Method and apparatus for directly modulating a laser diode using multi-stage driver circuitry
View Patent ↗An optical transmitter includes a laser driver capable of receiving data and applying the data to drive a laser diode over a transmission line having first and second ends. The first end of the transmission line is coupled to an output of the laser driver. A first terminal of an amplifier is coupled to the second end of the transmission line. A second terminal of the amplifier is coupled to the laser diode. The signal amplitude applied at the first terminal controls optical output amplitude of the laser diode.
1. An optical transmitter comprising:
a driver circuit capable of receiving data and applying the data to drive a laser diode;
a transmission line having first and second ends, the first end being coupled to an output of the driver circuit;
an amplifier having a first terminal coupled to the second end of the transmission line and a second terminal coupled to the laser diode, wherein signal amplitude applied at the first terminal controls an optical output amplitude of the laser diode;
a first resistor disposed between the first end of the transmission line and positive voltage supply; and
a second resistor disposed between the second end of the transmission line and ground, wherein the first and second resistors, respectively, enable a substantial matching of an output impedance of the driver circuit and an input impedance of the amplifier to the characteristic impedance of the transmission line.
2. The optical transmitter of claim 1 , wherein the amplifier comprises a transistor.
3. The optical transmitter of claim 1 , wherein the amplifier comprises a bipolar transistor configured as a common collector amplifier.
4. The optical transmitter of claim 1 , wherein the amplifier comprises a bipolar transistor configured as a common emitter amplifier.
5. The optical transmitter of claim 1 , wherein the amplifier comprises a FET configured as a common drain amplifier.
6. The optical transmitter of claim 5 , wherein the FET comprises a PHEMT.
7. The optical transmitter of claim 1 , wherein the amplifier comprises a FET configured as a common source amplifier.
8. The optical transmitter of claim 7 , wherein the FET comprises a PHEMT.
9. The optical transmitter of claim 1 , wherein the transmission line is selected from a group consisting of a co-planar transmission line and a micro strip.
10. The optical transmitter of claim 1 , wherein the driver circuit is not in a same package as the laser diode, whereby heat dissipation near laser diode is reduced.
11. The optical transmitter of claim 1 , further comprising a third resistor disposed between the second end of the transmission line and the positive voltage supply, wherein a parallel combination between the second and third resistors enables said substantial matching between the characteristic impedance of the transmission line and the input impedance of the amplifier.
12. The optical transmitter of claim 1 , further comprising an AC coupling capacitor in series with the second resistor, whereby reducing power dissipation and improving frequency performance.