Electrically controlled source of D-shaped multimode optical fiber

Abstract

The application relates to the field of two-dimensional material optoelectronics and communication, in particular to an electrically controlled signal source of a D-shaped multimode optical fiber. The application integrates a graphene gate regulating structure on a D-shaped multimode optical fiber microcavity, adjusts the pump frequency and pump power of an externally connected narrow-linewidth laser, simultaneously, adjusts the Fermi level of the top graphene film by applying an external voltage, changes the refractive index of the D-shaped multimode optical fiber microcavity, and then finely adjusts the frequency of the overall device output microwave signal, so that the microwave signal output and accurate regulation of about 11 GHz are realized. Compared with other microwave signal sources based on optical technology, the application has the advantages of small device volume, high integration degree, adoption of an all-fiber structure, convenient access to an optical fiber information transmission network, and effective overcoming of the defects of high phase noise, complex structure, narrow tuning range and the like.

Description

Technical Field

[0001] This invention relates to the fields of two-dimensional material optoelectronics and communications, specifically to an electrically controlled signal source for a D-shaped multimode optical fiber, which achieves electrical control of approximately 11 GHz signals output from the microcavity based on the modulation of a graphene gate structure. Background Technology

[0002] With the continuous development of information technology, people's demand for information is rapidly increasing, and the amount of information transmitted is growing exponentially. The growth of communication-related services also increases the demand for bandwidth. Currently, the rapid growth of information capacity far outpaces the development of electronic communication, and bandwidth limitations have emerged due to the constraints of electronic technology. Furthermore, the exchange of information at network nodes in current communication systems involves "electro-optical" and "optical-electrical" conversions, leading to the so-called "electronic bottleneck." Therefore, establishing an all-optical information system can avoid the shortcomings of electronic technology, thereby achieving a significant increase in communication capacity and speed.

[0003] For all-optical information systems, high-quality tunable microwave sources play a crucial role, and optical technology has significant advantages in achieving high-quality tunable microwave sources. Tunable microwave sources based on optical technology can avoid the "electro-optical" conversion at the source node in the system, which can greatly improve the transmission rate and capacity. Therefore, it is very important to make full use of the bandwidth advantage of optical technology to achieve high-frequency tunable microwave signal generation and control.

[0004] Currently, methods for generating microwave signals based on optical techniques mainly include external modulation using intensity or phase modulators, photoelectric oscillators, and injection-locked methods. Among these methods, external modulation and injection-locked methods produce microwave signals with high phase noise and low conversion efficiency. Photoelectric oscillator generation methods are relatively complex in achieving broadband tuning. Therefore, generating microwave signals with low phase noise, wide-range tuning capability, and high stability based on optical technology is of great importance.

[0005] Stimulated Brillouin scattering (SBS) is a nonlinear interaction between incident pump light and Stokes light through phonons in an optical fiber medium. The pump light wave generates an acoustic wave through electrostriction, which in turn modulates the refractive index of the medium. The refractive index grating formed by the refractive index modulation scatters the pump wave through Bragg diffraction, causing a frequency shift in the pump light. This process can be viewed as one pump photon generating one Stokes photon and one acoustic phonon, with energy and momentum conserved. SBS has been widely applied in long-distance sensing, Brillouin lasers, and optical signal processing. Brillouin lasers, in particular, have attracted considerable attention due to their extremely low phase noise and high stability. However, the large threshold of SBS results in relatively large sizes for lasers based on it, with fiber ring cavity-based Brillouin lasers being a prime example. While Brillouin microcavity lasers can significantly reduce device size while maintaining a high quality factor, these devices are highly susceptible to external environmental factors, severely limiting the tunability of Brillouin lasers. Summary of the Invention

[0006] To address the aforementioned problems and shortcomings, and to solve the issues of high phase noise, low conversion efficiency, and relatively complex tuning in existing optical-based microwave signal sources, this invention provides an electrically controlled signal source based on a D-shaped multimode optical fiber and an integrated graphene gate modulation structure.

[0007] An electrically controlled signal source made of D-shaped multimode fiber is composed of D-shaped multimode fiber, graphene gate modulation structure and double-ended reflective surface.

[0008] The core diameter of the D-shaped multimode fiber is 50-100 micrometers, and the fiber diameter is 125-250 micrometers. The polishing area of ​​the D-shaped multimode fiber is located at the center of the two high reflectivity films, and the length of the polishing area is 0.5-2 millimeters. The distance between the plane of the polishing area and the axial center of the fiber is less than the fiber core radius by 0.5-2 micrometers.

[0009] The dual-end reflective surfaces are two high-reflectivity films disposed at both ends of the D-shaped multimode fiber, spaced 2.5 cm to 10 cm apart. These high-reflectivity films have a reflectivity greater than 99.99% within the 1540 nm to 1560 nm range, resulting in a quality factor greater than 10 for the D-shaped multimode fiber and the dual-end reflective surfaces. 6 D-shaped multimode fiber microcavity.

[0010] The graphene gate control structure comprises a gold-graphene-gold planar heterojunction, and an alumina film and a graphene film stacked sequentially thereon. The two gold electrodes of the gold-graphene-gold heterojunction are distributed on both sides of the fiber core axis, with a width of less than 2 micrometers. The length of the gold-graphene-gold heterojunction along the fiber axis is 200-500 micrometers, and its width is 5-10 micrometers greater than the diameter of the multimode fiber core. The alumina film completely covers the graphene film in the gold-graphene-gold heterojunction that is not covered by the gold electrodes, while the graphene film on top of the alumina film completely covers the alumina film. The top graphene film serves as the gate, and the alumina film serves as the dielectric layer, with a thickness of 200-500 nanometers. The gold electrodes at both ends of the graphene in the gold-graphene-gold heterojunction serve as the source and drain, respectively.

[0011] Furthermore, the high reflectivity film is composed of alternating layers of high refractive index medium and low refractive index medium, wherein the low refractive index medium layer is SiO2 and the high refractive index medium layer is TiO2, and the total number of medium layers is ≥20.

[0012] Furthermore, the high-reflectivity film is prepared in a ceramic insert, which facilitates easy connection with external components.

[0013] Furthermore, by adjusting the pump frequency and pump power of the external narrow-linewidth laser input to the D-shaped multimode fiber microcavity, and simultaneously by controlling the Fermi level of the graphene film (the gate of the device) through an applied voltage, the refractive index of the D-shaped multimode fiber microcavity is altered, thereby achieving precise control of the overall device's output microwave signal frequency. The narrow-linewidth laser has a linewidth <100kHz, a tuning range of 1545nm-1555nm, and a tuning accuracy of 0.001nm.

[0014] The working mechanism of this invention is as follows: by precisely adjusting the pump frequency and pump power of the D-shaped multimode fiber microcavity input to the narrow-linewidth laser, the device outputs a Brillouin laser of approximately 11 GHz. Due to the multimode nature of the microcavity itself, the frequency difference between the corresponding Stokes signal and the input pump is not limited by the microcavity's FSR, thus enabling the output of the corresponding microwave signal. Simultaneously, the graphene gate control structure integrated in the polished surface region can change the refractive index of the composite microcavity through an applied voltage, thereby achieving precise control of the output microwave signal frequency. This is because the down-conversion shift of the pump light signal by stimulated Brillouin scattering is determined by the nonlinear medium. This invention uses common optical fibers to fabricate the microcavity, resulting in a Brillouin frequency shift of approximately 11 GHz, which is related to the composite refractive index of the device. Therefore, this invention designs a graphene gate control structure integrated on the polished surface of the D-shaped multimode fiber microcavity, which can achieve frequency control of the output microwave signal through an applied voltage.

[0015] In summary, this invention combines optical engineering, communication engineering, metamaterials, and micro / nano fabrication. By integrating a graphene gate modulation structure onto a D-shaped fiber microcavity, it achieves microwave signal output and precise modulation at approximately 11 GHz. Compared to other optical-based microwave signal sources, this invention features small device size and high integration; it employs an all-fiber structure, enabling convenient access to fiber optic information transmission networks; and it effectively overcomes drawbacks such as high phase noise, complex structure, and narrow tuning range. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the graphene gate modulation structure of the present invention;

[0017] Figure 2 This is a schematic diagram of the structure of the D-shaped multimode fiber microcavity in the embodiment.

[0018] Figure 3 This is a schematic diagram of the testing system of the present invention;

[0019] Figure 4 This is a schematic diagram illustrating the variation of the Brillouin signal beat frequency with the applied voltage in the embodiment.

[0020] Figure reference numerals: 1-Device gate metal lead, 2-Dielectric layer, 3-Device source / drain, 4-Top layer graphene film (device gate), 5-Heterojunction graphene film, 6-Fiber core, 7-Ceramic ferrule coated with high reflectivity film, 8-Narrow linewidth laser, 9-Polarization controller, 10-Fiber isolator, 11-D-shaped multimode fiber microcavity, 12-Voltage regulator, 13-Fiber attenuator, 14-Photodetector, 15-Spectrum analyzer. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0022] This embodiment provides an electrically controlled signal source based on a D-shaped multimode fiber microcavity with an integrated graphene gate modulation structure. It leverages the high quality factor of the multimode fiber microcavity and the excitation of Brillouin lasers due to the multimode characteristics, and through a designed graphene-based gate modulation structure, it achieves precise and wide-range modulation of the Brillouin laser. The electrically controlled signal source structure of the D-shaped multimode fiber microcavity with integrated graphene gate modulation structure is as follows: Figure 1 As shown, it includes: device gate metal lead 1, dielectric layer 2 (alumina thin film), device source / drain 3, top graphene film (device gate) 4, heterojunction graphene film 5, optical fiber core 6, and ceramic ferrule coated with high reflectivity film 7.

[0023] The heterojunction graphene film 5, the top graphene film (device gate) 4, the device source / drain 3, and the dielectric layer 2 constitute a graphene-based gate control structure. The electrically controlled microwave source consists of the graphene gate control structure and ceramic ferrules coated with high-reflectivity films on both sides of the D-shaped fiber polishing region. The D-shaped multimode fiber is fabricated using a fiber polishing system. The length of the D-shaped polishing region of the obtained D-shaped multimode fiber is 0.5-2 mm, the distance between the plane of the polishing region and the axial center of the fiber is less than the fiber core radius of 0.5-2 micrometers, the distance between the ceramic ferrules coated with high-reflectivity films on both sides of the D-shaped polishing region is 2.5 cm-10 cm, and the quality factor of the D-shaped multimode fiber microcavity composed of the D-shaped multimode fiber and the double-ended high-reflectivity films is greater than 10. 6 The graphene gate control structure is arranged along the axial center of the D-shaped polished region. This structure consists of a heterojunction graphene film 5, a top graphene film (device gate) 4, a device source / drain 3, and an alumina dielectric layer 2. The two gold electrodes of the gold-graphene-gold heterojunction are distributed on both sides of the fiber core along the axial direction. The width of the two gold electrodes is less than 2 micrometers. The length of the gold-graphene-gold heterojunction along the fiber axial direction is 200-500 micrometers, and the width is 5-10 micrometers greater than the diameter of the multimode fiber core. The alumina film completely covers the graphene film in the gold-graphene-gold heterojunction that is not covered by the gold electrodes, while the top graphene film of the alumina film completely covers the alumina film. The top graphene film serves as the gate, and the alumina film serves as the dielectric layer with a thickness of 200-500 nanometers. The gold electrodes at both ends of the graphene in the gold-graphene-gold heterojunction serve as the source and drain, respectively.

[0024] Specifically: In this embodiment, the length of the D-shaped polished region of the obtained D-shaped multimode fiber is 1 mm, the distance between the polished region plane and the axial center of the fiber is less than the fiber core radius of 1.5 micrometers, the distance between the two reflecting surfaces on both sides of the D-shaped polished region is 5 cm, and the quality factor of the D-shaped multimode fiber microcavity composed of the D-shaped multimode fiber and the double-ended high-reflection film is 5*10. 6 In this structure, the gold electrodes of the gold-graphene-gold heterojunction are distributed on both sides along the optical fiber core axis. The graphene is located directly above the exposed optical fiber core in the polished area. The central graphene is in contact with the gold electrodes on both sides, with a distance of 5 micrometers between the two gold electrodes. A single gold-graphene-gold heterojunction has a length of 300 micrometers and a width of 40 micrometers along the optical fiber axis. The alumina film is 300 nanometers thick and covers the entire D-shaped polished area. The top layer of graphene is located directly above the dielectric layer of the alumina film and completely covers the alumina film. A voltage is applied through metal leads.

[0025] The D-shaped multimode fiber integrating the graphene gate control structure is placed on a temperature controller, with a stable temperature of 30 degrees Celsius to minimize environmental temperature instability. The tunable narrow-linewidth laser 8 serves as the pump light input. The pump light signal passes through a polarization controller 9 and an optical fiber isolator 10, entering the microcavity of the D-shaped multimode fiber integrating the graphene gate control structure and generating a microwave signal with a frequency of approximately 11 GHz. This microwave signal is coupled into the optical fiber via a ceramic ferrule 7 and transmitted to an optical fiber attenuator 13. It is then collected by a spectrum analyzer 15 via a photodetector 14. At this point, precise control of the output microwave signal frequency can be achieved by applying a voltage to the gate control structure through the metal lead 1 connected to the top graphene film 4.

[0026] Specifically, in this embodiment, the sweep frequency range of the tunable narrow linewidth laser is 1552-1553 nanometers, the laser linewidth is 10 kHz, and the minimum scanning accuracy is 50 Hz. Selecting these parameters can significantly improve the repeatability and stability of microwave signals.

[0027] In this embodiment, when the input pump wavelength is 1552.2 nm, a first-order Brillouin signal can be excited in the D-shaped multimode fiber microcavity 11 with an integrated graphene gate modulation structure. The output microwave signal is observed to be at 11.1 GHz using a spectrum analyzer. To adjust the output microwave signal, a bias voltage of 0.02 V is applied to the source / drain 3 of the device, and a voltage of 0 V-1 V is applied to the gate 1 of the device. This allows the range of the device's output microwave signal to be changed from 11.1 GHz to 11.2 GHz. (See diagram) Figure 4 The figure shows the change in the output signal spectrum when a voltage of 0V-1V (interval of 0.25V) is applied through the device gate metal lead 1.

[0028] As can be seen from the above embodiments, this invention significantly reduces the device size and lowers the threshold of the stimulated Brillouin process by integrating a graphene gate modulation structure onto a D-shaped multimode fiber microcavity. By adjusting the pump frequency and pump power of an external narrow-linewidth laser input, and simultaneously by controlling the graphene Fermi level through an applied voltage to change the refractive index of the D-shaped multimode fiber microcavity, efficient control of the output microwave signal can be achieved while significantly reducing the stimulated Brillouin excitation threshold, realizing microwave signal output and precise control at approximately 11 GHz. Compared with other optical-based microwave signal sources, this invention has advantages such as small device size, high integration, an all-fiber structure for easy access to fiber optic information transmission networks, and effectively overcomes drawbacks such as high phase noise, complex structure, and narrow tuning range.

Claims

1. An electrically controlled signal source for a D-shaped multimode optical fiber, characterized in that: It consists of a D-shaped multimode optical fiber, a graphene gate modulation structure, and a double-ended reflective surface; The core diameter of the D-shaped multimode fiber is 50-100 micrometers, and the fiber diameter is 125-250 micrometers. The polishing area of ​​the D-shaped multimode fiber is located at the center of the two high reflectivity films. The length of the polishing area is 0.5-2 millimeters, and the distance between the plane of the polishing area and the axial center of the fiber is less than the fiber core radius of 0.5-2 micrometers. The dual-end reflective surfaces are two high-reflectivity films disposed at both ends of the D-shaped multimode fiber, spaced 2.5 cm to 10 cm apart. These high-reflectivity films have a reflectivity greater than 99.99% within the 1540 nm to 1560 nm range, resulting in a quality factor greater than 10 for the D-shaped multimode fiber and the dual-end reflective surfaces. 6 D-shaped multimode fiber microcavity; The graphene gate control structure consists of a gold-graphene-gold planar heterojunction, and an alumina film and a graphene film stacked thereon. The two gold electrodes of the gold-graphene-gold heterojunction are distributed on both sides of the fiber core axis, and the width of the two gold electrodes is less than 2 micrometers. The graphene is located directly above the fiber core exposed in the polishing area. The length of the gold-graphene-gold heterojunction along the fiber axis is 200-500 micrometers, and the width is 5-10 micrometers greater than the diameter of the multimode fiber core. The alumina film completely covers the graphene film in the gold-graphene-gold heterojunction that is not covered by the gold electrodes, while the top graphene film completely covers the alumina film. The top graphene film serves as the gate, and the alumina film serves as the dielectric layer with a thickness of 200-500 nanometers. The gold electrodes at both ends of the graphene in the gold-graphene-gold heterojunction serve as the source and drain, respectively.

2. The electrically controlled signal source of the D-shaped multimode optical fiber as described in claim 1, characterized in that: The high-reflectivity film is composed of alternating layers of high-refractive-index and low-refractive-index dielectric materials. The low-refractive-index dielectric layer is SiO2, and the high-refractive-index dielectric layer is TiO2. The total number of dielectric layers is ≥20.

3. The electrically controlled signal source of the D-shaped multimode optical fiber as described in claim 1, characterized in that: The high-reflectivity film is prepared in a ceramic insert and is connected to an external component through the ceramic insert.

4. The electrically controlled signal source of the D-shaped multimode optical fiber as described in claim 1, characterized in that: By adjusting the pump frequency and pump power of an external narrow-linewidth laser input to a D-shaped multimode fiber microcavity, and simultaneously controlling the Fermi level of the graphene by applying an external voltage to the top graphene film, the refractive index of the D-shaped multimode fiber microcavity is changed, thereby achieving precise control of the output microwave signal frequency of the overall device. The pump wavelength of the narrow-linewidth laser strictly corresponds to the reflection wavelength of the double-ended reflector, with a linewidth < 100 kHz, a tuning range of 1545 nm to 1555 nm, and a tuning accuracy of 0.001 nm.

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