Optical: systems and elements – Optical amplifier – Free electron
Reexamination Certificate
1998-03-24
2001-04-17
Moskowitz, Nelson (Department: 3662)
Optical: systems and elements
Optical amplifier
Free electron
C359S333000, C372S002000, C372S074000
Reexamination Certificate
active
06219175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a unidirectional optical amplifier capable of application to many fields, such as electrical engineering, electronic engineering, information engineering and opto-electronics, which amplifies light only in one direction.
2. Prior Art
Prior art methods for effecting optical amplifying include a laser, a traveling-wave tube, and a propagating wave amplification of light due to an interband electron transition.
The laser is a typical opto-electronics element or opto-electronics device for generating light and for amplifying light. The direction of light to be amplified is possibly reversed, and both forward and backward waves may be amplified. Accordingly, when the emitted light is reflected at the surface of a lens, optical fiber, optical disk or the like, and is incident on the laser as return light, this return light has also been amplified. Therefore, the oscillating characteristic and the amplifying characteristic of a laser are deteriorated, and excess noise is generated.
As countermeasures to the above malfunction suggested at present, the typical method is a technique that reentering of return light is generally prevented by providing at an output side of a laser an isolator for passing light only in a single, desired direction. It is, however, only possible to make optical isolators of magnetic material with bulk shape as the main material, and the price thereof is high, so the utility thereof may be limited. On this account, the optical isolator is utilized for fundamental study in the optical field and in optical fiber communication systems of large capacity, but applications requiring small size and low price, the optical disk technology, can not utilize the optical isolator, and thus characteristic deterioration and noise generation due to the return light becomes a technical obstacle in utilizing a laser.
Also, there is a system for performing high-speed information processing by light by integrating the light generating section, amplifier section, modulating section or the like, which utilizes a laser, with each other as an optical integrated circuit. However, in this system, the light returns from a forward section to a backward section, so that a problem emerges that a composition as an optical circuit having a composite function cannot be completed.
Moreover, the traveling-wave tube is a unidirectional electron tube having the highest operable frequency over the upper limit of operable frequency of a usual electron tube having unidirectional electronic functionality or a transistor (about 1000 MHz). This traveling-wave tube makes an electromagnetic wave propagate by using a delayed transmission line made of metal. An electron beam emitted from an electron gun gives energy to this electromagnetic wave and the electromagnetic wave is amplified when the speed of the electron beam and the propagation speed of the electromagnetic wave are coincident with each other. Other electromagnetic wave components traveling in the reverse direction are not amplified. However, the higher the frequency, the shorter the wavelength, so that the upper limit of usable frequency of a traveling-wave tube is determined by manufacturing techniques for the metal of the transmission path. As a result, the traveling-wave tube can not be utilized with frequencies in the range of dozens of GHz or more (wavelengths of several cm or less). Accordingly, fabrication of a traveling-wave tube capable of applying light having a wavelength of less than 1 &mgr;m exceeds the limitations of current manufacturing techniques, and is impossible at this time.
Moreover, in the prior art of traveling wave amplification of light by interband electron transition, there have been attempts at unidirectional amplification of light using a semiconductor laser performing generation and amplification of light by electron transitions from conduction band to valence band in a semiconductor and by taking a value of momentum of light, h&bgr;/2&pgr; (where, h is Plank's constant, and &bgr; is wave number of light) that may be ignored in most cases because its value is usually small. In this case, since scattering of an electron is extremely large, clear unidirectional amplifying action has not been confirmed.
SUMMARY OF THE INVENTION
The present invention has as its object to provide a unidirectional optical amplifier capable of performing optical amplifying that is not influenced by the return light.
To this end, according to a first aspect of the present invention, there is provided a unidirectional optical amplifier comprising an optical dielectric waveguide having a high refraction index for leading light from a light input terminal to a light output terminal and a straight electron beam transit section extended in the direction of electron beam transit, and including an amplifier section for amplifying light in one direction by utilizing an energy level sufficiently higher than a Fermi level, an emissive section for emitting an electron beam into the electron beam transit section, and an electron absorption section for absorbing the electron beam emitted from the electron beam transit section, characterized by the electron beam transit section being comprised so that the effective mass of an electron in the amplifier section becomes small, and by the optical dielectric waveguide and the electron beam transit section being arranged in such a manner that a wave number of light in the amplifier section is increased and the electric field component of light is generated in the electron beam transit direction.
In an embodiment of the present invention, the electron beam transit section of the amplifier section for amplifying light in one direction by utilizing an energy level sufficiently higher than a Fermi level is constituted by a material of a high refractive index so as to make the effective mass of an electron small, and the optical dielectric waveguide of the amplifier section is constituted in such a manner that a wave number of light in said amplifier section is made large and the electric field component of light is generated in the direction of electron beam transit. Accordingly, some of the light will, as a result, seep into the electron beam transit section. In a typical embodiment, the path of the propagated light will intersect the electron beam transit section in plural locations.
According to this embodiment of the present invention, the effective mass of an electron in the amplifier section is made small, and a wave number of light is made large (in other words, a propagation speed of light in the direction of electron beam transit is made small), so that the unidirectional optical amplifier for realizing optical amplification that is not influenced by the return light can be provided. The degree to which these phenomena occur is highly dependent upon the shape and the high refractive index of the optical dielectric waveguide.
Also in this embodiment of the invention, amplification occurs by way of the aforementioned seepage of light into the electron beam transit section. In this manner, the seeped light receives energy from the electron beam by intersecting with it, the electron beam having been radiated from the electron radiating section and having decreased effective electron mass within the electron beam transit section.
In a preferred embodiment of the present invention, the amplifier section is so constructed that the optical dielectric waveguide is wound on and around the electron beam transit section in a spiral shape.
According to a preferred embodiment of the present invention, the optical dielectric waveguide for constituting the amplifying section is wound on and around the electron beam transit section in a spiral shape at its periphery.
According to a preferred embodiment of the present invention, the optical dielectric waveguide is wound on and around the electron beam transit section. A wave number of light in the amplifier section is made large by means of this constitution and by means of a hi
Frank Robert J.
Gluck Jeffrey W.
Kanazawa University
Moskowitz Nelson
Venable
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