Method and device for measuring polarization extinction ratio signal

Abstract

The invention discloses a method and device for measuring a polarization extinction ratio signal, and the method comprises the following steps: dividing stable wide-spectrum light emitted by a white light source into two beams, one beam is used as signal light, and the other beam is used as reference light; the signal light reflected by each event point of the to-be-detected distributed polarization-maintaining device is coupled with the reference light passing through the delay line to generate a beat frequency interference signal; obtaining a distance-return loss curve, and determining the position of each event point according to the peak position; changing a delay line scanning range, changing polarization state directions of the signal light through a polarization controller, and performing delay line scanning in each polarization state direction; and finding echo reflection peaks of all fast and slow axes on the multiple groups of curves corresponding to each event point, converting the echo reflection peaks into return loss values of the fast and slow axes of the corresponding event point, calculating the maximum difference value of the return loss values of the fast and slow axes, and calculating the actual extinction ratio of the corresponding event point according to the extinction ratio definition. The method is simple and high in measurement precision.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement, and in particular to a method and a device for measuring a polarization extinction ratio signal. Background Art

[0002] White light interferometry is an effective method and solution for measuring weak optical signals. By using the extremely short coherence length of white light, the intensity detection and distance positioning of extremely weak signals can be achieved.

[0003] The current mainstream method for measuring the extinction ratio of polarization-maintaining devices is to control the polarization direction of the incident light through a polarizer, and monitor the magnitude of the output optical power in the fast and slow axis directions at the same time. When the optical power difference in the two directions reaches the maximum, it is the polarization-maintaining ability of the device, that is, the extinction ratio. Polarization extinction ratio (PER) is an important parameter used to quantify the ability of optical fiber components to maintain the incident polarization state. PER is expressed in decibels (dB), representing the ratio of the optical power of the desired polarization state to the optical power of the undesired polarization state. It is an important parameter in optical communication systems, especially when dealing with polarization-sensitive components and signals.

[0004] The traditional method is a transmission measurement, and what is detected is the extinction ratio of the entire device from the input end to the output end, and it cannot measure the situation of multiple event points inside the device. Summary of the invention

[0005] In view of the defect that the current conventional measurement of the extinction ratio of a polarization-maintaining device is an overall power measurement and a distributed measurement of specific event points inside a device or module cannot be performed, the present invention proposes a method and system for measuring the extinction ratio by white light interferometry, which can realize distributed measurement of the polarization extinction ratio of each event point position of the polarization-maintaining device.

[0006] The technical solution adopted by the present invention is: A method for measuring a polarization extinction ratio signal is provided, comprising the following steps: The stable broad-spectrum light emitted by the white light source is divided into two beams, one as signal light passes through the polarization controller and enters the distributed polarization-maintaining device to be tested, and the other as reference light enters the delay line; The signal light reflected by each event point of the distributed polarization-maintaining device to be measured is coupled with the reference light passing through the delay line to generate a beat frequency interference signal; By scanning the delay line and demodulating the beat frequency interference signal, a distance-return loss curve is obtained, and the position of each event point is determined according to the peak position in the distance-return loss curve; The delay line scanning range is set according to the event point position, the polarization state direction of the signal light is changed by the polarization controller, and the delay line scanning is performed in each polarization state direction; For each event point, multiple sets of distance-return loss curves under different polarization states are obtained. The echo reflection peaks of all fast and slow axes on the multiple sets of curves are found and converted into return loss differences of the corresponding event points. The maximum difference between the fast and slow axis return loss values ​​is calculated, and then the actual extinction ratio of the corresponding event point is calculated according to the definition of the extinction ratio.

[0007] Following the above technical solution, the polarization controller adjusts the polarization direction of the signal light to any direction between 0-360°.

[0008] According to the above technical solution, the scanning range of the delay line is greater than twice the fast and slow axis delay difference of the current event point.

[0009] Following the above technical solution, the optical path of the reference light is continuously changed by controlling the delay line to move the position of the internal reflector and continuously changing the optical path of the light passing therethrough.

[0010] Following the above technical solution, the polarization state direction of the signal light is randomly changed by a polarization controller.

[0011] The present invention also provides a device for measuring a polarization extinction ratio signal, comprising: White light source, used to emit stable broad spectrum light; A first optical fiber coupler is used to split the stable broadband light into two beams, one of which is the signal light and the other is the reference light; The measuring arm includes a circulator, a polarization controller and a distributed polarization-maintaining device to be measured, wherein the signal light enters the polarization controller through an output end of the circulator, and the signal light reflected by each event point of the distributed polarization-maintaining device to be measured is output through another output end of the circulator; a reference arm, including a delay line through which the reference light is output; A second optical fiber coupler is used to couple the signal light reflected by the measuring arm with the reference light passing through the delay line to generate a beat frequency interference signal; A distance-return loss curve generator, used to analyze the scanning signal and beat frequency interference signal of the delay line to generate a distance-return loss curve; A controller is used to determine the position of each event point according to the peak position in the distance-return loss curve; and to set the delay line scanning range according to the event point position, and to change the polarization state direction of the signal light by controlling the polarization controller, and to perform delay line scanning in each polarization state direction; The extinction ratio calculation module is used to obtain multiple sets of distance-return loss curves under different polarization states for each event point, find the echo reflection peaks of all fast and slow axes on the multiple sets of curves and convert them into return loss differences of the corresponding event points, calculate the maximum difference between the fast and slow axis return loss values, and then calculate the actual extinction ratio of the corresponding event point according to the extinction ratio definition.

[0012] Following the above technical solution, the polarization controller is an electric polarization controller.

[0013] According to the above technical solution, the delay line is an optical fiber delay line.

[0014] According to the above technical solution, the controller controls the polarization state direction of the polarization controller to be any direction in the range of 0-360°.

[0015] Following the above technical solution, a plurality of reflectors are arranged inside the delay line, and the controller controls the delay line to move the position of the internal reflectors, thereby continuously changing the optical path of the light passing therethrough to continuously change the optical path of the reference light.

[0016] The beneficial effects of the present invention are as follows: the present invention utilizes the characteristic that when light is transmitted in a polarization-maintaining device, its fast and slow axes will produce a time delay difference, and utilizes white light interference scanning to separate the interference of two delayed lights in distance, and accurately measures the return loss of the two optical signals, and then calculates the extinction ratio through the return loss. The present invention realizes the polarization extinction ratio of each event point position of the distributed measurement polarization-maintaining device, without considering the influence of the polarization direction of the incident light when the sample is docked with the measurement structure and the working main axis direction of the device to be measured, and has a simple structure and high measurement sensitivity.

[0017] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A flow chart of a method for measuring a polarization extinction ratio signal according to an embodiment of the present invention; Figure 2 Schematic diagram of an extinction ratio measurement device based on white light interferometry according to an embodiment of the present invention; Figure 3 is a distance-return loss curve, which includes reflection peak signals of n event points inside the distributed polarization-maintaining device to be tested; Figure 4 Schematic diagram of the angle between the polarization direction of the incident light and the fast and slow axis directions of the polarization-maintaining device; Figure 5 It is a schematic diagram of the fast and slow axis return loss signal after the distance of a certain event point is magnified in the distance-return loss curve; Figure 1 In the figure: 1. White light source; 2. First fiber coupler; 3. circulator; 4. Delay line; 5. Polarization controller; 6. Distributed polarization-maintaining device to be tested; 7. Second fiber coupler. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] It should be noted that the illustrations provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0022] In the present invention, it is also necessary to explain that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0023] In addition, it should be noted that the features of the various embodiments of the present invention may be combined or combined in part or in whole, and may interact and operate in different ways as will be appreciated by those skilled in the art. Each embodiment may be implemented independently of one another, or in an associated relationship.

[0024] Example 1 like Figure 1 As shown, the method for measuring the polarization extinction ratio signal according to the embodiment of the present invention comprises the following steps: S1, split the stable broad-spectrum light emitted by the white light source into two beams, one as signal light entering the distributed polarization-maintaining device to be tested through the polarization controller, and the other as reference light entering the delay line; S2, the signal light reflected by each event point of the distributed polarization-maintaining device to be measured is coupled with the reference light passing through the delay line to generate a beat frequency interference signal; S3, obtaining a distance-return loss curve by scanning the delay line and demodulating the beat frequency interference signal, and determining the position of each event point according to the peak position in the distance-return loss curve; S4, setting the delay line scanning range according to the event point position, changing the polarization state direction of the signal light through the polarization controller, and performing delay line scanning in each polarization state direction; S5. For each event point, multiple sets of distance-return loss curves under different polarization states are obtained. The echo reflection peaks of all fast and slow axes on the multiple sets of curves are found and converted into the return loss difference of the corresponding event point. The maximum difference between the fast and slow axis return loss values ​​is calculated, and then the actual extinction ratio of the corresponding event point is calculated according to the definition of the extinction ratio.

[0025] Furthermore, the polarization controller adjusts the polarization state direction of the signal light to any direction between 0 and 360°; the scanning range of the delay line is greater than the distance length of each event point caused by the delay of the fast and slow axes (taking the Xn event point as an example, the delay line scanning range should at least cover the position of the fast and slow axes at point Xn).

[0026] Furthermore, the optical path of the reference light can be continuously changed by controlling the delay line to move the position of the internal reflector and continuously changing the optical path of the light passing therethrough. The polarization state direction of the signal light can also be randomly changed by a polarization controller.

[0027] Among them, return loss is the return loss, which is the size (intensity) of the light reflected back after the incident light passes through the optical link to be measured, corresponding to the signal height (peak height) in the distance-return loss curve. According to the vertical coordinate of the measured peak, the specific corresponding return loss can be obtained by corresponding calibration and conversion. Specifically, a standard return loss component can be used for actual measurement, and a corresponding relationship between the peak value and the return loss value can be established in advance, and the table can be looked up for later measurement.

[0028] During the specific measurement, the delay line is scanned first to determine the positions of all event points. Each event point position will correspond to two very close peaks on the fast and slow axes (such as Figure 3 Find an event point X1, X2, ..., X n , then adjust the polarization controller to a random direction so that the delay line is at X n Adjust the polarization controller again to make the polarization direction different from the last time (different from all previous directions), and continue to scan the fiber delay line near this point. Repeat this step, and obtain multiple sets of distance-return loss curves in different polarization states for each event point. Find the echo reflection peaks of all fast and slow axes on the multiple sets of curves, and calculate the maximum difference between the fast and slow axis return loss reflection peaks (such as Figure 4 As shown in the figure), and converted into the return loss difference △RL of the corresponding event point max (like Figure 5 As shown, in each set of curves, when the polarization direction is on the fast axis or the slow axis, the return loss difference is the largest).

[0029] The mathematical formula for polarization extinction ratio (PER) is:

[0030] Among them, P Desiredis the optical power in the desired polarization state, P Undesired is the optical power in the unwanted polarization state.

[0031] In the present invention, PER=P 快轴 / P 慢轴 Or PER=P 慢轴 / P 快轴 , where P 快轴 is the optical power of the fast axis transmitted light, P 慢轴 It is the optical power of the slow axis transmitted light. It mainly depends on whether the working axis is the fast axis or the slow axis. The one with a larger value is the main axis and is used as the numerator in the calculation formula.

[0032] If the fast axis is used as the main axis in this embodiment, PER=(P 快轴 / P 入射 ) / (P 慢轴 / P 入射 ) That is, PER = IL 快 / IL 慢 , where IL 快 is the transmission light loss of the fast axis, IL 慢 Is the transmission light loss of the slow axis. After conversion to logarithmic coordinates, PER (dB) = IL 快轴 (dB)-IL 慢轴 (dB).

[0033] After using white light interferometry, the measured echo signal is the reflected signal. The fast / slow axis echo reflected light will pass through the DUT twice, while the transmitted light only passes through the DUT once, so the loss is halved, PER (dB) = IL 快轴 (dB)-IL 慢轴 (dB) = 2 △RL max , thus obtaining the actual extinction ratio of the corresponding event point.

[0034] The method utilizes the characteristic that when light is transmitted in a polarization-maintaining device, its fast and slow axes will produce a delay difference. By using white light interference scanning, two delayed lights are separated in distance for interference, and the maximum return loss of the two light reflection signals is accurately measured. The transmission return loss is then calculated based on the relationship between the return loss of the reflected light and the transmission return loss, and the extinction ratio is finally calculated. The present invention can calculate the polarization extinction ratio of each event point position through a distributed measurement of the polarization-maintaining device, without considering the influence of the polarization direction of the incident light when the sample is docked with the measurement structure and the direction of the working main axis of the device to be measured. The structure is simple and the measurement sensitivity is high.

[0035] Example 2 This embodiment is a device, which is mainly used to implement the above method embodiment.

[0036] like Figure 2As shown, the device for measuring the polarization extinction ratio signal of this embodiment includes: A white light source 1, for emitting stable broad-spectrum light; A first optical fiber coupler 2 is used to split the stable broadband light into two beams, one of which is the signal light and the other is the reference light; The measuring arm includes a circulator 3, a polarization controller 5 and a distributed polarization-maintaining device 6 to be measured, wherein the signal light enters the polarization controller through an output end of the circulator 3, and the signal light reflected by each event point of the distributed polarization-maintaining device 6 to be measured is output through another output end of the circulator 3; A reference arm, comprising a delay line 4, through which the reference light is output; A second optical fiber coupler 7 is used to couple the signal light reflected by the measuring arm with the reference light passing through the delay line 4 to generate a beat frequency interference signal; A distance-return loss curve generator (not shown in the figure), used to analyze the scanning signal and the beat frequency interference signal of the delay line to generate a distance-return loss curve; A controller (not shown in the figure) is used to determine the position of each event point according to the peak position in the distance-return loss curve; and to set the delay line scanning range according to the event point position, and to change the polarization state direction of the signal light by controlling the polarization controller, and to perform delay line scanning in each polarization state direction; The extinction ratio calculation module (not shown in the figure) is used to find the echo reflection peaks of all fast and slow axes on multiple sets of curves based on multiple sets of distance-return loss curves in different polarization states obtained for each event point, and take the maximum difference between the fast and slow axis return loss reflection peaks as the return loss difference of the corresponding event point, and then calculate the actual extinction ratio of the corresponding event point according to the extinction ratio definition.

[0037] The polarization controller 5 may be an electric polarization controller. The delay line 4 may be an optical fiber delay line. The polarization state direction of the polarization controller may be controlled by the controller to be any direction in the range of 0-360°.

[0038] Specifically, a plurality of reflectors are arranged inside the delay line 4, and the controller controls the delay line to move the positions of the internal reflectors, thereby continuously changing the optical path of the light passing therethrough to continuously change the optical path of the reference light.

[0039] The output end of the white light source 1 is connected to the input end of the first fiber coupler 2, one of the output ends of the first fiber coupler 2 is used as a signal light and connected to the first port of the circulator 3, the second port of the circulator 3 is connected to the polarization controller 5 and sequentially connected to the distributed polarization-maintaining device 6 to be tested, and the third port of the circulator 3 is connected to the second fiber coupler 7; the other output end of the first fiber coupler 2 is used as a reference light and connected to the delay line 4, and the delay line 4 is connected to the second fiber coupler 7.

[0040] The white light source 1 emits a broad spectrum of light, which is divided into two paths through the first fiber coupler 2. One path enters the first port of the circulator 3 as signal light, and enters the polarization controller 5 through the second port of the circulator 3. The polarization controller 5 can adjust the polarization direction of the incident light entering the distributed polarization-maintaining device 6 to be tested to any direction within 360°. The incident light of any polarization direction enters the distributed polarization-maintaining device 6 to be tested, and the echo light signal reflected back in real time comes out from the third port of the circulator 3 and enters the second fiber coupler 7. The other path of the first fiber coupler 2 enters the delay line 4 as reference light. After the delay line 4 is running, the optical path of the reference light is continuously adjusted, and finally enters the second fiber coupler 7. Beat frequency interference occurs here with the signal light reflected back from the distributed polarization-maintaining device 6 to be tested. Because white light is broad spectrum light, its coherence length is extremely short (generally in the order of um to tens of um. It can be approximately considered that coherence occurs when the optical paths of the two paths are completely equal.

[0041] The optical fiber delay line, the electric polarization controller, and the collection and processing of data can all be controlled and processed by the controller or the host computer instructions.

[0042] When constructing the interference structure, the total optical path length of the reflected light of the distributed polarization-maintaining device 6 to be measured is controlled to fall within the total optical path length range of the reference light scanned by the delay line 4 .

[0043] The method for measuring the extinction ratio by the above device mainly includes the following steps: Step 1. According to Figure 2 Build the entire device; Step 2. Obtain the distance-return loss curve (distance = speed × time) by scanning the optical fiber delay line. The peak position on the curve corresponds to the return loss signal of the fast axis or slow axis. Calibrate according to the peak value (e.g., by looking up a table) to obtain the return loss value. Step 3, find the specific position Xn of the peak value of each event point in the distance-return loss curve, such as Figure 3 As shown; Step 4, randomly change the polarization state of the signal light N times through the polarization controller. When a polarization state direction is determined, set the delay line scanning range to be near Xn and scan the optical fiber delay line once; Step 5. Obtain the return loss value RL of the fast and slow axis echo reflection peaks under N groups of different polarization states at each event point. 快 and RL 慢 ; Step 6. Find the group with the largest difference in fast and slow axis return loss peak value among all groups of return loss test results to obtain the specific return loss size and calculate the return loss difference △RL max Finally, according to the definition of extinction ratio, △RL max Multiplying by 2 gives the actual extinction ratio at the sample position corresponding to the current reflection peak; By repeating the above steps, the specific extinction ratios of all event points Xn in the distance-return loss curve can be calculated.

[0044] Wherein, in step 1, the polarization type of the light source of the white light interference structure is single mode, and the wavelength of the light source can be in the range of O band, C band or L band.

[0045] The delay line can be a fiber delay line. In step 2, the optical path of the light passing through it can be changed by controlling the scan, thereby changing the length (optical path) of the entire reference arm. The delay line scanning range can be set according to the event point position (more efficient), or the full range can be scanned each time.

[0046] The polarization controller may be an electric polarization controller. In Step 4, the polarization state of light may be changed to any direction by squeezing the optical fiber to deform the optical fiber.

[0047] In summary, the present invention utilizes the characteristic that the fast and slow axes of the distributed polarization-maintaining device will produce a time delay difference, and uses white light interference scanning to separate the interference of two delayed lights in distance, and accurately measures the return loss of the two reflected light signals, and then calculates the extinction ratio through the relationship between the transmitted light and the reflected light. The polarization extinction ratio of each event point position of the distributed polarization-maintaining device does not need to consider the influence of the polarization direction of the incident light when the distributed polarization-maintaining device to be tested is connected to the test device and the direction of the working main axis of the distributed polarization-maintaining device. It only needs to find the peak point on the corresponding distance-return loss curve to calculate the corresponding return loss. It has a simple structure and high measurement accuracy.

[0048] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0049] The order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0050] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for measuring a polarization extinction ratio signal, characterized in that: The following steps are involved: The stable broad-spectrum light emitted by the white light source is divided into two beams, one as signal light passes through the polarization controller and enters the distributed polarization-maintaining device to be tested, and the other as reference light enters the delay line; The signal light reflected by each event point of the distributed polarization-maintaining device to be measured is coupled with the reference light passing through the delay line to generate a beat frequency interference signal; By scanning the delay line and demodulating the beat frequency interference signal, a distance-return loss curve is obtained, and the position of each event point is determined according to the peak position in the distance-return loss curve; The delay line scanning range is set according to the event point position, the polarization state direction of the signal light is changed by the polarization controller, and the delay line scanning is performed in each polarization state direction; For each event point, multiple sets of distance-return loss curves under different polarization states are obtained. The echo reflection peaks of all fast and slow axes on the multiple sets of curves are found and converted into return loss differences of the corresponding event points. The maximum difference between the fast and slow axis return loss values ​​is calculated, and then the actual extinction ratio of the corresponding event point is calculated according to the definition of the extinction ratio.

2. The method for measuring the polarization extinction ratio signal according to claim 1, characterized in that: The polarization controller adjusts the polarization direction of the signal light to any direction between 0 and 360 degrees.

3. The method for measuring polarization extinction ratio signal according to claim 1, characterized in that: The scanning range of the delay line is greater than twice the delay difference between the fast and slow axes of the current event point.

4. The method for measuring polarization extinction ratio signal according to claim 1, characterized in that: The optical path length of the reference light is continuously changed by controlling the delay line to move the position of the internal reflector and continuously changing the optical path length of the light passing therethrough.

5. The method for measuring polarization extinction ratio signal according to claim 1, characterized in that: The polarization direction of the signal light is randomly changed by the polarization controller.

6. A device for measuring a polarization extinction ratio signal, characterized in that: include: White light source, used to emit stable broad spectrum light; A first optical fiber coupler is used to split the stable broadband light into two beams, one of which is the signal light and the other is the reference light; The measuring arm includes a circulator, a polarization controller and a distributed polarization-maintaining device to be measured, wherein the signal light enters the polarization controller through an output end of the circulator, and the signal light reflected by each event point of the distributed polarization-maintaining device to be measured is output through another output end of the circulator; a reference arm, including a delay line through which the reference light is output; A second optical fiber coupler is used to couple the signal light reflected by the measuring arm with the reference light passing through the delay line to generate a beat frequency interference signal; A distance-return loss curve generator, used to analyze the scanning signal and beat frequency interference signal of the delay line to generate a distance-return loss curve; A controller is used to determine the position of each event point according to the peak position in the distance-return loss curve; and to set the delay line scanning range according to the event point position, and to change the polarization state direction of the signal light by controlling the polarization controller, and to perform delay line scanning in each polarization state direction; The extinction ratio calculation module is used to find the echo reflection peaks of all fast and slow axes on multiple sets of curves based on multiple sets of distance-return loss curves in different polarization states obtained for each event point and convert them into return loss values ​​of the corresponding event points, calculate the maximum difference between the fast and slow axis return loss values, and then calculate the actual extinction ratio of the corresponding event point according to the extinction ratio definition.

7. The device for measuring polarization extinction ratio signal according to claim 6, characterized in that: The polarization controller is an electric polarization controller.

8. The device for measuring polarization extinction ratio signal according to claim 6, characterized in that: The delay line is a fiber optic delay line.

9. The device for measuring polarization extinction ratio signal according to claim 6, characterized in that: The controller controls the polarization state direction of the polarization controller to be any direction in the range of 0-360°.

10. The device for measuring polarization extinction ratio signal according to claim 6, characterized in that: A plurality of reflectors are arranged inside the delay line, and the controller controls the delay line to move the positions of the internal reflectors, thereby continuously changing the optical path of the light passing therethrough to continuously change the optical path of the reference light.

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