Laser line width measuring device based on short optical fiber
By using a short-fiber laser linewidth measurement device, which splits the laser beam using an adjustable short-fiber delay line device and selects an appropriate fiber length, the measurement inaccuracy caused by 1/f noise in the delay self-heterodyne technique is solved, achieving higher precision and a wider range of laser linewidth measurement.
Patent Information
- Application Number
- CN202520171185.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-25
- Publication Date
- 2026-01-02
- Estimated Expiration
- 2035-01-25
AI Technical Summary
Existing delayed self-heterodyne techniques suffer from 1/f frequency noise, resulting in inaccurate laser linewidth measurements and making them unsuitable for measuring narrow-linewidth lasers.
A laser linewidth measurement device based on short optical fibers is adopted, using an adjustable short optical fiber delay line device. By splitting the laser beam and utilizing multiple short delay fibers of different lengths, 1/f frequency noise is avoided, thereby improving measurement accuracy.
It effectively avoids the influence of 1/f noise, improves the accuracy and measurement range of laser linewidth measurement, and is suitable for laser measurement of various linewidths.
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Figure CN223756292U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of laser linewidth measurement, in particular to a delay self-heterodyne measurement technology. BACKGROUND
[0002] Narrow-linewidth lasers play a crucial role in many frontier fields, such as atomic physics research, nonlinear optical frequency conversion, high-precision detection, and high-speed coherent optical communication. The linewidth of a narrow-linewidth laser is usually determined by noise characteristics (including quantum noise and technical noise). Generally, a lower noise level corresponds to a narrower linewidth, which greatly expands the application range of narrow-linewidth lasers. In the development process of narrow-linewidth lasers, accurate measurement of the linewidth is undoubtedly a crucial step.
[0003] Currently, there are various techniques for measuring narrow laser linewidths, among which the delay self-heterodyne (DSH) technique is widely used due to its simple operation and good stability. In the DSH measurement process, the laser output generates a "beat frequency" phenomenon in the electrical frequency spectrum range, and the beat frequency signal is then detected and recorded by an electrical spectrum analyzer (ESA). Generally, a delay line is required for DSH measurement, and the delay time needs to be greater than six times the laser coherence time. However, this long delay length introduces 1 / f frequency noise, causing the spectrum transmitted to the ESA to be broadened, resulting in inaccurate laser linewidth measurement results.
[0004] In summary, the existing delay self-heterodyne technique is not suitable for measuring narrow-linewidth lasers due to the presence of 1 / f frequency noise, which leads to inaccurate laser linewidth measurement results. UTILITY MODEL CONTENT
[0005] The purpose of the present application is to solve or alleviate the above problems, and to provide a laser linewidth measurement device based on a short optical fiber.
[0006] The laser linewidth measurement device based on a short optical fiber of the present application comprises a first coupler, an acousto-optic modulator, an adjustable-grade short optical fiber delay line device, a second coupler, a high-speed photodetector, and an electrical spectrum analyzer. The laser to be measured is divided into two beams by the first coupler, one of which enters the acousto-optic modulator, and the other enters the adjustable-grade short optical fiber delay line device. The laser emitted from the acousto-optic modulator and the laser emitted from the adjustable-grade short optical fiber delay line device are combined by the second coupler, and then detected by the high-speed photodetector. The detection data is sent to the electrical spectrum analyzer.
[0007] Optionally, the adjustable-grade short optical fiber delay line device comprises at least two short delay optical fibers with different lengths.
[0008] Optionally, the adjustable short fiber delay line device comprises: a first short delay optical fiber, a second short delay optical fiber, a third short delay optical fiber, a first single-pole single-throw switch, a second single-pole single-throw switch, a third single-pole single-throw switch, a fourth single-pole single-throw switch, a fifth single-pole single-throw switch, a first single-pole double-throw switch, and a second single-pole double-throw switch; one end of the first single-pole single-throw switch, a first fixed end of the first single-pole double-throw switch, and a first fixed end of the second single-pole double-throw switch are connected, and the connection point is the input end of the adjustable short fiber delay line device; the other end of the first single-pole single-throw switch is connected to one end of the first short delay optical fiber, and the other end of the first short delay optical fiber, a second fixed end of the second single-pole double-throw switch, one end of the second single-pole single-throw switch, and one end of the third single-pole single-throw switch are connected; a movable end of the second single-pole double-throw switch is connected to one end of the second short delay optical fiber, and the other end of the second short delay optical fiber, the other end of the third single-pole single-throw switch, one end of the fourth single-pole single-throw switch, and a second fixed end of the first single-pole double-throw switch are connected; a movable end of the first single-pole double-throw switch is connected to one end of the third short delay optical fiber, and the other end of the third short delay optical fiber is connected to one end of the fifth single-pole single-throw switch.
[0009] Optionally, the other end of the second single-pole single-throw switch, the other end of the fourth single-pole single-throw switch, and the other end of the fifth single-pole single-throw switch are connected, and the connection point is the output end of the adjustable short fiber delay line device.
[0010] Optionally, the first short delay optical fiber, the second short delay optical fiber, and the third short delay optical fiber have different lengths.
[0011] Optionally, the length of the first short delay optical fiber is 500 meters, the length of the second short delay optical fiber is 1000 meters, and the length of the third short delay optical fiber is 2000 meters.
[0012] Optionally, the short fiber-based laser linewidth measurement device further comprises a variable optical attenuator connected to the incident end of the first coupler.
[0013] The short fiber-based laser linewidth measurement device further comprises a first variable optical attenuator and a second variable optical attenuator; the first variable optical attenuator is located between the first coupler and the acousto-optic modulator; and the second variable optical attenuator is located between the first coupler and the adjustable short fiber delay line device.
[0014] The application is based on the principle of DSH measurement, uses an adjustable short optical fiber delay line device for delay, the device has multiple gears, different gears correspond to different lengths of delay optical fiber, which not only can effectively avoid 1 / f frequency noise and improve the measurement accuracy of laser linewidth, but also expand the measurement range of laser linewidth, and is suitable for the measurement of various linewidth lasers. BRIEF DESCRIPTION OF DRAWINGS
[0015] Figure 1 is a structural schematic diagram of a short optical fiber-based laser linewidth measurement device according to an embodiment of the application;
[0016] Figure 2 is a structural schematic diagram of an adjustable short optical fiber delay line device according to an embodiment of the application. DETAILED DESCRIPTION
[0017] The embodiments of the application will be described in detail below with specific reference to specific examples. Those skilled in the art can easily understand other advantages and effects of the application from the content disclosed in the specification. The application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.
[0018] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", means the presence of the stated features, operations, elements, components, items, kinds and / or groups, but does not exclude the presence or addition of one or more other features, operations, elements, components, items, kinds and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean any one or any combination. Therefore, "A, B or C" or "A, B and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B and C". This definition applies only when the combination of elements, functions or operations is inherently mutually exclusive.
[0019] In view of the problem that the existing delay heterodyne technology is not accurate in measuring laser linewidth due to 1 / f frequency noise, and is not suitable for narrow linewidth laser measurement, the application provides a short optical fiber-based laser linewidth measurement device, which uses a short optical fiber as a delay optical fiber, and the length of the optical fiber is adjustable, so that 1 / f frequency noise can be avoided when measuring various linewidth lasers, and the measurement accuracy is improved.
[0020] As Figure 1As shown, the laser linewidth measurement device based on short optical fiber according to this application embodiment includes: a first coupler 1, an acousto-optic modulator 4, an adjustable short optical fiber delay line device 5, a second coupler 6, a high-speed photodetector 7, and an electrical spectrum analyzer 8. The laser to be measured is split into two laser beams by the first coupler 1. One laser beam enters the acousto-optic modulator 4 to achieve precise laser frequency shift, and the other beam enters the adjustable short optical fiber delay line device 5. The laser beams emitted from the acousto-optic modulator 4 and the adjustable short optical fiber delay line device 5 are combined by the second coupler 6, and the beat frequency signal of the combined beam is detected by the high-speed photodetector 7. The detection data is sent to the electrical spectrum analyzer 8 to realize the data acquisition and visualization of the optical signal.
[0021] In one implementation, the laser linewidth measurement device based on short optical fiber may further include a variable optical attenuator connected to the incident end of the first coupler 1. The laser to be measured is attenuated by the variable optical attenuator before entering the first coupler 1, preventing other optical components in the laser linewidth measurement device from being damaged by the high-power laser.
[0022] In another implementation, the laser linewidth measurement device based on short optical fiber may further include two variable optical attenuators, wherein the first variable optical attenuator 2 is located between the first coupler 1 and the acousto-optic modulator 4 and is used to attenuate the optical power entering the acousto-optic modulator 4, and the second variable optical attenuator 3 is located between the first coupler 1 and the adjustable short optical fiber delay line device 5 and is used to attenuate the optical power entering the adjustable short optical fiber delay line device 5.
[0023] The aforementioned adjustable short fiber delay line device 5 includes at least two short delay fibers of different lengths. When in use, the length of the delay fiber can be selected according to the actual situation.
[0024] In one implementation, the adjustable short fiber delay line device 5 includes three short delay fibers of different lengths, and various combinations of the three short delay fibers are realized through an optical switch, so that the adjustable short fiber delay line device 5 has multiple fiber length settings.
[0025] like Figure 2 As shown, the adjustable short fiber delay line device 5 includes: a first short delay fiber 5-3, a second short delay fiber 5-10, a third short delay fiber 5-14, a first single-pole single-throw switch 5-1, a second single-pole single-throw switch 5-5, a third single-pole single-throw switch 5-8, a fourth single-pole single-throw switch 5-12, a fifth single-pole single-throw switch 5-16, a first single-pole double-throw switch 5-6, a second single-pole double-throw switch 5-7, a third coupler 5-2, a fourth coupler 5-4, a fifth coupler 5-9, a sixth coupler 5-11, a seventh coupler 5-13, and an eighth coupler 5-15.
[0026] One end of the first single-pole single-throw switch 5-1, the first fixed end of the first single-pole double-throw switch 5-6, and the first fixed end of the second single-pole double-throw switch 5-7 are connected, and the connection point is the input end of the adjustable range short optical fiber delay line device 5.
[0027] The other end of the first single-pole single-throw switch 5-1 is connected to one end of the first short delay optical fiber 5-3 through the third coupler 5-2, the other end of the first short delay optical fiber 5-3 is connected to one end of the fourth coupler 5-4, the other end of the fourth coupler 5-4, the second fixed end of the second single-pole double-throw switch 5-7, one end of the second single-pole single-throw switch 5-5, and one end of the third single-pole single-throw switch 5-8 are connected.
[0028] The movable end of the second single-pole double-throw switch 5-7 is connected to one end of the second short delay optical fiber 5-10 through the fifth coupler 5-9, the other end of the second short delay optical fiber 5-10 is connected to one end of the sixth coupler 5-11, the other end of the sixth coupler 5-11, the other end of the third single-pole single-throw switch 5-8, one end of the fourth single-pole single-throw switch 5-12, and the second fixed end of the first single-pole double-throw switch 5-6 are connected.
[0029] The movable end of the first single-pole double-throw switch 5-6 is connected to one end of the third short delay optical fiber 5-14 through the seventh coupler 5-13, the other end of the third short delay optical fiber 5-14 is connected to one end of the eighth coupler 5-15, and the other end of the eighth coupler 5-15 is connected to one end of the fifth single-pole single-throw switch 5-16.
[0030] In one implementation, the second coupler 6 has multiple input ends and one output end, the other end of the second single-pole single-throw switch 5-5, the other end of the fourth single-pole single-throw switch 5-12, and the other end of the fifth single-pole single-throw switch 5-16 are directly connected to the respective input ends of the second coupler 6.
[0031] In another implementation, the second coupler 6 has two input ends and one output end, the other end of the second single-pole single-throw switch 5-5, the other end of the fourth single-pole single-throw switch 5-12, and the other end of the fifth single-pole single-throw switch 5-16 are connected together, and the connection point is connected to one input end of the second coupler 6.
[0032] The lengths of the first short delay optical fiber 5-3, the second short delay optical fiber 5-10, and the third short delay optical fiber 5-14 are 500m, 1000m, and 2000m, respectively.
[0033] The length of the delay fiber includes seven levels of 500m, 1000m, 1500m, 2000m, 2500m, 3000m and 3500m, and when the laser linewidth is measured by using the above device, a proper length level can be selected according to actual conditions. The specific operation mode is as follows:
[0034] 1. When the 500m level is selected, the first single-pole single-throw switch 5-1 and the third single-pole single-throw switch 5-8 are closed, and the remaining single-pole single-throw switches are all opened, and the two single-pole double-throw switches are right-throw (as shown in the figure, the left-throw is the first fixed end, and the right-throw is the second fixed end); Figure 2
[0035] 2. When the 1000m level is selected, the fourth single-pole single-throw switch 5-12 is closed, and the remaining single-pole single-throw switches are all opened, and the second single-pole double-throw switch 5-7 is left-throw, and the first single-pole double-throw switch 5-6 is right-throw;
[0036] 3. When the 1500m level is selected, the first single-pole single-throw switch 5-1 and the fourth single-pole single-throw switch 5-12 are closed, and the remaining single-pole single-throw switches are all opened, and the two single-pole double-throw switches are right-throw;
[0037] 4. When the 2000m level is selected, the fifth single-pole single-throw switch 5-16 is closed, and the remaining single-pole single-throw switches are all opened, and the first single-pole double-throw switch 5-6 is left-throw, and the second single-pole double-throw switch 5-7 is right-throw;
[0038] 5. When the 2500m level is selected, the first single-pole single-throw switch 5-1, the third single-pole single-throw switch 5-8 and the fifth single-pole single-throw switch 5-16 are closed, and the remaining single-pole single-throw switches are all opened, and the two single-pole double-throw switches are right-throw;
[0039] 6. When the 3000m level is selected, the fifth single-pole single-throw switch 5-16 is closed, and the remaining single-pole single-throw switches are all opened, and the first single-pole double-throw switch 5-6 is right-throw, and the second single-pole double-throw switch 5-7 is left-throw;
[0040] 7. When the 3000m level is selected, the first single-pole single-throw switch 5-1 and the fifth single-pole single-throw switch 5-16 are closed, and the remaining single-pole single-throw switches are all opened, and the two single-pole double-throw switches are right-throw.
[0041] The laser linewidth measurement device based on a short optical fiber in the embodiment of the application is installed on a stable optical platform to protect the components and reduce external interference, and to ensure that the device works in a stable environment.
[0042] For the selection of the length of the optical fiber, the length thereof should be such that the envelope of the power spectral density (PSD) is clear and the envelope period is small, i.e. the extreme values are closer to the center frequency, so that the signal characteristics can be more accurately obtained, which is beneficial to subsequent linewidth measurement and analysis; meanwhile, the length of the optical fiber should be such that most of the extreme values are higher than the noise floor of the system, so as to reduce the interference of the noise on the measurement results, so as to improve the accuracy of the measurement. Under the above requirements, the length of the optical fiber is shortened as much as possible, so as to reduce the influence of the 1 / f noise.
[0043] When the short-fiber-based laser linewidth measurement device of the embodiment of the present application is used for measurement, a suitable gear is selected, and a laser light source to be measured is started. The laser beam is divided into two paths through the first coupler 1. The light entering the adjustable-gear short-fiber delay line device 5 will produce a certain delay, and the light entering the acousto-optic modulator 4 will produce a frequency shift. The two paths of light are recombined at the second coupler 6 to produce a beat frequency signal. The beat frequency signal is detected by the high-speed photoelectric detector 7 and converted into an electrical signal, which is then transmitted to the electrical spectrum analyzer 8. The coherent envelope obtained by measurement is observed on the electrical spectrum analyzer 8. The extreme points on the envelope are determined, and the difference Δs between the two extreme points is calculated. The initial conditions are substituted into the following formula:
[0044]
[0045] In the above formula, S H is the larger one of the two extreme points, S L is the smaller one of the two extreme points, m and k are natural numbers, wherein m = 0 represents the extreme point closest to the center frequency, m = 1 represents the second closest extreme point to the center frequency, and m ≠ k, |k-m| = 1, c is the speed of light, n is the refractive index of the delay optical fiber, and L is the length of the delay optical fiber.
[0046] The initial linewidth value Δf is calculated. The initial linewidth value obtained by calculation is substituted into the demodulation process. After a certain number of loop calculations, the Lorentz line shape is finally obtained, and the -3dB bandwidth is determined. The bandwidth is the laser linewidth obtained by measurement.
[0047] Taking the delay optical fiber length as 1000 meters, the initial conditions m = 0, k = 1, S H = 1.5, and S L = 0.5 as an example, the initial linewidth value is calculated to be 5.46 kHz. The initial linewidth value is used for demodulation, and the final linewidth is 5 kHz.
[0048] If the adjustable-gear short-fiber delay line device 5 in the above short-fiber-based laser linewidth measurement device is replaced by a 50km long delay optical fiber, the above measurement process is repeated, and the corresponding linewidth value is calculated to be 30.7 kHz.
[0049] The line width result obtained by the measuring device is compared with the 30.7kHz line width result obtained by a traditional long delay scheme, so that the accuracy and advantages of the device are verified.
[0050] The laser line width measuring device based on a short optical fiber has a short delay optical fiber, and the delay optical fiber length has multiple adjustable gears, so that a suitable gear can be selected according to requirements, 1 / f noise is effectively avoided, measurement accuracy is improved, and the device can be suitable for measuring lasers with various line widths.
Claims
1. A short-fiber-based laser linewidth measurement apparatus, characterized by, It comprises: a first coupler (1), an acousto-optic modulator (4), an adjustable short optical fiber delay line device (5), a second coupler (6), a high-speed photodetector (7) and an electrical spectrum analyzer (8); The laser to be measured is divided into two beams by the first coupler (1), one of which enters the acousto-optic modulator (4) and the other enters the adjustable short optical fiber delay line device (5). The laser emitted from the acousto-optic modulator (4) and the laser emitted from the adjustable short optical fiber delay line device (5) are combined by the second coupler (6) and then detected by the high-speed photodetector (7). The detection data is sent to the electrical spectrum analyzer (8).
2. The short-fiber-based laser linewidth measurement apparatus according to claim 1, wherein, The adjustable short optical fiber delay line device (5) comprises at least two short delay optical fibers with different lengths.
3. The short-fiber-based laser linewidth measurement apparatus according to claim 1 or 2, wherein The adjustable short optical fiber delay line device (5) comprises a first short delay optical fiber (5-3), a second short delay optical fiber (5-10), a third short delay optical fiber (5-14), a first single-pole single-throw switch (5-1), a second single-pole single-throw switch (5-5), a third single-pole single-throw switch (5-8), a fourth single-pole single-throw switch (5-12), a fifth single-pole single-throw switch (5-16), a first single-pole double-throw switch (5-6) and a second single-pole double-throw switch (5-7). One end of the first single-pole single-throw switch (5-1), the first fixed end of the first single-pole double-throw switch (5-6) and the first fixed end of the second single-pole double-throw switch (5-7) are connected, and the connection point serves as the input end of the adjustable short optical fiber delay line device (5). The other end of the first single-pole single-throw switch (5-1) is connected to one end of the first short delay optical fiber (5-3), and the other end of the first short delay optical fiber (5-3), the second fixed end of the second single-pole double-throw switch (5-7), one end of the second single-pole single-throw switch (5-5) and one end of the third single-pole single-throw switch (5-8) are connected. The movable end of the second single-pole double-throw switch (5-7) is connected to one end of the second short delay optical fiber (5-10), and the other end of the second short delay optical fiber (5-10), the other end of the third single-pole single-throw switch (5-8), one end of the fourth single-pole single-throw switch (5-12) and the second fixed end of the first single-pole double-throw switch (5-6) are connected. The movable end of the first single-pole double-throw switch (5-6) is connected to one end of the third short delay optical fiber (5-14), and the other end of the third short delay optical fiber (5-14) is connected to one end of the fifth single-pole single-throw switch (5-16).
4. The short-fiber-based laser linewidth measurement apparatus according to claim 3, wherein The other end of the second single-pole single-throw switch (5-5), the other end of the fourth single-pole single-throw switch (5-12) and the other end of the fifth single-pole single-throw switch (5-16) are connected, and the connection point serves as the output end of the adjustable short optical fiber delay line device (5).
5. The short-fiber-based laser linewidth measurement apparatus according to claim 3, wherein The first short delay optical fiber (5-3), the second short delay optical fiber (5-10) and the third short delay optical fiber (5-14) have different lengths.
6. The short-fiber-based laser linewidth measurement apparatus according to claim 3, wherein The length of the first short delay optical fiber (5-3) is 500 meters, the length of the second short delay optical fiber (5-10) is 1000 meters, and the length of the third short delay optical fiber (5-14) is 2000 meters.
7. The short-fiber-based laser linewidth measurement apparatus according to claim 1, wherein A variable optical attenuator is further included, which is connected with the incident end of the first coupler (1).
8. The short-fiber-based laser linewidth measurement apparatus of claim 1, wherein, A first variable optical attenuator (2) and a second variable optical attenuator (3) are further included. The first variable optical attenuator (2) is located between the first coupler (1) and the acousto-optic modulator (4). The second variable optical attenuator (3) is located between the first coupler (1) and the adjustable short optical fiber delay line device (5).