JPS61224736A - Laser diode modulator - Google Patents

Abstract

PURPOSE:To suppress unnecessary lighting due to ringing by designing the titled modulator that a bias current is brought into a value close to a threshold value at the leading of a data and set further lower other than the leading of data even when the level of a high speed data is consecutive as '1', '0'. CONSTITUTION:A prescribed delay is given to a signal from a clock signal terminal 7 by a delay circuit 91 to obtain a pulsive bias current IB2. Further, a bias current IB1 close to the threshold value flows normally to obtain an amplitude smaller than the threshold current. Then the leading time of a data pulse signal is made coincident with the peak value of the pulsive bias current IB2. Since the bias current IB2 reaches a value close to the threshold value at the leading of data in this way, even when the level of a high speed data is consecutive as '1', '0', the operation is not defective. Since the level is set further lower than the threshold value other than the leading of data, unnecessary lighting due to ringing is suppressed.

Description

[Detailed Description of the Invention] [Summary] This is a laser diode modulation device in which a bias current value is set so as not to cause malfunctions such as jitter in the laser diode.

[Industrial Application Field] The present invention relates to a device that emits light by superimposing a signal and a bias current when operating a laser used for pulse communication or the like.

[Prior Art] As shown in FIG. 4, a modulation device that causes a laser diode to emit light using a modulation signal is known in principle. In FIG. 4, the laser diode 1 always flows its bias current In at a constant value, and the modulation signal 1p flows in a pulsed manner due to the signal from the input signal terminal 2. FIG. 5 is an operational waveform diagram of bias current and pulses. In FIG. 5, when the bias current exceeds the threshold 1th as a characteristic of the laser diode,
The current passing through the diode increases rapidly, causing the diode to emit light. If the bias current is increased to exceed the threshold value Hh by applying a pulse, a light emission output corresponding to the presence or absence of the pulse can be obtained. If a bias current Io with a value close to the threshold value is constantly flowing, light can be emitted immediately by applying a pulse with a small amplitude. Therefore, the bias current Io is set to a value that is, for example, 2III^ smaller than the threshold value Ith. In order to obtain light emission corresponding to the data signal without time delay even when the pulse signal becomes high-speed and changes from "0" to "1" like a 400MHz data signal, it is necessary to maintain a bias current close to the threshold value at all times. The current flowing through the circuit shown in Fig. 4 is controlled by the control signal from the pulse current control signal terminal 3.
F) The current 1p of the diode 1 is also controlled by the control signal potential from the potential control signal terminal 4. The magnitude of the bias current In is controlled by a control signal from the bias current control signal terminal 5. Terminal Va
t indicates an operating DC potential source. The waveform shown in Figure 5B is
A pulse signal from terminal 2 produces a laser diode light emission waveform as shown in FIG. 5C.

[Problems to be Solved by the Invention] When a high-speed pulse continues as "1" and "O" as shown in FIG. 5C as the applied pulse in FIG. Ringing is a phenomenon that occurs in the 0 section RG where the amplitude of 0 cannot be completely maintained at the 0" portion and becomes wavy. At this time, the bias current may exceed the threshold 1th, so the light from the laser diode 1 The signal also had the drawback of emitting a little light when it should not have emitted light.Also, when 60"11111 continues, the driving element cannot immediately follow the amplitude of "1", causing a time delay (jitter) in operation. was there.

[Means for Solving the Problems] A laser diode modulation device that superimposes a bias current and a modulation data signal to obtain a light emission signal has a configuration shown in the principle diagram of FIG. 1. That is, a data signal is applied to the laser diode 1 from the input signal terminal 2 via the control unit 6, a signal for controlling the bias current Is is applied from the bias current control terminal 5, and a data signal is applied from the clock signal terminal 7. Apply a clock signal to define the A signal is applied to both control units 8.9 to control the current value. The bias current of the laser diode has a pulsating waveform having the period of the clock signal. Note that Vgg indicates a DC potential source.

[Function] In FIG. 1, the bias current pulsates with the period of the clock signal, and its maximum value is set so as not to exceed the threshold of the laser diode, so that the laser is likely to emit light when a data signal is applied. Therefore, even if the data is high-speed, there will be no delay in the light emission of the diode.

[Example] FIG. 2 is a diagram showing the configuration of an embodiment of the present invention.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts.

3 is a pulse current control signal terminal, 4 is a reference potential control signal terminal, and 91 is a phase adjustment delay circuit. Transistors, resistors, and inductances are shown using commonly used symbols.

A signal from the clock signal terminal 7 is given a predetermined delay by a delay circuit 91 as will be described later, and a current having a waveform shown in FIG. 3A is obtained as a pulsating bias current 182. Third
The figure is an operational waveform diagram for FIG. 2. Further, IB+ is a basic bias current and has a smaller amplitude than I+ shown in FIG. 5A. As shown in FIG. 3B, it is appropriate that the rise time of the data pulse signal coincides with the peak time of Ta2.

[Effects of the Invention] In this way, according to the present invention, the bias current has a value close to the threshold value at the rising edge of data, so even when high-speed data continues as "1"'0', the operation does not become defective. Since the threshold value is set lower than the threshold value except at the time of the rising edge of In this case, since the bias current has a value closer to the threshold value for the 11'' pulse, there is an effect that jitter does not occur.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle configuration of the present invention, Fig. 2 is a diagram showing the configuration of an embodiment of the invention, and Fig. 3 is a diagram showing the configuration of the embodiment of the present invention.
FIG. 4 is a configuration diagram of a conventional laser diode modulation device, and FIG. 5 is an operation waveform diagram of FIG. 4. 1 - Laser diode 2 - Data signal input/output device terminal 3 - Pulse current control signal terminal 4 - Reference potential control signal terminal 5 - Bias current control signal terminal 6.8.9
-・Control unit 7 - Clock signal terminal Patent applicant Fujitsu Ltd. Agent Patent attorney Eisuke Suzuki Figure 1 Figure 2 "1""O"'1"O'"'0""1" No. 3 Cause Figure 4 Figure 5

Claims (1)

[Claims] In a laser diode device that emits light by applying a modulation data signal to a laser diode through which a bias current is constantly flowing, the bias current is synchronized with a clock signal for defining the modulation data signal. A laser diode modulation device characterized in that the pulsating current is set so that the peak value does not exceed a threshold value of the laser diode.