The passive optical network based on wavelength division multiple access (WDM-PON) can provide almost unlimited bandwidth to the subscriber with protocol transparency. To realize WDM-PON, the development of a low cost WDM source is key issue. The wavelength-locked Fabry-Perot laser diode (FP-LD) was proposed as a low-cost WDM source. By injecting spectrum sliced Broadband Light Source (BLS), the FP-LD is forced to oscillate in a quasi-single mode. Thus, the BLS is one of the basic building block for the proposed light source.
In this paper, we proposed a new BLS based on mutually injected FP-LDs. The proposed BLS consists of two FP-LDs, optical coupler and isolators. Mode spacing of used FP-LDs is 100 GHz and length between two FP-LDs is 0.5 m. By mutual injection between two FP-LDs, we can achieve the broaden linewidth and reduced mode partition noise. Thus, it is reasonable to be used as a BLS.
We analyzed the effects of length between two FP-LDs, optical power, detuning of gain envelope and lasing mode in mutually injected FP-LDs. The length between two FP-LDs produced the periodic noise peaks. The first noise peak frequency must be higher than transmission bit rate. The difference of optical power of two FP-LDs induced the low relative intensity noise (RIN). The characteristic of the proposed BLS was almost independent of detuning of both gain envelope and lasing mode.
We demonstrate error free transmission of 3-channel 155 Mb/s WDM signals based on wavelength locked FP LDs based on the proposed BLS. The channel spacing is 100 GHz and the transmission distance is 20 km of standard single mode fiber. There is no bit error rate degradation induced by crosstalk. The proposed BLS requires about 4 dB higher injection power compared with the ASE based BLS.
The proposed BLS is compact and realized at a low cost for the wavelength-locked FP-LD. Thus, it will reduce the cost of WDM-PON.