A low‐cost passive optical network for television broadcasting and high‐speed bidirectional communications in intelligent buildings

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A low

‐cost passive optical network for television

broadcasting and high

‐speed bidirectional

communications in intelligent buildings

, Gerd Keiser a , San‐Liang Lee a , Kuo‐Chieh Lai a , Huan‐Chia Chang a , Chih‐Lung Tseng a & Jau‐Ji Jou a

a

Department of Electronic Engineering , National Taiwan University of Science and Technology , Taipei 106, Taiwan, R.O.C.

b

Department of Electronic Engineering , National Taiwan University of Science and Technology , Taipei 106, Taiwan, R.O.C. Phone: 886–2–27336382; 886–953–021648 E-mail: Published online: 04 Mar 2011.

To cite this article: Zih‐Rong Lin , Cheng‐Kuang Liu , Gerd Keiser , San‐Liang Lee , Kuo‐Chieh Lai , Huan‐Chia Chang ,

Chih‐Lung Tseng & Jau‐Ji Jou (2010) A low‐cost passive optical network for television broadcasting and high‐speed bidirectional communications in intelligent buildings, Journal of the Chinese Institute of Engineers, 33:5, 707-716

To link to this article: http://dx.doi.org/10.1080/02533839.2010.9671660

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A LOW-COST PASSIVE OPTICAL NETWORK FOR TELEVISION

BROADCASTING AND HIGH-SPEED BIDIRECTIONAL

COMMUNICATIONS IN INTELLIGENT BUILDINGS

Zih-Rong Lin, Cheng-Kuang Liu*, Gerd Keiser, San-Liang Lee, Kuo-Chieh Lai, Huan-Chia Chang, Chih-Lung Tseng, and Jau-Ji Jou

ABSTRACT

In this paper, a low-cost passive optical network scheme is presented for intel-ligent buildings located in areas having difficulty with wireless signal reception. The network can simultaneously broadcast digital-video-broadcasting-terrestrial (DVB-T) signals and can transmit high-speed data bidirectionally using a Fabry-Pérot laser diode (FP-LD) injection-locked by a vertical cavity surface-emitting laser (VCSEL). Results are shown for the broadcast of DVB-T signals over an 1-km multimode fiber (MMF) and for non-return-to-zero (NRZ) data over a 25-km single mode fiber (SMF). Downstream and upstream transmission bit rates are 10 Gbps and 1.25 Gbps, respectively. Maintaining TV signal quality at 40%, receiver sensitivities are -20.2 dBm and -22.58 dBm for downstream and upstream transmissions, respectively. In addition, the constraint of injection-locking and the limitation of optical power are also analyzed.

Key Words: fiber optics communication, digital video broadcasting (DVB), optical

injection-locking, fixed-mobile convergence.

*Corresponding author. (Tel: 886-2-27336382; 886-953-021648; Email: ckliu@mail.ntust.edu.tw)

The authors are with the Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, R.O.C.

I. INTRODUCTION

Modern intelligent buildings (including enter-prise facilities and smart homes) have premises distribution systems that allow occupants to take ad-vantage of new technology as it becomes available at a minimum cost (Flax, 1991). In addition to having modular and flexible internal communication networks, intelligent buildings also depend on high-quality ex-ternal landline and radio communication links. Al-ways available and accountable standard-definition and high-definition TV, data communication, and multimedia services are essential in an intelligent building. Recently, the demands for digital conver-gence such as multimedia service, cloud technology, cloud service, video on demand, and interactive TV

have increased demand for radio-over-fiber (ROF) techniques. Since all digital bits are alike, multime-dia services can be multiplexed seamlessly and de-livered in a digital format. With digital TV, the convergence of TV and optical access network tech-nologies is relatively inexpensive (Chand, 1999). Although, there has been much progress in digital TV broadcast and fixed mobile convergence, the cover-age area is still limited. For instance, difficulties in wireless signal reception exist in some regions such as some valleys and in corner areas between high and large buildings, as shown in Fig. 1. These situations can result in dead zones where no or only very weak signals are received. A building with limited exter-nal communication interfaces can hardly be called intelligent. Fortunately, one may find an alternative: building a base station with an optical fiber solution. A wavelength-division-multiplexing passive optical network (WDM-PON) is a good candidate for the bi-directional simultaneous transmission of data and digital broadcast video signals (Jung, 2001; Son, 2003), al-though its cost is generally high. Cost-reduction

708 Journal of the Chinese Institute of Engineers, Vol. 33, No. 5 (2010)

designs are essential in optical communications, es-pecially in high-speed and broadband communica-tions (Lin, 2009).

Radio over WDM-PON (Lu, 2005; Tzeng, 2009) has many advantages. ROF transport systems are used to enhance the radio coverage of wireless applications and to provide broadband services, such as intelli-gent transport systems (ITS) and local area networks (LAN). Previous ROF transport systems focused on using a distributed feedback (DFB) laser diode. However, using expensive DFB lasers may not be a good solution for optical network units/users (ONUs), since system cost reduction is one of the key issues in access networks. The less expensive VCSEL and FP-LD are two attractive candidates for use in fiber access networks, as far as the network cost is con-cerned. Although the operating characteristics of DBF lasers are superior to these two devices, an op-tical injection-locking technique (Tseng, 2008; Hung, 2003) can be adopted to improve their performance. In addition, the application of a VCSEL to radio-over-fiber has been reported to achieve some system cost reduction (Yee, 2006; Constant, 2008). Furthermore, we can make use of PON methodologies, which were developed to deliver bandwidth intensive applications to end users in a cost-effective and future-proof manner. As a low-cost alternative to wavelength-spe-cific upstream transmitters, we have proposed a scheme to use optical injection-locked FP-LDs as di-rectly modulated upstream transmitters, whereby the external injection-locking light is furnished by a VCSEL. The VCSEL not only carries downstream DVB-T signals to users from a receiving base station on the top of a building, but also serves as a master laser to optically injection-lock an upstream slave FP-LD in each ONU. Aiming at the solution to dead-zone situations in corner areas between high and large buildings or in some valleys, as shown in Fig. 1, we present in this article a combined study of the above

mentioned technologies.

This paper is organized as follows. In Section II, we describe the basic configuration of the system and give a brief discussion of the proposed scheme setup. Section III is devoted to experimental results and discussion. First, the DVB-T signal broadcast experiments are reported and discussed. We show that by using a VCSEL the DVB-T signal can be suc-cessfully modulated and transmitted over a 1-km MMF. Secondly, for the simultaneously transmitted high-speed bidirectional data experiments, we discuss methods to adjust the bistable region of the DVB-T signals and present bidirectional performance data. Injection technology based on conditions and roles of VCSEL and FP-LD are also demonstrated in this section. Finally, the main results are summarized in Section IV.

II. PROPOSED SCHEME

One solution to receiving DVB-T signals in a shadowed area or a dead zone for ubiquitous multi-media communication developments is shown in Fig. 1. Here ROF techniques are used to improve the per-formance of high-speed communication by adopting a VCSEL and an FP-LD combination, together with an injection-locking technique. Using this technique, we proposed a novel scheme as shown in Fig. 2. There are three transmission paths in our proposed scheme for television broadcasting and high-speed com-munications.

Path 1. In the base station, a TV broadcasting signal

is transmitted optically to the ONUs, as shown in Fig. 2. The DVB-T signal received by an antenna is applied through the Bias-T to modulate the C-band VCSELs and is then transmitted via a 1-km MMF to the ONUs to achieve a stable and high-quality ROF en-vironment.

Path 2. At the ONU, a 50/50 coupler is used to split

the power coming from the C-band VCSEL into two ports. One port leads the DVB-T signal to a receiver (Rx), a set top box (STB), and a monitor; the other port goes to a FP-LD. The FP-LD is injection-locked by the laser light from the C-band VCSEL and is directly modulated by the upstream 1.25 Gbps NRZ (27_{-1) pseudorandom sequence (PRBS)}

data provided by a pulse pattern generator (PPG). Data is then transmitted to the cen-tral office (CO) via a 25-km SMF. The DVB-T downstream data and the digital upstream data are carried by the same wavelength of 1550 nm (λC).

Path 3. At the CO, downstream 10 Gbps NRZ (231_-1) Radio Signal

VCSEL

FP-LD ONU

CO

Fig. 1 A low-cost PON for television broadcasting and high-speed bidirectional communications in a valley

ACKNOWLEDGMENTS

This work was supported in part by the National Science Council of the R.O.C. through 2219-E-011-003, NSC-98-3114-P-011-001-Y and NSC-97-2218-E011-007-MY3 projects.

NOMENCLATURE

λC optical communications wavelength

range 1530 nm to 1565 nm

λC1 ... λCn upstream lightwaves λL1 ... λLn downstream lightwaves

λL optical communications wavelength

range 1565 nm to 1625 nm

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Manuscript Received: Dec. 11, 2009 Revision Received: Mar. 10, 2010 and Accepted: Apr. 10, 2010