WO2004015693A2

WO2004015693A2 - Optical unit with light-emitting source

Info

Publication number: WO2004015693A2
Application number: PCT/IB2003/003326
Authority: WO
Inventors: Gwenole Stouthuysen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2002-08-09
Filing date: 2003-07-23
Publication date: 2004-02-19
Also published as: AU2003251098A8; TW200418006A; WO2004015693A3; AU2003251098A1

Abstract

The invention relates to an optical unit which comprises a support (1) and a light source (5) supported by the support and which accommodates an optical guiding system for guiding the light beam emitted by the light source. In order to allow the optical unit to contain a high-power light source, a thermally insulating element (23) is provided between the light source and the support.

Description

Optical unit with light-emitting source

The invention relates to an optical unit comprising a support which supports a light-emitting device for emitting a light beam and accommodates an optical guiding system for guiding the light beam.

US-A 5,600,619 discloses an optical head comprising a laser optical system provided with a semiconductor laser which is mounted in a moving part of an actuator. The moving part is made of a metallic material and forms a heat radiator, whereby heat conduction from the heat radiator to the semiconductor laser is limited. During operation, heat generated by the semiconductor laser is transferred to the heat radiator and is then radiated from the surface of the heat radiator to the external space of the optical head. In the known optical head, the laser optical system or at least portions thereof are liable to temperature changes during use. It was found that this adversely affects the scanning function of a scanning device provided with such an optical head, particularly when a higher power semiconductor laser is applied. Such a laser is required for e.g. writing information into a DVD disc. It is an object of the invention to improve the optical unit as described in the preamble in such a way that a high-power light source can be used without or at least without seriously influencing the optical guiding system.

This object is achieved by the optical unit according to the invention, which unit is characterized in that the light-emitting device is secured to the support in a thermally insulated manner. By this feature it is prevented or at least countered to a major extent that heat generated by the light-emitting device is transferred to the support. A favorable effect thereof is that the optical guiding system remains cool or at least sufficiently cool, so that the mutual positions of and/or mutual distances between the several components of the optical guiding system are not or hardly affected by temperature changes during use of the light- emitting device. In other words, the temperature gradient across the support and thus across the optical guiding system is small to zero, so that the optical unit according to the invention guarantees a stable light path. This makes the optical unit particularly suitable for use in high- power scanning devices, such as those required, for example, in DVD+R or DVD+RW optical players, and in miniaturized devices, such as small form factor optical devices. Generally, the light-emitting device comprises a semiconductor laser. The optical guiding system usually comprises several optical components, like a beam splitter, a collimator lens, a mirror, a servo-lens.

In general, the support further supports a light-receiving device, usually comprising a multi-split photodiode. When the optical unit is used in an optical player, the light beam originating from the light-emitting device is intended to form a scanning spot on an information layer of a writable and/or readable optical disc. An objective lens is used in order to focus the light beam to the required spot. This lens may be a part of the optical unit, in which case the optical unit is constructed as or is a part of a movable portion of a focusing actuator, or the lens may be a part of a movable portion of a focusing actuator of which a stationary portion is carried by a frame or even by the support of the optical unit. If the focusing actuator is provided on the support, the optical unit is mounted on or is part of a movable body, such as a slide or a pivotable arm, in order to move the objective lens along the disc surface. It is to be noted that the term "light beam" does not solely refer to visible light, but also to invisible light.

A practical embodiment of the optical unit according to the invention is characterized in that the light-emitting device is attached to the support via a thermally insulating element. A suitable thermally insulating material for manufacturing this insulating element is a plastics, particularly a polymer, such as polymethylmetacrylate (PMMA) - commonly called plexiglass - or glass fiber strengthened epoxy resin. Generally, the support is made of a metallic material, such as an AlZn alloy. The heat transfer coefficient of polymers can be 100 and more times smaller than the heat coefficient of metallic materials, so that the thermally insulating element is able to substantially block the transfer of heat from the light-emitting device to this support and thus to the optical guiding system. Preferably, the thermally insulating element has the form of a plate or disc which is provided with a window for allowing the light beam originating from the light- emitting device to pass. The window may be a transparent part of the insulating element or an opening in the plate or disc. In an alternative embodiment, the entire thermally insulating plate-shaped element is transparent. In a further embodiment of the optical unit according to the invention, the light-emitting device is mounted on or in a metal carrier, for instance by means of a press fit. In this case the thermally insulating element extends between the metal carrier and the support. It is favorable to provide the metal carrier with cooling fins in order to improve the transfer of heat to the external space around the optical unit. The invention further relates to an optical player having a drive unit for rotating an optical disc, particularly of the CD- or DVD type, and having a scanning device - including an objective lens and a light-receiving device - for scanning the optical disc, particularly the information layer or layers of the disc. In the optical player according to the invention, the scanning unit comprises the optical unit according to the invention. In this optical player, a high-output light-emitting device may be applied as, during operation of the optical unit, the temperature gradient from the light-emitting device to the objective lens and to the light receiving element is small enough to prevent signal degradation caused by a mutual shift of the optical components of the optical unit owing to heat produced in the light- emitting device. The invention also relates to the scanning device used in the optical player according to the invention.

With reference to the Claims, it is to be noted that the various characteristic features as defined in the set of Claims may occur in combination.

The above-mentioned and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiments described hereinafter.

In the drawings: Fig. 1 diagrammatically shows an embodiment of the optical unit according to the invention in perspective and partly in dismounted state,

Fig. 2 depicts the embodiment of Fig. 1 at a different angle, Fig. 3 is a sectional view taken on the line III-III in Fig. 1, Fig. 4 is a sectional view taken on the line IV-IV in Fig. 1 and Fig. 5 diagrammatically shows an embodiment of the optical player according to the invention.

The embodiment of the optical unit according to the invention as depicted in Figs. 1 to 4 comprises a support 1 being apart of a slide la. The slide la and the support 1 is made of an AlZn alloy in this example, but may be made of any other suitable material. The slide la is provided with two bearing surfaces 3a and 3b for cooperation with guiding shafts. The optical unit further comprises a light-emitting device 5, generally also called a radiation source, such as a semiconductor laser, and an optical guiding system for guiding the light beam, or generally the radiation beam, emitted by the emitting device 5. The optical guiding system comprises a variety of optical components attached to the support 1 as elucidated hereinafter.

The optical guiding system used here comprises a beam splitter which is mounted on the support 1. The optical guiding system further comprises a collimator lens 9 and a mirror

11, both mounted on the support 1. The mirror 11 is arranged at an angle of 45° with respect to the light beam. Furthermore, the optical guiding system comprises a servo-lens 13 and a beam shaper 14.

The embodiment shown in Figs. 1 to 4 is provided with a scanning device comprising a lens system having an objective lens 15 and a light-receiving device 17 having an optical detector, particularly comprising a photodiode system. The objective lens 15, which has an optical axis 15 a, is designed for forming a scanning spot on a surface to be scanned. For this reason a focusing actuator 19 is provided, which actuator 19 has a stationary portion which is mounted on the slide la and a movable portion which is movably connected to the stationary portion and carries the objective lens 15. It is to be noted that the light-emitting device, the components of the optical guiding system, the optical guiding system itself, the scanning device, the light-receiving device, and the actuator applied in the optical unit and device according to the invention may be devices, systems, and components known per se or may be of constructions or structures known per se. The device as shown in Figs. 1 to 4 is particularly designed for reading information present on and writing information into an information carrier having an information track, particularly an optical disc, such as a DVD-RW. To read information from the optical disc, the light-emitting device 5 generates a continuous light beam which passes the beam shaper 14, the beam splitter 7, the collimator lens 9, and the mirror 11 and which is focused into a scanning spot on the optical disc by the objective lens 15. The light beam is reflected by the optical disc such that the reflected light beam contains information corresponding to a series of elementary information characteristics present in the information track of the optical disc. The reflected light beam is guided to the light-receiving device 17 via the objective lens 15, the mirror 11, the collimator lens 9, the beam splitter 7, and the servo-lens 13, so that the light-receiving device 17 supplies a detection signal which corresponds to the scanned information on the optical disc. To write information into an optical disc, the light-emitting device 5 generates a light beam which corresponds to the information to be written and which is guided via the optical guiding system to the objective lens 15, whereby a series of successive elementary information characteristics on the information track of the optical disc is generated in the scanning spot.

In the optical unit according to the invention, the light-emitting device is mounted on the support in a thermally insulating manner. In the optical unit as disclosed in Figs. 1 to 4, the light-emitting device 5 is mounted in an opening 21a of a metal plate-shaped carrier 21, made of copper, aluminum, or another suitable metallic material. A thermally insulating plate-shaped element 23 is provided between this carrier 21 and the support 1. This insulating element 23 is provided with an opening 23a serving as a window for allowing the light beam generated by the light-emitting device 5 to pass. In this embodiment the insulating element 23 is made of polymethylmetacrylate. Instead of with the opening 23 a, the insulating element 23 may be provided with a transparent portion in front of the light-emitting device 5. The carrier 21 and the insulating element 23 are fixed to the support 1 by means of screws. Of course other suitable mounting means, such as a glue, may be used as well.

If so desired, the metal carrier 21 may be provided with cooling-fins in order to improve the heat transfer to the environment.

The embodiment of the optical player in accordance with the invention shown in Fig. 5 has a frame 100 which rotatably supports a spindle 102 for an optical disc 103, in this embodiment a DVD + RW, and has two magnetic yokes 104 of a slide device unit 106, which yokes are secured to the frame 100. The device unit 106 further comprises two drive coils 108 which cooperate with the magnetic yokes 104. The drive coils 108 are arranged on a slide 110 which is capable of performing radial translational movements along guiding shafts 112 only depicted schematically. The slide 110 may be the slide la as depicted in the Figs. 1 to 4, but may alternatively be another slide provided with an actuator and the optical unit according to the invention. The optical player has further a disc drive unit 114 for rotating the disc 103 in a rotation direction R around the spindle 102.

It has been found that such an optical player meets the high precision requirements relating to the mutual positions and alignment of the several optical components of the optical guiding system as well as the positions of these components with regard to the optical lens system, the light-emitting device and the light-receiving device, also when a high-power light-emitting device is provided. From measurements it appears that in that case the support hardly heats up during operation of the light-emitting device and, as far as it does heat up, this takes place uniformly and only to such a small extent that deformations, if any, and shifts, if any, can be fully compensated for the generally applied control electronics of the optical player. Due to this property the optical unit and optical player according to the invention are particularly suitable for writing optical systems in which the writing process cannot be stopped for recalibrating the whole setup.

It is to be noted that the invention is not limited to the examples shown herein. It is possible, for example, to combine some of the components mentioned or to omit a component. Moreover, the terms "optical unit" and optical player also denote magneto- optical devices.

Claims

CLAIMS:

1. An optical unit comprising a support which supports a light-emitting device for emitting a light beam and accommodates an optical guiding system for guiding the light beam, characterized in that the light-emitting device is secured to the support in a thermally insulated manner.

2. An optical unit as claimed in Claim 1 , characterized in that the light-emitting device is attached to the support via a thermally insulating element.

3. An optical unit as claimed in Claim 2, characterized in that the thermally insulating element is made of a polymer.

4. An optical unit as claimed in Claim 1, characterized in that the thermally insulating element is a plate-shaped element provided with a window for allowing the light beam to pass through.

5. An optical unit as claimed in Claim 2, characterized in that the light-emitting device is mounted on or in a metal carrier, the thermally insulating element extending between the metal carrier and the support.

6. An optical unit as claimed in Claim 5, characterized in that the metal carrier is provided with fins.

7. A scanning device for scanning an optical disc, which scanning device comprises an objective lens and a light-receiving device and further comprises the optical unit as claimed in any one of the preceding Claims.

8. An optical player having a drive unit for rotating an optical disc and a scanning device as claimed in Claim 7.