JPH0340531A - Optical transmitter - Google Patents

Abstract

PURPOSE:To improve response to a change in an external temperature by reading out threshold current data in accordance with the detected external temperature and impressing the read data to a semiconductor laser diode(LD). CONSTITUTION:When the external temperature is increased, the optical output power of the LD 3 is dropped and the voltage drop of a diode 41 is reduced. A storage device 43 outputs voltage corresponding to the input voltage of an input terminal 401 from a terminal 402 and impresses the output voltage to the base of a transistor 44, so that a DC bias current flowing into the LD 3 is the same as a threshold current against a change in the temperature and the optical output power of the LD 3 is held at a constant value. When the external temperature is lowered, the optical output power of the LD 3 is held at the constant value by the reverse operation. Thus, the response to a change in the external temperature can be improved.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical transmitter used for optical communications and the like.

BACKGROUND OF THE INVENTION In general, the light output of a semiconductor laser diode (hereinafter referred to as LD) changes as shown in the left side of FIG. 3 due to changes in external temperature "l" and "2 r T3. Therefore, L.D.
If the current I (direct current bias current is IB, pulse current of the transmitted data is I) is - constant, the outputs P1 to P3 of the optical transmitter correspond to temperature changes T1 to T as shown in Figure 3.
3 will vary. Therefore, the optical output is stabilized by passing a direct current through the LD to control the change in the optical output.

Next, a conventional example is shown in FIG. 1 is an input digital signal, which is input to the LD drive circuit 2. The LD drive circuit 2
Connected to D3. 5 is a photodiode (PD) that receives the output light of the LD 3 and converts it into an electrical signal.

Reference numeral 6 denotes a DC bias control circuit that causes a DC bias current IB to flow through the LD3 by the PD5.

Next, the operation of the above conventional example will be explained.

In FIG. 2, when the external temperature rises and the optical output of LD3 decreases, the current of PD5 that monitors the optical output of LD3 decreases. As a result, in the DC bias control circuit 6, the base voltage of the transistor (TR) 63 is increased by the differential amplifier 61 and the feedback resistor 62, the DC bias current IB flowing to the LD 3 is increased, and the optical output power is kept constant. Become.

When the external temperature decreases, the DC bias current IB flowing through the LD3 decreases due to an operation opposite to the above operation example.

As a result, the optical output of the LD 3 decreases, and the optical output power becomes constant.

In this way, even with the conventional optical transmitter described above, the optical output power can be kept constant regardless of changes in external temperature.

Problems to be Solved by the Invention However, in the conventional optical transmitter described above, as shown in FIG. 2, the DC bias control circuit 6 has a circuit configuration with negative feedback. There was a problem in that the response to keep the optical output power constant was slow.

The present invention solves these conventional problems, and aims to provide an optical transmitter that can improve response to changes in external temperature.

Means for Solving the Problems In order to achieve the above object, the present invention provides an element for detecting external temperature and a means for pre-storing dark value current data of a semiconductor laser diode according to the external temperature. The threshold current data is read out according to the external temperature and applied to the semiconductor laser diode.

Effect of the Invention According to the above configuration, the threshold current data read from the storage means is applied to the semiconductor laser diode, so the response is faster than that of the conventional negative feedback circuit, and therefore the response to external temperature fluctuations is faster. can be improved.

Example FIG. 1 shows the configuration of an embodiment of the present invention.

The input digital signal 1 is transmission data and is input to the LD drive circuit 2. The output side of the LD drive circuit 2 is connected to the LD3. The DC bias control circuit 4 is connected to the LD 3 so that a DC bias current flows therethrough. The DC bias control circuit 4 has an external temperature detection diode 41, an input terminal 401, and an output terminal 402, and is composed of a device 43 storing a threshold current at which the LD 3 emits light, a transistor 44, and a resistor 42.45. A resistor 42 is connected to the diode 41, and a connection between the diode 41 and the resistor 42 is connected to an input terminal 401 of a storage device 43. An output terminal 402 of the memory device 43 is connected to the base of a transistor 44 for supplying DC bias current, a resistor 45 is connected to the emitter of the transistor 44, and an LD3 is connected to the collector.

Incidentally, as shown in FIG. 3, the LD3 is at a temperature of T1°T2.
The threshold current, that is, the current for emitting light, differs depending on T, and therefore, the transistor 4
The voltage applied to the base of 4 is stored in advance in the storage device 43.

Next, the operation of the present invention will be explained. In FIG. 1, when the external temperature rises, the optical output power of the LD 3 decreases and the voltage drop across the diode 41 decreases. As a result, the storage device 43 outputs a voltage corresponding to the increased voltage at the input terminal 401 from the terminal 402 and applies it to the base of the transistor 44 . Therefore, the DC bias current flowing through LD3 becomes the same as the threshold current with respect to temperature changes, and LD3
can keep the optical output power constant. When the external temperature drops, the optical output power of the LD 3 can be kept constant by performing an operation opposite to that of the above example.

Therefore, according to the above embodiment, fluctuations in the external temperature are detected by the voltage drop across the diode 41, and the voltage applied to the base of the transistor 44 is adjusted to the memory device 43 in accordance with this voltage drop.
Since the light is read from the LD 3, the optical output of the LD 3 can be made constant in a short time even when the power is turned on.

As described in detail, the present invention reads the threshold current data of the semiconductor laser diode from the storage device according to the external temperature, so the response is faster than that of the conventional negative feedback circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of an optical transmitter in an embodiment of the present invention. FIG. 2 is a circuit diagram of a main part of a conventional optical transmitter. FIG. 3 is a diagram showing the input current versus optical output temperature characteristic of the LD. l... Input digital signal, 2... Laser diode drive circuit, 3... 1/-the diode, 4... DC bias control circuit, 41... Diode, 42...
Resistance, 43... memory device.

Claims (1)

[Claims] A semiconductor laser diode that outputs an optical signal, a temperature detection element that detects an external temperature, threshold current data of the semiconductor laser diode according to the external temperature is stored in advance, and the threshold current data of the semiconductor laser diode is stored in advance according to the external temperature detected by the temperature detection element. An optical transmitter comprising means for reading threshold current data and applying it to the semiconductor laser diode.