Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-06-09
2002-05-28
Lee, John D. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S037000, C385S090000, C385S092000
Reexamination Certificate
active
06394665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser module for a wavelength divisional multiplex (WDM) system. More particularly, the invention relates to a semiconductor laser module capable of accurately materializing a desired oscillation wavelength and fit for WDM system.
2. Description of the Related Art
A semiconductor laser module has a semiconductor optical amplifier in combination with an optical fiber for propagating the laser light generated by the semiconductor optical amplifier efficiently depending on the application. Further, the semiconductor optical amplifier essentially consists of a light-emitting element as a light source, and an optical resonator including a pair of reflectors for mutually reflecting the light emitted from the light-emitting element.
FIG. 4
is a diagram illustrating the structure of a typical semiconductor laser module. As shown in
FIG. 4
, a semiconductor laser
35
is packaged on a base
30
via a sub-mount
31
in the ordinary semiconductor laser module. One side of the base
30
has a perpendicular edge face and an optical system
32
is attached thereto as shown in FIG.
4
. Further, a ferrule
21
holding the optical fiber
20
is securely passed through a through-hole provided in the side wall of the package
10
. The edge face of the optical fiber
20
is so arranged as to face the semiconductor laser
35
via the optical system
32
, so that the light emitted from the semiconductor laser
35
is efficiently coupled to the optical fiber
20
.
Further, a series of functional members mentioned above is normally housed in the package
10
in such a state that the functional members are orderly mounted on temperature control elements such as Peltier effect elements
34
. The functional members are also made to keep the operating temperature constant under feedback control using a temperature detection element (not shown) that is mounted on the sub-mount
31
together with the semiconductor laser
35
.
With the progress of information processing technology now, it is clearly demanded that the transmission density be improved even in the optical information communication field using semiconductor laser modules. The reason for this is that an amount of information to be transmitted has increased to an extremely greater extent in addition to expansion of a field of utilization.
In order to satisfy the above demand, a WDM system is now in progress. In other words, the WDM system allows the transmission speed to be practically improved by superposing a plurality of optical signals having different wavelengths and transmitting the optical signals thus superposed through one light transmission line.
FIG. 5
is a conceptual diagram illustrating a WDM system configuration.
A system shown in
FIG. 5
includes a plurality of light sources
101
, a mixer
103
, a branching device
104
and a plurality of receivers
105
. The plurality of light sources
101
each have discrete wavelengths &lgr;
1
, &lgr;
2
. . . &lgr;n. The mixer
103
injects the light signals emitted from the light sources
101
into a light transmission line
102
. The branching device
104
separates the light signals propagated through the light transmission line
102
on a wavelength basis. The plurality of receivers
105
receive the respective light signals thus separated by the branching device
104
.
As the above, The light sources
101
in the WDM system each have the discrete wavelengths. In the case of a 1.55 &mgr;m band, for example, it has been standardized to use 32 wavelengths increasing at 0.8 nm intervals from 1535.8 nm as shown in the following table 1.
TABLE 1
Channel
Wavelength
1
1535.8
2
1536.6
3
1537.4
4
1538.2
5
1539.0
6
1539.8
7
1540.6
8
1541.4
9
1542.1
10
1542.9
11
1543.7
12
1544.5
13
1545.3
14
1546.1
15
1546.9
16
1547.7
17
1548.5
18
1549.3
19
1550.1
20
1550.9
21
1551.7
22
1552.5
23
1553.3
24
1554.1
25
1554.9
26
1555.8
27
1556.6
28
1557.4
29
1558.2
30
1559.0
31
1559.8
32
1560.6
When it is attempted to obtain the plurality of oscillation wavelengths at the narrow intervals mentioned above, the light sources are required to have monochromatism and stability. Hence, no satisfactory characteristics are available from a method of directly utilizing the oscillation wavelength of a Fabry-Pérot type semiconductor laser with both edge faces of a semiconductor chip as mirrors of the resonator. Consequently, it has been proposed to obtain desired characteristics by incorporating a diffraction grating into the semiconductor laser element to make a DFB(distribute feedback) or DBR(distributed Bragg reflector) laser.
In the DFB or DBR laser, the oscillation wavelength is determined by the diffraction wavelength of the diffraction grating formed within the semiconductor laser and the gain of the active layer. In other words, as shown in
FIG. 6
, the reflection spectrum A of the diffraction grating, the longitudinal mode B of the optical resonator including the diffraction grating, and the gain C of the semiconductor optical amplifier have respectively different characteristics. Accordingly, laser oscillation is produced at a wavelength where the product of these characteristics is maximized.
Further, by sufficiently sharpening the reflection spectrum A of the diffraction wavelength of the diffraction grating, the diffraction wavelength becomes actually a substantial oscillation wavelength as shown in FIG.
7
. Today, the oscillation spectrum width of the DFB laser has reached GHz order and this can be utilized satisfactorily for the WDM system in view of sharpening the spectrum.
As stated above, the characteristics of the diffraction grating that substantially determine the oscillation wavelength are determined in the laser manufacturing process. It is consequently hard to manufacture semiconductor lasers having specific oscillation wavelengths at narrow intervals conforming to the standards shown in Table 1.
As the diffraction grating is incorporated in the semiconductor laser, the diffraction grating will be directly affected by the temperature characteristics of the semiconductor, and the oscillation wavelength may vary with the environmental temperature change and the heat generation of the semiconductor laser itself. Although the oscillation wavelength changes slightly, it cannot be disregarded for the WDM system using the plurality of light sources with different wavelengths at 0.8 nm intervals.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel semiconductor laser module having different oscillation wavelengths at slight intervals.
A semiconductor laser module according to the invention comprises a light-emitting element emitting light, a package, an optical resonator and an optical fiber. The package houses the light-emitting element therein. The optical resonator has a pair of opposed reflectors for reflecting the light emitted from the light-emitting element. The optical fiber leads out laser light generated in the light-emitting element through the optical resonator. The optical fiber has a diffraction grating disposed close to an end portion of the optical fiber. One of the reflectors of the optical resonator is a reflective film formed on one edge face of the light-emitting element and the other reflector thereof is the diffraction grating disposed close to the end portion of the optical fiber.
The above-mentioned semiconductor laser module preferably comprises an optical connector attached to the end portion of the optical fiber, wherein the optical fiber is connected to the package via the optical connector. In the semiconductor laser module, it is advantageous that the optical connector resiliently supports the optical fiber therein and wherein when the optical connector is attached to the package, the optical fiber is abutted against the package so as to be automatically positioned.
A semiconductor laser module according to the invention features that an optical fiber is provided with part of an optical resonat
Doan Jennifer
Lee John D.
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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