This application relates in general to telecommunication network. More specifically, the present invention provides a system and method for band blockers that are to be used in optical telecommunication networks. In a specific embodiment, a wavelength division multiplexing system is capable of using wavelength channels at different channel spacing, which can be as low at 25 GHz, through the use of band blockers afforded by the present invention. As an example, band blockers according to the present invention separate frequency channels into multiple bands, each band consists of a predetermined number of channels characterized by the same channel spacing, but it should be understood that embodiments of the present invention have a wide range of applicability.
With advent of the information super highway, telecommunication techniques and infrastructures developed at a rapid pace in the recent years. Telecommunication networks are becoming faster and more reliable. One of the innovations that allowed for faster network has been the introduction of optical telecommunication networks, in which data are transmitted through fiber optical lines.
To take advantage of the characteristics of optical networks, wavelength division multiplexing (WDM) is used. The WDM technique involves multiplexing multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. This technique allows for a multiplication in capacity, thereby also making it possible to perform bidirectional communications over a single strand of fiber. The true potential of optical fiber is fully exploited when multiple beams of light at different frequencies are transmitted on the same fiber. For example, this techniques can be seen is a form of frequency division multiplexing (FDM), but is commonly referred as wavelength division multiplexing. The term “wavelength-division multiplexing” is commonly applied to an optical carrier (which is typically described by its wavelength), whereas frequency-division multiplexing typically applies to a radio carrier (which is more often described by frequency). However, since wavelength and frequency are inversely proportional, and since radio and light are both forms of electromagnetic radiation, the two terms are closely related.
A modern WDM optical transport system is typically capable of transmitting several tens and hundreds of wavelengths (or channels) over a distance of several hundreds and even thousands kilometers. Each wavelength/channel may carry several or several tens of Gb/s data. However, not all channels are starting from and/or going to the same destination. Wavelengths/channels may be dropped and added at any POP (Point Of Presence) along an optical fiber WDM transmission line.
A convenient and cost-effective solution is to add/drop wavelengths in optical domain to/from a multi-wavelength WDM signal using an Optical Add/Drop Multiplexer (OADM). An even more desirable solution is to have a reconfigurable OADM (ROADM) and thus the number and allocation of add/drop wavelengths can be provisioned as demands change without affecting channels already in-services. For example, a reconfigurable optical add-drop multiplexer (ROADM) is a form of optical add-drop multiplexer that adds the ability to remotely switch traffic from a WDM system at the wavelength layer. This allows individual wavelengths carrying data channels to be added and dropped from a transport fiber without the need to convert the signals on all of the WDM channels to electronic signals and back again to optical signals.
FIG. 1 is a simplified diagram illustrating a conventional broadcast and select ROADM system. The system 100 is implemented with a power splitter that divides an incoming WDM line signal between the drop and main paths. In the drop path, specific wavelengths/channels are selected using a wavelength demultiplexer or a filter. In the main path, a wavelength blocker (WB) blocks any selected (drop) channels and passes through others (express). As an example, a coupler may be used thereafter to add channels to the main path.
The use of broadcast and select ROADM based systems typically requires the use of wavelength blockers (WB). Depending on the application, a WB can be constructed with one or more arrayed waveguide grating (AWG). For example, a couple of AWGs may be arranged in a back-to-back as an array of on-off switches in between.
FIG. 2 is a simplified diagram of a conventional AWG based WB. As shown, an AWG converts an input WDM signal into N demultiplexed output signals. For example, each output signal is connected to an on-off switch, and therefore can be blocked or passed independently. Another AWG multiplexes the modified WDM channels back to the output WDM line signal. As an example, when on-off switches are replaced with 1×2 switches, functions such as the wavelength blocking and channel-adding, can be accomplished in one step in a single module. For example, such module is often referred to as an Add Module.
FIG. 2b is a simplified diagram of a conventional Add Module. Typically, for a 40-channel WDM system at 100 GHz spacing, there are often more than 160 fiber splicing between 40 egress and ingress ports of AWGs and switches. Such fiber cabling complexity escalates as channel count doubles at 50 GHz spacing.
In addition to the AWG based blockers, there are also other types of WB, such as those based on free-space optics.
Shown in FIG. 3 is a simplified diagram illustrating a MEMS based-system for performing wavelength blocking. Often, a MEMS based WB uses a diffraction grating to separate the input WDM line signal spatially. Dispersed wavelengths/channels are directed to an array of MEMS mirrors or liquid crystal (LC) cells. Each mirror or cell is actively controlled electrically so that any channel may be blocked or passed through. Pass-through channels are reflected back typically to the same grating to form the output WDM line signal.
Conventional WB, such as those discussed above, are often inadequate for various applications. Among other things, conventional WBs are often incapable of providing small channel spacing (e.g., 25 GHz) and multiple channel spacing.
Therefore, improved systems and methods for band blocking is desired.