Fiber-to-the-home (FTTH) has been considerable attention to provide converged voice, data, and video services cost effectively. However, we cannot provide voice service, when electric power is out of order at customer’s home. It can be compared with current copper based voice line that can provide voice service regardless electric power condition, since the electric power to the subscriber is supplied from the central office. This may be very important for emergency cases. Thus we call the emergency voice communication channel ‘Lifeline’.
In this paper, we proposed a method of the Lifeline communication in a wavelength division multiple access (WDM-PON) based on the wavelength-locked Fabry-Perot laser diodes. The FTTH based on WDM-PON provides protocol transparency. Thus we can transmit the voice signal only, when the electric power is out of order at subscriber’s home. In this way, the power consumption of the subscriber’s equipment can be reduced considerably. Further reduction of the power consumption is achieved with reverse or below threshold biased FP LD. This mode of operation is possible, since we inject optical power, i.e., broad band light, from the central office to FP LD located at subscriber’s home.
We investigate feasibility of the Lifeline communication based on the reverse-biased Fabry-Perot laser diode. Here the reverse-biased Fabry-Perot laser diode works as an electro-absorption modulator. The power consumption at the laser is about 3 mW. So we can reduce the power consumption enough to operate with small size rechargeable battery which is cheap and small enough to use as a back-up. However, due to low extinction ratio and output power of the reverse-biased Fabry-Perot laser diode, the additional optical amplifier is needed at the central office to compensate the link loss.
To increase the extinction ratio and output power, the Fabry-Perot laser diode should be forward biased. However, the bias current is maintained below the lasing threshold. The power consumption of the laser is increase to about 10 mW. But with the enough extinction ratio and the output power, the optical amplifier at the central office can be eliminated.
현재의 가입자 망에서는 기술의 발달로 인하여 더 많은 대역폭을 요구하고 있으며 이러한 요구를 만족시키기 위해 Fiber-to-the-home이 활발하게 연구되고 있다. Fiber-to-the-home의 경우 광섬유를 이용해 필요한 만큼의 대역폭을 제공할 수 있지만, 정전 시에 외부와 통신이 불가능한 한계가 있다. 이러한 한계를 극복하기 위해서 본 논문에서는 WDM-PON 구조를 바탕으로 하여 기존의 고속 데이터 전송에 쓰이는 장비를 바탕으로 저전력으로 동작시켜서 음성 채널을 확보하고자 한다. 음성 채널 확보를 위해 기존의 사용 영역이 아니었던 문턱 전류 아래에서 구동하였고, 이와 더불어 역 방향으로 바이어스 시켜서 동작시켜서 음성 채널 통신이 가능함을 보였다. 다만, 역 바이어스로 구현할 경우, 링크 손실이 크기 때문에 이를 보상하기 위한 추가적인 광 증폭기가 필요하였다. 이러한 비상 음성 채널이 마련되었기 때문에 FTTH 도입에 도움을 줄 것으로 기대된다.
