Abstract:
A laser source is located in a relatively cool accessible location. Because there is adequate heat dissipation for the laser source, changes in the laser wavelength that arise from laser temperature changes are minimized. The invention described here includes the use of optical fiber to deliver light from the laser source. The laser reliability is improved because of reduced temperature and temperature fluctuations are experienced by the laser source. Because the laser source can be placed outside the drives hermetic seal, the laser can be easily replaced in the field, if required.

Description:
RELATED APPLICATIONS 
     The present application is related to and claims priority from Provisional Application Ser. No. 60/128,748, filed Apr. 12, 1999, and is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally related to the use of optical drive laser sources and is more specifically related to the use of optical drive laser sources in relatively low temperature and/or low temperature variation environments. 
     BACKGROUND 
     In virtually all optical disk drives to date, light is provided by a source laser located inside the drive. The laser is located in a physically warm place inside the drive and is fairly inaccessible. In such prior art drives a great deal of effort is devoted to providing adequate heat dissipation such that heat buildup and/or heat variations within the optical drive will not affect the operating wavelength of the laser. Heat buildup and/or heat variations may likewise shorten the lifetime of the laser, which would then require significant effort to remove and replace from within the sealed enclosure that it is disposed. 
     What is needed, therefore, is a method and apparatus such that the aforementioned limitations of the prior art are addressed. 
    
    
     DESCRIPTION OF THE FIGURES 
     In FIG. 1 a perspective view of a multi-disk optical drive  100 . 
     In FIG. 2 there is seen a diagram of the prior art, wherein a laser source  201  provides a source of light from within a housing  202  of an optical drive. 
     In FIG. 3 there is seen a laser source  352  of the present invention. 
     In FIG. 4 there is seen a lens disposed between the laser source  352  and the optical fiber  315 . 
    
    
     SUMMARY OF THE INVENTION 
     The present invention provides a laser source that is not exposed to the heat and heat variations within the housing of an optical disk drive. The laser source may, consequently, exhibit better performance characteristics for a given cost over that of the prior art. Furthermore, the present invention does not require opening of the optical disk drive housing for replacement and/or service, and thus reduces the costs associated therewith. 
     The present invention comprises an optical drive including: at least one optical head; at least one source of light for delivering light to the optical head; and a housing; wherein the at least one optical head is disposed within the housing and wherein the at least one source of light is disposed outside the housing. 
     The at least one source of light may comprise a diode laser source such as Fabry Perot laser source or a stable single frequency laser source. 
     The optical drive may further comprise at least one optical fiber, wherein the at least one optical fiber is disposed in an optical path between the at least one optical head and the at least one source of light for directing the light between the at least optical head and the at least one source of light. 
     The optical drive may further comprise an optical switch, wherein the optical switch is disposed in the optical path for directing the light between the at least one optical head and the at least one source of light. 
     The optical fiber may comprise a single-mode optical fiber, a single mode polarization maintaining optical fiber, or a low birefringence optical fiber. 
     The at least one optical head may consist of one optical head. 
     The at least one optical fiber may consist of one optical fiber. 
     The housing may comprise a standardized form factor. 
     The optical head may comprise a flying optical head. 
     The optical head may comprise a magneto-optical head. 
     The present invention may comprise an optical drive, including: a housing; at least one optical head; light delivery means for delivering light to the at least one optical head with minimized wavelength fluctuations. 
     The means for delivering the light nay be disposed outside the housing. 
     The present invention includes a method for delivering light to an optical head of an optical drive, comprising the steps of: disposing an optical head with an optical drive housing; disposing a source of the light in a location that comprises a relatively cool and/or stable temperature; and directing the light between the optical head and the source of light. 
     The present invention may further comprise the step of disposing the source of light outside the optical drive housing. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring in detail to the drawings wherein similar parts are identified by like reference numbers, there is seen in FIG. 1 a  perspective view of a multi-disk optical drive  100 . In this view it is seen that a head assembly  105  may comprise individual optical heads  125 , each of which is coupled to individual arms  120  through respective suspensions  122 . In one embodiment, the optical heads  125  may comprise flying optical heads. Flying optical heads are understood to comprise air bearing surfaces that interact to aerodynamically maintain the optical heads  125  a distance above respective rotating disks  155 . In other embodiments, the optical heads  125  may comprise magneto-optical heads. The rotating disks  155  are rotated at a high speed, for example 10,000 RPM, by a high speed spindle motor assembly  171 . FIG. 1 further illustrates a group of individual optical fibers  115 , which are all coupled to an optical switch  130  at one end and to individual ones of the optical heads  125  at an opposite end. The optical switch  130  selectively directs light  160 / 161  between a laser source (which is discussed below) and a particular one of the individual optical fibers  115 . The optical fibers  115  direct the light  160 / 161  between the optical switch  130  and a particular optical head  125 . 
     Referring now to FIG. 2, there is seen a diagram of the prior art, wherein a laser source  201  provides a source of light from within a housing  202  of an optical drive. In the prior art the laser source  201  is in close proximity to the optical switch  230 . The light  161  from the laser source  201  is delivered as a collimated beam. The collimated light is directed by the optical switch  230  to a particular optical fiber  215  and by the fiber to a particular optical head  225 . The particular optical head  225  directs the light  162  to a respective disk  255 . The light is reflected back from the disk  255  towards the head  225 , and is directed from the optical head  225  by the optical fiber  215  towards the optical switch  230 . Properties of the reflected light  162  are detected using various optical detection techniques which are well known in the art for the particular optical disk technology utilized, for example, magneto-optical, optical, etc. 
     In prior art drives, significant heat is generated by various components of the optical drive, for example, by the spindle motor, the electronic drive circuitry, as well as the laser source itself. This heat causes the temperature within a sealed housing  202  which the optical drive components are disposed to be raised to a temperature which is significantly above the ambient temperature outside the housing. The ambient temperature outside of the housing can vary between 5 and 45 degrees Celsius. However, even if the air flow within the housing  202  is vented, the temperature range within the housing of prior art optical drives can vary as much as between 5 and 70 degrees Celsius. It is understood, therefore, that a high temperature and/or temperature variations can act to degrade the performance as well as the lifetime of the laser source  201 . 
     Referring now to FIG. 3, there is seen a laser source  352  of the present invention. The present invention utilizes the laser io source  352  to provide a source of light to the optical drive  100  in a new and novel manner. To this end, in the present invention the laser source  352  is located outside a housing  302  comprising the optical disk drive  100 . Such housings are well known in the art and comprise various standardized form factors, for example, a half height form factor, etc, within which may be disposed disks of various radii, for example, 5 inches, 3.5 inches, etc. By placing the laser source  352  outside of the optical disk drive housing  302  it is understood that the laser source  352  would be easy to replace and/or service in the event that it were to fail. In the prior art this approach has not been considered for a number of reasons, one in particular being, that a means for accurate alignment for directing the light towards the head  125  and/or back from the head  125  has not existed. The present invention identifies that an optical fiber  115  of the type disclosed in FIG. 1, which is used to direct the light  160 / 161  between the optical switch  130  and the optical heads  125 , can also be used to accurately direct light between the laser source  352  and the optical switch  130 . Accordingly, in one embodiment of the present invention an optical fiber  315  is disposed between the laser source  352  and the optical switch  130 . The optical fiber  315  may be routed from outside of the housing  302  to within the housing through a suitably dimensioned aperture. The optical fiber  315  enables routing of the light between the laser source  352  and the optical switch  130  along an optical path that can be aligned accurately and with little effort. The laser source  352  that is thus used can have looser tolerances (and is thus can be less expensive than the prior art laser sources) because it is not exposed to the heat and heat variations within the housing  302  of the optical drive  100 . It is understood that detection of the return laser light  161  may be done by placing a beam splitter and appropriate detection optics and circuitry (not shown) in the optical path before or after the optical fiber  315 . 
     Referring now to FIG. 4, there is seen a lens disposed between the laser source and the optical fiber. In one particular embodiment, a ball lens  492  may be used to focus light from the laser source  352  onto the optical fiber  315  because it can be manufactured and/or procured cheaply. It is understood, however, that any other suitable lens design could be used to focus the light from the laser source  352 . The laser source  352 , lens  492 , and optical fiber  315  may be coupled together on a suitable substrate and mounted on a thermoelectric cooler if so desired. 
     It is understood that the particular laser source  352  selected can vary depending upon particular system requirements and can be selected to be a conventional Fabry Perot laser source or stable single frequency laser source. Stable frequency laser sources include distributed feedback laser sources (DFB) or distributed Bragg reflector sources (DBR). 
     It is understood, that in a magneto-optical embodiment, the optical fiber  315  would preferably be of a variety that can accurately convey polarization orientations of data bits stored on the disks  155 . In one magneto-optical embodiment, the optical fibers  115 / 315  may be single mode polarization maintaining optical fibers, while in other embodiments, the optical fibers  115 / 315  may be single mode or low-birefringence optical fibers. 
     It is also understood, that in a single optical head and single disk embodiment (not shown) the optical switch  130  would not necessarily be required. In such an embodiment, only one optical fiber  315  would be needed to direct the light between the laser source  352  and the optical head  125 . 
     It is further understood, that in a two optical head and single disk embodiment (not shown) the optical switch  130  would also not necessarily be required. In such an embodiment two optical fibers  315  could be used to direct light between two laser sources  352  and their respective optical heads  125 . In such an embodiment, the cost of using two laser sources may be less than the cost of using the optical switch. It is understood that these concepts can be extended to any number of disks and laser sources. 
     In addition, while the present invention has been described to include placement of a laser source  352  outside of a disk drive housing  302 , it is understood that the optical fiber  315  could be used to route light from a laser source located at some relatively low and/or stable temperature location within the housing  302 . 
     Accordingly, while the present invention has been described wherein with reference to particular embodiments thereof, a latitude of modification, various changes, and substitutions are intended with the present invention, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departure from the scope of the invention.