Moshe Nazarathy

Progress in externally modulated AM CATV transmission systems

Recent advances in electronic linearization of AM CATV transmitters based on externally modulated diode pumped Nd:YAG lasers are presented. The theoretical principles and practical issues related to the methods of feedforward and predistortion linearization, the factors affecting system performance and the emerging devices, circuits, subsystems, and systems architectures are reviewed. In experiments based on a predistortion linearized system, transmission over two fibers of 30 km each, wherein each fiber carries 80 NTSC channels, is now routinely achieved with a CNR>50 dBc, a CTB<-65 dBc, and a CSO of typically -70 dBc. As the number of channels broadcast over each fiber is reduced from 80 to 60, CNR increases to 52 dBc. The fiber links served by the system under test each have 12-dB link budget, and include four connectors per fiber, with no degradation observed in one link when the connectors were opened on the other link.

Real-time long range complementary correlation optical time domain reflectometer

The improved performance of an optical time-domain reflectometer (OTDR) through the application of a correlation technique using codes with complementary autocorrelation properties is discussed. The theoretical foundations of the method are presented along with experimental results exhibiting the best one-way range reported to date for a practical long-haul, long-wavelength OTDR system. >

Spectral analysis of optical mixing measurements

A general rigorous theory of optical heterodyne and homodyne measurements is presented. The power spectrum of the photocurrent resulting from two uncorrelated optical beams mixing on a photodetector is derived. In particular, a rigorous analysis is presented for the delayed self-homodyne method which is used to characterize laser source linewidth by a Mach-Zehnder interferometer with a delay exceeding the source coherence length. Existing treatments are generalized to address non-Lorentzian laser sources of arbitrary lineshape. The analysis is further generalized to cover the case of modulated nonstationary sources. An example of the application of this theory is given. It is shown how the theory may be used to interpret an experimental result obtained using the gated delayed self-homodyne technique for characterizing the frequency chirp of laser sources under modulation. >

Unidirectional diode-laser-pumped Nd:YAG ring laser with a small magnetic field.

Single-mode operation of a monolithic semiconductor-laser-pumped unidirectional ring Nd:YAG laser has been demonstrated at 1319 and 1338 nm. The ring design optimizes the polarization eigenvalue difference between counterpropagating modes of the ring. The laser threshold is 4.5 mW, and the magnetic-field requirement for unidirectional operation is approximately 100 G.

Spread spectrum frequency response of coded phase reversal traveling wave modulators

Application of aperiodic phase reversals to the electrode pattern of a Mach-Zehnder traveling wave modulator according to suitable pseudorandom sequences considerably improves the high-frequency response for fixed drive voltage. Simulations for a family of devices based on the Barker codes are presented, in the presence of frequency dependent microwave losses and impedance mismatch, using a new theorem relating the modulation transfer function to the Laplace transform of the electrode pattern evaluated on a parabolic contour in the s -plane. Projecting from our recent experimental results on 4 and 5 bit Barker codes, at 1.3-μm wavelengths, a 2-cm-long 13-bit Barker code device fabricated in LiNbO 3 will exhibit 5-dB optical modulation bandwidth in excess of 50 GHz with a half-wave voltage less than 8 V.

Spread-spectrum nonlinear-optical interactions: quasi-phase matching with pseudorandom polarity reversals

Optical nonlinear interactions may be made broadband while maintaining a high conversion efficiency by applying spread-spectrum pseudorandom spatial modulation.

Velocity-mismatch compensation in traveling-wave modulators using pseudorandom switched-electrode patterns

The modulation impulse response of a traveling-wave modulator with an arbitrary aperiodic switched-electrode pattern is directly derived in the time domain. It is shown that applying the phase reversals according to a suitable pseudorandom sequence considerably increases the bandwidth-to-drive-voltage ratio figure of merit. This improvement is attributed to the spread-spectrum properties of pseudorandom sequences and may be obtained by appropriate choice of such sequences. Examples are given for modulators based on the Barker codes.

A Fabry-Perot etalon with one phase-conjugate mirror

Abstract A resonating structure composed of a plane-stratified lossless medium and a phase-conjugate mirror with loss or gain is analyzed by means of a scattering matrix method as well as by tracking the multiple reflections to their steady state. The amount of miscorrection in the presence of losses or gains in the PCM is explicitly evaluated.

5-mm-resolution optical-frequency-domain reflectometry using a coded phase-reversal modulator

Network analysis optical-frequency-domain reflectometry is demonstrated with what is to our knowledge the highest resolution reported to date (5 mm in fiber) and a dynamic range of 73 dB (electrical). The system uses a novel 13-bit Barker-coded phase-reversal optical modulator, a high-speed photodiode, and a commercial microwave vector network analyzer.

Diffraction transforms in homogeneous birefringent media

The Fresnel–Kirchhoff free-space diffraction transform is generalized to describe paraxial-beam propagation in homogeneous birefringent media, extending Fourier optics to anisotropic homogeneous media. Canonical operator formalism is used for the derivation. The method is applied to designing an optical Fourier transformer in a biaxial crystal.