21oC 23oC 25oC 27oC 29oC
Fig. 4.8 (a) Optical spectrum of injected WRC-FPLD at the temperature from 21oC to 29oC.
1556.0 1556.5 1557.0 1557.5 -60
-45 -30 -15 0
Power (dB m)
Wavelength (nm)
21
oC 23
oC 25
oC 27
oC 29
oC
Fig. 4.8 (b) BER of temperature-controlled WRC-FPLD with different injection locked mode number.
As shown in Fig. 4.8(b), there is only a tiny positive power penalty on the BER by 0.6 dB during the WRC-FPLD temperature sweep. Both the spectral shift and the power attenuation concurrently occurs during the change of WRC-FPLD temperature, leading to the different injection-locked mode matching and output powers at different temperatures.
Although the WRC-FPLD output power can be affected by both the wavelength matching and the operating temperature, our observations confirm that the temperature effect induced degradation of inner laser efficiency is more pronounced than wavelength matching effect.
That is, the receiving power at a specific BER should be inevitably enlarged by increasing the WRC-FPLD operating temperature. Nevertheless, such a degration only induces a power penalty of < 1dB between 21oC to 29oC. The word of “color-free” describes request of the wavelength-matching between master and slave laser. The system can be named color-free while the wavelength-matching can be ignored in the operation. Our proposed system in 4th chap., both the spectral shift and the power attenuation occur during the change of WRC-FPLD temperature, leading to the different injection-locked mode matching and output
powers at different temperatures. The results conclude that there is a positive power penalty on the BER by 0.6 dB which could be ignored of the wavelength-matching. However our proposed system still have 0.6-dB sensitivity penalty that could be described as
“quasi-color-free”.
Fig. 4.9(a) Injection-locking power dependent wavelength lock-in range of one longitudinal mode in the slave WRC-FPLD transmitter at the ONU end.
At last, the quasi-color-free RZ transmission performed by the pulsated master WRC-FPLD injection-locked slave WRC-FPLD can be achieved up to 16 DWDM channels.
The transmitted RZ data-stream all-optical converted from the modulated NRZ data-stream, and the measured BER transmission performance versus receiving power are shown in Figs.
9(a) and 9(b). A receiving sensitivity for 2.5Gb/s back-to-back transmission at BER<10-10 can be -25.6 dBm. A well-opened RZ eye pattern can be obtained with a relatively large dynamic range, in which the rising and falling time (defined as the duration between 20% and 80% of on-level amplitude) are 48 ps and 52 ps, respectively. The best and worst power penalties of the adjacent 16 channels after 25-km SMF propagation are 0.9 dB and 2 dB, respectively. The various power penalties are attributed to linear-dispersion data
transmission distortion and the initial wavelength mismatch. With appropriate temperature tuning of the slave WRC-FPLDs, the variation on receiver sensitivity penalty at BER=10-10 can be confined within 1.6 dB under a temperature shift of 15oC. The acceptable tolerance of the wavelength locking bandwidth can be enhanced with increasing RF power to improve gain-switching mode linewidth. By adjusting the cavity length, the longitudinal mode spacing of master WRC-FPLD could be further modified to match the ITU-T defined DWDM channels for practical WDM-PON application.
-30 -28 -26 -24 -22 -20
Fig. 4.9(b) BER analysis of wavelength injection locked WRC-FPLD at different channels and measured pulsed RZ eye diagrams (inset)
The power budget in our system could be considered including the fiber loss of 5 dB, the WDM coupler loss of 2 dB, the AWG loss of 4 dB, and the circulator loss of 1 dB. The output optical power of pulse injection WRC-FPLD is -10 dBm. As the transmission receiver sensitivity was measured as -25 dBm, the system allows an additional 3-dB loss for the whole WDM-PON link.
4.4 Summary
We demonstrated a novel bi-directional DWDM-PON with return-to-zero (RZ) data-format at 2.5 Gb/s by using both the down- and up-stream slave WRC-FPLDs coherently injection-locked by a pulsated WRC-FPLD based quasi-colorless master source with more than 10-mA threshold reduction. Both the down- and up-stream slave WRC-FPLDs are directly modulated by PRBS NRZ data and coherently injection-locked by the gain-switched master WRC-FPLD after 200-GHz AWG channelization to perform the bi-directional RZ data transmission at 2.5 Gb/s over 25 km. The proposed scheme involves a gain-switched WRC-FPLD coherent injection source with lower noise than ASE and employs the quasi-color-free WRC-FPLD transmitters with relatively large tolerance on locking bandwidth.
Receiving back-to-back and worst transmission sensitivities transmission are -25.6 dBm and -23.6 dBm, respectively, and the rising and falling time of pulsed RZ eye pattern can be obtained with 48 ps and 52 ps. The best side-mode suppression ratio of 42 dB and the lowest timing root-mean-square jitter of 40 dB and 16 ps, respectively, for the pulsed RZ data-stream are observed. This system is an appropriate balance between coherent and incoherent injection solutions. The proposed pulsed RZ network could further be applied to a RZ binary-phase-shift-keying (BPSK) network or hybrid DWDM/OTDM PON architecture.
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