COMBINEUR SPECTRAL MONOMODE

Abstract

The invention relates to a single-mode spectral combiner, comprising: - at least two input optical fibers (3), each adapted to interface with an upstream optical fiber (9) intended to inject a single-mode light signal; - a single output optical fiber (5) adapted to interface with a single-mode downstream optical fiber (11) selected to carry any one of the injected single-mode light signals; and - a linking optical fiber (7) connecting the input optical fibers to the single output optical fiber, and in that at least one input optical fiber (3) is adapted to be connected in an aligned manner with an upstream optical fiber (9) that can be intended to inject a single-mode light signal having a wavelength shorter than the cutoff wavelength of the input optical fiber. Figure for abbreviation: Figure 1

Description

Title of the invention: SINGLE-MODE SPECTRAL COMBINER Technical field

[0001] The present invention relates to the field of spectral multiplexing in optical fibers and more particularly, to devices operating in different spectral ranges which can be used in optical fiber sensors. State of the prior art

[0002] In the field of optical fibers, there are different ranges of working wavelengths. The main ranges used in both telecoms and in detection (sensing) and through POF "Power Over Fiber" energy fibers are ranges around the following values: 850nm; 1300nm; and 1550nm.

[0003] The optical fibers commonly used for detection and long-distance telecommunications are single-mode optical fibers. When using this type of optical fiber, a certain working wavelength range must be respected. Indeed, each single-mode optical fiber is only single-mode over a given spectral interval. Below the lower limit of the interval, the optical fiber becomes multimode, that is, several modes can propagate in it.

[0004] Single-mode optical fiber types and their associated spectral ranges include the following: "SMF28" [1260 - 1625nm]; "HI1060" [980 -1650nm]; "SM980" [980 - 1550nm]; "SM800" [830 - 980nm]; and "780HP" [780 - 970nm],

[0005] As can be seen, none of the conventional optical fibers mentioned above are single-mode across the entire spectral range from 850nm to 1550nm. Thus, if one has an optical device (for example, a telecom transmitter or a fiber optic sensor interrogator) operating at 850nm, it will have to be connected to a single-mode fiber at 850nm. And if one has an optical device operating at 1550nm, it will have to be connected to a single-mode fiber at 1550nm. However, it turns out that it can be useful to be able to work at these two wavelengths in parallel or sequentially.

[0006] Currently, to be able to work at different wavelengths, an architecture is used comprising several physical interfaces like that illustrated in [Fig. 6]. This architecture comprises a first interface 301 connectable to a source 151 at 850nm using a first single-mode optical fiber 311 at 850nm, a second interface 302 connectable to a source 152 at 1300nm using a second single-mode optical fiber 312 at 1300nm, and a third interface 303 connectable to a source 153 at 1550nm using a third optical fiber 313 single-mode at 1550nm. Since there are no single-mode optical fibers from 850 to 1550nm, each interface must be connected to a single-mode fiber suitable for the light source.

[0007] This type of parallelization of interfaces is cumbersome and requires care to use the right optical fiber according to the desired application. This can generate connection errors for an inexperienced user.

[0008] The object of the present invention is to overcome the aforementioned drawbacks by proposing a method and a device making it possible to work at several wavelengths by facilitating interfacing over a range from 850nm to 1550nm in a simple, efficient and flexible manner. Presentation of the invention

[0009] The subject of the invention is a single-mode spectral combiner, comprising:

[0010] -at least two input optical fibers, each being adapted to interface with an upstream optical fiber intended to inject a single-mode light signal,

[0011] -a single output optical fiber adapted to interface with a downstream single-mode optical fiber selected to carry any of the injected single-mode light signals, and

[0012] -a connecting optical fiber connecting the input optical fibers to the single output optical fiber, and in that at least one input optical fiber is adapted to be connected in an aligned manner with an upstream optical fiber which may be intended to inject a single-mode light signal having a wavelength less than the cut-off wavelength of the input optical fiber.

[0013] This allows for a single interface to freely connect any type of single-mode fiber using sources of different wavelengths.

[0014] Advantageously, the combiner comprises at least one optical connector adapted to connect an input optical fiber to an upstream optical fiber by aligning their optical axes.

[0015] The optical connector thus guarantees the alignment of the optical fibers with each other for optimal signal coupling.

[0016] Alternatively, the combiner comprises at least one input optical fiber connected by optical welding to an upstream optical fiber by aligning their optical axes.

[0017] Welding provides a permanent bond between two fibers while ensuring extremely precise alignment.

[0018] Advantageously, the injected light signals propagate in a single-mode manner in the connecting optical fiber.

[0019] Thus, it is possible to transit in a single-mode manner in the same fiber optical linking both an 850nm signal and a 1550nm signal.

[0020] Advantageously, the input optical fibers consist of a single type of single-mode optical fiber.

[0021] This makes it possible to simplify the configuration of the combiner.

[0022] Advantageously, the combiner comprises N input optical fibers, each input optical fiber being adapted to interface with a light source having a predetermined wavelength, via a corresponding upstream optical fiber, and the single output optical fiber being adapted to interface with any type of downstream optical fiber.

[0023] Advantageously, the upstream optical fibers are intended to inject single-mode light signals in spectral ranges comprising the following ranges: 850nm, 1300nm, and 1550nm.

[0024] Advantageously, the connecting optical fiber consists of a single-mode optical fiber in the spectral range 1260nm to 1625nm.

[0025] The invention also relates to a fiber optic sensor comprising a single-mode spectral combiner according to any one of the preceding characteristics, the fiber optic sensor being configured to exploit different spectral ranges in order to carry out different physical measurements.

[0026] The invention also relates to a spectral combination method, comprising the following steps:

[0027] - interfacing at least two input optical fibers with at least two corresponding upstream optical fibers intended to inject single-mode light signals,

[0028] -interfacing a single output optical fiber with a single-mode downstream optical fiber selected to carry any of the injected single-mode light signals, the input optical fibers being connected to the single output optical fiber via a link optical fiber, and

[0029] -connecting in an aligned manner at least one input optical fiber with an upstream optical fiber which may be intended to inject a single-mode light signal having a wavelength less than the cut-off wavelength of the input optical fiber.

[0030] Other advantages and characteristics of the invention will appear in the detailed non-limiting description below. Brief description of the figures

[0031] Embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings, in which:

[0032] [Fig.l] very schematically illustrates a single-mode spectral combiner, according to one embodiment of the invention;

[0033] [Fig.2] very schematically illustrates experimental tests in different optical fiber segments, according to one embodiment of the invention;

[0034] [Fig.3] very schematically illustrates a single-mode spectral combiner, according to a preferred embodiment of the invention;

[0035] [Fig.4] illustrates very schematically a particular example of the spectral combiner single-mode [Fig.3] comprising three input optical fibers;

[0036] [Fig.5] very schematically illustrates a fiber optic sensor, according to one embodiment of the invention; and

[0037] [Fig.6] very schematically illustrates an architecture of several optical interfaces, according to the prior art. Description of the embodiments

[0038] The principle of the invention is to have a single connection interface for optical fibers regardless of the wavelength circulating in these optical fibers.

[0039] [Fig.l] very schematically illustrates a single-mode spectral combiner, according to one embodiment of the invention. This figure also represents a single-mode spectral combination method, according to one embodiment of the invention.

[0040] Generally speaking, a spectral combiner is a wavelength division multiplexing device known as WDM (Wavelength Division Multiplexing) known in the state of the art. Its function is to circulate several light signals of different wavelengths on a single optical fiber by mixing them at the input by means of a multiplexer and separating them at the output by means of a demultiplexer.

[0041] A feature of the spectral combiner of the present invention is that it is a WDM wavelength division multiplexing device having a single output adapted to interface with one of a plurality of optical fibers adapted to carry any one of a set of single-mode light signals.

[0042] Thus, in accordance with the invention, the single-mode spectral combiner 1 comprises at least two input optical fibers 3, a single output optical fiber 5, and a connecting optical fiber 7.

[0043] Each input optical fiber 3 is adapted to interface with an upstream optical fiber 9 intended to inject a single-mode light signal. More particularly, [Fig. 1] illustrates, by way of example, first 31 and second 32 input optical fibers adapted to be connected with corresponding first 91 and second 92 upstream optical fibers. The first 91 and second 92 upstream optical fibers are intended to inject light signals of wavelengths X1 and X2 respectively. By way of example, the first 91 and second 92 upstream optical fibers are optical fibers of the SM800 and SMF28 types respectively, having in spectral ranges [830 - 980nm] and [1260 - 1625nm] and injecting light signals of wavelengths Xi=850nm and X2=1550nm respectively. It will be noted that as a variant, the second upstream optical fiber 92 may be of the HI1060 type having a spectral range [980 - 1650nm]. Of course, the upstream optical fibers 9 may inject single-mode light signals according to other spectral ranges including for example a wavelength of 1300nm.

[0044] Advantageously, the input optical fibers 3 are made up of a single type of single-mode optical fiber. According to the example of [Fig. 1], the first 31 and second 32 input optical fibers are both of the SMF28 type. Alternatively, they may be of the HI1060 type.

[0045] However, according to another embodiment one of the input optical fibers 3 may be of the SMF28 type while the other may be of the HI1060 type.

[0046] The single output optical fiber 5 is adapted to interface with a single-mode downstream optical fiber 11 selected to carry any one of the injected single-mode light signals. According to this example, the single output optical fiber 5 may be of the SMF28 or HI1060 type. The downstream optical fiber 11 may be a first single-mode downstream optical fiber 111 at 850nm or a second single-mode downstream optical fiber 112 at 1550nm depending on the desired light signal. Thus, one or other of the single-mode light signals of wavelengths Xi and X2 injected into the single-mode spectral combiner 1 may be recovered at the output.

[0047] The connecting optical fiber 7 within which the single-mode light signals can pass, connects the input optical fibers 31, 32 to the single output optical fiber 5. It will be noted that the connecting optical fiber 7 and the output optical fiber 5 may be the same optical fiber. For example, the connecting optical fiber 7 is made up of a single-mode optical fiber in the spectral range 1260nm to 1625nm and may be of the SMF28 or HI1060 type.

[0048] At least one input optical fiber 3 is adapted to be connected in an aligned manner with an upstream optical fiber 9. The latter may be intended to inject a single-mode light signal having a wavelength less than the cut-off wavelength of the corresponding input optical fiber 3.

[0049] Indeed, the alignment of the optical axes between an input optical fiber 3 and an upstream optical fiber 9 allows the injected light signal to be single-mode in the input 3, link 7 and output 5 optical fibers even if they are not supposed to be so in their spectral ranges. Thus, the injected light signals propagate in a single-mode manner in the link optical fiber.

[0050] When the optical axes between two optical fibers are aligned, only the centrosymmetric modes are excited. This optimizes the coupling rate between the two optical fibers because the centrosymmetric modes are Gaussian in nature. In contrast, a offset between the optical axes in the connection of the two optical fibers, excites modes which are not centrosymmetric, consequently reducing the coupling between these two fibers.

[0051] Advantageously, the connection between an input optical fiber 3 with an upstream optical fiber 9 is made by means of an optical connector 13 adapted to align the optical axes of the two fibers.

[0052] Alternatively, the connection between an input optical fiber with an upstream optical fiber is made by optical welding aligning the optical axes of the two fibers permanently.

[0053] [Fig.2] very schematically illustrates experimental tests in different segments of optical fibers, according to one embodiment of the invention.

[0054] The tests relate to the analysis of the profile of a light coming for example from a source 15 at 850nm in different segments of optical fibers. In particular, an optical fiber 17 of the SM800 type carrying a light signal of 850nm is connected sequentially to first 171, second 172 and third 173 segments of optical fibers of the SM800, SMF28 and SM800 types respectively. The connection between each two consecutive segments is carried out in an aligned manner using suitable connectors 13 or by optical welding.

[0055] The tests consist of measuring the profile of the light signal at the output of each of the first 171, second 172 and third 173 segments of optical fibers.

[0056] The measured profile of the mode of the light at 850nm at the SI output of the first segment 171 of single-mode optical fiber at 850nm (SM800) is a Gaussian profile 191. This profile 191 is expected because it is the profile of the fundamental mode which is the single mode propagating in the single-mode optical fiber of the first segment 171.

[0057] The light profile measured at the output S2 of the second segment 172 of optical fiber of the SMF28 type is a quasi-Gaussian profile 192 and it is the profile that a light at 850nm would have in a single-mode fiber at 850nm. This test shows that by aligning the optical axes between the first 171 and second 172 segments of optical fibers, a light at 850nm is mainly guided by the fundamental mode in an optical fiber supposed to be single-mode only in the spectral range [1260 -1625nm].

[0058] Finally, the light profile measured at the output S3 of the third segment 173 of optical fiber of the SM800 type is also a quasi-Gaussian profile 193. As a result, the light can be coupled from an SMF28 optical fiber to another single-mode optical fiber at 850nm with a very good transmission efficiency greater than 95%.

[0059] The aligned connection of the optical axes thus makes it possible to guide the light at 850nm in a quasi-monomode manner in an SMF28 optical fiber which is supposed to be monomode only in the spectral range [1260 - 1625nm]. Furthermore, given that the light at 850nm is quasi-single-mode in an SMF28 fiber, it is possible to re-couple it to an 850nm single-mode fiber (for example SM800) with a very good coupling rate greater than 95%.

[0060] In summary, the tests in [Fig.2] show that the 850nm light remains quasi-single-mode in an SMF28 optical fiber when the light is injected from an SM800 optical fiber to an SMF28 optical fiber by ensuring that the axes of the SM800 and SMF28 optical fibers coincide. In practice, this is achieved by making a fiber-to-fiber splice or by using optical connectors. Efficiency is increased by ensuring that the SMF28 optical fiber does not exhibit any changes in its optical and mechanical parameters (for example, no micro or macro bends and no alteration of its refractive index).

[0061] Of course, the fact that the tests work well for a light signal at 850nm, implies that it works even better for any signal whose wavelength is greater than 850nm because we are getting even closer to the signal where we are single-mode at 1300nm in a fiber of the SMF28 type.

[0062] It will be noted that if optical fibers (for example, HI1060, SM980) are used with lower cut-off wavelengths than those (for example, SMF28) used to carry out the tests, the results can only be further improved.

[0063] [Fig.3] very schematically illustrates a single-mode spectral combiner, according to a preferred embodiment of the invention.

[0064] According to this example, the single-mode spectral combiner 1 comprises N input optical fibers 3 adapted to interface with N upstream optical fibers 9 intended to inject N single-mode light signals of wavelengths Xi to XN. The N input optical fibers 3 are connected via a link optical fiber to the single output optical fiber 5. Any input optical fiber 3 having a cutoff wavelength greater than the wavelength of the single-mode light signal injected by a corresponding upstream optical fiber 9 is adapted to be connected in an aligned manner with this upstream optical fiber 9. In this way, a single-mode light signal having the same wavelength X; as that injected into the spectral combiner 1 is recovered at the single output 5 of the single-mode spectral combiner 1.

[0065] [Fig.4] very schematically illustrates a particular example of the single-mode spectral combiner of [Fig.3] comprising three input optical fibers.

[0066] According to this example, the first 31, second 32 and third 33 input optical fibers as well as the connecting optical fiber 7 and the single output optical fiber 5 are all of the SMF28 type.

[0067] The first 31, second 32 and third 33 input optical fibers are intended to be connected to first 91, second 92 and third 93 upstream optical fibers coming from the first 151, second 152 and third 153 light signal sources. of wavelengths 850nm, 1310nm and 1550nm respectively.

[0068] Each input optical fiber is of the SMF28 type associated with the interval [1260 -1625nm]. Therefore, it is supposed to be single-mode only for the wavelengths 1310nm and 1550nm of the second 152 and third 153 sources. However, by making an aligned connection between the optical axis of the first input optical fiber 31 and the optical axis of the first upstream optical fiber 91, the optical signal at 850nm can be guided in a quasi-single-mode manner in the first input optical fiber, the link fiber and the single output fiber.

[0069] Thus, by activating the first source 151 and connecting to the single output optical fiber 5 a downstream optical fiber 111 monomode at 850nm, it is possible to recover at the output a monomode optical signal having a wavelength of 850nm. Similarly, by activating the second source 152 and connecting to the single output optical fiber 5 a downstream optical fiber 112 monomode at 1310nm, it is possible to recover at the output a monomode optical signal with a wavelength of 1310nm, and so on.

[0070] Furthermore, several sources can be activated simultaneously. For example, by activating the first 151 and second 152 sources, single-mode light signals of wavelengths 850nm and 1310nm are transported by the first 31 and second 32 input optical fibers to be combined by multiplexing within the connecting optical fiber 7 making it possible to recover a multimode light signal at the single output 5.

[0071] The single-mode spectral combiner 1 of the present invention is thus a spectral multiplexing component having the particularity of being single-mode (or possibly multi-mode) over the entire working wavelength ranges. It is a single interface for connecting any type of optical fiber without having to worry about the compatibility of the wavelengths with the optical fiber used.

[0072] [Fig.5] very schematically illustrates a fiber optic sensor, according to one embodiment of the invention.

[0073] The fiber optic sensor 21 comprises a single-mode spectral combiner 1 comprising a plurality of input optical fibers 3 and a single output optical fiber 5, according to the embodiments of Figs. 1, 3 and 4.

[0074] The optical fiber sensor 21 is thus configured to exploit different spectral ranges in order to carry out different physical measurements. The two main ones are around 850nm and 1550nm. Thus, any optical measurement fiber can be freely used without worrying about the interface.

[0075] Of course, various modifications can be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples.

Claims

Claims

1. Single-mode spectral combiner, characterized in that it comprises: - at least two input optical fibers (3) each being adapted to interface with an upstream optical fiber (9) intended to inject a single-mode light signal, - a single output optical fiber (5) adapted to interface with a downstream single-mode optical fiber (11) selected to transport any one of the injected single-mode light signals, and - a connecting optical fiber (7) connecting the input optical fibers to the single output optical fiber, and in that at least one input optical fiber (3) is adapted to be connected in an aligned manner with an upstream optical fiber (9) which may be intended to inject a single-mode light signal having a wavelength less than the cut-off wavelength of the input optical fiber.

2. Combiner according to claim 1, characterized in that it comprises at least one optical connector (13) adapted to connect an input optical fiber (3) to an upstream optical fiber (9) by aligning their optical axes.

3. Combiner according to claim 1, characterized in that it comprises at least one input optical fiber (3) connected by optical welding to an upstream optical fiber (9) by aligning their optical axes.

4. Combiner according to any one of the preceding claims, characterized in that the injected light signals propagate in a single-mode manner in the connecting optical fiber (7).

5. Combiner according to any one of the preceding claims, characterized in that the input optical fibers (3) consist of a single type of single-mode optical fiber.

6. Combiner according to any one of the preceding claims, characterized in that it comprises N input optical fibers (3), each input optical fiber being adapted to interface with a light source having a predetermined wavelength, via a corresponding upstream optical fiber, and the single output optical fiber (5) being adapted to interface with any type of downstream optical fiber.

7. Combiner according to any one of the preceding claims, characterized in that the upstream optical fibers (9) are intended to inject single-mode light signals in spectral ranges comprising the following ranges: 850nm, 1300nm, and 1550nm.

8. Combiner according to any one of the preceding claims, characterized in that the connecting optical fiber (7) consists of a single-mode optical fiber in the spectral range 1260nm to 1625nm.

9. A fiber optic sensor comprising a single-mode spectral combiner (1) according to any one of the preceding claims, the fiber optic sensor (21) being configured to exploit different spectral ranges in order to carry out different physical measurements.

10. Spectral combining method, characterized in that it comprises the following steps: - interfacing at least two input optical fibers (3) with at least two corresponding upstream optical fibers (9) intended to inject single-mode light signals, - interfacing a single output optical fiber (5) with a single-mode downstream optical fiber (11) selected to transport any one of the injected single-mode light signals, the input optical fibers being connected to the single output optical fiber via a connecting optical fiber, and - connecting in an aligned manner at least one input optical fiber (3) with an upstream optical fiber (9) which may be intended to inject a single-mode light signal having a wavelength less than the cut-off wavelength of the input optical fiber.