JPH03180080A - Light-source device - Google Patents

Abstract

PURPOSE:To make it possible to obtain a high-frequency pulse light according with a set value in the intensity of light by setting a synthetic time constant of a light-emitting element, a light-sensing element and a first amplifier and a time constant of a second amplifier to be equal to each other. CONSTITUTION:A feedback control amplifier 6 introducing output signals SB and SC of first and second amplifiers 4 and 5 and controlling a current of a current source so that a difference between the two signals will be zero, is provided. Values of capacitors C1 and C2 and resistors r1 and r2 are set beforehand so that a synthetic time constant tau3 of a light-emitting element 2, a light-sensing element 3 and the amplifier 4 and the time constant tau2 of the amplifier 5 will be equal to each other. In other words, a set voltage Er is switched also synchronously with this pulse light and, in addition, the waveform thereof is delayed with the same time constant as a photoelectric conversion signal coming via the light-sensing element 3. The same delayed waveforms of them are compared with each other by the feedback control amplifier 6 and controlled. According to this constitution, the intensity of the pulse light can be made accord exactly with the set value even in a high frequency zone.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device that applies pulsed current from a current source to a light emitting element via a switch to obtain pulsed light.

<Prior Art> Pulsed light as shown in FIG. 4 is used in laser printers, devices for writing signals onto optical disks, and the like. In such a device, it is necessary to control the intensity of the pulsed light to a preset value, and conventionally, pulsed light having a set intensity has been obtained using a light source device as shown in FIG.

In the device shown in FIG. 2, a current is applied from a current source 1 to a light emitting element 2, but this current is turned on and off by a switch sw3 on the way, so that a light emitting element 2 is irradiated with pulsed light from the light emitting element 2. The pulsed light emitted from the light receiving element 2 is converted into an electric signal according to the intensity of the light by the light receiving element 3. Fourth
The figure shows an example of an electrical signal output from the light receiving element 3. Note that, as the light emitting element 2, for example, a laser diode, a light emitting diode, etc. are used, and the light receiving element 3
For example, a photoelectric conversion element such as a photodiode or a phototransistor is used.

The amplitude VH of the pulse signal in FIG. 4 corresponds to the intensity of the pulsed light. Therefore, in the device shown in FIG.
The hold circuit 11 samples this voltage VH and
The current value of the current source 1 is controlled by a feedback control amplifier 6 so that it matches the set voltage Er. The intensity of light output from the light emitting element 2 is determined by the value of the flowing current, so the intensity of the light becomes a set value. The timing controller 12 controls the operation timing of the switch SW3 and the sample-and-hold circuit 11, and operates the sample-and-hold circuit 11 at time t1 shown in FIG.

<Problems to be Solved by the Invention> The conventional device shown in FIG. 2 cannot properly control when the rising and falling frequencies of the pulsed light output from the light emitting element 2 become high (or when the pulse width of the pulsed light becomes narrow). The problem is that it disappears.

Let me explain this. In the apparatus shown in FIG. 2, in order to match the intensity of light output from the light emitting element 2 with a set value, an electric signal corresponding to the intensity of this light is obtained from the light receiving element 3. and,
On the assumption that this electrical signal means the intensity of the pulsed light, it is compared with the setting (fi [r) and controlled to match this.

However, when the pulsed light becomes high-speed, the light receiving element 3 cannot follow it, and the photoelectrically converted signal output from the light receiving element 3 has a waveform as shown in FIG. 3 (4), for example. That is, in the high frequency region, the electric signal output from the light receiving element 3 differs from the actual light intensity. This makes it impossible to perform accurate control. Additionally, in the high frequency range, there is a limit to the response of the sample-and-hold circuit.
It becomes impossible to sample the output of the light receiving element 3 at a desired time.

Therefore, in the device shown in FIG. 2, when trying to obtain high-speed pulsed light, it is necessary to replace both the light receiving element 3 and the sample-and-hold circuit 11 with ones that can operate at high speed, but such devices are expensive. .

The purpose of the present invention is to use a light receiving element with common characteristics to
An object of the present invention is to provide a light source device that can obtain high-frequency pulsed light whose light intensity matches a set value.

Means for Solving the Problems> In order to solve the above problems, the present invention provides an apparatus for applying a current from a current source to a light emitting element (2) via a first switch (sIAi) to obtain pulsed light. A light-receiving element (3) that receives pulsed light from the element and converts it into an electric signal 9, an amplifier that amplifies the output signal of this light-receiving element with a time constant τ1, and operates in synchronization with the first switch. Second switch (SW2
), and this pulse signal (S
A second amplifier that amplifies E) with a time constant τ2 and the output signals (SB, SC) of the first and second amplifiers are introduced, and the current of the current source is controlled so that the difference between the two signals becomes zero. The combined time constant τ3 of the light emitting element, the light receiving element, and the first amplifier is set equal to the time constant τ2 of the second amplifier.

<Operation> Even if the irradiated pulsed light has a waveform like that shown in Figure 3 (1),
If a light receiving element with common characteristics is used, its output waveform in the high frequency region will be as shown in FIG. 3 (4).

In the present invention, the set voltage is switched in synchronization with this pulsed light, and the waveform is delayed by the same time constant as the photoelectric conversion signal that passes through the light receiving element.Then, these same delayed waveforms are fed back to each other. Since the control amplifier performs comparison and control, the intensity of the pulsed light can be accurately matched to the set value even in the high frequency range.

<Example> Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing an embodiment of the light source device according to the present invention, and FIG. 3 is a time chart of signals of various parts of the device shown in FIG.

In FIG. 1, l is a current source, S-1 is a switch, and 2 is a light emitting element. The output current value of the current source 1 is controlled by a feedback control amplifier 6, which will be described later. The switch 3141 has two contacts a and b, and contact a is
It is connected to a common potential through the light emitting element 2, and the contact point S is directly connected to the common potential. As the switch 5141, for example, a transistor, a relay, etc. can be used.As the light emitting element 2, for example, a laser diode, a light emitting diode, etc. can be used, as described in the conventional example.

3 is a light receiving element, 4 and 5 are amplifiers, 6 is a feedback control amplifier, Sn2 is a switch, and Er is a set voltage.

The light receiving element 3 receives the pulsed optical signal SA from the light emitting element 2, converts it into an electrical signal SD according to the intensity of the optical signal SA, and outputs the electrical signal SD. As explained in the conventional example, the light receiving element 3 also uses, for example, a photodiode, a phototransistor, etc. In the present invention, even if a particularly high-speed element is used as the light receiving element 3, the high-frequency pulse You can get light.

The amplifier 4 amplifies the output signal SO of the light receiving element 3 by a time constant of 1. This time constant τ1 may be realized by any means, but in FIG.
This is realized by connecting a parallel circuit of a capacitor C1 and a resistor ``1'' between the input and output of the resistor ``1''.The resistor ``3'' is an input resistance, and together with the resistor ``1'', it determines the amplification degree.However, When the light receiving cable 3 is of the current output type, r3 is unnecessary.

The voltage value of the set voltage Er may be adjusted by a controller (not shown). This set voltage value E
By changing r, the intensity of the pulsed light obtained from the device can be changed.

The switch SW2 has two contacts a and b, the contact a is connected to the set voltage [r, and the contact S is connected to a common potential. Then, it is switched in synchronization with the switch 5141 by a signal from the switch controller 7.

Therefore, assuming that there is no time delay due to the light emitting element 2 (the light emitting element 2 is an element capable of high-speed response), and assuming that the switch 1 and Sn2 have the same response, the pulsed optical signal SA and the switch 2 The old G11.1014 is switched at the same time as the pulse output SE.

As this switch SW2, an analog switch, a relay, etc. can be used.

The amplifier 5 converts the output signal SE of the switch SW2 into a time constant τ
It is amplified by 2. This time constant τ2 may be realized by any means, but in FIG. 1, it is realized by connecting a parallel circuit of a capacitor C2 and a resistor "2" between the input and output of the operational amplifier u2.

The feedback control amplifier 6 inputs the output signals SB and SC of the amplifier 4.5 and controls the current value of the current source 1 so that the difference between these two signals becomes zero.

Here, in the present invention, capacitors C1 and C2 and resistors rl
, and set the value of r2.

Add explanation. If the switch S-1 can be turned on or turned off very quickly, the output current of the contact a of the switch 3141 has no waveform dullness up to an extremely high frequency range (in other words, it has an extremely high rise (and sharp standing edges) is the ideal pulse waveform.

This ideal pulsed current waveform is converted into a pulsed optical signal S^ by the light emitting element 2, and then converted into an electric signal SD again by the light receiving element 3.
is converted into a signal S, delayed by a time constant τ1 in an amplifier 4,
It becomes B. Therefore, the light emitting element 2, the light receiving element 3 and the amplifier 4
Assuming that the composite time constant of τ3 is τ3, the ideal pulse current waveform becomes the signal SB after passing through the time constant τ3. To explain this using an example, since we are now trying to obtain high-frequency pulsed light, we naturally use a high-speed element that can respond to high frequencies as the light-emitting element 2, so the amount of signal delay in the light-emitting element 2 is It is pine-like and small, while the light receiving element 3 is
As described above, since elements with common characteristics are used, the waveform of the passing signal SA is blunted in the high frequency range.

Further, the amplifier 4 also has a time constant τ1, which further blunts the waveform of the passing signal SO in the high speed region. Therefore, the time constant τ
3 can be said to be mainly a composite time constant of the light receiving element 3 and the amplifier 4.

Next is amplifier 5111! The circuit of I will be explained. Similarly to the above, the output signal SE of the switch 5142 has an ideal pulse waveform with no waveform blunting up to the high frequency region. Output. And τ2=
Capacitor C2 and resistor ``2'' are determined so that τ3.

The operation of the apparatus shown in FIG. 1 constructed as above will be explained with reference to FIG. 3. The switch 5141 is turned on and off by the switch controller 7, and the light emitting element 2 emits pulsed light SA as shown in FIG. 3(1). As described above, since a sufficiently high-speed element is used for the light emitting element 2, the waveform of the pulsed light S^ is a waveform without dullness even in the high frequency range discussed in the present invention.

On the other hand, since the switch 3142 is also turned on and off in synchronization with the switch SW1, the pulse signal applied to the amplifier 5 has the same phase as the waveform shown in FIG. be.

■ When the pulsed light SA has a low frequency f1, the output signal of the amplifier 4 at this time is 881. SC output signal of amplifier 5
1, the frequency f1 is low, so the waveform is less blunt, as shown in Fig. 3 (2) and (5), and the amplitude fkj1v8 of the signal 381 is proportional to the intensity of the light, and the signal S
The amplitude VC of C1 corresponds to the set voltage [''.The two waveforms in Fig. 3 (2) and (5) have the same phase, so the values (amplitudes) of these two signals SB1 and SC1 are By controlling the current source 1 with the feedback control amplifier 6 so that the values are the same, the intensity of the pulsed light SA can be made to match the set value.

■ When the pulsed light SA has a relatively high frequency f2, if the output signal of the amplifier 4 at this time is SB2 and the output signal of the amplifier 5 is SC2, then since the frequency f2 is relatively high, the waveform becomes dull and the waveform becomes dull. It becomes as shown in Figure 3 (3), +6). However, since the time constant τ2 of the amplifier 5 is set equal to the composite time constant τ3 of the light receiving element 3 and the amplifier 4flll, the two waveforms shown in FIG. 3 (3) and (6) cannot be correctly feedback-controlled. The waveforms are congruent. That is, since the waveform on the set value side is also blunted in the same way as the waveform blunted by the light receiving element 3, the intensity of the pulsed light S^ can be made to match the set value.

■ When the pulsed light SA has a high frequency f3, the output signal of amplifier 4 at this time is 383, and the output signal of amplifier 5 is SC.
3, the frequency f3 is high, so the waveform is greatly blunted and becomes as shown in Fig. 3 (4) and (7). Since it is set equal to, Figure 3 (4)
The two waveforms (7) and (7) become congruent waveforms if feedback control is performed correctly. That is, the intensity of the pulsed light S^ can be made to match the set value.

Here, the frequency f1. f2. f3 means the frequency of the rising or falling edge of the pulse, that is, the sharpness of the waveform, and does not simply refer to the repetition frequency.

In addition, although the example above has been explained in which τ1 and τ2 are adjusted by a capacitor and a resistor provided in the feedback circuit of the amplifier 4.5, the means for adjusting τ1 and τ2 is not limited to this.6 For example,
In addition to the amplifiers 4, 5, a low-pass filter may be provided and adjusted thereby.

Furthermore, as a modification of the invention, a shutter (mechanical means or liquid crystal) that passes or blocks the output light of the light emitting element 2 may be used instead of obtaining the pulsed light using the switch Su1.

Furthermore, if a mechanical switch is used as the switch 3141 and a semiconductor switch is used as the switch 3142, a time difference will occur between the two signals S8 and SC. To correct this, a delay line may be inserted into the control line of switch 5142.

Effects of the Present Invention> As described above, according to the present invention, the following effects can be obtained.

■ Expensive sample/hold circuit is not required.

■ It is possible to obtain pulsed light with a sharp waveform by using an inexpensive light-receiving element with common characteristics instead of using an expensive high-speed light-receiving element.

(2) Since the amplifier 4 waits for the time constant τ1, the amplifier 4 does not require high speed. Generally, an amplifier that does not require high speed can have a high gain.

Therefore, even if weak pulsed light is emitted from the light emitting element 2, it can be sufficiently amplified and applied to the feedback control amplifier.

That is, according to the present invention, even weak pulsed light can be output with a value equal to the set value after normal feedback control.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the light source device according to the present invention, FIG. 2 is a diagram showing a conventional example, FIG. 3 is a time chart h of signals of each part of the device shown in FIG. It is a figure which shows the operation|movement of an example. l... Current source, 2... Light emitting element, 3... Light receiving element, 4°5... Amplifier, 6... Feedback control amplifier, 5t41, SW2... Switch. Figure Figure

Claims (1)

[Claims] A device for obtaining pulsed light by applying current from a current source to a light emitting element (2) via a first switch (SW1), which receives pulsed light from the light emitting element and converts it into an electrical signal. a first amplifier that amplifies the output signal of the light receiving element with a time constant τ1, and a second switch (SW2) that operates in synchronization with the first switch.
), and this pulse signal (S
A second amplifier that amplifies E) with a time constant τ2 and the output signals (SB, SC) of the first and second amplifiers are introduced, and the current of the current source is controlled so that the difference between the two signals becomes zero. 1. A light source device comprising: a feedback control amplifier for controlling a light emitting element, a light receiving element, and a first amplifier; and a time constant τ2 of the second amplifier set to be equal.