Coherent light generators – Laser logic system
Reexamination Certificate
1999-02-01
2001-12-18
Davie, James W. (Department: 2881)
Coherent light generators
Laser logic system
C372S026000, C372S050121
Reexamination Certificate
active
06331990
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to optical signal conversion and amplification. In particular, it improves on the devices and methods of U.S. Pat. No. 5,604,628 issued Feb. 18, 1997, U.S. Pat. No. 5,742,045 issued Apr. 21, 1998, and U.S. Pat. No. 5,748,653 issued May 5, 1998, the disclosures of which are hereby incorporated by reference. The present invention improves the Lasers with Optical Gain Control (“LOGiC”) devices and methods of these patents by providing a mechanism for signal amplification and conversion of a frequency-modulated (“FM”), a wavelength-multiplexed (“WM”), or an amplitude-modulated (“AM”) optical signal into an amplified amplitude-modulated optical signal.
The LOGiC devices offer the possibility of integrating all-optical high-speed communications and signal processing. These devices can route signals, exercise logic functions, and filter spontaneous emission. A LOGiC device typically comprises a semiconductor main laser with a control beam that enters the side of the laser cavity at right angles (see
FIG. 1
for a block diagram). The main laser can be an in-plane laser (IPL), a vertical cavity laser (VCSEL), or an electrically/optically-pumped semiconductor amplifier. The control beam can originate from a monolithically integrated optical amplifier or semiconductor laser or from a fiber/waveguide that is butt-coupled to the side of the main laser. In operation, increasing control-beam power P
c
(with angular frequency &ohgr;
c
) causes output-beam power P (with angular frequency &ohgr;) to decrease. Other optical modulation is possible for fiber lasers that use DBR mirrors and two longitudinal modes.
Although a number of LOGiC devices have been developed for signal routing, optical filtering, and Boolean logic, these devices do not have optical gain—defined by
G
opt
≡
|
ⅆ
P
ⅆ
P
c
|
--
since
G
opt
is less than one for devices of the prior art. Optical gain G
opt
>1 is required to regenerate, amplify, and condition optical signals and to cascade LOGiC devices in multi-element circuits. When the optical gain is greater than one (G
opt
>>1), small variations in an input signal P
c
result in large changes of an output signal P, hence amplification.
In addition, the LOGiC devices of the prior art do not explicitly address the possibility of optical FM demodulation. Demodulation and wavelength conversion are important for optical signal routers and communications systems. FM communications links are generally chosen over AM links when low-noise characteristics are important. However, there is no single, integrable device that can convert a FM signal into an AM signal, as is typical of a FM discriminator in communications equipment.
Therefore the LOGiC devices of the prior art can be improved by adding mechanisms for optical gain, demodulation, and wavelength conversion.
OBJECTS AND SUMMARY OF THE INVENTION
One object of the present invention is to provide apparatus and method to amplify optical signals.
Another object of the present invention is to provide apparatus and method to convert FM optical signals to AM optical signals.
Another object of the present invention is to provide apparatus and method to convert FM optical signals to AM optical signals at effective efficiencies.
Still another object of the present invention is to provide monolithically integrable apparatus to convert FM optical signals to AM optical signals.
Yet another object of the present invention is to provide apparatus and method to convert FM optical signals to AM optical signals that are substantially noise-free even when amplified.
A further object of the present invention is to provide apparatus and method for high-speed conversion of FM optical signals to AM optical signals.
Yet a further object of the present invention is to provide apparatus and method to convert FM optical signals to AM optical signals that produce an identical AM electrical output signal.
Briefly stated, the apparatus and method of the present invention demodulates a FM, WM, or AM optical input beam, amplifies the signal impressed on it, and then modulates the signal amplitude of an output beam without intervening electronics. The device can be made from any semiconductor laser, including edge-emitting lasers and VCSELs. Light transmitted through the waveguide (the “control beam”) interacts with the carrier population of the laser, reducing the available gain and thereby the output intensity. There are three key advantages of the present invention (i) a FM control beam produces an AM output beam from the main-laser, (ii) the amplitude of the AM beam depends directly on the differential gain ∂G/∂&ohgr;, and (iii) the apparatus and method of the present invention provides gain for all LOGiC devices presently known. The present invention works with available and future semiconductor lasers, including those emitting in the blue as well as those operating at 670, 850, 980, 1300, and 1500 nm. The 1300 and 1500 nm lasers are of particular importance for fiber communications.
According to an embodiment of the invention, apparatus to manipulate the optical properties of light comprises: at least one first source of stimulated optical emission emitting an output beam; at least one second source of optical emission emitting a control beam; and structure permitting the control beam to interact with the output beam, whereby the output beam is modulated.
According to a feature of the invention, a method of processing an optical signal comprises the steps of: fabricating a first source of stimulated optical emission; coupling to the first source a second source of optical emission; applying a bias to at least one of the first and second sources, the bias being a one of optical and electrical; and extracting from said first source an optical signal modulated by said second source.
According to another feature of the invention, apparatus to manipulate information encoded into an emission of light comprises: first means for generating a stimulated optical emission from at least one first source of stimulated optical emission; second means for generating an optical emission from at least one second source of optical emission; and the optical emission modulating the stimulated optical emission.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the pertinent art from the following detailed description of a preferred embodiment of the invention and the related drawings, in which like reference numerals designate the same elements.
REFERENCES:
patent: 4607916 (1986-08-01), Sanford
patent: 5748653 (1998-05-01), Parker
Parker Michael A.
Shire Douglas B.
Tang Chung L.
Burstyn Harold L.
Davie James W.
Inzirillo Gioacchino
Mancini Joseph A.
The United States of America as represented by the Secretary of
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