JPS59200539A - Burst light output stabilization driving system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a driving method for stabilizing optical output in a source network, and particularly to a driving method for stabilizing burst optical output of a semiconductor light emitting device.

[Prior art and its problems]

Improving office work efficiency is important for improving society's productivity1.In the so-called office automation system that handles these demands, inexpensive terminal equipment such as personal computers is replaced by relatively expensive leased equipment such as data file servers. There have been reports on the development of bus-type or star-type networks in order to realize inexpensive network systems for divided or distributed use.

Signals handled on such networks are usually so-called burst signals in which, for example, 10 or more high-speed signals are transmitted only for a certain period of time.

However, with such optical transmission technology, problems that did not occur with transmission technology using coaxial cables have arisen, especially when dealing with burst signals. This is also clear from the fact that the luminous efficiency of a semiconductor light emitting device made of, for example, a semi-integrated laser (hereinafter abbreviated as LD) is very sensitive to temperature.

That is, the semiconductor light emitting device is affected by its own heat generation during burst signal transmission, and for example, in an LD, the output decreases due to an increase in threshold current, which causes a thermal sag phenomenon during burst signal transmission. It becomes.

As a method for suppressing such a thermal sag phenomenon caused by a semiconductor light emitting device, so-called analog control has been developed in which the driving current of the semiconductor light emitting device is controlled by slightly increasing or decreasing.

However, in such analog control, the frequency of several MHz
In order to require a negative feedback loop response for the above burst signal,
It requires expensive high-speed circuit elements, and because it performs the two functions of adding and reducing the drive current of the semiconductor light emitting element, oscillation occurs due to delays in the photodetector elements and transistors in the circuit, making the circuit itself unstable. There was a problem with becoming.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned problems, and it is an object of the present invention to provide an optical output stabilization drive system that stabilizes a feedback loop suitable for burst signal transmission of a semiconductor light emitting device.

[Summary of the invention]

In a burst light output stabilization drive method in which a part of the burst light output of a semiconductor light emitting element is photodetected by a semiconductor photodetection element, and the burst light output is stabilized and controlled using this photodetection signal, the photodetection signal is Alternatively, when the photodetection signal is smaller than the first or second reference signal by comparison with the second reference signal, the bias signal of the semiconductor light emitting element is increased, and photodetection No. 41 detects the first or second reference signal. The present invention provides a burst light output stabilization drive system in which the bias signal is held at a constant value when it is less than the reference signal.

〔Effect of the invention〕

According to the present invention, the photodetection signal of the semiconductor photodetection element and the first or second reference signal are compared and output as a digital output,
Since the bias signal of the semiconductor light emitting element is controlled to be increased or held at a constant value using this digital output, the stability of the feedback loop is improved and the design of the stabilization control loop is also very easy.

Further, regarding the bias of the semiconductor light emitting element, the circuit configuration is simplified because it is sufficient to simply increase the bias signal. Therefore, according to the present invention, it is possible to obtain a burst light output stabilization drive system that is inexpensive and has excellent stability.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows a block diagram of a circuit used in this embodiment. That is, a pulse driver (2) having a burst data input terminal (1), and a transmission request signal input terminal (3).
A semiconductor light emitting device (5) made of, for example, an LD, is provided with a bias application section (4) having a bias application section (4), and a signal obtained by superimposing the outputs of the pulse drive section (2) and the bias application section (4) is inputted. is provided. Also, this LD (5)
A semiconductor photodetector element (hereinafter abbreviated as PD) (6) consisting of, for example, a PIN photodiode, detects the optical output of
A comparator 18 for comparing the output of this PD (61) and a reference signal input terminal (a signal input from the force) is provided.

The output of this comparator (8) is input to a bias application section (4) and controls the output of the bias application section (4).

Next, the operation according to the present invention will be explained by referring to the operation of each part in the above-mentioned circuit configuration.

FIGS. 2(a) to 2(e) are time charts showing signal waveforms during the operation of each part 1 to 0 in FIG. 1 and the output waveform of LD +5).

First, a burst data signal (Fig. 2 (a)) is input from the burst data input terminal (1) to the pulse driver (2). A transmission request signal (FIG. 2(b)) is input from the signal input terminal (3) to the bias application section (4).

In addition to the transmission request signal, the bias application section (4) also receives a comparator (
8) Output is input. The comparator (8) compares the photodetection signal of the PD (6) with the first or second reference signal, and then becomes Low when the photodetection signal is smaller than the reference signal.

When it is large, Hl gh is output. The bias applying section (4) operates only when receiving the transmission request signal (FIG. 2(b)) and the Low output of the comparator (8), and biases the LD (5).

Normally, before inputting the burst data signal (Fig. 2(a)), or more precisely, before inputting the transmission request signal (Fig. 2(b)),
Since the LD (5) is not emitting light, the light detection signal is from the LD (
5) is smaller than the first reference signal corresponding to the threshold value, and the output of the comparator (8) is Low.

Therefore, the bias applying section (4) receives the transmission request signal (second
It operates for the first time when the LD (Figure (b)) is input, and the LD (
The bias of 5) continues as long as the transmission request signal (Fig. 2 (b)) and the low output of the comparator (8) are input to the bias applying section (4), but as the applied bias increases, the LD ( 5) The bias light also increases, and along with this, P
The photodetection current of D(6) increases and becomes smaller than the first reference signal corresponding to the threshold of LD(5).
The output of 8) becomes High.

Therefore, the bias applying section (4) receives the transmission request signal (second
(b)) is input, the output of the comparator (8) is H.
Since it is set to high, it does not operate and there is no increase in bias to LD (5). As a result, LD (5) is biased to the threshold value, and at this bias, LD C5
) a thermal sag phenomenon occurs and the photodetection signal of PD (61) is the first
When the reference signal of the LD (5) becomes smaller than the reference signal of
) bias is held at the threshold.

In this way, the transmission request signal [LI]5) is transmitted as the transmission request signal (FIG. 2(b)
) is biased to the threshold value. Thereafter, the data signal (Fig. 2(a)) is input to the LD (5) K via the pulse driver (4), and the LD (5) emits light in response to the burst data signal (Fig. 2(a)). Do this. In the burst mode, the reference signal input to the comparator (8) is L
Simultaneously with the input of the burst data signal (FIG. 2(a)) to D(5), the first reference signal is switched to the second reference signal. This second reference signal is a burst data signal (
Although the thermal sag phenomenon of the LD (5) as shown in FIG. 2(a) occurs, the optical output of the LD (5) decreases due to the thermal sag phenomenon of the LD (5).

Note that the burst data signal (FIG. 2(a)) is superimposed on the bias signal from the bias applying section (4) and sent to the LD (5).
is input. However, in this case, as the optical output of the LD (5) decreases, the photodetection current of the PD (61) decreases, and therefore becomes smaller than the second reference signal, and the output of the comparator (8) becomes Low.

Therefore, the bias applying section (4) operates, LD+5) is biased, and the optical output of LDt51 is transmitted until the transmission of the thermal sag (FIG. 2(a)) of LD(5) is completed.

Generally, when LD +5) is emitting light, the optical output of LD +51 tends to decrease as the temperature of LD (5) increases.

That is, PD C6), comparator (8), bias application section (
4), it corresponds exactly.

Next, the operation of the bias application section (4) will be explained with reference to a circuit diagram showing an example of the bias application section (4) shown in FIG.

The bias application section (4) is provided with a constant current source switch consisting of a constant current source (10), a first transistor qυ, and a second transistor (12).

When the output of the comparator (8) is Low by the logic gate (13), the first transistor OD is turned OFF and the second transistor (121 is turned ON). Charge capacitor 04).

Further, when the output of the comparator (8) is High, the first transistor 0υ is turned on, the second transistor (121 is turned off), and the capacitor Oa is not charged.

That is, when the output of the comparator (8) is Low, the 0th capacitor is charged, and the rising voltage across this capacitor α causes the L
Increase the bias current of D (6) to increase the optical output.

Further, when the output of the comparator (8) is High, charging of the capacitor 0 (a) is stopped and the bias current of the LD (5) is kept constant.

Therefore, when charging the capacitor σ field with the output of the comparator (8) as shown in FIG. 2(a), the capacitor (
As shown in FIG. 2(e), the terminal output of the terminal 141 continues to rise by being repeatedly charged or held depending on the low level or high level of the output of the comparator (d).

Although the - and one embodiment of the present invention have been described above, the feature of the present invention is that the bias control loop of the LD C5) has only the function of increasing the bias of the LD (5+).

That is, compared to a conventional loop having an increase/decrease function, oscillation phenomenon does not occur and stability is extremely high. This is caused by a high-speed burst data signal (LD f5 as shown in Fig. 2(a)).
is the burst light output of the LD (5) due to heat (Fig. 2 (
Within the period c)), LD(5) is based on the fact that only thermal monotonous power reduction occurs. This is because the period of high-speed burst light output (FIG. 2(c)) is several ms at most, and therefore, rapid fluctuations in the temperature of the LD f5 due to the external environment are not considered within this period.

Note that the discharge of the 0th capacitor is based on the data signal (Fig. 2 (a)
)) It is sufficient to add a switch (151) that obtains the disconnection information and shorts it.The bias control loop of LD f5 should include a digital system, and moreover, it should control only a single direction of the bias of LD (5). Therefore, level design of the entire loop, which was a problem with analog increase/decrease control systems, becomes easier, and the loop can be stabilized.

In other words, the circuit is inexpensive, has high performance, and the burst light of the LD (7).
Output can be stabilized and driven.

Incidentally, in the above, the semiconductor light emitting device is a semiconductor laser (L
Although the case of D) f5) has been described, it is clear that the present invention can also be applied to the case of a light emitting diode (LED').

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a circuit used in one embodiment of the present invention;
Figures (a) to (e) are time charts showing signal waveforms and output waveforms during operation of each part of the circuit diagram shown in Figure 1, and Figure 3 shows an example of the bias application section shown in Figure 1. FIG. ■...Burst data input terminal, 2...Pulse drive unit, 3...Transmission request input terminal, 4...Bias application unit, 5...Semiconductor light emitting element, 6...Semiconductor detection element, 7... Reference signal input terminal, 8... Comparator, 10.
...constant current source, 11.12...transistor, 13.
...Logic gate, 14...Capacitor, 15...Switch. Agent Patent attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 8 1ρ /,? H/′

Claims (5)

[Claims] (1) In a burst light output stabilization drive method in which a part of the burst light output of a semiconductor light emitting element is photodetected by a semiconductor photodetection element, and the burst light output is stabilized and controlled based on the photodetection signal, the burst light output is stabilized and controlled. The detection signal is compared with a first or second reference signal, and when the photodetection signal is smaller than the first or second reference signal, the bias signal of the semiconductor light emitting element is increased, and the photodetection signal is increased. 1. A burst optical output stabilization drive system characterized in that the bias signal is held at a constant value when the signal is larger than a first or second reference signal. (2) The first reference signal corresponds to a threshold value of the semiconductor light emitting device.
Burst optical output stabilization drive method described in . (3) Burst light output stabilization according to claim 1, wherein the second reference signal corresponds to a burst signal input to the semiconductor light emitting element for outputting the burst light. Drive system. (4) The semiconductor light emitting device is characterized in that, when a burst signal is input to the semiconductor light emitting device for outputting the burst light, the bias signal is inputted prior to inputting the burst signal. The burst light output stabilization drive method described in item 1. (5) When inputting a burst signal to the semiconductor light emitting device for outputting burst light, the reference signal changes from a first reference signal to a second reference signal. The described burst optical output stabilization drive method.