Coherent light generators – Particular beam control device – Having particular beam control circuit component
Reexamination Certificate
1999-12-23
2001-08-28
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular beam control device
Having particular beam control circuit component
C372S029010, C372S029011, C372S029012, C372S034000, C372S038100, C372S038010, C372S038020, C372S038040, C372S038070
Reexamination Certificate
active
06282216
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a burst mode optical transmitter circuit for converting burst data into an optical signal to be transmitted.
With recent developments in multimedia communication techniques, optical communication of high speed and large capacity has been realized. In such an optical communication system, there are continuous data communication and burst data communication in a fiber-optic subscriber system. The present invention relates to a burst mode optical transmitter circuit for converting burst data into an optical signal to stably transmit the data.
2. Description of the Related Art
FIG. 15
is a diagram, for explaining a prior art example, in which
101
represents a semiconductor laser,
102
a monitoring photodiode,
103
a current-to-voltage converting circuit (I/V),
104
an automatic power control (APC) amplifier,
105
a driving circuit,
107
a holding circuit, D a diode, and C a capacitor.
The driving circuit
105
supplies a driving current to the semiconductor laser
101
according to input data DATA in the burst mode. The optical output of the semiconductor laser
101
is transmitted through a not-shown optical fiber to a receiving side. A part of the optical output is detected by the monitoring photodiode
102
. The detected output is converted by the current-to-voltage converting circuit
103
into a voltage and is input into the APC amplifier
104
. The APC amplifier
104
compares the signal output from the current-to-voltage converter
103
with a reference value and applies a signal corresponding to the difference obtained by the comparison to the holding circuit
107
.
The holding circuit
107
includes a diode D and a capacitor C to constitute a peak hold circuit. The value held by the capacitor C is applied as a current control signal to the driving circuit
105
whereby, when the optical output from the semiconductor laser
101
becomes larger than a predetermined value, the driving current supplied from the driving circuit
105
to the semiconductor laser
101
is decreased and, in contrast, when the optical output from the semiconductor laser
101
becomes smaller than a predetermined value, the driving current from the driving circuit
105
to the semiconductor laser
101
is increased. Thus the optical output is stabilized.
During an interrupt period of the data DATA input in the burst mode, the current control signal is held in the capacitor C in the holding circuit
107
. Accordingly, even when the data DATA is input, after the interrupt period, the output of the semiconductor laser
101
is immediately controlled to have a predetermined level so that an optical signal can be transmitted. That is, the holding circuit
107
holds the current control signal to be input into the driving circuit
105
during the interrupt period of the burst data.
The semiconductor laser
101
has a light output characteristic with respect to the driving current as shown in FIG.
16
. Because of this fact, the optical output can be stabilized as mentioned before. However, the light output characteristic is such that when the ambient temperature T or the temperature of the semiconductor laser
101
itself is lowered to be T
1
which is lower than T
2
as illustrated, the optical output is greatly increased even when the driving current is the same. To cope with this, a temperature compensating circuit to compensate for the temperature characteristic has been proposed to be implemented into the circuit.
When burst data is converted into an optical signal and is transmitted, cases where the interrupt period of the burst data is relatively long may often occur. For example, when data DATA is input according to the burst mode as shown in
FIG. 17
, the LD current, i.e., the current to drive the semiconductor laser, is controlled by the above-mentioned control so that the optical output is made constant.
Then, when data is input again after an interrupt period of the data DATA, the ambient temperature may be changed, for instance, from day temperature to night temperature and so forth. In particular, when the temperature is lowered, and when the driving current is supplied from the driving circuit
105
to the semiconductor laser
101
based on the current control signal held in the holding circuit
107
, there is a problem in that the optical output from the semiconductor laser
101
is greatly increased so that the semiconductor laser
101
is destroyed.
In another prior art, an APC circuit is provided in which an optical output from a semiconductor laser is monitored to be sampled and held, the held value is compared with a reference value, and the result of the comparison is input into a control voltage supplying unit. In such an APC circuit, it has been proposed to provide a temperature compensating current generating unit and a temperature compensating voltage generating unit as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 9-260720. In this case, the current corresponding to the ambient temperature is generated from the temperature compensating current generating unit and is input into the temperature compensating voltage generating unit by which the current is converted into a voltage which is then input to the control voltage supplying unit. This APC circuit, however, has a problem of complex construction and therefore of being expensive.
In still another prior art, there has been provided an APC circuit in which an optical output from a semiconductor laser is monitored to be sampled and held, the held value is compared with a reference value, and the driving current of the semiconductor laser is controlled by the compared result. In this APC circuit, the sample and hold circuit is reset at the time of turning on or off of the power supply so as to prevent an erroneous operation of the APC circuit, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-131675. This prior art, however, does not relate to the transmission of burst data, and the above-mentioned problem which is caused when the temperature is changed in an interrupt period of the burst data, and the means to solve the problem are not disclosed in this prior art.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a burst optical transmission apparatus in which the optical transmission can be performed stably with a simple construction even when the ambient temperature is changed during a relatively long interruption in burst data.
To attain the above object, there is provided, according to a first aspect of the present invention, a burst mode optical transmitter circuit comprising: a semiconductor laser for converting data input in a burst mode into an optical signal; a photodiode for monitoring the light output from the semiconductor laser; a current-voltage converting circuit for converting the current detected by the photodiode into a voltage; an APC amplifier for comparing the output signal from the current-voltage converting circuit with a reference value; a holding circuit for holding, as a current control signal, the output signal from the APC amplifier, and having a reset function to reset the held current control signal; a driving circuit for controlling, according to the current control signal held in the holding circuit and the data, the current to be supplied to the semiconductor laser; and a data interruption detecting circuit for detecting an interrupt period of the data input to the driving circuit to reset the holding circuit.
According to a second aspect of the present invention, the holding circuit may comprise a peak detecting circuit for detecting a peak value of the output signal from the APC amplifier, and a switching circuit for resetting the peak detecting circuit by the reset signal from the data interruption detecting circuit.
According to a third aspect of the present invention, the holding circuit may comprise a switching circuit for switching and holding the current control signal in response to the output signal from the APC amplifier and for sw
Ikeuchi Tadashi
Inoue Tadao
Matsuyama Toru
Takauji Toshiyuki
Ueno Norio
Arroyo Teresa M.
Fujitsu Limited
Menefee James
Staas & Halsey , LLP
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