WO1998035257A1

WO1998035257A1 - Switching arrangement for switching and coupling a light beam into at least one output fibre

Info

Publication number: WO1998035257A1
Application number: PCT/EP1998/000633
Authority: WO
Inventors: Steffen Glöckner; Rolf GÖRING
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1997-02-07
Filing date: 1998-02-06
Publication date: 1998-08-13
Also published as: DE19706053B4; DE19706053A1; EP0958520A1

Abstract

A switching arrangement is disclosed for switching and coupling a light beam irradiated by at least one optical element, such as an input fibre (2), into at least one output fibre among a number of output fibres (6). A beam deflecting and collimating optic (1) connected to an adjusting device with an adjusting element (10) is associated with the irradiated light beam or input fibre (2). Depending on an adjustment signal, the adjusting element (10) laterally shifts the input fibre (2) and the beam deflecting and collimating optic (1) in relation to one another, so that the collimated beam may be coupled via a deflecting optic (4) and a focusing optic (5) into at least one output fibre among a number of output fibres (6) arranged at a distance from the beam deflecting and collimating optic.(1).

Description

Switching arrangement for switching and coupling a light bundle into at least one output fiber

The invention relates to a switching arrangement for switching and coupling a light beam into at least one output fiber according to the preamble of the main claim.

Mono odefaserschalter are important components for optical communications and ^'optical metrology. A fiber switch is used to couple light that is emitted from one or more input single-mode fibers into different output single-mode fibers, with an adjusting mechanism ensuring that the light can be switched into the different output channels or fibers. Various configurations are conceivable for the arrangement of the input single-mode fibers and output single-mode fibers, for example with an MxN Fiber switch M input channels switchable into N output channels.

A number of arrangements for fiber switches are known which implement the switching function by moving the input fiber with respect to the output fibers. These concepts essentially use purely mechanical principles. From US 4,896,935 an IxN fiber switch is known which has an input fiber which is rotated in one plane in such a way that it can serve a plurality of output fibers which are arranged radially, the input and the corresponding output fiber in each switching position are almost in contact, so that no optical components are required to guarantee high coupling efficiencies. The required rotary movement can be made possible by various actuators, but the switching times between adjacent channels are significantly shorter than between the outer channels. The maximum possible number of output fibers N is limited by the arrangement of all fibers next to one another in one plane. Assembly requires difficult alignment of the individual fibers.

An improvement is described in US Pat. No. 5,479,541, the same structure being chosen and only each fiber additionally being provided with a collimation lens. It has been shown that the required adjustment tolerances of the output modules, ie the output fibers with collimation optics, are more favorable, which enables more cost-effective production. Otherwise, the disadvantages described above remain. US Pat. No. 5,434,936 discloses a switching arrangement in which the input fiber is connected to a rotating mechanism and the longitudinal fiber axis lies parallel to the rotating axis, but is offset laterally to the rotating axis. The output fibers are arranged in the same way. The switching function is implemented using magnetic forces and each output fiber is additionally provided with a permanent magnet, which is intended to ensure that the optimal position of the fibers relative to one another is set and maintained when switching to the corresponding output fiber. In this arrangement, too, the number of output fibers is very limited, essentially due to the actuation mechanism and the greatly increasing manufacturing effort when adding further output fibers.

Another arrangement (US Pat. No. 5,483,608) attempts to solve the problem of inexpensive assembly in that all the output fibers are in guides, for example in V-grooves, and the input fiber is brought into the guide of the corresponding output fiber during the switching process and up to the stop is moved to the output fiber. The required accuracy of the various positioning movements is thus greatly reduced. A large number of output fibers is possible with this arrangement, but due to the large travel ranges required, the switching can only take place very slowly.

All solutions according to the prior art have the disadvantage that they cannot simultaneously guarantee a large number of output channels N, short switching times and simple and therefore inexpensive installation. The invention is therefore based on the object of providing a switching arrangement for switching and coupling a light bundle emitted by at least one input fiber into an output fiber of a plurality of output fibers, which ensures a large number of output channels, short switching times and simple and therefore inexpensive installation , where it should also be as compact as possible.

This object is achieved by the characterizing features of the main claim in conjunction with the features of the preamble.

Characterized in that the emitted light bundle or the input fiber is assigned a beam deflection and collimation optics and a preferably miniaturized adjusting device is provided which laterally displaces the input fiber and the beam deflection and collimation optics relative to one another such that the collimated beam bundle into at least one

Output fiber of the plurality of output fibers arranged at a distance from the beam deflection and collimation optics can be coupled, a large number of output channels (typically N = 10-200), which are preferably arranged in two dimensions, can be provided. The travel ranges required are extremely short and thus enable short switching times (typically 1 ms) and it can be built very simply and compactly. The deflected optical beams are processed in such a way that they can be efficiently coupled into the output fibers by means of deflecting optics and separate focusing optics. Overall, the switching arrangement according to the invention forms a microsystem, in which each output fiber has a separate coupling optics, all of which Coupling optics (focusing optics and deflection optics) are at least partially arranged in the array. The possibility of using lens and / or fiber arrays with equidistant spacing of the fibers or lenses is made possible by the deflecting optics, which deflect the collimated deflected bundle back into the original direction. Due to the design as a microsystem, the lens defects are so small that no complicated objectives are necessary, but "single lenses" can be used with limited diffraction. According to the invention, all individual lenses in the system have small lateral dimensions (beam deflection and collimation optics, focusing optics).

Advantageous further developments and improvements are possible through the measures specified in the subclaims. Inexpensive piezo actuators that are commercially available in large variations of the performance features can be used as control elements. Furthermore, a measuring device connected to a processing unit can be provided, which measures the position of the respective deflected beam in relation to the optimal position for coupling into the respective output fiber, and the processing unit generates a control signal for the steep elements. This ensures that the individual positions of the output fibers can be approached with high precision and thus guarantees the stability of the optical parameters in the event of changing environmental conditions, such as temperature and air humidity. Due to the two-dimensional arrangement of the output channels or the output fibers, arrays of optical and electronic components (for example detectors) can be used, which are inexpensive to manufacture and assemble, as well as the large number of Further promote output channels. Very simple micro-optical components, such as microlenses, microlens arrays, prism arrays, which can be produced with comparatively little effort, can be used.

The optical functioning of the micro-optical components is diffraction-limited, which enables efficient coupling into the output fibers (losses <1 dB). The adjustment paths of the control elements are in the range of a few 10 μm, so that switching times in the range of

1 ms to less than 100 μm can be achieved. High channel isolations can also be achieved (50 dB). In addition, the switching arrangement according to the invention is functional in any wavelength ranges, the materials used here having to be adapted to the corresponding wavelength ranges with regard to their properties, such as transparency and refractive index.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

1 is a schematic side view of the switching arrangement according to the invention in different positions of the deflection and collimation optics with respect to the input fiber,

2 is a perspective view of the embodiment of FIG. 1,

Fig. 3 is a view of a plurality of quadrant detectors in one two-dimensional array are arranged, and

4 shows schematic views for the adjustment possibilities of the input fiber and the deflection and collimation optics relative to one another.

In Figs. 1 and 2, a 1 × N switching arrangement is shown, which has an input fiber 2 and a plurality of output fibers 6. The output fibers 6 are arranged two-dimensionally in accordance with FIG. 2 and, forming a two-dimensional array, are mounted and fastened in a holder 11. A lens 1 is arranged in front of the input fiber 2 as a deflection and collimation optics, which lens is arranged in two directions, for example x- and y-direction, in relation to the input fiber 2 via an adjusting element 10, the adjustment directions of which are indicated by the arrows 12 , is movable. The lens is preferably designed as a microlens with a small focal length, for example 1 mm with a diameter of 0.5-1 mm.

At a sufficient distance 3 from the lens 1, which must be selected so that the respective deflected and collimated beams are spatially separated from one another, a detector device 7 for determining the position of the respective deflected beam relative to the optimal coupling position into the output fibers 6 is one Downstream deflection optics 4 and a subsequent focusing optics arrangement 5 are provided, which consists of a plurality of focusing optics assigned to the respective output fiber, both the individual focusing optics and the output fibers in the same lateral Chen distance from each other. The deflecting optics 4 and the focusing optics arrangement 5, as can be seen in FIG. 2, are designed as prism arrays and microlens arrays. The lens array as focusing optics 5 has a numerical aperture adapted to the output fibers.

3 shows the detector arrangement 7, which has a plurality of quadrant detectors arranged in rows and columns, consisting of four

Individual elements 8a, b, c, d exist. The central region 9 encircled by the individual segments 8a to 8d is transparent. The detector device 7 is connected to a processing unit (not shown) which, depending on the output signals of the respective quadrant detector, generates a control or regulating signal to the actuating element 10 designed as a piezo element. Depending on the control signal, the deflection and collimation optics are adjusted in two directions relative to the input fiber 2. In the exemplary embodiment shown, the adjusting element designed as a piezo actuator, the electronic processing unit and the detector arrangement form the adjusting device for the lens 1, which is shown as a “control loop”. In another embodiment, the detector arrangement 7 as a measuring device for the position of the beam can be dispensed with and only the processing unit can be provided, so that the actuating device consists of an actuating element and processing unit or a control unit, the processing or control unit being the control signal as a control signal for the actuating element is generated depending on the position of the output fiber and the position of the lens and / or the input fiber. The switching arrangement works as follows. The input single-mode fiber 2 emits a beam 15 at its end. Depending on the position of the output fiber 6 into which the beam 13 is to be coupled, the processing unit (not shown) supplies an actuating signal to the piezo actuator 10, which laterally shifts the lens 1 connected to it relative to the input fiber 2. 1 shows three different beam paths for coupling into three different output fibers 6. The lens 1 serves both as collimation optics and as a beam deflector. The individual deflected and collimated beams 15 are after the route

3 of the free space expansion spatially separated from each other. In the plane that is about the distance 3 from the

Lens 1 is removed, the detector device 7 is arranged and the bundles can be transformed according to the output channels or output fibers 6 separately. The individual prisms 4a, 4b of the prism array which are designed differently from one another

4 cause a deflection of the respective individual beam in such a way that it again runs parallel to the optical axis. The subsequent lens array 5 with the numerical aperture adapted to the output fibers 6 focuses the individual bundles on the output fibers 6 in each case.

The respective quadrant detector of the detector arrangement 7 measures and determines the position of the respective deflected bundle and delivers the measurement signal to the processing unit (not shown). In this unit it is determined whether the measured beam is in an optimal position relative to the respective output fiber 6 and accordingly a control signal for controlling the actuating element is tes 10 generated. The adjusting element 10 adjusts the lens 1 until it deflects the beam in accordance with the optimal position.

Different configurations of the prism array 4 and the lens array 5 are possible. Of course, they can be arranged separately from each other as individual elements. A further system integration is possible if the prism array 4 and the lens array 5 are mounted on one and the same substrate. The deflection optics 4 can also be designed as a single lens, the focal length of which corresponds to the distance from the beam deflection and collimation optics.

It is also conceivable for the deflection optics to be dispensed with, but here the lateral distances between the output fibers differ from one another. There are small additional losses that can be tolerated depending on the application.

4 shows the adjustment options of the input fiber and the deflection and collimation optics relative to one another. In Fig. 4a) the lens 1 is adjusted two-dimensionally, ie in two directions, in Fig. 4b) the input fiber 2 is adjusted in two directions and the lens 1 is fixed, in Fig. 4c) the input fiber 2 is in one direction and the lens 1 is adjusted in the other direction and FIG. 4d) the deflection and collimation optics are realized by two lenses 13 and 14, the one lens 13 being moved in one direction and the other lens 14 in the other direction. Through the explanations according to FIGS. 4c) and 4d), mechanical decoupling of the x and y movements during displacement can be achieved. An example of the implementation of the switching arrangement according to the invention now follows.

A wavelength range of λ = 0.78 μm is selected. The input fiber 2 has a waist diameter of 4 μm. The following deflection and collimation optics have a focal length of f = 1 mm and a numerical aperture of 0.25. The collimated bundles after the collimation optics have a waist diameter of about 250 μm. This corresponds to a Rayleigh length of 6 cm. If the collimation optics are now deflected by v = 15 μm between two adjacent positions, the bundle is deflected by an angle θ = v / f = 15 mrad. At a distance of 3.3 cm after the collimation lens, the centers of the neighboring bundles are 500 μm apart. This is equal to the lateral distance (pitch dimension) of the following optics. The individual quadrant detectors enclose a transparent area with a diameter of 450 μm, so that the width of the detector structures is approximately 20 μm. In this case, the detector elements can consist of silicon. To implement a 1 x 25 switch, prism structures with angles of 0, ± 1.72 ° and ± 3.43 ° with a refractive index of 1.5 would be necessary. The

Lens arrays should have a numerical aperture of 0.25 and an aspherical surface shape. The working distance of the fibers from the lens array is approximately 1 mm. The required adjustment range of the piezo actuator is 60 μm x 60 μm. The switching times for this adjustment are of the order of 1 ms.

In the examples described above, the light beam emitted by an input fiber is coupled into one or more output fibers. Instead of Providing an input fiber can also be used with a free space bundle, for example from a laser, which is focused with a first optical system in such a way that the focus has similar dimensions and the local position of the radiation emitted by the fiber (in the "pure" fiber switch) Light beam.

Claims

claims

1. Switching arrangement for switching and coupling a light beam emitted by at least one optical element into at least one output fiber of a plurality of output fibers, the emitted light bundle being assigned a beam deflection and collimation optics (1, 13, 14) and an actuating device ( 10.7) is provided, which laterally shifts the emitted light bundle and the beam deflection and collimation optics (1,13,14) relative to one another, characterized in that the beam deflection and collimation optics are followed by a deflection optics (4) which the col - Limited deflected beams are deflected in the direction parallel to the optical axis and that each output fiber is assigned focusing optics which couples the respective beams into the output fiber.

2. Switching arrangement according to claim 1, characterized in that the optical element emitting the light beam is an input fiber.

3. Switching arrangement according to claim 1 or 2, characterized in that both the individual focusing optics (5) and the output fibers (6) lie at the same lateral distance from one another.

4. Switching arrangement according to one of claims 1 to 3, characterized in that the deflecting optics (4) is designed as a lens, the focal length corresponds to the distance to the beam deflection and collimation optics.

5. Switching arrangement according to one of claims 1 to 4, characterized in that the deflecting optics

(4) as a prism array and / or the focusing optics (5) are designed as a lens array.

6. Switching arrangement according to claim 4 and 5, characterized in that the prism and lens array are applied to one and the same substrate.

7. Switching arrangement according to one of claims 1 to 6, characterized in that the actuating device has at least one actuating element (10) which is actuated as a function of an actuating signal.

8. Switching arrangement according to claim 7, characterized in that the actuating element as a piezo actuator

(10) is formed.

9. Switching arrangement according to one of claims 1 to 8, characterized in that the adjusting device comprises a measuring device (7) which the

Measures the position of the respective deflected beam in relation to the optimal position for coupling into the respective output fiber (6) and that a processing unit connected to the measuring device (7) generates the control signal for the at least one control element (10) depending on the measurement signals.

10. Switching arrangement according to claim 9, characterized in that the measuring device has a plurality of several individual segments comprising detectors, which are preferably ring-shaped with a central transparent region (9).

11. Switching arrangement according to one of claims 1 to

10, characterized in that the beam deflection and collimation optics (1) is designed as a microlens, which preferably has a focal length of ≤ 1 mm.

12. Switching arrangement according to one of claims 1 to

11, characterized in that the deflection and collimation optics (1) with respect to the emitted light bundle or the input fiber (2) in at least one direction and / or the emitted light bundle or the input fiber (2) with respect to the Deflection and collimation optics (1) can be laterally displaced in at least one direction.

13. Switching arrangement according to claim 12, characterized in that the deflection and collimation optics consist of two lenses (13, 14) which can each be displaced in different directions.

14. Switching arrangement according to one of claims 1 to 13, characterized in that the output fibers are mounted two-dimensionally in the array.