Optical waveguides – Directional optical modulation within an optical waveguide – Electro-optic
Reexamination Certificate
2002-02-25
2004-08-31
Lee, John D. (Department: 2874)
Optical waveguides
Directional optical modulation within an optical waveguide
Electro-optic
C385S003000, C385S008000, C385S009000, C385S014000
Reexamination Certificate
active
06785430
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to communications and, more specifically, the present invention relates to optical communications.
2. Background Information
The need for fast and efficient optical-based technologies is increasing as Internet data traffic growth rate is overtaking voice traffic pushing the need for fiber optical communications. Transmission of multiple optical channels over the same fiber in the dense wavelength-division multiplexing (DWDM) systems and Gigabit (GB) Ethernet systems provide a simple way to use the unprecedented capacity (signal bandwidth) offered by fiber optics. Commonly used optical components in the system include wavelength division multiplexed (WDM) transmitters and receivers, optical filter such as diffraction gratings, thin-film filters, fiber Bragg gratings, arrayed-waveguide gratings, optical add/drop multiplexers and lasers.
Lasers are well known devices that emit light through stimulated emission, produce coherent light beams with a frequency spectrum ranging from infrared to ultraviolet, and may be used in a vast array of applications. For example, in optical communications or networking applications, semiconductor lasers may be used to produce light or optical beams on which data or other information may be encoded and transmitted.
Other devices used in optical communications or networking applications are fiber-based Bragg gratings. A fiber Bragg grating is an optical fiber with periodic changes in the refractive index of fiber core materials along the fiber length, which may be formed by exposure of the photosensitive core to an intense optical interference pattern. With the changes in the refractive index along the fiber length, optical beams at a particular wavelength are reflected by the fiber Bragg grating while other wavelengths are allowed to propagate through the fiber.
A limitation with fiber Bragg gratings is that the particular wavelength that is reflected by the fiber Bragg grating is substantially fixed. Consequently, if different wavelengths of light are to be reflected, different fiber Bragg gratings are utilized. In some known fiber Bragg gratings, nominal adjustments to the reflected wavelength may be provided by physically or mechanically stretching the optical fiber of the fiber Bragg grating to modify the length of the optical fiber. The disadvantage of this technique is that the amount of adjustment to the reflected wavelength is relatively small and the optical fiber may suffer damage from the physical stress and strain of the stretching.
Additional devices used in optical communications include optical transmitters which are key components in broadband DWDM networking systems and in Gigabit (GB) Ethernet systems Currently, most optical transmitters are based on a number of fixed wavelength lasers combined with an external modulator or in some cases a directly modulated laser. After light produced from a laser is modulated, it is multiplexed with an external multiplexer and then sent to an optical fiber network where it may be amplified or directed by an optical switch, or both. Separate lasers and modulators are used for each transmission channel, since the lasers typically produce a fixed wavelength. The costs of producing lasers and associated components are very high, however, and using separate components for each wavelength of light to be transmitted can be expensive and inefficient.
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