GB2053505A

GB2053505A - Scanning Beam Deflection Amplifier

Info

Publication number: GB2053505A
Application number: GB7924066A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1979-07-10
Filing date: 1979-07-10
Publication date: 1981-02-04

Abstract

The deflection of a light beam 10 is achieved by directing the beam on to a scanning mirror 12 and this deflection is amplified by returning the beam to the mirror 12 at least once by means of beam reflection devices, e.g. lens(es) 16 and 20 and mirrors 14 and 18 as shown. <IMAGE>

Description

SPECIFICATION Beam Deflection Amplifier The present invention relates to beam deflection amplifiers and more particularly to a deflection amplifier for a light beam.

Beam deflection amplification is relevant to both optical data recording and thermal imaging.

Beam deflection amplification enables higher data recording rates to be achieved with scanning laser beam recorders and offers the possibility of high scanning rates in thermal imaging.

The upper data rate of scanning laser beam recorders is often limited by the angular sweep rate of the beam. An increase in data recording rate may be achieved with a mirror scanner by reflecting the beam several times off the same mirror. The advantage however is only realised when the mirror aperture remains fixed.

It is an object of the present invention to provide a beam deflection amplification system utilising a relatively small scanning mirror.

According to the present invention there is provided a beam deflection amplifier including a scanning mirror and beam reflection means associated with the scanning mirror to reflect a beam impinging on the scanning mirror back to the scanning mirror to increase the angle of deflection produced by the scanning mirror.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 shows a simple single return configuration of a beam deflection amplifier according to the present invention, Figure 2 shows a double return configuration beam deflection amplifier, Figure 3 shows a multiple return configuration, Figure 4 shows the configuration of Figure 3 with a two lens system and, Figure 5 shows a single return configuration as shown in Figure 1 using curved mirrors.

The present invention will be described with reference to a laser beam which is typically used in a data recording system in which a high scanning rate is desirable.

A laser beam will resolve 'n' points per line where n is given by: 07ra n= 2A where 6=angular sweep of the beam a=incident beam width to the 1/e2 points of the gaussian beam profile A=wavelength of the laser light e=natural logarithm Consequently, for a given line scanning rate, the potential data recording rate of a laser beam increases with increase in 0. 'n' increases with 'a' but since this implies using a larger scanning mirror, there is unlikely to be significant improvement in data recording rate.

Three beam scanning configurations shown in the diagrams all rely on a lens or lenses to return the beam back to the scanning mirror. The scan mirror is situated on axis and in the focal plane of the lens for telecentric operation.

The configurations shown in Figures 1 and 2 return an unfocussed beam whilst the configuration shown in Figure 3 produces a focussed scanning spot.

In Figures 1, 2 and 3 the lens is equipped with two returning mirrors placed behind the lens which send the beam symmetrically back through the lens. The beam is brought to a focus midway between the two returning mirrors. In Figure 4 two lenses are used and in Figure 5 two curved mirrors are substituted for the lens and mirror arrangements.

Referring now to Figure 1, the input beam 10 is reflected by a scanning mirror 1 2 onto a first return mirror 14 via a lens 16. The mirror 14 in turn reflects the beam onto a second return mirror 18 and from these the beam is reflected back to the scan mirror 12 via a second lens 20. The lenses 16 and 18 may be formed from a single large lens covering the entire area if this is physically practical. The output beam 22 produced by mirror 12 is thus reflected through twice the normal scan angle.

The arrangement of Figure 2 shows a similar system in which the same reference numerals are used. In Figure 2 however, the configuration is arranged such that the input beam 10 is reflected by mirror 12, mirror 14 and mirror 18 back to mirror 12 and then is reflected back along the same path to mirror 18, mirror 14 and back to mirror 1 2 before returning along the same path. In practice however, the input and output beams would be separated by introducing a small offset in the scan mirror 12.

With multiple passes through the lens, the third configuration shown in Figure 3, offers high angular gain and a focussed scanning spot. It is suited to amplifying small mirror excursions such as those produced by piezoelectric scanning mirrors. Beam angle amplification of ten times the angular excursion of the scan mirror are obtained after five bounces off the scan mirror. The beam is prone to distortion after several passes. High quality optics is, therefore, essential.

In the configuration shown in Figure 3, the lens aperture is best utilised when the beam is reflected off the scan-mirror. The output beam 22 impinges onto a recording plane 24 where the data is recorded or replayed.

In the configuration of Figure 4 two lenses are shown and since the output beam 22 does not pass through a lens it will be unfocussed. It is possible to arrange for the beam to pass through one of the lenses to give a focussed output beam.

It is possible to utilise in certain circumstances one or two curved reflecting mirrors instead of the mirrors 14 and 1 8 in which case the lenses 16, 20 may be dispensed with.

This may not be possible in some circumstances however, if the angular displacement of the beam is too high. Such an arrangement is shown in Figure 5 in which similar reference numerals are used as previously.

Claims

1. A beam deflection amplifier including a scanning mirror and beam reflection means associated with the scanning mirror to reflect a beam impinging on the scanning mirror back to the scanning mirror to increase the angle of deflection produced by the scanning mirror.

2. A beam deflection amplifier as claimed in claim 1 in which said beam reflection means includes a first lens and associated first mirror and a second lens and an associated second mirror said light beam being reflected from said scanning mirror via said first lens on to said first mirror and from said first mirror back to said scanning mirror via said second mirror and said second lens.

3. A beam deflection amplifier as claimed in claim 2 in which said first and second lenses are combined together in a single large lens.

4. A beam deflection amplifier as claimed in claim 1 in which said beam reflection means comprises first and second parabolic mirrors.

5. A beam deflection amplifier substantially as described with reference to any one of the accompanying drawings.