Semiconductor laser device

Details Semiconductor laser device Semiconductor laser device

2003-02-06

2004-10-12

Wong, Don (Department: 2828)

Coherent light generators

Particular active media

Semiconductor

C372S011000, C372S019000, C372S043010, C372S045013, C372S099000, C372S101000, C372S108000, C372S029020

Reexamination Certificate

active

06804282

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device used as a light source for optical information processing, a signal source for optical communications, or an excitation light source for fiber amplifiers.
2. Background Art
FIG. 20
is a diagram of a fiber grating laser taken from the journal article “Fiber Grating and Its Applications” by Tohru Inoue, in IECE transactions, Vol. 85, No. 2, pp 126-128, February, 2002. In a fiber grating laser
52
shown in the figure, a fiber grating
54
having a reflectance of R
fg
is provided within an optical fiber
53
. Light of a specific wavelength entering the optical fiber
53
is reflected by the fiber grating
54
. On the other hand, a semiconductor laser
55
is configured such that its front end face
56
has a reflectance (R
f
) corresponding to low reflection or no reflection, and its back end face
57
has a reflectance (R
r
) corresponding to high reflection. Reference numeral
58
denotes the optical waveguide region of the semiconductor laser
55
. In this arrangement, a resonator is formed between the fiber grating
54
and the back end face
57
of the semiconductor laser
55
, thereby stabilizing the oscillation wavelength of the laser light.
Use of such a fiber grating laser, however, makes the structure of the device complicated. Furthermore, it is necessary to combine the semiconductor laser and the optical fiber, producing a coupling loss therebetween.
The present invention has been devised in view of the above problems. It is, therefore, an object of the present invention to provide a semiconductor laser device capable of stably extracting from its semiconductor laser element laser light whose wavelength exhibits only a small change, without using any fiber grating.
Other objects and advantages of the present invention will become apparent from the following description.
JP-A No. 10-186104 discloses a multilayer antireflective film whose reflectance curve has two separate bottoms (low reflectance points) and a peak therebetween in a required wavelength band. Further, JP-A No. 11-214799 discloses a multilayer film whose reflectance is 10
−4
% to 10% at the center wavelength and the reflection spectrum characteristic curve has minimum values on both sides of the center wavelength. Still further, JP-A No. 2-241075 discloses a semiconductor laser device in which a film whose reflectance depends on the wavelength is formed.
However, the multilayer antireflective film described in the JP-A No. 10-186104 was devised to obtain a low reflectance over a wide range of wavelengths, and therefore the oscillation of the semiconductor laser is suppressed at each of the two bottoms and the peak. The purpose of the present invention, on the other hand, is to stably extract from a semiconductor laser element itself laser light whose wavelength exhibits only a small change, without using any fiber grating. Furthermore, as described later, the multilayer films of the present invention are used to cause the semiconductor laser to oscillate at a wavelength &lgr;
1
at which the reflectance is maximized. Therefore, the purpose and the effect of the present invention are different from those described in the above patent publication.
Further, the refractive indexes of first films for realizing the reflectance characteristics described in the above three patent publications are each larger than the square root of the effective refractive index n
c
of a respective semiconductor laser element. Therefore, these multilayer films are different from those of the present invention.
SUMMARY OF THE INVENTION
The features and advantages of the present invention may be summarized as follows.
According to one aspect, a semiconductor laser device comprises a semiconductor laser element having an effective refractive index of n
c
, and a multilayer film formed on at least one of the two end faces of the semiconductor laser element. The multilayer film has a structure in which a first film with a refractive index of n
1
and a second film with a refractive index of n
2
are alternately laminated, the first film being formed such that the first film is in contact with the one of the two end faces. The refractive index n, and the refractive index n
2
satisfy relations expressed by the formulas, n
1
<(n
c
)
1/2
and n
2
>(n
c
)
1/2
. A reflectivity characteristic of the multilayer film is such that a reflectivity of the multilayer film is maximized at a wavelength &lgr;
1
in a predetermined wavelength region and minimized at wavelengths &lgr;
2
and &lgr;
3
on a shorter-wavelength side and a longer-wavelength side of the wavelength &lgr;
1
, respectively.
Other and further objects, features and advantages of the invention will appear more fully from the following description.


REFERENCES:
patent: 5031186 (1991-07-01), Takigawa et al.
patent: 6343088 (2002-01-01), Mungino et al.
patent: 6487227 (2002-11-01), Kuramachi
patent: 2002/0176466 (2002-11-01), Yoon
patent: 02-241075 (1990-09-01), None
patent: 10-186104 (1998-07-01), None
patent: 11-214799 (1999-08-01), None
“Fiber Grating and Its Application”, Akira Inoue, Journal of the Institute of Electronics, Information and Communication Engineers, vol. 85, No. 2, pp. 126-128, Feb. 2002.

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