Linearized Bragg grating assisted electro-optic modulator
View Patent ↗The invention provides a new linearized electro-optic modulator in which linearization is achieved by modulating the index of a Bragg grating reflector placed in the arm(s) of a Michelson Interferometer. This grating-assisted Michelson Interferometer (GAMI) modulator operates as either an intensity or amplitude modulator, and is shown to significantly improve the linearity of microwave photonics links. Furthermore, this modulator improves the performance of optical communication systems using advanced modulation formats.
1. An optical modulator, comprising:
a Michelson interferometer having an optical amplitude divider having four ports; a first port being an optical input; a second and a third port being connected to a first and a second interferometric arms; the fourth port being an optical output;
at least one of the interferometric arms is terminated by a first Bragg grating;
the first Bragg grating is made from a material whose refractive index is variable upon applying a time variable electrical signal; and
a first pair of electrodes applying the time variable electrical signal to the first Bragg grating, further comprising
a phase shifter applying a phase shift in one of the arms, the phase shifter introduces a 90-degrees round trip phase shift; thus the modulator producing an intensity modulated optical signal.
2. The optical modulator of claim 1 , wherein the optical input is CW signal.
3. The optical modulator of claim 1 , wherein the optical input is optically modulated signal.
4. The optical modulator of claim 1 , wherein the amplitude divider is a coupler.
5. The optical modulator of claim 1 , further comprising a second Bragg grating in one of the said interferometric arms; the second Bragg grating being the same as the first Bragg grating; and a second pair of electrodes applying a second electrical signal to the second Bragg grating.
6. The optical modulator of claim 5 , wherein one electrode is common for both gratings.
7. The optical modulator of claim 5 , the modulator producing an intensity modulated optical signal by applying electrical signal to the first pair of electrodes; applying a DC signal to the second pair of electrodes; and the phase shifter introduces a 90-degrees round trip phase shift.
8. The optical modulator of claim 5 , the modulator producing an amplitude modulated optical signal by applying electrical signal to the first pair of electrodes; applying the same, but inverted signal to the second pair of electrodes; and the phase shifter introduces a 180-degrees round trip phase shift.
9. The modulator of claim 8 , wherein the modulator is made on a silicon substrate.
10. The modulator of claim 9 , wherein the gratings are made from InP.
11. An optical phase and amplitude modulator, comprising:
a first divider splitting incoming laser radiation into an I and a Q optical inputs;
a first Michelson interferometer having a second optical amplitude divider having four ports; a first port being the Q input; a second and a third port being connected to a first and a second interferometric arms; the fourth port being a Q output;
said first interferometric arm is terminated by a first Bragg grating;
said second interferometric arm is terminated by a second Bragg grating;
a first phase shifter introducing 180 degrees round trip phase shift in the second arm;
a second Michelson interferometer having a third optical amplitude divider having four ports; a fifth port being the I input; a sixth and a seventh port being connected to a third and a fourth interferometric arms; the eighth port being an I output;
said third interferometric arm is terminated by a third Bragg grating;
said fourth interferometric arm is terminated by a fourth Bragg grating;
all Bragg gratings are made from a material whose refractive index is variable upon applying a time variable electrical signal;
a second phase shifter introducing 180 degrees round trip phase shift in the fourth arm;
a third phase shifter introducing 90 degrees phase shift in the Q output;
a combiner combining the I and the Q outputs thus outputting a phase and amplitude modulated optical signal, wherein
a first time variable Q electrical signal is applied to a first pair of electrodes changing a refractive index of the first Bragg grating;
a second time variable (−Q) electrical signal which is an inverted first Q electrical signal is applied to a second pair of electrodes changing a refractive index of the second Bragg grating;
a third time variable I electrical signal is applied to a third pair of electrodes changing a refractive index of the third Bragg grating;
a fourth time variable (−I) electrical signal which is an inverted third I electrical signal is applied to a fourth pair of electrodes changing a refractive index of the fourth Bragg grating.
12. The modulator of claim 11 , wherein the output optical signal is a QAM signal.
13. The modulator of claim 11 , wherein the output optical signal is an OFDM signal.
14. The modulator of claim 11 , wherein all dividers are 50/50 dividers.
15. The modulator of claim 11 , wherein all dividers are tunable.