JPH01155672A - Laser diode drive circuit - Google Patents

Abstract

PURPOSE:To improve an output laser ray in waveform deterioration due to a mark rate detecting circuit by a method wherein a laser diode supplied with a constant voltage is drive through an input data and a mark rate of input data is detected from a current which is outputted from a constant voltage circuit. CONSTITUTION:A laser diode 1 is modulated through an input data of the order of Gb/s through the intermediary of a field effect transistor FET 61, and an average power enables the laser diode 1 to emit a prescribed output laser ray and make an average current which modulates the laser diode 1 flow through the intermediary of the FET 61 directly connected with the diode 1, where a high frequency component contained in the current is removed through a condenser C1 connected with a source of the FET 61, therefore an average current without a high frequency component flows through a resistor R1 through the intermediary of a transistor 42, where an average potential difference generated is sent to an APC through the intermediary of an operational amplifier 21 as a value corresponding to a mark rate.

Description

[Detailed Description of the Invention] [Summary] For example, with respect to a laser diode drive circuit used in optical fiber cable transmission, the present invention aims to improve waveform deterioration of output light caused by a mark rate detection circuit, using input data. A laser diode drive means for driving a laser diode, a constant voltage circuit that supplies a constant voltage to the laser diode drive means, and a mark rate detection circuit that detects the mark rate of the input data from the current output from the constant voltage circuit. It is configured to have the following.

[Industrial application field]

The present invention relates to a laser diode drive circuit used, for example, in optical fiber cable transmission.

FIG. 3 is a block diagram of an example of an electrical/optical converter.

FIG. 4 shows an explanatory diagram of the operation of FIG. 3. The operation shown in FIG. 3 will be explained below with reference to FIG.

First, in FIG. 3, when the ambient salinity is constant and the duty factor (hereinafter referred to as mark rate) of data input to the laser diode drive circuit 3 is set to 4, the automatic power control section (Automatic Power C.

ntrol (hereinafter abbreviated as APC) 5, the bias current was set at the point ■ (threshold current point) in Figure 4 so that the average power of the output light from the laser diode 1 was a predetermined value. shall be.

Next, when the ambient temperature changes, the average power of the output light changes, and this is detected by the photodiode 51 and the APC
5, the APC controls the bias current so that the average power becomes a predetermined value.

Also, the mark rate detection circuit 2 detects the mark rate of the above data, but if the mark rate shifts from the above value,
The bias current shifts to the point (■) or (■) in FIG. 4, and the average power shifts from the predetermined value. Therefore, the APC 5 controls the bias current so that the average power becomes a predetermined value in the same manner as described above.

Here, when inserting this mark rate detection circuit into this electrical/optical converter, it is necessary to prevent waveform deterioration of the output light as much as possible.

[Conventional technology]

FIG. 5 shows a block diagram of a conventional example. In the figure, resistance R7~
The R3+operational amplifier 21 portion is a component of the mark rate detection circuit.

In the figure, a laser diode 1 emits output light that is modulated by data at a mark rate of 2 (for example, high-speed data on the order of Gb/s) applied via a field effect transistor (hereinafter abbreviated as FET) 31. and a resistor R,,FET 31. An average current i of the current modulating the laser diode flows through the constant voltage circuit 4. Therefore, the average potential difference generated across resistor R1 is expressed as resistor RZ+R3
+ added to the APC (not shown) via operational amplifier 21.

Now, when the mark rate shifts from 172, the average potential difference of the resistor R0 shifts from when the mark rate is 1/2, but
The APC compensates for this shift by operating the bias current as indicated by the dot (■) in FIG.

Incidentally, the capacitor CI is used to remove high frequency components from the above-mentioned average current i, and thereby the source of the FET is maintained at a constant voltage.

[Problem that the invention seeks to solve]

Here, the resistor R of the mark rate detection circuit is inserted between the laser diode 1 and the FET 31.

High frequency components on the order of GHz will pass through this resistor R, but for such high frequency components, it is not pure resistance but includes resistance and actance, and the waveform of the laser diode output light deteriorates. There is a problem. This degrades the error rate of the received waveform.

[Means for solving problems]

FIG. 1 shows a block diagram of the principle of the present invention.

In the figure, 6 is a laser diode drive means for driving a laser diode using input data, 4 is a constant voltage circuit that supplies a constant voltage to the laser diode drive means,
2 is a mark rate detection circuit that detects the mark rate of the input data from the current output from the constant voltage circuit.

[Effect]

The present invention combines the mark rate detection circuit 2 with the constant voltage circuit 4 and the weight #(
-V).

With this arrangement, the high frequency component is removed by the capacitor CI, and since the average current i of the current modulating the laser diode flows through the mark rate detection circuit 2, the mark rate can be detected from this.

Further, the laser diode 1 and the laser diode driving means 6
Since they are directly connected, waveform deterioration of the output light is improved.

〔Example〕

FIG. 2 shows a block diagram of an embodiment of the invention.

Here, the FET 61 and the capacitor CI are components of the laser diode driving means 6, and the operational amplifier 41. Transistor 42. The resistor R4 is a component of the constant voltage circuit 4 and the operational amplifier 21. Resistors R2 and R3 represent constituent parts of the mark rate detection circuit 2. Note that the same reference numerals indicate the same objects throughout the figures.

In the figure, a laser diode 1 emits an output light whose average power is a predetermined value by being modulated by data on the order of 2 Gb/s, which is applied via a FET 61, and the average current modulating the laser diode A current flows through the directly connected FET 61, but the high frequency components contained in this current are removed by the capacitor CI connected to the sources of FE and T.

Therefore, this average current without high frequency components flows through the transistor 42 to the resistor R, and the average potential difference generated here is passed through the operational amplifier 21 to AI'C (not shown) as a value corresponding to the mark rate. sent to.

That is, since the laser diode 1 and the FET 61 are directly connected, waveform deterioration can be improved.

In addition, a predetermined constant voltage without temperature characteristics is applied to the ten terminals of the constant voltage circuit 4 and the operational amplifier 41, and a voltage such that the FET can drive the laser diode is applied to one terminal.
The source voltage of the ET is kept constant by feeding it back to one terminal.

〔Effect of the invention〕

As described above in detail, the present invention has the effect of improving the waveform deterioration of the laser diode output light.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the principle of the present invention, Figure 2 is a block diagram of an embodiment of the present invention, and Figure 3 is an electrical/
FIG. 4 is an explanatory diagram of the operation of FIG. 3, and FIG. 5 is a block diagram of a conventional example. In the figure, 1 is a laser diode, 2 is a mark rate detection circuit, 4 is a constant voltage circuit, and 6 is a laser diode driving means. 1000 wo figures

Claims (1)

[Claims] Laser diode driving means (6) for driving the laser diode (1) using input data, a constant voltage circuit (4) for supplying a constant voltage to the laser diode driving means, and the constant voltage. A laser diode drive circuit comprising: a mark rate detection circuit (2) that detects a mark rate of the input data from a current (i) output from the circuit.