LD/PD module

Details LD/PD module LD/PD module

2001-11-15

2003-08-05

Davie, James (Department: 2828)

Coherent light generators

Particular temperature control

Heat sink

C385S049000, C385S088000

Reexamination Certificate

active

06603782

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an LD/PD module for optical communications, in particular, aims at proposing a low-cost, small sized LD/PD module. Sometimes a term “optical communication device” is used for signifying an LD/PD module, an LD module and a PD module collectively in this description. LD/PD modules having both a transmitting (LD) part and a receiving (PD) part are suffering from the problem of the invasion of electric and optical signals of the transmitting portion into the receiving portion. The phenomenon of the flow of electrical/optical signals from the LD to the PD is called “crosstalk”. The signals generated by the LD are noise for the PD portion. The crosstalk should be excluded from the PD portion.
This application claims the priority of Japanese Patent Application No.2000-372295 filed on Dec. 7, 2000 which is incorporated herein by reference.
The crosstalk includes electrical crosstalk and optical crosstalk. Size-reduction of LD/PD modules enhances the crosstalk by bringing the PD closer to the LD. Miniaturization of LD/PD modules requires exclusion of the electrical/optical crosstalk. The purpose of the present invention is to propose low-cost, compact optical communication modules by suppressing the optical/electrical crosstalk.
2. Description of Related Art
FIG. 1
shows one of the most prevalent LD/PD modules. A laser diode (LD) as a light source is stored in a cylindrical, metallic package. A photodiode (PD) is also stored in another cylindrical, metallic package. The LD module
1
and the PD module
2
are connected via optical fibers
3
and
4
with a central station (not shown in the figures). Pins
9
and
9
fix the LD module
1
and the PD module
2
to a print circuit board
5
and connect the LD
1
and the PD
2
to some of the wiring patterns on the board
5
. The print circuit board
5
maintains a transmitting circuit
6
and a receiving circuit
7
.
A metallic shield plate
8
stands at a boundary between the transmitting circuit
6
and the receiving circuit
7
for suppressing electric crosstalk from the transmitting circuit
6
to the receiving circuit
7
. The metallic shield plate
8
which is grounded (connected to the earth level on the circuit board) absorbs electromagnetic noise. The metallic packages prohibit light of the LD
1
from leaking and forbid the PD
2
from receiving the LD light. The LD/PD device of
FIG. 1
succeeds in lowering electrical/optical crosstalk between the LD and the PD.
The LD/PD device having a discrete structure of
FIG. 1
has drawbacks of forbidding further size/cost-reduction. The metal-packaged LD module
1
and the metal-packaged PD module
2
are large and expensive. The print circuit board
5
for mounting the transmitting circuit
6
and the receiving circuit
7
is wide. The discrete LD/PD module of
FIG. 1
has attained to the limit of reducing the size and alleviating the cost. Still further size/cost reduction of LD/PD modules is indispensable for the prevalence of the optical communications systems.
A promising candidate is a planar type module preparing a silicon bench having V-grooves and an insulating overcoat, producing metallized wiring patterns on the silicon bench, mounting PD/LD chips on the patterns and fitting optical fibers into the V-grooves for facing the front ends to the PD and the LD. The planar type module is proposed by, e.g.,
{circle around (1)} R. Takahashi, K. Murakami, Y Sunaga, T. Tokoro, M. Kobayashi, “Packaging of optical semiconductor chips for SFF optical transceiver”, PROCEEDINGS OF THE 1999 ELECTRONICS SOCIETY CONFERENCE OF IEICE, C-3-28, p133 (1999).
FIG. 2
shows the plan view of the module proposed by {circle around (1)}. A SiO
2
insulating layer
11
is made upon a rear portion of a flat silicon substrate
10
. Two parallel V-grooves
12
and
13
are formed upon a front portion of the silicon substrate. A transmitting fiber
14
and receiving fiber
15
are fitted into the V-grooves
12
and
13
on the substrate. Metallized patterns
16
,
18
and
19
are printed upon the insulating layer
11
of the substrate
10
. An LD chip
22
is mounted upon the pattern
18
. A PD chip
23
is mounted upon the pattern
19
. A monitoring PD
70
is fitted upon the pattern
16
behind the LD
22
.
The LD makes transmitting light signals S which are in proportion to the driving current. The LD chip emits the light signals from both the front end and the rear end. The forward transmitting light signals S propagate in the transmitting fiber
14
to the central station. The rear light is detected by the PD
70
which always monitors the average power of the LD. The receiving light signals R which have been generated in the central station propagate in the receiving fiber
15
and go into the PD
23
. The PD
23
makes photocurrent which is in proportion to the receiving light signals. An upper half above a dotted line
26
is a transmitting portion (B) and a lower half below the dotted line
26
is a receiving portion (C). Both the portions B and C are built upon the common silicon substrate
11
which is far smaller than the print circuit board
5
of FIG.
1
.
The planar type module has advantages over the discrete one of FIG.
1
. The V-grooves
12
and
13
, the PD/LD mounting patterns
18
and
19
and the monitoring PD mounting pattern
16
can be made on the silicon bench
10
at a stroke. The fibers
14
and
15
, the LD and the PD can be exactly positioned by the grooves or marks without positive alignment, which is called “passive alignment”. Unification of the tiny silicon bench allows the module to reduce the size and the cost. The size/cost-reduction will raise an industrial value of the tiny on-silicon planar module.
The planar module mounting electronic devices, optoelectronic devices and fibers in two dimensions on the bench are an excellent and promising technique. The use of the silicon single crystal substrate enables device makers to employ the well-matured silicon photolithography technics. The photolithography can either form the V-grooves with a narrow spacing on the silicon substrate and position PDs and LDs at the determined spots with preciseness.
On the contrary, the PD module and the LD module of
FIG. 1
require active alignment of searching the optimum spots of the PD and the LD by supplying current to the LD, guiding the LD light via the fiber to the PD, measuring the power, displacing the LD and maximizing the output power. The active alignment which should determined the optimum spots for the LD with a ±1 &mgr;m tolerance and for the PD with a ±5 &mgr;m tolerance requires much time and high cost.
The planar type module shown by
FIG. 2
which mounts the fibers and the device chips on the silicon bench dispenses with the time-consuming, costly active alignment. The module determines the positions of the optoelectronic devices (LDs, PDs) by referring to the marks printed on the Si bench (substrate) and the positions of the fibers by the grooves. The mounting mode without the alignment step is called “passive alignment”. The planar type module has a possibility of alleviating the cost by eliminating the time-consuming alignment.
The passive alignment enables the planar type modules to position optoelectronic devices (LDs, PDs) and electronic devices (AMPs) to the optimum spots with sufficient coupling efficiency by referring to the marks printed on the silicon substrate without lightening the LDs and detecting the light by the PDs. The planar type communications modules are promising technology which will accomplish high precision mounting without active alignment.
Another advantage of the planar type modules is the grooves formed on the silicon substrates for mounting optical fibers. In the case of the LD/PD modules which exchange signals with e.g., the central station via two parallel optical fibers, formation of V-grooves which has the spacing equal to the standardized fiber spacing will enhance the productivity and cut the cost down. Despite the promising prospects, the pl

Affiliated with

Also associated with

Rating

LD/PD module does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with LD/PD module, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and LD/PD module will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3093719