Nikolai Stelmakh

Phase-sensitive image amplification with elliptical Gaussian pump

We numerically analyze phase-sensitive parametric amplification of a multi-pixel text image and demonstrate that ∼10-dB gain is achievable with ∼10-kW total pump peak power, which makes it compatible with compact pump sources.

Measurement of spatial modes of broad-area diode lasers with 1-GHz resolution grating spectrometer

A 1-GHz resolution double-pass grating spectroscopy of broad-area diode lasers is performed. Measurements of spatial and spectral distribution of emitting power are performed as a function of pumping current. Results are confronted with the mode structure of gain-guided waveguide. Nonlinear coupling of lateral modes has been observed and quantified

Quantum properties of a spatially-broadband traveling-wave phase-sensitive optical parametric amplifier

We present the quantum theory of a spatially-multimode traveling-wave phase-sensitive optical parametric amplifier (OPA) pumped by a beam with arbitrary spatial profile. By using Greens functions of the classical OPA, we derive the normally-ordered quadrature correlators at the OPA output, which provide complete quantum description of the phase-sensitive OPA and enable determination of its independently-squeezed eigenmodes. Two analytically treatable examples of plane-wave pump and infinite spatial bandwidth of the crystal are discussed in detail.

Estimation of the spatial bandwidth of an optical parametric amplifier with plane-wave pump

We analyze the spatial-frequency dependence of the gain of phase-insensitive and phase-sensitive optical parametric amplifiers with plane-wave pumping. We discuss the dependence of their spatial bandwidths on pump power and crystal length, L, and observe that the well-known (k s/L)1/2 approximation of spatial bandwidth is not very accurate (here k s is the signal beams wavevector magnitude). We derive an alternative approximation that is highly accurate at large gains and moderately accurate at low gains. The differences between the phase-insensitive and phase-sensitive amplifier bandwidths are shown to be insignificant for gains above several dB. Maximum phase-sensitive gain and bandwidth are realized by imposing an optimum phase profile onto the input signals spatial spectrum, which has nearly parabolic shape with added series of π/2 phase discontinuities at spatial frequencies outside the main bandwidth of the amplifier. We show that, apart from the discontinuities, such a profile can be closely approximated by placing the image plane into the middle of the nonlinear crystal (converging input beam). The phase discontinuities contribute an additional narrow component to the point-spread function of the phase-sensitive amplifier.

Harnessing Multimode Broad-Area Laser-Diode Emission Into a Single-Lobe Diffraction- Limited Spot

A spectrally resolved phase manipulation technique external to the laser cavity is used to reshape the multimode emission of a conventional broad-area laser diode into a diffraction-limited single-lobe spot. A mode conversion efficiency of 60% with a total insertion loss of 25% has been demonstrated with conventional optical elements and a binary phase mask.

Spatial modes of phase-sensitive parametric image amplifiers with circular and elliptical Gaussian pumps

We develop a method for finding the number and shapes of the independently squeezed or amplified modes of a spatially-broadband, travelling-wave, frequency- and polarization-degenerate optical parametric amplifier in the general case of an elliptical Gaussian pump. The obtained results show that for tightly focused pump only one mode is squeezed, and this mode has a Gaussian TEM(00) shape. For larger pump spot sizes that support multiple modes, the shapes of the most-amplified modes are close to Hermite- or Laguerre-Gaussian profiles. These results can be used to generate matched local oscillators for detecting high amounts of squeezing and to design parametric image amplifiers that introduce minimal distortion.

Degenerate and nondegenerate lateral-mode patterns in quantum cascade lasers

We experimentally investigate near-field lateral-mode patterns of 10–25-μm-wide quantum cascade wide-ridge lasers with few lateral modes using a 1-GHz-resolution spatially resolving midinfrared spectrometer. The results supported by simple box-model theory demonstrate that, depending on the laser geometry, one can either obtain lateral-mode frequency degeneracy or find the high-order lateral modes to be blueshifted or redshifted from the fundamental. We show that, with proper laser geometry, all longitudinal and lateral modes can be frequency nondegenerate and, therefore, be easily suited for spatiospectral mode combining to increase brightness.

Electrooptically tunable folded arrayed waveguide grating multiplexer

Channel tunability of 10 GHz has been demonstrated in a 40-channel 50-GHz-spaced folded silica-on-silicon arrayed waveguide grating (AWG) multiplexer using quadratic nonlinearity in phosphorous-doped glass and a specially shaped electrode. Such AWG can be stabilized and tuned around ITU grid without power-consuming thermoelectric coolers.

Compact representation of the spatial modes of a phase-sensitive image amplifier

We compute eigenmodes of spatially-broadband optical parametric amplifier with elliptical Gaussian pump and find compact representation of well-amplified modes by the space of the first few Laguerre- or Hermite-Gaussian modes of appropriate waist.

Quantum enhancement of a coherent ladar receiver using phase-sensitive amplification

We demonstrate a balanced-homodyne LADAR receiver employing a phase-sensitive amplifier (PSA) to raise the effective photon detection efficiency (PDE) to nearly 100%. Since typical LADAR receivers suffer from losses in the receive optical train that routinely limit overall PDE to less than 50% thus degrading SNR, PSA can provide significant improvement through amplification with noise figure near 0 dB. Receiver inefficiencies arise from sub-unity quantum efficiency, array fill factors, signal-local oscillator mixing efficiency (in coherent receivers), etc. The quantum-enhanced LADAR receiver described herein is employed in target discrimination scenarios as well as in imaging applications. We present results showing the improvement in detection performance achieved with a PSA, and discuss the performance advantage when compared to the use of a phase-insensitive amplifier, which cannot amplify noiselessly.