Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2000-08-04
2003-03-18
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S233000, C257S257000, C257S184000, C257S199000, C257S212000, C257S234000, C257S252000, C257S226000, C257S277000, C257S228000
Reexamination Certificate
active
06534794
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a semiconductor light-emitting unit including a semiconductor light-emitting diode and also relates to optical head apparatus and optical disk system including the light-emitting unit. More particularly, the present invention relates to measures to be taken to ensure good emission characteristics for the light-emitting diode.
Recently, various types of optical or magneto-optical disk systems have rapidly increased their demand and expanded their applications. These systems are used for optically writing, reading and erasing information onto/from a high-density, large-capacity optical or magneto-optical storage medium like optical disk or optical card using an optical memory. As for optical disks with a pit pattern, for example, digital audio disks, videodisks, document file disks and disks with data files have found broader and broader applications.
To write or read information onto/from a storage medium like an optical disk, an optical system is needed to make a light beam, which has been produced by a semiconductor light-emitting diode and then condensed to a spot of a very small size, incident on the storage medium. That is to say, to write or read the information onto/from the storage medium successfully and accurately, the optical system as a whole should be constructed with very high precision before everything else. For example, basic functions of an optical head apparatus, which is a key section of an optical disk system, are roughly classified into: condensing the light beam to a very small spot down to the limit of diffraction; performing focus and tracking controls over the optical system; and detecting a pit signal. These functions are implementable by appropriately combining various types of optical systems and photoelectric conversion methods depending on the intended applications. Examples of these combinations include: a semiconductor light-emitting unit including a semiconductor laser diode and a photodetector as a unit; an optical head apparatus (or an optical pickup) including the light-emitting unit, prism and lens; and an optical disk system (or optical disk drive) including the optical head apparatus and a storage medium.
As for an optical disk system applicable to compact discs (CDs), a semiconductor laser diode, operating at a wavelength of around 800 nm belonging to the so-called “infrared region” of the spectrum, has often been used as its light source. Recently, however, remarkable progress has been achieved in the design technologies for optical systems and semiconductor laser diodes, operating at an even shorter wavelength and yet producing far higher output power, have been developed one after another. As a result, the storage capacity of optical disks has also been increasing year after year.
Also, to provide a downsized and more reliable optical disk system or optical head apparatus at a lower cost, an optical system for an optical head apparatus is simplified by using a hologram according to a proposed technique. Such a technique is disclosed by Wai-Hon Lee in “Holographic Optical Head for Compact Disc Applications”, Optical Engineering Vol. 28, No. 6, pp. 650-653 (1989).
In the optical disk systems like these, automatic power control (APC) is usually carried out to keep the intensity of radiation emitted from the semiconductor laser diode constant such that write and read operations can be performed even more stably and reproducibly using the semiconductor laser diode.
However, the known optical disk systems have a problem in the relationship between the amount of current I injected into a semiconductor laser diode and the intensity L of radiation emitted from the laser diode, which will be herein called “I-L characteristic”.
FIG. 12
illustrates the I-L characteristics using the operating temperature of a semiconductor laser diode as a parameter. As shown in
FIG. 12
, the operating temperatures are defined by the three ambient temperatures of 0, 30 and 80° C. in the illustrated example. In
FIG. 12
, at room temperature (i.e., 30° C.), the radiation starts to be emitted from the semiconductor laser diode at a predetermined current value (i.e., a threshold current value). Then, a substantially linear relationship will be maintained between the current and the emission intensity until the intensity reaches a predetermined value. In contrast, at an elevated temperature (i.e., 80° C.), the amount of current needed to start the emission and the quantity of heat generated both increase compared to the room-temperature result. Accordingly, if a high intensity should be attained at such an elevated temperature, then the resultant I-L characteristic cannot be linear anymore. That is to say the gain of the emission with respect to the current supplied decreases. Such a bend of the I-L characteristic is curve, i.e., variation in differentiated intensity of emission with respect to the current value, will be herein called a “kink” of a high-temperature I-L characteristic.
If a semiconductor laser diode is operated under such conditions as causing the kink in the high-temperature I-L characteristic, then the APC control over an optical disk system including the laser diode will lose its stability. Also, if even higher output power should be attained (i.e., if the emission to be attained corresponds to a point on the high-temperature I-L characteristic curve which is even greater than the point where the kink is caused), the far field pattern (FFP) of the emission might be out of order, thus possibly deteriorating the convergence. Accordingly, the semiconductor laser diode should be operated under such conditions as eliminating the kinks from the high-temperature I-L characteristic and yet required emission intensity should be attained. However, to increase the emission intensity of the semiconductor laser diode, the amount of the current injected should be increased. Then, the operating temperature of the semiconductor laser diode rises from the ambient temperature, and therefore, the kink is more likely to be caused in the high-temperature I-L characteristic.
To solve this problem, a known semiconductor laser diode for optical disk system has its structure or material modified such that a greater amount of current can be supplied thereto at room temperature to attain the emission intensity exceeding that corresponding to the point where the kink is caused in the high-temperature I-L characteristic. For example, the amount of current supplied may be defined at the point A shown in FIG.
12
. Another known semiconductor laser diode has its heat dissipation ability improved to minimize the temperature rise resulting from the injection of an increased amount of current.
However, if that type of semiconductor laser diode, which has its heat dissipation ability improved to eliminate kinks from the high-temperature I-L characteristic, is operated at a low ambient temperature, then a kink is caused in the low-temperature I-L characteristic when a large amount of current is supplied. For example, if the amount of current supplied is increased at a low temperature (e.g., 0° C. shown in FIG.
12
), then a kink is observable in the I-L characteristic curve. Accordingly, if a known optical disk system, which has had its heat dissipation ability improved to eliminate the kinks from the high-temperature I-L characteristic, is used at a low temperature (e.g., 10° C. or less), then the kink is likely to be caused in the low-temperature I-L characteristic, thus possibly deteriorating its emission performance.
SUMMARY OF THE INVENTION
An object of the present invention is providing (1) a semiconductor light-emitting unit that can attain a high emission intensity in a broad temperature range by ensuring good heat dissipation ability for a semiconductor laser diode and by eliminating kinks from its low-temperature I-L characteristic, and (2) optical head apparatus and optical disk system including that unit.
An inventive semiconductor light-emitting unit includes: a semiconductor light-emitting diode; a
Kochi Yasuyuki
Komma Yoshiaki
Nakanishi Hideyuki
Yoshikawa Akio
LandOfFree
Semiconductor light-emitting unit, optical apparatus and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor light-emitting unit, optical apparatus and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor light-emitting unit, optical apparatus and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3070549