CN110926758B - Device for measuring hybrid optical fiber mode - Google Patents
Device for measuring hybrid optical fiber mode Download PDFInfo
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- CN110926758B CN110926758B CN201911241626.0A CN201911241626A CN110926758B CN 110926758 B CN110926758 B CN 110926758B CN 201911241626 A CN201911241626 A CN 201911241626A CN 110926758 B CN110926758 B CN 110926758B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/59—Transmissivity
Abstract
The invention discloses a device for measuring a hybrid optical fiber mode, which is characterized in that firstly, a transmissivity curve of the optical fiber mode measuring device with transmissivity changing along with the current of an adjustable direct-current power supply when light beams in different modes are independently input is calibrated; then measuring the transmissivity of the mixed mode light beam to be measured input to the optical fiber mode measuring device under the current state of a plurality of adjustable direct current power supplies; finally, calculating the proportion of each mode component in the mixed mode light beam; the method has the characteristics of easy realization of the device, simple detection method, low cost and the like.
Description
Technical Field
The invention belongs to the technical field of optical communication, and particularly relates to a device for measuring a hybrid fiber mode.
Background
As the capacity of single-mode fiber transmission systems is getting closer to their capacity limit with the development of fiber communication technology, fiber space division multiplexing is considered as one of the effective ways to further expand the transmission capacity. The space division multiplexing technology comprises a few-mode optical fiber, a multi-core few-mode optical fiber and the like. The mode division multiplexing system based on few-mode optical fiber is obviously different from the traditional single-mode optical fiber transmission, a plurality of modes can be transmitted in the same optical fiber, and the number of supported modes determines the transmission capacity of the system. Therefore, it is necessary to know the mode excitation state in the optical fiber and to be able to transmit information such as which modes and the ratio of each mode.
At present, the common few-mode optical fiber analysis methods include the following methods: the method mainly solves the transmission mode of the waveguide by establishing and analyzing Maxwell integral or partial differential equations, and has the defects that strict analysis solution can be obtained only under the condition that certain specific optical fiber structures and refractive index distribution are relatively simple, and the theoretical analysis and modeling of complex special-shaped structures or complex refractive index distribution are very difficult, and even modeling analysis cannot be performed; the second is a numerical calculation method, which is based on Maxwell equation set, uses discrete mathematical model to replace continuous mathematical model, and solves the numerical solution by simulating the electromagnetic field problem of the actual optical fiber device, mainly including finite difference method, finite element method, finite time domain difference method, beam propagation method, etc., and still needs to set the optical fiber structure and refractive index distribution first, and set boundary conditions, etc.; and thirdly, combining a gray level co-occurrence matrix algorithm with a light spot pattern to calculate a mode coupling coefficient excited in the multimode fiber so as to obtain an excitation coefficient of each mode in the fiber, wherein the method has the defects of low sensitivity and large error.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a device for measuring a hybrid fiber mode, which is used for measuring the proportion of each mode component in a light beam of the hybrid fiber mode.
To achieve the above object, the present invention provides an apparatus for measuring a hybrid fiber mode, comprising: the optical fiber coupling device comprises a collimating lens, a beam splitter, an 1/4 wave plate, a focusing lens, a multimode magneto-optical fiber ring with an electromagnetic loading unit, an optical input port, an optical output port, an optical monitoring port and a power supply interface;
wherein, on the multimode magneto-optical fiber ring, a plurality of turns of electrified conducting wires are tightly wound as an electromagnetic loading unit, and two ends of the electrified conducting wires are connected with an external adjustable direct current power supply through a power interface; when the adjustable direct current power supply is electrified for the electromagnetic loading unit, an external magnetic field along the light propagation direction is provided for the multimode magneto-optical fiber ring;
the optical input port is connected with a mixed multimode optical fiber to be detected, and an optical signal transmitted in the mixed multimode optical fiber is input to the measuring device through the optical input port;
the collimating lens collimates the optical signal, and then the optical signal is divided into two parallel beams by the light splitting plate, one beam of light becomes eigen-state circularly polarized light in the multimode magneto-optical fiber ring through the 1/4 wave plate, then the eigen-state circularly polarized light is focused to the input port of the multimode magneto-optical fiber ring through the first focusing lens and coupled into the multimode magneto-optical fiber ring, the multimode magneto-optical fiber ring changes the light propagation characteristic in the multimode magneto-optical fiber ring under the action of the magnetic field of the electromagnetic loading unit, the eigen-state circularly polarized light is output to the first optical power meter through the output port, and the optical output power after passing through the measuring device is measured through the first optical power meter;
the other beam of light is focused to the optical monitoring port through a second focusing lens and is input to a second optical power meter connected with the optical monitoring port, and the optical input power input to the measuring device is measured through the second optical power meter;
the specific process of measuring the hybrid fiber mode by the measuring device is as follows:
(1) when each mode in the mixed optical fiber mode is calibrated and independently input into the optical fiber mode measuring device, the optical output power after passing through the measuring device is measured through the first optical power meter and recorded as
Measuring optical input power to the measuring device by a second optical power meter
Then calculating the transmissivity of the multimode magneto-optical fiber ring in each mode, and finally drawing a transmissivity curve of the transmissivity changing along with the size of a magnetic field applied to the multimode magneto-optical fiber ring;
(2) when the measuring device works, the optical output power after passing through the measuring device is measured by the first optical power meter and is recorded as PoutMeasuring the optical input power P to the measuring device by a second optical power meterinThen, calculating the transmissivity of the multimode magneto-optical fiber ring or the insertion loss of the whole measuring device;
(3) adjusting the adjustable direct-current power supply, changing the current in the electromagnetic loading unit to enable the current in the electromagnetic loading unit to be different from the current value in the electromagnetic loading unit in the step (2), and then repeating the process in the step (2);
(4) measuring the transmissivity of the mixed mode light beam to be measured input to the measuring device under the state that a plurality of adjustable direct current power supplies output current according to the method in the step (3);
(5) and (4) calculating the proportion of each mode component in the mixed mode light beam to be measured according to the measurement data in the steps (1) and (4).
The invention aims to realize the following steps:
the invention relates to a device for measuring a hybrid optical fiber mode, which is characterized in that firstly, a transmissivity curve of the optical fiber mode measuring device with transmissivity changing along with the current of an adjustable direct-current power supply when light beams in different modes are independently input is calibrated; then measuring the transmissivity of the mixed mode light beam to be measured input to the optical fiber mode measuring device under the current state of a plurality of adjustable direct current power supplies; finally, calculating the proportion of each mode component in the mixed mode light beam; the method has the characteristics of easy realization of the device, simple detection method, low cost and the like.
Drawings
FIG. 1 is a block diagram of an embodiment of an apparatus for measuring hybrid fiber modes according to the present invention;
fig. 2 is a plot of the transmission calibrated for the different modes when input individually.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Examples
FIG. 1 is a block diagram of an embodiment of an apparatus for measuring hybrid fiber modes according to the present invention.
In this embodiment, as shown in fig. 1, the apparatus for measuring a hybrid fiber mode according to the present invention includes: the optical fiber coupling device comprises a collimating lens, a beam splitter, an 1/4 wave plate, a focusing lens, a multimode magneto-optical fiber ring with an electromagnetic loading unit, an optical input port, an optical output port, an optical monitoring port and a power supply interface;
wherein, on the multimode magneto-optical fiber ring, a plurality of turns of electrified conducting wires are tightly wound as an electromagnetic loading unit, and two ends of the electrified conducting wires are connected with an external adjustable direct current power supply through a power interface; when the adjustable direct current power supply is electrified for the electromagnetic loading unit, an external magnetic field along the light propagation direction is provided for the multimode magneto-optical fiber ring; in addition, the light splitting plate adopts a 50:50 light splitting plate;
the optical input port is connected with a mixed multimode optical fiber to be detected, and an optical signal transmitted in the mixed multimode optical fiber is input to the measuring device through the optical input port;
the collimating lens collimates the optical signal, and then the optical signal is divided into two parallel beams by the light splitting plate, one beam of light becomes eigen-state circularly polarized light in the multimode magneto-optical fiber ring through the 1/4 wave plate, then the eigen-state circularly polarized light is focused to the input port of the multimode magneto-optical fiber ring through the focusing lens 1 and coupled into the multimode magneto-optical fiber ring, the multimode magneto-optical fiber ring changes the light propagation characteristic in the multimode magneto-optical fiber ring under the action of the magnetic field of the electromagnetic loading unit, the eigen-state circularly polarized light is output to the optical power meter 1 through the output port, and the optical output power after passing through the measuring device is measured through the optical;
another beam of light is focused to the optical monitoring port through the focusing lens 2 and is input to the optical power meter 2 connected with the optical monitoring port, and the optical input power input to the measuring device is measured through the optical power meter 2;
in this embodiment, LP is measured by a measuring device01、LP11、LP21、LP31The beam detection of four hybrid fiber modes is illustrated as an example. The multimode magneto-optical fiber used in the measuring device has the ring length of 30 cm, the core radius of 10 mu m, the refractive index of 1.482, the cladding radius of 20 mu m and the refractive index of 1.477. Coupling efficiency rho of input light beam and multimode magneto-optical fiber ring0The transmission loss coefficient alpha of the optical fiber is 0.1 and 0.3 dB/m.
The following specific process for measuring four hybrid fiber modes by the measuring device is as follows:
(1) when each mode in the mixed optical fiber mode is calibrated and independently input into the optical fiber mode measuring device, the optical output power after passing through the measuring device is measured by the optical power meter 1 and recorded as
Measuring the optical input power to the measuring device by means of an optical power meter 2
Then calculating the transmissivity of the multimode magneto-optical fiber ring in each mode, and finally drawing a transmissivity curve of the transmissivity changing along with the size of a magnetic field applied to the multimode magneto-optical fiber ring; wherein, the ratio of the output optical power to the input optical power isTransmittance of light
The insertion loss 10lg (P) of the whole measuring device can be calculated according to the transmissivityin/Pout)；
In this embodiment, the multimode magneto-optical fiber ring and the electromagnetic loading unit are the core of the fiber mode detection device, and the selected multimode magneto-optical fiber ring can support 4 modes, LP01, LP11, LP21 and LP31 respectively. Before the measuring device is used for measuring the four mixed-mode beams in the multimode magneto-optical fiber ring, the device must be calibrated. As shown in fig. 2, transmission curves in four modes were calibrated. Obviously, when four modes are input into the optical fiber mode detection device independently, the corresponding transmittance changes along with the magnetization generated by the electromagnetic loading unit in the multimode magneto-optical fiber ring, namely, the transmittance has mode dependence. Wherein, the working range of the measuring device corresponds to the magnetization of 350-360 Oe.
(2) When the measuring device works, the optical power meter 1 measures the optical output power passing through the measuring device and records the optical output power as PoutThe optical input power P to the measuring device is measured by the optical power meter 2inThen, calculating the transmissivity of the multimode magneto-optical fiber ring or the insertion loss of the whole measuring device;
(3) adjusting the adjustable direct-current power supply, changing the current in the electromagnetic loading unit to enable the current in the electromagnetic loading unit to be different from the current value in the electromagnetic loading unit in the step (2), and then repeating the process in the step (2);
(4) measuring the transmissivity of the mixed mode light beam to be measured input to the measuring device under the state that a plurality of adjustable direct current power supplies output current according to the method in the step (3);
in the embodiment, the output current of the adjustable DC power supply is changed so that the magnetization intensity provided by the electromagnetic loading unit is in the range of 350-360 Oe, and a set of magnetization intensity values such as 350Oe, 352Oe, 355Oe and 359Oe is selected from the magnetization intensity provided by the electromagnetic loading unit. According to steps (2) to (4), the transmittance of the mixed light beam under the set of magnetic fields through the optical fiber mode detection device is measured by the optical power meters 1 and 2, respectively, and can be represented by the following vectors:
(5) and (4) calculating the proportion of each mode component in the mixed mode light beam to be measured according to the measurement data in the steps (1) and (4).
For a set of employed magnetization values 350Oe, 352Oe, 355Oe, 359Oe, the transmittance of each mode in the set of magnetization values is obtained from the transmittance curve, and is expressed by the following vector:
wherein each row corresponds to a different pattern and each column corresponds to a different magnetization value.
Finally, the proportion of each mode component in the four mixed-mode beams can be calculated as follows:
that is, in the four mixed-mode light beams to be measured, the ratios of the LP01, LP11, LP21 and LP31 modes are 10%, 60%, 10% and 20%, respectively.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (3)
1. An apparatus for measuring a hybrid fiber mode, comprising: the optical fiber coupling device comprises a collimating lens, a beam splitter, an 1/4 wave plate, a focusing lens, a multimode magneto-optical fiber ring with an electromagnetic loading unit, an optical input port, an optical output port, an optical monitoring port and a power supply interface;
wherein, on the multimode magneto-optical fiber ring, a plurality of turns of electrified conducting wires are tightly wound as an electromagnetic loading unit, and two ends of the electrified conducting wires are connected with an external adjustable direct current power supply through a power interface; when the adjustable direct current power supply is electrified for the electromagnetic loading unit, an external magnetic field along the light propagation direction is provided for the multimode magneto-optical fiber ring;
the optical input port is connected with a mixed multimode optical fiber to be detected, and an optical signal transmitted in the mixed multimode optical fiber is input to the measuring device through the optical input port;
the collimating lens collimates the optical signal, and then the optical signal is divided into two parallel beams by the light splitting plate, one beam of light becomes eigen-state circularly polarized light in the multimode magneto-optical fiber ring through the 1/4 wave plate, then the eigen-state circularly polarized light is focused to the input port of the multimode magneto-optical fiber ring through the first focusing lens and coupled into the multimode magneto-optical fiber ring, the multimode magneto-optical fiber ring changes the light propagation characteristic in the multimode magneto-optical fiber ring under the action of the magnetic field of the electromagnetic loading unit, the eigen-state circularly polarized light is output to the first optical power meter through the output port, and the optical output power after passing through the measuring device is measured through the first optical power meter;
the other beam of light is focused to the optical monitoring port through a second focusing lens and is input to a second optical power meter connected with the optical monitoring port, and the optical input power input to the measuring device is measured through the second optical power meter;
the specific process of measuring the hybrid fiber mode by the measuring device is as follows:
(1) when each mode in the mixed optical fiber mode is calibrated and independently input into the optical fiber mode measuring device, the optical output power after passing through the measuring device is measured through the first optical power meter and recorded as
Measuring optical input power to the measuring device by a second optical power meter
Then calculating the transmissivity of the multimode magneto-optical fiber ring in each mode, and finally drawing a transmissivity curve of the transmissivity changing along with the size of a magnetic field applied to the multimode magneto-optical fiber ring;
(2) when the measuring device works, the optical output power after passing through the measuring device is measured by the first optical power meter and is recorded as PoutMeasuring the optical input power P to the measuring device by a second optical power meterinThen, calculating the transmissivity of the multimode magneto-optical fiber ring or the insertion loss of the whole measuring device;
(3) adjusting the adjustable direct-current power supply, changing the current in the electromagnetic loading unit to enable the current in the electromagnetic loading unit to be different from the current value in the electromagnetic loading unit in the step (2), and then repeating the process in the step (2);
(4) measuring the transmissivity of the mixed mode light beam to be measured input to the measuring device under the state that a plurality of adjustable direct current power supplies output current according to the method in the step (3);
(5) and (4) calculating the proportion of each mode component in the mixed mode light beam to be measured according to the measurement data in the steps (1) and (4).
2. The apparatus of claim 1, wherein the number of modes supported by the multimode magneto-optical fiber loop determines a detection range of the hybrid fiber mode.
3. The apparatus according to claim 1, wherein the magnitude of the magnetic field provided by the electromagnetic loading unit is determined by the output current of the adjustable dc power supply, and the magnetization provided by the electromagnetic loading unit is adjusted within a range of 350 to 360Oe by adjusting the output current of the adjustable dc power supply.
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