JPH022226A - Optical output stabilizing circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration in the optical output waveform against the fluctuation of the combination of mark rates by detecting each mark rate of 2 systems of data strings and using a sum signal of the detection signal so as to adjust a reference voltage, varying the bias current of a light emitting diode to adjust the optical output. CONSTITUTION:A mark rate detection circuit 16 consists of low pass filter comprising a resistor R1 and a capacitor C1 and a mark rate detection circuit 17 consists of low pass filter comprising a resistor R2 and a capacitor C2. An optical output detection circuit 15 consists of a photodiode PD, a resistor R and a capacitor C to extract a mean value and when the optical level is increased, an output VPD is lowered, and the optical level is decreased. When the optical level is decreased, the relation is opposite to above and then the constant control (APC) of the optical level is implemented in this way. The reference voltage of the APC is given by an offset circuit 19. The sum of outputs VMD1, VMD2, of the mark rate detection circuits 16, 17 revises the reference voltage to correct the mark rate.

Description

[Detailed Description of the Invention] [Summary of the Invention] Regarding an optical output stabilization circuit in an optical ternary transmission system, the optical output waveform is deteriorated even when the combination of mark rates of two data streams changes. The purpose of the present invention is to provide a light output stabilizing circuit which is equipped with a light emitting element having an automatic power control circuit, and which changes the light output in one direction with the first data string and in the opposite direction with the second data string. Change the light output to 1st. In an optical output stabilization circuit in an optical ternary transmission system that multiplexes a second data string, a circuit that detects a mark rate of a first data string, a circuit that detects a mark rate of a second data string; An adder circuit for the outputs of these detection circuits is provided, and the reference voltage of the automatic power control circuit is adjusted using the output of the adder circuit to compensate for the mark rate.

[Industrial application field]

The present invention relates to an optical output stabilizing circuit in an optical three-value transmission system.

Optical ternary transmission method (M-TPC: Modified Time) that multiplexes two data streams on optical output.
Polarity Control 1). Figure 5 shows the outline.

(a) is the original data and consists of two systems of data strings D1 and D2. In this example, the data string DI is 10110. Data string D2
is 10010, and the interval between solid lines is 1 bit of these data. (b) is the transmission data (optical output M-TPC) obtained by multiplexing these.If the first half (odd slot) of each 1-bit interval of the data string D1 is 1, it is a positive pulse, if it is 0, it is 0, and each of the data string D2 is If the second half (even numbered bit) of one bit interval is 1, a negative pulse is obtained, and if it is 0, a 0 is obtained.

In addition, in the optical output M-TPC, the above positive pulse has a large optical output,
0 is medium, negative pulse is small (or 0). (C) is a clock regenerated from the received output, consisting of CLKl with phase 0 and CLK2 with phase π, which are the data strings Di, D2
It deviates from π/2. At the rising edge of clock CLKI (
Read the optical output M-TPC in b), and if it is positive, raise it, and if it is 0, lower it, and the data DI in (d) is obtained.Read the optical output M-TPC at the rising edge of CLK2, and if it is negative, raise it, and if it is 0, then it will fall. When the signal falls, data D2 (d) is obtained, and thus the demodulated output (d) of the transmitted data (a) is obtained.

The present invention relates to a circuit for varying the optical output depending on the mark rate in such an optical three-value transmission system.

[Conventional technology]

In the optical binary transmission system, an optical output stabilization circuit that takes mark rate fluctuations into consideration is known. However, in the optical three-level transmission method,
An optical output stabilization circuit that compensates for any combination of mark rates of two data streams has not yet been proposed. This is also because optical binary transmission is common, and the development of optical multilevel transmission systems such as optical ternary has not progressed sufficiently. However, in cases such as multiplexing multi-channel television signals and performing optical digital transmission, the optical multilevel transmission system is important as a transmission method for television signals of more channels, and as the optical multilevel transmission system Output stabilization circuits are important.

FIG. 6 shows changes in the optical output waveform depending on the mark rate. (a
) is when the mark ratio MR of data strings DI and D2 are both 1/2, (b) is when the mark ratio of data string D1 is larger than 172, and (C) is when the mark ratio is smaller than 1/2. D2 is set to MR=1/2 in both cases. Note that the mark rate is the on/off ratio for a predetermined period for each data string Di, D2. In (a), the 1 of data D2 is 0, and the 1 of data D1 is 1. In (b), the whole goes down and collapses, and in (C), the whole goes up and the extinction ratio deteriorates (D2's 1). (1 does not become 0). This is because the average light output is controlled by APC to be the same, and when both mark rates are 1/2, the planned state is set as shown in (d) (1 of Di is 1.0 is 0.5, D2
1 is set to 0), when the mark rate of Dl becomes large, the average optical output remains unchanged (a shift in the Fz force direction occurs, resulting in state (b)). On the other hand, when the mark rate of Dl becomes small, a shift in the F direction occurs in order to keep the average optical output unchanged, resulting in the state (C).

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical output stabilizing circuit that does not cause deterioration of the optical output waveform even when the combination of mark rates of two data streams changes in an optical three-value transmission system. It is something to do.

[Means to solve the problem]

FIG. 1 shows the configuration of the present invention. 10 is a light emitting element that produces light output. 11.12 is the data string DI.

D2 and drives the light emitting diode 10.

13 is a light output detection circuit, 14 is a circuit for controlling the bias current of the light emitting diode 10, and 15 is a voltage source for supplying a reference voltage to the circuit 14.

These 13.14.15 are the APC (8 automatic power control) for the light emitting diode 10.
rol C1rcuit) circuit. 16.17
is a circuit that detects each mark rate of the data strings D1 and D2. 18 is an addition circuit, mark rate detection circuit 16.17
, and adjust the reference voltage 15 based on the result.

[Effect]

In the present invention, each mark rate of the two data strings Di and D2 is detected by the circuits 16 and 17, and the reference voltage 15 is adjusted by the addition (subtraction in a physical sense) signal of this detection signal, and the reference voltage 15 is Adjust the optical output by changing the bias current. An example of the adjusted light output (relative light output) is shown in the table below.

Table 1 Unit: dBr As shown in this table, the mark rates of data strings D1 and D2 are both 1/8.1/4.・・・・・・When the ratio is equal to 7/8, the reference voltage is not corrected (relative light output is 0.Odlr)
.

When the mark rate of Dl becomes higher than the mark rate of D2, the relative optical output is increased according to the degree, and conversely, when the mark rate of Dl becomes lower than the mark rate of D2, the relative optical output is decreased.

This makes it possible to avoid distortion of the optical output waveform and deterioration of the extinction ratio.

As is clear from FIG. 5(b) and FIG. 6(d), when the mark rate of the data string D1, which is a positive (increasing side) pulse, is high, the average optical output becomes large, and when it is negative (decreasing side) When the mark rate of the data string D2 that becomes a pulse is high, the average optical output becomes small. Since APC makes this constant, Figure 6(b) (
As shown in C), the O level (optical output when the data strings Di and D2 are O) is varied so that the average power becomes constant. Mark rate compensation ensures that the O level remains unchanged. Of course, this control is performed only on (combinations of) mark rates, and not on power supply voltage fluctuations, secular changes, and other optical output changes (such as optical output changes due to power supply voltage fluctuations, etc.). is removed by APC.

〔Example〕

FIG. 2 shows an embodiment of the present invention. Mark rate detection circuit 16
is composed of a low-pass filter including a resistor R8 and a capacitor CI, and an inverted signal DI of the data string D1 is added thereto. The output VMDI is as shown in FIG. 3(b).

Similarly, the mark rate detection circuit 17 includes a resistor R2 and a capacitor C.
2 low-pass filters, and an inverted signal D2 of the data string D2 is added thereto. The output ■HDt is as shown in FIG. 3(C). Although these have slopes opposite to the mark rate, the absolute values of the slopes are made equal by adjusting the value of RC. In this way, if the mark rates of data strings D1 and D2 are equal, the addition control signal ΔVMIII + ΔVMDZ becomes 0.
, DI(7)? −” If the rate is large, it can be negative, and if the mark rate of Dl is small, it can be positive. Note that ΔV M D I
r ΔvMoz indicates the amount of variation when the mark rate is 1/2 as a reference.

The optical output detection circuit 13 is composed of a photodiode PD, a resistor R for taking out an average value, and a capacitor C, and the output VPD is as shown in FIG. 3(a). In other words, as the light level increases, the output (2) decreases, so the output of the operational amplifier OP decreases, the conductivity of the transistor Q decreases, and the bias current I decreases.
, decreases and the light level falls. The opposite is true when the light level decreases, and thus constant light level control (AP
C) is performed. An offset circuit 19 provides a reference voltage for this APC. Mark rate detection circuit 16.17 output ■. I+vMD! The sum changes this reference voltage and performs mark rate correction.

The slope of the output of the optical output detection circuit 13 is matched to the slope of the addition control signal. If the output of the photodetector circuit decreases as the light level increases (this is taken as a positive direction), the addition control signal also changes in the positive direction, and conversely, the output of the photodetector circuit increases as the light level increases (this is taken as a negative direction). direction), the addition control signal also changes in the negative direction. This is done using a resistor R and a capacitor q.

FIG. 4 shows another embodiment of the invention. In this example, the data string D1 is applied to the gate of the field effect transistor Q,
Further, the data string D2 is applied to the gate of the field effect transistor Q, and mark rate detection and addition are performed by these transistors, resistors R3 to R6, and capacitor C3.
The summation signal is obtained at node N1 and is applied to the output of operational amplifier OPI through resistor R1. A reference voltage 15 is applied to the output of the operational amplifier, and the output of this operational amplifier is applied to the output of the operational amplifier OP3 through a filter. The output of the photodetection circuit is sent to the operational amplifier OP3 via the operational amplifier OP2 that constitutes the voltage follower OPz.
The output of the operational amplifier OF3 controls the transistor Q2, which in turn controls the light emission of the laser diode 10.

The operational amplifier OP adjusts the reference voltage according to the mark rate, and the operational amplifier OP3 performs APC using the adjusted reference voltage. Data string DI, D
Laser diode 100 emission control by 2 is 10 R
:+Q+, 10 Performed on the path Rb-Q2.

[Effects of the Invention] As explained above, according to the present invention, the difference in mark rate between each system, which occurs in an optical ternary transmission system that includes an APC circuit and multiplexes and transmits two systems of data using optical output, It can prevent deterioration of the optical output waveform and is effective in transmitting multi-channel TV signals.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the invention, Fig. 3 is a characteristic diagram for explaining the operation of Fig. 2, and Fig. 4 is another embodiment of the invention. A circuit diagram showing an example, FIG. 5 is an explanatory diagram of an optical three-value transmission system, and FIG. 6 is an explanatory diagram of optical output waveform deterioration due to mark rate. In FIG. 1, 10 is a light emitting element, DI is the first data string, and D2
is the second data string.

Claims (1)

[Claims] 1. A light emitting element (10) having an automatic power control circuit (13, 14, 15) is provided, the light output is changed in one direction by the first data string (D1), and the light output is changed in one direction by the first data string (D1). In an optical output stabilization circuit in an optical ternary transmission system that multiplexes the first and second data streams on the optical output by changing the data stream (D2) in the opposite direction, the mark rate of the first data stream is a detection circuit (16);
a circuit (17) for detecting the mark rate of the second data string;
An adder circuit (1) for the outputs of these detection circuits (16, 17)
8), wherein the reference voltage (15) of the automatic power control circuit is adjusted by the output of the adder circuit to compensate for the mark rate.