Optical system for realizing frequency sweeping through cyclic cascade spreading

Abstract

The invention relates to an optical system for realizing frequency sweeping through cyclic cascade broadening, which belongs to the technical field of optics, and comprises an ultrafast pulse laser, two couplers, a positive dispersion cyclic broadening system, a negative dispersion cyclic broadening system, a polarization maintaining optical fiber and a delay line, the two ends of the positive and negative dispersion circulation broadening systems are respectively communicated with the coupler through polarization maintaining optical fibers, and the positive and negative dispersion circulation broadening systems can also be subjected to position exchange. In the invention, the optical system for realizing frequency sweeping through cyclic cascade spreading is linear based on the dispersion relation of the spectrum of the ultrafast laser pulse in a certain bandwidth, so that the linear uniform distribution of each spectrum in the bandwidth in a time domain can be realized after the ultrafast laser pulse is spread through a dispersion device; and meanwhile, the frequency sweeping bandwidth as high as THz can be realized, so that the frequency sweeping speed can be effectively improved, the frequency hopping at the splicing part is reduced or prevented, and the system cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical technologies, and particularly to an optical system for achieving frequency sweeping through cyclic cascaded broadening. Background Art

[0002] 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 to be measured, and the Doppler frequency shift caused by the mixing or interference is calculated and analyzed, so as to achieve accurate measurement of the distance and speed of the target. Since the FMCW lidar is based on optical coherence technology, it has strong anti-interference ability and great application prospects, and is a potential research direction and hot spot.

[0003] The frequency-swept light source is the core device directly determining the performance of the FMCW lidar. All reported frequency-sweeping implementation methods are electrical modulation that requires an arbitrary waveform generator as the modulation source, and it is very difficult to break through 100 GHz in the achieved frequency-sweeping bandwidth; although some studies can be extended to THz through multiple splicing, there are a series of problems such as slow frequency-sweeping speed, frequency jump at the splicing point, and high system cost. For this reason, an optical system for achieving frequency sweeping through cyclic cascaded broadening is proposed. Based on the characteristic that the spectrum of an ultrafast laser pulse is linear within a certain bandwidth, after the ultrafast laser pulse is broadened by a dispersion device, the linear uniform distribution of each spectrum within this bandwidth in the time domain can be achieved, so that a frequency-sweeping bandwidth up to THz can be achieved. Summary of the Invention

[0004] The present invention provides an optical system for achieving frequency sweeping through cyclic cascaded broadening, solves the problems raised in the above background art, realizes the linear uniform distribution of each spectrum within the bandwidth in the time domain, and can achieve a frequency-sweeping bandwidth up to THz.

[0005] The solution of the present invention to the above technical problems is as follows: An optical system for realizing frequency sweeping through cyclic cascaded broadening, comprising 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. Both 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 another coupler through the delay line. Here, the positive and negative dispersion cyclic broadening systems can also be swapped in position. The positive dispersion cyclic broadening system and the negative dispersion cyclic broadening system both 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. There are two couplers. The optical switch 1 is connected to one end 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 coupler through the polarization-maintaining fiber, and the other EDFA is connected to the other end coupler through the polarization-maintaining fiber and the delay fiber. The two couplers are connected to the optical switch 2 through the polarization-maintaining fiber. One side coupler is connected to the optical switch 3 through the polarization-maintaining fiber.

[0006] Based on the above technical solutions, the present invention can be further improved as follows.

[0007] Further, the EDFA is an erbium-doped fiber amplifier, the CFBG is a positive or negative dispersion chirped fiber Bragg grating, the coupler is a fiber coupler. The CFBG can be customized according to requirements for its dispersion parameters or the time domain width of single-time dispersion broadening (for example, the time domain width of single-time dispersion broadening is 1.2 nanoseconds). The EDFA is used to compensate for the energy lost in each cycle. The specific energy amplification requirements need to be customized or adjusted according to actual needs.

[0008] Further, the time domain width of the ultrafast laser pulse of the ultrafast pulsed laser is femtosecond or picosecond.

[0009] Further, the speeds of the optical switch 1, the optical switch 2, and the optical switch 3 are all nanosecond-level or faster, and the optical switch 1, the optical switch 2, and the optical switch 3 are controlled by an external circuit or a signal generator for switch timing.

[0010] The beneficial effects of the present invention are as follows: The present invention provides an optical system for realizing frequency sweeping through cyclic cascaded broadening, having the following advantages:

[0011] 1. The optical system that realizes frequency sweeping through cyclic cascading broadening is based on the characteristic that the dispersion relationship of the spectrum of an ultrafast laser pulse is linear within a certain bandwidth. As a result, after the ultrafast laser pulse is broadened by a dispersive device, a linear and uniform distribution of each spectrum within this bandwidth in the time domain can be achieved, enabling a frequency-sweeping bandwidth of up to THz. Thus, the frequency-sweeping speed can be effectively increased, frequency jumps at the splicing points can be reduced or prevented, and the system cost can be lowered.

[0012] 2. The optical paths of the optical system that realizes frequency sweeping through cyclic cascading broadening are all connected by polarization-maintaining fibers. The positive and negative dispersion cyclic broadening systems correspond to the cases of using positive and negative dispersion CFBGs respectively. The femtosecond or picosecond ultrafast pulsed laser is evenly divided into two paths by a 50:50 coupler and introduced into the positive and negative dispersion cyclic broadening systems respectively, and sawtooth waveforms with exactly opposite frequency-sweeping in the time domain of the spectrum are output respectively. By precisely controlling the time difference between the two sawtooth waveform frequency sweeps, precise control of the splicing point of the two beams of light can be achieved, and the two beams of light can be spliced into a triangular waveform frequency sweep by a 50:50 coupler.

[0013] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it in accordance with the content of the description, the following takes the preferred embodiments of the present invention and combines with the drawings to describe in detail as follows. The specific implementation manners of the present invention are given in detail by the following embodiments and their drawings. Description of the Drawings

[0014] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0015] Figure 1 is a flowchart of an optical system for realizing frequency sweeping through cyclic cascading broadening provided by an embodiment of the present invention;

[0016] Figure 2 is a flowchart of a positive or negative dispersion cyclic broadening system in an optical system for realizing frequency sweeping through cyclic cascading broadening provided by an embodiment of the present invention. Detailed Description of the Preferred Embodiments

[0017] The following combines the attached Figure 1 , 2 to describe the principles and features of the present invention. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. In the following paragraphs, the present invention will be described more specifically by way of example with reference to the drawings. According to the following description and the claims, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0018] It should be noted that when a component is referred to as "fixed to" another component, it can be directly on the other component or there may be an intermediate component. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0020] As Figure 1 , 2 shown, the present invention provides an optical system for realizing frequency sweeping through cyclic cascaded broadening, including an ultrafast pulse 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 pulse laser is connected to the coupler through the polarization-maintaining fiber. There are two couplers. Both ends of the negative dispersion cyclic broadening system are connected to the couplers 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 another coupler through the delay line. Here, the positive and negative dispersion cyclic broadening systems can also be swapped in position;

[0021] Both the positive dispersion cyclic broadening system and the negative dispersion cyclic broadening system 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. There are two couplers. The optical switch 1 is connected to one end 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 coupler through the polarization-maintaining fiber, and the other EDFA is connected to the other end coupler through the polarization-maintaining fiber and the delay fiber. The two couplers are connected to the optical switch 2 through the polarization-maintaining fiber. One side coupler is connected to the optical switch 3 through the polarization-maintaining fiber.

[0022] 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 a fiber coupler.

[0023] Preferably, the time domain width of the ultrafast laser pulse of the ultrafast pulse laser is femtosecond or picosecond.

[0024] Preferably, the optical switches 1, 2, and 3 all have a speed of nanosecond or faster, and the optical switches 1, 2, and 3 are controlled by an external circuit or a signal generator for their switching time sequence.

[0025] The specific working principle and usage method of the present invention are as follows:

[0026] Figure 2 In the optical system shown, the optical paths are all connected by polarization-maintaining fibers. The time domain width of the ultrafast laser pulse is femtosecond or picosecond. It is introduced into the ring cavity through a 50:50 coupler. The CFBG can customize its dispersion parameters or the time domain width of the single-pass dispersion broadening according to requirements. 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 a speed of nanosecond (or faster) are strictly controlled by an external circuit or a signal generator for their switching time sequence, which is used to coordinate the switching time of the entire system and the number of cycles of light in the circulating cavity. The number of cycles is jointly determined by the length of the ring cavity and the time domain width of the single-pass dispersion broadening of the CFBG (such as 1.2 nanoseconds). The length of the delay fiber needs to be matched according to the time domain width of the broadened pulse to be achieved. The optical energy output by the optical switch 3 accounts for 90% (or other ratios, such as 80%) after being distributed by a 10:90 (or other ratios, such as 20:80) coupler. This system can achieve a sawtooth waveform sweep in the nanosecond to microsecond range.

[0027] Figure 1 In the optical system shown, the optical paths are all connected by polarization-maintaining fibers. The positive and negative dispersion cyclic broadening systems are Figure 2 the optical systems shown. Corresponding to the cases of using positive and negative dispersion CFBGs respectively, the femtosecond or picosecond ultrafast pulsed laser is evenly divided into two paths by a 50:50 coupler and introduced into the positive and negative dispersion cyclic broadening systems respectively, and sawtooth waveform sweeps with exactly opposite spectral time domain distributions are output respectively. The delay line is a polarization-maintaining delay fiber, and its length is Figure 1 the product of the time domain width of the broadened pulse output by the optical system in and the transmission speed of light in the fiber, which is used to precisely control the time difference between the two sawtooth waveform sweeps so as to achieve precise control of the splicing point of the two paths of light. The two paths of light are spliced into a triangular waveform sweep by a 50:50 coupler.

[0028] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0029] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention; any ordinary technician in the industry can smoothly implement the present invention according to the illustrations in the specification and the above description; however, any minor changes, modifications, and equivalent variations made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications, and evolutions made to the above embodiments based on the substantial technology of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

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

2. An optical system for achieving frequency sweeping by cyclic cascade 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 a fiber coupler.

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

4. The optical system for realizing frequency sweeping by cyclic cascade broadening according to claim 1, characterized in that: The speeds of the optical switches 1, 2 and 3 are all in nanoseconds or faster, and the switching timing of the optical switches 1, 2 and 3 is controlled by a peripheral circuit or a signal generator.

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