RU197260U1 - Fiber optic polarized diversity optical signal receiving device - Google Patents

Abstract

The utility model relates to the field of fiber-optic measuring devices based on interferometric-type fiber-optic phase sensors and is intended for use in fiber-optic interferometric sensors as a photodetector to prevent polarization attenuation of the signal on the receiving side of the measuring device. A fiber optic device for receiving a polarized optical signal contains an input optical fiber optically connected to an input port of a splitter, the three output ports of which are connected to three linear fiber optic polarizers, which are connected to a splitter using birefringent optical fibers, and the transmission axis of the polarizers with the birefringence axes of the connecting optical fibers and are oriented at an angle of 120 ° relative to each other. Each polarizer is connected to a photodiode, the splitter is an integrated optical circuit containing channel waveguides formed on a quartz substrate, forming a symmetrical tree topology, and additionally contains an output port that is connected via fiber to an additional photodiode. The technical result is a decrease in the temperature effect on polarization-dependent losses, which prevents the polarization attenuation of the signal, as well as the convenience and flexibility of installation. 4 ill.

Description

The utility model relates to the field of fiber-optic measuring devices based on interferometric-type fiber-optic phase sensors and is intended for use in fiber-optic interferometric sensors (hereinafter referred to as the sensor) as a photodetector to prevent polarization signal attenuation.

The principle of operation of the device is based on independent registration, as a rule, of three photodiodes of the interference optical signal, previously divided by power into three equal parts, each of which passes through a separate linear polarizer, while the transmission axes of the three polarizers are mutually oriented at an angle of 120 ° relative to each other .

It is known (patent US 005448058 A, G02F 1/01, publ. 5.09.1995) a device for detecting an optical signal with preventing the attenuation of the polarization signal in a fiber optic interferometric sensor system.

The device contains an array of three photodiodes, each of which has the shape of a circle sector with an angle of 120 °, and together they form a complete circle. The parallelepiped-shaped film polarizers, when connected, form a regular hexagon. Polarizers with their own orientation of the polarization axes are oriented relative to each other by 120 °. Each polarizer covers the pad of its own photodiode. Thus, regardless of the state of polarization of the radiation incident on the array of photodiodes, there is a polarization component that will coincide with the transmission axis of at least two photodiodes, and, therefore, the sensor will have non-zero visibility for any polarization state of the interfering beams.

The disadvantages of the known solutions are the high complexity of manufacturing an array of non-standard shape photodiodes in the form of circle sectors, as well as the difficulty of accurately setting the orientation of the film polarizers.

A device is known, selected as a prototype for the proposed device, (Polarization Diversity Receiver. Leaflet LIGHTEL True Color Components www.lightel.com), which is a device of a polarized-distributed receiver, used in fiber-optic sensors, which reduces the effect of polarization signal attenuation .

The device contains an input optical fiber (hereinafter referred to as a fiber) optically connected to the input port of a fiber optic splitter (hereinafter referred to as a splitter) made on an isotropic fiber and having one input port and three output ports to which three polarized PIN photodiodes are optically connected (hereinafter - photodiode). The transmission axes of the polarizers of the photodiodes are oriented at an angle of 120 ° relative to each other. The fiber segments between the splitter and the photodiode are about 25 mm long.

The disadvantages of the known solution are temperature instability, since the fiber lengths between the splitter and the photodiode slightly differ due to the design, and also have a length of about 25 mm, so the phase of the radiation incident on the photodiodes will be different, which can lead to polarization signal attenuation.

Solved technical problem - improving the design of the device to achieve a technical result.

The technical result achieved is a decrease in the polarization attenuation of the interference optical signal due to a decrease in the temperature effect on the polarization-dependent losses.

The problem is solved as follows.

A fiber-optic device for receiving a polarized diversity optical signal containing an input optical fiber optically connected to an input port of a splitter, the three output ports of which are connected using birefringent optical fibers with three linear fiber-optic polarizers (hereinafter referred to as the polarizer), the transmission axes of each of which coincide with the birefringence axes of the connecting optical fibers and are oriented at an angle of 120 °, and each polarizer is optically connected to the photodiode. The splitter is an integrated optical circuit containing channel waveguides formed on a quartz substrate, forming a symmetrical tree topology, and additionally contains an output port that is connected via fiber to an additional photodiode.

The essence of the claimed utility model is illustrated as follows. The device is based on a splitter, which is an integrated optical circuit containing channel waveguides formed on a quartz substrate, forming a symmetrical tree topology and having one input port and four output ports. An input optical fiber is optically connected to the input port of the splitter.

Three output ports of the splitter are connected to three fiber-optic linear polarizers using birefringent optical fibers, and the transmission axes of the polarizers coincide with the birefringence axes of the connecting (birefringent) optical fibers and are oriented at an angle of 120 ° relative to each other.

An additional output port of the splitter connected with an additional fiber to an additional photodiode is necessary to obtain a design with waveguides of equal length. The splitter is symmetric for the conditions of division of the front of the light wave, and the optical path, and as a result, the polarization state at the output of all waveguides, will be mutually identical. In addition, an additional output port serves to control the optical power, and also with its help it is possible to assess the state of radiation polarization.

Due to the use of birefringent optical fibers, the temperature effect on them does not affect the change in the state of polarization and phase at the output. Due to the use of a symmetrical splitter and birefringent optical fibers in the design of the device, the temperature stability of the device is achieved, which leads to a decrease in the polarization attenuation of the signal.

The essence of the proposed solution is illustrated in FIG. 1, FIG. 2, FIG. 3, FIG. 4, where in FIG. 1 shows a diagram of a device, FIG. 2 - output fibers on a quartz base with v-grooves, in FIG. 3 shows an embodiment of a device with an input fiber glued into a quartz tube; FIG. 4 is an embodiment of a device with an input fiber glued to a base with a v-groove.

In FIG. 1, 2, 3, 4 the following notation is accepted:

1 - input optical fiber (hereinafter referred to as input fiber),

2 - input port

3 - splitter

4, 5, 6 - output ports,

7, 8, 9 - birefringent optical fibers (hereinafter - birefringent output fibers),

10, 11, 12 - linear fiber-optic polarizers (hereinafter referred to as the polarizer)

13, 14, 15 - photodiodes,

16 - additional output port,

17 - output optical isotropic fiber (hereinafter - the output fiber),

18 - additional photodiode,

19 - quartz base with 4 v-grooves,

20 - cover

21 - quartz tube

22 - quartz base with the 1st v-shaped groove,

23 - clamping cover.

The fiber-optic device for receiving the polarized diversity optical signal (Fig. 1) contains an input optical fiber 1, optically connected to the input port 2 of the splitter 3, three output ports 4-6 of which are connected using birefringent output fibers 7-9 with three linear fiber optical polarizers 10-12, each polarizer 10-12 connected to the photodiode 13-15, and an additional output port 16 through the output optical fiber 17 is connected to the additional photodiode 18.

In FIG. 2 three output fibers 7-9, the birefringence axes of which are located at angles of 120 °, and the output fiber 17 is located on the quartz base 19 and pressed against the quartz base 19 by a cover 20.

In FIG. 3, the splitter 3 is connected on one side to the input fiber 1 glued to the quartz tube 21, and on the other hand, connected to the quartz base 19 having v-grooves for the birefringent output fibers 7-9, 17 pressed against the cover 20.

In FIG. 4, the splitter 3 is connected on one side to the input fiber 1 glued to the quartz base 22 with a v-groove and a pressure cap 23, and on the other hand, to the quartz base 19 having v-grooves for the birefringent output fibers 7-9, and the output fiber 17 pressed against the cover 20.

The devices of FIG. 3 and in FIG. 4 differ only in the technology of connecting the input fiber 1 with the splitter 3. The technologies presented are equivalent in achieving a technical result.

The operation of the device is as follows: the incoming optical signal, with an unknown and random state of polarization, propagates through the input optical fiber 1 and gets through input port 2 to the splitter 3, in which the radiation is divided by power into four ports and on each of the four output ports 4 -6, 16 of the splitter 3 radiation is formed with the same state of polarization. After that, from the three output ports 4-6 of the splitter 3, the radiation enters through the birefringent output fibers 7-9 to the fiber-optic linear polarizers 10-12 and then to the photodiodes 13-15. The fourth additional output port 16 of the splitter 3, to which the additional fiber 17 is optically connected, can be used to control the total power of the optical radiation by connecting with an additional photodiode 18.

As a specific example of the device, it is proposed to use a splitter, which is an integrated optical circuit containing channel waveguides formed on a quartz substrate, forming a symmetrical tree topology with one input port and four output. The length of the splitter is not more than 10 mm, and the distance between the output ports is about 0.25 mm, and in the prototype the fibers between the splitter and the photodiode were isotropic, and their length was 25 mm. Since the temperature effect leads to a change in the polarization and phase of the radiation in an isotropic fiber, but not in birefringent, the region in which the temperature effect affects the propagating radiation in the prototype is 25 mm, and in the claimed solution - 10 mm, so the proposed utility model It is more stable to temperature influences. The integrated optical circuit has a bevel on the input and output ports to reduce back reflections from the ends. On the input port side, a single-mode fiber is placed, the end of which is glued to a quartz capillary or quartz base with a v-groove for more reliable optical connection of the fiber to the splitter. The optical fiber is glued onto a UV curable adhesive in a capillary or quartz base with a v-groove, which also has a bevel. Three birefringent optical fibers connected optically with polarizers and one additional fiber must be connected to the output ports of the splitter; for this, it is proposed to use a quartz base with four v-grooves, the distance between which coincides with the distance between the output ports of the splitter. Three birefringent optical fibers connected to polarizers are oriented in a quartz base with four v-shaped grooves at angles of 0 °, 120 ° and 240 °, and the fourth fiber is oriented randomly. In this way, four fibers are glued onto the UV-curable adhesive in the v-grooves of the quartz base, which also has a bevel. Then, on the one hand, an input fiber is joined to the integrated optical circuit in a quartz tube or quartz base with a v-shaped groove, and on the other hand, fibers glued into the v-shaped grooves. Docking is fixed to UV curable adhesive.

Thus, the above shows that the claimed utility model is feasible and ensures the achievement of a technical result, which consists in reducing the temperature effect on the polarization-dependent losses, which ensures a decrease in the polarization attenuation of the signal. In addition, fiber-optic components are used in the design of the device, which provides convenience and flexibility of installation.

Claims (1)

A fiber optic device for receiving a polarized diversity optical signal containing an input optical fiber optically connected to an input port of a splitter, three output ports of which are connected to three linear polarizers, and each polarizer is connected to a photodiode, characterized in that the polarizers are made of fiber optic and connected with a splitter using birefringent optical fibers, and the transmission axis of the polarizers coincide with the birefringence axes of the connecting optical their fibers oriented at an angle of 120 ° relative to each other splitter is an integrated optical circuit comprising a channel waveguide formed on a quartz substrate, forming a symmetrical tree topology and comprises an additional output port, which is connected via an optical fiber with an additional photodiode.

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