A device and method for measuring polarization-dependent loss of polarization-maintaining optical fiber device

Abstract

A device and method for measuring polarization-dependent loss of a polarization-maintaining optical fiber device, belonging to the technical field of optical fiber communication, solves the technical problem of how to accurately measure the polarization-dependent loss of a device using a polarization-maintaining optical fiber; through the constructed measuring device, the value of the polarization-dependent loss PDL of an optical device whose input end is a polarization-maintaining optical fiber is measured, and the calculation of PDL only needs to record the maximum value and the minimum value in the optical power meter, and the difference between the two values ​​is the required value, and the measuring method is simple; a waveform generator sends a signal to a phase modulator to change the voltage value and thus change the polarization state of light, which is more accurate than adjusting a polarization rotator to change the polarization state of light.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber communication, and relates to a device and method for measuring polarization-related loss of a polarization-maintaining optical fiber device. Background Art

[0002] Polarization dependent loss (PDL) is the maximum transmission difference of an optical device or system under all polarization states. It is the ratio of the maximum transmission to the minimum transmission of an optical device under all polarization states. Polarization dependent loss has now become a standard indicator for describing the characteristics of passive optical devices. There are currently two main PDL measurement methods: polarization scanning method and fixed state method. The polarization scanning method is a relative measurement method. Its actual measurement value reflects the deviation value of the optical power as the polarization state of the incident light changes. The difference between the maximum and minimum values ​​in the measured power value is the PDL. The fixed state method is a measurement method derived from the transmission characteristics of polarized light using the Mueller matrix and Lagrange extremum method.

[0003] In the prior art, the polarization-dependent loss of a device is measured by connecting the device to be measured to the measurement system using an ordinary optical fiber, changing the polarization state of the incident light by adjusting a polarization rotator to act on the ordinary optical fiber, recording the deviation value of the polarization state of the incident light, and then calculating the PDL. This method is only applicable to ordinary optical fiber devices. If it is a polarization-maintaining optical fiber device, this method cannot be used to measure it. This is because the polarization state of the polarization-maintaining optical fiber cannot be changed, so a polarization rotator cannot be used.

[0004] The function of a polarization beam splitter (PBS) is to split a beam of light into two beams of linearly polarized light with orthogonal polarization directions: horizontal polarization and vertical polarization, and separate them into two different propagation directions, which are usually perpendicular to each other.

[0005] A method for measuring polarization-dependent loss (PDL) is disclosed in a Chinese invention patent application entitled "Measurement Method for Polarization-Dependent Loss (PDL)" with a publication date of June 27, 2007 and publication number 1988419A. The technical solution is to allow an incident modulated optical signal to enter a birefringent device, then pass through an analyzer, a PDL-to-be-measured device in sequence, and finally enter a polarimeter; the polarization rotator is rotated one circle along the polarization axis, and the maximum and minimum DOP values ​​that appear in this process are recorded respectively, and the PDL value of the device is calculated according to the following formula, which is as follows:

[0006]

[0007] Although the above technical solution can quickly and effectively measure the PDL value in an optical device or system under single wavelength or multi-wavelength conditions, the above technical solution is not suitable for measuring the polarization-dependent loss of a polarization-maintaining optical fiber device.

[0008] If the four-state measurement rule is used, four polarization states need to be generated to measure the PDL of the device, but eight power values ​​need to be measured to calculate the PDL. The noise and measurement error of the power meter will greatly affect the measurement error of the PDL. Secondly, since it is necessary to measure the power that does not pass through and passes through the device under test, the stability of the light source will have a great error impact on the measurement result. Summary of the invention

[0009] The technical problem to be solved by the present invention is how to accurately measure the polarization-related loss of a device using a polarization-maintaining optical fiber.

[0010] The present invention solves the above technical problems through the following technical solutions:

[0011] A polarization-dependent loss measuring device is used to measure the polarization-dependent loss of a polarization-maintaining optical fiber device, comprising: a waveform generator (1), a laser (2), an optical power meter (3), a phase modulator (4) and a delay line (5); the first channel of the waveform generator (1) is connected to the input end of the laser (2), and the output end of the laser (2) is connected to the polarization-maintaining optical fiber device through a first pigtail (P1); the second channel of the waveform generator (1) is connected to the input end of the phase modulator (4), one output port of the phase modulator (4) is connected to the polarization-maintaining optical fiber device through a second pigtail (P2), the other output port is connected to one end of the delay line (5), and the other end of the delay line (5) is connected to the polarization-maintaining optical fiber device through a fourth pigtail (P4); the optical power meter (3) is connected to the polarization-maintaining optical fiber device through a third pigtail (P3).

[0012] The present invention measures the polarization dependent loss (PDL) value of an optical device whose input end is a polarization-maintaining optical fiber by means of a constructed measuring device. The calculation of PDL only requires recording the maximum value and the minimum value in the optical power meter (3). The difference between the two values ​​is the desired value. The measuring method is simple.

[0013] As a further improvement of the technical solution of the present invention, the light pulse emitted by the laser (2) enters from the first pigtail (P1) of the polarization-maintaining optical fiber device, and is divided into two polarized light beams after passing through the polarization-maintaining optical fiber device, wherein the path of one polarized light beam is: the second pigtail (P2) → phase modulator (4) → delay line (5) → fourth pigtail (P4); the path of the other polarized light beam is: the fourth pigtail (P4) → delay line (5) → phase modulator (4) → second pigtail (P2); the paths of the two polarized light beams form a loop with equal distance and opposite direction, and return to the polarization-maintaining optical fiber device to overlap and form a Sagnac loop; the position of the delay line (5) is adjusted so that the phase modulator (4) is placed in an asymmetric position of the Sagnac loop, and the phase modulator (4) separates the Sagnac loop into two sections of optical fiber, and the time difference of the light pulse passing through the two sections of optical fiber is greater than the rise and fall time of the voltage signal loaded by the waveform generator (1).

[0014] As a further improvement of the technical solution of the present invention, the polarization-maintaining optical fiber device is a polarization beam splitter (PBS) or a polarization circular beam splitter (PCIR).

[0015] As a further improvement of the technical solution of the present invention, if the first pigtail (P1) is connected to the laser (2), then the third pigtail (P3) is connected to the optical power meter (3); if the first pigtail (P1) is connected to the optical power meter (3), then the third pigtail (P3) is connected to the laser (2).

[0016] As a further improvement of the technical solution of the present invention, the first pigtail (P1), the second pigtail (P2), the third pigtail (P3), and the fourth pigtail (P4) are all polarization-maintaining optical fibers.

[0017] As a further improvement of the technical solution of the present invention, the phase modulator (4) is a polarization-maintaining phase modulator.

[0018] A measuring method using the measuring device comprises the following steps:

[0019] Step 1): Build a measuring device;

[0020] Step 2): Turn on the first channel and the second channel of the waveform generator (1), set the parameters of the two channels respectively, and confirm that the waveforms of the two channels are normal;

[0021] Step 3): By rotating the knob of the waveform generator (1), the phase value of the voltage output by the second channel is adjusted, thereby changing the polarization state of the light, from 0° to 360°, observing the reading of the optical power meter (3), and recording the maximum and minimum values ​​of the reading;

[0022] Step 4): Calculate the polarization dependent loss PDL.

[0023] As a further improvement of the technical solution of the present invention, the parameters in step 2) include: waveform, frequency, delay, high and low levels, and duty cycle.

[0024] As a further improvement of the technical solution of the present invention, the adjustment step value from 0° to 360° in step 3) is set to 1°.

[0025] As a further improvement of the technical solution of the present invention, the calculation formula for calculating the polarization-dependent loss PDL in step 4) is: PDL = max (Power P3) - min (Power P3), where max (Power P3) and min (Power P3) represent the maximum and minimum readings on the optical power meter (3), respectively.

[0026] The advantages of the present invention are:

[0027] (1) The present invention measures the polarization-dependent loss (PDL) of an optical device whose input end is a polarization-maintaining optical fiber by means of a constructed measuring device. The calculation of PDL only requires recording the maximum value and the minimum value in the optical power meter (3). The difference between the two values ​​is the desired value. The measuring method is simple.

[0028] (2) The waveform generator (1) sends a signal to the phase modulator (4), thereby changing the voltage value and thus changing the polarization state of the light. This is more accurate than adjusting the polarization rotator to change the polarization state of the light. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural diagram of a device for measuring polarization-dependent loss of a polarization-maintaining optical fiber device according to a first embodiment of the present invention;

[0030] Figure 2 It is a structural diagram of a device for measuring polarization-dependent loss of a polarization-maintaining optical fiber device according to a second embodiment of the present invention;

[0031] Figure 3 It is a flow chart of a method for measuring polarization-dependent loss of a polarization-maintaining optical fiber device according to embodiments 1 and 2 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0034] Embodiment 1

[0035] like Figure 1 As shown, the device for measuring polarization-dependent loss of polarization-maintaining optical fiber devices in this embodiment includes a waveform generator 1, a laser 2, an optical power meter 3, a phase modulator 4 and a delay line 5. The device to be measured in this embodiment is a four-port polarization beam splitter PBS.

[0036] The four-port polarization beam splitter has four pigtails P1, P2, P3, and P4, all of which are polarization-maintaining optical fibers, wherein the pigtail P1 is connected to the laser 2, the pigtail P2 is connected to the in port of the phase modulator 4, the pigtail P3 is connected to the optical power meter 3 for measuring the optical power, and the pigtail P4 is connected to one end of the delay line 5; the laser 2 is connected to the CH1 port of the waveform generator 1; the phase modulator 4 is connected to the CH2 port of the waveform generator 1, and the out port of the phase modulator 4 is connected to the other end of the delay line 5; the phase modulator 4 adopts a polarization-maintaining phase modulator.

[0037] The light pulse emitted by laser 2 enters from the pigtail P1 of PBS, and is divided into two polarized light beams after passing through PBS. The path of one polarized light beam is: PBS→pigtail P2→phase modulator 4→delay line 5→pigtail P4→PBS; the path of the other polarized light beam is: PBS→pigtail P4→delay line 5→phase modulator 4→pigtail P2→PBS; the paths of the two polarized light beams form a loop with equal distance and opposite direction, and return to PBS to overlap and form a Sagnac loop.

[0038] The position of the delay line 5 is adjusted so that the phase modulator 4 is placed in an asymmetric position of the Sagnac loop. Its time asymmetry must be greater than the rise and fall times of the voltage signal loaded by the waveform generator 1, that is, the phase modulator 4 separates the Sagnac loop into two sections of optical fiber. The time difference of the light pulse passing through the two sections of optical fiber must be greater than the rise and fall times of the voltage signal loaded by the waveform generator 1 to ensure the accuracy of the measurement results.

[0039] Since the input end of PBS is the polarization-maintaining fiber P1, the traditional solution cannot measure it; connect the pigtail P2 of PBS to the in port of the phase modulator 4, connect the pigtail P4 to the delay line 5, and connect to the out port of the phase modulator 4 through the delay line 5, send a signal to the phase modulator 4 through the waveform generator 1, change the voltage value of the phase modulator 4, and thus change the polarization state of the light in the Sagnac loop; read the maximum and minimum values ​​through the optical power meter 3, and the PDL is the difference between the maximum and minimum values.

[0040] In this embodiment, the positions of the laser 2 and the optical power meter 3 can be interchanged, that is, if the laser 2 is connected to the pigtail P1, then the optical power meter 3 is connected to the pigtail P3; if the optical power meter 3 is connected to the pigtail P1, then the laser 2 is connected to the pigtail P3.

[0041] Figure 3 This is a flow chart of a method for measuring polarization-dependent loss of a polarization-maintaining optical fiber device. The method includes the following steps:

[0042] 1. According to Figure 1 The device shown is used to measure the polarization-dependent loss of polarization-maintaining optical fiber devices;

[0043] 2. Turn on waveform generator 1, set the waveform, frequency, delay, high and low levels, duty cycle and other parameters output by CH1 and CH2 of waveform generator 1 respectively, and confirm that the pulse waveform output by CH1 and the sine waveform output by CH2 are normal;

[0044] 3. Adjust the phase (delay) value of the voltage output from the CH2 port by rotating the knob of waveform generator 1, thereby adjusting the polarization state of the light from 0° to 360° (set to 1° in steps). At this time, the optical power will change, and the reading on the optical power meter 3 will change accordingly. Observe the reading of the optical power meter 3 and write down the maximum value max (Power P3) and the minimum value min (Power P3).

[0045] 4. Calculate the polarization dependent loss PDL using the formula: PDL = max(Power P3) - min(Power P3).

[0046] Embodiment 2

[0047] like Figure 2 As shown, different from the first embodiment, the device under test in this embodiment is a circular polarization beam splitter (PCIR). In this embodiment, the PBS in the first embodiment is replaced with a circular polarization beam splitter (PCIR). The light emitted by the laser 2 enters from the pigtail P1 of the circular polarization beam splitter, passes through the PBS in the PCIR and is split into two polarized lights, which are respectively returned to the PCIR by the pigtail P2 and the pigtail P4 through the same optical path with opposite directions, and are superimposed to form a Sagnac loop. Figure 3 As shown, the measuring method of this embodiment is the same as the measuring method of the first embodiment.

[0048] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polarization-dependent loss measurement device, characterized in that: The device is used to measure the polarization-dependent loss of a polarization-maintaining optical fiber device, comprising: a waveform generator (1), a laser (2), an optical power meter (3), a phase modulator (4), and a delay line (5); the first channel of the waveform generator (1) is connected to the input end of the laser (2), and the output end of the laser (2) is connected to the polarization-maintaining optical fiber device through a first pigtail (P1); the second channel of the waveform generator (1) is connected to the input end of the phase modulator (4), one output port of the phase modulator (4) is connected to the polarization-maintaining optical fiber device through a second pigtail (P2), the other output port is connected to one end of the delay line (5), and the other end of the delay line (5) is connected to the polarization-maintaining optical fiber device through a fourth pigtail (P4); the optical power meter (3) is connected to the polarization-maintaining optical fiber device through a third pigtail (P3); The light pulse emitted by the laser (2) enters from the first pigtail (P1) of the polarization-maintaining optical fiber device, and is divided into two polarized light beams after passing through the polarization-maintaining optical fiber device. The paths of the two polarized light beams form a loop with equal distance and opposite directions, and return to the polarization-maintaining optical fiber device to overlap to form a Sagnac loop. The position of the delay line (5) is adjusted so that the phase modulator (4) is placed in an asymmetric position of the Sagnac loop. The phase modulator (4) separates the Sagnac loop into two sections of optical fiber. The time difference of the light pulse passing through the two sections of optical fiber is greater than the rise and fall time of the voltage signal loaded by the waveform generator (1).

2. The polarization-dependent loss measuring device according to claim 1, characterized in that: The path of one of the polarized light beams is: the second pigtail (P2) → phase modulator (4) → delay line (5) → fourth pigtail (P4); the path of the other polarized light beam is: the fourth pigtail (P4) → delay line (5) → phase modulator (4) → second pigtail (P2).

3. A polarization-dependent loss measuring device according to claim 1 or 2, characterized in that: The polarization-maintaining optical fiber device is a polarization beam splitter (PBS) or a polarization circular beam splitter (PCIR).

4. The polarization-dependent loss measuring device according to claim 1, characterized in that: If the first pigtail (P1) is connected to a laser (2), then the third pigtail (P3) is connected to an optical power meter (3); if the first pigtail (P1) is connected to an optical power meter (3), then the third pigtail (P3) is connected to a laser (2).

5. The polarization-dependent loss measuring device according to claim 1, characterized in that: The first pigtail (P1), the second pigtail (P2), the third pigtail (P3), and the fourth pigtail (P4) all use polarization-maintaining optical fibers.

6. The polarization-dependent loss measuring device according to claim 1, characterized in that: The phase modulator (4) is a polarization-maintaining phase modulator.

7. A measuring method using the measuring device according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1): Build the measuring device; Step 2): Open the first channel and the second channel of the waveform generator (1), set the parameters of the two channels respectively, and confirm that the waveforms of the two channels are normal; Step 3): By rotating the knob of the waveform generator (1), adjust the phase value of the voltage output by the second channel, thereby changing the polarization state of the light, from 0° to 360°, observe the reading of the optical power meter (3), and write down the maximum and minimum readings; Step 4): Calculate the polarization dependent loss PDL.

8. The measuring method according to claim 7, characterized in that: The parameters in step 2) include: waveform, frequency, delay, high and low levels, and duty cycle.

9. The measuring method according to claim 7, characterized in that: In step 3), the adjustment step value from 0° to 360° is set to 1°.

10. The measuring method according to claim 7, characterized in that: The calculation formula for polarization-dependent loss PDL in step 4) is: PDL=max(Power P3)-min(Power P3), where max(Power P3) and min(Power P3) represent the maximum and minimum readings on the optical power meter (3), respectively.

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