JPS5922425B2 - Laser diode extinction ratio control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a laser diode extinction ratio control circuit that simultaneously provides stability of optical output and stability of photoelectrically converted pulse output.

(Applicable technology) Figure 1 shows a system diagram of a conventional laser diode optical output control circuit.

In Figure 1, LDM is a laser diode mount, LD is a laser diode, PD is a photodiode, c is a capacitor, A is an amplifier circuit that amplifies the electrical output of PD, and Ab is the output of A and the variable resistor RV. CCb is a circuit that compares and amplifies the reference potential given by the laser diode LD.
A constant current circuit CCp supplies a pulse current I to the laser diode LD via a high speed switching circuit SW.
Constant current circuit that supplies p, OPT, OUT is optical output, S
in is a modulation input, the top is configured like a power supply, and the second
The figure is an explanatory diagram of the operation. In Figure 2, P is the optical output, I is the laser diode current (IB+Ip), Ti,
T2 is the temperature of the laser diode, IBI is the bias current of the laser diode LD at temperature Ti, IB2
is the bias current of the laser diode LD at temperature T2, Ip is the pulse current turned ON10FF by a high-speed switching circuit that operates according to the modulation input Sin, P
ave is the average light output, plmax is the maximum light output at temperature Ti, P, min are the minimum light output at temperature Ti,
P, max is the maximum light output at temperature T2, P, min
is the minimum optical output at temperature T2, and the optical output is composed of a photo diode PDl amplifier circuit A1 comparison amplifier circuit Abl constant current circuit CCb so that the average output Pave is always constant even if the temperature of the laser diode LD changes. Output control loop operates.

The change in optical output P versus laser diode current shown in Figure 2 is a case in which the change in optical output P versus laser diode current is parallel to the temperature, but the change in optical output P versus laser diode current shown in Figure 3 is In the case of a laser diode that has a characteristic that the change in output P does not move parallel to the temperature, the average optical output does not change even if the temperature changes, but the photoelectrically converted pulse component becomes smaller as the temperature rises.

(PlmaX-Plmin>P2mBx-P2min)
Therefore, in an optical output control circuit in which the laser diode pulse current 1p is constant and the DC bias current 1b is varied, if the change in laser diode current 1 versus optical output P does not move parallel to the temperature, There was a drawback that the photoelectrically converted pulse output changed with temperature (extinction ratio changed).

(Problem to be solved by the invention) The present invention is characterized by controlling both the DC bias Ib of the laser diode and the amplitude of the pulse current 1p, and its purpose is to control the amplitude of the optical output and the photoelectrically converted pulse output so that the amplitude does not fluctuate (quenching This will be explained in detail below.

(Structure and operation of the invention) FIG. 4A is a system diagram of an embodiment of the present invention, where LDM is a laser diode mount, LD is a laser diode, PD is a photo diode, and A is an electrical output of the PD. SHb is a sample-and-hold circuit that samples and holds the output of amplifier circuit A when the photoelectric conversion output is minimum, and SHp is the amplifier circuit A when photoelectric conversion output is maximum.
A sample-and-hold circuit that samples and holds the output of
RVp is a variable resistor that generates a reference voltage Vp, Ab is a sample hold circuit SHb
a comparison amplifier circuit that compares and amplifies the output of and a reference voltage Vb;
Ap is a comparison amplification circuit that compares and amplifies the output of the sample-and-hold circuit SHp and the reference voltage Vp, and CCb is a laser beam that supplies a bias current 1b proportional to the output of the comparison amplification circuit Ab.
The constant current circuit CCp supplies the diode LD with a pulse current 1p whose amplitude is proportional to the output of the comparison amplifier circuit AP (
The constant current circuit that supplies the laser diode LD (via the high-speed switching circuit SW), SW receives the modulation input Sin and converts the current 1p supplied from the constant current circuit CCp to 0N/
A high-speed switching circuit that turns 0FF and supplies it to the laser diode LD.Sin is a modulation input, 0PT and 0UT are optical outputs, and 1E is a power supply.

Figure 4B is an explanatory diagram of the operation of the pulse generation circuit SPG, where a is the waveform of the modulation input Sin, and b is the sample given to the sample-and-hold circuit SHb that samples and holds the output on the extinction side (when the photoelectric conversion output is minimum).・Pulse waveform, c
samples the output of the light emitting side (when the photoelectric conversion output is maximum).
This is the waveform of a sample pulse given to the sample hold circuit SHp.

Figure 5 is an explanatory diagram of the operation of Figure 4A, where P is the optical output, I is the laser diode current (Ib + Ip), Tl and T2 are the laser diode temperatures, Ibl is the bias current at temperature T1, and Ib2 is the temperature. Bias current at T2,
IPl is a pulse current at temperature T1, IP2 is temperature T
2, Pave is the average optical output, Plm
ax is the maximum light output at temperature T1, P, m formula is temperature T
2, Plmin is the minimum optical output at temperature T1, and P2min is the minimum optical output at temperature T2.

It has been shown that even if the temperature fluctuates, the maximum luminous output and the minimum luminous output do not change (the extinction ratio does not change), and neither the average output nor the photoelectrically converted pulse output changes. At minimum light output, photo diode PDl amplifier circuit A1 sample/hold circuit SHb, comparison amplifier circuit Ab
The minimum light output is stabilized by the light output control circuit consisting of the constant current circuit CCbl, and at the maximum light output, the photo diode PDl amplifier circuit A1 sample-and-hold circuit SHPl comparison amplifier circuit APl constant current circuit CCPl high-speed switching This is because the maximum light emission output is stabilized by the light output control circuit constituted by the circuit SW. Fourth
FIG. 6 specifically shows each part of the system diagram in FIG.

The amplifier circuit A is composed of a resistor R1 and an operational amplifier A1.
Comparison amplifier circuit Ab consists of resistors R2, R3} and operational amplifier A.
Consists of 2. The comparison amplifier circuit Ap is composed of resistors R4 and R5 and an operational amplifier A3. The constant current circuit CCb is composed of an operational amplifier A4, transistors TRl} and R6. The constant current circuit CCp is composed of an operational amplifier A5, a transistor TR4, and a resistor R7. The high-speed switching circuit SW is composed of transistors TR2, TR3, inverter INVl resistors R8, R9, capacitors Cl, C2}, and bias power supply -Eb, and the modulation input signal Sin
When the pulse of is positive polarity, TR2 is 0N. ．． TR3 is 0F
When F1 is negative polarity, TR2 is 0FF, . TR3 becomes 0N, and the current supplied from the constant current circuit CCp flows through TR3 instead of the current flowing through TR2. That is, the modulated input signal Si
A pulse current 1p controlled by n is supplied to the laser diode LD. The pulse generating circuit SPG is a monostable multi-vibrator MMl that performs up-edge operation,
Monostable multi-vibrator M with down edge operation
It is composed of M2, MM3, and MM4, and its operation is as shown in FIG. A, b, c, d, and e in FIG. 7 correspond to those in FIG. 6, and Tl, t2, t3, and t4 are MMl and M, respectively.
These are the time constants of M2, MM3, and MM4. (Effects of the Invention) As explained above, the embodiment has a light output control loop that operates at the minimum light emission time and a light output control loop that operates at the maximum light emission time, so the extinction ratio of the laser diode can be kept constant, and the light output control loop operates at the maximum light emission time. There is an advantage that the output can be stabilized and the amplitude of the photoelectrically converted pulse output can be stabilized at the same time.

In addition to the stability of temperature vs. optical output, the present invention has good stability of temperature vs. photoelectrically converted pulse amplitude (extinction ratio does not fluctuate).
It has advantages and can be used in laser diode drive circuits of optical transmission devices.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a conventional laser diode optical output control circuit, Figures 2 and 3 are diagrams explaining the operation of Figure 1, and Figure 4
Figure A is a system diagram of an embodiment of the present invention, and Figure 4B is Figure 4Af.
) Figure 5 is a diagram explaining the operation of the SPG, Figure 5 is a diagram explaining the operation of Figure 4A, Figure 6 is a specific circuit diagram of Figure 4A, and Figure 7 is a diagram explaining the operation of the SPG in Figure 6. . LDM...Laser diode mount, LD...
・Laser diode, PD...photo diode, 0PT, 0UT...light output, Ib, Ibl, Ib2
...Bias current, IP, IPl, IP2...Pulse current, A...Photoelectric conversion output amplification circuit, Ab, Ap...
...Comparison amplifier circuit, CCb, CCp...constant current circuit,
SW...High speed switching circuit, C, Cl, C2...
・Capacitor, Sin...Modulation signal input, -E, -E
b...Power supply, P...Optical output, PllnO, p2ma
x...Maximum optical output, Plmin, p2min...Minimum optical output, Pave...Average optical output, Tl, T2...
・Laser diode temperature, I...Laser diode current (Ib+Ip), SHb, SHp...Sample and hold circuit, SPG...Pulse generation circuit, RV
, RVb, RVp...Variable resistor, Vb, Vp...゜Reference voltage, Rl, R2, R3, R4, R5, R6, R7
, R8, R9...Resistor, TRl, TR2, TR3,
TR4...transistor, MMl, MM2, MM3,
MM4...monostable multi-pipelator, Tl9t2
9t39t4I''3MMLMM2PMM3 and MM4 time constants.

Claims (1)

[Claims] 1. In a laser diode pulse modulation circuit that generates a laser beam corresponding to an input pulse signal Sin, an optical signal proportional to the optical outputs OPT and OUT of the laser diode LD is received and converted into an electrical signal. A photoelectric conversion element PD,
a sample and hold circuit SHp that samples and holds the output of the photoelectric conversion element PD when the photoelectric conversion output is maximum;
a sample and hold circuit SHb that samples and holds the output of the photoelectric conversion element PD when the photoelectric conversion output is minimum;
a pulse generation circuit SPG that receives a modulation input signal Sin and supplies sample pulses b and c to the sample and hold circuits SHp and SHb; and a sample and hold circuit SH
a circuit Ab that compares and amplifies the output of Vb and a reference voltage Vb;
A circuit Ap that compares and amplifies the output of the sample-and-hold circuit SHp and a reference voltage Vp, and a first constant current circuit CCb that supplies a bias current Ib proportional to the output of the comparison amplifier circuit Ab to the laser diode LD. Amplifier circuit Ap
A modulated pulse current Ip with an amplitude proportional to the output of the laser
The second constant current circuit CCp supplies the diode LD and the second constant current circuit CCp supplies the input pulse signal Sin.
1. A laser diode extinction ratio control circuit comprising: a high-speed switching circuit SW for controlling a laser diode extinction ratio control circuit. 2. The high-speed switching circuit SW has a differential transistor switching circuit, the first and second constant current circuits are composed of operational amplifier transistors, and the pulse generation circuit includes two sets of two-stage connected monostable multivibrators. A laser diode extinction ratio control circuit according to claim 1, wherein the photoelectric conversion element is a photodiode.