Trw Limited

Northrop Grumman Systems Corporation

Bruce A Ferguson

David Lawrence Rollins

Mark Kintis

Eric L Upton

Elizabeth Twyford Kunkee

Lawrence J Lembo

Stephen R Perkins

Richard A Fields

Juan C Carillo, Jr

An analog optical link ( ) that provides high-fidelity over bandwidths greater than 1 GHz is presented. The analog optical link ( ) includes a transmitter ( ) having an optical modulator ( ) and a receiver ( ) having an optical demodulator ( ). In one embodiment, the modulator ( ) is a phase modulator ( ) and particularly a pre-emphasis phase modulator ( ) that operates as a frequency modulator at low frequencies. The demodulator ( ) is a frequency demodulator ( ) that includes a feed-forward function for cancelling noise.

Wideband, high-fidelity analog optical link design

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 modulator ( ) that operates as a phase modulator at high frequency and as a frequency modulator at low frequencies to provide a suitable signal-to-noise ratio over a wide frequency band. The modulator ( ) includes an optical waveguide and opposing RF electrodes ( ) formed in the waveguide ( ). An RF input signal is applied to the electrodes ( ) to create an electric field that changes the index of refraction of the waveguide ( ) to affect the propagation speed of an optical carrier signal ( ), and thus provide the modulation. The electrodes ( ) are long velocity-matched electrodes that provide the RF loss versus RF frequency needed to produce the desired V&pgr; versus RF frequency over the entire bandwidth. The lower V&pgr; at lower RF frequencies will emphasize the lower frequencies and improve the low-frequency fidelity of the optical link by boosting the low-frequency signals above the excess link noise generated in the demodulator ( ).

Optical phase modulator design incorporating pre-emphasis

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.

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Redondo Beach, CA, United States of America

Bruce A Ferguson