MEMS-tunable 10 Gb/s APD receiver for broadcast and select CATV networks Jill D. Berger, Doug Anthon, Joe Drake, and Fedor Ilkov Iolon, Inc., 1870 Lundy Ave., San Jose, California 95131 jberger@iolon.com Jason Shreeram and Carlos Verdonck Scientific-Atlanta, Inc., 5030 Sugarloaf Parkway, Lawrenceville, GA 30044 jason.shreeram@sci-atl.com Abstract: A 10 Gb/s receiver combining a MEMS-tunable optical filter and avalanche photodiode in a common butterfly provides tuning over 5 THz with –26 dBm receiver sensitivity and ± 5 GHz wavelength control, to enable dynamic provisioning for broadcast and select CATV networks. © 2004 Optical Society of America OCIS Codes: (060.2380) Fiber optics sources and detectors; (060.4250) Networks 1. Network architecture The term convergence is used in the cable television (CATV) industry to describe the deployment and management of multiple signals in different formats over a single network. CATV traffic consists of a bi-directional mixture of analog video signals and mixed-protocol digital signals, with digital video, high speed data, Gigabit Ethernet, TDM voice and DVB/ITU/ASI all being used in various systems. These signals are managed so they can be efficiently transmitted through the network and connected to the end user via a single coaxial cable or optical fiber. Convergence can take place in either the electrical, optical or system domain, with the network architecture being chosen to optimize this process. Convergence in the electrical domain is carried out using a variety of IEEE and ITU standards, such as SONET Layer 1, Resilient Packet Ring, and MPLS. Convergence in the optical domain requires wavelength management and optical performance monitoring, not only for conventional base-band digital signals but also for sub-carrier modulated analog video and digital QAM signals, in both the forward and reverse directions. In the system domain an efficient transition must be made between the requirements of the different optical signals and the requirements of coaxial cable. The high capacity optical fiber links need to be managed in a way that is compatible with existing multi-vendor network equipment and RF signal requirements. Efficient convergence at all levels is required to ensure that a digital signal transmitted over a fiber as Gigabit Ethernet in one part of the system can ultimately be transmitted to an end user as a sub-carrier multiplexed 256 QAM electrical signal. One important growth area for CATV networks is that of video on demand (VOD), which requires efficient distribution of a large number of data streams through the network. The problem, in this case, is to provide an efficient distribution network that has sufficient flexibility to accommodate unpredictable traffic fluctuations without requiring excessive initial investment. One method for achieving this goal involves a tunable multi-wavelength bi-directional digital ring at 10 Gb/s in a broadcast and select architecture with tunable lasers at each head end and tunable receivers at each network node [1]. Figure 1 shows the basic node in this architecture, where a combination of multi-band filters and broadband tap couplers are used to provide a set of fixed wavelength channels as well as a large number of wavelengths that can be accessed in either fiber direction by the tunable receiver used for the VOD signals. The purpose of the fixed wavelength channels is to accommodate legacy services presently transported on individual fibers. The availability of these channels is important for integrating new and existing services into the network and is an important benefit of increased flexibility in the optical layer. As initially deployed, the number of tunable lasers at the head end will be determined by anticipated traffic levels, with a few additional lasers being necessary to provide redundancy. The number of lasers can be smaller than the number of nodes, as the less-used nodes can share a single transmitter. Each node will have two tunable receivers, allowing for both redundancy and traffic growth. Each laser broadcasts in both directions around the ring, so the 1×2 switch at the node provides redundancy in the event of a fiber failure. Using tunable devices at both the laser and receiver enables the network to be provisioned for dynamic optical switching and bandwidth on demand [2]. The principle advantage of the broadcast- and-select architecture is the ability to start with a bandwidth model for today’s network and migrate to a future higher bandwidth model through software. In order to efficiently deploy new VOD services in existing networks as well as meet future traffic demands, the network must be capable of dynamic asset deployment. By placing a broadband splitter at the input of a VOD receiving hub, sufficient optical level can be designed into the network to accommodate the everything-on- demand network model and easily adapt the network to transport up to 10 times the capacity of the initial design.