直調雙波長雷射載波之光微波整合網路通訊

directly modulated dual-wavelength laser carrier based MMWoF wireless communication network

林重佑(Chung-Yu Lin)

指導教授 ： 林恭如

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10520

摘要

隨著現今影音技術的發展與進步，人們對於傳輸容量的需求越來越高，因此各國紛紛提出第五代(5G)行動網路的構想，並持續對其進行開發與研究。此外，為減少損耗與延伸傳輸距離，毫米波無線與光纖有線整合系統(MMWoF)勢必將被引進未來5G行動網路中，至於在毫米波載波頻段的選用，以28及39 GHz最被認為有機會採用，另外，47-GHz毫米波頻段未來亦將被廣泛應用於個人衛星通訊網路，因此，本論文將以上述三個頻段為主，建構直調雙波長雷射載波之光微波整合網路通訊。
首先，藉由非線性調變馬詹德調變器(MZM)將單波長光源轉換為中心載波抑制之雙波長光源(CCS-DSB)，並搭配偏差注入技術以雙模方式注入鎖定無色雷射二極體，同時直調正交分頻多工(OFDM)之正交振幅調制(QAM)調變格式以達36-Gbit/s光基頻25公里單模光纖及4-Gbit/s 39-GHz毫米波無線背靠背(BtB)傳輸，藉由將雙波長注入光源的其中一載波注入鎖定無色雷射二極體之選定模態，以及另一注入載波偏離所有共振模態，能有效降低雷射相對強度雜訊(RIN)至-104 dBc/Hz、抑制四波混頻(FWM)效應、以及有效弱化雙波長注入光源殘留之中心載波，使中心載波抑制比(CCSR)提升至38 dB。另外，若將兩分散式回饋雷射二極體(DFBLD) 與CCS-DSB注入光源相比，其產生之毫米波會因兩DFBLD各自之波長擾動而變得相對不穩定，反之，CCS-DSB注入光源可以得到線寬小於3 kHz的穩定毫米波。
接著，我們發現雙波長偏差注入產生之FWM成分會在光纖傳輸中引入額外色散，進而劣化傳輸訊號品質，因此不同波長間距的CCS-DSB注入光源被拿來比較，當波長間距由28 GHz拓寬至47 GHz時，可有效將25公里單模光纖傳輸之36-Gbit/s訊號誤碼率(BER)由3.2×10-3降低至2.1×10-3，在無線BtB傳輸方面，藉由選用較好之低雜訊放大器與平衡混頻器，可將傳輸訊號的訊號雜訊比(SNR)由15.66提升至24.46 dB，然而受限於毫米波元件之頻率響應，在1.6公尺無線傳輸時，28-GHz毫米波展示了最佳的傳輸結果，其傳輸速率達12 Gbit/s 。
最後，為了進一步避免雙模光源之色散現象，在頭端我們利用單波長注入鎖定無色雷射二極體取代雙波長光源以進行下行傳輸，並在遠端節點(RN)藉由MZM將其轉換成載有訊號之雙波長載波，以進行MMW無線傳輸至光纖網路單元(ONU)，並探討無色雷射二極體腔長對訊號傳輸性能之影響，此外，其下行單波長載波同時也被再利用來注入鎖定上行用之無色雷射二極體，實現一個載波複用之全雙工毫米波高密度分波多工被動光纖網路(MMW-DWDM-PON)，在經過25公里單模光纖傳輸後，其下行與上行訊號的傳輸速率分別為54和36 Gbit/s，且其28-GHz毫米波1.6公尺無線傳輸的訊號速率則可被提升至16 Gbit/s。

關鍵字

光微波整合系統 ； 雙波長注入鎖定 ； 第五代行動網路

並列摘要

With increasing demand on transmission capacity raised from modern communication and entertainment platforms technologies such as high-definition (HD) and 4k resolution videos, the fifth generation (5G) mobile wireless communication will become very popular in the near future and is emphasized as a research spotlight nowadays. In particular, the requested millimeter wave (MMW) carrier frequencies of 28 and 39 GHz are currently investigated under progress to allow 1-Gbit/s (or more) data transmission in free space. In addition, the 47-GHz MMW carrier for personal satellite application is also emerging to expand the personal communication band. To further extend the free-space transmission distance, a fusion of wireless MMW with wired fiber-optic communication networks is introduced in this thesis.
Firstly, by using a nully biased Mach-Zehnder modulator (MZM) to modulate a single-wavelength light into a central carrier suppressed double sideband (CCS-DSB) master, the directly encoded dual-wavelength colorless laser diode is performed to demonstrate 36-Gbit/s 64-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) optical baseband 25-km single mode fiber (SMF) and 4-Gbit/s 16-QAM OFDM back-to-back (BtB) wireless 39-GHz MMW transmissions. With dual-wavelength deviated injection-locking, the central carrier suppression ratio (CCSR) and relative intensity noise (RIN) of the dual-wavelength carrier can be improved to 38 dB and to -104 dBc/Hz, respectively. In comparison, the dual-DFBLD master injection-locking mixed MMW carrier is relatively unstable due to the individual DFBLDs at free-running condition. With the CCS-DSB master, the MMW carrier self-beat from the dual-mode optical carrier exhibits a narrow linewidth of <3 kHz with high purity and stability.
However, when the dual-wavelength optical carrier is transmitted over a 25-km in SMF, its accompanied four-wave mixing (FWM) components inevitably induces additional chromatic dispersion to degrade the transmitted data quality. To suppress the FWM dispersion, three CCS-DSB masters with different wavelength spacings are discussed and compared, which synthesizes three MMW carrier frequencies of 28, 39, and 47 GHz for implementing the 5G personal mobility and satellite communications. The 47-GHz CCS-DSB injection has shown its capability to provide 36-Gbit/s 64-QAM OFDM transmission with the lowest BER of 2.1×10-3 after 25-km SMF, as its weakest FWM modes greatly suppress the chromatic dispersion of the OFDM data. By properly selecting the low-noise amplifier and the balanced mixer for BtB wireless MMW pre-amplification and down-conversion, the signal-to-noise ratio (SNR) of the 39-GHz MMW carried 16-QAM OFDM data can be improve from 15.7 to 24.5 dB. In addition, the 28-GHz MMW carrier can wireless transmit the 12-Gbit/s 16-QAM OFDM data over a free-space distance of 1.6 m to show an average SNR of 15.3 dB, which fits the FEC criterion.
Finally, the single-wavelength carrier is used to replace the dual-mode one for optical baseband down- and up-stream transmission to further suppress the chromatic dispersion occurred in SMF, which therefore demonstrates a carrier-reused full-duplex 28-GHz MMW dense wavelength division multiplexing passive optical network (DWDM-PON) system with optical baseband 54-Gbit/s down-stream, 36-Gbit/s up-stream, associated with a MMW up-converted band 16-Gbit/s wireless data transmissions. Therein, the single-wavelength optical carrier transmits baseband data from optical line terminal (OLT) to remote node (RN), which then transfers into a dual-wavelength carrier for optically heterodyne beating into a MMW carrier to further enable wireless transmitting the data to an optical network unit (OUN). In addition, the up-stream data is carried by another slave colorless laser diode injection-locked by reusing the down-stream carrier without the need of data-erasing, which avoids the wavelength selection problem occurred from identifying or addressing up- and down-stream channels. Furthermore, the effect of cavity length of the colorless laser diode on the performances wired and wireless data transmissions is investigated. Among all laser transmitters with different lengths, the 600-?m colorless laser diode embedded MMW wireless carrier can provide the lowest BER after 1.6-m free-space transmission, because its best optical baseband transmission performance also supports the optimization on self-heterodyne transferring the MMW carrier to enable the low-noise and long-distance wireless transmission.

並列關鍵字

MMWoF ； dual-wavelength injection-locking ； fifth generation network

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