U.S. patent application number 13/770458 was filed with the patent office on 2013-06-27 for optical pulse tester using light emitting device.
This patent application is currently assigned to ANRITSU CORPORATION. The applicant listed for this patent is Anritsu Corporation. Invention is credited to Hiroshi MORI, Shintaro MORIMOTO, Yasuaki NAGASHIMA.
Application Number | 20130161516 13/770458 |
Document ID | / |
Family ID | 45593829 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130161516 |
Kind Code |
A1 |
MORIMOTO; Shintaro ; et
al. |
June 27, 2013 |
OPTICAL PULSE TESTER USING LIGHT EMITTING DEVICE
Abstract
To provide a small and high-performance optical pulse tester
using a light emitting device including semiconductor light
emitting element capable of emitting light beams with wavelengths
in a plurality of wavelength ranges with a high optical output. An
optical pulse tester includes: a light emitting device including a
semiconductor light emitting element having first and second light
emitting end facets formed by cleavage respectively, and a light
emitting element driving circuit which applies a driving current to
each of a plurality of active layers; a light receiving section
which converts returned light of the optical pulse from the optical
fiber to be measured into an electric signal; and a signal
processor which analyzes a loss distribution characteristic of the
optical fiber to be measured on the basis of the electric signal
converted by the light receiving section.
Inventors: |
MORIMOTO; Shintaro;
(Atsugi-shi, JP) ; MORI; Hiroshi; (Atsugi-shi,
JP) ; NAGASHIMA; Yasuaki; (Atsugi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Anritsu Corporation; |
Atsugi-shi |
|
JP |
|
|
Assignee: |
ANRITSU CORPORATION
Atsugi-shi
JP
|
Family ID: |
45593829 |
Appl. No.: |
13/770458 |
Filed: |
February 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13151597 |
Jun 2, 2011 |
8401044 |
|
|
13770458 |
|
|
|
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Current U.S.
Class: |
250/338.1 |
Current CPC
Class: |
B82Y 20/00 20130101;
H01S 5/1021 20130101; H01S 5/0287 20130101; H01S 5/1092 20130101;
H01S 5/1203 20130101; H01S 5/4087 20130101; H01S 5/34306
20130101 |
Class at
Publication: |
250/338.1 |
International
Class: |
G01M 11/00 20060101
G01M011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2010 |
JP |
2010-182234 |
Claims
1. An optical pulse tester comprising: a light emitting device
including: a semiconductor light emitting element having first and
second light emitting end facets formed by cleavage respectively,
in which a plurality of active layers having gain wavelengths in
different wavelength ranges are disposed on a semiconductor
substrate so as to be optically coupled in a guiding direction of
light from the first light emitting end facet toward the second
light emitting end facet in order of the length of the gain
wavelength, a lower electrode is formed on a bottom surface of the
semiconductor substrate and a plurality of upper electrodes for
applying a driving current to each of the plurality of active
layers is formed above the plurality of active layers, at least one
diffraction grating with a Bragg wavelength equivalent to a short
gain wavelength is formed near an active layer with the short gain
wavelength between two adjacent active layers and near the
interface between the two active layers, and light generated in an
active layer with a longest gain wavelength oscillates in a
resonator formed by the first and second light emitting end facets
and light generated in an active layer with a short gain wavelength
oscillates in a resonator formed by the diffraction grating and the
second light emitting end facet and both the light beams are
emitted from the second light emitting end facet; and a light
emitting element driving circuit which applies a driving current to
each of the plurality of active layers and which short-circuits the
upper electrode provided above an active layer with a short gain
wavelength to the lower electrode provided on the bottom surface of
the semiconductor substrate so that when a driving current is
applied to one of the plurality of active layers, a leakage current
does not flow into an active layer with a shorter gain wavelength
adjacent to the active layer to which the driving current is
applied, in which the driving current applied by the light emitting
element driving circuit has a pulse form so that the semiconductor
light emitting element emits an optical pulse and the light
emitting device outputs the optical pulse emitted from the second
light emitting end facet of the semiconductor light emitting
element to an optical fiber to be measured; a light receiving
section which converts returned light of the optical pulse from the
optical fiber to be measured into an electric signal; and a signal
processor which analyzes a loss distribution characteristic of the
optical fiber to be measured on the basis of the electric signal
converted by the light receiving section.
2. The optical pulse tester according to claim 1, wherein a
reflectance with respect to light emitted from the second light
emitting end facet of the semiconductor light emitting element is
set to be lower than a reflectance with respect to light emitted
from the first light emitting end facet of the semiconductor light
emitting element.
3. The optical pulse tester according to claim 1, wherein the
plurality of active layers of the semiconductor light emitting
element includes first and second active layers, the gain
wavelength of the first active layer is 1.52 to 1.58 .mu.m, and the
gain wavelength of the second active layer is 1.28 to 1.34 p.m.
4. The optical pulse tester according to claim 2, wherein the
plurality of active layers of the semiconductor light emitting
element includes first and second active layers, the gain
wavelength of the first active layer is 1.52 to 1.58 .mu.m, and the
gain wavelength of the second active layer is 1.28 to 1.34
.mu.m.
5. The optical pulse tester according to claim 1, wherein the
plurality of active layers of the semiconductor light emitting
element includes first to third active layers, the gain wavelength
of the first active layer is 1.60 to 1.65 .mu.m, the gain
wavelength of the second active layer is 1.52 to 1.58 .mu.m, and
the gain wavelength of the third active layer is 1.28 to 1.34
.mu.m.
6. The optical pulse tester according to claim 2, wherein the
plurality of active layers of the semiconductor light emitting
element includes first to third active layers, the gain wavelength
of the first active layer is 1.60 to 1.65 .mu.m, the gain
wavelength of the second active layer is 1.52 to 1.58 .mu.m, and
the gain wavelength of the third active layer is 1.28 to 1.34
.mu.m.
Description
[0001] This is a divisional of application Ser. No. 13/151,597,
filed Jun. 2, 2011.
TECHNICAL FIELD
[0002] The present invention relates to an optical pulse tester
using a light emitting device.
BACKGROUND ART
[0003] In the field of optical communication, a system which
outputs light beams with a plurality of wavelengths is used. For
example, in the case of a system of outputting laser beams with two
wavelengths, a configuration is adopted in which two semiconductor
lasers manufactured for respective wavelengths are prepared and
output light beams from the semiconductor lasers are mixed to be
output (for example, refer to Patent Document 1).
[0004] In contrast, the inventor of this application proposes, as a
two-wavelength laser light source configured without requiring such
a complicated optical system, a semiconductor light emitting
element capable of emitting laser beams with a plurality of
wavelengths from a single chip by connecting a plurality of active
layers with very different gain wavelengths in series and disposing
a diffraction grating inside to realize independent oscillation of
each wavelength (refer to Patent Document 2).
RELATED ART DOCUMENTS
Patent Documents
[0005] [Patent Document 1] Japanese Unexamined Patent Application
Publication No. 2008-209266 [0006] [Patent Document 2] Japanese
Patent Application No. 2009-34080 (Japanese Unexamined Patent
Application Publication No. 2010-192601)
DISCLOSURE OF THE INVENTION
Problem that the Invention is to Solve
[0007] However, in the configuration disclosed in Patent Document
2, when applying a driving current to an active layer for a long
wavelength for oscillation, a leakage carrier flows into an
adjacent active layer for a short wavelength. Since this causes
free carrier absorption, there has been a problem in that output is
reduced.
[0008] The present invention has been made to solve such a problem,
and it is an object of the present invention to suppress an optical
output reduction caused by absorption of light, which is emitted
and amplified by an active layer for a long wavelength, by carriers
leaking from the active layer for a long wavelength when the light
passes through an active layer for a short wavelength in a
semiconductor light emitting element in which active layers with a
plurality of different gain wavelengths are connected in
series.
Means for Solving the Problem
[0009] According to an aspect of the present invention, an optical
pulse tester includes: a light emitting device including: a
semiconductor light emitting element having first and second light
emitting end facets formed by cleavage, respectively, wherein a
plurality of active layers having gain wavelengths in different
wavelength ranges are disposed on a semiconductor substrate so as
to be optically coupled in a guiding direction of light from the
first light emitting end facet toward the second light emitting end
facet in order of the length of the gain wavelength, a lower
electrode is formed on a bottom surface of the semiconductor
substrate and a plurality of upper electrodes for applying a
driving current to each of the plurality of active layers is formed
above the plurality of active layers, at least one diffraction
grating with a Bragg wavelength equivalent to a short gain
wavelength is formed near an active layer with the short gain
wavelength between two adjacent active layers and near the
interface between the two active layers, and light generated in an
active layer with a longest gain wavelength oscillates in a
resonator formed by the first and second light emitting end facets
and light generated in an active layer with a short gain wavelength
oscillates in a resonator formed by the diffraction grating and the
second light emitting end facet and both the light beams are
emitted from the second light emitting end facet; and a light
emitting element driving circuit which applies a driving current to
each of the plurality of active layers and which short-circuits the
upper electrode provided above an active layer with a short gain
wavelength to the lower electrode provided on the bottom surface of
the semiconductor substrate so that when a driving current is
applied to one of the plurality of active layers, a leakage current
does not flow into an active layer with a shorter gain wavelength
adjacent to the active layer to which the driving current is
applied, in which the driving current applied by the light emitting
element driving circuit has a pulse form so that the semiconductor
light emitting element emits an optical pulse and the light
emitting device outputs the optical pulse emitted from the second
light emitting end facet of the semiconductor light emitting
element to an optical fiber to be measured; a light receiving
section which converts returned light of the optical pulse from the
optical fiber to be measured into an electric signal; and a signal
processor which analyzes a loss distribution characteristic of the
optical fiber to be measured on the basis of the electric signal
converted by the light receiving section.
[0010] Through this configuration, since a semiconductor light
emitting element capable of making light beams with wavelengths in
a plurality of wavelength ranges oscillate in a plurality of
longitudinal modes can operate with a high optical output, a small
and high-performance optical pulse tester can be realized.
[0011] Moreover, in the optical pulse tester according to the
aspect of the present invention, a reflectance with respect to
light emitted from the second light emitting end facet is set to be
lower than a reflectance with respect to light emitted from the
first light emitting end facet.
[0012] Moreover, in the optical pulse tester according to the
aspect of the present invention, the plurality of active layers may
include first and second active layers, the gain wavelength of the
first active layer may be 1.52 to 1.58 .mu.m, and the gain
wavelength of the second active layer may be 1.28 to 1.34 .mu.m.
Through this configuration, light with a wavelength of about 1.3
.mu.m and light with a wavelength of about 1.55 .mu.m can be made
to oscillate in a plurality of longitudinal modes using one
element.
[0013] Moreover, in the optical pulse tester according to the
aspect of the present invention, the plurality of active layers may
include first to third active layers, the gain wavelength of the
first active layer may be 1.60 to 1.65 .mu.m, the gain wavelength
of the second active layer may be 1.52 to 1.58 .mu.m, and the gain
wavelength of the third active layer may be 1.28 to 1.34 .mu.m.
Through this configuration, light with a wavelength of about 1.3
.mu.m, light with a wavelength of about 1.55 .mu.m, and light with
a wavelength of about 1.625 .mu.m can be made to oscillate in a
plurality of longitudinal modes using one element.
Advantage of the Invention
[0014] The present invention provides a small and high-performance
optical pulse tester using light emitting device including a
semiconductor light emitting element capable of emitting light
beams with wavelengths in a plurality of wavelength ranges with a
high optical output.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a view showing a light emitting device of a first
embodiment of the present invention.
[0016] FIG. 2 is a view showing another aspect of the light
emitting device of the first embodiment of the present
invention.
[0017] FIG. 3 is a view showing a light emitting device of a second
embodiment of the present invention.
[0018] FIG. 4 is a view showing another aspect of the light
emitting device of the second embodiment of the present
invention.
[0019] FIG. 5 is a block diagram showing the configuration of an
optical pulse tester of a third embodiment of the present
invention.
[0020] FIG. 6 is a view showing the characteristics of a
semiconductor light emitting element of the light emitting device
of the first embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] Hereinafter, embodiments of a semiconductor light emitting
element, a driving method of a semiconductor light emitting
element, a light emitting device, and an optical pulse tester using
a light emitting device of the present invention will be described
with reference to the accompanying drawings.
First Embodiment
[0022] A first embodiment of the light emitting device related to
the present invention is shown in FIGS. 1 and 2. A light emitting
device 50 is configured to include a semiconductor light emitting
element 10 and a light emitting element driving circuit 2.
[0023] As shown in FIGS. 1 and 2, for example, the semiconductor
light emitting element 10 includes: an n-type semiconductor
substrate 11 formed of n-type InP (indium.phosphorus); an n-type
InP cladding layer 12; a first gain region I having a first active
layer 13a which is formed of InGaAsP
(indium.gallium.arsenide.phosphorus) with a gain wavelength
.lamda..sub.1; and a second gain region II having a second active
layer 13b which is formed of InGaAsP with a gain wavelength
.lamda..sub.2 (<.lamda..sub.1).
[0024] Here, the gain wavelength is assumed to be a peak wavelength
of a desired longitudinal mode among oscillation wavelengths of a
plurality of longitudinal modes which will be described later. In
the present embodiment, wavelengths 1.55 .mu.m and 1.3 .mu.m used
in an optical pulse tester are used as examples of the gain
wavelengths .lamda..sub.1 and .lamda..sub.2 for explanation. In
addition, the gain wavelengths .lamda..sub.1 and .lamda..sub.2 may
be values in the range of 1.52.ltoreq..lamda..sub.1.ltoreq.1.58 and
1.28.ltoreq..lamda..sub.2.ltoreq.1.34, respectively.
[0025] Alternatively, any combination from the respective
wavelength ranges of 1.28 to 1.34, 1.47 to 1.50, 1.52 to 1.55, and
1.60 to 1.65 may be selected (in this case, they are selected such
that .lamda..sub.1>.lamda..sub.2 is satisfied. The unit is
.mu.m).
[0026] The first and second active layers 13a and 13b are disposed
along the guiding direction of light and are optically coupled by
the butt-joint method. In addition, the first and second active
layers 13a and 13b referred to herein include a multiplex quantum
well (MQW) structure and separate confinement heterostructure (SCH)
layers with the MQW structure interposed therebetween.
[0027] In addition, a p-type InP cladding layer 14 and a contact
layer 15, which is formed of p-type InGaAs
(indium.gallium.arsenide), are laminated in this order on top
surfaces of the first and second active layers 13a and 13b.
[0028] In addition, a lower electrode 16 is formed on the bottom
surface of the n-type semiconductor substrate 11 by vapor
deposition, and a first upper electrode 17a for a first gain region
I and a second upper electrode 17b for a second gain region II are
formed on the contact layer 15 by vapor deposition.
[0029] In addition, the semiconductor light emitting element 10 has
first and second light emitting end facets 10a and 10b formed by
cleavage, respectively. A high-reflection (HR) coat 18a is formed
on the first light emitting end facet 10a and a low-reflection (LR)
coat 18b is formed on the second light emitting end facet 10b, such
that the reflectance with respect to light emitted from the second
light emitting end facet 10b is lower than the reflectance with
respect to light emitted from the first light emitting end facet
10a.
[0030] Here, it is preferable that the reflectance of the first
light emitting end facet 10a formed with the HR coat 18a is set to
90% or more and the second light emitting end facet 10b formed with
the LR coat 18b is set to about 1 to 10%.
[0031] Moreover, in the second gain region II of the n-type InP
cladding layer 12, a diffraction grating 20 having a Bragg
wavelength .lamda..sub.g of 1.3 .mu.m and a coupling coefficient
.kappa. of 100 cm.sup.-1 or more is formed near a butt-joint
coupling portion 19 between the first and second active layers 13a
and 13b.
[0032] In addition, the diffraction grating 20 may be formed in a
lower portion of the second active layer 13b as shown in FIG. 1, or
may be formed within the p-type InP cladding layer 14 above the
second active layer 13b (not shown). In addition, the diffraction
grating may also be formed near the first light emitting end facet
10a of the first gain region I.
[0033] A method of manufacturing the semiconductor light emitting
element with such a structure is disclosed in detail in Patent
Document 2.
[0034] The light emitting element driving circuit 2 has a function
of applying a driving current between a corresponding upper
electrode and a lower electrode in order to make light with a
desired wavelength oscillate and also has a function of
short-circuiting other upper electrodes to the lower electrode
(described in detail later).
[0035] Next, a driving method of the semiconductor light emitting
element 10 in the light emitting device 50 of the present
embodiment configured as described above will be described.
[0036] First, the operation will be described. When a driving
current is applied between the first upper electrode 17a for the
first gain region I and the lower electrode 16, the inside of the
first active layer 13a has a light emitting state. Light with a
wavelength of about 1.55 .mu.m generated in the first active layer
13a is not absorbed in the second active layer 13b which has a gain
wavelength of 1.3 .mu.m and is not reflected by the diffraction
grating 20 which has the Bragg wavelength .lamda..sub.g of 1.3
.mu.m, and propagates through the first and second active layers
13a and 13b. The light with a wavelength of about 1.55 .mu.m
generated in the first active layer 13a oscillates in a plurality
of longitudinal modes of about 1.55 .mu.m and is emitted from the
second light emitting end facet 10b which is formed with the LR
coat 18b, in the resonator formed by the first and second light
emitting end facets 10a and 10b.
[0037] As described above, when a driving current is applied
between the first upper electrode 17a for the first gain region I
and the lower electrode 16, the inside of the first active layer
13a has a light emitting state. However, since the isolation
resistance between the first and second upper electrodes 17a and
17b is limited, a portion of the current leaks into the second
active layer 13b.
[0038] Therefore, in the driving method of the present invention,
when emitting light in the first gain region I, the second upper
electrode 17b and the lower electrode 16 are made to be
short-circuited as shown in FIG. 1. As a result, since optical
absorption caused by carriers when a leakage current from the first
gain region I flows through the second gain region II is
suppressed, the laser beam output efficiency based on light
emission of the first gain region I is improved.
[0039] As shown in FIG. 6, this greatly improves the saturation
conditions of 1.55 .mu.m light output especially at the time of a
high current. Accordingly, a high-output operation is realized.
Since an output of 200 mW or more from the second light emitting
end facet is obtained, high performance of 35 dB or more is
obtained as a dynamic range when this is used for an optical time
domain reflectometer which is a representative example of the
optical pulse tester.
[0040] On the other hand, when a driving current is applied between
the second upper electrode 17b for the second gain region II and
the lower electrode 16 as shown in FIG. 2, the inside of the second
active layer 13b has a light emitting state.
[0041] Light with a wavelength of about 1.3 .mu.m generated in the
second active layer 13b propagates through the second active layer
13b. Since 90% or more of this 1.3 .mu.m light is reflected by the
diffraction grating 20 which has a Bragg wavelength .lamda..sub.g
of 1.3 .mu.m, optical absorption in the first active layer 13a with
a gain wavelength of 1.55 .mu.m is suppressed. Therefore, the light
with a wavelength of about 1.3 .mu.m generated in the second active
layer 13b oscillates in a plurality of longitudinal modes of about
1.3 .mu.m and is emitted from the second light emitting end facet
10b formed with the LR coat 18b in the resonator formed by the
diffraction grating 20 and the second light emitting end facet
10b.
[0042] In this case, most of the light with a wavelength of about
1.3 .mu.m generated in the second active layer 13b is hardly
incident on the first active layer 13a. Accordingly, the effect
obtained by short-circuiting the first upper electrode 17a as shown
in FIG. 6 becomes smaller than that in the above case.
[0043] As described above, in the driving method of the
semiconductor light emitting element in the light emitting device
of the present embodiment, the saturation of an optical output is
suppressed by short-circuiting the other upper electrode to the
lower electrode when applying a driving current between one upper
electrode and the lower electrode. As a result, a high optical
output can be realized. In particular, by short-circuiting an upper
electrode for a short wavelength when making light with a long
wavelength oscillate, a large effect can be acquired.
Second Embodiment
[0044] A second embodiment of the light emitting device related to
the present invention will be described with reference to the
accompanying drawings. The same configuration as in the first
embodiment will not be described. In the present embodiment,
wavelengths 1.625 .mu.m, 1.55 .mu.m, and 1.3 .mu.m used in an
optical pulse tester are used as examples of the gain wavelengths
.lamda..sub.1, .lamda..sub.2, and .lamda..sub.3 for explanation. In
addition, the gain wavelengths .lamda..sub.1, .lamda..sub.2, and
.lamda..sub.3 may be values in the range of
1.60.ltoreq..lamda..sub.1.ltoreq.1.65,
1.52.ltoreq..lamda..sub.2.ltoreq.1.58, and
1.28.ltoreq..lamda..sub.3.ltoreq.1.34, respectively.
[0045] Alternatively, any combination from the respective
wavelength ranges of 1.28 to 1.34, 1.47 to 1.50, 1.52 to 1.55, and
1.60 to 1.65 may be selected (in this case, they are selected such
that .lamda..sub.1>.lamda..sub.2>.lamda..sub.3 is satisfied.
The unit is .mu.m).
[0046] FIGS. 3 and 4 are views showing the second embodiment of the
light emitting device related to the present invention. A light
emitting device 51 is configured to include a semiconductor light
emitting element 30 and a light emitting element driving circuit
2.
[0047] As shown in FIGS. 3 and 4, the semiconductor light emitting
element 30 includes a first gain region I having a first active
layer 33a which is formed of InGaAsP with a gain wavelength
.lamda..sub.1 of 1.625 .mu.m, a second gain region II having a
second active layer 33b which is formed of InGaAsP with a gain
wavelength .lamda..sub.2 of 1.55 .mu.m, and a third gain region III
having a third active layer 33c which is formed of InGaAsP with a
gain wavelength .lamda..sub.3 of 1.3 .mu.m.
[0048] The first, second, and third active layers 33a, 33b, and 33c
are disposed in this order along the guiding direction of light and
are optically coupled by the butt-joint method. In addition, the
first, second, and third active layers 33a, 33b, and 33c referred
to herein include an MQW structure and SCH layers with the MQW
structure interposed therebetween.
[0049] In addition, a lower electrode 16 is formed on the bottom
surface of the n-type semiconductor substrate 11 by vapor
deposition, and a first upper electrode 37a for a first gain region
I, a second upper electrode 37b for a second gain region II, and a
third upper electrode 37c for a third gain region III are formed on
the contact layer 15 by vapor deposition.
[0050] In addition, the semiconductor light emitting element 30 has
first and second light emitting end facets 30a and 30b formed by
cleavage, respectively. Similar to the first embodiment, an HR coat
18a is formed on the first light emitting end facet 30a, and an LR
coat 18b is formed on the second light emitting end facet 30b.
[0051] Moreover, in the second gain region II of the n-type InP
cladding layer 12, a diffraction grating 40a having a Bragg
wavelength .lamda..sub.ga of 1.55 .mu.m and a coupling coefficient
.kappa. of 100 cm.sup.-1 or more is formed near a butt-joint
coupling portion 39a between the first and second active layers 33a
and 33b. Here, the pitch of the diffraction grating 40a is about
0.24 .mu.m.
[0052] Similarly, in the third gain region III of the n-type InP
cladding layer 12, a diffraction grating 40b having a Bragg
wavelength .lamda..sub.gb of 1.3 .mu.m and a coupling coefficient
.kappa. of 100 cm.sup.-1 or more is formed near a butt-joint
coupling portion 39b between the second and third active layers 33b
and 33c.
[0053] In addition, the diffraction gratings 40a and 40b may be
formed in lower portions of the second and third active layers 33b
and 33c as described above and as shown in FIG. 2, or may be formed
within the p-type InP cladding layer 14 above the second active
layer 33b and (or) the third active layer 33c (not shown). In
addition, the diffraction grating may also be formed near the first
light emitting end facet 30a of the first gain region I.
[0054] Next, a driving method of the semiconductor light emitting
element 30 in the light emitting device 51 of the present
embodiment configured as described above will be described.
[0055] First, the operation will be described. As shown in FIG. 3,
when a driving current is applied between the first upper electrode
37a for the first gain region I and the lower electrode 16, the
inside of the first active layer 33a has a light emitting state.
Light with a wavelength of about 1.625 .mu.m generated in the first
active layer 33a is not absorbed in the second active layer 33b
which has a gain wavelength of 1.55 .mu.m and the third active
layer 33c which has a gain wavelength of 1.3 .mu.m and is not
reflected by the diffraction grating 40a with the Bragg wavelength
.lamda..sub.ga of 1.55 .mu.m and the diffraction grating 40b with
the Bragg wavelength .lamda..sub.gb of 1.3 .mu.m, and propagates
through the first, second, and third active layers 33a, 33b, and
33c. The light with a wavelength of about 1.625 .mu.m generated in
the first active layer 33a oscillates in a plurality of
longitudinal modes of about 1.625 .mu.m and is emitted from the
second light emitting end facet 30b formed with the LR coat 18b, in
the resonator formed by the first and second light emitting end
facets 30a and 30b.
[0056] As described above, when a driving current is applied
between the first upper electrode 37a for the first gain region I
and the lower electrode 16, the inside of the first active layer
33a has a light emitting state. However, since the isolation
resistance between the first and second upper electrodes 37a and
37b is limited, a portion of the current leaks into the second
active layer 33b.
[0057] Therefore, in the driving method of the present invention,
when emitting light in the first gain region I, the second upper
electrode 37b and the lower electrode 16 are made to be
short-circuited. As a result, since optical absorption caused by
carriers when a leakage current from the first gain region I flows
through the second gain region II is suppressed, the laser beam
output efficiency based on light emission of the first gain region
I is improved. Although the third upper electrode 37c may also be
short-circuited to the lower electrode 16 in addition to
short-circuiting the second upper electrode 37b to the lower
electrode 16, it is clear that it is important to short-circuit the
second upper electrode 37b adjacent to the first gain region I in
order to achieve the effect.
[0058] This significantly suppresses the saturation of 1.625 .mu.m
light output especially at the time of a high current. Accordingly,
a high-output operation is realized.
[0059] On the other hand, when a driving current is applied between
the second upper electrode 37b for the second gain region II and
the lower electrode 16 as shown in FIG. 4, the inside of the second
active layer 33b has a light emitting state. Since 90% or more of
light with a wavelength of about 1.55 .mu.m generated in the second
active layer 33b is reflected by the diffraction grating 40a which
has a Bragg wavelength .lamda..sub.ga of 1.55 .mu.m, optical
absorption in the first active layer 33a with a gain wavelength of
1.625 .mu.m can be suppressed. In addition, light with a wavelength
of about 1.55 .mu.m generated in the second active layer 33b is not
absorbed in the third active layer 33c with a gain wavelength of
1.3 .mu.m and is not reflected by the diffraction grating 40b with
the Bragg wavelength .lamda..sub.gb of 1.3 .mu.m, and propagates
through the second and third active layers 33b and 33c. The light
with a wavelength of about 1.55 .mu.m generated in the second
active layer 33b oscillates in a plurality of longitudinal modes of
about 1.55 .mu.m and is emitted from the second light emitting end
facet 30b formed with the LR coat 18b in the resonator formed by
the diffraction grating 40a and the second light emitting end facet
30b.
[0060] Also in this case, the third upper electrode 37c is
short-circuited to the lower electrode 16, as described in the
first embodiment, in order to suppress a leakage current to the
third active layer 33c, through which light moves back and forth,
as a part of the resonator. This greatly improves about 1.55 .mu.m
light wavelength light output especially at the time of a high
current. Although the first upper electrode 37a may also be
short-circuited to the lower electrode 16 simultaneously, the
effect is larger when short-circuiting the third upper
electrode.
[0061] On the other hand, when a current is applied between the
third upper electrode 37c for the third gain regions III and the
lower electrode 16, the inside of the third active layer 33c has a
light emitting state (not shown).
[0062] Since 90% or more of light with a wavelength of 1.3 .mu.m
generated in the third active layer 33c is reflected by the
diffraction grating 40b which has a Bragg wavelength .lamda..sub.gb
of 1.3 .mu.m, optical absorption in the first active layer 33a with
a gain wavelength of 1.625 .mu.m and the second active layer 33b
with a gain wavelength of 1.55 .mu.m can be suppressed. The light
with a wavelength of about 1.3 .mu.m generated in the third active
layer 33c oscillates in a plurality of longitudinal modes of about
1.3 .mu.m and is emitted from the second light emitting end facet
30b formed with the LR coat 18b in the resonator formed by the
diffraction grating 40b and the second light emitting end facet
30b. Therefore, the optical output is improved by short-circuiting
the first upper electrode 37a and the second upper electrode 37b as
described in the first embodiment, but the effect is small.
Moreover, in this case, it is needless to say that short-circuiting
the second upper electrode 37b adjacent to the third gain region
III is important.
[0063] As described above, in the driving method of the
semiconductor light emitting element in the light emitting device
of the present embodiment, the saturation of an optical output is
suppressed by short-circuiting other upper electrodes to the lower
electrode when applying a driving current between one upper
electrode and the lower electrode. As a result, a high optical
output can be realized. In particular, by short-circuiting an
adjacent upper electrode for a short wavelength when making light
with a long wavelength oscillate, a large effect can be
acquired.
Third Embodiment
[0064] The light emitting devices 50 and 51 of the first and second
embodiments capable of making light beams with wavelengths in a
plurality of different wavelength ranges oscillate in a plurality
of longitudinal modes can be used as light sources of the optical
pulse tester. Hereinafter, an embodiment of the optical pulse
tester using the light emitting devices 50 and 51 will be described
with reference to the accompanying drawings.
[0065] As shown in FIG. 5, an optical pulse tester 55 of a third
embodiment includes: a light emitting section 1 that has the
semiconductor light emitting elements 10 and 30 and a light
emitting element driving circuit 2', which applies a pulsed driving
current for emitting a optical pulse to the semiconductor light
emitting elements 10 and 30, and that is a light emitting device
which outputs to an optical fiber to be measured 3 the optical
pulse emitted from the second light emitting end facets 10b and 30b
of the semiconductor light emitting elements 10 and 30; a light
receiving section 4 that converts returned light of the optical
pulse from the optical fiber to be measured 3 into an electric
signal; and a signal processor 5 which analyzes the loss
distribution characteristic of the optical fiber to be measured 3
on the basis of the electric signal converted by the light
receiving section 4.
[0066] The light emitting element driving circuit 2' in the third
embodiment applies a pulsed driving current unlike the light
emitting element driving circuit 2 in the first and second
embodiments.
[0067] In addition, the signal processor 5 controls a timing at
which the light emitting element driving circuit 2' applies a
driving current to the semiconductor light emitting elements 10 and
30.
[0068] In addition, the optical pulse tester 55 of the present
embodiment includes an optical coupler 7, which outputs the optical
pulse from the light emitting section 1 to a band pass filter (BPF)
6 and also outputs the returned light from the optical fiber to be
measured 3 to the light receiving section 4, an optical connector 8
for optical coupling to the optical fiber to be measured 3, and a
display section 9 which displays a processing result of the signal
processor 5.
[0069] Next, an operation of the optical pulse tester 55 of the
present embodiment configured as described above will be described.
In addition, in the following explanation, the optical pulse tester
55 of the present embodiment is assumed to include the
semiconductor light emitting element 10.
[0070] First, a pulsed driving current is applied to the first gain
region I (or the second gain region II) of the semiconductor light
emitting element 10 by the light emitting element driving circuit
2', and the second upper electrode 17b (or the first upper
electrode 17a) is short-circuited to the lower electrode 16. Then,
an optical pulse of about 1.55 .mu.m (or about 1.3 .mu.m) is output
from the light emitting section 1.
[0071] In this case, upper and lower electrodes are short-circuited
in a gain region where light is not emitted.
[0072] In addition, the optical pulse output from the light
emitting section 1 is incident on the optical fiber to be measured
3 through the optical coupler 7, the BPF 6, and the optical
connector 8. The optical pulse incident on the optical fiber to be
measured 3 becomes returned light and is received in the light
receiving section 4 through the optical coupler 7.
[0073] The returned light is converted into an electric signal by
the light receiving section 4 and is then input to the signal
processor 5. Then, the loss distribution characteristic of the
optical fiber to be measured 3 is calculated by the signal
processor 5. The calculated loss distribution characteristic is
displayed on the display section 9.
[0074] As described above, since the optical pulse tester 55 of the
present embodiment includes the semiconductor light emitting
element capable of making light beams with wavelengths in a
plurality of different wavelength ranges oscillate with a high
optical output using one element, miniaturization and high
performance can be realized.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
[0075] 1: light emitting section (light emitting device) [0076] 2,
2': light emitting element driving circuit [0077] 3: optical fiber
to be measured [0078] 4: light receiving section [0079] 5: signal
processor [0080] 10, 30: semiconductor light emitting element
[0081] 10a, 30a: first light emitting end facet [0082] 10b, 30b:
second light emitting end facet [0083] 13a, 33a: first active layer
[0084] 13b, 33b: second active layer [0085] 18a: high-reflection
(HR) coat [0086] 18b: low-reflection (LR) coat [0087] 19, 39a, 39b:
butt-joint coupling portion (interface) [0088] 20, 40a, 40b:
diffraction grating [0089] 33c: third active layer [0090] 50, 51:
light emitting device [0091] 55: optical pulse tester
* * * * *