Cholesteric liquid crystal cell devices and systems

Details Cholesteric liquid crystal cell devices and systems Cholesteric liquid crystal cell devices and systems

2001-12-05

2004-12-21

Chowdhury, Tarifur R. (Department: 2871)

Optical waveguides

With optical coupler

Switch

C385S016000, C385S017000, C385S024000, C385S140000, C359S247000, C359S252000, C359S253000, C359S259000, C349S196000, C349S197000, C398S065000

Reexamination Certificate

active

06834137

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is related to fiberoptic network devices and systems, and in particular, to cholesteric liquid crystal cell devices and switch systems.
In fiberoptic networks light signals are used to carry information over optical fibers. Different techniques are used to control optical signals from the sender to the receiver. For example, time slots (time division multiplexing) or wavelengths (wavelength division multiplexing) may be used to define communication channels over an optical fiber. To carry out these operations, fiberoptic networks use many devices and systems of varying complexity. But speed has always been a prime objective in network operations. Hence one goal has been the creation of all-optical fiberoptic networks. Rather than converting incoming optical signals to electrical signals which are then processed by the network device or system and then reconverted back to outgoing optical signals, an all-optical network maintains the communication signals as optical signals as they pass through the network devices and systems. In this manner, the network loses no conversion time.
One promising technology toward this goal has been microelectromechanical system (MEMS) switches. Though there are many variations, the basic operation of a MEMS switch is the direction of light beams from an array of input optical fibers into an array of output optical fibers by an array of mirrors which selectively direct the incoming light beams to the arrayed ends of the output optical fibers. The position of each mirror is controlled by the selective application of deflection voltages. As the name implies, the mirrors in MEMS switches are also very small to provide the theoretical advantages of higher operational speeds due to the small inertial mass of the mirrors, lowered manufacturing costs from semiconductor processing circuit technology used to manufacture the mirror array with lower unit costs, and ease of installation and maintenance from the presumed small size of the MEMS switch. However, these advantages have not been realized thus far. Reliability, a prime concern for all networks, has reportedly been a problem with MEMS switches. Apparently the mechanical properties of these systems, the stress and strain on the mirrors (or their supports), add to the complexity of the systems and detract from their reliability.
To avoid these problems, the present invention utilizes cholesteric liquid crystal cells which form network devices and systems without the mechanical disadvantages of a MEMS and other optomechanical systems. Furthermore, the network devices and systems of the present invention retain the advantages of small size described above.
SUMMARY OF THE INVENTION
The present invention provides for a cholesteric liquid crystal cell unit for receiving incident light. The unit has a first cholesteric liquid crystal cell which receives the incident light and which reflects circularly polarized light of one state of the incident light or transmits the incident light, responsive to a control signal. The unit also has a second cholesteric liquid crystal cell arranged with respect to the first cholesteric liquid crystal cell to receive the light transmitted by the first cholesteric liquid crystal cell. The second cholesteric liquid crystal cell is selected to reflect or transmit light from the first cholesteric liquid crystal cell responsive to the control signal when the first cholesteric liquid crystal cell reflects the circularly polarized light of the one state or transmits the incident light respectively. In one embodiment of the cell unit, a &pgr;-phase waveplate element is located between the first and second cholesteric liquid crystal cells.
The present invention also provides for an optical switch device which has a first sleeve holding first and second optical fibers fixed in a central longitudinal channel, a first collimating GRIN lens proximate an end face of the first sleeve, a second sleeve holding a third optical fiber in a central longitudinal channel, and a second collimating GRIN lens proximate an end face of the second sleeve. The two GRIN lenses face each other with a cholesteric liquid crystal cell unit as described above. The first and second sleeves, the first and second GRIN lenses, the cholesteric liquid crystal cell unit are arranged and oriented with respect to each other so that light from the first optical fiber passes through, and back from, the first collimating GRIN lens, and the cholesteric liquid crystal cell unit into the second optical fiber when the cholesteric liquid crystal cell unit reflects light responsive to the control signal, and light from the first optical fiber passes through the first collimating GRIN lens, the cholesteric liquid crystal cell unit, and the second collimating GRIN lens into the third optical fiber when the cholesteric liquid crystal cell units transmits light responsive to the control signal. With the cholesteric liquid crystal cell unit reflecting light responsive to a first control signal voltage and transmitting light responsive to a second control signal voltage, the device can be operated as an attenuator by using control signal voltages intermediate the first and second control signal voltages so that the cholesteric liquid crystal cell unit proportionally transmits and reflects light.
The present invention provides for an WDM add/drop multiplexer device which has a first sleeve, a network input optical fiber and a network output optical fiber fixed in a first sleeve channel, a first collimating GRIN lens proximate the first sleeve, a second sleeve, an add optical fiber and a drop optical fiber fixed in a second sleeve channel, and a second collimating GRIN lens proximate the second sleeve. The first and second collimating GRIN lenses are directed toward each other with a wavelength-dependent filter proximate the first collimating GRIN lens. The wavelength-dependent filter transmits light at selected wavelengths and reflects light at other wavelengths. A cholesteric liquid crystal cell unit lies between the wavelength-dependent filter and the second end face of the second GRIN lens. The first and second sleeves, the first and second GRIN lenses, the wavelength-dependent filter, and the cholesteric liquid crystal cell unit are arranged and oriented with respect to each other so that light from the network input optical fiber at the other wavelengths passes through, and back from, the first collimating GRIN lens and the wavelength-dependent filter into the network output optical fiber, and so that light from the network input optical fiber at the selected wavelengths passes through, and back from, the first collimating GRIN lens, the wavelength-dependent filter, and the cholesteric liquid crystal cell unit into the network output optical fiber when the cholesteric liquid crystal cell units reflects light responsive to the control signal, and so that light from the first optical fiber at the selected wavelengths passes through the first collimating GRIN lens, the cholesteric liquid crystal cell unit, and the second collimating GRIN lens into the drop optical fiber when the cholesteric liquid crystal cell units transmits light responsive to the control signal. Light from the add optical fiber at the selected wavelengths passes through the second collimating GRIN lens, the cholesteric liquid crystal cell unit, the wavelength-dependent filter and the second collimating GRIN lens into the network output optical fiber when the cholesteric liquid crystal cell units transmits light responsive to the control signal.
The present invention also provides for an optical switch system which has an array of input optical fibers, an array of first output optical fibers, an array of second output optical fibers, and a switching matrix of cholesteric liquid crystal cell units. Each liquid crystal cell unit reflects or transmits light selectively responsive to control signals and is arranged with respect to the array of input optical fibers, the array of first output optical fibers and the array

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