Optical modifier and method for the manufacture thereof

Details Optical modifier and method for the manufacture thereof Optical modifier and method for the manufacture thereof

2001-09-04

2004-12-14

Ullah, Akm Enayet (Department: 2874)

Optical waveguides

With optical coupler

Particular coupling structure

C385S015000, C385S031000

Reexamination Certificate

active

06832031

ABSTRACT:

The present invention relates to an optical modifier, for example, for feeding in or feeding out signals of single or a plurality of wavelength channels into or from wave guides, and to a method for the manufacture thereof.
In particular in telecommunications and data communication, it has become normal to transmit information optically, that is to say, for example, via optical guides. Optical guides are in general thin fibres of highly transparent optical materials, which conduct light along their longitudinal direction by means of numerous total internal reflections. The light, generally entering via a smooth entry surface, follows all the curves of the fibres and at the end emerges from an end surface that is generally also smooth. The electrical signals that are to be transmitted are converted, after suitable modulation, by an electro-optical converter into light signals—mostly in the infra-red range, are fed into the optical wave guide, transmitted by the optical wave guide, and at the end are reconverted into electrical signals by means of an opto-electrical converter. In order to increase the rate of transmission of the optical wave guide, it has become usual to transmit several different communications signals simultaneously via one optical wave guide. For this, the communications signals are modulated. For the different communications signals, different respective carrier frequencies are used, wherein the individual discrete frequency components of the whole transmitted signal are often also referred to as channels. After transmission of the individual communications signals or respectively wavelength channels, via the optical wave guide, the individual signals have to be separated and demodulated.
In the prior art devices are therefore known for adding and selecting wavelength coded signals (light of a specific wavelength or specific wavelengths), so-called multiplexer or de-multiplexer arrangements. Such devices use optical fibres that have a large information carrying density. The purpose of the devices is to separate out relevant information or respectively a relevant wavelength channel from the large amount of information transmitted. For this separation, narrow band reflectors can, for example, be used that allow certain light frequencies to pass almost unhindered, while selected frequencies are reflected. When the light emerges from the glass fibres, there is, however, inevitably an expansion of the beam, which leads to either significant reduction in intensity at the focussing point, that is to say at the point where the filtered light is evaluated, or the use of appropriate lens systems, for example, gradient refractive index lenses (GRIN lenses) is necessary in order to collimate the light onto the corresponding focussing point.
The embodiment with the lenses has the disadvantage, however, that they are on the one hand very expensive, and on the other hand very precise calibration is necessary, and moreover the focussing properties are also still dependent on the wavelength. This calibration must usually be done expensively by hand as the core diameter, for example, of the optical single mode fibres is only 9 &mgr;m. The known multiplexer/de-multiplexer arrangements also take up a lot of space which translates into correspondingly bulky embodiments of the respective optical components. The cause of this is, in addition to the geometric expansion of the lens system, the inherent property of glass fibres not to be able to be deflected or bent at will. It is not possible, for example, to bend glass fibres with a radius smaller than approximately 20 to 30 mm, as losses become too great because in part the conditions for total internal reflection are no longer satisfied. Appropriately large deflecting loops therefore have to be laid out that take up a significant amount of space in the optical systems. There is thus a need for an optical modifier that can intentionally affect one or more wavelength channels, that is inexpensive to manufacture, that allows feeding in and feeding out of light with as low a loss as possible in the most confined of spaces, and wherein at the same time the optical modifier is easy to calibrate.
This object is solved according to the invention in that there is provided at least one coupling device with a curved reflecting surface and a wave modifying element. A wave modifying element is understood to be any element that, placed in the beam path, affects one, several, or even all of the wavelength channels of the optical channel. To affect is understood as being, for example, to reflect, absorb, amplify, attenuate, interrupt or polarise.
The coupling device serves to feed in and feed out signals, for example, into and out of glass fibres. Because a reflecting surface is provided that is curved, the optical lens system can be omitted, as the beam expansion occurring at the end of a glass fibre is at least partially compensated for by the curved surface.
An embodiment is particularly preferred wherein a section through the curved surface of the coupling device corresponds approximately to a portion of a parabola, a hyperbola, or an ellipse. In other words, all the second order plane curves that are often described as cone sections, apart from a straight line, are particularly suitable for the profile for the curved surface. The reflecting surface is curved such that it follows a portion of an imaginary second order plane curve. These shapes have particularly good focussing properties so they are particularly suitable for use in a coupling device. Thus, for example, a beam expanding at the focal point of an ellipse, that is reflected on the ellipse, is focussed at the other focal point of the ellipse. Consequently, the whole amount of light emergent at the first focal point is available in almost point form at the other focal point. On the other hand, a beam expanding at the focal point of a parabola is reflected on the parabola such that the reflected light is substantially parallel. This parallel light can now be used to impinge upon the light-modifying element. Because the light is substantially parallel, it is ensured that the light-modifying element receives all the communications signals almost without loss.
A particularly advantageous embodiment provides that the reflecting surface of the coupling device has approximately the shape of a portion of a paraboloid of revolution, an ellipsoid of revolution, or a hyperboloid of revolution. In other words, the reflecting surface follows at least little by little the external surface of a solid generated by revolution. This means that a section through the reflecting surface along a section plane perpendicular to the axis of rotation has approximately the shape of a segment of a circle, while a section along a plane in which the axis of rotation lies has approximately the shape of a portion of a parabola, hyperbola or ellipse. Such a curved reflecting surface has particularly suitable focussing properties, so the losses caused by feeding in and feeding out are very small and the use of a collimator is unnecessary.
In order to obtain particularly good focussing properties, it is advantageous when at least a transmitting or receiving element is arranged in the proximity of a focal point of the reflecting surface. A transmitting or receiving element is understood as being any light manipulating systems such as, for example, the end surfaces of glass fibres and optical wave guides, as well as focussing systems such as, for example, gradient refractive index structures or mirror optics, and also light-emitting structures such as, for example, LEDs or lasers, or light-receiving structures such as, for example, photo-diodes or electro-optical converters. The focal points of the curved surfaces correspond to the focal points of the imaginary hyperbola, parabola, or ellipse that the reflecting surface follows.
Thus, a parabola is, for example, defined as the number of points that are equidistant from a fixed point, the so-called focal point, and a fixed straight line, the so-called directrix. If pa

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