&lt;title&gt;Miniaturized high-NA blue objective&lt;/title&gt; (2002)

Miniaturisedhigh-NAblueob jectiveB.H.W. Hendriks,M.A.H. vanderAa,J.van Asand C.T.LiedenbaumPhilips ResearchLab oratories, ProfessorHolstlaan 4,5656AA Eindhoven,TheNetherlandsABSTRACTIn order to enable optical storage in p ortable devices, a small optical drive building heightand thus small sizedob jectives are needed.A small version of the DVR ob jective, having numerical ap erture of 0.85 and op eratingwavelength= 405 nm is required, in order to hae sucient storage capacity on a small sized disc.In this pap erwe present a miniaturised DVR ob jective made of plastic.It has a building height of only 1.335 mm, enablingoptical storage for various mobile applications.Making the ob jective out of plastic eases the manufacturing andhandling.Furthermore, the two element ob jectivewas designed to havelow temp erature dep endence whichwascon rmed exp erimentally.Exp eriments with this ob jectiveshowed that readout of a 25 GB RW12cmdiscisp ossible.Furthermore, some considerations on the b ene ts and exp ected problems in miniaturising the actuatorare presented.Keywords:High-NA ob jective, Optical recording, Miniaturisation1. INTRODUCTIONThe increasing level of comp onent miniaturisation in p ortable devices like mobile phones, digital still and videocameras, noteb o oks and palmtop, not only enables smaller and easier to handle devices for the end user, but atthe same time imp ose stringent requirements up on the parts as well as the manufacturability of the completesystem.Since all of the aforementioned applications require storage of data in one form or another, wewouldlike to fo cus in this pap er on the implications of this trend on optical storage devices.Up until now the level ofintegration in optical pickup units has b een mo dest, and it is not at all clear whether the high manufacturingcosts weigh up to the burden of handling small discrete optical comp onents.Tohave sucient capacityon asmallsizeddisc,aversion oftheDVRob jective1(numericalap ertureof0.85op eratingatwelength405 nm) is required.Here wepresent results obtained with a miniaturised plastic DVR ob jective.It has a building height of only1.335 mmenabling optical storage applications for various mobile applications.Design andmanufacturing ofthe ob jective will b e discussed.Results on optical recording exp eriments p erformed with this ob jective will b epresented.Furthermore, we will present some considerations on the advantages of going to smaller comp onentsandmoresp eci callysmallermasses.Theinuenceonforinstanceactuatoreciencyresultingpowerconsumption (an equally imp ortant asp ect in mobile devices) will b e discussed.2. MINIATURISEDHIGH-NAOBJECTIVE2.1.Designasp ectsWhen decreasing the size of the ob jective, the handling and, therefore, the manufacturing of such an ob jectiveb ecomes increasingly more dicult.Contrary to ordinary sized ob jectives used inCD, DVDor DVR opticalrecording systems, for miniaturised high-NA ob jectives this handling must b e taken into account in the design.Currently there are three di erentways to manufacture aspherical ob jective lenses:(1) glass moulding, (2)glass photop olymer replication and (3) plastic injection moulding.In the glass moulding pro cess a glass preformis heated ab ove the melting temp erature, and by press moulding in an aspherical mould this preform acquirestherequiredasphericalshap e.2Inglassphotop olymerreplicationpro cessonestartswithatruncatedspherical glass b o dy.A droplet of UV curable resin is applied on top of this lens b o dyAn aspherical mould isFurther author information:Send corresp ondence to Benno H.W. Hendriks:E-mail:b enno.hendriks@philips.com,Telephone:+31 (0)40 2744627