A terahertz waveband optical comb frequency conversion device

Abstract

This invention discloses a terahertz band optical comb frequency converter, belonging to the field of frequency conversion technology. The frequency converter includes an optical fiber interface, an optical fiber focusing lens, a frequency converter chip, a hemispherical silicon lens, and an electrical interface. The frequency converter chip includes antenna electrodes, a photoconductor, and an InP substrate. An external 1560nm femtosecond optical comb signal sequentially passes through the optical fiber interface and the optical fiber focusing lens onto the frequency converter chip; simultaneously, an external terahertz signal under test passes through the hemispherical silicon lens onto the frequency converter chip. The antenna electrodes and the electrical interface are connected by a circuit. This invention offers a wider response bandwidth: the response bandwidth is increased through the design of internal defects in the photoconductor; higher sensitivity: the sensitivity of the frequency converter is improved through antimony doping and tungsten oxide thin film design; and higher reliability: the tungsten oxide thin film design and special protection design of the antenna electrodes can respectively avoid damage to the frequency converter caused by optical and electrical signals, thereby improving reliability and service life.

Description

Technical Field

[0001] This invention belongs to the field of frequency conversion technology, specifically relating to a terahertz band optical comb frequency conversion device. Background Technology

[0002] Frequency is a fundamental parameter of terahertz electromagnetic waves. Researching precise measurement methods for terahertz frequencies and establishing terahertz frequency metrological standards is of great significance for parameter calibration of terahertz instruments and equipment, as well as applications in fields such as 6G communication. Taking terahertz instruments and equipment as an example, there are over a hundred institutions worldwide engaged in the research and development of terahertz instruments and equipment. my country imports a large number of terahertz radiation sources, power meters, spectrometers, and other instruments and equipment annually, and domestic manufacturers have also launched various types of terahertz instruments and equipment. On the one hand, the frequency parameters of terahertz sources need to be accurately calibrated to evaluate their performance; on the other hand, the values ​​of terahertz frequency measuring instruments need to be traceable. Establishing terahertz frequency metrological standards can effectively solve the metrological needs of terahertz instruments and equipment. Due to its high uncertainty level and stable values, frequency metrological methods based on terahertz band optical combs have attracted much attention.

[0003] The frequency converter is the core of a terahertz optical comb device. Its working principle is as follows: a near-infrared optical comb signal with a center wavelength of 1560nm is incident on the frequency converter. Different spectral components in the near-infrared optical comb signal undergo a difference frequency process in the photoconductor within the frequency converter. During this process, the carrier envelope phase offset frequency f0 of the near-infrared optical comb is mutually canceled out, simultaneously generating spectral components with frequencies in the terahertz band. These spectral components also possess the essential characteristics of an optical comb signal, such as equal comb tooth spacing, high accuracy, and high stability, thus forming a terahertz optical comb.

[0004] Existing implementation schemes for frequency converters used in terahertz optical combs are generally as follows: Figure 1 As shown, it mainly consists of a frequency conversion chip (including antenna electrodes, InGaAs / InAlAs photoconductors, and InP substrate), a hemispherical silicon lens, and an electrical interface.

[0005] The working process of this scheme is as follows: A femtosecond optical comb pulse in the 1560nm band is incident on an InP substrate frequency converter chip coated with metal antenna electrodes. Different spectral components in the near-infrared optical comb signal generate a terahertz optical comb signal under the difference frequency action of the photoconductor in the chip. Simultaneously, the downconverter device is also equipped with an electrical interface, which is connected to the antenna electrodes of the frequency converter chip. This interface is used to output the electrical signal generated after the measured terahertz signal beats the terahertz optical comb, and the frequency value of the measured terahertz signal is calculated by measuring the frequency of this electrical signal.

[0006] The existing technical solutions have the following drawbacks:

[0007] (1) Narrow response bandwidth. Existing solutions are limited by the properties of the photoconductor materials themselves, resulting in a narrow response bandwidth. The upper limit of the effective response frequency is generally 2.3 THz. Figure 3 As shown.

[0008] (2) Low sensitivity. The damage threshold of the frequency converter chip in the existing solution is low, resulting in low response sensitivity.

[0009] (3) Short lifespan. Because femtosecond lasers have a damaging effect on photoconductor materials, and photoconductor chips are easily damaged by external electrical signals, existing frequency converters have poor reliability and a lifespan of only a few months or even less. Summary of the Invention

[0010] In view of the above-mentioned technical problems in the prior art, the present invention proposes a terahertz band optical comb frequency converter device, which is reasonably designed, overcomes the shortcomings of the prior art, and has good performance.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A terahertz band optical comb frequency converter includes an optical fiber interface, an optical fiber focusing lens, a frequency converter chip, a hemispherical silicon lens, and an electrical interface.

[0013] The frequency converter chip includes a photoconductor, an antenna electrode, and an InP substrate; wherein, the photoconductor is an antimony-doped multilayer semiconductor with a sheet structure and a tungsten oxide thin film disposed on its upper surface; the antenna electrode is deposited on the upper surface of the tungsten oxide thin film and a protection circuit is disposed thereon; the InP substrate is located on the lower surface of the photoconductor.

[0014] An external 1560nm femtosecond optical comb signal is applied to the frequency converter chip sequentially through an optical fiber interface and an optical fiber focusing lens; at the same time, an external terahertz signal being measured is focused onto the frequency converter chip after being focused by a hemispherical silicon lens.

[0015] The antenna electrodes and electrical interface are connected via wiring.

[0016] The fiber optic focusing lens is configured to converge the 1560nm femtosecond optical comb pulse introduced by the fiber optic pigtail, and the focal point of the converged light spot acts on the antenna electrode gap on the photoconductor.

[0017] A photoconductor is configured to perform a difference frequency reaction on the 1560nm femtosecond optical comb teeth incident on it, thereby generating a terahertz optical comb signal.

[0018] Antenna electrodes are configured to protect the photoconductor and transmit electrical signals to the electrical interface;

[0019] An InP substrate is configured to provide a substrate for the epitaxial growth of a photoconductor; its thickness is 12 μm.

[0020] A hemispherical silicon lens is configured to focus the measured terahertz wave incident on the frequency converter into the electrode gap of the frequency converter.

[0021] The electrical interface is configured to output electrical signals transmitted from the antenna electrodes to it.

[0022] Preferably, the fiber optic focusing lens has a cylindrical sleeve structure with a diameter of 3.2 mm, a length of 10.5 mm, and a focal length of 2 mm, which can converge a light spot with a diameter of 50 μm.

[0023] Preferably, the antenna electrode is made of metal and includes a positive electrode and a negative electrode. The positive and negative electrodes are parallel electrodes and are both rectangular in structure with a length of 80 μm and a width of 2 μm. The electrode gap between the positive and negative electrodes is 5 μm. The protection circuit on the antenna electrode includes a diode, which is connected to the antenna electrode through a gold wire. The diode is a MURS260T3 with a rated output current of 2A and a junction temperature range of -65℃ to +175℃. This is used to prevent external electrical signals from damaging the frequency converter chip and to improve reliability and service life.

[0024] Preferably, the photoconductor is prepared by epitaxial growth of InGaAs and InAlAs materials with an overlap of 4% antimony. After epitaxial growth, defects are generated inside the photoconductor through a bombardment process to shorten the carrier lifetime in the photoconductor, thereby expanding the response bandwidth of the frequency converter. A thin film of tungsten oxide with a thickness of 285.13 nm is prepared between the photoconductor and the electrode. On the one hand, this can increase the transmittance of the 1560 nm femtosecond optical comb pulse and improve the detection sensitivity of the measured terahertz signal. On the other hand, the enhanced bonding between the photoconductor material and tungsten oxide can effectively reduce the instantaneous damage and cumulative effect of the femtosecond optical comb pulse on the photoconductor, thereby increasing the device lifespan.

[0025] Preferably, the hemispherical silicon lens is made of high-resistivity silicon material.

[0026] Preferably, the electrical interface is a BNC interface.

[0027] Preferably, a defect refers to a small hole of irregular shape or size.

[0028] A fiber optic pigtail introduces a femtosecond optical comb pulse in the 1560nm band into a fiber optic focusing mirror. After being focused by the fiber optic focusing mirror, the comb pulse is incident on a frequency conversion chip on an InP substrate coated with metal antenna electrodes. Different spectral components in the near-infrared optical comb signal output terahertz optical comb signals with equal comb tooth spacing under the difference frequency action of the photoconductor. At this time, the terahertz signal to be measured is incident on the frequency conversion chip and beats with the terahertz optical comb signal. The electrical signal generated under the beat frequency action is output through the antenna electrodes and electrical interface. The frequency value of the terahertz signal to be measured can be calculated by measuring the frequency of this electrical signal.

[0029] The beneficial technical effects of this invention are as follows:

[0030] (1) Wider response bandwidth: The response bandwidth is increased by designing internal defects in the photoconductor, and the response bandwidth of this frequency converter can reach around 6THz;

[0031] (2) Higher sensitivity: The sensitivity and signal-to-noise ratio of the frequency converter are improved by antimony doping and tungsten oxide thin film design, with a signal-to-noise ratio of up to 20dB at 4THz;

[0032] (3) Higher reliability: Through the design of tungsten oxide thin film and special protection design of antenna electrodes, damage to frequency converters caused by optical and electrical signals can be avoided, thereby improving reliability and service life. Attached Figure Description

[0033] Figure 1 A schematic diagram of an existing photoconductive antenna frequency converter implementation scheme;

[0034] Figure 2 A schematic diagram of a terahertz band optical comb frequency converter device;

[0035] Figure 3 This is a schematic diagram showing the response bandwidth test results of the existing solution;

[0036] Figure 4 This is a schematic diagram of the response spectrum test results of the frequency converter in this invention. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0038] This invention addresses the need for high-performance frequency converters in terahertz band optical comb signal generation, proposing an improved frequency converter. This device incorporates innovative design features, including doping of the photoconductor material and defect introduction, effectively improving the frequency converter's response bandwidth, sensitivity, and lifespan. Specific details are as follows: Figure 2 As shown.

[0039] The solution mainly consists of an optical fiber interface, an optical fiber focusing lens, a frequency conversion chip (including antenna electrodes, InGaAs / InAlAs defective photoconductors, and InP substrate), a super-hemispherical silicon lens, and an electrical interface.

[0040] The working process of the solution is as follows:

[0041] A fiber optic pigtail introduces a femtosecond optical comb pulse in the 1560nm band into a fiber optic focusing mirror. After being focused by the fiber optic focusing mirror, the comb pulse is incident on a frequency conversion chip on an InP substrate coated with metal antenna electrodes. Different spectral components in the near-infrared optical comb signal output terahertz optical comb signals with equal comb tooth spacing under the difference frequency action of the photoconductor. At this time, the terahertz signal to be measured is incident on the frequency conversion chip and beats with the terahertz optical comb signal. The electrical signal generated under the beat frequency action is output through the antenna electrodes and electrical interface. The frequency value of the terahertz signal to be measured can be calculated by measuring the frequency of this electrical signal.

[0042] The core characteristics of downconverters are:

[0043] (1) Fiber optic focusing lens. It has a cylindrical sleeve structure with a diameter of 3.2 mm, a length of 10.5 mm, and a focal length of 2 mm, which can focus a light spot with a diameter of 50 μm. It is used to focus the 1560 nm femtosecond optical comb pulse introduced by the fiber optic pigtail, and the focal point of the focused light spot acts on the photoconductor on the gap between the antenna electrodes.

[0044] (2) Antenna electrodes. The antenna electrodes are made of gold and have a parallel electrode structure. Both the positive and negative electrodes are rectangular with a length of 80 μm and a width of 2 μm. The gap between the positive and negative electrodes is 5 μm. A diode is designed on the electrode. The diode is the MURS260T3 produced by ON Semiconductor. The maximum reverse voltage is 600V, the rated output current is 2A, and the junction temperature range is -65℃ to +175℃. It is connected to the electrode with gold wire to ensure electrical connection and reliability.

[0045] (3) Photoconductor. The photoconductor is prepared by overlapping growth of InGaAs and InAlAs materials and doping them with 4% antimony. After epitaxial growth, defects are generated inside the material through a bombardment process. The introduction of these defects can effectively shorten the carrier lifetime of the material, thereby expanding the response bandwidth of the downconverter device. A thin film of tungsten oxide (n=1.3678) with a thickness of 285.13 nm is prepared between the photoconductor and the electrode. On the one hand, this can increase the transmittance of the 1560 nm femtosecond optical comb pulse and improve the detection sensitivity of the measured terahertz signal. On the other hand, the enhanced bonding between the photoconductor material and tungsten oxide can effectively reduce the instantaneous damage and cumulative effect of the femtosecond optical comb pulse on the photoconductor, thereby increasing the device lifespan.

[0046] (4) Hemispherical silicon lens. The hemispherical silicon lens is made of high-resistivity silicon material and is used to focus the incident terahertz wave into the electrode gap of the downconverter device.

[0047] (5) Electrical interface. The electrical interface is a BNC interface, which is connected to the antenna electrodes via a cable and is used to output the measured terahertz signal and the electrical signal generated by the terahertz optical comb beat frequency.

[0048] like Figure 4 As shown, this invention offers several advantages: First, it boasts a wider response bandwidth: the design of internal defects in the photoconductor increases the response bandwidth, achieving a bandwidth of approximately 6 THz. Second, it exhibits higher sensitivity: antimony doping and tungsten oxide thin film design enhance the sensitivity and signal-to-noise ratio of the frequency converter, achieving a signal-to-noise ratio as high as 20 dB at 4 THz. Third, it demonstrates higher reliability: the tungsten oxide thin film design and special protection design for the antenna electrodes prevent damage to the frequency converter from optical and electrical signals, thereby improving reliability and lifespan.

[0049] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A terahertz band optical comb frequency converter, characterized in that: Includes fiber optic interface, fiber optic focusing lens, frequency converter chip, hemispherical silicon lens and electrical interface; The frequency converter chip includes a photoconductor, an antenna electrode, and an InP substrate; wherein, the photoconductor is an antimony-doped multilayer semiconductor with a sheet structure and a tungsten oxide thin film disposed on its upper surface; the antenna electrode is deposited on the upper surface of the tungsten oxide thin film and a protection circuit is disposed thereon; the InP substrate is located on the lower surface of the photoconductor. An external 1560nm femtosecond optical comb signal is applied to the frequency converter chip sequentially through an optical fiber interface and an optical fiber focusing lens; at the same time, an external terahertz signal being measured is focused onto the frequency converter chip after being focused by a hemispherical silicon lens. The antenna electrodes and electrical interface are connected via wiring. The fiber optic focusing lens is configured to converge the 1560nm femtosecond optical comb pulse introduced by the fiber optic pigtail, and the focal point of the converged spot acts on the antenna electrode gap on the photoconductor. A photoconductor is configured to perform a difference frequency reaction on the 1560nm femtosecond optical comb teeth incident on it, thereby generating a terahertz optical comb signal. Antenna electrodes are configured to protect the photoconductor and transmit electrical signals to the electrical interface; An InP substrate is configured to provide a substrate for the epitaxial growth of a photoconductor; its thickness is 12 μm. A hemispherical silicon lens is configured to focus the measured terahertz wave incident on the frequency converter into the electrode gap of the frequency converter. The electrical interface is configured to output electrical signals transmitted from the antenna electrodes to it.

2. The terahertz band optical comb frequency converter according to claim 1, characterized in that: The fiber optic focusing lens has a cylindrical sleeve structure with a diameter of 3.2 mm, a length of 10.5 mm, and a focal length of 2 mm, which can converge a light spot with a diameter of 50 μm.

3. The terahertz band optical comb frequency converter according to claim 1, characterized in that: The antenna electrodes are made of metal and include a positive and a negative electrode. The positive and negative electrodes are parallel electrodes and are both rectangular in shape, with a length of 80μm and a width of 2μm. The electrode gap between the positive and negative electrodes is 5μm. The protection circuit on the antenna electrodes includes a diode, which is connected to the antenna electrodes through a gold wire. The diode is a MURS260T3 with a rated output current of 2A and a junction temperature range of -65℃ to +175℃, used to prevent external electrical signals from damaging the frequency converter chip.

4. The terahertz band optical comb frequency converter according to claim 1, characterized in that: The photoconductor is prepared by epitaxial growth of InGaAs and InAlAs materials with an overlap of 4% antimony. After the epitaxial growth is completed, defects are generated inside the material by bombardment. A thin film of tungsten oxide material with a thickness of 285.13 nm is prepared between the photoconductor and the electrode.

5. The terahertz band optical comb frequency converter according to claim 1, characterized in that: The super-hemispherical silicon lens is made of high-resistivity silicon material.

6. The terahertz band optical comb frequency converter according to claim 1, characterized in that: The electrical interface is a BNC interface.

7. The terahertz band optical comb frequency converter according to claim 1, characterized in that: Defects refer to small holes that are irregular in shape or size.

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