Abstract

We investigate to generate coherent and frequency-lock optical multi-carriers by using cascaded phase modulators and recirculating frequency shifter (RFS) based on an EDFA loop. The phase and amplitude relation of RF signals on two cascaded phase modulators and the impact of EDFA gain are investigated. Experimental results are in good agreement with the theoretical analysis. The performance of 113 coherent and frequency-lock subcarriers with tone-to-noise ratio larger than 26dB and amplitude difference of 5dB obtained after a tilt filter covering totally 22.6nm shows that this scheme is a promising technique for the coming Tb/s optical communication.

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Figures (9)

Fig. 1
Fig. 1

Schematic configuration of the RFS based on cascade phase modulators.

Fig. 2
Fig. 2

(a) The number of generated subcarriers as a function of modulation index R 1 and R 2 for cascaded phase modulators PM1 and PM2; (b) The number of generated subcarriers as a function of modulation index Rand phase deviation Δ ϕ .

Fig. 3
Fig. 3

(a) The number of generated subcarriers and (b) the normalized calculated power MSD vary with modulation index R(1.5~2.4) and phase deviation Δ ϕ (−0.45π~0.45π).

Fig. 4
Fig. 4

The principle for multi-carriers generation.

Fig. 5
Fig. 5

The optical spectrum of (a) after PM1; (b) after PM2.

Fig. 6
Fig. 6

Optical spectrum after PM2 for different phase deviation.

Fig. 7
Fig. 7

Optical spectrum after OC2 varies with different EDFA output power: (a) 11.5dBm; (b) 15.5dBm; (c) 19.5dBm; (d) 21.5dBm.

Fig. 8
Fig. 8

The amount of generated subcarriers with the tone-to-noise rate lager than 30dB varies with different EDFA output power.

Fig. 9
Fig. 9

Optical spectrum of stable multi-carriers obtained after WSS: (a) total subcarriers obtained; (b) subcarriers from 1562nm to 1564 nm.

Equations (10)

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E o u t = E i n exp ( j π V d V π )
E o u t = E c exp ( j π R sin 2 π f s t ) = E o exp ( j 2 π f c t ) exp ( j π R sin 2 π f s t )
E o u t = E o exp ( j 2 π f c t ) exp ( j π R sin 2 π f s t ) = E o { J 0 ( π R ) exp ( j 2 π f c t ) + J 1 ( π R ) [ exp ( j 2 π ( f c + f s ) t ) exp ( j 2 π ( f c f s ) t ) ] + J 2 ( π R ) [ exp ( j 2 π ( f c + 2 f s ) t ) exp ( j 2 π ( f c 2 f s ) t ) ] + J 3 ( π R ) [ exp ( j 2 π ( f c + 3 f s ) t ) exp ( j 2 π ( f c 3 f s ) t ) ] + ... } = n = + J n ( π R ) exp [ j 2 π ( f c + n f s ) ]
E o u t E o n = m + m J n ( π R ) exp [ j 2 π ( f c + n f s ) t ]
E o u t = E c exp ( j π R 1 sin ( 2 π f s t ) ) exp ( j π R 2 sin ( 2 π f s t + Δ ϕ ) ) = E c exp { j π [ R 1 sin ( 2 π f s t ) + R 2 sin ( 2 π f s t + Δ ϕ ) ] } = E c exp [ j π R c sin ( 2 π f s t + φ ) ]
R c = R 1 2 + 2 R 1 R 2 cos Δ ϕ + R 2 2
R c = R 2 + 2 cos Δ ϕ = 2 R cos Δ ϕ 2
E o u t _ 1 E o n = N 1 / 2 N 1 / 2 J n ( π R c ) exp [ j 2 π ( f c + n f s ) t ] = E c n = N 1 / 2 N 1 / 2 J n ( π R c ) exp ( j 2 π n f s t )
F ( t ) = g r exp ( j θ r ) exp ( a r ) n = N 1 / 2 N 1 / 2 J n ( π R c ) exp ( j 2 π n f s t )
E o u t _ 1 = E c n = N 1 / 2 N 1 / 2 J n ( π R c ) exp ( j 2 π n f s t ) E o u t _ 2 = E c n = N 1 / 2 N 1 / 2 J n ( π R c ) exp ( j 2 π n f s t ) + E o u t _ 1 F = E o u t _ 1 ( 1 + F ) E o u t _ 3 = E o u t _ 1 + E o u t _ 2 F = E o u t _ 1 ( 1 + F + F 2 ) ...... E o u t _ K = E o u t _ 1 ( 1 + F + F 2 + ...... + F K )

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