Ultra-bandwidth white noise source based on chaotic micro-ring optical frequency combs

Abstract

The present invention relates to the technical field of communication, and particularly relates to an on-chip ultra-wideband white noise generation method based on chaotic micro-ring optical frequency combs. An implementation of the method comprises semiconductor lasers, micro-ring resonant cavities, and a photoelectric detector, and is characterized in that the semiconductor lasers, the micro-ring resonant cavities, and the photoelectric detector are all integrated on a same chip substrate. Continuous light outputted from the semiconductor lasers is injected into the micro-ring resonant cavities, so that four-wave mixing, self-phase modulation, cross-phase modulation, and dispersion jointly occur, and then after the continuous light is outputted via straight-through ends of the micro-ring resonant cavities, equidistant chaotic optical frequency combs are generated, thereby achieving high-bandwidth noise signals via heterodyning of multiple chaotic optical frequency combs. Compared with existing noise sources, the present invention has the advantages of structural simplicity, compact size, low power consumption, high stability, and expandable bandwidth.

Description

An ultra-wideband white noise source based on chaotic micro-ring optical frequency comb Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to an ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb. Background Art

[0002] Noise is an unavoidable and addressable problem in most systems. Early research efforts focused on reducing or eliminating noise. However, as research progressed, it became increasingly clear that noise significantly impacts the interference immunity of test instruments and the performance evaluation of communication systems. By inputting precisely known noise into the device, module, or system under test, it is possible to measure receiver sensitivity, evaluate antenna performance, analyze amplifier parameters, calibrate radiometer output, and verify radar interference immunity. Therefore, noise sources are specialized scientific instruments with important applications in numerous fields, including communications, remote sensing, military affairs, and astronomy. Generating high-bandwidth, uniform spectral density, and easy-to-implement noise sources has become a crucial area of ​​research.

[0003] Currently, most noise sources are based on random processes in electronic devices. A typical approach is to control and amplify the noise in physical devices such as resistors, avalanche diodes, and field-effect transistors to generate Gaussian white noise. However, this method can only generate noise with a bandwidth on the order of MHz. Furthermore, these noise sources often require an electrical amplifier to amplify the output noise, making the entire system more complex. Furthermore, as the bandwidth increases, the output noise flatness deteriorates.

[0004] Noise generation devices based on photonics can break through the bottleneck of electronic bandwidth and thus achieve broadband noise signal generation. Typical optical noise includes laser phase noise, amplified spontaneous emission noise, etc. In addition, chaotic lasers can also be used as noise sources due to their high bandwidth, large amplitude, and noise-like characteristics. For example, the phase noise based on vertical cavity surface emitting lasers can generate optical noise signals of nearly 1 GHz [Physical Review E, 2010, 81 (5), 051137]; the use of superluminescent diodes combined with photoelectric conversion devices can also generate broadband noise signals with a bandwidth of about 12 GHz [Optics Letters, 2011, 36 (6), 1020-1022]; the use of chaotic lasers generated by two semiconductor lasers with external feedback for optical heterodyning can generate noise signals with a bandwidth of 16.7 GHz [Optics Letters, 2017, 25 (4), 3153-3164]. Compared with the noise signals generated by electronic technology, the noise signal bandwidth obtained by noise sources based on photonics has been greatly enhanced.

[0005] However, most of these devices are constructed from multiple discrete optical components, resulting in complex structures, large size, susceptibility to environmental influences, and poor stability. The resulting bandwidth is limited to only a dozen Gigabits, and the noise bandwidth is not scalable, which limits the application of these noise sources. Therefore, it is crucial to develop an on-chip white noise source that is high-bandwidth, scalable, has uniform spectral density, is highly stable, and is easy to implement.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to avoid the shortcomings of the prior art and provide an on-chip ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb.

[0008] The purpose of the present invention can be achieved by adopting the following technical measures to design an on-chip ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb, including:

[0009] The chip substrate, semiconductor laser array, microring resonator array, photodetector, and optical waveguide are integrated on the same chip substrate, and the devices are connected by optical waveguides. Laser light from the semiconductor laser is transmitted through the optical waveguide and coupled into the microring resonator. Due to modulation instabilities and high-order nonlinear effects within the microring, a chaotic optical frequency comb is generated after exiting the microring. This chaotic optical frequency comb appears as an evenly spaced frequency comb in the optical frequency domain and as a randomly fluctuating chaotic signal in the time domain. By adjusting the radius of the microring resonator, the free spectral range of the generated chaotic optical frequency comb is varied, increasing the free spectral range of the generated chaotic optical frequency comb. This comb is ultimately coupled to the same waveguide, generating beat frequencies. The beat frequencies between the modes generate spectra of different frequency bands, which are then spliced ​​and superimposed. The resulting spectrum is then converted to ultra-wideband white noise via photoelectric conversion in the photodetector.

[0010] Among them, semiconductor lasers, microring resonators, optical waveguides, and photodetectors are integrated onto the same substrate by bonding, realizing a hybrid integrated on-chip white noise source structure based on a chaotic microring optical frequency comb.

[0011] The center wavelength of the laser output from the semiconductor laser is consistent. The line width of the laser output from the semiconductor laser must be smaller than the line width of the resonance peak in the microring resonator to ensure that the pump light can be coupled into the ring waveguide of the microring resonator. In addition, the center wavelength of the laser output light must be smaller than the wavelength corresponding to the nearest resonance frequency, that is, located at the blue detuning point of the resonance peak of the microring resonator.

[0012] The microring resonator includes any of the following structures: all-pass, up-down, non-concentric, and racetrack. The ring waveguide and straight waveguide materials of the microring resonator are silicon, lithium niobate, and high-refractive-index-difference doped glass. The quality factor of the selected microring resonator is Q>10 5.

[0013] Among them, the nonlinear effects in the microring resonator include four-wave mixing, self-phase modulation, cross-phase modulation, etc.

[0014] The free spectral range of the chaotic microring optical frequency comb can be achieved by changing the circumference of the microring resonator, and the radius of the microring resonator increases in sequence. The free spectral range of the chaotic microring optical frequency comb is calculated by the following formula: Where Δλ represents the free spectral range of the microring resonator, λ is the central wavelength of the laser output light, and n g is the group refractive index of the microring resonator waveguide, and L is the circumference of the microring resonator.

[0015] Chaotic microring optical frequency combs with different free spectral ranges are coupled to the same waveguide. Beating between these modes generates white noise with corresponding center frequencies. The center frequency of this white noise is determined by the frequency difference between the corresponding modes. The white noises with different center frequencies are combined to produce ultra-wideband white noise. Furthermore, by increasing the number of channels and teeth in the chaotic microring optical frequency comb, more beats between the modes are generated, ultimately increasing the white noise bandwidth.

[0016] The advantages and positive effects of realizing the on-chip ultra-wideband white noise source based on the chaotic micro-ring optical frequency comb provided by the present invention are:

[0017] 1. This technical solution provides a hybrid integrated on-chip white noise source. By introducing a chaotic microring optical frequency comb, the microring resonator, semiconductor laser, optical waveguide, and photodetector are integrated on the same chip and connected by optical waveguides. Compared with discrete technical solutions, it has a simple structure and the advantages of smaller size, low power consumption, and high stability.

[0018] 2. This technical solution uses optical methods to achieve the generation of broadband white noise, and through the method of photoelectric conversion, it effectively avoids the bottleneck of electronic bandwidth. By increasing the number of channels of the chaotic micro-ring optical frequency comb and the number of comb teeth of a single channel optical frequency comb, it can achieve the generation of white noise with higher bandwidth, which is scalable. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic structural diagram of an on-chip ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb provided by the present invention.

[0020] FIG2 is a schematic diagram of a single-channel chaotic optical frequency comb spectrum of an ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb provided by the present invention.

[0021] FIG3 is a schematic diagram of the spectrum of a single mode of a ten-channel chaotic optical frequency comb of an ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb provided by the present invention.

[0022] FIG4 is a schematic diagram of the power spectrum results of an on-chip ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb provided by the present invention. DETAILED DESCRIPTION

[0023] The technical measures of the present invention are further described in detail below in conjunction with specific embodiments so that those skilled in the art can have a clearer understanding of the purposes, advantages, and technical measures of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the practical cases in the present invention, any other practical examples obtained by other technicians in this field without performing creative work can be classified as protected by the present invention.

[0024] As shown in FIG1 , the structure of an ultra-wideband white noise source based on a chaotic microring optical frequency comb provided by the present invention includes: a chip substrate 1 , a semiconductor laser 2 , a microring resonant cavity 3 , an optical waveguide 4 , and a photodetector 5 .

[0025] The semiconductor laser 2, microring resonator 3, optical waveguide 4, and photodetector 5 are all integrated on a chip substrate 1. Laser light emitted by the semiconductor laser 2 is coupled into the microring resonator 3 as pump light, generating a microring chaotic comb due to modulation instabilities and high-order nonlinear effects within the microring. All components are connected via the optical waveguide 4 to enable transmission of optical signals throughout the entire optical path. The microring resonator 3 generates m chaotic microring optical frequency combs with different free spectral ranges, which are then combined into one channel through waveguide transmission. Beating frequencies between corresponding longitudinal modes produce spectra with different frequency bands, with the intervals between the comb teeth determined by the frequency difference between the comb teeth. By appropriately selecting the optical frequency difference between the frequency bands, the resulting frequency bands with different center frequencies are spliced ​​together, and the photodetector 5 ultimately outputs ultra-wideband white noise.

[0026] The pump light of the chaotic micro-ring optical frequency comb is set to 0 mode, and the two adjacent modes of the pump light are defined as +1 mode and -1 mode respectively. Taking the beat frequency between the single modes (+1 mode) of the two chaotic micro-ring optical frequency combs as an example, assuming that the center wavelengths of the two modes are λ1 and λ2 respectively, the beat frequency between the two modes will generate white noise in two frequency bands. Among them, the center frequency of one frequency band is at the DC component, and the center frequency of the other frequency band is f th It is determined by the optical frequency difference of the two modes and can be expressed as f th =c / λ1-c / λ2. The beat frequency effect between modes corresponds to the convolution in the principle. In principle, the photocurrent i(t) of the photodetector can be expressed as the convolution of the detector response function r(t) and the two laser light fields E1(t) and E2(t): Therefore, the power spectrum S(f) of the detector output electrical signal is expressed as: S(f) = |F{i(t)}| 2 =|R(f)|2 ×[S(ν1)*S(ν1)+S(ν2)*S(ν2)+2S(ν1)*S(ν2)], where S(ν1) represents the spectral density of the first mode and S(v2) represents the spectral density of the second mode. v1 and v2 are the center frequencies of the two modes, respectively.

[0027] Specifically, the present invention uses a silicon photonic chip as a substrate and integrates a semiconductor laser, a microring resonator, an optical waveguide, and a photodetector on the chip by bonding. The microring resonator adopts an all-through structure and is made of high-refractive-index-difference doped glass. The Q value of the microring is in the range of 2×10 6 ~3×10 6 . As shown in Figure 2, the chaotic microring optical frequency comb is a wide-spectrum light source composed of a series of discrete, equally spaced laser modes. It contains hundreds of modes in the range of 1500nm to 1600nm, and the interval between adjacent longitudinal modes is about 0.4nm. The center wavelength of each longitudinal mode (except the pump light) of each chaotic microring optical frequency comb can be adjusted by changing the radius of the microring resonant cavity. After the m chaotic microring optical frequency combs with different center wavelengths are coupled to one waveguide through m waveguides, the beat effect between the modes will produce a spectrum with the corresponding center frequency. The center frequency of the spectrum is determined by the frequency difference between the modes. The generated spectra are spliced ​​together to eventually produce ultra-wideband white noise.

[0028] Specifically, we take a ten-way chaotic microring optical frequency comb as an example. The center wavelength of the semiconductor laser output is 1553nm. By changing the radius of the microring resonant cavity, the free spectrum range of the ten-way chaotic microring optical frequency comb is adjusted to 41GHz, 42GHz, ..., 50GHz. As shown in Figure 3, the first mode (λ1, λ2, ..., λ 10 ) have a frequency difference of 1 GHz. After the beat frequencies between the ten modes pass through the photodetector, they can generate white noise in ten frequency bands. The center frequency of the frequency band increases by 1 GHz, and a white noise with a bandwidth of 10 GHz (10×1 GHz) can be generated. The second mode (λ 11 ,λ 12 、···、λ 20 ) are all 2GHz, and the center frequency of the corresponding frequency band increases by 2GHz. The frequency of the nth mode is (λ 10n+1 ,λ 10n+2 、···、λ 10n+10) are all n GHz, and the center frequencies of the corresponding generated frequency bands are sequentially increased by n GHz. Bands with different center frequencies are spliced ​​together to ultimately generate broadband white noise. Because the chaotic microring optical frequency comb covers a range of several hundred nanometers, n can reach over 100. By increasing the number of paths (m) and teeth (n) in the chaotic optical frequency comb, even wider bandwidth white noise can be generated, as shown in Figure 4.

[0029] It is particularly important to note that the disclosed on-chip ultra-wideband white noise source based on a chaotic microring optical frequency comb utilizes the beat action of multiple chaotic microring optical frequency combs and generates white noise through photoelectric conversion. The spectral range of the chaotic microring optical frequency comb can reach hundreds of nanometers and contain hundreds of modes. Therefore, the beat action of multiple chaotic microring optical frequency combs can achieve broadband white noise. By introducing a chaotic microring optical frequency comb and integrating the microring resonator, semiconductor laser, waveguide, and photodetector on a single chip and connecting them via optical waveguides, an on-chip white noise source with a compact structure, high integration, and small size is achieved. Unlike existing technologies, this structure is relatively simple, offering the advantages of high stability and low power consumption. Furthermore, by increasing the number of chaotic microring optical frequency comb channels and the number of teeth in a single channel, the present invention can significantly increase the bandwidth of generated white noise, demonstrating scalability.

[0030] The above are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An ultra-wideband white noise source based on a chaotic micro-ring optical frequency comb, comprising m semiconductor lasers, a micro-ring resonator with the same number as the semiconductor lasers, and a photodetector; wherein: Semiconductor lasers, micro-ring resonators, and photodetectors are all integrated on the same chip substrate, and the devices are connected through optical waveguides; The continuous light output by the semiconductor laser is transmitted through the optical waveguide and then injected into the micro-ring resonant cavity. A series of nonlinear effects and dispersion will occur in the micro-ring resonant cavity, resulting in a significant broadening of the spectrum. A chaotic optical frequency comb with equal frequency spacing is output through the direct port of the microring resonator. The radius of the microring resonator is designed to generate chaotic optical frequency combs with different free spectrum ranges. The chaotic optical frequency comb generated by each microring resonator is coupled to a waveguide and then input into a photodetector, and finally an ultra-wideband white noise is output from the photodetector.

2. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: The central wavelength of the laser output by the semiconductor laser is located at the blue detuning point of the resonance peak of the microring resonator, that is, the pump wavelength is smaller than the wavelength corresponding to the nearest resonance frequency.

3. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: The laser line width output by the semiconductor laser is smaller than the line width of the resonance peak of the microring resonator.

4. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: The structure of the micro-ring resonant cavity can be an all-through type, an up-down path type, a non-concentric circle type or a racetrack type.

5. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: When the laser output from the semiconductor laser is injected into the microring resonator, four-wave mixing, self-phase modulation, cross-phase modulation and dispersion will occur.

6. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: The free spectral range of the chaotic optical frequency comb can be controlled by changing the radius of the microring resonant cavity, and the free spectral range of the generated multi-path chaotic optical frequency comb increases successively, and the frequency detuning between the corresponding modes of the chaotic optical frequency comb will gradually increase; the free spectral range of the chaotic microring optical frequency comb is calculated by the following formula: Where Δλ represents the free spectral range of the microring resonator, λ is the central wavelength of the laser output light, and n g is the group refractive index of the microring resonator waveguide, and L is the circumference of the microring resonator.

7. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: After multiple chaotic optical frequency combs are aggregated into one waveguide, the beat frequencies of modes with different frequency detuning produce white noise with corresponding center frequencies. The generated spectra can be spliced ​​together to finally output ultra-wideband white noise.

8. The ultra-wideband white noise source based on chaotic micro-ring optical frequency comb according to claim 1, characterized in that: The number of paths and teeth of the chaotic optical frequency comb is increased to achieve the generation of white noise with a higher bandwidth.

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