Gain controllable optical amplifier and applications thereof

An optical amplifier for amplifying a power of an input signal, comprising:

• (A) a rare earth doped fiber having an input side and an output side, for amplifying the power of the input signal;
• (B) a pump-source coupled to said output side of said rare earth doped fiber having an output propagating contra-directionally with respect to the input signal;
• (C) a compensation-signal source coupled with the input side of the rare earth doped fiber having a compensation-signal propagating co-directionally with respect to the input signal for compensating the power of the input signal;
• (D) an optical receiver, coupled with the input side of the rare earth doped fiber, for measuring power of a propagating amplified-spontaneous-emission (ASE) generated by the pump-source in the rare earth doped fiber;
• (E) a compensation-signal controller for controlling power of the compensation-signal source in response to the measured power of the ASE;
• (F) a modulator for modulating the compensation-signal source to produce a monitor signal,
• wherein said compensation signal transmits said monitor signal to a previous optical element connected to said input side of said rare earth doped fiber.

An optical amplifier for amplifying a power of an input signal, comprising:

• (A) a rare earth doped fiber having an input side and output side, for amplifying the power of the input signal;
• (B) a pump-source coupled to said output side of said rare earth doped fiber having an output propagating contra-directionally with respect to the input signal;
• (C) an optical receiver, coupled to the output side of the rare earth doped fiber, for measuring power of the input signal;
• (D) a filter coupled with the input side of the rare earth doped fiber for filtering a power of a propagating amplified-spontaneous-emission (ASE) generated by the pump-source;
• and
• (E) an attenuation controller for controlling an attenuation of the filtered power of the ASE in response to the measured power of the input signal, and for outputting the filtered power of the ASE after the attenuation to the output side of the rare earth doped fiber contra-directionally with respect to the output signal.

An optical amplifier for amplifying a power of an input signal, comprising:

• (A) a rare earth doped fiber having an input side and an output side, for amplifying the power of the input signal;
• (B) a pump-source coupled to said output side of said rare earth doped fiber having an output propagating contra-directionally with respect to the input signal;
• (C) a wavelength-selective reflector, coupled to the input side of the rare earth doped fiber, for reflecting a light having a specific wavelength as a compensation signal, and
• (D) a filter coupled to the input side of the rare earth doped fiber for selecting the compensation signal.

A distribution system comprising:

• (A) a first optical coupler for mixing original input signals, and for distributing the original input signals after mixing as a distributed input signal;
• (B) an optical amplifier connected to the first optical coupler for amplifying power of the distributed input signal, and for outputting the amplified input signal as an output signal, wherein the optical amplifier includes:
• (i) a rare earth doped fiber having an input side and an output side, for amplifying the power of the input signal;
• (ii) a pump-source coupled to said output side of said rare earth doped fiber having an output propagating contra-directionally with respect to the input signal;
• (iii) a compensation-signal source coupled with the output side of the rare earth doped fiber having a compensation-signal propagating contra-directionally with respect to the input signal for compensating the power of the input signal;
• (iv) an optical receiver, coupled with the input side of the rare earth doped fiber, for measuring power of a propagating amplified-spontaneous-emission (ASE) generated by the pump-source in the rare earth doped fiber;
• and
• (v) a compensation-signal controller for controlling power of the compensation-signal source in response to the measured power of the ASE;
• and (C) a second optical coupler coupled to the optical amplifier for mixing and distributing the output signal.

A local area network system comprising:

• (A) a first optical coupler for mixing original input signals from previous local area networks, and for distributing the mixed input signals;
• (B) an optical amplifier connected to the first optical coupler for amplifying a power of the distributed input signals, and for outputting the amplified input signals as an output signal, wherein the optical amplifier includes:
• (i) a rare earth doped fiber having an input side and an output side, for amplifying the power of the input signal;
• (ii) a pump-source coupled to said output side of said rare earth doped fiber having an output propagating contra-directionally with respect to the input signal;
• (iii) a compensation-signal source coupled with the output side of the rare doped fiber having a compensation-signal propagating contra-directionally with respect to the input signal for compensating the power of the input signal;
• (iv) an optical receiver, coupled with the input side of the rare earth doped fiber, for measuring power of a propagating amplified-spontaneous-emission (ASE) generated by the pump-source in the rare earth doped fiber;
• and
• (v) a compensation-signal controller for controlling power of the compensation-signal source in response to the measured power of the ASE;
• and
• (C) a second optical coupler for mixing the output signals of the optical amplifier, and for distributing each of the mixed output signals to a next local area network.

A method for controlling amplification of an optical amplifier using a rare earth doped fiber pumped by constant output of a pump-source propagating contra-directionally with respect to the input signal, comprising the steps of:

• (A) measuring a power of a propagating amplified-spontaneous-emission (ASE) generated by the pump-source in the rare earth doped fiber at an input side of the rare earth doped fiber;
• (B) computing a value for power of a compensation-signal based on a measured power of the ASE;
• (C) controlling power of the compensation-signal charged contra-directionally with respect to the input signal based on the value computed in the computation step (B);
• and
• (D) repeating the steps (A), (B) and (C) if deviation of the measured ASE power from a target ASE power exceeds a predetermined value.

A method for controlling amplification of an optical amplifier for an input signal, using a rare earth doped fiber having an input side and an output side pumped by constant output of a pump-source propagating contra-directionally with respect to the input signal, comprising the steps of:

• (A) measuring a power of a propagating amplified-spontaneous-emission (ASE) generated by the pump-source in the rare earth doped fiber at the input side of the rare earth doped fiber;
• (B) measuring a power of the input signal;
• (C) controlling attenuation of the ASE based on the measured power of the input signal;
• (D) outputting said attenuated ASE to the output side of said rare earth doped fiber contra-directionally with respect to said input signal ASE;
• and
• (E) repeating the steps (A), (B), (C) and (D) if deviation of said measured ASE power from a target ASE power exceeds the predetermined value.

An optical amplifier for amplifying an input signal comprising:

• (A) a rare earth doped fiber having an input side and an output side, for amplifying the power of the input signal;
• (B) pump-source means for generating an amplified-spontaneous-emission (ASE) contra-directionally with respect to the input signal;
• and
• (C) compensation-signal means coupled to the rare earth doped fiber for compensating power of the input signal in response to power of the ASE, wherein said compensation-signal means includes means for measuring power of said ASE.

An optical amplifier for amplifying an input signal comprising:

• (A) a rare earth doped fiber having an input side and an output side, for amplifying the power of the input signal;
• (B) pump-source means for generating an amplified-spontaneous-emission (ASE) Contra-directionally with respect to the input signal;
• and
• (C) compensation-signal means coupled to the rare earth doped fiber for compensating power of the input signal in response to power of the ASE, wherein said compensation means includes:
• (D) filter means coupled to the input side of the rare earth doped fiber for filtering said ASE;
• and
• reflecting means for reflecting said filtered ASE through rare earth doped fiber co-directionally with respect to said input signal.