Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-05-12
2001-08-21
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S202100, C359S203100, C359S212100, C359S226200, C359S368000, C359S017000, C345S007000, C347S260000, C235S457000, C235S462490, C235S462490, C235S470000
Reexamination Certificate
active
06278538
ABSTRACT:
The invention relates to an optical scanner comprising a radiation source for generating a radiation beam, and means for giving the radiation beam a scanning movement in a first direction through an angular range &Dgr;&thgr;
1
, and in a second direction through an angular range &Dgr;&thgr;
1
.
The invention also relates to a plurality of applications in which use is made of such an optical scanner.
A scanner of the type described in the opening paragraph is used in, for example, an optical scanning microscope. Such a microscope is described in, for example, the thesis: “Signal detection and interpretation in scanning optical microscopy” by J .P .H . Benschop. In the microscope described in this thesis, a point source is imaged on an object by means of an objective lens. The scanning movement of the beam is realized by means of a combination of two mirrors. The mirrors are positioned with respect to each other in such a way that each mirror reflects the light incident thereon at substantially right angles. A small tilt of the mirrors is converted into an angular variation in the direction of propagation of the light beam. A telescope, i.e. a set of two lenses, is arranged between the two mirrors and ensures that the mirrors are imaged on each other in order to realize a two-dimensional scanning movement starting from one point.
Drawbacks of the scanner described here are the relatively low scanning rate caused by the two mechanical rotations of the mirrors and the presence of the telescope, which does not contribute to the compactness of the system.
It is an object of the present invention to provide an optical scanner which is compact and with which relatively high scanning rates can be achieved.
To this end, the optical scanner according to the invention is characterized in that the radiation source is tunable in wavelength, and the means comprise a grating and a rotating reflecting element.
The scanning movement through one angular range is realized by rotating the reflecting element. The scanning movement through the other angular range is realized by varying the wavelength of the laser. In fact, the deflection on the grating is dependent on the wavelength of the incident light. In this way, a wavelength scan is converted into an angular scan.
In each scanning movement which is based on a mechanical movement, the scanning rate will be limited due to the inertia of this mechanical movement. Since a two-dimensional scanning movement is realized in this case by means of only one mechanical movement, it is possible to realize a scanning rate which is higher than that realized in the case of two mechanical movements. In fact, the limitation of the scanning rate due to the wavelength modulation technique is considerably smaller than the limitation due to a mechanical movement.
A preferred embodiment of the optical scanner according to the invention is characterized in that the reflecting element and the grating are integrated with each other.
This has the advantage that, instead of two points of rotation, namely one for each reflecting element and the lenses required therefor, only one point of rotation is present in this embodiment according to the present invention, and these lenses can be dispensed with. This also means that the system can be given a considerably more compact form.
Moreover, the number of separate components is reduced. The rotation of the element about an axis perpendicular to the grating lines and situated in the plane of the grating will not have any influence on the effect of the grating on the incident beam. The grating only has effect on the scanning movement when the wavelength of the incident beam varies. Thus, the two scanning movements are not coupled.
A further embodiment of the optical scanner according to the invention is characterized in that the laser is a pulsed diode laser.
By making use of a pulsed laser beam, depth information can be obtained. The distance between the laser and an object can be determined in any arbitrary direction by registering the instant when the reflected laser pulse echo is detected. Two angle co-ordinates and one position co-ordinate are thus scanned on the basis of one scanning angle, a wavelength scan and a time measurement. This embodiment of the optical scanner is very suitable in, for example applications in which objects are scanned, and in an optical scanning microscope.
The rate of the wavelength scan is not influenced by the inertia of a mechanical rotation in the optical scanner according to the invention. The mechanical movement yields scanning rates up to approximately 1 kHz in one direction, while scanning rates of approximately 100 kHz can be realized with the wavelength scan in the other direction.
The optical scanner described above may be used to great advantage in a plurality of applications which will hereinafter be described in greater detail.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 5189533 (1993-02-01), Taguchi et al.
patent: 5204523 (1993-04-01), Appel et al.
patent: 5333144 (1994-07-01), Liedenbaum et al.
patent: 5545886 (1996-08-01), Metlisky et al.
patent: 5768001 (1998-06-01), Kelley et al.
patent: 0517517A1 (1992-09-01), None
patent: 62-56931A (1987-03-01), None
J.P.H. Benchop, “Signal Detection and Interpretation in Scanning Optical Microscopy” May 1989.
Phan James
U.S. Philips Corporation
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