JPH04343284A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a direct current bias circuit of a semiconductor laser device used for a high speed optical communication to prevent the laser device from deteriorating in optical output waveform, where the direct current bias circuit is possessed of a leakage preventing effect that prevents input signals from leaking to it and the leakage of input signals concerned is one of factors which deteriorate the device in output waveform. CONSTITUTION:A direct current bias circuit composed of the first resistor 12, an inductor 10, and the second resistor 13 is connected in this order to a semiconductor laser 4 in series, and a capacitor 11 is connected between the bias input terminal of a semiconductor laser case and a ground. By this setup, a semiconductor laser device of this design is able to stably output laser rays of waveform adaptable for a high speed digital communication more than 2.5Gb/s.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device used as a light emitting source for optical communications for large-capacity, long-distance transmission.

0002

2. Description of the Related Art The circuit configuration of a conventional semiconductor laser device will be explained with reference to FIG. A bias circuit 5 and a signal input circuit 7 are connected to a semiconductor laser 4 whose anode side is grounded to a metal case 1 of the semiconductor laser device. The bias circuit 5 uses a chip coil or a chip inductor as an inductance 10, and further includes a bonding wire for connection and a circuit patterned on an alumina substrate or the like. The signal input circuit 7 includes a resistor 3 for impedance matching and a circuit for connecting a microstrip line, bonding wire, etc.

The semiconductor laser 4 is DC biased from a bias input terminal 6 through a bias circuit 5 including an inductor 10 . On the other hand, the structure is such that the signal is applied from the signal input terminal 8 to the semiconductor laser 4 via the signal input circuit 7 including the impedance matching resistor 3, superimposed on the DC bias current.

0004

In general, when this type of semiconductor laser device is applied to high-speed optical digital communications, it is important that an extremely stable optical output waveform can be obtained for high-frequency signals. Roughly speaking, the causes of optical output waveform deterioration are caused by three frequency characteristics of the semiconductor laser, the semiconductor laser module, and the drive circuit. Countermeasures have been taken for each of these factors, but currently, the frequency characteristics of the semiconductor laser module itself are the most limiting factor in the performance of the device.

In addition to the semiconductor laser, the semiconductor laser module includes a light receiving element for monitoring the optical output light of the semiconductor laser, a Peltier element for temperature control, a thermistor for temperature detection, and furthermore, a light receiving element for monitoring the optical output light of the semiconductor laser, and a thermistor for temperature detection. It has a complex structure with an optical coupling system including a lens for taking out the optical fiber to the outside, making it difficult to design a structure that prioritizes only high frequency characteristics.

Generally, the anode side of a semiconductor laser is grounded to a case, and the cathode side is connected to a bias circuit and a signal input circuit. Although the frequency characteristics are greatly influenced by the circuit and structure described above, the causes of waveform deterioration can be summed up in the following three points.

(1) Parasitic inductance between the anode side of the semiconductor laser element and the case (GND).

(2) Parasitic inductance of the signal input circuit.

(3) Leakage of input signals to the bias circuit side.

For (1) and (2), measures have been taken to reduce parasitic inductance by making the connection lines as short as possible. The present invention relates to problem (3). 100~ for conventional semiconductor laser equipment
Although a bias circuit with an inductance of 200 mH prevents high-frequency input signals from leaking to the bias circuit side, the prevention effect is not sufficient, and as shown in FIG. 5(d), the small signal response characteristics are 2 to 2. A large ripple is observed near 5GH.

[0011]

[Means for Solving the Problems] In the semiconductor laser device of the present invention, as a bias circuit for the semiconductor laser chip, a resistor and an inductance are connected in series with the semiconductor laser chip, and a capacitance is inserted between the bias input terminal of the case and the case GND. has been done. With this configuration, it is possible to realize a bias circuit having a function of effectively preventing input signals from leaking into the bias circuit side, which is a cause of the waveform deterioration described above.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. 1 to 3 show embodiments of the present invention. The semiconductor laser 4 has its anode side grounded to the metal case 1 of the semiconductor laser device, and is connected to the semiconductor laser anode terminal (case GND terminal) of the metal case. On the other hand, the cathode side of the semiconductor laser is connected to a bias circuit 5 and a signal input circuit 7.

The input signal applied to the semiconductor laser is introduced through a signal input terminal 8 provided on the metal case 1 of the semiconductor laser device, and is connected to an impedance matching resistor whose resistance value is determined according to the drive device that emits the input signal. 3
The signal is superimposed on a DC bias current through a signal input circuit 7 including a DC bias current, and is applied to a semiconductor laser.

On the other hand, the bias circuit, which has one side connected to the bias input terminal 6 provided in the case of the semiconductor laser device and the other side connected to the cathode side of the semiconductor laser, is constructed as shown in FIGS. 1 to 3. , was constructed in the following three ways.

(1) Consists of only 20Ω resistor 2 (Figure 1)
(2) 20Ω resistor 2, 20nH in series with the semiconductor laser
The inductor 10 and bias input terminal 6 are connected, and the inductor 10 is connected between the bias input terminal 6 and the case ground (GND).
Configuration with 00pF capacitance 11 connected (Figure 2)
(3) A first resistor 12 of 20Ω in series with the semiconductor laser.
, an inductance of 20nH, a second resistor 13 of 10Ω, and a capacitance of 100pF between the bias input terminal 6 and the case GND (Figure 3).This is one of the causes of waveform deterioration mentioned above. The effect of preventing leakage of input signals to the bias circuit increases in the order of FIGS. 1, 2, and 3.

The bias circuit configuration has a function of effectively preventing leakage of input signals to the bias circuit side.
10Ω from the semiconductor laser side in series with the semiconductor laser
second resistor, 0-50nH inductance, 20Ω
The configuration is such that a capacitance 2 of 0 to 200 pF is connected between the bias input terminal and the ground in the order of the first resistor.
The second resistance is 0Ω, the inductance is 0nH, and the capacitance is 0pF. The embodiment of FIG. 2 is a special case in which the second resistance is 0Ω. The small signal characteristics of the semiconductor laser devices shown in FIGS. 1 to 3 are shown in FIGS. 5(a), (b), and (c), respectively.
).

[0017]

As explained above, in the semiconductor laser device of the present invention, a first resistor, an inductance, and a second resistor are connected in series to the semiconductor laser as a bias circuit for the semiconductor laser, and a bias input terminal of the case is connected to the semiconductor laser in series. A capacitance is connected between the case GND and the case GND. In this configuration, in order to effectively prevent input signal leakage to the bias circuit side, which is one of the causes of waveform deterioration mentioned above, the first resistor is 20Ω, the second resistor is 10Ω, and the inductance is 0 to 0. 50nH, 2.5G by setting the capacitance between 0 and 200pF.
A semiconductor laser device capable of supporting optical digital communication at b/s or higher can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a conventional semiconductor laser device.

FIG. 5 is a small signal response characteristic diagram of the present invention and a characteristic diagram of a conventional semiconductor laser device.

[Explanation of symbols]

1 Metal case of semiconductor laser device 2 Resistor 3 Impedance matching resistor 4 Semiconductor laser 5 Bias circuit 6 Bias input terminal 7 Signal input circuit 8 Signal input terminal 9 Semiconductor laser anode terminal (case GND terminal) 10 Inductance 11 Capacitance 12 First resistor 13 Second resistance

Claims (3)

[Claims] 1. A semiconductor laser device comprising a semiconductor laser, a DC bias circuit that applies a DC bias current to the semiconductor laser, and a signal input circuit for a high frequency signal that is applied superimposed on the DC bias current. A semiconductor laser device characterized in that a bias circuit is composed only of resistors. 2. A semiconductor laser device comprising a semiconductor laser, a DC bias circuit that applies a DC bias current to the semiconductor laser, and a signal input circuit for a high frequency signal that is applied superimposed on the DC bias current. A semiconductor laser device, wherein the bias circuit includes a resistor and an inductance connected in series to the semiconductor laser chip, and a capacitance connected to ground at a bias input terminal portion of a semiconductor laser device container. 3. A semiconductor laser device comprising a semiconductor laser, a DC bias circuit that applies a DC bias current to the semiconductor laser, and a signal input circuit for a high frequency signal that is applied superimposed on the DC bias current. The bias circuit is characterized in that a first resistor, an inductance, and a second resistor are connected in series with the semiconductor laser, and a capacitance is connected between the bias input terminal portion of the semiconductor laser device container and the ground. Semiconductor laser equipment.