanate.

[0043] Specifically, the optical waveguide of the electro-optic modulator includes:

[0044] An input waveguide 5, whose input end is connected to the light source 17, and whose output end is connected to the input end of the beam splitter 6;

[0045] an output waveguide 9, whose input end is electrically connected to the output end of the optical combiner 8, and whose output end is used to output an electro-optical frequency comb;

[0046] Two modulation waveguides 7 are arranged in parallel, and their input ends are respectively connected to the output ends of the optical beam splitter 6 , and their output ends are respectively connected to the input ends of the optical beam combiner 8 .

[0047] The two modulation arms of the electro-optic modulator correspond to the two modulation waveguides 7 respectively, and are used to modulate the optical signals in the two modulation waveguides 7 respectively.

[0048] Specifically, the output end of the output waveguide 9 is connected to an application device of the flat electro-optical frequency comb.

[0049] Specifically, the application device of the flat electro-optical frequency comb can be an optical signal processor 10. The output waveguide 9 outputs the flat electro-optical frequency comb to the optical signal processor 10, and the optical signal processor 10 is used to further process and use the flat electro-optical frequency comb according to application requirements. The optical signal processor 10 can be arranged on the buried oxide layer 2 of the present invention, or can be arranged outside the system described in the present invention.

[0050] Specifically, each modulation arm includes a modulation ground electrode 13 and a modulation signal electrode 14 arranged in parallel;

[0051] Specifically, the branch line coupler includes an electrode, two output ports and a plurality of transmission lines 4; the two output ports are an in-phase port (I-port) and a quadrature port (Q-port), respectively; the plurality of transmission lines 4 are connected end to end to form a transmission line frame, which is located between the electrode and the two output ports and has two different impedances.

[0052] Specifically, the transmission line 4 can be a uniform transmission line or a non-uniform transmission line. The branch line coupler of the uniform transmission line can achieve uniform power distribution. The transmission line 4 in this embodiment is a uniform transmission line, and four transmission lines 4 are connected end to end to form a square transmission line frame.

[0053] Since symmetrical arrangement of electrodes is beneficial to ensuring the operational stability of the branch line coupler, the present invention arranges two groups of electrodes, each group of electrodes including two ground electrodes 18 and one signal electrode 19. However, when the branch line coupler is actually operating, only one group of electrodes is required to work.

[0054] The branch line coupler has a higher tolerance to capacitance errors generated during manufacturing, and the signals output from the two output ports of the branch line coupler have a certain phase difference and amplitude offset difference, which can meet the conditions for generating a flat electro-optical frequency comb.

[0055] Specifically, the system may also include:

[0056] The two electrical transition structures 16 correspond one to one with the two output ports of the branch line coupler; one end of the electrical transition structure 16 is electrically connected to the corresponding output port, and the other end passes through the oxide insulating layer 3 and is electrically connected to one end of the corresponding modulation arm.

[0057] Furthermore, one end of the electrical transition structure 16 connected to the corresponding modulation arm has two sub-connection ends, and the two sub-connection ends pass through the oxide insulating layer 3 and are electrically connected to one end of the corresponding modulation ground electrode 13 and modulation signal electrode 14 .

[0058] Specifically, four first through holes 15 are opened on the oxide insulation layer 3 ; the four first through holes 15 correspond one-to-one to the four sub-connection ends of the two electrical transition structures 16 , and the sub-connection ends are penetrated in the corresponding first through holes 15 .

[0059] Specifically, the electro-optic modulator may further include:

[0060] Two matching resistors 11 are arranged on the outer surface of the oxidized insulating layer 3 and correspond one to one with the two modulation arms; the two connecting ends of the matching resistor 11 respectively pass through the oxidized insulating layer 3 and are electrically connected to the corresponding modulation ground electrode 13 and the end of the modulation signal electrode 14 away from the electrical transition structure 16.

[0061] By setting the matching resistor 11, a balanced impedance can be provided for the modulation arm, which is beneficial to improving the signal transmission quality and transmission efficiency. In order to avoid mutual interference between the matching resistor 11 and the modulation arm, the present invention sets the matching resistor 11 on the outer surface of the oxidized insulating layer 3, and uses the oxidized insulating layer 3 to isolate the matching resistor 11 from the modulation arm.

[0062] Specifically, four second through holes 12 are formed on the oxide insulating layer 3 ; the four second through holes 12 correspond one-to-one to the four connection ends of the two matching resistors 11 , and the connection ends of the matching resistors 11 are inserted into the corresponding second through holes 12 .

[0063] Specifically, the system may also include:

[0064] The oxide cladding is coated on the transmission line 4 and two output ports of the branch line coupler. By using the oxide cladding to cover the devices on the branch line coupler except the ground electrode 18 and the signal electrode 19, the influence of environmental factors such as temperature and humidity on the branch line coupler can be effectively avoided, and the operation stability of the system can be improved.

[0065] Specifically, the working principle of the present invention is as follows:

[0066] The light source 17 generates a continuous single-wavelength optical signal, which is coupled into the input waveguide 5 through a branch line coupler, and then equally divided into two paths through an optical beam splitter 6, and respectively subjected to electrical signal loading modulation through two modulation arms. The obtained modulated signals are mixed through an optical combiner 8 to form a flat electro-optical frequency comb, which is output to a subsequent optical signal processor 10 for the next step of signal processing and use.

[0067] Furthermore, based on the phase difference and amplitude offset difference of the output signals of the two output ports of the branch line coupler, the present invention can not only adjust and set the components of the system to achieve the optimal generation conditions of the flat electro-optical frequency comb, but also predict the bandwidth and conversion efficiency of the optical frequency comb, so as to output a low-noise, stable flat electro-optical frequency comb, such as Figure 2 Compared with the existing optical frequency comb generation system based on discrete components, the present invention reduces the volume of the system, reduces the energy consumption ratio of the system, improves the cost-effectiveness of the system, and enhances the operational stability of the system based on the advantages of monolithic integration.

[0068] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A monolithically integrated flat electro-optical frequency comb generation system, characterized in that: The system comprises: substrate; A buried oxide layer formed on the substrate; An electro-optic modulator comprises an optical waveguide and two modulation arms; the optical waveguide and the two modulation arms are arranged on the buried oxide layer, and an input end of the optical waveguide is connected to a light source; An oxidized insulating layer, covering the surface of the optical waveguide and the two modulation arms; A branch line coupler is arranged on the outer surface of the oxide insulating layer, and its two output ports are electrically connected to two modulation arms respectively; the electro-optic modulator outputs a flat electro-optical frequency comb under the coupling action of the branch line coupler.

2. The system according to claim 1, characterized in that The system further comprises: Two electrical transition structures correspond one to one with the two output ports of the branch line coupler; one end of the electrical transition structure is electrically connected to the corresponding output port, and the other end passes through the oxide insulating layer and is electrically connected to one end of the corresponding modulation arm.

3. The system according to claim 2, characterized in that The modulation arm comprises a modulation ground electrode and a modulation signal electrode arranged in parallel; One end of the electrical transition structure connected to the corresponding modulation arm has two sub-connection ends, and the two sub-connection ends respectively pass through the oxidized insulating layer and are electrically connected to one end of the corresponding modulation ground electrode and modulation signal electrode.

4. The system according to claim 3, characterized in that Four first through holes are formed on the oxidized insulating layer; the four first through holes correspond one-to-one to the four sub-connection ends of the two electrical transition structures, and the sub-connection ends are inserted into the corresponding first through holes.

5. The system according to claim 3, characterized in that The electro-optic modulator further comprises: Two matching resistors are arranged on the outer surface of the oxidized insulating layer and correspond to the two modulation arms one by one; the two connecting ends of the matching resistors respectively pass through the oxidized insulating layer and are electrically connected to the corresponding modulation ground electrode and one end of the modulation signal electrode away from the electrical transition structure.

6. The system according to claim 5, characterized in that Four second through holes are formed on the oxidized insulating layer; the four second through holes correspond one-to-one to the four connecting ends of the two matching resistors, and the connecting ends of the matching resistors are inserted into the corresponding second through holes.

7. The system according to claim 1, characterized in that The light source is arranged on the surface of the buried oxide layer away from the substrate and located at the input end side of the electro-optic modulator; the oxide insulating layer covers the surface of the light source.

8. The system according to claim 1, characterized in that The system further comprises: An oxide cladding is coated on the transmission line of the branch line coupler.

9. The system according to claim 1, characterized in that The electro-optic modulator is a single-drive Mach-Zehnder modulator or an orthogonal phase modulator.

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