Coherence Modulation Of Light Research Articles

Electric Field Sensing Scheme Based on Matched $ \hbox{LiNbO}_{3}$ Electro-Optic Retarders

In this paper, a wideband-electric-field-sensing scheme that uses optically matched integrated optics electrooptic devices and coherence modulation of light is described. In a coherence modulation scheme, the integrated optics sensor detects the electric field and imprints it around an optical delay. The optical delay is generated by a birefringent optical waveguide in a lithium niobate (LiNbO3) integrated optics two-wave interferometer. The modulated optical delay, acting as an information carrier, is transmitted through an optical fiber channel. At the receiver, light is demodulated by a second integrated optics two-wave interferometer, which also introduces a second optical delay. The optical delays on the sensor and demodulator are matched at the same value. The integrated optics demodulator measures the autocorrelation of light around the optical delay value, and the imprinted electric field is recuperated as a linear variation of the received optical power. The matching of the sensor and demodulator allows a direct detection of the electric field, giving a unique feature to this fiber-integrated optics scheme. The experimental setup described here uses two pigtailed LiNbO3 electrooptic crystals: one acting as the electric field sensor and the other acting as the optical demodulator. The wideband sensing range on the experimental setup corresponds to frequencies between 0 and 20 kHz.

An all-fibre and integrated optics electric field sensing scheme using matched optical delays and coherence modulation of light

Sensing electric fields occupying large bandwidths are interesting in practical applications related to natural phenomena and also in man-made hard electromagnetic industrial environments. In this work, an electric field sensor scheme, using coherence modulation of light, in an all-fibre configuration is described. The scheme uses lithium niobate (LiNbO3), integrated optics sensors. In a coherence modulation scheme, the LiNbO3 sensor detects the electric field and imprints it around an optical delay. The optical delay, acting as an information carrier, is transmitted through an optical fibre channel. At the receiver, light is demodulated by using a two-wave interferometer, introducing a second optical delay which is matched to the sensor's one. The demodulator can be implemented using either a second LiNbO3 crystal or an all-fibre optical retarder. Both alternatives are studied in this paper. The optical demodulator measures the optical autocorrelation around the optical delay and the electric field is recovered as a linear variation of the received optical power. Matching of the sensor and demodulator allows direct detection of the electric field, giving an unequal feature of an all-fibre scheme. The bandwidth of the sensing scheme is between 0 and 20 kHz.

Electric field sensing system using coherence modulation of light

This paper describes an experimental setup for detecting electric fields using electrooptic lithium niobate (LiNbO/sub 3/) sensors and coherence modulation of light. In this detection scheme, the sensed electric fields modulate optical delays, which are introduced by LiNbO/sub 3/ coherence modulators when associated to low-coherence optical sources. The optical delays act as coherence-multiplexed carriers of the sensed electric fields and are transmitted through an optical fiber channel. At the receiver, the electric fields are detected by measuring the auto-correlation of the received light by using two-wave interferometers, which are matched to the introduced optical delays on the sensing devices.

Highly unbalanced GaAlAs–GaAs integrated Mach–Zehnder interferometer for coherence modulation at 1.3 μm

A novel integrated III–V semiconductor waveguide modulator specially designed to generate an optical delay of 100 μm is presented. This is achieved by simultaneous propagation of the TE fundamental mode in both of the arms of a highly unbalanced Mach–Zehnder interferometer with a 29 μm length difference between both arms. In order to minimize the losses in this complex curved structure, trenches were etched on the outsides of curved sections. The modulator has a contrast of 34%, a switching voltage of 6 V with a 10 mm long electrode and is suitable for the transmission and multiplexing of signals by coherence modulation of light in an optical fiber network powered by a short coherence source, such as a 1.3 μm superluminescent diode.

A GaAlAs-GaAs integrated coherence modulator

This paper presents a novel integrated III-V semiconductor waveguide modulator specially designed to generate optical delays of several hundred micrometers. This is achieved by simultaneous propagation of transverse electric (TE) and transverse magnetic (TM) lowest order modes in an original layered waveguide exhibiting a group birefringence greater than 0.02 at 1.3 /spl mu/m. The device has 40% contrast, a switching voltage of 7 V with a 10-mm long electrode and is suitable for transmission and multiplexing of signals by coherence modulation of light in an optical fiber network powered by a short coherence source such as a superluminescent diode.

Linear phase tracking in a coherence modulation electrical sensor system using integrated LiNbO/sub 3/ modulator/demodulator

We report an interferometric sensor system, based on coherence modulation of light and LiNbO/sub 3/ integrated optics technology. We describe a phase detection scheme designed to retrieve the absolute phase variations produced by a sensor system where the sensor signal is electronically applied to an electro-optic modulator. The system consists of an imbalanced LiNbO/sub 3/ Mach-Zehnder transducer fed by a self-powered charge generating sensor, and an optoelectronic central processing unit including a second electrooptic Mach-Zehnder working as an optical demodulator and featuring a matched path-imbalance. Electrical feedback is applied to this second interferometer in an active demodulation scheme, allowing a linear tracking of the signal phase up to 7-/spl pi/ radians.

Electro-optic systolic processor with a pipeline architecture

An optical pipeline architecture based on coherence modulation of light is advanced. The processing elements are formed by electro-optic modulators set in series in which the data flow propagates from a low-coherence light beam. Initial experimental verifications are reported for bulk devices and show that a potential computing speed of 1011 additions/multiplications per second can be expected.

An acousto-optic correlator working by coherence modulation of light

Demonstration of coherence modulation of light is reported for the first time in the area of acousto-optic signal processing. The method allows electro-optic modulation of broadband sources to be used in acousto-optic time integrating correlators, with a modulation depth and a dynamic range comparable to those of coherent systems. Though a single coherence-modulated channel is used, it demonstrates that a generalization of the method to several channels is possible.

DIGITAL OPTICAL COMPUTING: A NEW APPROACH OF SYSTOLIC ARRAYS BASED ON COHERENCE MODULATION OF LIGHT AND INTEGRATED OPTICS TECHNOLOGY

In optical computing, matrix-vector products are usually computed using systolic processors formed by acousto-optic cells illuminated by laser beams. We report a new approach based on coherence modulation of light. In this method, matrix-vector products are implemented electro-optically by a cascade of modulators forming a computing array. Several inputs can be operated on in parallel, and a number of operations can be performed digitally at one time. The demonstrator that was built in the frame of the European Programme "ESPRIT II Basic Research Action" to test this concept, is reported together with new results obtained using integrated optics technology.

An LiNbO/sub 3/ integrated coherence modulator

The authors describe the principle of operation and the performance of a newly integrated LiNbO/sub 3/ modulator specially designed to generate optical delays of several millimeters. This is achieved by using the simultaneous propagation of the TE and TM modes in a waveguide and by taking benefit of the high natural birefringence of LiNbO/sub 3/. This modulator is well-suited to coherence modulation of light in fiber-optic transmissions. When powered by a short coherence source, the large optical delays induced by a cascade of such modulators can be used as information carriers to transmit several signals simultaneously. A demonstration is reported using a single source and two modulators in cascade to transmit signals simultaneously. >

Polarization-independent transmission on a single mode fiber using coherence modulation of light

A polarization-independent transmission link on a single mode fiber at 1300-nm wavelength is demonstrated using coherence multiplexing. The use of a source with a very short coherence length (about 200 mu m) allows an easy implementation of the suitable optical delays (some millimeters) using LiNbO/sub 3/ modulators matched to fiber interferometers. Experiments were conducted with transmission of analog signals and baseband TV signals on a 2500-m-long single mode fiber. The polarization-independence of the method is obtained at the cost of relatively high losses. The high losses are introduced by the interferometers that are required at both ends of the link (theoretical losses of -3 dB/interferometer). They are physically inherent in the coding and detection process, which requires optical delays greater than the coherence length, and hence cannot be decreased. >