System of method for dynamic range extension
View Patent ↗The present invention generally relates to the operation of optical network equipment such as optical amplifiers. In one aspect, a method of operating an optical amplifier is provided such that output of the optical amplifier avoids the effects of operating an optical gain medium in a non-linear (kink) region of an L-I curve. The method generally includes operating an optical gain medium in a fully off state or fully on state above the kink region with a PWM signal. In another aspect, the effects of the kink region may be compensated for by utilizing a lookup table. A sample of the optical power of an amplified optical signal may be used to select an entry in the lookup table that compensates for non-linearities in the kink region. In yet a further aspect, a lookup table may be used to control a pulse modulator to compensate for non-linearites in the kink region of the L-I curve.
1. An optical amplifier system comprising:
an optical gain medium configured to receive an input optical signal and output an amplified optical signal;
a pump laser optically coupled to an input of the optical gain medium; and
a pump controller configured to generate a pulse width modulated control signal to control the pump laser to operate alternately above and below a non-linear region of a power-current curve of the pump laser,
wherein the non-linear region is located at a high power portion of the power-current curve of the pump laser that is above a linear region of the power-current curve of the pump laser.
2. The optical amplifier of claim 1 , wherein the pulse width modulated control signal includes a high current output state that corresponds to a maximum output power of the pump laser.
3. The optical amplifier of claim 1 , wherein the pulse width modulated control signal includes a low current output state that corresponds to a minimum output power of the pump laser.
4. The optical amplifier of claim 1 , wherein the amplified optical signal is controlled by the widths of the pulses.
5. The optical amplifier of claim 1 , further including a photo-detector and electrical signal conditioning unit optically coupled to the output of the optical gain medium and coupled to the pump laser.
6. The optical amplifier of claim 1 , further comprising a fiber Bragg grating optically coupled between the optical gain medium and the pump laser.
7. The optical amplifier of claim 1 , wherein the optical gain medium is an Erbium-doped fiber.
8. The optical amplifier of claim 1 , wherein the high power portion of the power-current curve of the pump laser is above a portion of the power-current curve of the pump laser corresponding to a pump laser drive current of 100 mA.