Optical system for realizing frequency sweeping by cyclic cascade broadening

Abstract

The present invention relates to the technical field of optics, and relates to an optical system for realizing frequency sweeping by cyclic cascade broadening. The optical system comprises an ultrafast pulse laser, couplers, a positive dispersion cyclic broadening system, a negative dispersion cyclic broadening system, a polarization-maintaining optical fiber, and a delay line; the ultrafast pulse laser is communicated with the couplers by means of the polarization-maintaining optical fiber; two couplers are provided; two ends of the positive dispersion cyclic broadening system are respectively communicated with the couplers by means of the polarization-maintaining optical fiber; two ends of the negative dispersion cyclic broadening system are respectively communicated with the couplers by means of the polarization-maintaining optical fiber; and the positions of the positive dispersion cyclic broadening system and the negative dispersion cyclic broadening system are also interchangeable. In the optical system for realizing frequency sweeping by cyclic cascade broadening of the present invention, on the basis of the characteristic that a dispersion relationship of spectra of an ultrafast laser pulse in a certain bandwidth is linear, after the ultrafast laser pulse is broadened by means of a dispersion device, the linear uniform distribution of the spectra in the bandwidth in a time domain can be realized, so that a frequency sweeping bandwidth of up to THz can be realized, thereby effectively improving the frequency sweeping speed, reducing or avoiding the frequency hopping at the splicing position, and reducing the system costs.

Description

An optical system that achieves frequency sweeping through cyclic cascaded broadening

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 202510214817.7, filed on February 26, 2025, entitled "An optical system for achieving frequency sweeping through cyclic cascade broadening", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of optical technology, and in particular to an optical system that achieves frequency sweeping through cyclic cascade broadening. Background Technology

[0004] Frequency modulated continuous wave (FMCW) is a radar and lidar technology that uses continuously transmitted frequency-modulated signals to achieve ranging. In an FMCW lidar system, the transmitted signal is mixed or interfered with the received signal reflected from the target. By calculating and analyzing the Doppler frequency shift caused by the mixing or interference, accurate measurement of the target's distance and velocity can be achieved. Because FMCW lidar is based on optical coherence technology, it has strong resistance to external interference and shows great application potential, making it a promising research direction and a hot topic.

[0005] The frequency sweeping light source is the core component that directly determines the performance of FMCW lidar. Reported frequency sweeping implementations all rely on electrical modulation using an arbitrary waveform generator as the modulation source, making it difficult to achieve a sweeping bandwidth exceeding 100 GHz. While some studies have extended it to THz through multiple splicing, these methods suffer from slow sweeping speeds, frequency jumps at splicing points, and high system costs. Therefore, this paper proposes an optical system for frequency sweeping through cyclic cascaded broadening. This system leverages the linear dispersion of ultrafast laser pulses within a certain bandwidth. By broadening the ultrafast laser pulse through a dispersive device, a linear and uniform temporal distribution of the spectrum within that bandwidth can be achieved, thus enabling a sweeping bandwidth up to THz. Summary of the Invention

[0006] This invention provides an optical system that achieves frequency sweeping through cyclic cascaded broadening, solving the problems mentioned in the background art above, realizing a linear and uniform distribution of each spectrum in the time domain within the bandwidth, and achieving a frequency sweeping bandwidth of up to THz.

[0007] The present invention solves the above-mentioned technical problems as follows: An optical system for achieving frequency sweeping through cyclic cascaded broadening includes an ultrafast pulsed laser, a coupler, a positive dispersion cyclic broadening system, a negative dispersion cyclic broadening system, a polarization-maintaining fiber, and a delay line. The ultrafast pulsed laser is connected to the coupler through the polarization-maintaining fiber. Two couplers are provided. The two ends of the negative dispersion cyclic broadening system are respectively connected to the coupler through the polarization-maintaining fiber. One end of the positive dispersion cyclic broadening system is connected to the coupler through the polarization-maintaining fiber, and the other end is connected to the other coupler through the delay line. The positions of the positive and negative dispersion cyclic broadening systems can also be interchanged. The positive dispersion cyclic broadening... Both the system and the negative dispersion cyclic broadening system include optical switch 1, couplers, EDFA, CFBG, optical switch 2, optical switch 3, time-delay fiber, and polarization-maintaining fiber. There are two couplers. Optical switch 1 is connected to one end of the coupler through the polarization-maintaining fiber. There are two EDFAs. The two EDFAs are connected to both ends of the CFBG through the polarization-maintaining fiber. One EDFA is connected to one end of the coupler through the polarization-maintaining fiber, and the other EDFA is connected to the other end of the coupler through the polarization-maintaining fiber and the time-delay fiber. The two couplers are connected to optical switch 2 through the polarization-maintaining fiber, and one of the couplers is connected to optical switch 3 through the polarization-maintaining fiber.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the EDFA is an erbium-doped fiber amplifier, the CFBG is a positive or negative dispersion chirped fiber Bragg grating, the coupler is an optical fiber coupler, and the CFBG can be customized in terms of its dispersion parameters or the time domain width of a single dispersion broadening (e.g., a time domain width of 1.2 nanoseconds for a single dispersion broadening) according to requirements. The EDFA is used to compensate for the energy lost in each cycle, and the specific energy amplification requirements need to be customized or adjusted according to actual needs.

[0010] Furthermore, the ultrafast laser pulse time domain width of the ultrafast pulse laser is femtosecond or picosecond.

[0011] Furthermore, the optical switches 1, 2, and 3 all operate at speeds in the nanosecond range or faster, and their switching timing is controlled by external circuitry or a signal generator.

[0012] The beneficial effects of this invention are: This invention provides an optical system that achieves frequency sweeping through cyclic cascaded broadening, which has the following advantages:

[0013] 1. This optical system that achieves frequency sweeping through cyclic cascade broadening is based on the linear dispersion relationship of the spectrum of ultrafast laser pulses within a certain bandwidth. This allows the ultrafast laser pulses to achieve a linear and uniform distribution of each spectrum in the time domain within that bandwidth after being broadened by the dispersive device. This enables a frequency sweeping bandwidth of up to THz, thereby effectively improving the frequency sweeping speed, reducing or preventing frequency jumps at splicing points, and reducing system costs.

[0014] 2. In this optical system that achieves frequency sweeping through cyclic cascaded broadening, all optical paths are connected by polarization-maintaining fibers. The positive and negative dispersion cyclic broadening systems correspond to the cases of using positive and negative dispersion CFBG, respectively. The femtosecond or picosecond ultrafast pulse laser is split into two paths by a 50:50 coupler and fed into the positive and negative dispersion cyclic broadening systems, respectively. The outputs are sawtooth waveforms with exactly opposite time-domain spectral distributions for frequency sweeping. By precisely controlling the time difference of the two sawtooth waveform frequency sweeps, precise control of the splicing point of the two optical paths can be achieved. The two optical paths can be spliced ​​into a triangular waveform frequency sweep by a 50:50 coupler.

[0015] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Specific embodiments of the present invention are given in detail below with reference to the accompanying drawings. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0017] Figure 1 is a flowchart of an optical system for achieving frequency sweeping through cyclic cascade broadening according to an embodiment of the present invention;

[0018] Figure 2 is a flowchart of a positive or negative dispersion cyclic broadening system in an optical system that achieves frequency sweeping through cyclic cascade broadening, according to an embodiment of the present invention. Detailed Implementation

[0019] The principles and features of the present invention are described below with reference to Figures 1 and 2. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. The invention is described more specifically in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0020] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a component in between. When a component is considered "connected to" another component, it can be directly connected to the other component or may have a component in between. When a component is considered "set on" another component, it can be directly set on the other component or may have a component in between. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] As shown in Figures 1 and 2, this invention provides an optical system for frequency sweeping through cyclic cascaded broadening, including an ultrafast pulsed laser, a coupler, a positive dispersion cyclic broadening system, a negative dispersion cyclic broadening system, a polarization-maintaining fiber, and a delay line. The ultrafast pulsed laser is connected to the coupler through the polarization-maintaining fiber. There are two couplers. The two ends of the negative dispersion cyclic broadening system are connected to the coupler through the polarization-maintaining fiber, and one end of the positive dispersion cyclic broadening system is connected to the coupler through the polarization-maintaining fiber, while the other end is connected to the other coupler through the delay line. The positions of the positive and negative dispersion cyclic broadening systems can also be interchanged.

[0023] Both the positive dispersion cyclic stretching system and the negative dispersion cyclic stretching system include optical switch 1, couplers, EDFA, CFBG, optical switch 2, optical switch 3, time-delay fiber, and polarization-maintaining fiber. There are two couplers. Optical switch 1 is connected to one end of the coupler through the polarization-maintaining fiber. There are two EDFAs. The two EDFAs are connected to both ends of the CFBG through the polarization-maintaining fiber. One EDFA is connected to one end of the coupler through the polarization-maintaining fiber, and the other EDFA is connected to the other end of the coupler through the polarization-maintaining fiber and the time-delay fiber. The two couplers are connected to optical switch 2 through the polarization-maintaining fiber, and one coupler is connected to optical switch 3 through the polarization-maintaining fiber.

[0024] Preferably, the EDFA is an erbium-doped fiber amplifier, the CFBG is a positive or negative dispersion chirped fiber Bragg grating, and the coupler is an optical fiber coupler.

[0025] Preferably, the ultrafast pulse time domain width of the ultrafast pulse laser is femtosecond or picosecond.

[0026] Preferably, the speeds of optical switches 1, 2, and 3 are all at the nanosecond level or faster, and the switching timing of optical switches 1, 2, and 3 is controlled by external circuits or a signal generator.

[0027] The specific working principle and usage method of this invention are as follows:

[0028] In the optical system shown in Figure 2, all optical paths are connected by polarization-maintaining fibers. The ultrafast laser pulse has a time domain width of femtoseconds or picoseconds and is introduced into the ring cavity through a 50:50 coupler. The CFBG can be customized in terms of its dispersion parameters or the time domain width of a single dispersion broadening as required. The EDFA is used to compensate for the energy loss in each cycle. The specific energy amplification requirements need to be customized or adjusted according to actual needs. Three optical switches with speeds in the nanosecond range (or faster) are strictly controlled by external circuits or signal generators to coordinate the switching time of the entire system and the number of cycles of light in the ring cavity. The number of cycles is determined by the length of the ring cavity and the time domain width of a single dispersion broadening of the CFBG (e.g., 1.2 nanoseconds). The length of the delay fiber needs to be matched to the time domain width of the broadened pulse to be achieved. The light energy output by optical switch 3 is distributed at a ratio of 90% (or 80%) through a 10:90 (or other ratios, such as 20:80) coupler. This system can achieve sawtooth waveform frequency sweeps in the nanosecond to microsecond range.

[0029] In the optical system shown in Figure 1, all optical paths are connected by polarization-maintaining fibers. The positive and negative dispersion cyclic broadening system is the same as the optical system shown in Figure 2. Corresponding to the cases of positive and negative dispersion CFBG respectively, the femtosecond or picosecond ultrafast pulse laser is split into two paths by a 50:50 coupler and fed into the positive and negative dispersion cyclic broadening system respectively. The output frequency sweep of the two paths is a sawtooth waveform with exactly opposite spectral time domain distribution. The delay line is a time-delay polarization-maintaining fiber, the length of which is the product of the broadened pulse time domain width output by the optical system in Figure 1 and the light propagation speed in the fiber. It is used to precisely control the time difference of the two sawtooth waveform frequency sweeps, thereby achieving precise control of the splicing point of the two optical paths. The two optical paths are spliced ​​into a triangular waveform frequency sweep by a 50:50 coupler.

[0030] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Content not described in detail in this specification is prior art known to those skilled in the art.

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. An optical system for achieving frequency sweeping through cyclic cascaded stretching, comprising an ultrafast pulsed laser, a coupler, a positive dispersion cyclic stretching system, a negative dispersion cyclic stretching system, a polarization-maintaining fiber, and a delay line, characterized in that: The ultrafast pulsed laser is connected to a coupler via a polarization-maintaining fiber. Two couplers are provided. The two ends of the negative dispersion cyclic stretching system are connected to the coupler via polarization-maintaining fibers. One end of the positive dispersion cyclic stretching system is connected to the coupler via a polarization-maintaining fiber, and the other end is connected to another coupler via a delay line. The positions of the positive and negative dispersion cyclic stretching systems can also be interchanged. Both the positive and negative dispersion cyclic stretching systems include an optical switch 1, a coupler, an EDFA, a CFBG, an optical switch 2, an optical switch 3, a delay fiber, and a polarization-maintaining fiber. Two couplers are provided. The optical switch 1 is connected to one end of the coupler via a polarization-maintaining fiber. Two EDFAs are provided. Two EDFAs are connected to both ends of the CFBG via polarization-maintaining fibers. One EDFA is connected to one end of the coupler via a polarization-maintaining fiber, and the other EDFA is connected to the other end of the coupler via a polarization-maintaining fiber and a delay fiber. Both couplers are connected to the optical switch 2 via a polarization-maintaining fiber, and one coupler is connected to the optical switch 3 via a polarization-maintaining fiber.

2. The optical system for achieving frequency sweeping through cyclic cascaded broadening according to claim 1, characterized in that, The EDFA is an erbium-doped fiber amplifier, the CFBG is a positive or negative dispersion chirped fiber Bragg grating, and the coupler is an optical fiber coupler.

3. The optical system for achieving frequency sweeping through cyclic cascaded broadening according to claim 1, characterized in that, The ultrafast pulse time domain width of the ultrafast pulse laser is femtosecond or picosecond.

4. The optical system for achieving frequency sweeping through cyclic cascaded broadening according to claim 1, characterized in that, The optical switches 1, 2, and 3 all operate at speeds in the nanosecond range or faster, and their switching timing is controlled by external circuitry or a signal generator.

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