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Our Products
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SMC - 19 Optical Components |
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Basic Concept
Optical glass fibres are ideal
transportation media for light. Not only telecommunications
benefit from this fact; a lot of other applications also exploit
the idea. At the beginning and at the end of transportation via
the fibre, the light needs to be conditioned. This is done
through elements we know from classical optics. Besides others,
the following techniques are commonly applied. |
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| Telescope and focusing | |
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The light which leaves the fibre
has certain divergence which depends on the kind of the fibre
and the wavelength of the light. In order to generate an almost
parallel light beam a lens is used with a focal length of f1
which is placed in such a way that its focal point coincides
with the fibre exit. The reverse process is the focusing of a
parallel beam. Such situations occur for e.g. when the light
enters a fibre again. |
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| Beam splitting | |
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For this task, either beam splitter
plates or cubes are used. Beam splitter cubes (BSC) have the
advantage that no beam displacement occurs, as is the case when
using plates. The incident light is splitted into two fractions.
The splitting ratio depends on the coating design of the beam
splitting cube. Commonly, this ratio is 1:1. This means that
both beams have half the incident intensity. Furthermore, the
direction of one beam is changed by 90° with respect to the
other. |
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| Quarter wave plate | |
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Such a plate is commonly
manufactured from natural quartz and has a certain thickness. If
the thickness is a multiple of a quarter for a given wavelength,
than the plate effects the polarisation state of light which
passes the plate. Hereby, the orientation of the optical axis of
the quartz plate, with respect to the polarisation direction of
the light, plays an important role. Using a quarter wave plate
between two crossed polarisers, for example, the outgoing light
intensity can be modified by turning the plate. |
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| Optical diode | |
| Finally, the combination of a quarter wave plate and a polarising beam splitter cube can also be used as a so-called optical diode. This means that light can pass only in one direction via this combination. To verify this within the experiment, a mirror is used to change the direction of the light. If the quarter wave plate is turned into the position where it changes the polarisation direction of the back coming light by 90°, then it will be reflected at the polarising beam splitter cube. Such arrangements are very important to protect the laser source against back scattered light which would cause unstable operation of the laser. | |
