Apparatus for linearization of optic modulators using a feed-forward predistortion circuit

Claim 2

A predistortion circuit for linearizing an optic modulator, said predistortion circuit being operative in response to an input signal (X), comprising: means for providing a first signal(X); means for providing a second signal 2(X); and means for combining said first and second signals to provide a modulating signal 2(X)-sin(X), such that the optic modulator receiving said modulating signal generates a linear output signal(X).

Claim 3

The circuit of claim 1, wherein said means for providing said first signal comprises an optic modulator.

Claim 4

The circuit of claim 2, wherein said optic modulator comprises a Mach-Zehnder modulator.

Claim 5

The circuit of claim 1, wherein said means for providing said first signal comprises: an input line having an input voltage; a positive reference branch; a negative reference branch; an output line having an output voltage; and wherein said positive reference branch comprises a positive reference voltage and a first diode, and said negative reference branch comprises a negative reference voltage and a second diode, said positive and negative reference branches being connected to a single node between said input line and said output line, said diodes being similarly biased such that said output voltage follows said input voltage when said diodes are not conducting, and said output voltage bends when said diodes are conducting, thereby producing said first signal.

Claim 6

The circuit of claim 1, wherein said means for providing said second signal comprises an amplifier.

Claim 7

The circuit of claim 1, wherein said means for combining said first signal and said second signal to provide said modulating signal comprises a power combiner.

Claim 8

A circuit for modulating an optic signal, said circuit being operative in response to an input signal(X), comprising: means for providing a first signal having a waveform sin(X); means for providing a second signal having a waveform 2(X); means for combining said first and second signals to provide a modulating signal having a waveform 2(X)-sin(X); and means for modulating the optic signal with said modulating signal, said means for modulating having a transfer function sin(X), such that the optic signal is modulated to produce a linear output signal(X).

Claim 9

A circuit for modulating an optic signal, said circuit being operative in response to an input signal(X), comprising: means for providing a first signal having a waveform sin(X); means for providing a second signal having a waveform 2(X); means for combining said first and second signals to provide a modulating signal having a waveform 2(X)-sin(X); and means for modulating the optic signal with said modulating signal, said means for modulating having a transfer function sin(X), such that the optic signal is modulated to produce a linear output signal(X).

Claim 10

The circuit of claim 7, wherein said means for providing said first signal comprises an optic modulator.

Claim 11

The circuit of claim 8, wherein said optic modulator comprises a Mach-Zehnder modulator.

Claim 12

The circuit of claim 7, wherein said means for providing said first signal comprises: an input line having an input voltage; a positive reference branch; a negative reference branch; an output line having an output voltage and wherein said positive reference branch comprises a positive reference voltage and a first diode, said negative reference branch comprises a negative reference voltage and a second diode, said positive and negative reference branches being connected to a single node between said input line and said output line, said diodes being similarly biased such that said output voltage follows said input voltage when said diodes are not conducting, and said output voltage bends when said diodes conduct, thereby producing said first signal.

Claim 13

The circuit of claim 7, wherein said means for providing said second signal comprises an amplifier.

Claim 14

The circuit of claim 7, wherein said means for combining said first signal and said second signal to provide said modulating signal comprises a power combiner.

Claim 15

The circuit of claim 7, wherein said means for modulating the optic signal with said modulating signal comprises an optic modulator.

Claim 16

The circuit of claim 13, wherein said optic modulator comprises a Mach-Zehnder modulator.

Claim 17

An optical modulating system having a linearized transfer function comprising: an optical modulator for receiving a light source input and a modulating input for modulating said light source input, said optical modulator comprising a non-linear transfer function; and a predistortion system for linearizing said non-linear transfer function of said optical modulator, said predistortion system comprising: a non-linear element for receiving an input signal(X) and for responding with an output signal H(X), said input signal(X) having a signal power; means for providing an output signal (A*X) in response to said input signal(X). means for combining said output signal H(X) of said non-linear element with said output signal (A*X), said means for combining generating an output signal, (A*X)-H(X), having a signal power; and means for matching said signal power of said input signal (X) with said signal power of said output signal, (A*X)-H(X), of said means for combining such that said signal power are substantially equal, said means for matching generating an output signal received by said optical modulator as said modulating input, thereby linearizing said non-linear transfer function of said optical modulator.

Claim 18

An optical modulating system having a linearized transfer function comprising: an optical modulator for receiving a light source input and a modulating input for modulating said light source input, said optical modulator comprising a non-linear transfer function; and a predistortion system for linearizing said non-linear transfer function of said optical modulator, said predistortion system comprising: a non-linear element for receiving an input signal(X) and for responding with an output signal H(X), said input signal(X) having a signal power; means for providing an output signal (A*X) in response to said input signal(X). means for combining said output signal H(X) of said non-linear element with said output signal (A*X), said means for combining generating an output signal, (A*X)-H(X), having a signal power; and means for matching said signal power of said input signal (X) with said signal power of said output signal, (A*X)-H(X), of said means for combining such that said signal power are substantially equal, said means for matching generating an output signal received by said optical modulator as said modulating input, thereby linearizing said non-linear transfer function of said optical modulator.

Claim 19

The optical modulating system of claim 15, wherein said output signal, H(X), of said non-linear element is sin(X).

Claim 20

The optical modulating system of claim 15, wherein said output signal, (A*X), of said means for providing an output signal (A*X) in response to said input signal(X) is (2*X).

Claim 21

The optical modulating system of claim 15, wherein said output signal, H(X), of said non-linear element comprises a Taylor series expansion yielding a first term(X).

Claim 22

The optical modulating system of claim 15, wherein said non-linear element comprises an optic modulator.

Claim 23

The optical modulating system of claim 19, wherein said optic modulator comprises a Mach-Zehnder modulator.

Claim 24

The optical modulating system of claim 15, wherein said non-linear element comprises: an input line having an input voltage; an output line having an output voltage; a positive reference branch comprising: a positive reference voltage; and a first diode; a negative reference branch comprising: a negative reference voltage; and a second diode; and wherein said positive and said negative reference branches are connected to a single node between said input line and said output line, and said first and second diodes are similarly biased, such that said output voltage follows said input voltage when said diodes are not conducting, and said output voltage bends when said diodes conduct, thereby producing said output signal H(X).

Claim 25

The optical modulating system of claim 15, wherein said means for providing an output signal (A*X) comprises an amplifier.

Claim 26

The optical modulating system of claim 15, wherein said means for matching said signal power comprises an attenuator.

Claim 27

The optical modulating system of claim 15, wherein said means for matching said signal power comprises an amplifier.

Claim 28

The optical modulating system of claim 15, wherein said output signal, H(X), of said non-linear element comprises a delay, and said means for providing an output signal (A*X) comprises: a delay; and means for matching said delay of said means for providing an output signal (A*X) with said delay of said output signal, H(X), of said non-linear element.

Claim 29

The optical modulating system of claim 25, wherein said means for matching said delay comprises an amplifier and a cable having a predetermined length.