U.S. patent application number 14/982503 was filed with the patent office on 2017-08-10 for laser apparatus with capacitor disposed in vicinity of laser diode.
This patent application is currently assigned to SUMITOMO ELECTRIC DEVICE INNOVATIONS, INC.. The applicant listed for this patent is SUMITOMO ELECTRIC DEVICE INNOVATIONS, INC.. Invention is credited to Yoshiki Oka.
Application Number | 20170225250 14/982503 |
Document ID | / |
Family ID | 46161277 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170225250 |
Kind Code |
A9 |
Oka; Yoshiki |
August 10, 2017 |
LASER APPARATUS WITH CAPACITOR DISPOSED IN VICINITY OF LASER
DIODE
Abstract
A laser assembly is disclosed. The laser assembly includes a
carrier for mounting a semiconductor laser diode (LD) and a
capacitor thereon. The carrier provides, in a top surface thereof,
a metal pattern having a die area for mounting the LD through a
brazing material, a mounting area, and an auxiliary area for
absorbing a surplus brazing material. The capacitor is mounted on
the mounting area closer to the LD through another brazing
material.
Inventors: |
Oka; Yoshiki; (Yokohama-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC DEVICE INNOVATIONS, INC. |
Yokohama-shi |
|
JP |
|
|
Assignee: |
SUMITOMO ELECTRIC DEVICE
INNOVATIONS, INC.
Yokohama-shi
JP
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20160129513 A1 |
May 12, 2016 |
|
|
Family ID: |
46161277 |
Appl. No.: |
14/982503 |
Filed: |
December 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13311064 |
Dec 5, 2011 |
|
|
|
14982503 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 35/262 20130101;
B23K 35/3013 20130101; H01L 2224/48091 20130101; H01L 2924/19107
20130101; B23K 3/0623 20130101; H01S 5/042 20130101; H01L
2224/48091 20130101; B23K 3/087 20130101; H01L 2924/00014 20130101;
B23K 1/0016 20130101; H01S 5/02256 20130101 |
International
Class: |
B23K 1/00 20060101
B23K001/00; B23K 35/26 20060101 B23K035/26; B23K 35/30 20060101
B23K035/30; H01S 5/022 20060101 H01S005/022; H01S 5/042 20060101
H01S005/042 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2010 |
JP |
2010-270799 |
Claims
1. A laser assembly comprising: a carrier; a metal pattern provided
on the carrier, the metal pattern including a die area, a mounting
area, and an auxiliary area, the die area and the auxiliary area
being provided with a brazing material; a semiconductor laser diode
(LD) mounted on the die area through the brazing material; and a
capacitor mounted on the mounting area through another brazing
material apart from the brazing material.
2. The laser assembly of claim 1, wherein the auxiliary area
extends substantially in parallel to the mounting area.
3. The laser assembly of claim 1, wherein the another brazing
material has a melting point lower than a melting point of the
brazing material.
4. The laser assembly of claim 3, wherein the brazing material is
gold-tin (AuSn), and the another brazing material is tin-antimony
(SnSb).
5. The laser assembly of claim 1, wherein the metal pattern stacks
titanium (Ti), platinum (Pt), and gold (Au).
6. The laser assembly of claim 1, wherein the carrier is made of
aluminum nitride.
7. A method to assemble a laser assembly, comprising steps of:
forming a metal pattern on a carrier, the metal pattern including a
die area, a mounting area, and an auxiliary area; depositing a
brazing material only on the die area and the auxiliary area of the
metal pattern; mounting a semiconductor laser diode (LD) on the die
area as absorbing a surplus brazing material in the auxiliary area;
applying another brazing material on the mounting area so as not to
be in contact with the brazing material; and mounting a capacitor
on the mounting area as interposing the another brazing material
between the mounting area and the capacitor.
8. The method of claim 7, wherein the process of mounting the
capacitor is performed at a temperature lower than a temperature
under which the process of mounting the LD is performed.
9. The method of claim 8, wherein the brazing material is gold-tin
(AuSn), and wherein the process of mounting the LD includes a
process of heating the carrier over 280.degree. C. and placing the
LD on the brazing material.
10. The method of claim 9, wherein the another brazing material is
tin-antimony (SnSb), and wherein the process of mounting the
capacitor includes a process of heating the carrier over
240.degree. C. but below 280.degree. C. and placing the capacitor
on the another brazing material.
11. The method of claim 7, wherein the process of depositing the
brazing material includes a process to evaporate the brazing
material by a thickness of 4 to 6 .mu.m.
12. The method of claim 7, wherein the process of applying the
another brazing material includes processes of: performing one of
processes of heating the carrier up to a temperature lower than a
temperature under which the process of mounting the LD on the die
area is carried out and placing a grain of the another brazing
material on the mounting area, and spreading the grain within the
mounting area not so as to be in contact with the brazing material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuous-in-part of a pending U.S.
patent application Ser. No. 13/311,064 filed Dec. 5, 2011 by Oka
for METHOD FOR FABRICATING OPTICAL SEMICONDUCTOR DEVICE, which is
hereby incorporated herein by reference in their entirety. This
patent application also claims priority to Japanese Patent
Application No. 2014-162643, filed Aug. 8, 2014, which is also
hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present application relates to a laser apparatus
comprising a semiconductor laser diode (LD) and a bypassing
capacitor disposed in a vicinity of the LD.
[0004] 2. Background Arts
[0005] In an optical communication system, an advanced technique to
utilize a phase of signal light has become popular to bring further
communication capacity. Such an optical communication system is
often called as the coherent communication system. FIG. 7
schematically illustrates an arrangement of an optical signal
source 100 used in the coherent communication system. The optical
signal source 100 shown in FIG. 7 provides an LD 102 biased with a
DC power supply 101 and an optical modulator 103. The LD 102 emits
continuous-wave (CW) light L11, and the optical modulator 103
modulates the CW light L11 to output a modulated light L12. The
optical signal source 100 sometimes installs a wavelength tunable
LD as the LD 102 disclosed in, for instance, the U.S. Pat. No.
7,362,782.
[0006] The LD 102 implemented in the optical signal source 100 is
strongly requested to generate the CW light with line width thereof
as narrower as possible. Electrical noises superposed on the bias
provided to the LD 102 degrade the line width. The DC power supply
101 inherently causes noises, but the bias line 104 sometimes
superposes noises by the electro-magnetic interference (EMI), in
particular, noises with high frequencies. A bias line for supplying
a DC bias usually accompanies with bypassing capacitors against the
ground. However, the bypassing capacitor is necessary to be
connected to the LD as close as possible because, when a
substantial bias line is left between the LD and the bypassing
capacitor, the left bias line causes noises. In particular, when
the optical modulator 103 modulates the CW light L11 by modulation
signals whose frequency reaches and sometimes exceeds 10 GHz, the
left bias line between the LD and the bypassing capacitor is
further preferable as short as possible.
SUMMARY OF THE INVENTION
[0007] One aspect of the present application relates to a laser
assembly that comprises a carrier, a metal pattern provided on the
carrier, an LD, and a capacitor. The metal pattern includes a die
area, a mounting area, and an auxiliary area. The die area and the
auxiliary area are provided with a brazing material. The LD is
mounted on the die area through the brazing material. A feature of
the laser assembly of the present application is that the capacitor
is mounted on the mounting area through another brazing material
that is apart from the brazing material.
[0008] Another aspect of the present application relates to a
method to assemble a laser assembly. The method includes steps of:
(1) forming a metal pattern on a carrier, where the metal pattern
includes a die area, a mounting area, and an auxiliary area; (2)
depositing a brazing material only on the die area and the
auxiliary area of the metal pattern; (3) mounting an LD on the die
area as absorbing a surplus brazing material in the auxiliary area;
(4) applying another brazing material on the mounting area so as
not to be in contact with the brazing material; and (5) mounting a
capacitor on the mounting area as interposing the another brazing
material between the mounting area and the capacitor.
BRIEF DESCRIPTION OF DRAWINGS
[0009] The foregoing and other purposes, aspects and advantages
will be better understood from the following detailed description
of a preferred embodiment of the invention with reference to the
drawings, in which:
[0010] FIG. 1 is a plan view of a laser assembly according to the
first embodiment of the present application;
[0011] FIG. 2 shows a cross section taken along the ling II-II
denoted in FIG. 1;
[0012] FIG. 3A is a plan view showing a process to assemble the
laser assembly according to an embodiment of the present
application, and FIG. 3B is a plan view showing a process
subsequent to the process of FIG. 3A;
[0013] FIG. 4A is a plan view showing a process to assembly the
laser assembly subsequent to the process shown in FIG. 3B, and FIG.
4B is a plan view of a process subsequent to the process shown in
FIG. 4A;
[0014] FIG. 5 shows a cross section of a conventional laser
assembly;
[0015] FIG. 6 is a plan view of a laser module that implements a
laser assembly shown in FIG. 1;
[0016] FIG. 7 schematically illustrates a circuit diagram of an
optical transmitter for a coherent communication system; and
[0017] FIG. 8 schematically shows a cross section an LD to be
assembled in a laser assembly shown in FIG. 1.
DESCRIPTION OF EMBODIMENTS
[0018] Next, some embodiments according to the preset application
will be described as referring to drawings. In the description of
the drawings, numerals or symbols same with or similar to each
other will refer to elements same with or similar to each other
without duplicating explanations.
[0019] FIG. 1 is a plan view of a laser assembly according to the
first embodiment of the present invention, and FIG. 2 shows a cross
section of a laser assembly 1 taken along the ling II-II appearing
in FIG. 1. The laser assembly 1 of the present embodiment, as shown
in FIGS. 1 and 2, provides a carrier 2 including a plurality of
metal patterns, 3 to 11, on a top surface thereof, a semiconductor
laser diode (LD) 12, a thermistor 13, a capacitor 14, and a
plurality of bonding wires, W.sub.1 to W.sub.9.
[0020] The carrier 2, which may be made of inorganic material such
as aluminum oxide (AlOx), aluminum nitride (AlN), and so on,
provides the metal patterns, 3 to 11, on a top surface 2a thereof.
The LD 12, the thermistor 13, and the capacitor 14 are mounted on
the metal patterns, and the bonding wires, W.sub.1 to W.sub.9,
connect the metal patterns, 3 to 11, to the LD 12 and the
thermistor 13. Although not illustrated in FIG. 2, the carrier 2
may provide a back metal on a back surface 2b opposite to the top
surface 2a, where the back metal may be a ground electrode.
[0021] The metal patterns, 3 to 11, may be made of stacked metal
coated or plated with gold (Au) and/or platinum (Pt) in the top of
the metal stack. The present embodiment provides the metal
patterns, 3 to 5, with stacked metals of titanium (Ti), platinum
(Pt), and gold (Au). Respective metal patterns, 3 to 11, supply
electronic power for heaters, which will be described later, bias
voltages, and bias currents to the LD 12. Specifically, the metal
pattern 3 provides the ground, while, the metal pattern 4 supplies
the bias current. The metal pattern 3, namely the ground pattern,
comprises die area 3a, a mounting area 3b, an auxiliary area 3c,
and a pad 3d. The die area 3a mounts the LD 12 thereon. The
mounting area 3b, which extends from the die area 3a substantially
in parallel to the auxiliary area 3c, mounts the capacitor 14. The
pad 3d is connected to the outside of the laser assembly to provide
the ground potential.
[0022] The LD 12 of the present embodiment has a type of, what is
called, a wavelength tunable LD having an optical axis extending in
parallel to an optical waveguide implemented within the LD 12. The
LD 12 may output light, whose wavelength may be tuned by supplying
the bias voltage and/or the bias current through the metal
patterns, 3 to 11, from the facet perpendicular to the optical
axis. The LD 12 is mounted on the die area 3a through a brazing
material 15. FIG. 1 denotes the brazing material 15 by hatched area
that covers the whole die area 3a and the auxiliary area 3c. The
brazing material 15 may be a solder made of eutectic metal or
electrically conductive resin. The LD 12 may provide a back metal
to be grounded through the brazing material on the metal pattern
3.
[0023] The LD 12 may include a semiconductor optical amplifier
(SOA) region, a gain region, and a tuning region along the optical
axis thereof. The SOA, which amplifies light generated by the gain
region, includes an electrode 21 to supply a bias current into the
SOA. The electrode 21 is connected to the metal pattern 5 by
bonding wires, W.sub.1 and W.sub.2. The gain region, which
generates light to be amplified in the SOA, provides an electrode
22 to supply a bias current into the gain region. The electrode 22
is connected to the metal pattern 4 through bonding wires, W.sub.3
and W.sub.4. The tuning region, which may tune the wavelength of
the light generated in the gain region, provides electrodes, 23 to
26, each connected to the metal patterns, 6 to 9, by respective
bonding wires, W.sub.5 to W.sub.8. The electrode 26 extending along
the optical axis within the whole tuning region is common to other
electrodes, 23 to 25. Although not shown in FIG. 1, several heaters
are provided between the electrodes, 23 to 25, and the common
electrode 26. The metal patterns, 6 to 8, supply the power to
respective heaters to tune the wavelength of the light generated in
the gain region. Thus, the wavelength of the light output from the
LD 12 through the facet may be tuned.
[0024] The thermistor 13 may sense a temperature of the top surface
2a of the carrier 2. The power supplied to respective heaters in
the tuning region may be controlled depending on the temperature of
the top surface 2a sensed by the thermistor 13. The thermistor 13
in one electrode thereof faces and comes in contact with the metal
pattern 10, and in another electrode thereof is connected to
another metal pattern 11 through the bonding wire W.sub.9.
[0025] The capacitor 14 is a type of a bypassing capacitor
connected in parallel to the LD 12 between the metal patterns, 3
and 4. The capacitor 14 provides two electrodes, one of which is
mounted on the mounting area 3b of the metal pattern 3, while, the
other is mounted on the metal pattern 4 each through respective
brazing materials, 16 and 17. The brazing materials, 16 and 17, for
mounting the capacitor 14 preferably has a melting temperature
lower than a melting temperature of the other brazing material 15
for mounting the LD 12 onto the die area 3a. In the present
embodiment, the former brazing material 16 on the mounting area 3b
is apart from the latter brazing material 15 on the die area 3a
even after the mount of the capacitor 14, that is, the metal
pattern 3 is exposed in the top surface thereof between the brazing
materials, 15 and 16.
[0026] FIG. 8 is a schematic cross-sectional diagram of the whole
configuration of an LD 12 to be mounted on an optical semiconductor
device according to a first embodiment. As illustrated in FIG. 8,
the LD 12 includes an SOA (Semiconductor Optical Amplifier) region
C; an SG-DFB (Sampled Grating Distribution Feedback) region A; and
a CSG-DBR (Chirped Sample Grating Distributed Reflector) region B,
where they are optically coupled in this order. The SG-DFB region A
and the CSG-DBR region B operate as a wavelength selection portion
to tune an emission wavelength, and the SOA region C has a function
to amplify laser light generated in the SG-DFB region A.
[0027] The SG-DFB region A includes a lower cladding layer 12b, an
active layer 12c, an upper cladding layer 12f, a contact layer 12g
and an electrode 12h, where they are stacked on a substrate 12a.
The CSG-DBR region B includes the lower cladding layer 12b, an
optical waveguide layer 12d, the upper cladding layer 12f, an
insulating layer 12j and heaters 12k, where they are also stacked
on the substrate 12a. Each of the heaters 12k provides a power
supply electrode 12m and a ground electrode 12n. The SOA region C
includes the lower cladding layer 12b, an optical amplification
layer 12t, the upper cladding layer 12f, a contact layer 12u and an
electrode 12v, where they are also stacked on the substrate
12a.
[0028] The substrate 12a, the lower cladding layer 12b and the
upper cladding layer 12f are common in the SG-DFB region A, the
CSG-DBR region B and the SOA region C, that is, the lower cladding
layer 12b and the upper cladding layer 12f are concurrently formed
at the same time. The active layer 12c, the optical waveguide layer
12d, and the optical amplification layer 12t are formed on the same
plane of the top surface of the lower cladding layer 12b. An AR
(Anti Reflection) layer 12q is formed on a facet of the substrate
12a, the lower cladding layer 12b, the active layer 12c and the
upper cladding layer 12f on the side of the SOA region C. The AR
layer 12q acts as a front facet of the LD 12. A reflection layer
12r is formed on a facet of the substrate 12a, the lower cladding
layer 12b, the optical waveguide layer 12d, and the upper cladding
layer 12f on the side of the CSG-DBR region B. The reflection layer
12r acts as a rear facet of the LD 12.
[0029] A plurality of diffraction gratings (corrugations) 12s are
formed in the lower cladding layer 12b of the SG-DFB region A and
the CSG-DBR region B with a preset interval. The SG-DFB region A
and the CSG-DBR region B have a plurality of segments. One segment
comprises of a portion having the diffraction grating 12s and
another portion next to the former portion without the diffraction
grating 12s. The diffraction grating 12s is made of a material
having a refractive index different from that of the lower cladding
layer 12b.
[0030] In the CSG-DBR region B, at least two of the segments have
lengths different from others. Thus, magnitudes of each of
reflection peaks attributed to the CSG-DBR region B depends on a
wavelength. On the other hand, each optical length of the segments
in the SG-DFB region A is substantially equal to each other.
Therefore, magnitudes of each of gain peaks attributed to the
SG-DFB region A shows independent on a wavelength. Using a Vernier
effect between the SG-DFB region A and the CSG-DBR region B, that
is, coinciding one of the reflection peaks attributed to the
CSG-DBR region B with one of the gain peaks attributed to the
SG-DFB region A, an emission wavelength of the LD 12 may be tuned.
Thus, the LD 12 may stably oscillate at the thus tuned
wavelength.
[0031] The substrate 12a may be made of, for example, n-type InP.
The lower cladding layer 12b has the n-type conductivity. The upper
cladding layer 12f has the p-type conductivity. The lower cladding
layer 12b and the upper cladding layer 12f may be, for example,
made of InP. The lower cladding layer 12b and the upper cladding
layer 12f confines light within the active layer 12c, the optical
waveguide layer 12d and the optical amplification layer 12t.
[0032] The active layer 12c is made of semiconductor material
showing an optical gain by the carrier injection. The active layer
12c may have the quantum well structure, in particular, a multi
quantum well structure (MQW), in which a plurality of well layers
each made of Ga.sub.0.32In.sub.0.68As.sub.0.92P.sub.0.08 having a
thickness of 5 nm and a plurality of barrier layers each made of
Ga.sub.0.22In.sub.0.78As.sub.0.47P.sub.0.53 having a thickness of
10 nm are alternately stacked.
[0033] The optical waveguide layer 12d may be, for example, made of
bulk semiconductor material of
Ga.sub.0.22In.sub.0.78As.sub.0.47P.sub.0.53.
[0034] The contact layer 12g may be, for example, made of p-type
Ga.sub.0.47In.sub.0.53As. The insulating layer 12j is a protection
layer and may be made of an insulator such as SiN or SiO.sub.2. The
heater 12k is a type of the thin film resistor made of NiCr. Each
heater 12k may extend over the several segments in the CSG-DBR
region B.
[0035] The electrodes 12h, the power supply electrode 12m and the
ground electrode 12n are made of conductive material such as Au
(gold). A back electrode 12p, namely, the back metal, is formed on
a back surface of the substrate 12a. The back electrode 12p may be,
for example, made of Au (gold). The back electrode 12p extends over
the SG-DFB region A, the CSG-DBR region B and the SOA region C,
that is, the back electrode 12p is provided in a whole back surface
of the LD 12.
[0036] The optical amplification layer 12t shows an optical gain is
by the current injection from the electrode 12v. The optical
amplification layer 12t may also have the MQW structure including
alternately stacked well layers made of
Ga.sub.0.35In.sub.0.65As.sub.0.99P.sub.0.01 with a thickness of 5
nm and barrier layers made of
Ga.sub.0.15In.sub.0.85As.sub.0.32P.sub.0.68 with a thickness of 10
nm. The optical amplification layer 12t may be a bulk semiconductor
material of Ga.sub.0.44 In.sub.0.56As.sub.0.95P.sub.0.05 The
contact layer 12u may be, for example, made of p-type
Ga.sub.0.47In.sub.0.53As.
[0037] Next, an operation of the LD 12 will be described. Under a
stable condition, that is, a predetermined driving current is
provided to the electrode 12h, each heater 12k generates heat at a
predetermined temperature, and the temperature of the LD 12 is set
in a predetermined temperature; the SG-DFB region A and the CSG-DBR
region B tune one wavelength, and the LD 12 oscillates at the tuned
wavelength. The laser light is optically amplified and output from
a front facet (on the side of the SOA region C).
[0038] Next, a process to assemble the laser assembly 1 will be
described as referring to FIGS. 3A to 4B of the plan views of the
carrier 2.
[0039] First, the process forms the metal patterns, 3 and 4, on the
top surface 2a of the carrier 2 as shown in FIG. 3A which
schematically shows the metal patterns. The process may form the
metal patterns, 3 and 4, by patterning a metal or stacked metals
deposited on the top surface 2a by, for instance, the metal
evaporation, or may form metal patterns, 3 and 4, by the selective
deposition of a metal or stacked metals. Next, the process may
selectively evaporate tin (Sn) and gold (Au) on the die area 3a and
the auxiliary area 3c as the brazing material 15 (FIG. 3B). The
AuSn film deposited on the metal pattern may have the composition
of gold (Au) to be about 70% and a thickness thereof around 5
.mu.m, preferably 4 to 6 .mu.m.
[0040] Then, the LD 12 is mounted on the die area 3a (FIG. 4A).
Specifically, heating the carrier 2 over 280.degree. C., preferably
up to 280 to 300.degree. C., the assembling process may place the
LD 12 on thus heated brazing material 15. The brazing material 15
may operate not only as an adhesive to fix the LD 12 but to secure
an electrically conductive path from the LD 12 to the ground
pattern 3. The auxiliary area 3c attributed to the die area 3a may
effectively absorb surplus solder 15 oozing out from a gap between
the metal pattern 3 and the LD 12 such that oozed brazing material
does not invade into the mounting area 3b due to the surface
tension of the brazing material. The mounting area 3b shows lesser
wettability for the melted brazing material 15 compared with the
auxiliary area 3c. Accordingly, the surplus brazing material 15
oozed out from the gap stays within the area where the brazing
material 15 exists.
[0041] Then, the process assembles the capacitor 14 on the metal
pattern 3 (FIG. 4B). Specifically, melting and spreading other
brazing materials, 16 and 17, on respective metal patterns 3 and 4;
the capacitor 14 is mounted on thus spread brazing materials, 16
and 17. During the melt and the spread of the brazing materials 16,
the brazing material 16 is effectively prevented from merging
together with the brazing material 15 spread in advance for
mounting LD 12. In an example, solder made of tin-antimony (SnSb)
is selected and melted at a temperature over 240.degree. C.,
preferably 260.degree. C., on the metal patterns 3 and 4. Because
of the lowered temperature for mounting the capacitor 14, the
former brazing material 15 for mounting the LD 20 is not melted at
all. In the process thus described, two brazing materials, 15 and
16, are spread independently in respective steps, that is, the
brazing material 15 is first spread in the die area 3a then the
other brazing material 16 is spread in the mounting area. After
mounting the capacitor 14, the bonding wire W.sub.3 is extended
from the LD 12 to the metal pattern 4, which configures a parallel
circuit of the LD 12 and the capacitor 14 between the metal
patterns, 3 and 4.
[0042] Next, advantageous reflecting within the laser assembly 1
will be described as comparing with a conventional arrangement.
FIG. 5 shows a cross section of a laser assembly 200 having a
conventional arrangement with respect to the LD 12 and the
capacitor 14. In the conventional arrangement, although not
explicitly illustrated in FIG. 5, the metal pattern 3, especially
the die area 3a does not accompany with the auxiliary area 3c,
which means that, when the LD 12 is set on the brazing material 15,
surplus portion 15a thereof oozes in all directions as shown in
FIG. 5. In particular, the LD 12 of the present embodiment arranges
the SOA region, the gain region, and the tuning region along the
optical axis thereof, which means that the LD 12 has an enough
slender plane shape. When such a slender chip is die bonded on the
carrier 2, an enough brazing material 15, namely, eutectic solder,
is required for bonding the chip securely. As a result, relatively
greater surplus solder oozes out in all directions. In the
conventional laser assembly, the metal patterns surrounding the die
area 3a are necessary to set a substantial space, sometimes wider
than 100 .mu.m, to the die area 3a for preventing the oozed solder
from coming in contact to the metal patterns, which inevitably
expands the size of the carrier 2. Also, such oozed surplus solder
forces a space between the LD 12 and the capacitor 14, which is
unfavorable from the viewpoint of the high speed operation of the
LD 12.
[0043] On the other hand, the LD assembly 1 of the present
embodiment provides the auxiliary area 3c next to the die area 3a
in the metal pattern 3. The auxiliary area 3c, where the brazing
material 15 is spread in advance to the mount of the LD 12, may
effectively absorb the surplus solder, namely, the brazing material
15 oozed out from the gap between the LD 12 and the metal pattern 3
so as to prevent the surplus solder 15 from spreading into the
mounting area 3b and coming in contact with the metal patterns
surrounding the die area 3a. Accordingly, the metal patterns
surrounding the die area 3a may be put closer to the die area
3a.
[0044] Moreover, the assembling process of the LD assembly uses
another brazing material, 16 and 17, namely, another eutectic alloy
for mounting the capacitor 14 on the mounting area 3b. The other
brazing material, 16 and 17, has the melting point lower than the
melting point of the former brazing material 15 to mount the LD 12.
Thus, the brazing material 16 may be spread close enough to the
brazing material 15 spread in advance, and the brazing material 15,
or the mounted LD 12, is not influenced by the process to mount the
capacitor 14. Accordingly, the capacitor 14 is able to be mounted
close enough to the LD 12, specifically, within 5 to 10 .mu.m from
the LD 12, which shows an advantage for the high speed operation of
the LD 12.
[0045] Next, some examples using the laser assembly 1, in
particular, a laser module installing the laser assembly 1 will be
described. FIG. 6 is a plan view of a laser module 50 installing
the laser assembly 1. The laser module 50 includes, in addition to
the laser assembly 1, a wavelength locker including first and
second beam splitters (BS), 61 and 62, a wavelength filter 64, and
first and second photodiodes (PD), 71 and 72.
[0046] The laser assembly 1 is mounted on a thermo-electric cooler
(TEC) 53 through the carrier 2 accompanied with a collimating lens
52 and electrically communicate with the outside through a
feedthrough 54 that includes a plurality of terminals wire-bonded
with the metal patterns, 3 to 10, on the carrier 2. Also, the
wavelength locker is mounted on another TEC 63 through a carrier.
The laser assembly 1 with the TEC 53 and the wavelength locker with
another TEC are installed within a housing 51.
[0047] The light output from the LD 12 is first collimated by the
collimating lens 52, then, enters the first BS 61. The first BS 62
splits the light, one of split light goes to the output port,
while, the other of the split light, which is bent by about
90.degree. by the first BS 61 goes to the second BS. The split
ratio of the first BS is set to be around 95:5, namely, about 95%
of the collimated light goes to the output port and only 5% goes
ahead to the send BS 62.
[0048] The second BS 62 further splits the light by about 50:50.
One of the split light goes to the first PD, while, the rest goes
to the wavelength filter 64 which inherently has specific
transmittance. The second PD 72 detects the light output from the
wavelength filter 64. On the other hand, the first PD 71 may detect
raw beam output from the LD 12, which means that the light output
from the LD 12 but not affected from any specific optical
characteristic. Thus, calculating the ratio of the output from the
second PD 72 against the output from the first PD 71, the practical
transmittance of the wavelength filter 64 may be determined.
Comparing thus obtained transmittance with the practical
transmittance of the wavelength filter, the wavelength of the light
currently output from the LD 12 may be precisely determined.
[0049] When the current wavelength of the LD 12 thus determined is
different from a target wavelength of the LD 12, the biases
supplied to the LD 12 and the power also supplied to the heaters of
the LD 12 may be adjusted such that the current wavelength becomes
coincident with, or closer to, the target wavelength.
[0050] The wavelength filter 64 may be, what is called, an etalon
filter that inherently shows a periodic transmittance. Setting the
target wavelength to be a point, at which the periodic
transmittance of the etalon filter in a slope thereof becomes
large, the current wavelength of the LD 12 may be precisely matched
with the target wavelength because of the increased gain of the
feedback loop described above.
[0051] Even in the laser module 50, the capacitor 14 may be mounted
enough closer to the LD 12 in the mounting area 3b but apart from
the die area, which enables the side of the carrier 2 small enough.
The smaller carrier 2 results in small heat capacity on the TEC 53.
Accordingly, the convergence of the current wavelength on the
target wavelength may be accelerated.
[0052] While particular embodiments of the present invention have
been described herein for purposes of illustration, many
modifications and changes will become apparent to those skilled in
the art. For instance, the auxiliary area 3c for absorbing the
surplus brazing material 15 is not always to be brought out from
the die area 3a along a direction same with that of the mounting
area 3b. When the auxiliary area 3c extends perpendicular to the
die area 3a toward one direction and the mounting area 3b also
extends perpendicular to the die area 3a but toward another
direction opposite to the former one, that is, the auxiliary area
3c faces the mounting area 3b as putting the die area 3a
therebetween, the capacitor 14 may be mounted further closer to the
LD 12.
[0053] The embodiment uses the capacitor 14 having the type of,
what is called, a chip capacitor with two electrodes thereof
laterally disposed. However, the laser assembly 1 may use a
capacitor with the type of a die capacitor with two electrodes
thereof vertically disposed. For such an arrangement, the die
capacitor 14 is mounted on the mounting area 3b as the bottom
electrode thereof faces and comes in contact to the mounting area
3b, while, the top electrode thereof is connected to the metal
pattern 4 with a bonding wire. Accordingly, the appended claims are
intended to encompass all such modifications and changes as fall
within the true spirit and scope of this invention.
* * * * *