JPS5937747A - Optical transmitting circuit - Google Patents

Abstract

PURPOSE:To obtain the same output from respective semiconductor lasers through a single driving circuit and to simplify the circuit, by providing plural constant current sources which supply biases to the semiconductor lasers independently and means which prevents signals except a direct current from passing through a signal band between the constant current sources and lasers. CONSTITUTION:An optical transmitting circuit is provided with one driving circuit 41, which drives (n) units of parallel-connected semiconductor lasers 1-(n). Constant current circuits 71-7n which supply bias currents and have feedback inputs are provided corresponding to the lasers 1-(n), and feedback signals are applied to the circuits 71-7n by photodiodes 81-8n. Coils 51-5n, and 61-6n are connected between the circuits 71-7n, and lasers 1-(n), and only direct currents are passed through by the coils 51-5n, and 61-6n to prevent signals from passing through the signal band. The lasers 1-(n) are driven by the single driving circuit 41 to obtain the same optically modulated signals from the lasers 1-(n), simplifying the constitution of the transmitting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical transmission circuit using a plurality of semiconductor lasers as light sources.

Generally, in optical communications, when the same signal is transmitted in multiple directions, or even in the same direction, there are cases where it is necessary to transmit more optical power than can be obtained from a single light source.

In such a case, the first idea is to provide a drive circuit for each light source and operate each light source in parallel, but this method requires a large number of drive circuits and is uneconomical. Here, if we consider a semiconductor light source as a light source, the terminal voltage of this light source is as low as 2 to 3μ, and the output optical power corresponds to the supplied current and does not correspond to the terminal voltage, so the current Suitable for driving. Therefore, even if a circuit in which multiple semiconductor light sources are connected in series is used, the power supply for one ordinary electronic circuit can supply a voltage of 5V to several tens of square meters, and the required drive current is the same as that of one light source because of the series connection. Because there is, the problem is better in terms of driving ability.

When using a light-emitting diode as this light source, since the light-emitting diode can obtain a light output proportional to the current from a region where the current is almost zero, it is not a problem to connect light-emitting diodes with similar current-light output characteristics in series. No, but
When using semiconductor lasers, the so-called threshold current of the laser varies individually and depending on the difference in ambient temperature, and the drive current must be controlled separately, and it is not possible to simply connect each semiconductor in series. The problem is that it is not possible to operate lasers in the same way.

Based on one or more considerations, it is an object of the present invention to provide an optical transmission circuit in which substantially the same modulated light output can be obtained from each of a plurality of semiconductor lasers using a single drive circuit.

The optical transmission circuit of the present invention includes - drive circuits, a plurality of semiconductor lasers driven by the drive circuits and connected in series, and a direct current applied to each of the semiconductor lasers independently. multiple constant current sources supplying as bias,
Furthermore, the device includes means connected between the constant current source and the semiconductor laser to allow only direct current to pass through and block signal bands.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In this embodiment, a drive circuit 41Fin drives semiconductor lasers 1 to n. Here, 11 is an integer from 2 to 9, but of course it may be a number larger than 1O.

In order to represent the numbers of other elements, numbers up to 9 are used.

Bias circuits 11 to lrl corresponding semiconductor lasers 1 to n
with a circuit that supplies a bias current that adapts to the

This bias current can be controlled by simply using a temperature-compensated DC current source if the range of change in the ambient temperature is small, or by controlling a portion of the output light of each semiconductor laser if further stabilization is required. The circuit detects the bias current and controls the bias current to keep the level constant. Here, for semiconductor lasers of the same type, there is not much difference in current change versus optical output change in the region where the current is larger than the threshold current, so-called differential stagger efficiency. Just fix it at an appropriate value.

In FIG. 0, the amplitude of the optical signal outputted from each semiconductor laser is almost equal and the object of the present invention is achieved. In FIG. Semiconductor laser 1 without including J1
It is an element that flows only in ~n, has high impedance in the required signal band for effective use, and exhibits a low resistance value against direct current such as bias current.

FIG. 2 is a specific configuration diagram of an embodiment of the present invention.

A part of the optical output of the semiconductor lasers 1 to n is detected by the photodiodes 81 to 8n, and the average optical output of each corresponding semiconductor laser 1 to n is determined by the stiffness detection value by the current sources 71 to 7n. One current of the output bias current is supplied to each semiconductor laser through coils 51 to 5n and 61 to 6nf so as to achieve the same value. Each coil 51-5n, 61
~6n for the drive current band generated by the drive circuit 41 [2
If the inductance is set to meet a sufficiently high impedance, the loss λ given to the signal component flowing to the semiconductor laser 1-n by the constant current sources 71-7nK can be almost ignored.

With such a configuration, all the semiconductor lasers 1 to n
Since an optimal bias current is provided and only one signal source 41 is required, it is economical and can be used with multiple semiconductor lasers.
We can obtain an optical transmitter circuit that can perform 1.Also, if the ambient temperature is constant, 4? If stabilization is not necessary, the entire configuration of the optical transmitter circuit can be made simpler by removing the photodiodes 81 to 8n from the circuit shown in FIG. 2 and simply setting the output value of each current source in the initial state.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of an embodiment of the present invention, and Fig. 2 is a specific configuration diagram of Fig. 1. In Fig. 0, 1 to n...
・Semiconductor laser, 11~In・Old・Constant current circuit, 21
~2n, 31~3n... Coupling element, 41...
...Drive circuit, 51-5n#61-6n...
coil. 71~7n... Constant current circuit with feedback input. 81 to 8n...photodiodes. Homare 1 mouth t7L Hayabusa 2 positive

Claims (1)

[Claims] A single drive circuit, a plurality of semiconductor lasers that are driven by this drive circuit and connected in series, a plurality of constant current sources that independently supply direct current as a bias to each of these semiconductor lasers, and these An optical transmission circuit including means for passing only direct current and blocking a signal band, each connected between a constant current source and a semiconductor laser.