Connecting device for coaxially transmission of light energy

 

(57) Abstract:

Connecting device for coaxially transmission of light energy is intended for connection of multimode radiation source having almost round profile of the emission divergence angle s, c multimode optical fiber cross-sectional area AC via an intermediate segment of the supply multimode optical fiber, the end of which the area of the cross-section area Af is connected to the said source of radiation, and one part of the fused optical fiber. Feeding the fiber has gradually tapering section and fused with the said multimode optical fiber (FF) in the field of gradually tapering section in the following ratio between the reception angle f supply fiber and the angle of emission s radiation source (LS): f = ks, where k is a positive constant greater than unity. Improved the efficiency of the transmission of radiation. 25 C.p. f-crystals, 11 ill.

The scope of the invention

The present invention relates generally to the connection or transfer of light energy between the radiation source and the optical guide, and in particular to a device for improving the efficiency of energy transfer between isteelaa feed to the end of the optical fiber is undesirable or impossible.

In the private preferred embodiment of the invention, which will be described in detail, the system operates as part of the optical amplifier. In this case, the radiation source includes a multimode semiconductor laser diode or an array of such diodes emitting radiation around a certain wavelength and acting as a pump source and an end of the optical conductor includes a single-mode core, the carrier running signal (single-mode radiation with a wavelength different from the wavelength of the pump), which should be strengthened.

In the above preferred embodiment, the aim of the invention is, in particular, implementation of high-performance connection between length of multimode optical fiber and the so-called single-mode dual membrane (SM-DC) optical fiber, although the invention should not be considered limited to this preferred application option. "Single-mode dual shell (SM-DC) optical fiber means a fiber which includes internal ("sm") core diameter of several microns, the first shell (or multimode core and the second shell. In practice there are many situations in which the fiber must obtain the window. For example, when you want to send two or more different radiation along a single conductor (radiation, different amplitude, wavelength, type of signal or code, and so on), you need to increase the number of different sources, which can also be of different types, and requires a certain separation of the optical paths that are listed in the destination guide. In addition, the device coaxiale connection may be required in the fiber laser device in which the axial pumping requires special mirrors (with a certain reflectivity), which must be permeable to the radiation of the pump and to have a high reflectivity to laser light.

Another situation in which you want coaxially submission described, for example in the patent application US-A-5170458 related to the optical amplifier receiving the radiation of the pumping indirectly.

There are several devices for connection (optional) a radiation source with an optical fiber, which include one or more of the following connectors:

- prism

- insert the optical conductor of any type (solid or composed of individual elements),

- promi (i.e., element of communication, including microlenses, or splitters, or other individual microscopic devices)

- intermediate optical fiber connected to the fiber end through the coupling element from the fused fibers.

In the first three examples, there is a significant problem of mechanical tolerances in the combination of devices, which makes them very expensive and critically challenging from the point of view of technology, as a rule, due to the poor efficiency of the connection.

Usually in telecommunication systems, including optical fiber amplifiers (OFA), i.e., segments appropriately doped single-mode optical fiber, connected in series in the communication line, these segments of the fiber feed radiation from one or more single-mode laser diodes by means of suitable connection elements of the fused fibers, each of which, in turn, is connected with one or more laser diodes. Such (sm) the elements of the linkage formed by merging or fusing two or more pieces of fiber may have an efficiency of up to 90%. In connection laser crystal using soedinitel diodes, to obtain high optical power in the system have to include a large number of diodes, reducing the reliability of the system as a whole.

To improve the output saturation power of the optical amplifier without increasing the number of pumping diodes, it has been proposed (see example US-A-4829529, Kafka) to use SM-DC optical fiber, activated by one or more diode matrix connected optical elements with the end face of the fiber.

The present invention relates to a device that allows the use of a multimode laser diode (diodes) or a diode matrix connected to the end of the fiber through an intermediate optical fiber and the coupling element from the fused fibers. The advantage of this device lies in the fact that multimode laser diodes can provide higher levels of power output than single-mode diodes, and have good performance and reliability.

As you know, multimode laser crystal emits radiation through a narrow slot with a thickness of about 1 micron and the allowable width of several tens of microns, while the light beam is highly divergent in the transverse plane and moderate consumption is W ith as much light as possible, usually used the segment of multimode fiber with a diameter of about 60 μm and a numerical aperture of about 0.35, while the numerical aperture (NA) of the optical fiber represents the sine of the angle of the tops of the maximum cone of meridional rays that can enter an optical fiber (or leave it).

This simple scheme direct connection gives the efficiency of the connection up to a maximum of 50%.

Background of the invention

EP-A-0136871 describes a pair of optical fibers of small diameter (12, 14) arranged side by side, with the first fiber (12) to form a passive conduit for the pump radiation, and the second fiber (14) is made of materials such as Nd-YAG, which has reinforcing properties on the signal frequency. The signal that must be amplified, passes through the second fiber (14) and the result is increasing. The first fiber (12) is pumped from one or both ends using a tapered rod, the associated optical. Many sources of pump radiation (60) is installed on the end surface (58) of the rod (50) to enter the collimated pump radiation in the wide end (52) of a conical rod (50).

Known to improve connections PNA, when this cylindrical lens focuses the transverse component of the laser beam in the core of the fiber. Here reference can serve as application EP-A-0565843, as well as the article "Mixed laser-fiber coupling element with a cylindrical lens, Maeda M. et al., Applied Optics, Vol. 16, N 7, July 1977, pp 1966-1970.

This cylindrical lens does not modify the deviation of the beam in the plane of the axis of the slot, so that at a certain distance from the laser crystal cross-section of the beam is significantly reduced and becomes round, and so it can be easily connected with a housing of the optical fiber.

Further, the connecting segment is fused with the end of the fiber (i.e., in the General case with fiber, which must be submitted to the radiation, or in particular with the fiber carrying the signal that must be amplified) at the other end of the supply connecting segment (Y - connector) or along parts of the feeding section of the connecting segment (X - connector). The coefficient of connection of such a connecting element is proportional to the ratio of the square of the core diameter of the receiving fiber to the square of the core diameter of the receiving fiber plus the square of the diameter of the veins feeding the fiber.

When using SM-DC-optic technology can provide ogopogo fiber. If multimode lived SM-DC fiber has the same diameter as the supply of the fiber (i.e., 60 μm), the ratio of the compound is about 0.5. To further increase the coefficient of connection SM-DC fiber, it is necessary to reduce the diameter of the veins feeding the fiber. At a diameter less than 20 μm, the coefficient of connection can theoretically reach values higher than 0.9.

However, with decreasing core diameter multimode feeding fibers to improve the transmission efficiency of the radiation element may extremely decrease the efficiency of transmission of radiation from the laser power supply to the fiber, even when using a cylindrical lens.

The objective of the invention

In this regard, the present invention is the creation of an improved and highly efficient devices for power transmission multimode radiation source to the optical fiber in coaxial direction, which does not have the above drawbacks.

Description of the invention

This problem can be solved by the invention, which includes a connecting device for coaxially transfer of light energy between the multimode radiation source, the beam which has essentially ecene Ac, through the period of interim supply multimode optical fiber, the end of which the area of the cross-section area Af is connected to the said source of radiation, and one part is fused with the above-mentioned optical fiber,

and characterized in that the said feeding fiber has a tapering section, i.e. the section with a gradually decreasing diameter, and fused with the said multimode optical fiber FF in the field of tapering section, and the fact that the ratio between the reception angle f supply fiber and divergence angle s of the source of radiation is expressed by the formula

f = ks,

where k is a positive constant greater than unity.

According to the invention, for transmitting radiation from a multimode laser crystal (or array of crystals) on a segment of multimode feed fiber, a cylindrical lens, so that the divergence angle of the emitted beam, propagating along the fiber, is less than the acceptance angle of the fiber. Feeding the fiber (or at the far end, or the entire length) is narrowed, i.e., heated and drawn to reduce its diameter, and then is formed the element of communication, such as twist and soldering, this narrowed the change of the invention, with the fiber carrying the signal.

The above sequence of operations is not required. For example, it may be formed in the coupling element and then connected to the multimode source or, alternatively, glued together with the already formed a connecting segment of multimode source. It is also possible other combinations.

The system according to the invention is explained next.

Specialists are well aware that the amount of radiation emitted by a unit surface area of the source per unit solid angle (the so-called "brightness") cannot be increased passive optics, therefore reducing the size of the cores of the fibers leads to an increase in the divergence angle of the beam propagating along the fiber. While this angle remains smaller than the NA of the fiber, the loss does not occur and therefore it is possible to create an effective connection between such narrow fiber and securenym fiber.

The connecting device according to EP-A-0136871 differs from the device according to this invention is the fact that supply fiber 12 in this patent is not alloyed with an optical fiber 14, and runs parallel to it within the connector shell 22. Further, although the supply of volokonovka (sources) pump, this is not the tapering portion which is adjacent to the fiber 14 and is used to connect with him.

A more detailed explanation is contained in the description of the accompanying drawings.

Additional, specific benefits are described in the accompanying claims.

Brief description of drawings

Next will be described a preferred but not limiting embodiments of the invention with references to the relevant drawings, where:

- Fig. 1 schematically shows the entire device for coupling a radiation source with an optical fiber through an intermediate segment of the optical fiber;

- Fig. 2 is a schematic front view of a multimode laser crystal, illustrating the form of the outgoing laser beam;

- Fig. 3 shows a diagram of the multimode radiation source comprising a semiconductor laser diode and a cylindrical lens that is connected with the connecting segment of multimode fiber;

- Fig. 4 shows a variant embodiment of the invention, in which the intermediate optical fiber narrowed in the field of connection and forms a Y-connector;

- Fig. 5 in detail shows the winding reduce the, showing intermediate multimode optical fiber and the optical path inside it to illustrate the General principle of the invention;

- Fig. 7 schematically shows the connection area and the light path to power SM-DC optical fiber carrying the signal in the form of a single-mode radiation with multimode beam carried in multimode vein;

- Fig. 8 shows a cross section of the end region of the connection;

- Fig. 9 shows a cross section of the end region of the connection if there is a shell of two fibers;

- Fig. 10 shows a cross-section of the end region of the connection essentially elliptical receiving fibers;

- Fig. 11 shows a cross section of the end region of the connection essentially rectangular receiving fiber.

Detailed description the preferred option of carrying out the invention

All figures use the same position to denote identical or similar components.

It is shown in Fig. 1 the connecting device comprises a multimode light source LS with essentially circular cross section of the beam and the divergence angle s, which is connected with one end of the intermediate segment of the Opti is inane CR with optical fiber FF, bearing information or similar signal, forming a so-called X-connector. Part of the intermediate fiber IF it can be, if necessary, minimized, as shown on the CF. Naturally, the fiber IF it can be glued at its other end with the formation of the so-called Y-connector.

As is known, the reception angle f of the optical fiber is a function of the refractive index of its core and the shell. According to the invention, the reception angle f of the intermediate fiber IF at its end connecting with the light source LS is greater than the divergence angle s of the multimode radiation source. Thus, it can be obtained with a high efficiency.

Fig. 2 shows a front view of a multimode laser diode LD, not to scale, with a thickness of about 1 micron and a width of about 50 microns. As shown, the emitted beam of a laser diode has an essentially elliptical cross-section with a divergence angle of about 35-40 degrees in the plane perpendicular to the light-emitting transition (i.e., the direction along the thickness of 1 μm), and a divergence angle of about 10-15 degrees in the plane of the light-emitting transition (plane along a width of 50 μm).

Three consecutive track B1, B2 and Vlach. Obviously, with a larger angle of divergence in accordance with the lower side of the rectangle at a certain distance from the surface of the diode cross-section of the laser beam (here B2) is essentially round, and then this distance relative dimensions of the ellipse are swapped (i.e. the major axis of the elliptical beam is rotated 90 degrees).

Fig. 3-7 illustrate a preferred device according to the invention, which is particularly useful when connecting multimode source of pump radiation from one end of the supply optical fibers, which, in turn, is connected with a segment SM-DC fiber, as a specific component of the optical amplifier.

In Fig. 3 of the semiconductor laser diode LD emits multimode radiation or light beam LB, is connected by means of the cylindrical lens CL with one end of the intermediate multimode optical fiber IF.

The cylindrical lens CL is elliptical light beam LB between the laser diode LD and the feeding fiber IF so, to gradually reduce the divergence of the transverse component of the laser beam until then, until it becomes equal to or perhaps even less, than spending the which communicates with the supply fiber. The means by which the components are positioned relative to each other, normal to the art and therefore not shown.

In accordance with the invention, the divergence angle of the s beam emerging from the cylindrical lens CL is less than the acceptance angle f feeding fibers to which it is connected. In terms of numerical aperture of the feeding fiber this means that the NA of the fiber should be greater than 0.3, to make a beam with s 35 degrees.

The other end of the feeding fiber IF (or far part of the power fibers) is fused together with the optical fiber FF, as shown in Fig. 4. Joint area denoted by CR, forms a so-called Y-connector, because the connection with the fiber FF occurs at the end of the feeding fiber IF.

Next it is shown that the optical fiber FF may also be active fiber of the fiber laser.

Also in accordance with the invention, the cross-sectional area of the supply fiber IF in the connections pane CR gradually decreases (the so-called adiabatic reduction of the diameter of the veins), until it reaches a value of from 0.8 to 0.1 initial value, i.e., the diameter at the place where the light beam LB enters the fiber. Other slavemaking the cross-sectional area tapering supply fiber and IF the initial area of its cross section is 0.01 to 0.7, and the most preferred amount is about 0.1.

Preferably, the tapering part of the power fibers was short as possible to the fiber at a strong reduction of its diameter has not lost strength.

This is done by pulling the fiber IF or at least parts of it at a given temperature, then winding constricted part on the signal fiber FF so that they are in contact (Fig. 5), and then the weak pull fibres at high temperature, so they stuck together. So get the best contact. Preferably gradually tapering portion of the multimode feed optical fiber IF fused with the said multimode optical fiber FF, is wound around the latter in the form of a spiral.

If you are using X-connector, at least a portion of the feeding fiber has a diameter gradually decreasing in the above range, and in this part it is connected with the receiving fiber FF.

With the help of Fig. 6 shows the principle on which the invention is based.

As mentioned above, the divergence angle and s multimode source LS is part of the reception angle f intermediate multimode is the angle of advance of the laser pump radiation, carry a supply of fiber, along the area of narrowing gradually increased.

Given that fusion between feeding fiber and IF the receiving fiber FF occurs along the entire tapered section of the feeding fiber IF, and that narrowing ends negligible diameter, the ratio between the finite divergence angle c and the initial angle s is:

c = s((Ac+Af)/Ac)1/2< / BR>
where Ac and Af is the cross-sectional area of the receiving fiber FF and nasusunog supply fiber IF, respectively.

If the specified values of Ac and Af is selected in such a way that c does not exceed the reception angle of the fibers will assume for simplicity that both NA fibers are equal), the reduction of the core diameter of the feeding fiber is lossless radiation from the fiber by increasing the angle of advancement of radiation.

If the fusing two fibers begins in the wrong place, where the narrowing of the supply fiber, as elsewhere within the tapering section, with the cross-sectional area of the supply fiber At, the above expression takes the form:

c = s(Af/At)1/2((At+Ac)/Ac)1/2< / BR>
that corresponds to a greater increase in the divergence angle.

To maintain an effective connection, numerical aperture multimode strands of the receiving fiber FF must be equal to or greater than the numerical aperture of the feeding fiber IF.

It should be noted that, as described above, the most effective compound is obtained in the case, if the contact between the said multimode optical fiber FF and the said feeding fiber IF is essentially along the entire tapered section of the fiber IF.

Fig. 8 shows a cross section of the junction of CR (before gluing the two fibers), where both optical fibers are essentially round cross-section and have no shell at the transition. For SM-DC fiber second (outer) shell shall be considered withdrawn.

Although an optimum connection is obtained in the absence of layers of membranes on both fibers, the invention approx the Yong additional constant coefficient, which depends on the thickness of the shell.

Fig. 9 shows the cross-section area of the connection CR with two round fibers remaining in the outer shells.

Fig. 10 shows the receiving multimode optical fiber, which has an essentially elliptical cross-section, and finally.

Fig. 11 shows the receiving multimode optical fiber, which has an essentially rectangular cross-section. Naturally, one or both of the supply fiber and IF the optical fiber FF can have one of the above cross-sections.

It is evident from Fig. 8, 9, 10 and 11 it is obvious that the ratio of the square of the veins Ac at the end that connects to the source LS, and square wires Af have made the end more than the ratio f/s reception angle f supply fiber and IF the initial divergence angle s of the radiation source LS.

When using single-mode core fiber lived preferably legarrette a relatively large number of ions of rare earth metals or transition metal ions, or a combination thereof.

For example, the single-lived may be doped with ions of ytterbium and erbium or neodymium ions, or only ions of ytterbium, or iredale ideas of the invention can be made various changes and transformations.

1. Connecting device for coaxially transfer of light energy between the multimode radiation source (LS), having an essentially circular cross-section beam with a divergence angle s, and a multimode optical fiber (FF) cross-sectional area Ac, through the intermediate segment of the supply multimode optical fiber (IF), at the end of which the area of the cross-section area Af is connected to the said source (LS), and one part is fused with the above-mentioned optical fiber (FF), characterized in that the said feeding fiber (IF) has gradually tapering section and fused with the said multimode optical fiber (FF) in the field of gradually tapering section in the following ratio between the reception angle f supply fiber (IF) and the divergence angle s of the radiation source (LS):

f = ks,

where k is a positive constant greater than unity.

2. The connecting device according to p. 1, characterized in that the constant k is greater than

((Af + Ac)/Ac)1/2,

where Af is the cross-sectional area of the supply fiber (IF), connected to the said source (LS);

Ac is the cross-sectional area multimode fiber (FF).

4. The connecting device according to any one of the preceding paragraphs, characterized in that said source (LS) contains a laser diode with a beam of essentially elliptical cross-section and a device for the transformation of the beam with elliptical cross-section in the beam with essentially circular cross section and divergence angle (s).

5. The connecting device according to any one of the preceding paragraphs, characterized in that said source (LS) contains a multimode semiconductor laser diode (LD) having essentially rectangular radiating aperture, and a cylindrical lens (CL), located in the light beam (LB) mentioned laser diode (LD) between the aforementioned laser diode (LD) and supply fiber (IF).

6. The connecting device according to any one of the preceding paragraphs, characterized in that the said multimode optical fiber (FF) contains additional concentric single-mode core.

7. The connecting device according to any one of paragraphs.1 to 5, characterized in that the said multimode optical fiber (FF) contains additional concentric single-mode alloy core.

8. The connecting device according to p. 7, ex and transition metals, or a combination thereof.

9. The connecting device according to p. 7, characterized in that the said singlemode lived doped with ions of ytterbium and erbium.

10. The connecting device according to p. 7, characterized in that the said singlemode lived doped by ions of neodymium.

11. The connecting device according to p. 7, characterized in that the said singlemode lived doped ytterbium ions.

12. The connecting device according to p. 7, characterized in that the said singlemode lived doped with chromium ions.

13. The connecting device according to any one of the preceding paragraphs, characterized in that the said optical fiber (FF) is an active fiber optical amplifier.

14. The connecting device according to any one of the preceding paragraphs, characterized in that the said optical fiber (FF) is the active fiber of the fiber laser.

15. The connecting device according to any one of the preceding paragraphs, characterized in that the said supply optical fiber (IF) is connected with the said multimode optical fiber (FF), forming the configuration of the X-connector.

16. The connecting device according to any one of the preceding paragraphs, ex the fiber (FF), forming the configuration of the Y-connector.

17. The connecting device according to any one of the preceding paragraphs, characterized in that as mentioned optical fiber (FF), and intermediate optical fiber (IF) do not have the layers of the shell in the area of fusion (CR).

18. The connecting device according to any one of paragraphs.1 to 16, characterized in that at least one of the above-mentioned optical fiber - optical fiber (FF) and the intermediate optical fiber (IF) is a layer of the shell in the area of fusion (CR).

19. The connecting device according to p. 1, characterized in that at least one of the above-mentioned optical fiber - optical fiber (FF) and the intermediate optical fiber (IF) - has an essentially circular cross-section.

20. The connecting device according to p. 1, characterized in that at least one of the above-mentioned optical fiber - optical fiber (FF) and the intermediate optical fiber (IF) - has an essentially elliptical cross-section.

21. The connecting device according to p. 1, characterized in that at least one of the above-mentioned optical fiber - optical fiber (FF) and the intermediate optical fiber (IF) - has an essentially rectangular eat the ratio between the minimum cross-sectional area tapering supply fiber and IF the initial area of its cross section is in the range from 0.01 to 0.7.

23. The connecting device according to p. 22, characterized in that the ratio between the minimum cross-sectional area tapering supply fiber and IF the initial area of its cross section is about 0.1.

24. The connecting device according to any one of the preceding paragraphs, characterized in that the ratio between the cross-sectional area of the supply fiber and IF the cross-sectional area of the receiving fiber FF in the connections pane CR is in the range of 0,01 - 0,99.

25. The connecting device according to p. 24, characterized in that the ratio between the minimum cross-sectional area tapering supply fiber and IF the cross-sectional area of the receiving fiber FF in the connections pane CR is about 0.1.

26. The connecting device according to any one of the preceding paragraphs, characterized in that the said gradually tapering part of these multimode feed optical fiber IF, fusion-bonded with the said multimode optical fiber

 

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