Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2001-04-19
2003-07-29
Paladini, Albert W. (Department: 2125)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S020000, C372S029020, C250S205000, C359S199200
Reexamination Certificate
active
06600762
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength-variable light source used in the field of optical communication, as well as to a device for measuring optical component loss using the wavelength-variable light source.
2. Description of the Related Art
FIG. 14
shows a wavelength-variable light source in the related-art. An antireflection coating
1
A is provided on one side of a semiconductor laser
1
, and the light exiting from the end covered with the antireflection coating
1
A is collimated by a lens
5
. The thus-collimated light is subjected to wavelength selection by a diffraction grating
2
, and the thus-selected light returns to the diffraction grating
2
by means of the mirror
3
. The light is again subjected to wavelength selection by the diffraction grating
2
, and the light is fed back to the semiconductor laser
1
, thereby effecting lasing.
The light output from the other end of the semiconductor laser
1
is converted into collimated light by means of a lens
6
. After having passed through an optical isolator
8
, the thus-collimated light is converged on an optical fiber
4
by means of a lens
7
.
The light source shown in
FIG. 14
is called a Littman type. During one round trip, the light is subjected to two rounds of wavelength selection by the diffraction grating
2
. The light source is superior in wavelength selection characteristic and has been known as one of the most popular methods.
In such a related-art wavelength-variable light source, as indicated by “output from ordinary wavelength-variable light source” shown in
FIG. 11
, the light that is output when the wavelength of the light is changed assumes an arch-shaped profile, because of gain distribution of the semiconductor laser
1
. Here, the characteristic of an “output from an ordinary wavelength-variable light source” is determined by means of consecutively plotting outputs P produced at respective wavelengths &lgr;.
In a case where a transmission loss of an optical component using such a light source is measured, a loss is measured by means of making an optical output flat (without a necessity of any reference), as shown in an example characteristic provided in an upper left position in FIG.
8
.
If a drive current of the semiconductor laser is subjected to auto power control (APC) for making an output flat, a drive current If must be changed greatly, as shown in FIG.
13
A.
A change in current induces mode hopping or multi-mode lasing, thus rendering the lasing state of the light source unstable. As a result, there may be a case where correct measurement of transmission loss become impossible.
Even if a light-variable attenuator is provided at the output side of the optical component, high-speed tracking of the output is difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a wavelength-changeable light source equipped with a semiconductor laser having one end surface covered with an antireflection coating and enhancing the flatness of an optical output.
Another object of the present invention is to enable stable measurement of transmission loss of an optical element with a smaller change in current even when APC is effected with use of a drive current and with less instability of the light source, through use of a wavelength-variable light source which produces an optical output of high flatness.
To solve the above-described problem, the present invention provides a wavelength-variable light source equipped with a semiconductor laser whose one end face is provided with an antireflection coating, the light source comprising:
a power correction filter which permits transmission of the light output from the semiconductor laser, thereby rendering the characteristics of the output light substantially flat.
According to the present invention, the wavelength-variable light source is provided with a power correction filter which permits transmission of the light output from the semiconductor laser whose one end face is provided with an antireflection coating, thereby improving the flatness of the output light.
Preferably, as shown in
FIG. 1
, the wavelength-variable light source is an external-resonator-type laser light source which converts the light output from the end face covered with the antireflection coating of the semiconductor laser into collimated light, returns the light to a wavelength selection optical element by means of a mirror after having subjected the light to wavelength selection by the wavelength selection optical element, subjects the light again to wavelength selection by the wavelength selection optical element, feeds back the light to the semiconductor laser, and converges and outputs light output from the other end face of the semiconductor laser on and to an optical fiber, a power correction filter being interposed between the semiconductor laser and the optical fiber.
Preferably, as shown in
FIG. 1
, a diffraction grating is employed as the wavelength selection optical element.
Preferably, as shown in
FIG. 2
, a beam splitter
9
is interposed between the semiconductor laser land the diffraction grating
2
for extracting a portion of diffracted light which is fed back from the diffraction grating
2
to the semiconductor laser, and the diffracted light extracted by the beam splitter
9
is converged on and output to the optical fiber
4
after have been caused to pass through the power correction filter
10
.
Preferably, as shown in
FIG. 2
, the wavelength-variable light source further comprises a rotation mechanism (designated by arrows) which changes a selected wavelength by means of a change in the angle of the mirror
3
.
Preferably, as shown in
FIG. 3
, avariable band pass filter
11
is used as the wavelength selection optical element.
Preferably, as shown in
FIG. 4
, a partial reflection mirror is employed as the mirror, and a portion of the light having been fed back to the semiconductor laser
1
is converged on and output to the optical fiber
4
.
Preferably, a beam splitter is interposed between the semiconductor laser and the variable band pass filter
11
for extracting a portion of diffracted light which is fed back from the variable band pass filter to the semiconductor laser, and the diffracted light extracted by the beam splitter
14
is converged on and output to the optical fiber
4
after have been caused to pass through the power correction filter
10
.
Preferably, as shown in
FIG. 6
, the power correction filter is a power correction film
4
provided on the end face of the optical fiber.
Preferably, as shown in
FIG. 8
, a wavelength-variable light source is provided in a light source section and corresponds to an optical component loss measurement device which connects the light output from the light source to an optical component
21
to be measured, and measures a transmission loss in the light having passed through the optical component
21
, wherein the light source section is a wavelength-variable light source
20
having any one of the above-described power correction filters
10
.
Preferably, the optical component loss measurement device connects the light output from the wavelength-variable light source having the power correction filter to an optical component to be measured and measures a transmission loss in the light having passed through the optical component. Hence, the light source is subjected to small current variation even during APC of a drive current. Thus, instability of the light source is diminished, thereby enabling stable measurement of a transmission loss in an optical component.
Preferably, a shown in
FIG. 8
, the optical component loss measurement device further comprises:
a light-receiving section
31
for receiving light having passed through the optical component
21
; and
a control section
32
for computing a transmission loss in the light having passed through the optical component from information about the wavelength of the light output from the wavelength-variable light source
20
having the power correction fil
Ando Electric Co. Ltd.
Fish & Richardson P.C.
Paladini Albert W.
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