Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-12-18
2002-01-29
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06342960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to digital optical transmitters and more specifically to a wavelength division multiplex transmitter using a plurality of the light wavelengths to simultaneously transmit independent digital signals into an optical waveguide.
2. Description of the Related Art
At present, optical fibers for transmitting digital signals use lasers or LEDs with substantially constant wavelength distributions for transmitting digital signals. The signals are serially transmitted as interruptions of light of the same wavelength—thus limiting the amount of data which can be transmitted over the optical fiber to the switching performance of the laser or modulator, the properties of the fiber and the sensitivity of the receiver. Each serial signal stream is separated into its component parts, such as different phone calls, by switching labeled packets of data out of the data stream and reassembling each separate call. To increase the signal carrying capacity of the optical fiber, lasers of different wavelengths are used in the same fiber. Each laser operates independently from the others but a separate laser is required for each wavelength. The lasers can be fabricated onto a single chip and addressed independently to produce multiple independent communication channels. This is called wavelength division multiplexing (WDM). Since this technology is being driven by the telecommunications industry, systems which operate over long distances with small numbers (32) of high speed (20 Giga bits per second plus) channels are preferred over systems with large numbers of channels (500 plus) which operate at moderate speeds (0.1 Giga bits per second). The long distance aspect of the preferred telecommunications solution constrains their operations to two small regions in the infrared portion of the spectrum near 1500 and 1300 Nano meters where silica glass has the lowest attenuation of the light signals per distance traveled. In situations where long distance communications are not required, such as an aircraft, launch vehicle or submarine, the constraints are considerably less and a much greater portion of the light spectrum is available for communications.
U.S. Pat. No. 5,367,585, issued to Ghezzo et al., discloses a photonic switch which functions by controlling the physical contact of two optical waveguides. When they are touching, light is coupled from one waveguide to the other. Otherwise the coupling is interrupted.
U.S. Pat. No. 5,231,388, issued to R. A. Stoltz, discloses a device that only generates three colors, and is therefore not suitable for WDM or spectral chip CDMA optical communications.
U.S. Pat. No. 5,089,903, issued to Kuwayama et al., discloses a device that uses cascaded holograms for correcting eye position dependent blurring of an image in a heads up display. While it does correct for distorted images, it does not manipulate wavelengths for the purpose of light use efficiency.
U.S. Pat. No. 5,757,536, issued to Ricco et al, discloses a micro electro mechanical (MEMS) programmable diffraction grating which can be used for a number of tasks such as for use as a correlation spectrometer or a multiplexer for combining multiple wavelengths. The patent discloses the controlling of displacement magnitudes of individual mems elements or the periodicity of these elements to produce a common diffraction angle. A grating directs the diffracted light to a common point in space such as a detector, an optical fiber, or a slit.
U.S. Pat. No. 5,500,610, issued to Goossen et al., discloses an optical modulator with two selectable reflectivity states. All light (incident and reflected) is normal to the device surface. The zero reflectivity state corresponds to air gap dimensions equaling zero or any number of half center frequency wavelengths while the maximum reflectivity occurs in cases where the gap has an additional ¼ wavelength of the center frequency. This device functions as a low Q resonant circuit that is alternately parallel (high reflectivity) and series (high absorbtivity) with the bandpass varying between 35 to 100 nanometers depending on how the device is constructed. It is therefore of little use in applications requiring dense WDM (256 spectral chips over 100 nanometers) or spectrally based CDMA protocol optical communications.
U.S. Pat. No. 5,459,610, issued to Bloom et al., discloses a mems device for modulating white light via controllable diffraction to produce red, green and blue output to an aperture capable of receiving the zero order diffracted beam. The illustrations depict the diffraction of white light applied to each pixel. This approach is not suitable for dense WDM modulators for embedded fiber optic networks for aircraft and space vehicles due to the poor utilization of the light sources. For example, blue light is distributed to all the pixels, including those which are required to diffract blue light. This is unavoidable, as an object of their invention was to simultaneously modulate and diffract white light to produce colored light. U.S. Pat. No. 5,311,360, issued to Bloom et al., discloses an apparatus for modulating light with a dynamic mems diffraction grating. In a description of the functioning of the unit as a display illuminated with white light, it is mentioned that each pixel splits the light into a spectrum. In the process the spectrums are rotated as necessary to produce what amounts to RGB color images when viewed normal to the surface. The patent states that the device can be used for fiber optic applications, but does not cover the approach used in the present invention.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to modulate a selected portion of portions of the light spectrum for the purpose of carrying digital signals.
It is another object to couple modulated portions of a broadband light signal into an optical fiber for the transmission of digital signals.
It is yet another object of the invention to enable the transmission of digital words across an optical fiber by the use of the states of the digital signals on separate wavelengths to encode the bits of a binary word.
It is still another object of the invention to enable transmission of digital words to be used as a data bus, and address bus, or a control bus.
It is still another object to enable the parallel transmission of digital bits, bytes, words, and word strings.
It is still another object of the invention to provide a transmitter for a wavelength division multiple access network.
These and other objects are achieved by the present invention, which is a wavelength division multiplex transmitter for modulating light from a broadband light source and coupling modulated light to an optical waveguide for digital optical communications. The wavelength division multiplex transmitter includes a diffraction grating for receiving and diffracting light from a broadband light source. A first reflecting element receives diffracted light from the diffraction grating. A spectrally programmable spatial light modulator (SLM) receives reflected diffracted light from the reflecting element and selectively modulates a selected set of wavelengths of the reflected light. A lens receives the selected set of wavelengths and directs them into an optical waveguide for digital communication. This provides enhanced utilization of each wavelength within the broadband light source.
A preferred SLM is a grating light valve (GLV). The GLV SLM surface can be divided up into small sections each of which can manipulate specific portions of the spectrum. Slight variations in these sections allow a series of adjacent spectral portions to be broken into separately controllable channels. The GLV comprises periodically spaced alternating fixed and movable microscopic metal composite ribbons mounted on a substrate. When the movable ribbons are pulled down electrostatically, the device functions as a diffraction grating. Conversely when the ribbons are up it functions as a mirror. The tuning
Chan Jason
Ginsberg Lawrence
Leung Christina Y.
The Boeing Company
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