Coherent optical orthogonal frequency division multiplexing (OFDM) reception using self optical carrier extraction
A method includes producing interference between a received optical OFDM signal and an optical carrier extracted from the received optical OFDM signal to provide optical coherent detection of the received optical OFDM signal. Preferably, producing the interference includes optically splitting the received optical OFDM signal into a first part that is filtered to extract the carrier from the received optical OFDM signal and a second part similar to the received optical OFDM signal.
1. A method comprising:
receiving an incoming light beam containing an optical OFDM signal carrying an optical carrier component, wherein data is fed to an electro-optical (EO) modulator sourced by a laser and the EO modulated output is filtered, amplified and sent over an optical fiber, wherein the optical carrier component from the incoming signal uses zero padding in OFDM modulation;
producing an interference light beam between a received optical OFDM signal and an optical carrier extracted from the received optical OFDM signal to provide optical coherent detection of the received optical OFDM signal,
wherein the incoming light beam and the interference light beam have one polarization state and have one central wavelength for homodyne detection, and
optically splitting the received optical OFDM signal into a first part that is filtered with an optical filter to extract the carrier from the received optical OFDM signal and a second part similar to the received optical OFDM signal; and
determining an error vector magnitude (EVM) as:
EVM
=
1
N
∑
j
=
1
N
[
I
j
-
I
~
j
2
+
Q
j
-
Q
~
j
2
]
1
N
∑
j
=
1
N
[
I
~
j
2
+
Q
~
j
2
]
where
I j is the I component of the j-th symbol received,
Q j is the Q component of the j-th symbol received,
Ĩ j is the ideal I component of the j-th symbol received,
{tilde over (Q)} j is the ideal Q component of the j-th symbol received.
2. The method of claim 1 , wherein the optical filter comprises one of a fixed bandpass filter for a certain wavelength, a tunable bandpass filter for incoming signals at different wavelengths, and a periodic bandpass or comb filter for incoming signals at different wavelengths on a certain wavelength grids.
3. A method comprising the steps of:
embedding an optical carrier component into a transmitted OFDM signal, wherein data is fed to an electro-optical (EO) modulator sourced by a laser and the EO modulated output is filtered, amplified and sent over an optical fiber;
splitting an incoming light beam containing a received optical OFDM signal into a first part and a second part, each part having optical spectrum characteristics of the received optical OFDM signal;
optically filtering the first part to extract an optical carrier from the received optical OFDM signal; and
receiving the extracted optical carrier and the second part into a coherent receiver,
generating an interference light beam, wherein the incoming light beam and the interference light beam have one polarization state and have one central wavelength for homodyne detection, and
optically splitting the received optical OFDM signal into a first part that is filtered with an optical filter to extract the carrier from the received optical OFDM signal and a second part similar to the received optical OFDM signal using a radio frequency carrier or including zero padding in OFDM modulation; and
determining an error vector magnitude (EVM) as:
EVM
=
1
N
∑
j
=
1
N
[
I
j
-
I
~
j
2
+
Q
j
-
Q
~
j
2
]
1
N
∑
j
=
1
N
[
I
~
j
2
+
Q
~
j
2
]
where
I j is the I component of the j-th symbol received,
Q j is the Q component of the j-th symbol received,
Ĩ j is the ideal I component of the j-th symbol received,
{tilde over (Q)} j is the ideal Q component of the j-th symbol received.
4. The method of claim 3 , wherein the step of receiving comprises producing an interference between the received optical OFDM signal and the extracted optical carrier.
5. The method of claim 4 , wherein the optical filtering comprises one of fixed bandpass filtering for a certain wavelength, tunable bandpass filtering for incoming signals at different wavelengths, and periodic bandpass filtering for incoming signals at different wavelengths on a certain wavelength grids.
6. The method of claim 3 , comprising splitting an incoming signal into a first branch at a coherent optical receiver as an incoming optical OFDM signal, and a second branch passing through a narrow band optical filter to extract an optical carrier component for interference at the coherent optical receiver for subsequent demodulation.
7. The method of claim 3 , comprising generating an optical OFDM signal with an optical carrier component by having a radio frequency carrier in a transmitter side.
8. The method of claim 3 , comprising providing tolerance to lasers with predetermined line width, wherein the optical OFDM signal does not degrade incoming signals with random phase changes or without carrier phase recovery.