Abstract Group IV photonics hold great potential for nonlinear applications in the near- and mid-infrared (IR) wavelength ranges, exhibiting strong nonlinearities in bulk materials, high index contrast, CMOS compatibility, and cost-effectiveness. In this paper, we review our recent numerical work on various types of silicon and germanium waveguides for octave-spanning ultrafast nonlinear applications. We discuss the material properties of silicon, silicon nitride, silicon nano-crystals, silica, germanium, and chalcogenide glasses including arsenic sulfide and arsenic selenide to use them for waveguide core, cladding and slot layer. The waveguides are analyzed and improved for four spectrum ranges from visible, near-IR to mid-IR, with material dispersion given by Sellmeier equations and wavelength-dependent nonlinear Kerr index taken into account. Broadband dispersion engineering is emphasized as a critical approach to achieving on-chip octave-spanning nonlinear functions. These include octave-wide supercontinuum generation, ultrashort pulse compression to sub-cycle level, and mode-locked Kerr frequency comb generation based on few-cycle cavity solitons, which are potentially useful for next-generation optical communications, signal processing, imaging and sensing applications.

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Nonlinear Group IV photonics based on silicon and germanium: from near-infrared to mid-infrared

Ge-on-Si is an attractive material platform for mid-IR broadband sources on a chip because of its wide transparency window, high Kerr nonlinearity and CMOS compatibility. We present a low-loss Ge-on-Si waveguide with flat and low dispersion from 3 to 11 µm, which enables a coherent supercontinuum from 2 to 12 µm, generated using a sub-ps pulsed pump. We show that 700-fs pump pulses with a low peak power of 400 W are needed to generate such a wide supercontinuum, and the waveguide length is around 5.35 mm.

Mid-IR supercontinuum generated in low-dispersion Ge-on-Si waveguides pumped by sub-ps pulses

A comparison study of shortwave (3–5-μm) and longwave (8–12-μm) measuring thermal imaging systems has been conducted. The study was limited to systems working in indoor conditions, as is typical in many industrial and scientific applications. A theory of the influence of measurement conditions and system parameters on the accuracy of temperature measurements has been developed. On the basis of the developed formulas an analysis of the influence of signal disturbances (because of incorrectly assumed emissivity, radiation reflected by the object, radiation emitted by system optics, limited transmittance of the atmosphere, and limited temperature resolution of the system) on the accuracy of temperature measurement has been made. It has been found that the shortwave systems in typical measurement conditions offer generally better accuracy in temperature measurement than the longwave ones do.

Comparison of shortwave and longwave measuring thermal-imaging systems.

On the basis of a modified version of the lowtran 6 model, an absolute comparison is made of typical and background-limited IR sensors operating in the 3–5-μm and 8–12-μm wavebands in a tropical maritime environment. Allowance is made for slant paths and a variety of targets and backgrounds including hot targets and backgrounds spectrally different from the targets. It is found that with current detector technology the 8–12-μm waveband is superior for all except very hot targets at long ranges. The validity of various approximations is also investigated, and in particular it is found that the blackbody composite background approximation should not be used for slant paths.

Comparison of performance of 3–5- and 8–12-μm infrared systems

Comparison of modeled atmosphere-dependent range performance of long-wave and mid-wave IR imagers

Selection of detector peak wavelength for optimum infrared system performance

The influence of detector peak wavelength on the performance of thermal imaging systems is analyzed. The radiation function, usually denoted by M ∗ , is used in the analysis since it contains the wavelength-dependent portion of the figures of merit for thermal imaging systems such as the noise equivalent temperature difference (NETD) and the minimum resolvable temperature (MRT). Computer calculations of the radiation function are carried out using a modified LOWTRAN III atmospheric model for clear conditions and haze with path lengths from 0.2 to 30km in the 3–14 μm wavelength region.

M. Lumpkin

Papers

Selection of detector peak wavelength for optimum infrared system performance

Selection of Detector Peak Wavelength for Optimum Infrared System Performance