JPH0664255B2 - Hologram deflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A wavelength tunable laser light source is arranged so that a hologram whose focal length changes according to the wavelength is inclined by a predetermined angle. It is possible to realize a formula, that is to say a deflection device without mechanically moving parts of the lens.

[Industrial application field]

The present invention relates to an optical deflecting device, and more particularly to a hologram deflecting device capable of controlling a deflection angle only by changing a wavelength on a light source side without moving a lens.

[Conventional technology]

The light deflecting device is generally a device such as a rotating polygon mirror or a vibrating mirror which is mechanically displaced by a motor or the like. There is also one using a hologram scanner, which is the same in that the hologram mechanically moves by a motor.

[Problems to be solved by the invention]

The deflection device having such a mechanically movable part has a problem that not only the device becomes large but also wear and lubrication of the movable part, and the control of the deflection angle depends on the mechanical accuracy of the mechanically movable part. There is a limit to the improvement of.

Aside from this, a deflecting device using a solid-state element such as an acousto-optic element has been put into practical use, but there is a problem that its deflection angle is small and its application is limited.

The problem to be solved by the present invention is to realize a deflecting device that can non-mechanically control the deflection angle, ignoring the idea of moving a lens or a mirror (mechanical deflection).

[Means for solving problems]

In order to achieve the above object, a deflecting device according to the present invention comprises a wavelength tunable laser and at least one hologram having a function of deflecting an optical axis of the laser by a predetermined angle and tilting the laser optical axis by a predetermined angle. In addition, the configuration is characterized in that the deflection control is performed by changing the wavelength of the laser beam to the hologram.

[Action]

The diffraction grating of the hologram is changed only by deflecting the wavelength of the laser, whereby the deflection angle of the laser beam by the hologram can be easily controlled.

〔Example〕

FIG. 1 shows the basic principle of the present invention. Basically, a hologram lens 11 whose focal length has wavelength dependence,
The wavelength tunable laser 13 is used. As is well known, the hologram lens 11 is a lens that collects light by utilizing the diffraction effect of light, and has a large wavelength dependency. The hologram lens 11 is arranged so as to be inclined with respect to the optical axis X of the variable wavelength laser 13 by a predetermined angle θ. Therefore, by changing the wavelength of the laser beam incident on the hologram lens 11, the deflection angle of the hologram lens changes as shown in the drawing, and as a result, the focal point can be scanned on the image plane M in the arrow direction. By utilizing the properties of the hologram lens, the present invention can realize a beam scanner by simply controlling the wavelength on the light source side without moving the hologram lens 11 at all. Incidentally, when the present invention is simply applied as a deflecting device and the beam scanning is not necessary, the hologram lens 11 does not need to be a lens, and a normal flat plate hologram having a plane wave grating (that is, it does not have a converging property). Needless to say,

As is well known, when the wavelength of the laser beam is changed, the hologram slightly changes not only its deflection angle but also its focal length. Therefore, it is desirable to obtain a predetermined image plane M in consideration of it. .

Here, the spatial frequency of the hologram (1 / the grid pitch)
, Where λ is the wavelength, sin θ ₂ + sin θ ₁ = λ However, θ ₁ = incident angle, θ ₂ = exit angle, so that, for example, = 1813 lines / mm, θ ₁ = θ ₂ = 45 °, λ = 780 nm Then λ is Δλ = 2 nm,
When Δλ = 20 nm is changed, the deflection angle is changed by 0.3 ° and 3 °. Further, in this case, if the distance from the hologram to the image plane M is 1000 nm, the scanning width is 5 to 52 nm, respectively.

The deflection angle is determined by the hologram arrangement angle θ,
In practice, a single hologram lens may not provide a sufficient deflection angle. Therefore, according to the present invention, as shown in FIG. 2, several flat plate holograms 15 (that is, not lenses) are arranged in a spiral shape, and the deflection angle is enlarged each time the flat plate hologram 15 is passed. Is also possible.

In the illustrated embodiment, each hologram lens 11 is tilted by approximately 45 ° with respect to the incident light beam, and is deflected by approximately 90 ° with respect to a beam having a predetermined wavelength each time it passes through the flat plate hologram 15. However, it is needless to say that the deflection amount is arbitrarily designed according to the position of the image forming surface (focal plane) M to be condensed and the number of the flat plate holograms 15.

In FIG. 2, the structure is similar to that of FIG. 1 for realizing a hologram scanner, and thus the light is finally condensed through the hologram lens 11, but the hologram lens 11 is not necessary if light collection is not necessary. Of course, the flat hologram 15 may be used instead.

Further, in FIG. 2, if the hologram lens 11 is only for condensing (imaging) light, that is, if it is not necessary to control the deflection angle according to the wavelength change of the beam, a glass lens or the like is used. It may be replaced with an ordinary optical lens.

The scanning width as a hologram scanner theoretically increases in proportion to the increase in the numbers of the flat plate hologram 15 and the hologram lens 11, and when the number of hologram stages becomes N, the deflection angle and the scanning width become N times.

The wavelength tunable laser 13 itself is known. Although various types of wavelength tunable lasers (tunable lasers) are known, a semiconductor laser is used in this embodiment.

FIG. 3 shows still another embodiment in which the present invention is applied to an information reading device such as a bar code reader (pen reader). In the figure, the light beam emitted from the wavelength tunable laser light source 13 is converted into a parallel light beam by the collimator lens 19, and then is reflected by 90 ° to the right, for example, by the half mirror 21 arranged at an angle of 45 ° with respect to the optical axis. .
This reflected beam is deflected by the flat plate hologram 15 which is arranged, for example, at an angle of 45 ° with respect to its optical axis, and is further condensed by the hologram lens 11 on the information medium (for example, bar code) S. The beam reflected by the information medium S is again deflected by the hologram lens 11 and the flat plate hologram 15, passes through the half mirror 21, and is imaged in the detector 25 by the condenser lens 23. Here, if the wavelength of the beam is changed by the wavelength tunable laser light source 13, the hologram lens 11 is used as described above.
The outgoing beam from the scanner is scanned and the barcode can be read by the detector 25. That is, also in this embodiment, a beam scanner can be realized non-mechanically only by changing the wavelength of the beam, and a barcode reader can be easily obtained by combining it with a detector.

FIG. 4 shows an example in which the present invention is applied to a tracking servo system of an optical disk head, which is basically the same as the embodiment of FIG. 3, and the description thereof will be omitted by giving the same reference numerals. The condenser lens 23 is for tracking on the optical disc 30, and its information is detected by the detector 25.
To detect.

In FIG. 4, two flat plate holograms 15 are arranged.

In any of the above embodiments, an appropriate achromatic lens can be provided, for example, behind the hologram in order to remove the aberration generated by the hologram.

[Effects of the Invention] As described above, according to the present invention, by combining a wavelength tunable laser light source and a wavelength-dependent hologram and controlling the wavelength on the light source side, an extremely simple structure having no mechanically movable part is provided. A hologram deflecting device is realized.

[Brief description of drawings]

FIG. 1 is an illustrative view showing a basic structure of a hologram deflecting device according to the present invention, FIG. 2 is an illustrative view showing a second embodiment of the present invention, and FIG. 3 is an illustrative view showing a third embodiment of the present invention. , FIG. 4 is an illustrative view showing a fourth embodiment of the present invention. 11 ... Hologram lens, 13 ... Wavelength variable laser light source, 15 ... Flat plate hologram.

Claims (1)

[Claims] 1. A wavelength tunable laser and at least one hologram having a function of deflecting an optical axis of the laser by a predetermined angle and inclined by a predetermined angle with respect to the laser optical axis. A hologram deflection device that controls deflection by changing the wavelength.