Quadrature optical phase modulators for lightwave systems
First Claim
1. A quadrature optical phase modulator comprising:
- first modulation means for phase modulating lightwaves in response to a first modulation signal v1 (t);
second modulation means for phase modulating lightwaves in response to a second modulation signal v2 (t);
an optical divider for coherently coupling an optical carrier to said first and second modulation means;
an optical combiner for coherently combining modulated optical carriers from said first and second modulation means and providing an output optical signal;
means for providing said first modulation signal v1 (t) to said first modulation means, where v1 (t) is of the form
space="preserve" listing-type="equation">v.sub.1 (t)Σ
β
.sub.i1 cos (ω
.sub.i1 t+δ
.sub.i1), whereβ
i1 =amplitude of the ith subcarrier,ω
i1 =frequency of the ith subcarrier, andδ
i1 =phase of the ith subcarrier; and
means for providing said second modulation signal v2 (t) to said second modulation means, where v2 (t) is of the form
space="preserve" listing-type="equation">v.sub.2 (t)=Σ
β
.sub.i2 cos (ω
.sub.i2 t+δ
.sub.i2)+v.sub.π
/2, whereβ
i2 =amplitude of the ith subcarrier,ω
i2 =frequency of the ith subcarrier,δ
i2 =phase of the ith subcarrier; and
v.sub.π
/2 =voltage required to produce a phase shift of π
/2 at the optical carrier frequency.
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Accused Products
Abstract
Optical communication methods and apparatus are disclosed for transmitting two or more optical signals with different optical carrier frequencies on a single optical fiber with high spectral efficiency. Each optical carrier is typically modulated with multiple modulated subcarriers. In one embodiment, an optical phase modulator provides cancellation of second order intermodulation products in each optical signal, thereby permitting the optical carrier frequencies to be spaced by 2fmax, where fmax is the maximum modulation frequency. In another embodiment, a single sideband optical phase modulator provides cancellation of second order intermodulation products and one signal sideband, thereby permitting the optical carrier frequencies to be spaced by fmax. Quadrature optical phase modulators for simultaneous transmission of two independent baseband digital data signals or two independent subcarrier multiplexed signals are disclosed.
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Citations
8 Claims
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1. A quadrature optical phase modulator comprising:
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first modulation means for phase modulating lightwaves in response to a first modulation signal v1 (t); second modulation means for phase modulating lightwaves in response to a second modulation signal v2 (t); an optical divider for coherently coupling an optical carrier to said first and second modulation means; an optical combiner for coherently combining modulated optical carriers from said first and second modulation means and providing an output optical signal; means for providing said first modulation signal v1 (t) to said first modulation means, where v1 (t) is of the form
space="preserve" listing-type="equation">v.sub.1 (t)Σ
β
.sub.i1 cos (ω
.sub.i1 t+δ
.sub.i1),where β
i1 =amplitude of the ith subcarrier,ω
i1 =frequency of the ith subcarrier, andδ
i1 =phase of the ith subcarrier; andmeans for providing said second modulation signal v2 (t) to said second modulation means, where v2 (t) is of the form
space="preserve" listing-type="equation">v.sub.2 (t)=Σ
β
.sub.i2 cos (ω
.sub.i2 t+δ
.sub.i2)+v.sub.π
/2,where β
i2 =amplitude of the ith subcarrier,ω
i2 =frequency of the ith subcarrier,δ
i2 =phase of the ith subcarrier; andv.sub.π
/2 =voltage required to produce a phase shift of π
/2 at the optical carrier frequency. - View Dependent Claims (2, 3, 4)
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5. A quadrature optical phase modulator comprising:
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first modulation means for phase modulating lightwaves in response to a first modulation signal v1 (t)+v.sub.π
;second modulation means for phase modulating lightwaves in response to a second modulation signal -v1 (t); third modulation means for phase modulating lightwaves in response to a third modulation signal v2 (t)+v.sub.π
/2 ;fourth modulation means for phase modulating lightwaves in response to a fourth modulation signal -v2 (t)-v.sub.π
/2 ;optical divider means for coherently coupling an optical carrier to said first, second, third and fourth modulation means; optical combiner means for coherently combining modulated optical carriers from said first, second, third and fourth modulation means and providing an output optical signal; and means for providing said first, second, third and fourth modulation signals to said first, second, third and fourth modulation means, respectively, where
space="preserve" listing-type="equation">v.sub.1 (t)=Σ
β
.sub.i1 cos (ω
.sub.i1 t+δ
.sub.i1),
space="preserve" listing-type="equation">v.sub.2 (t)=Σ
β
.sub.i2 cos (ω
.sub.i2 t+δ
.sub.i2),
space="preserve" listing-type="equation">β
.sub.i1, β
.sub.i2 =amplitude of ith subcarrier,
space="preserve" listing-type="equation">ω
.sub.i1, ω
.sub.i2 =frequency of ith subcarrier,
space="preserve" listing-type="equation">δ
.sub.i1, δ
.sub.i2 =phase of ith subcarrier,
space="preserve" listing-type="equation">v.sub.π
=voltage required to produce a phase shift of π
at the optical carrier frequency,and
space="preserve" listing-type="equation">v.sub.π
/2 =voltage required to produce a phase shift of π
/2 at the optical carrier frequency. - View Dependent Claims (6, 7, 8)
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Specification