Coherent light generators – Particular active media – Semiconductor
Patent
1997-06-10
2000-09-12
Davie, James W.
Coherent light generators
Particular active media
Semiconductor
372 45, H01S 3085
Patent
active
061187992
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a high-output semiconductor laser device which is used for communication, optical recording on an optical disk or the like, a laser printer, laser medical care, laser processing and the like, and more particularly, which is suitable to excitation of a solid-state laser and a harmonic conversion element which require a high power laser beam.
BACKGROUND OF THE INVENTION
With respect to an optical wave guide mechanism, semiconductor laser devices are classified into the gain guided type and the refractive index guided type. The former gain guided type is met with various application inconveniences since this type is unstable as to a transverse mode and astigmatism is large which indicates displacements of beam waists (i.e., a position at which the beam width is minimum) in directions parallel and perpendicular to the junction. On the other hand, the latter refractive index guided type is advantageous due to stability as to transverse mode and small astigmatism.
An example of a semiconductor laser of the refractive index guided type in a BH (Buried Heteroastructure) laser. A BH laser, with an active layer buried in a material having a low refractive index, is advantageous in that the BH laser is completely of the refractive index guided type, has a small threshold current Ith, oscillates in a basic transverse mode, and has small astigmatism. On the other hand, a BH laser is not suitable as a high-output laser, since damage or impurities introduced into the active layer during processing of the active layer functions as a non-emission recombination center.
Furthermore, as a laser of a type which creates a refractive index difference in the vicinity of an active layer, creates a refractive index distribution and confines a transverse mode, there are a CSP (Channeled Substrate Planar) laser and a VSIS laser. Since in the vicinity of an active layer in such a laser, current blocking layers having a large absorption coefficient of laser light are formed so that it is possible to control a relatively small refractive index difference, thus obtaining basic mods oscillations even with a large stripe width. However, this absorption serves as an internal loss, and therefore, the threshold current Ith becomes large and a differential efficiency becomes small.
To solve the problems above described, a semiconductor laser of the refractive index guided type with a small loss which uses a current blocking layer which is not absorbent and have a low refractive index has been proposed (IEEE Journal of Quantum Electronics, Vo.29, No.6, p.1889-1894. (1993)).
FIG. 8(a) is a structure view showing an example of the semiconductor laser of the refractive index guided type with a small loss and uses a non-absorbent current blocking layer mentioned above, while FIG. 8(b) is a graph showing a guided mode of the semiconductor laser. In FIG. 8(a), on a buffer layer 8 of GaAs, a clad layer 7 of AlGaAs, a wave guide layer 6 of AlGaAs, an active layer 5 of GaAs, a wave guide layer 4 of AlGAs, a clad layer 2 of AlGaAs, and a cap layer 1 of GaAs are formed in this order, and current blocking layers 3 which have higher Al-composition and a lower refractive index than that of the clad layer is formed in the clad layer to sandwich a stripe-shaped active region 10. This creates a refractive index difference between the active region 10 and buried regions 9 in which the current blocking layers 3 are formed, whereby a refractive index guide structure is obtained.
This structure is based on an SCH (Separate Confinement Heterostructure) structure which is generally used as a high-output semiconductor laser, where by burying the current blocking layers 3 having higher Al-composition and a lower refractive index than that of the clad layer in the vicinity of the active layer 5 to create a refractive index distribution in a transverse direction, the buried current blocking layers 3 do not absorb laser light to make an internal loss small and a basic transverse mode oscillations are realized up
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IEEE Journal of Quantum Electronics vol. 29, No. 6, pp. 1889-1894 (1993). (Jun.).
Fujimoto Tsuyoshi
Muro Kiyofumi
Naito Yumi
Okada Satoru
Okubo Atsushi
Davie James W.
Mitsui Chemicals Inc.
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