1. Field of the Invention
This invention relates generally to fiber optic transceivers and transponders, and in particular to the use of an optical network interface engine that is hardware programmable to be used with different application-specific optoelectronic front-ends and/or different host modules and transport protocols.
2. Description of the Related Art
Today's fiber optic based networks use optical transceivers (and transponders) between host electronics and the optical signals that propagate on the optical fiber. A transceiver contains the basic elements of an optical transmitter, an optical receiver, and other electronics to perform physical (PHY) layer protocol functions as well as functions to control these components. There are many applications for transceivers ranging from fiber to the home to data centers to long haul and high-performance communications, with each application imposing its own requirements. Today, transceivers are usually manufactured in a form factor called a pluggable like an XFP or SFP package, or as a board mountable component.
The performance and design of the transceiver as well as its cost is customized for the particular application. For example, if a transceiver is designed for one of today's framed transport protocols (e.g. SONET, SDH, FDDI, Gigabit Ethernet), the clock and data recovery elements in the transceiver will be designed based on continuous data flow rather than burst mode or unframed packet modes of transmission and reception. The receiver typically operates at either a fixed standardized bit rate or is selectable over a limited set of standardized bit rates specified by the protocol. Electronics and optics in the transceiver are also customized to the transport protocol and application.
For example, the optical transmitter within a transceiver includes optics that launches an optical signal onto the fiber. This optics varies depending on the application. For low-cost applications, ultra low cost lasers operating at 1310 nm or 830 nm with the capability to transmit over very short distances (typically less than 2 km) are commonly used. These lasers are often driven by the direct drive method where current from an electronic driver circuit is applied directly to the laser. In contrast, at longer distances at higher bit rates, more complex optics involving a higher performance laser and possibly an external optical modulator and optical amplifier may be used, as well as chirp and dispersion compensation techniques.
Today's state of the art in high performance transceivers must meet the needs of today's networks, including low cost, reliability and sparing (stocking of spare parts) and preferably also the needs of future networks including tenability, rapid reconfiguration, power efficiency and ability to be controlled in power efficient environments, and burst mode environments. The number of spare receivers kept on site in case of failure in a WDM network should be kept to a minimum in order to reduce the cost of operating a network. Today's WDM transceivers that operate in the 15xxnm and 16xxnm wavebands use either fixed channel lasers that adhere to the ITU frequency grid standard for dense WDM (DWDM) or coarse WDM (CWDM). However, in order to require only one laser, many transceivers today are moving to using a wavelength tunable laser that can cover either the C or L bands or both.
Another aspect of today's transceivers are the electronics that are used to drive the optics, to convert electronic signals between analog and digital forms, to acquire clock and data, and also microprocessors and I/O channels for controlling the transceivers. These circuits today consist of multiple dedicated chips to handle these functions. These chip sets and the auxiliary chips to operate between the transceiver and other external subsystems add to the expense for any one application. Since these components are typically customized for an application, the number of spare parts multiplies with the number of applications and transceiver types. There is typically also a mixture of chips used for digital only and digital/analog functions, thus adding to the complexity and cost of the transceiver. Typically, a different transceiver is required for each transport protocol or finite set of transport protocols such that a sparing card in a multi-service platform (one that supports communications across a wide variety of transport protocols) will require sparing of more than one type of transceiver depending on the services it supports.
Thus, different transceivers typically utilize different components (both optics and electronics) customized for a particular application and/or protocol. To switch protocols, the transceiver must be changed. More advanced transceivers may include different physical sections designed for different protocols, thus allowing the transceiver to be used with multiple protocols. These sections may be on multiple chips or a custom circuit like an ASIC. However, the set of possible protocols is fixed once the transceiver is manufactured and the protocol sections in the hardware are dedicated to each protocol. The transceiver typically cannot be programmed later by the user to implement a new or different protocol or interface to new or different optics.
Thus, there is a need for transceiver architectures that can provide more flexibility in supporting different protocols, host electronics and/or optoelectronic front-ends.