Trw Limited

Northrop Grumman Systems Corporation

Richard A Fields

David Lawrence Rollins

Mark Kintis

Eric L Upton

Elizabeth Twyford Kunkee

Lawrence J Lembo

Stephen R Perkins

Juan C Carillo, Jr

Bruce A Ferguson

James E Leight

An RF combiner ( ) that combines a plurality of RF signals ( ) in the optical domain. The combiner ( ) includes a single optical source ( ) that generates an optical beam ( ). The optical beam ( ) is directed through a series of optical modulators ( ), such as optical phase modulators. Each modulator ( ) is responsive to an RF signal ( ) that is to be combined with the other RF signals ( ). Each modulator ( ) modulates the optical signal ( ) with the RF signal ( ) so that the modulations combine in an additive manner. A single optical phase demodulator ( ) is used to demodulate the composite phase modulated optical beam ( ) to generate the combined RF signal ( ). Suitable delay devices ( ) can be used between the optical modulators ( ), or the RF signals can be matched so that the RF signals combine in phase.

RF combiner based on cascaded optical phase modulation

An optical device for use with an optical input beam comprising an optical thresholding device positioned along an optical path defined by the propagation direction of the optical input beam. If the combined intensity of the optical input beam and a control beam exceeds a threshold level, the optical beam passes through the thresholding device. Preferably, the optical thresholding device is a saturable absorber. When the device is configured as an optical comparator, the intensity of the optical input beam exceeds the threshold level and the thresholding device saturates and turns transparent so that the control beam passes through the thresholding device as an optical indicator beam. When the device is configured as an optical signal attenuator and the intensity of the optical input signal is negligible compared to that of the control beam, the combined intensity of the beams does not saturate the thresholding device.

Optical devices employing an optical thresholder

An optical inverting system employs a first optical structure having an index of refraction that varies with the intensity of an incident beam and a second optical structure having a constant index of refraction, and forming an interface therebetween. An optical pulse stream is combined with a laser beam and the combined beam is applied to the first optical structure, impinging the interface at a predetermined angle of incidence. If the angle of incidence is less than a critical angle, the beam is refracted into the second optical structure. If the angle of incidence is greater than the critical angle, the beam is completely reflected at the interface. Thus the output of the second optical structure is an inversion, and the output of the first optical structure is a level shifted replica, of the optical digital pulse stream.

Refractive index manipulating optical inverter

An optical device for use with an optical input beam comprises and optical thresholding device having a predetermined threshold level, and is positioned along an optical path defined by the propagation direction of the optical input beam. A source generates a control beam through the optical thresholding device, wherein if the combined intensity of the optical input beam and the control beam is large enough to exceed the threshold level of the thresholding device, the optical beam passes through he thresholding device. The thresholding device attenuates the optical beam as it passes therethrough. In a preferred embodiment, the optical thresholding device is a saturable absorber. When the device is configured as an optical comparator, the intensity of the optical input beam is large enough to exceed the threshold level of the thresholding device, the thresholding device saturates and turns transparent so that the control beam passes through the thresholding device as an optical indicator beam and the optical input beam passes through the thresholding device. When configured as an optical signal attenuator and the intensity of the optical input signal is negligible compared to that of the control beam the combined intensity of the optical input signal and the control beam do not saturate the thresholding device.

An optical analog-to-digital converter (,) that makes use of a downward-folding successive approximation conversion scheme that employs subtraction of optical signals. A pulsed optical signal (,) to be converted is applied as an input to each of a plurality of converter channels (,), where each channel (,) outputs one of the bits of the digital output of the converter (,). The input signal (,) to each channel (,) is sent to a thresholding device (,) that determines whether the intensity of the signal is greater than or less than a predetermined threshold value. The first channel thresholding device (,) compares the input signal (,) to a threshold value that is one-half of a known maximum intensity. Subsequent channel thresholding devices (,) compare the input signal to a threshold value that is one-half of the intensity used in the previous channel in a downward-folding scheme. If the intensity of the input signal (,) is greater than the threshold value in a particular channel (,), then that threshold value is subtracted from the input signal (,) in each of the successive channels before being applied to the thresholding device (,) in that channel (,). The subtraction elements (,) can be saturable absorbers or electro-absorption modules in a particular design. Additionally, the control signals from a particular channel (,) to each of the successive channels to determine whether subtraction will occur can be provided by an optically controlled switch (,), such as a saturable absorber, or an electrically controlled switch, such as an electro-absorption module.

Delayed pulse saturable absorber-based downward-folding optical A/D

The optical hold unit (100) of the present invention includes an optical modulator (108) that has an electrical input, an optical input, and an optical output. A 1.times.N optical splitter (106) is also provided that has an optical input and N optical outputs. In addition, N optical paths (112) are individually coupled to the N optical outputs and carry one of the N output signals. Each optical path has an associated propagation delay. Optical delay elements may be located in any of the N optical paths that carry the output signals. The optical delay elements serve to lengthen the propagation delay (114a-e) of the optical path (112a-e) in which the optical delay element is located. In an alternative embodiment, the optical hold unit (200) includes an optical modulator (108) that has an electrical input, an optical input, and an optical output. An optical resonator (202) is also provided and connected to the optical output of the modulator (108). The optical resonator (202) also includes a partially transmissive output (222) to which an optical path is connected. The optical resonator (202) may also include a gain medium (208) or an optical switch (210).

Optical sample and hold architecture

An optical quantizer (10) that employs a chain of optical thresholding devices (16) positioned in the propagation path of an optical input beam (12) to be quantized. Each optical thresholding device (16) saturates and turns transparent if the intensity of the optical beam (12) that impinges it is above a predetermined threshold level designed into the device (16). If the input beam (12) saturates the optical thresholding device (16), the device (16) outputs an indicator signal (22) identifying the saturation. The input beam (12) propagates through the optical thresholding device (16) with some attenuation caused by the saturation, and impinges subsequent optical thresholding devices (16) in the chain. Eventually, the attenuation of the input beam (12) caused by the multiple saturations will decrease the beam intensity below the threshold level of the next optical thresholding device (16). The number of indicator signals (22) gives an indication of the intensity of the input beam (12). The optical thresholding devices (16) can provide optical or electrical indicator signals (22) depending on the type of thresholding device (16) used.

Repetitive absorptive thresholding optical quantizer

An optical analog-to-digital converter (10) which fully operates in the optical domain and utilizes an upward-folding successive approximation approach for conversion. The converter (10) includes a plurality of optical stages (14, 16, 18) where each stage (14, 16, 18) generates a digital bit. Each stage (14, 16, 18) includes an optical threshold switch (30, 56, 78) that sets the bit high when the switch (30, 56, 78) is closed. When a sample amplitude of the analog signal is compared to a threshold value and found to exceed the threshold value, the bit is set to 'high' and the sample is passed directly onto the next stage (14, 16, 18). If the sample amplitude is found to be less than the threshold value, the bit is set to 'low' and an intensity equal to the maximum signal intensity minus the threshold intensity is added to the sample amplitude. Each successive stage (14, 16, 18) compares the normalized signal sample to thresholds growing closer and closer to the maximum signal intensity. Multiple bits can be obtained by cascading stages.

Upward-folding successive-approximation optical analog-to-digital

A frequency modulation-based optical analog-to-digital converter utilizes a downward-folding, successive approximation approach. A series of stages is utilized to generate bits in the digital signal. In each stage, complementary low and high bandpass filters collectively cover a bandpass frequency range from a low frequency to a high frequency. The high frequency filtered signal from the high bandpass filter is observed to obtain a bit in the digital word. By performing the folding operations in the frequency domain, the converter avoids the difficult task of optical power subtraction, relying instead on frequency down-conversions. The high frequency filtered signal passed by the high bandpass filter is then downconverted and added to the low pass filter signal to generate a modulated signal for the next stage.

Frequency modulation-based folding optical analog-to-digital converter

An optical inverter (10) that uses a saturable absorber (28) to distinguish between a logical one and a logical zero. A low power laser (18) generates an optical beam that is split into a first beam that propagates among a first beam path (24) and a second beam that propagates along a second beam path (26). The saturable absorber (28) is an optical switch that is positioned in the first beam path (24), and is switched from an opaque mode to a transparent mode when it receives an optical input signal. The first beam and the second beam are recombined as an optical output beam in an optical combiner (30). The first beam path (24) and the second beam path (26) have a length relative to each other such that the first and second beams are 180.degree. out of phase when they reach the optical combiner (30). Therefore, if the saturable absorber (28) is switched to the transparent mode, the first and second beams combine destructively and the optical output beam is dark, or a logical zero. When the saturable absorber (28) is in the opaque mode, the first beam is blocked so that the optical output beam is the second beam, providing a logical one. A second saturable absorber (34) can be provided to receive the optical output beam from the combiner (30) to absorb residual light when the output beam is dark. Additionally, an optical amplifier (36) can be provided to receive the optical output beam from the combiner (30) to amplify the optical output beam to a consistent, predetermined output level.

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Redondo Beach, CA, United States of America

Richard A Fields