JPS6072282A - System of driving burst photo output - Google Patents

Abstract

PURPOSE:To enable the reduction in the overshoot of photo output, without the decrease in the efficiency of network, by slackening the speed of bias increase only in the neighborhood of set levels. CONSTITUTION:The current value of a current source 13 that charges a capacitor 11 is controlled by means of a difference circuit 14 receiving the difference signal between the detected output of a semiconductor laser 5 and the reference signal. When the photo output is small, i.e., the difference between the reference signal is large, the current value of the source 13 is large. Therefore, its charging speed is high, and the potential increases rapidly; however, the access of the photo output to the set level slackens the speed. Accordingly, the increase in the photo output nearly in uniformity from beginning without rapid increase in the neighborhood of the set level is enabled. Since the bias increase is duller in the neighborhood of the set level, even when the loop has some delay, the overshoot of output due to it is hardly observed.

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 an optical 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 social productivity. Like this f! In the so-called office automation system that handles requests, inexpensive terminal devices such as personal computers are used to divide or decentralize relatively expensive leases such as data file servers, in order to realize an inexpensive network system. There have been reports on the development of bus-type or star-type networks.

The number of signals handled on such a network is 12, for example 101.
It is common to use a so-called burst signal in which high-speed data of vlJ4z or higher is transmitted only for a certain period of time.

Furthermore, outside the burst signal period, the semiconductor light emitting device must stop emitting all its optical output so as not to interfere with signal exchange between other stations. In other words, it is necessary for the semiconductor laser not to output even its bias emission. However, bias emission is indispensable for performing sieving speed operation in semiconductor lasers.
Normally, in response to these conflicting demands, a method is adopted in which, for example, a signal called a transmission request signal is received a short period before the burst signal is emitted, the bias light is emitted, and the burst signal is then waited for manually. Historically, optical output has been stabilized by detecting the output of a semiconductor laser and controlling the laser bias by comparing the output with a reference signal.

FIG. 1 shows a block diagram of the above function, and has both a burst input (1) and a transmission request signal (3) as inputs. FIG. 2 shows the bias application section in FIG. 1. Components having the same functions as those in FIG. 1 are designated by the same numbers. The transmission request signal shown in FIG. 3(b) is inputted prior to the burst signal (a).

The comparator (8) outputs High when the detected light output is higher than the reference signal 7, and outputs Low otherwise. Therefore, when the transmission request signal is input, the comparator output shows Low, and the transistor H operates by the logic operation of the logic gate 0 to charge the capacitor αυ. Semiconductor laser (5
), the potential of the capacitor undergoes V/I conversion by the bias transistor (1), and a current is applied. The transistor (10) continues to operate until the potential of the capacitor αυ increases linearly. When the optical output also increases and exceeds the reference signal level, the output of the comparator (8) is inverted and becomes High, and the potential of the capacitor αυ increases linearly. ) starts operating, the capacitor αυ is no longer charged, and as a result, the semiconductor laser (6) is set to the specified level.In an ideal system, this level is definitely set to the L constant level. However, in practice, each component circuit includes a time delay with respect to its operation. That is, when viewed as a negative feedback loop, it has a loop delay, but on top of that,
After the detection output and the reference signal output become the same in the comparator (8), the bias increase stops after a loop delay. Therefore, as shown in FIG. 309, the optical output is controlled to include an overshoot for a certain cent level. This is particularly remarkable in the semiconductor laser (6)Q. In other words, the normal set level is the threshold of the semiconductor laser (6), but as shown in Figure 4, near the threshold of the semiconductor laser (6), the optical output decreases with a slight increase in the input current. Changes greatly. Therefore, even if the potential rise of the charging capacitor Uυ is linear, the optical output is linear, and the optical output changes sharply near the threshold, and even a slight loop delay causes an overcoat of the optical output.

To solve this problem, it is possible to consider methods of slowing down the rate of rise of the bias current, such as increasing the capacity of the charge capacitor 11, or reducing the charge current value, but in this case, it takes time to raise the bias current by changing the set level. Therefore, considering that this period is an invalid time for the network, it cannot be made larger than necessary.

Note that the bias application section shown in Fig. 2 only has the function of increasing the bias current, but this means that during the burst signal period of several milliseconds at most, the external temperature does not change and the own temperature increases. This is because only the output paper under-print phenomenon due to heat generation occurs, so that the noise is only increased σ, and there is no need to include reduction control. Figure 3) shows the capacitor potential, and it can be seen that every time the optical output decreases and becomes lower than the reference level, the transistor (10) operates to increase the bias.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned problems, and aims to stabilize a feedback loop suitable for device signal transmission of semiconductor light emitting devices with less overshoot of optical output and without reducing network efficiency. The object of the present invention is to provide an optical output driving method that provides a high-speed optical output.

[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 compared with the second reference signal, the bias signal of the semiconductor light emitting element is increased, and the rate of increase of the bias signal is increased. A burst light output driving method is provided in which the determination is made according to the difference between the second reference signal and the photodetection signal.

〔Effect of the invention〕

According to the present invention, since the bias rising speed is slowed only near the set level, the time required to bring the bias to the cent level does not change much, and overshoot can be drastically reduced.

[Embodiments of the invention]

An embodiment of the invention will be shown using FIGS. 5 and 6.

The key point of the invention is to control the current value of the current source (first floor) that charges the capacitor (lυ) by taking the difference signal between the detection output of the semiconductor laser (5) and the reference signal, for example, using a difference circuit. The circuit sections other than circuit 04) are the same as the conventional example.Therefore, the burst stabilization circuit consists of 2
It has a heavy loop mechanism. Figure 6) shows the potential of the capacitor, but when the optical output is small, BiJ
If the difference from the reference signal is small, the current value is large, so its charging speed is fast and the potential rises rapidly, but as the optical output approaches the set level, the speed slows down. Therefore, the increase in light output is
Unlike the conventional example, it does not suddenly increase near the set level, and it is now possible to raise it almost uniformly from the beginning. Near the set level, the rise in output is the sharpest, so even if there is a slight delay in the loop, the output output due to the loop is hardly observed.
·is.

Other examples include the capacitance of a capacitor (lυ), the emitter resistance of a transistor (131), or the power supply connected to the emitter resistance of a transistor (19).
Control using a differential signal may also be considered. It is clear that the mold may be modified in various ways without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional example, FIGS. 2 and 3 are a detailed diagram of a bias application NS and an optical output characteristic diagram of the conventional example, and FIG. 3 is a diagram of an embodiment of the present invention and an optical output characteristic diagram. DESCRIPTION OF SYMBOLS 1...Burst data input terminal, 2...Curse drive section, 3...Transmission request input terminal, 4...No(IAS applying section, 5...Semiconductor light emitting element, 6...Semiconductor detection Element, 7... Reference signal input terminal, 8... Comparator, 9.1
0...Transistor, 12...Logic gate, 11...
Capacitor, 13... Control current source, 14 - Differential circuit. Agent Patent Attorney Kensuke Chika (and 1 other person) @Figure 1 Figure 2 Figure 3 Figure 4/'$i, Tane

Claims (1)

[Scope of Claims] (1) A part of the burst light output of a semiconductor light emitting element is optically detected by a semiconductor light detection element, and the burst light output is stabilized and controlled by the light detection signal. In the method, the photodetection 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 adjusted. and the rate of increase of the bias signal is determined according to the difference between the first or second reference signal and the photodetection signal. . (2) The rate of increase of the bias signal is large when the difference between the first or second reference signal and the photodetection signal is large; The method of claim 1, wherein the signal corresponds to a threshold value of the semiconductor light emitting device. (4) The burst light output WW operation 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. (5) 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. Burst light output % &(& driving method according to item 1. (6) When inputting a burst signal to the semiconductor light emitting element for outputting burst light, the reference signal is changed from the first reference signal to the second reference signal. The burst light output W driving method according to claim 1 is characterized in that: