Radio frequency input device of superspeed optical...

Details Radio frequency input device of superspeed optical... Radio frequency input device of superspeed optical...

1999-11-05

2001-11-27

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S245000

Reexamination Certificate

active

06323986

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio frequency (RF) input device of a superspeed optical communications module which controls the performance of a module in the superspeed (2.5 Gbps, 10 Gbps) optical communications module.
2. Description of the Related Art
A 2.5/10 Gbps module, an essential component of superspeed optical communications, has drastically improved performance by changing the shape of a microstrip line used in the prior art, in order to improve characteristics such as 3 dB bandwidth and RF return loss, which are essential parameters of the module.
FIG. 1A
is a plan configuration view of an RF input device of a conventional superspeed optical communications module.
FIG. 1B
is an equivalent circuit diagram of the RF input device of FIG.
1
A. As shown in
FIGS. 1A and 1B
, an RF input device of a superspeed optical communications module includes a microstrip line pattern
5
of a constant width formed on a microwave substrate
6
. An electroabsorption modulated laser (EML) chip
9
comprised of a laser diode
9
a
and a modulator
9
b
is mounted on a thin film resistor
8
and an EML submount
10
. The microstrip line pattern
5
is connected to the thin film resistor
8
and the EML chip
9
by bonding wires
7
. Here, the bonding wire is usually an Au wire having a thickness of 1 mm, and the length thereof is as short as possible to minimize a generated inductance component. A thin film or chip resistor
8
having a resistance of 45 to 55&OHgr; is connected to the EML chip
9
to achieve impedance matching with the EML chip
9
.
Reference numeral
1
in
FIG. 1B
denotes an inductance component due to a bonding wire used within a module, reference numeral
2
denotes a 2.5 Gbps or 10 Gbps EML, and reference numeral
3
denotes a thin film resistor or chip resistor having a resistance of 45 to 55&OHgr; used to achieve impedance matching of a high speed module.
The microstrip line
5
is a metallic line formed so that the characteristic impedance simply matches with a resistance of 50&OHgr;. The thus-formed microstrip line
5
cannot solve degradation of module characteristics caused by the bonding wire
7
and a capacitance component formed in the EML chip
9
and other parts, and has an 8 GHz 3 dB bandwidth (|S
21
|) and an RF return loss (|S
11
|) of about 11 dB as shown in
FIG. 2
, so that it becomes a problem in high-speed transmission. That is, the microstrip line
5
does not meet a current specification of 15 dB or more, so that there is a problem in its operation at 10 Gbps. Also, a great deal of heat is generated due to simultaneous consumption of direct current and alternating current power in a resistance of 45 to 55&OHgr;.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a radio frequency (RF) input device of a super RF optical communications module whereby a 3 dB frequency bandwidth is improved and an RF return loss associated with impedance matching is improved, by changing the shape of a microstrip line which is an essential part.
Accordingly, to achieve the above object, the present invention provides a radio frequency (RF) input device of an optical communications module including: a microstrip line pattern comprised of an impedance matching area connected to an external circuit for achieving impedance matching, a capacitance area for generating a predetermined capacitance, and an inductance area for generating a predetermined inductance; an electroabsorption modulated laser connected to the inductance area in the microstrip line pattern; and a first thin film resistor for impedance matching connected between a connection point of the microstrip line pattern and the electroabsorption modulated laser and a ground point.
In the present invention, it is preferable that the resistance of the first resistor is 40 to 60&OHgr;. Preferably, the RF input device of an optical communications module further includes a bonding wire having an inductance of less than 2 nH between the first resistor and a node at which the electroabsorption modulated laser and the microstrip line pattern are connected to each other. Also, it is preferable that the inductance area and the capacitance area are formed so that the inductance and capacitance are between 0.01 nH and 1 nH and between 0.01 pF and 0.2 pF, respectively, and then are controlled according to the characteristics of a connected electroabsorption modulated laser.
Also, it is preferable that the RF input device of an optical communications module further includes a second thin film resistor connected in series to the modulator to improve the performance of the optical communications module; a bonding wire having an inductance of less than 2 nH between the second thin film resistor and the electroabsorption modulated laser; and two capacitors of 200 pF and 0.1&mgr;F connected in parallel to each other between the first thin film resistor and the ground point.


REFERENCES:
patent: 5184243 (1993-02-01), Henmi et al.
patent: 5371755 (1994-12-01), Murata et al.
patent: 5548607 (1996-08-01), Tsang
patent: 5790719 (1998-08-01), Mitomi et al.

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