Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2001-06-07
2002-10-15
Davie, James (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
Reexamination Certificate
active
06466595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to laser diode systems and, more specifically, to a laser diode driver circuit which provides an automatic power control (APC) for a laser diode for use in laser diode systems such as a photo pickup, an optoelectronic transceiver, etc.
2. Description of the Prior Art
As is well known in the art, the laser diode changes in the driving current-to-optical output power characteristic due to temperature variation or aging. For this reason, there have been proposed various techniques of feedback controlling the current flowing through a laser diode on the basis of an error or difference between a reference value and a detected value of the optical output power emitted by the laser diode so as to keep constant the extinction ratio, i.e., the ratio between the maximum output power at the time of light emitting operation of the laser diode and the minimum output power at the time of light extinguishing operation of the laser diode. Hereinafter, the level of the maximum output power, which corresponds to binary ones, is referred to as the peak level; and the level of the minimum output power, which corresponds to binary zeros, is referred to as the bottom level.
One of such techniques is disclosed, for example, in Japanese patent publication No. 2,856,247 (1998).
FIG. 1
is a diagram showing the arrangement of a prior art laser diode (LD) driving circuit
0
of the APC method disclosed in the publication. In
FIG. 1
, the LD driving circuit comprises: an LD
1
; a monitoring photodiode
2
so positioned and oriented as to be optically coupled with LD
1
to produce a photo-current Ipd; a current-to-voltage (C/V) converter
3
for converting the photo-current Ipd into a detected voltage Vo, which is directly proportional to the optical power transmitted by LD
1
; a peak error detector
4
for providing a peak error signal indicative of the error or difference between a peak reference voltage Vpeak and each peak value Vop of the detected voltage Vo; a bottom error detector
5
for providing a bottom error signal indicative of the error or difference between a bottom reference voltage Vbottom and each bottom value Vob of the detected voltage Vo; a bias current driver
9
for supplying LD
1
with a bias current Ib of a level for an extinction operation of LD
1
; and a modulation current driver
8
for supplying LD
1
with a modulation current Im which, together with the bias current Ib, constitutes a driving current at the time of a light emitting operation of LD
1
.
Bias current driver
9
comprises a current source
91
having a control input terminal, which is supplied with the bottom error signal from the bottom error detector
5
, and accordingly having a capability of providing a bias current Ib variable in response to the bottom error signal. Modulation current driver
8
comprises: a differential pair of transistors
81
and
82
having their gates supplied with a differential pair of modulation signals Data and {overscore (Data)} and having their drains connected with the cathode terminal of LD
1
and the power supply Vcc, respectively; and a current source
83
having its take-in terminal connected with the source terminals of transistors
81
and
92
, its output terminal coupled to the ground, and its control input terminal supplied with the peak error signal from the peak error detector
4
, thereby to be capable of causing a current Ip variable in response to the peak error signal. Since modulation current driver
8
causes the current Ip to flow through LD
1
only when the modulation signal Data is high or logical “1”, a modulation signal Data of a low level or logical “0” will cause a driving current Ib to flow through LD
1
thereby to cause LD
1
to be inactive, and a modulation signal Data of the high level or logical “1” will cause a driving current Ib+Ip to flow through LD
1
thereby to cause LD
1
to radiate an optical energy. It is noted that the differential modulation signals Data and {overscore (Data)} are a pair of binary signals which change in a complementary manner between a higher level and a lower but non-zero level as shown by the two upper graphs in FIG.
13
.
A portion of the optical energy emitted from LD
1
is detected by photodiode
2
as a photo-current Ipd, which is converted by C/V converter
3
into a voltage Vo proportional to the emitted optical energy. The voltage Vo is supplied to the above-mentioned peak
4
and bottom
5
error detectors.
The peak error detector
4
comprises: a peak hold circuit
41
for detecting and holding the peak level Vop of the output voltage Vo from C/V converter
3
; an operational amplifier
42
; and a feed-back resistor
43
connected between the output terminal and the inverting input terminal of op-amp
42
. The non-inverting input terminal of op-amp
42
is connected with the node between serially connected resistors
11
and
12
spanning the power supply potential Vcc and the ground thereby to be supplied with a reference voltage Vpeak. Op-amp
42
has its inverting input terminal further coupled with the peak hold circuit
41
output Vop and its output terminal further connected with the control input of the current source
83
within modulation current driver
8
so as to supply a peak error signal based on the difference between the peak level Vop and the reference voltage Vpeak to the current source
83
control input. The magnitude of the current Ip which modulation current driver
8
flows through LD
1
is controlled such that the peak level (or envelope) Vop of the C/V converter
3
output Vo matches the reference voltage Vpeak, i.e., the peak error signal from op-amp
42
becomes zero in the level.
The bottom error detector
5
comprises: a bottom hold circuit
51
for detecting and holding the bottom level Vob of the output voltage Vo from C/V converter
3
; an operational amplifier
52
; and a feed-back resistor
53
connected between the output terminal and the inverting input terminal of op-amp
52
. The non-inverting input terminal of op-amp
52
is connected with the node between serially connected resistors
13
and
14
spanning the peak hold circuit
41
output Vop and the ground thereby to be supplied with a reference voltage Vbottom. Op-amp
52
has its inverting input terminal also coupled with the bottom hold circuit
51
output Vob and its output terminal also connected with the control input of the current source
91
within bias current driver
9
so as to supply a bottom error signal based on the difference between the bottom level Vob and the reference voltage Vbottom to the current source
91
control input. The magnitude of the bias current Ib which bias current driver
8
flows through LD
1
is controlled such that the bottom level Vob of the C/V converter
3
output Vo matches the reference voltage Vbottom, i.e., the bottom error signal from op-amp
52
becomes zero in the level.
In this way, the prior art LD driver provides such a control as continuously maintains constant peak and bottom output optical powers (or a constant extinction ratio) of LD
1
by changing the modulated current Ip and the bias current Ib supplied to LD
1
in response to the photo-current Ipd detected by photodiode
2
.
However, in the prior art LD driver, the bottom level or envelope of the output optical power emitted by LD
1
(i.e., the bias current Ib flowed by current source
91
of bias current driver
9
) is controlled to be constant on the basis of the reference voltage Vbottom into which the peak level Vop of the C/V converter
3
output Vo is divided. For this reason, it is only after the stabilization of the peak level of the output optical power of LD
1
(or the C/V converter
3
output Vo) that the bottom level of the output optical power (or the bottom reference voltage Vbottom) can be stabilized. Thus, the prior art LD driver has a problem of taking a significant start-up time till the bottom level of output optical power reaches a stable or stationary state.
Also, generally speaking, t
LandOfFree
Laser diode driving method and circuit which provides an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser diode driving method and circuit which provides an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser diode driving method and circuit which provides an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2993000