Photon transistors

Details Photon transistors Photon transistors

2002-07-18

2004-09-07

Dang, Hung Xuan (Department: 2873)

Optical waveguides

With optical coupler

C385S050000

Reexamination Certificate

active

06788838

ABSTRACT:

BACKGROUND
The present invention relates to optical devices. In particular, the present invention is related to switching devices, signal-processing devices, and logic implemented using photonic optical devices. More particularly, the present invention is related to a new class of optical devices, operated on the principle of transfer photon resistance, that are capable of performing multiple functions on signals carried by lightwaves or photons, including all-optical and electro-optical switching. The broad functionalities of these devices are similar to that of electronic transistors, except that electronic transistors operate on signals carried by RF current or electrons while the devices of the current invention operate on signals carried by lightwave or photons.
The current generation of computers utilizes a plurality of electronic transistor components. These transistors modulate the resistance to the motion of electrons (and thus current) in order to accomplish a wide variety of switching, amplification, and signal processing functions. Transistor electronic action controls or affects the motion of a stream of electrons through “transfer (electron) resistance” via the action of another stream of electrons.
Electronic transistors are typically fabricated using semiconductors such as Silicon (Si), and to a far less extent Gallium Arsenide (GaAs). Computing functions are performed by such electronic transistors integrated or grouped together as logic circuits on a very large scale with high device density. Due to various reasons discussed below, however, electronic transistor computing in present implementations is ultimately limited to the maximum data clock speeds of a few GHz. Semiconductor electronic switches generally are thought to have theoretical upper limits on their performance. Achievable minimum switching times are thought to be in the tens of picoseconds (10-20 ps), while minimum achievable switching power consumption and operational energy are thought to be around 1 microwatt (1 &mgr;W) and tens of femto-joule (10-20 fJ) levels, respectively. Such levels imply that high frequencies of operation may be possible for electronic computing.
Dense, high-frequency electronic circuit operations utilizing such electronic transistors present several persistent problems and complexities that, whether surmountable or not, are issues of concern to circuit designers. Even though electronic transistors that can operate at faster than tens of GHz do exist, the problems of electromagnetic interference (or “crosstalk”), radiation, and parasitic capacitance in dense circuits limit the clock speed of electronic computers to a range of a few GHz as the signal wavelength through the circuit becomes comparable to the circuit size. Furthermore, high-frequency electronic circuits can suffer seriously from the problems of electromagnetic interference and radiation.
It is thought that an optical circuit for which the signals are carried by light instead of electrical current may be used to eliminate the problems involving electromagnetic interference. In order for an optical circuit to perform useful computational or signal processing functions, however, there must be a way to switch optical signals using other optical signals or electrical signals. The former case is referred to as “all-optical switching” and the latter case as “electro-optical switching”.
Presently, fiber-optic communication systems typically use electro-optical switching. These optical communications systems have significant advantages over electrical communications systems utilizing electronic or radio-frequency (~10
9
Hertz) circuitries, partly because of the high frequency of light (~10
14
to 10
15
Hertz), which allows much broader bandwidths to be used to transmit signals. However, current electro-optical switches are large in size (usually at centimeter sizes or larger) and expensive. This makes it difficult to bring the high bandwidth fiber communication systems directly to the customer's location, an undertaking which will require low-cost components capable of complex electro-optical signal processing. Thus, low-cost electro-optical devices and circuits capable of high-density of integration would be desirable. Besides optical communications, such low-cost integrated electro-optical devices and circuits can also aid in data transmission between electronic circuits or subcircuits or within an electronic integrated circuit. A greater percentage of optical signals used in such devices would help to reduce electromagnetic radiation or interference and decrease transmission speed within each device. This could lead to improved performance for high-speed electronic computers as well.
A future goal in optical communications systems is to replace part of the system with all-optical devices or circuits, which would enable faster operation. Such all-optical devices or circuits would also lead to the realization of ultrafast all-optical computers. Thus, devices that are capable of electro-optical operations or a mixture of electro-optical and all-optical operations would be very desirable.
Because optical pulses can be very short (in the femtosecond range), it is often suggested that all-optical switching can be very fast. There have been attempts to construct switches that partially use light beams to switch light beams in an attempt to increase speed. In such attempts, switching an optical beam with another optical beam typically involves electronics to translate an optical signal at some point to an electrical signal which is then returned back to an optical signal at a subsequent time. Optical communications systems based on such switches are not “all-optical communications” because of this interface with electronic componentry. All-optical communications that allow the switching of light with light without the involvement of electronics as an intermediate step would reduce or eliminate the complexities inherent in the inclusion of electronic elements.
Below, examples of current art relating to all-optical switches as well as electro-optical switches are described.
There have been various attempts to switch light with light without the use of electronics. A typical method of switching one light beam via another light beam utilizes a Mach-Zehnder interferometer with a nonlinear optical medium. This implementation may be referred to as a nonlinear optical Mach-Zehnder interferometer. An exemplary Mach-Zehnder Interferometer
100
is illustrated in FIG.
1
. The nonlinear optical Mach-Zehnder Interferometer
100
of
FIG. 1
includes a pair of mirrors M
1
102
, M
2
104
and a pair of 50 percent beam splitters BS
1
106
, BS
2
108
. A Signal Beam Input
110
input into the Interferometer
100
is split into a pair of beams
112
,
114
via the 50 percent beam splitter BS
1
106
. The beams
112
and
114
are recombined at the beam splitter BS
2
108
to form a pair of resultant beams. If the beams
112
and
114
face equal optical path lengths as the beams
112
and
114
traverse the upper and lower arms, respectively, of the Interferometer
100
, then the beams
112
and
114
will constructively interfere to become Signal Beam Output A
116
and destructively interfere to become Signal Beam Output B
118
. Hence, in this event, no signal beam will be output as beam
118
(as the destructive interference cancels the power at Signal Beam Output B), while the full combined signal beam will be output as beam
116
.
A Nonlinear Refractive Index Medium
120
of length Lm, known to those skilled in the art as an optical Kerr medium, is positioned in the upper arm of the Mach-Zehnder Interferometer
100
, as shown in
FIG. 1. A
Control Beam Input
122
with a polarization orthogonal to that of the beam
112
is introduced via a polarization beam splitter PBS
1
124
. The Control Beam Input
122
propagates through and exits the medium
120
and is output from the Interferometer
100
via a polarization beam splitter PBS
2
126
. The medium
120
has nonlinear optical properties, in that exposing the medium
120
to a

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