Time-frequency matching distribution weak feedback line width compression structure adaptive to FDML (frequency division multiplexing laser) frequency sweeping laser

Abstract

The invention provides a time-frequency matching distributed weak feedback line width compression structure adaptive to an FDML (frequency division multiplexing laser), which comprises a distributed feedback device and a reflecting device, and is characterized in that an input / output port of a resonant cavity in the FDML is respectively connected with the distributed feedback device and the reflecting device through a beam splitter; the resonant cavity transmits the current sweep frequency band laser signal to the distributed feedback device and the reflection device, and the distributed feedback device filters the current sweep frequency band laser signal and reversely transmits a scattered signal with a reduced line width back to the resonant cavity; and the reflection device reflects the current sweep frequency band laser signal back to the resonant cavity, so that the scattering signal and the reflected laser signal synchronously reach the resonant cavity, synchronous oscillation is performed in the resonant cavity, and the line width of the current sweep frequency band laser signal is compressed into the line width of the scattering signal. According to the invention, large-wavelength-range stable line width compression of the FDML frequency sweeping laser can be realized.

Description

Technical Field

[0001] The invention belongs to the field of laser line width compression, and in particular relates to a time-frequency matching distributed weak feedback line width compression structure adapted to an FDML frequency sweeping laser. Background Art

[0002] High coherence and high-speed swept lasers are widely used in coherent detection, optical communication, biomedicine and other fields, and have extremely high scientific value and commercial potential. The scanning speed of the swept laser determines the imaging speed or frame rate of the application, the instantaneous line width determines the detection distance or imaging depth of the application, and the scanning range determines the resolution of the application. Figure 1 As shown in the figure, the traditional frequency-sweeping laser is based on a continuous wave laser architecture, which realizes frequency-sweeping laser operation by adding a wavelength control device to the laser structure. This laser architecture is limited by the characteristic time limit of the laser. If the scanning speed is too fast and the laser oscillation is lower than this time limit, problems such as sharp power drop, high noise, and spectral shape distortion will occur. In other words, in the traditional frequency-sweeping laser architecture, the scanning speed and coherence length cannot be taken into account at the same time. Fourier domain mode locking (FDML) was proposed to break through the bottleneck of traditional laser scanning speed, such as Figure 2 As shown, by introducing a longer delay in the resonant cavity, the driving period of the swept filter is precisely matched with the transit time of the photons in the cavity, so that all laser wavelengths within the scanning range oscillate simultaneously, greatly improving the scanning speed, which can currently reach hundreds of kHz.

[0003] Theoretically, the FDML laser architecture does not have the defect that the scanning speed and instantaneous linewidth cannot be improved at the same time. However, the instantaneous linewidth of the current FDML swept laser is in the order of ten GHz, and the coherence length is less than a centimeter, which is difficult to meet the needs of high-coherence applications. At present, there is no linewidth compression method that can perfectly adapt to the FDML laser architecture. There are three reasons: 1. The scanning range of FDML lasers is often hundreds of nm, and there are few methods that can achieve stable linewidth compression in such a large wavelength range. 2. FDML lasers do not have the concept of longitudinal modes in traditional lasers. The intrinsic linewidth of the laser is independent of the resonant cavity and is only determined by the filtering bandwidth of the swept filter. At present, the typical bandwidth of the swept filter is in the order of ten GHz. 3. The FDML laser architecture is different from the traditional single-frequency laser architecture. The laser wavelength in the cavity has a highly precise time-space matching mechanism. Traditional linewidth compression schemes often have a counterproductive effect because they destroy this matching mechanism. Summary of the invention

[0004] The present invention provides a time-frequency matching distributed weak feedback linewidth compression structure adapted to an FDML frequency sweeping laser, so as to solve the problem that the linewidth of the FDML laser cannot be stably compressed over a large wavelength range at present.

[0005] According to a first aspect of an embodiment of the present invention, a time-frequency matching distributed weak feedback linewidth compression structure adapted for an FDML frequency sweeping laser is provided, characterized in that it comprises a distributed feedback device and a reflective device, the input / output port of a resonant cavity in the FDML frequency sweeping laser is connected to the distributed feedback device and the reflective device respectively through a beam splitter, the resonant cavity transmits a current frequency sweeping band laser signal to the distributed feedback device and the reflective device respectively, the distributed feedback device filters the current frequency sweeping band laser signal, and transmits the linewidth-reduced scattered signal back to the resonant cavity; the reflective device reflects the current frequency sweeping band laser signal back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and compresses the linewidth of the current frequency sweeping band laser signal to the linewidth of the scattered signal.

[0006] In an optional implementation, the resonant cavity transmits the laser signal after line width compression to the distributed feedback device and the reflection device respectively; the distributed feedback device filters the laser signal after line width compression, and transmits the scattered signal with further reduced line width back to the resonant cavity; the reflection device reflects the laser signal after line width compression back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and further compress the line width of the laser signal after line width compression to the line width of the scattered signal, and repeat this cycle until the line width compression of the laser signal in the current scanning frequency band reaches equilibrium.

[0007] In another optional implementation, a frequency sweeper is provided in the resonant cavity;

[0008] The frequency sweeper sweeps the laser signal generated in the resonant cavity so that the laser signals of different wavelength bands in the resonant cavity are periodically output from the resonant cavity in sequence, and the resonant cavity outputs the laser signal of the same wavelength band in the next cycle while receiving the scattered signal and the reflected laser signal.

[0009] In another optional implementation, the sweeper is the original sweep filter in the resonant cavity, and the reflector is a reflector; the output end of the resonant cavity is connected to the first end of the circulator, the second end of the circulator is connected to the first end of the beam splitter, and the third end is connected to the input end of the resonant cavity, and the second end of the beam splitter is respectively connected to the distributed feedback device and the reflector.

[0010] In another optional implementation, the reflective device is a reflective frequency sweeper placed outside the resonant cavity;

[0011] For the swept middle section of the laser signal in the resonant cavity, the resonant cavity transmits the laser signals of all wavelengths to the distributed feedback device and the reflective device respectively, the distributed feedback device filters the laser signals of all wavelengths, and transmits the scattered signals with reduced line width back to the resonant cavity; the reflective device sweeps the laser signals of all wavelengths it receives, and transmits the laser signal of the current swept frequency band back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and compress the line width of the laser signals of all wavelengths to the current swept frequency band; the resonant cavity transmits the laser signal of the current swept frequency band to the distributed feedback device and the reflective device respectively.

[0012] In another optional implementation, for the beginning and end sections of the frequency sweep of the laser signal in the resonant cavity, the resonant cavity transmits the laser signals of all wavelengths to the distributed feedback device and the reflection device respectively, the distributed feedback device filters the laser signals of all wavelengths, and transmits the scattered signals with reduced line width back to the resonant cavity; the reflection device sweeps the laser signals of all wavelengths it receives, and transmits the laser signal of the current frequency sweep band back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and compress the line width of the laser signal of the current frequency sweep band to: the intersection of the line width of the scattered signal and the laser signal of the current frequency sweep band; the resonant cavity transmits the laser signal with compressed line width to the distributed feedback device and the reflection device respectively.

[0013] In another optional implementation, the reflection-type sweeper is a sweep filter originally in the resonant cavity and with a reflection function added thereto; the output end of the resonant cavity is connected to the first end of the circulator, the second end of the circulator is connected to the first end of the beam splitter, the third end is connected to the input end of the resonant cavity, and the second end of the beam splitter is respectively connected to the distributed feedback device and the reflection-type sweeper;

[0014] The reflective frequency scanner periodically scans the received laser signal in sequence according to the band, so that laser signals of different bands are periodically input into the resonant cavity in sequence, and the resonant cavity receives the laser signal of the same band in the next cycle while outputting the laser signal of the corresponding band after line width compression.

[0015] In another optional implementation, the sum of the optical path from the beam splitter to the distributed feedback device and the additional optical path introduced by integrating the distributed feedback device is equal to the sum of the optical path from the beam splitter to the reflector device and the additional optical path introduced by integrating the reflector device, thereby ensuring that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously.

[0016] In another optional implementation, the distributed feedback device is an integrated distributed feedback device.

[0017] In another optional implementation, the scattered signal is a Rayleigh scattered signal.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention utilizes the characteristic that the line width of the scattered signal is narrower than the excitation light, uses the distributed feedback device as a filter, and transmits the scattered signal with reduced line width back to the resonant cavity. In the resonant cavity, the scattered signal plays a role in line width compression and noise suppression. The line width compression degree of the FDML swept-frequency laser is determined by the line width of the scattered signal transmitted back by the distributed feedback device, rather than by the filtering bandwidth of the swept-frequency filter. The dependence of the line width compression on the filtering bandwidth of the swept-frequency filter is eliminated, which facilitates further compression of the line width of the FDML swept-frequency laser. In addition, the distributed feedback device can generate a scattered signal with reduced line width when receiving a laser signal of any wavelength, and its working bandwidth is large, so The filtering of the distributed feedback device is adaptive and suitable for the wide range line width compression of the FDML swept frequency laser. Since the intensity of the scattered signal is usually weak, the present invention further provides a reflector, which is used to reflect the laser signal back to the resonant cavity, and provide the necessary resonant power to the resonant cavity, so as to ensure the smooth oscillation of the laser signal in the resonant cavity. The present invention enables the scattered signal and the reflected laser signal to arrive at the resonant cavity at the same time, so as to achieve the time-frequency matching of the scattered signal and the laser signal, and can avoid the leading or lagging laser signal from destroying the dynamic balance of the FDML architecture, and ensure the stability of the oscillation in the resonant cavity, thereby ensuring the stability of the line width compression in the resonant cavity.

[0020] 2. The present invention realizes the reflection and frequency sweeping functions by dividing them into two devices, placing the frequency sweeper in the resonant cavity and the reflector outside the resonant cavity. The frequency sweeper can directly select the original frequency sweeping filter in the resonant cavity without selecting a reflective frequency sweeping filter. This reduces the restrictions on the types of frequency sweeping filters and has better compatibility. In addition, the laser transmitted to the distributed feedback device is the laser filtered by the frequency sweeping filter, and the line width compression effect is better.

[0021] 3. The present invention integrates the reflection and frequency sweeping functions into one device, and places the device outside the resonant cavity. At this time, compared with the middle section of the frequency sweeping, the compression effect of the beginning and end sections of the frequency sweeping is slightly different. The beginning and end sections of the frequency sweeping can be swept to obtain the laser signal with the required compression effect difference; or the beginning and end sections of the frequency sweeping are not swept to obtain laser signals with the same compression effect in each sweeping section. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of a traditional frequency-sweeping laser;

[0023] Figure 2 This is a schematic diagram of the current FDML swept laser structure;

[0024] Figure 3 It is a schematic diagram of an embodiment of the structure of the time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency-sweeping laser of the present invention;

[0025] Figure 4 It is a schematic structural diagram of another embodiment of the time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency-sweeping laser of the present invention;

[0026] Figure 5 It is the adaptive filtering effect of the Rayleigh scattering signal transmitted back by the distributed feedback device. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0028] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0029] See also Figure 3 , is a schematic diagram of an embodiment of the structure of the time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser of the present invention. The structure may include a distributed feedback device 1 and a reflector 2. The input / output port of the resonant cavity 4 in the FDML frequency sweeping laser 3 is connected to the distributed feedback device 1 and the reflector 2 respectively through a beam splitter 5. The resonant cavity 4 transmits the current frequency sweeping band laser signal to the distributed feedback device 1 and the reflector 2 respectively. The distributed feedback device 1 filters the current frequency sweeping band laser signal and transmits the linewidth-reduced scattered signal (i.e., the distributed feedback signal in the figure) back to the resonant cavity 4; the reflector 2 reflects the current frequency sweeping band laser signal back to the resonant cavity 4, so that the scattered signal and the reflected laser signal arrive at the resonant cavity 4 synchronously, oscillate synchronously in the resonant cavity 4, and compress the linewidth of the current frequency sweeping band laser signal to the linewidth of the scattered signal.

[0030] Thereafter, the resonant cavity transmits the laser signal after line width compression to the distributed feedback device and the reflection device respectively; the distributed feedback device filters the laser signal after line width compression, and transmits the scattered signal with further reduced line width back to the resonant cavity; the reflection device reflects the laser signal after line width compression back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and further compress the line width of the laser signal after line width compression to the line width of the scattered signal, and repeats this cycle until the line width compression of the laser signal in the current sweep frequency band reaches equilibrium.

[0031] In this embodiment, a frequency sweeper 5 may be provided in the resonant cavity, and the frequency sweeper 5 sweeps the laser signal generated in the resonant cavity 4, so that the laser signals of different bands in the resonant cavity 4 are periodically outputted from the resonant cavity in sequence, and the resonant cavity outputs the laser signal of the same band in the next cycle while receiving the scattered signal and the reflected laser signal. In this way, the distributed feedback device can sequentially output laser signals of different bands after line width compression. The frequency sweeper 5 may be the original frequency sweeping filter in the resonant cavity, and the reflective device may be a reflector; the output end of the resonant cavity is connected to the first end of the circulator, the second end of the circulator is connected to the first end of the beam splitter, and the third end is connected to the input end of the resonant cavity, and the second end of the beam splitter is respectively connected to the distributed feedback device and the reflective device. The sum of the optical path from the beam splitter to the distributed feedback device and the additional optical path introduced by integrating the distributed feedback device is equal to the sum of the optical path from the beam splitter to the reflector device and the additional optical path introduced by integrating the reflector device, thereby ensuring that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously.

[0032] It can be seen from the above embodiments that since the laser spectrum generally presents a Lorentz or Gaussian line shape, the frequency center power is high and can excite strong backscattering, while the edge power is low and the excited scattering intensity is low or even no excitation occurs, the spectral width of the scattered signal is smaller than the excitation light. The present invention utilizes the characteristic that the line width of the scattered signal is narrower than the excitation light width, and uses the distributed feedback device as a filter to transmit the scattered signal with reduced line width back to the resonant cavity. In the resonant cavity, the scattered signal plays a role in line width compression and noise suppression. The line width compression degree of the FDML swept-frequency laser is determined by the line width of the scattered signal transmitted back by the distributed feedback device, rather than by the filtering bandwidth of the swept-frequency filter. This eliminates the dependence of the line width compression on the filtering bandwidth of the swept-frequency filter, and facilitates further compression of the line width of the FDML swept-frequency laser. In addition, the distributed feedback device can generate a scattered signal with reduced line width when receiving a laser signal of any wavelength, and its working bandwidth is large, so The filtering of the distributed feedback device is adaptive and suitable for the wide range line width compression of the FDML swept frequency laser; since the intensity of the scattered signal is usually weak, the present invention further provides a reflector, which is used to reflect the laser signal back to the resonant cavity, and provide the necessary resonant power to the resonant cavity, thereby ensuring the smooth oscillation of the laser signal in the resonant cavity; the present invention enables the scattered signal and the reflected laser signal to arrive at the resonant cavity at the same time, thereby achieving time-frequency matching of the scattered signal and the laser signal, which can avoid the leading or lagging laser signal from destroying the dynamic balance of the FDML architecture, ensure the stability of the oscillation in the resonant cavity, and thus ensure the stability of the line width compression in the resonant cavity.

[0033] The present invention realizes the reflection and frequency sweeping functions by dividing them into two devices, placing the frequency sweeper in the resonant cavity and the reflector outside the resonant cavity. The frequency sweeper can directly select the original frequency sweeping filter in the resonant cavity without selecting a reflective frequency sweeping filter. This reduces the restrictions on the types of frequency sweeping filters and has better compatibility. Moreover, the laser transmitted to the distributed feedback device is the laser filtered by the frequency sweeping filter, and the line width compression effect will be better.

[0034] See also Figure 4 , which is a structural schematic diagram of another embodiment of the time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML swept-frequency laser of the present invention. Figure 4 and Figure 3 The difference between the structures shown is that the reflection device can be a reflection type frequency sweeper placed outside the resonant cavity 4 .

[0035] For the frequency sweeping middle section of the laser signal in the resonant cavity, the resonant cavity transmits the laser signals of all wavelengths to the distributed feedback device and the reflecting device respectively, the distributed feedback device filters the laser signals of all wavelengths, and transmits the scattered signals with reduced line width back to the resonant cavity; the reflecting device sweeps the laser signals of all wavelengths received by it, and transmits the laser signal of the current frequency sweeping band back to the resonant cavity, so that the scattered signal and the reflected laser signal synchronously arrive at the resonant cavity, synchronously oscillate in the resonant cavity, and compress the line width of the laser signals of all wavelengths to the current frequency sweeping band; the resonant cavity transmits the laser signal of the current frequency sweeping band to the distributed feedback device and the reflecting device respectively, the distributed feedback device filters the laser signal of the current frequency sweeping band, and transmits the scattered signal with reduced line width back to the resonant cavity; the reflecting device reflects the laser signal of the current frequency sweeping band back to the resonant cavity, so that the scattered signal and the reflected laser signal synchronously arrive at the resonant cavity, synchronously oscillate in the resonant cavity, and compress the line width of the laser signal of the current frequency sweeping band to the line width of the scattered signal.

[0036] Thereafter, the resonant cavity transmits the laser signal after line width compression to the distributed feedback device and the reflection device respectively; the distributed feedback device filters the laser signal after line width compression, and transmits the scattered signal with further reduced line width back to the resonant cavity; the reflection device reflects the laser signal after line width compression back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and further compress the line width of the laser signal after line width compression to the line width of the scattered signal, and repeats this cycle until the line width compression of the laser signal in the current sweep frequency band reaches equilibrium.

[0037] For the beginning and end sections of the frequency sweep of the laser signal in the resonant cavity, the resonant cavity transmits the laser signals of all wavelengths to the distributed feedback device and the reflector device respectively, the distributed feedback device filters the laser signals of all wavelengths, and transmits the scattered signals with reduced line width back to the resonant cavity; the reflector sweeps the laser signals of all wavelengths it receives, and transmits the laser signal of the current frequency sweeping band back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and compress the line width of the laser signal of the current frequency sweeping band to: the scattered signal and the laser signal of the current frequency sweeping band are The line width intersection of the laser signal of the frequency band; the resonant cavity transmits the laser signal after the line width compression to the distributed feedback device and the reflection device respectively, the distributed feedback device filters the laser signal after the line width compression, and transmits the scattered signal with further reduced line width back to the resonant cavity; the reflection device reflects the laser signal after the line width compression back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and further compress the line width of the laser signal after the line width compression to the line width of the scattered signal, and repeat this cycle until the line width compression of the laser signal in the current frequency sweeping band reaches equilibrium.

[0038] In this embodiment, the reflective frequency sweeper can be a frequency sweep filter that is originally in the resonant cavity and has a reflection function added; the output end of the resonant cavity is connected to the first end of the circulator, the second end of the circulator is connected to the first end of the beam splitter, the third end is connected to the input end of the resonant cavity, and the second end of the beam splitter is respectively connected to the distributed feedback device and the reflective frequency sweeper; the reflective frequency sweeper periodically and sequentially sweeps the received laser signal according to the band, so that laser signals of different bands are periodically and sequentially input into the resonant cavity, and the resonant cavity receives the laser signal of the same band in the next cycle while outputting the laser signal of the corresponding band after line width compression. In this way, the distributed feedback device can sequentially output laser signals of different bands after line width compression. The sum of the optical path from the beam splitter to the distributed feedback device and the additional optical path introduced by integrating the distributed feedback device can be equal to the sum of the optical path from the beam splitter to the reflector and the additional optical path introduced by integrating the reflector, so that the scattered signal and the reflected laser signal can be ensured to arrive at the resonant cavity synchronously. The distributed feedback device may be an integrated distributed feedback device, and may be a distributed optical fiber, etc., and the scattered signal may be a Rayleigh scattered signal.

[0039] It can be seen from the above embodiments that the present invention utilizes the characteristic that the line width of the scattered signal is narrower than the excitation light width, uses the distributed feedback device as a filter, and transmits the scattered signal with reduced line width back to the resonant cavity. In the resonant cavity, the scattered signal plays a role of line width compression and noise suppression. The line width compression degree of the FDML swept-frequency laser is determined by the line width of the scattered signal transmitted back by the distributed feedback device, rather than by the filtering bandwidth of the swept-frequency filter, thereby eliminating the dependence of the line width compression on the filtering bandwidth of the swept-frequency filter, and facilitating further compression of the line width of the FDML swept-frequency laser. In addition, the distributed feedback device can generate a scattered signal with reduced line width when receiving a laser signal of any wavelength, and its working bandwidth The filtering of the distributed feedback device is adaptive, and is suitable for the wide range linewidth compression of the FDML swept-frequency laser. Since the intensity of the scattered signal is usually weak, the present invention also provides a reflector to reflect the laser signal back to the resonant cavity, and provide the necessary resonant power to the resonant cavity, thereby ensuring the smooth oscillation of the laser signal in the resonant cavity. The present invention enables the scattered signal and the reflected laser signal to arrive at the resonant cavity at the same time, thereby achieving time-frequency matching of the scattered signal and the laser signal, and preventing the leading or lagging laser signal from destroying the dynamic balance of the FDML architecture, thereby ensuring the stability of the oscillation in the resonant cavity, and thus ensuring the stability of the linewidth compression in the resonant cavity. The adaptive filtering effect of the Rayleigh scattered signal transmitted back by the distributed feedback device can be as follows: Figure 5 shown.

[0040] In addition, the present invention integrates the reflection and frequency sweeping functions into one device, and places the device outside the resonant cavity. At this time, compared with the middle section of the frequency sweeping, the compression effect of the beginning and end sections of the frequency sweeping is slightly different. The beginning and end sections of the frequency sweeping can be swept to obtain the laser signal with the required compression effect difference; or the beginning and end sections of the frequency sweeping are not swept to obtain laser signals with the same compression effect in each sweeping section.

[0041] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0042] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. A time-frequency matching distributed weak feedback linewidth compression structure adapted to FDML swept laser, characterized in that: The invention comprises a distributed feedback device and a reflective device. The input / output port of the resonant cavity in the FDML frequency sweeping laser is respectively connected to the distributed feedback device and the reflective device through a beam splitter. The resonant cavity transmits the laser signal of the current frequency sweeping band to the distributed feedback device and the reflective device respectively. The distributed feedback device filters the laser signal of the current frequency sweeping band and transmits the scattered signal with reduced line width back to the resonant cavity. The reflective device reflects the laser signal of the current frequency sweeping band back to the resonant cavity, so that the scattered signal and the reflected laser signal synchronously arrive at the resonant cavity, synchronously oscillate in the resonant cavity, and compress the line width of the laser signal of the current frequency sweeping band to the line width of the scattered signal.

2. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 1, characterized in that: The resonant cavity transmits the laser signal after line width compression to the distributed feedback device and the reflection device respectively; the distributed feedback device filters the laser signal after line width compression, and transmits the scattered signal with further reduced line width back to the resonant cavity; the reflection device reflects the laser signal after line width compression back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and further compress the line width of the laser signal after line width compression to the line width of the scattered signal, and repeats this cycle until the line width compression of the laser signal in the current sweep frequency band reaches equilibrium.

3. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 1 or 2, characterized in that: A frequency sweeper is provided in the resonant cavity; The frequency sweeper sweeps the laser signal generated in the resonant cavity so that the laser signals of different wavelength bands in the resonant cavity are periodically output from the resonant cavity in sequence, and the resonant cavity outputs the laser signal of the same wavelength band in the next cycle while receiving the scattered signal and the reflected laser signal.

4. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 3, characterized in that: The sweep frequency meter is the original sweep frequency filter in the resonant cavity, and the reflective device is a reflector; the output end of the resonant cavity is connected to the first end of the circulator, the second end of the circulator is connected to the first end of the beam splitter, and the third end is connected to the input end of the resonant cavity, and the second end of the beam splitter is respectively connected to the distributed feedback device and the reflective device.

5. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 1 or 2, characterized in that: The reflective device is a reflective frequency sweeper placed outside the resonant cavity; For the swept middle section of the laser signal in the resonant cavity, the resonant cavity transmits the laser signals of all wavelengths to the distributed feedback device and the reflective device respectively, the distributed feedback device filters the laser signals of all wavelengths, and transmits the scattered signals with reduced line width back to the resonant cavity; the reflective device sweeps the laser signals of all wavelengths it receives, and transmits the laser signal of the current swept frequency band back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and compress the line width of the laser signals of all wavelengths to the current swept frequency band; the resonant cavity transmits the laser signal of the current swept frequency band to the distributed feedback device and the reflective device respectively.

6. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 5, characterized in that: For the beginning and end sections of the frequency sweep of the laser signal in the resonant cavity, the resonant cavity transmits the laser signals of all wavelengths to the distributed feedback device and the reflective device respectively, the distributed feedback device filters the laser signals of all wavelengths, and transmits the scattered signals with reduced line width back to the resonant cavity; the reflective device sweeps the laser signals of all wavelengths it receives, and transmits the laser signal of the current frequency sweep band back to the resonant cavity, so that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously, oscillate synchronously in the resonant cavity, and compress the line width of the laser signal of the current frequency sweep band to the intersection of the line widths of the scattered signal and the laser signal of the current frequency sweep band; the resonant cavity transmits the laser signal with compressed line width to the distributed feedback device and the reflective device respectively.

7. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 5, characterized in that: The reflection type sweeper is the original sweep filter in the resonant cavity with a reflection function added; the output end of the resonant cavity is connected to the first end of the circulator, the second end of the circulator is connected to the first end of the beam splitter, the third end is connected to the input end of the resonant cavity, and the second end of the beam splitter is respectively connected to the distributed feedback device and the reflection type sweeper; The reflective frequency scanner periodically scans the received laser signal in sequence according to the band, so that laser signals of different bands are periodically input into the resonant cavity in sequence, and the resonant cavity receives the laser signal of the same band in the next cycle while outputting the laser signal of the corresponding band after line width compression.

8. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 1 or 2, characterized in that: The sum of the optical path from the beam splitter to the distributed feedback device and the additional optical path introduced by integrating the distributed feedback device is equal to the sum of the optical path from the beam splitter to the reflector device and the additional optical path introduced by integrating the reflector device, thereby ensuring that the scattered signal and the reflected laser signal arrive at the resonant cavity synchronously.

9. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 1, characterized in that: The distributed feedback device is an integrated distributed feedback device.

10. The time-frequency matching distributed weak feedback linewidth compression structure adapted to the FDML frequency sweeping laser according to claim 2, characterized in that: The scattered signal is a Rayleigh scattered signal.

Images