Broadband Light Source using Mutually Injected Fabry-Perot Laser Diodes for WDM-PON

We propose a new broadband light source (BLS) based on the mutual injection between two ARcoated F-P LDs. We demonstrate colorless operation of WDM-PON by using the proposed BLS and Manchester coded data. The passive optical network (PON) based on wavelength division multiplexing (WDM) has been investigated for fiber-to-the-home (FTTH). The WDM-PON is very attractive to provide almost unlimited bandwidth to the subscribers with the protocol and the bit rate transparencies. However, implementation of WDM-PON requires a cost-effective WDM source. Recently, the wavelength locked Fabry-Perot laser diode (F-P LD) with external spectrum sliced broadband light injection was proposed [1]. It is very effective solution to reduce the installation and management costs using wavelength independent operation of the optical network termination (ONT). In implementing the wavelength locked F-P LD, we can use a light emitting diode (LED), a superluminescent diode (SLD), or an amplified spontaneous emission (ASE) source based on EDFA as a broadband light source (BLS). The LED doesn’t have enough output power and the others are expensive solution even though they can provide much higher output power compared with the LED. In this paper, we propose and demonstrate a costeffective BLS by using mutually injected AR-coated F-P LDs. We also demonstrate WDM-PON with the wavelength locked F-P LDs by injecting the proposed BLS as an injection source. We use Manchester coded data to have the wavelength independent operation of an ONT. The proposed BLS is shown in dotted box of Fig. 1. It consists of two AR-coated F-P LDs, a 50:50 optical coupler, and two isolators. The reflectivity of the front facet and the mode spacing of the F-P LDs are 1% and 100 GHz, respectively. The fiber length between the two F-P LDs is 50 cm. We realized an unpolarized BLS by polarization multiplexing with two polarization controllers (PCs) and a polarization beam splitter (PBS). Fig. 2(a) shows the measured optical spectra of the F-P LD 1 and 2 without mutual injection. By mutual injection between the two F-P LDs, the 3 dB linewidth broadens up to 0.2 nm. The output spectrum of the mutually injected F-P LDs looks like the spectrum sliced broadband light as shown in Fig. 2(b). The center wavelength of gain envelope was shifted toward the long wavelength compared with individual F-P LD. It results from the decrease of threshold current because of mutual injection between two AR-coated F-P LDs. -60 -50 -40 -30 -20 -10