Semiconductor laser device

Details Semiconductor laser device Semiconductor laser device

1999-04-15

2001-09-18

Scott, Jr., Leon (Department: 2881)

Coherent light generators

Particular component circuitry

Optical pumping

Reexamination Certificate

active

06292500

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device including a semiconductor laser chip.
A semiconductor laser device provides an optical output by operating a semiconductor laser chip with the application of a forward bias thereto. However, if a surge voltage has been applied to the semiconductor laser chip, then an excessive amount of surge current flows through the semiconductor laser chip in the forward direction, resulting in an excessive optical output. Consequently, the performance of the semiconductor laser chip itself deteriorates.
First, a conventional surge-suppressive semiconductor laser device will be described with reference to FIGS.
8
(
a
) and
8
(
b
).
FIG.
8
(
a
) is perspective view of a conventional semiconductor laser device. As shown in FIG.
8
(
a
), a semiconductor laser chip
23
, made of GaAlAs, is formed over a ceramic capacitor
21
with a laser mount
22
interposed therebetween. The ceramic capacitor
21
is connected in parallel to the semiconductor laser chip
23
via a wire
24
.
FIG.
8
(
b
) is circuit diagram of the conventional semiconductor laser device. As shown in FIG.
8
(
b
), the semi-conductor laser chip
23
and the ceramic capacitor
21
are connected in parallel to each other. When a surge voltage is applied to the semiconductor laser device, the ceramic capacitor
21
absorbs a surge current, which is a transient current, thus preventing an excessive amount of current from being supplied to the semiconductor laser chip
23
. Also, if the impedance of the ceramic capacitor
21
is made sufficiently smaller than that of the semiconductor laser chip
23
by increasing the capacitance of the ceramic capacitor
21
, then the surge current can be absorbed even more effectively.
In the conventional semiconductor laser device, in order to absorb the surge current sufficiently, the impedance of the ceramic capacitor
21
should be smaller than that of the semiconductor laser chip
23
. Thus, the capacitance of the ceramic capacitor
21
should be set larger than the junction capacitance of the semiconductor laser chip
23
.
However, suppose a reference voltage, applied to a laser driver for driving the semiconductor laser chip
23
, fluctuates; the semiconductor laser chip
23
is superimposed with a radio frequency voltage; or a pulse voltage is applied to the semiconductor laser chip
23
when the capacitance of the ceramic capacitor
21
is larger than the junction capacitance of the semiconductor laser chip
23
. In each of these situations, radio frequency components leak to the ceramic capacitor
21
connected in parallel to the semiconductor laser chip
23
. As a result, the response characteristics of the semiconductor laser chip
23
adversely deteriorate.
SUMMARY OF THE INVENTION
An object of the present invention is providing a surge-suppressive semiconductor laser device exhibiting excellent response characteristics even if a radio frequency voltage has been superimposed or if the device is modulated with pulses.
In order to achieve this object, a first exemplary semiconductor laser device according to the present invention includes: a semiconductor laser chip including an anode and a cathode; and a field effect transistor. The anode is connected to the drain of the field effect transistor. The gate of the field effect transistor is connected to the drain of the field effect transistor. And the cathode is connected to the source of the field effect transistor.
In the first semiconductor laser device, when a voltage exceeding a threshold voltage of the field effect transistor is applied to the semiconductor laser chip, a surge current flows through, and can be absorbed by, the field effect transistor. Also, since the field effect transistor starts to operate only when a voltage exceeding the threshold voltage of the field effect transistor is applied to the semiconductor laser chip, the response of the semiconductor laser chip does not deteriorate even if a radio frequency voltage has been superimposed or the device has been modulated with a pulse voltage.
A second exemplary semiconductor laser device according to the present invention includes: a semiconductor laser chip including an anode and a cathode; and a bipolar transistor. The anode is connected to the collector of the bipolar transistor, and the cathode is connected to the emitter of the bipolar transistor.
In the second semiconductor laser device, when a voltage exceeding an avalanche voltage between the collector and the emitter of the bipolar transistor is applied to the semiconductor laser chip, a surge current flows through, and can be absorbed by, the bipolar transistor. Also, the bipolar transistor starts to operate only when a voltage exceeding the avalanche voltage between the collector and emitter of the bipolar transistor is applied to the semiconductor laser chip. Thus, the response of the semiconductor laser chip does not deteriorate even if a radio frequency voltage has been superimposed or the device has been modulated with a pulse voltage.
A third exemplary semiconductor laser device according to the present invention includes: a semiconductor laser chip including an anode and a cathode; a field effect transistor; and a bipolar transistor. The anode is connected to the collector of the bipolar transistor. The cathode is connected to the emitter of the bipolar transistor. The drain of the field effect transistor is connected to the collector of the bipolar transistor. The source of the field effect transistor is connected to the base of the bipolar transistor. And the gate of the field effect transistor is connected to the drain of the field effect transistor.
In the third semiconductor laser device, only when a voltage exceeding a threshold voltage of the field effect transistor is applied to the semiconductor laser chip, the field effect transistor starts to operate. In response thereto, a base current is injected into the bipolar transistor and a surge current flows through, and can be absorbed by, the bipolar transistor. Also, since the field effect transistor starts to operate only when a voltage exceeding the threshold voltage of the field effect transistor is applied to the semiconductor laser chip, the response of the semiconductor laser chip does not deteriorate even if a radio frequency voltage has been superimposed or the device has been modulated with a pulse voltage.
A fourth exemplary semiconductor laser device according to the present invention includes: a semiconductor laser chip including an anode and a cathode; and a surge absorber including a diode and a capacitor that are connected in series to each other. The anode is connected to one terminal of the surge absorber. The cathode is connected to the other terminal of the surge absorber. And the diode is connected to the semiconductor laser chip to have the same polarity.
The fourth semiconductor laser device includes a surge absorber including a diode and a capacitor that are connected in series to each other. Since the bias voltage of the diode is relatively low during the normal operation of the semiconductor laser device, the impedance of the diode is larger than that of the semiconductor laser chip. Thus, it is possible to prevent the modulated components from leaking from the laser chip into the surge absorber even if a radio frequency voltage has been superimposed, for example. As a result, the response characteristics of the semiconductor laser chip do not deteriorate.
A fifth semiconductor laser device according to the present invention includes: a semiconductor laser chip including an anode and a cathode; a first diode including an anode and a cathode; and a second diode including an anode and a cathode. The anodes of the first and second diodes are connected in common. The anode of the semiconductor laser chip is connected to the cathode of the first diode. And the cathode of the semiconductor laser chip is connected to the cathode of the second diode.
In the fifth semiconductor laser device, when a surge voltage is applied to the sem

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