Calibration of laser systems
View Patent ↗A method for determining a condition of the laser system includes determining a change in a laser current from an initial value. A method for measuring a laser current includes determining a difference between the values of a power supply current, which is the value of the laser current. A method for measuring a transmitted power includes generating a first control signal that sets a magnitude of a bias current supplied to a laser, generating a second control signal that sets a of a modulation current supplied to the laser, and determining a difference between values of a high and a low transmitted powers. A method for measuring a received optical power includes determining a received OMA corresponding to the power signal, which is the transmitted OMA minus a known loss through a calibration fiber that couples the laser transmitter to the laser receiver.
1. A method for a laser system to measure a value of a bias current to a laser, comprising:
completing a bias current path from a cathode of the laser to ground so the bias current flows through the laser;
measuring a first value of a power supply current to the laser system from a supply rail;
blocking the bias current path from the cathode of the laser to ground so the bias current does not flow through the laser;
measuring a second value of the power supply current to the laser system from the supply rail; and
determining a difference between the second value and the first value of the power supply current, wherein the difference is the value of the bias current.
2. The method of claim 1 , wherein said completing the bias current path comprises closing a switch coupling a current source and ground so the current source sinks the bias current from the laser to ground.
3. The method of claim 2 , further comprising, when the bias current path is blocked, turning on a second current source to draw a second current from the supply rail, wherein the second current is equal to a base leakage current drawn by the current source when the bias current path is complete.
4. The method of claim 1 , further comprising turning off a photo detector.
5. The method of claim 1 , further comprising turning off a current source that provides a modulated current to the laser.
6. A laser system, comprising:
a laser having an anode coupled to a supply rail;
a first current source coupled to a cathode of the laser to sink a bias current from the laser to ground;
a first switch between the first current source and ground; and
a controller outputting a control signal to a first control terminal of the first switch, wherein the controller can open the first switch to block a bias current path from the laser to ground; and
a second switch coupling a second current source to the supply rail, the second switch having a second control terminal receiving the control signal, the second current source drawing a second current from the supply rail when the second switch is closed, the second current being equal to a base leakage current drawn by the first current source when the bias current path is complete.
7. The laser system of claim 6 , further comprising:
a photo detector; and
a third switch in a monitoring current path of the photo detector, the controller outputting another control signal to a third control terminal of the third switch, wherein the controller can open the third switch to block the monitoring current path.
8. The laser system of claim 7 , further comprising an analog-to-digital converter coupled by the third switch to the photo detector.
9. The laser system of claim 6 , wherein the first current source comprises:
a current mirror coupled between the cathode of the laser and ground, the current mirror receiving a reference current signal and sinking the bias current from the laser to ground, wherein the switch couples a terminal of a transistor in the current mirror to ground.
10. The laser system of claim 9 , wherein the first current source further comprises:
a digital-to-analog converter converting a digital input signal to an analog voltage signal;
a voltage-to-current converter converting the analog voltage signal to a second reference current signal; and
a second current mirror coupled to the supply rail, the second current mirror receiving the second reference current signal and sourcing the reference current signal to the current mirror.