Optical communications – Optical communication over freee space – Compensation
Reexamination Certificate
2000-04-18
2003-11-11
Negash, Kinfe-Michael (Department: 2633)
Optical communications
Optical communication over freee space
Compensation
C398S135000, C398S197000
Reexamination Certificate
active
06647212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmitter receiver for performing optical communication over, for example, an optical transmission medium. More particularly, this invention is concerned with an optical transmitter receiver having a power-of-transmitted light control means for setting the power of light to be transmitted from the optical transmitter receiver to a proper value.
2. Description of the Related Art
An optical transmitter receiver in accordance with the present invention is configured as, for example, shown in FIG.
1
.
Referring to
FIG. 1
, paired optical transmitter receivers
1
a
and
1
b
are optically connected to each other over an optical fiber
3
, which is an optical transmission medium, between two apparatuses
2
a
and
2
b
. The optical transmitter receivers la and
1
b are connected to the apparatuses
2
a
and
2
b
with physical layer control apparatuses
4
a
and
4
b
between them.
The optical transmitter receivers
1
a
and
1
b
have the same configuration. The internal configuration of the optical transmitter receiver
1
b
shown on the right-hand side of
FIG. 1
is therefore not illustrated.
The optical transmitter receiver
1
a
shown on the left-hand side of
FIG. 1
will be described below.
Referring to
FIG. 1
, the optical transmitter receiver
1
a
consists of a transmitter
5
and a receiver
6
.
The transmitter
5
is, as illustrated, composed of a laser diode
5
a
that is a light emitting device, a drive circuit
5
b
for driving the laser diode
5
a
, and a shutdown circuit
5
c
for controlling driving performed by the drive circuit
5
b.
The laser diode
5
a
converts an input signal into a laser beam whose intensity is proportional to the level of the input signal, and transmits the laser beam to the other optical transmitter receiver
1
b
over the optical fiber
3
.
Moreover, the drive circuit
5
b
drives the laser diode
5
a
to luminescence according to transmission data Tx Data fed from the physical laser control unit
4
a.
The shutdown circuit
5
c
actuates the drive circuit
5
b
according to a transmission instruction signal Tx Enable fed from the physical layer control apparatus
4
a.
In contrast, the receiver
6
is, as shown in
FIG. 1
, composed of a photodiode
6
a
serving as a light receiving device, a current-voltage amplifier
6
b
, a post-amplifier
6
c
, a peak hold circuit
6
d
, and a signal detection circuit
6
e.
The photodiode
6
a
receives a light signal sent-from the other optical transmitter receiver
1
b
(shown on the right-hand side in the drawing) over the optical fiber
3
, and outputs an electric signal proportional to the light signal.
The current-voltage amplifier
6
b
amplifies an output signal of the photodiode
6
a.
The post-amplifier
6
c
amplifies an output signal of the current-voltage amplifier
6
b
, and transmits a resultant signal as reception data Rx Date to the physical layer control apparatus
4
a.
The peak hold circuit
6
d
detects the peak of the output signal of the current-voltage amplifier
6
b.
The signal detection circuit
6
d
detects a signal output from the peak hold circuit
6
d
and transmits a reception acknowledgement signal to the physical layer control apparatus
4
a.
The physical layer control apparatus
4
a
controls communications according to a protocol whose level is higher by one step than the protocol according to which the optical transmitter receiver
1
a
performs communications. Transmission data Tx Date and a transmission instruction signal Tx Enable are sent from the apparatus
2
a
to the optical transmitter receiver
1
a
. The optical transmitter receiver
1
a
transmits reception data Rx Data and a reception acknowledgement signal Rx SD to the apparatus
2
a.
When the optical transmitter receivers
1
a
and
1
b
have the foregoing components, if the apparatus
2
a
outputs transmission data to the associated physical layer control apparatus
4
a
, the physical layer control apparatus
4
a
feeds the transmission instruction signal Rx Enable to the shutdown circuit
5
c
in the transmitter
5
of the optical transmitter receiver
1
a
. Consequently, the drive circuit
5
b
is actuated.
When the physical layer control apparatus
4
a
feeds transmission data Tx Date to the drive circuit
5
b
in the transmitter
5
of the optical transmitter receiver
1
a
, the drive circuit
5
b
drives the laser diode
5
a
according to the transmission data. This causes the laser diode
5
a
to emit light whose intensity is proportional to the transmission data.
A laser beam emitted from the laser diode
5
a
included in the other optical transmitter receiver
1
b
falls on the photodiode
6
a
in the receiver
6
of the optical transmitter receiver
1
a
over the optical fiber
3
. This causes the photodiode
6
a
to output an electric signal proportional to the incident light. The electric signal is amplified by the current-voltage amplifier
6
b
, and then further amplified by the post-amplifier
6
c
. An output signal of the post-amplifier
6
c
is input as reception data Rx Data to the physical layer control apparatus
4
a
. An output signal of the current-voltage amplifier
6
b
has its peak detected by the peak hold circuit
6
d
. A reception acknowledgement signal Rx SD is input to the physical layer control apparatus
4
a
via the signal detection circuit
6
e
. The physical layer control apparatus
4
a
transmits reception data to the apparatus
2
a.
The internal configuration of the optical transmitter receiver
1
b
is identical to that of the optical transmitter receiver
1
a
. The apparatus
2
a
transmits transmission data Tx Data to the other apparatus
2
b
, and the other apparatus
2
b
transmits transmission data Tx Data to the apparatus
2
b
. Consequently, optical communication is performed between the apparatuses
2
a
and
2
b.
A description will be made of an optical fiber adopted as the optical fiber
3
and characterized by an optical transmission loss of 0.1 dB/m relative to any wavelength &lgr; of light to be transmitted, for example, 650, 780, 850, 1300, 1500, or 1550 nm.
Specifically, a plastic optical fiber is adopted. The sensitivity of the photodiode
6
a
is set to 0.5 A/W, and a gain to be produced by the current-voltage amplifier
6
b
is set to 4 k&OHgr;. A maximum amplitude of a signal that can be output from the current-voltage amplifier
6
a
is set to 1 Vp-p, and a minimum amplitude of a signal that can be input to the post-amplifier
6
c
is set to 0.2 Vp-p. In practice, for example, a silicon pin photodiode and a bipolar chip set will do.
Since the maximum output level of the current-voltage amplifier
6
b
is 1 Vp-p and the minimum input level of the post-amplifier
6
c
is
0
.
2
Vp-p, a dynamic range offered for an output of the current-voltage amplifier
6
b
is from 0.2 to 1.0 Vp-p.
Since a gain to be produced by the current-voltage amplifier
6
b
is 4 k&OHgr;, a dynamic range offered for an input of the current-voltage amplifier
6
b
is from 0.05 to 0.25 mAp-p.
Since the sensitivity of the photodiode
6
a
is 0.5 A/W, a dynamic range offered for an input of the photodiode
6
a
is from 0.1 to 0.5 mWp-p.
Assuming that light received by the optical transmitter receiver
1
a
or
1
b
falls on the photodiode with the power thereof 100% maintained, a dynamic range offered for received light by the optical transmitter receiver
1
a
or
1
b
is from 0.1 to 0.5 mWp-p.
Assume that the optical fiber
3
has lengths ranging from 0 to 70 m. In this case, when the power of light transmitted from the optical transmitter receiver
1
a
or
1
b
is 0.5 mWp-p, the power of light received by the other optical transmitter receiver
1
b
or
1
a
varies as expressed with a curve E in FIG.
2
. When the optical fiber
3
has a length of 0 m, the power of received light is 0.5 mWp-p. When the optical fiber
3
has a length of 70 m, the power of received light is 0.1 mWp-p. This range of powers agrees with the aforesaid dynamic range offered by the opti
Mogi Takayuki
Ookawa Sumihiro
Toriumi Yoichi
Yoshida Hideki
Negash Kinfe-Michael
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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