WO2006051447A1

WO2006051447A1 - Opto-electronic module, and method for aligning components in an opto-electronic module

Info

Publication number: WO2006051447A1
Application number: PCT/IB2005/053586
Authority: WO
Inventors: Jan Mink; Ronald J. Asjes
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-11-09
Filing date: 2005-11-03
Publication date: 2006-05-18

Abstract

A method is described for aligning components in an opto-electronic module (1) which comprises: a light source (10) for generating a light beam (13), an optical fibre (30) having a tip (31) for receiving a light beam, and an optical system (20) for receiving the light beam (13) from the light source (10) and for directing the light beam (23) to the tip (31) of the optical fibre (30). The method comprises the steps of: measuring the amount of light (33) travelling in the optical fibre (30), and providing a measuring signal (So) indicating the measured amount of light; adjusting a position of at least one component of the group comprising the light source (10), the optical system (20) and the optical fibre (30) on the basis of the measuring signal (So).

Description

Opto-electronic module, and method for aligning components in an opto-electronic module

The present invention relates in general to the field of optical communication, more particular communication where optical fibres are used as a communication path. However, the present invention is more broadly applicable in situations where a light beam is to be entered into an optical fibre.

Systems for optical telecommunication, comprising optical fibres for guiding light beams, are commonly known. Optical fibres have an input end, and the light beam to be transported needs to be efficiently coupled into this input end. The light beam may originate from a light source such as a laser device, a LED, etc, or from the output end of a previous optical fibre. Between the light source and the input end of the optical fibre, one or more optical components are arranged for focussing the light beam onto the input end of the optical fibre.

A problem in this respect concerns the fact that the light source, the optical components and the input end of the optical fibre need to be aligned very accurately. Any misalignment will cause a reduction of the amount of optical energy coupled into the optical fibre. In many applications, the tolerance of alignment is less than 1 μm. This tolerance needs to be met on assembly, but also during the lifetime of the assembly.

In a customary process for manufacturing such assembly, the components of the assembly are arranged in position on a support, carefully manipulated until their respective positions are within the required tolerance, and then fixed to the support, for instance by laser welding. In the step of fixing it is virtually unavoidable that the optimal alignment is lost, so an addition step of fine-tuning is necessary. Then, the products need to be examined to check whether they meet the specifications; if not, they are rejected, which amounts to waste.

US-6.210.046-B1 discloses a fibre optic connector system where an optical component is mounted to an actuator for active fine-tuning of the position of this optical component during the lifetime of the assembly. The actuator is controlled with a feed back loop, which includes a light sensor detecting a part of the light beam. The position control system aims for a maximum feed back signal, which should correspond with the optimal amount of light energy being coupled into the fibre.

This known system has several disadvantages.

In this known system, a part of the light beam reflects back from the tip of the fibre, re-enters the optical system between light source and fibre, and is deflected over 90° to be directed towards a sensor. Deflecting the reflected light beam requires the use of a beam¬ splitter; the described system actually comprises a two-part lens with integrated beam¬ splitter. Further, the measurement is based on the assumption that a best- focus condition corresponds to a maximum sensor signal, and that a best-coupling condition corresponds to a minimum sensor signal. Thus, the best-focus condition in combination with the best-coupling condition does not necessarily correspond to recognizable extreme (maximum, minimum) of the sensor signal. In any case, the sensor of the known system does not actually measure the amount of light coupled in to the fibre.

The present invention aims to eliminate or at least reduce some and preferably all of said disadvantages.

Further, the said publication only discloses manipulation of an optical lens in three dimensions (X, Y, Z). Such manipulation may be insufficient to achieve optimal results. A further important objective of the present invention is to reduce this problem.

According to an important aspect of the present invention, a sensor senses a portion of the light beam actually received by the fibre. To that end, light is coupled out of the fibre again, which may be done close to the tip or at a larger distance. Since the feedback is now based on the amount of light actually received by the fibre, improved alignment accuracy can be achieved.

According to another important aspect of the present invention, a component is manipulated in five dimensions: X, Y, Z and horizontal tilt and vertical tilt. The manipulated component may be a lens, the input end of the fibre, or the light source, or a combination of two or three of said components. Tilting such component or components allows the use of optical lenses with smaller numerical aperture, hence cheaper lenses.

These and other aspects, features and advantages' of the present invention will be further explained by the following description with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which the single figure schematically shows an opto-electronic module.

The single figure schematically shows an opto-electronic module 1 according to the present invention, suitable for use in a fibre-optic telecommunication system 100. The module 1 comprises a light source 10, an optical system 20, and an optical fibre 30.

The light source 10 comprises, in this example, a laser diode 11 and a laser driver 12 for controlling the output power of the laser diode 11. The laser diode 11 generates a laser beam 13, of which the intensity depends on the control action of the driver 12. Since laser devices, especially laser diodes, are known per se, while the present invention does attempt to improve on laser devices, it is not necessary here to describe in great detail the design and functioning of a laser diode. The same applies, mutatis mutandis,, to laser drivers.

Although the module 1 may be used as a module for generating an autonomous light signal, the module is typically used for generating a light signal carrying information, for which purpose the light signal may be modulated in a known per se manner. Illustratively, the laser driver 12 receives an electrical input signal Si from any suitable source, and drives the laser diode 11 in accordance with the received input signal.

The optical system 20 comprises at least one lens 21; the optical system 20 may comprise just one single lens, but the optical system 20 may also comprise multiple lenses, complex lenses, etc. The lens 21 receives the laser beam 13, and produces a focused laser beam (now indicated at 23) focussed onto the tip 31 of the optical fibre 30. The part of the laser beam 23 which is actually coupled into the fibre 30 is indicated at 33.

The fibre 30 may be any suitable optical fibre; since optical fibres are known per se, it is not necessary here to describe in great detail the design of an optical fibre.

The module 1 further comprises a position control system 40. The position control system 40 comprises at least one actuator 41, an actuator drive circuit 42 for driving the actuator 41, and a light sensor 43 generating a sensor output signal So which is received by the actuator drive circuit 42. The actuator drive circuit 42 continuously drives the actuator 41 on the basis of the sensor output signal So. The actuator drive circuit 42 is designed to drive the actuator 41 in such a way that the power of the light 33 in the fibre 30 is at a maximum.

According to an important aspect of the present invention, the light sensor 43 is positioned to sense a fraction of the light 33 actually travelling in the fibre 30. The light sensor 43 may be positioned at an output end of the fibre 30 (not shown), but it is more convenient that the light sensor 43 be positioned adjacent the fibre 30 at a relatively small distance from the input tip 31 of the fibre 30, as illustrated. When positioned adjacent the fibre 30, the light sensor 43 receives a portion 34 of the light 33 in the fibre 30. Depending on circumstances, this sensed light portion 34 may be light leaking naturally out of the fibre 30 via the cylindrical outer surface of the fibre. If such leakage is negligible, or at least insufficient for obtaining a sufficiently strong measuring signal, it is also possible that the sensor 43 is associated with coupling means for coupling a portion of light out of the fibre 30. Since such coupling means are known per se, while further the present invention does not attempt to improve such coupling means, it is not necessary here to describe the design and functioning of such coupling means in greater detail. By way of example, it is noted that such coupling means may comprise an intentionally roughened portion (not shown) of the outer surface of the fibre.

The actuator 41 may be any suitable actuator, for instance an electro-magnetic actuator (coil) or a piezo-electric actuator. Since suitable actuators are known per se, while the present invention does not attempt to improve on such actuators, it is not necessary here to describe in greater detail the design and operation of actuators.

In the illustrative example of the figure, the actuator 41 is associated with the lens 21 of the optical system 20, for adjusting the position of the lens 21. In cases where the optical system 20 comprises two or more lenses, the actuator 41 may adjust the position of only one lens of the optical system, or the position of the optical system 20 as a whole; it is, however, also possible that multiple actuators are provided, each one for adjusting the positioning of a different lens.

Instead of being associated with the optical system 20, the actuator may, alternatively, also be associated with the light source 10 for adjusting the positioning of the laser diode 11, or with the fibre 30 for adjusting the positioning of the input end of the fibre 30. It is even possible that the position control system 40 comprises two or even three actuators, one being associated with the optical system 20, one being associated with the light source 10, one being associated with the fibre 30. For sake of simplicity, these possibilities are not illustrated separately.

According to an important aspect of the present invention, the actuator 41 and the actuator drive circuit 42 are designed for adjusting a position in three orthogonal directions, indicated as X (horizontally), Y (vertically), and Z (axially). In a preferred embodiment, the actuator 41 and the actuator drive circuit 42 are designed for adjusting a position in an angular direction (tilt). This may involve adjusting the position in a horizontal (XZ-)plane by rotation about a vertical (Y-)axis (horizontal tilt), or adjusting the position in a vertical (YZ-)plane by rotation about a horizontal (X-)axis (vertical tilt). More preferably, the actuator 41 and the actuator drive circuit 42 are designed for vertical tilt as well as horizontal tilt.

The present invention foresees an embodiment where the actuator 41 and the actuator drive circuit 42 are designed for adjusting by tilt only (vertical tilt or horizontal tilt, or both). In a preferred embodiment, the actuator 41 and the actuator drive circuit 42 are designed for adjusting a position in at least one linear dimension (X or Y or Z, or a combination of two or all three of these dimensions) as well as for adjusting a position in at least one lilt dimension (vertical tilt or horizontal tilt, or both). In the most preferred embodiment, the actuator 41 and the actuator drive circuit 42 are designed for adjusting a position in five dimensions (X, Y, Z, vertical tilt, horizontal tilt). Further, in an embodiment where the position control system 40 comprises two or more actuators, adjusting the position of different components, it is preferred that each actuator provides for five-dimensional adjustment, but it is also possible that one actuator provides for, for instance, vertical tilt while another actuator provides for, for instance, horizontal tilt. Assembling the module 1 in accordance with the present invention is relatively easy and low-cost. The light source 10, the optical system 20, the input end of the fibre 30, and the actuator 41, and typically also the sensor 43, are placed on a support (not shown), typically in a housing (not shown), with relaxed tolerances: for instance, the tolerances may be 10 μm or higher. The housing is closed, and the actuator drive circuit 42 is switched on. The actuator drive circuit 42 then performs an initialization step to find the optimum actuator position; this reduces the tolerances, typically to better than 1 μm. During the life-time of the module, the actuator drive circuit 42 maintains optimum actuator position. The actuator drive circuit 42 automatically adapts the optimum actuator position to changing circumstances like ageing, temperature, etc. During the life-time of the module, it may happen that the actuator drive circuit 42 is switched off. In this condition, the position(s) of the actuator(s) is(are) no longer controlled, and may drift away from the optimum position. Therefore, each time that the actuator drive circuit 42 is switched on again, it may be necessary to perform the initialization step again. To reduce the time required for such initialization step, the actuator settings corresponding to the optimum actuator position are preferably stored in a settings memory 44 associated with the actuator drive circuit 42. The actuator drive circuit 42 is adapted to store the actuator settings into said settings memory 44 each time after performing the initialization step. In order to take into account possible changes in the optimum actuator position, the actuator drive circuit 42 is preferably adapted to also store the actuator settings into said settings memory 44 each time it is switched off.

It should be clear to a person skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appending claims.

For instance, a position control system 40 capable of tilt adjustment, preferably five-dimensional adjustment, is also applicable in combination with an optical system comprising a beam splitter or the like, coupling out light reflected back from the tip of the fibre. In the above, the present invention has been explained with reference to block diagrams, which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, digital signal processor, etc.

In the above, the "optimum" position is described as the position corresponding to maximum amount of light in the fibre. However, this is not always necessary: a value less than maximum may be optimal to ensure the possibility of optimizing other parameters such as disturbing reflections or the sensor output current. Thus, it is possible to vary the output power level of the fibre while maintaining the working point of the laser diode stationary. Hence, the laser behaviour and therefore the system performance can remain the same. Keeping the laser current constant means that the measuring cycle is simplified.

Claims

CLAIMS:

1. Method for aligning components in an opto-electronic module (1) which comprises: a light source (10) for generating a light beam (13), an optical fibre (30) having a tip (31) for receiving a light beam, and an optical system (20) for receiving the light beam (13) from the light source (10) and for directing the light beam (23) to the tip (31) of the optical fibre (30); the method comprising the steps of: measuring the amount of light (33) travelling in the optical fibre (30), and providing a measuring signal (So) indicating the measured amount of light; adjusting a position of at least one component of the group comprising the light source (10), the optical system (20) and the optical fibre (30) on the basis of the measuring signal (So).

2. Method according to claim 1, wherein the step of measuring the amount of light comprises the step of coupling out of the optical fibre (30) a portion (34) of the light (33) travelling in the optical fibre (30).

3. Opto-electronic module (1) which comprises: a light source (10) for generating a light beam (13), an optical fibre (30) having a tip (31) for receiving a light beam, and an optical system (20) for receiving the light beam (13) from the light source (10) and for directing the light beam (23) to the tip (31) of the optical fibre (30); the module (1) further comprising a position control system (40) for adjusting a position of at least one component of the group comprising the light source (10), the optical system (20) and the optical fibre (30); the position control system (40) comprising: - at least one actuator (41); a sensor (43) adapted for receiving a fraction of the light (33) travelling in the fibre (30), and for generating a measuring signal (So); an actuator drive circuit (42) coupled to receive the sensor output signal (So), and adapted for driving the actuator (41) on the basis of the sensor output signal (So).

4. Opto-electronic module according to claim 3, wherein the light sensor (43) is positioned adjacent the fibre (30) at a relatively small distance from the input tip (31) of the fibre (30).

5. Opto-electronic module according to claim 3, wherein the light sensor (43) is associated with coupling means for coupling a portion of light out of the fibre (30).

6. Method for aligning components in an opto-electronic module (1) which comprises: a light source (10) for generating a light beam (13), an optical fibre (30) having a tip (31) for receiving a light beam, and an optical system (20) for receiving the light beam

(13) from the light source (10) and for directing the light beam (23) to the tip (31) of the optical fibre (30); the method comprising the steps of: - providing a measuring signal (So) indicating the amount of light (33) travelling in the optical fibre (30); adjusting a position of at least one component of the group comprising the light source (10), the optical system (20) and the optical fibre (30) on the basis of the measuring signal (So); - wherein the step of adjusting a position includes the step of tilting the said component in a horizontal plane or in a vertical plane, or both.

7. Opto-electronic module (1) which comprises: a light source (10) for generating a light beam (13), an optical fibre (30) having a tip (31) for receiving a light beam, and an optical system (20) for receiving the light beam (13) from the light source (10) and for directing the light beam (23) to the tip (31) of the optical fibre (30); the module (1) further comprising a position control system (40) for adjusting a position of at least one component of the group comprising the light source (10), the optical system (20) and the optical fibre (30); the position control system (40) comprising: at least one actuator (41); a sensor (43) adapted for generating a measuring signal (So) indicating the amount of light (33) travelling in the optical fibre (30); an actuator drive circuit (42) coupled to receive the sensor output signal (So), and adapted for driving the actuator (41) on the basis of the sensor output signal (So); wherein an actuator is designed for adjustment by a tilt movement.

8. Opto-electronic module according to claim 3 or 7, wherein an actuator is associated with the light source (10).

9. Opto-electronic module according to claim 3 or 7, wherein an actuator is associated with an input end of the fibre (30).

10. Opto-electronic module according to claim 3 or 7, wherein an actuator is associated with the optical system (20).

11. Opto-electronic module according to claim 10, wherein an actuator is associated with the optical system (20) as a whole.

12. Opto-electronic module according to claim 10, wherein an actuator is associated with one lens component (21) of the optical system (20).

13. Opto-electronic module according to claim 3, wherein an actuator is designed for adjustment by a tilt movement.

14. Opto-electronic module according to claim 13 or 7, wherein an actuator is designed for adjustment by a movement in any of five dimensions (X; Y; Z; vertical tilt; horizontal tilt).

15. Opto-electronic module according to claim 3 or 7, wherein the actuator drive circuit (42) is provided with a settings memory (44) for storing the actuator settings corresponding to the optimum actuator position.

16. Fibre-optic telecommunication system (100) comprising an opto-electronic module according to claim 3 or 7.