III‐V/silicon photonics for on‐chip and intra‐chip optical interconnects

In this paper III‐V on silicon‐on‐insulator (SOI) heterogeneous integration is reviewed for the realization of near infrared light sources on a silicon waveguide platform, suitable for inter‐chip and intra‐chip optical interconnects. Two bonding technologies are used to realize the III‐V/SOI integration: one based on molecular wafer bonding and the other based on DVS‐BCB adhesive wafer bonding. The realization of micro‐disk lasers, Fabry‐Perot lasers, DFB lasers, DBR lasers and mode‐locked lasers on the III‐V/SOI material platform is discussed.     

Novel low‐loss waveguide delay lines using Vernier ring resonators for on‐chip multi‐λ microwave photonic signal processors

In this paper, novel photonic delay lines (DLs) using Vernier/non‐identical ring resonators (VRRs) are proposed and demonstrated, which are capable of simultaneous generation of multiple different delays at different wavelengths (frequencies). The simple device architectures and full reconfigurability allow the DLs to be integrated with other functional building blocks in photonic integrated circuits to realize on‐chip, complex multi‐λ microwave photonic signal processors with reduced system complexity. To prove the concept, DLs using VRRs in cascaded and coupled configurations have been fabricated in TriPleX^TM waveguide technology, which enables a very low delay‐induced loss of approximately 0.18 dB/100 ps. The fabricated DLs demonstrated simultaneous generation of four incremental delays, where a maximum incremental step of 550 ps and a corresponding top delay of 1650 ps were measured for a bandwidth up to 1 GHz. To our knowledge, this is the first report on VRRs for delay generation functionalities.     

色散位移光纤中的四波混频现象的实验研究

采用不同波长和类型的光源作为入射光信号,对色散位移光纤中的四波混频进行了实验研究。实验比较了不同色散位移光纤链组合时产生的四波混频信号的大小,研究表明,为了减小四波混频,应该在每一放大器间距内将零色散点波长距信号光波长较远的光纤铺在最接近掺铒光纤放大器处,而零色散点波长距信号光波长较近的光纤应该远离掺铒光纤放大器。对实验中的各种现象进行了理论分析,提出了一些减小四波混频的有益建议,实验结果和理论分析基本一致。     

Periodic,quasi‐periodic,and random quadratic nonlinear photonic crystals

Quadratic nonlinear photonic crystals are materials in which the second order susceptibility χ⁽²⁾ is spatially modulated while the linear susceptibility remains constant. These structures are significantly different than the more common photonic crystals, in which the linear susceptibility is modulated. Nonlinear processes in nonlinear photonic crystals are governed by the phase matching requirements, which are determined by the reciprocal lattice of these crystals. Therefore, the modulation of the nonlinear susceptibility enables to engineer the spatial and spectral response in various three‐wave mixing processes. It enables to support the efficient generation of new optical frequencies at multiple directions. We analyze three wave mixing processes in nonlinear photonic crystals in which the modulation is either periodic, quasi‐periodic, radially symmetric or even random. We discuss both one‐dimensional and two‐dimensional modulations. In addition to harmonic generations, we outline several new possibilities for all‐optical control of the spatial and polarization properties of optical beams in specially designed nonlinear photonic crystals.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

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Composite‐Assisted Phase‐Matching: Efficient Wavelength Conversion in Nonlinear Optical Composite Materials Containing Metal Nanoparticles

A novel phase‐matching scheme which is based on the dispersion compensation in the nonlinear optical composite materials containing metal nanoparticles is proposed. Anomalous dispersion originating from the plasmon resonance in metal nanoparticles compensates the dispersion of the host nonlinear material, leading to the perfect phase‐matching and high efficiency of nonlinear optical wavelength conversion. The effectiveness of this approach is theoretically demonstrated, taking third‐order nonlinear processes such as the direct third‐harmonic generation and four‐wave mixing in ZnO composites containing silica‐core–silver‐shell nanoparticles as examples. The results show that with the proposed phase‐matching scheme, unprecedentedly high conversion efficiency can be obtained compared with preceding results in third‐order nonlinear optical solid‐state materials.     

Nonlinear photonic waveguides for on‐chip optical pulse compression

All‐optical signal processing on nonlinear photonic chips is a burgeoning field. These processes include light generation, optical regeneration and pulse metrology. Nonlinear photonic chips offer the benefits of small footprints, significantly larger nonlinear parameters and flexibility in generating dispersion. The nonlinear compression of optical pulses relies on a delicate balance of a material's nonlinearity and optical dispersion. Recent developments in dispersion engineering on a chip are proving to be key enablers of high‐efficiency integrated optical pulse compression. We review the recent advances made in optical pulse compression based on nonlinear photonic chips, as well as the future outlook and challenges that remain to be solved.

     

Waveguide sub‐wavelength structures: a review of principles and applications

Periodic structures with a sub‐wavelength pitch have been known since Hertz conducted his first experiments on the polarization of electromagnetic waves. While the use of these structures in waveguide optics was proposed in the 1990s, it has been with the more recent developments of silicon photonics and high‐precision lithography techniques that sub‐wavelength structures have found widespread application in the field of photonics. This review first provides an introduction to the physics of sub‐wavelength structures. An overview of the applications of sub‐wavelength structures is then given including: anti‐reflective coatings, polarization rotators, high‐efficiency fiber–chip couplers, spectrometers, high‐reflectivity mirrors, athermal waveguides, multimode interference couplers, and dispersion engineered, ultra‐broadband waveguide couplers among others. Particular attention is paid to providing insight into the design strategies for these devices. The concluding remarks provide an outlook on the future development of sub‐wavelength structures and their impact in photonics.

     

Simultaneous brightness enhancement and wavelength conversion to the eye‐safe region in a high‐power diamond Raman laser

Brightness enhancement in an external cavity diamond Raman laser designed for high power conversion of a neodymium (1064 nm) laser to the eye‐safe spectral region is reported. Using a multimode input beam pulsed at 36 kHz pulse repetition frequency, 16.2 W with 40% overall conversion efficiency was obtained at the second Stokes wavelength of 1485 nm. The output beam had a quality factor of which is a factor of 2.7 times lower than that of the input beam, resulting in a higher overall brightness. The output power, brightness, and brightness enhancement obtained represent significant advances in performance for Raman lasers as well as other competing kHz‐pulsed eye‐safe technologies.     

Flame temperature diagnostics with water lines using mid‐infrared degenerate four‐wave mixing

The feasibility of using degenerate four‐wave mixing (DFWM) for hot gas thermometry in the mid‐infrared spectral region is, for the first time, demonstrated by probing molecular ro‐vibrational transitions of water. DFWM spectra of hot water were recorded in specially designed flames, providing a series of temperatures varying from 1000 to 1900 K and, the dramatic spectral structure variations were used as temperature indicator. The intensity ratios between two hot water line groups at around 3231 cm⁻¹ were especially studied and composed into a calibration table for flame temperature measurement using DFWM spectra. The saturation properties of different lines were also studied by recording the line intensity ratios as a function of laser power, and the results indicated that saturated excitation was in favor of reliable temperature measurements. As validation, infrared DFWM spectra in an φ = 1.52 flat premixed methane/air flame were recorded, and a good temperature value was obtained. Moreover, the recently released HITEMP2010 database as well as its previous version HITEMP2000 were adopted to simulate the hot water spectra and to analyze the line intensity ratios. Copyright © 2011 John Wiley & Sons, Ltd.     

Fiber‐based light sources for biomedical applications of coherent anti‐Stokes Raman scattering microscopy

During the past decade coherent anti‐Stokes Raman scattering (CARS) microscopy has evolved to one of the most powerful imaging techniques in the biomedical sciences, enabling the label‐free visualization of the chemical composition of tissue in vivo in real time. While the acquisition of high‐contrast images of single cells up to large tissue sections enables a wide range of medical applications from routine diagnostics to surgical guidance, to date CARS imaging is employed in fundamental research only, essentially because the synchronized multiple wavelength pulsed laser sources required for CARS microscopy are large, expensive and require regular maintenance. Laser sources based on optical fibers can overcome these limitations combining highest efficiency and peak powers with an excellent spatial beam profile and thermal stability. In this review we summarize the different fiber‐based approaches for laser sources dedicated to coherent Raman imaging, in particular active fiber technology and passive fiber‐based frequency conversion processes, i.e. supercontinuum generation, soliton self‐frequency shift and four‐wave mixing. We re‐evaluate the ideal laser parameters for CARS imaging and discuss the suitability of different laser concepts for turn‐key operation required for routine application in clinics.

     

Phase‐matching properties of BaGa4S7 and BaGa4Se7: Wide‐bandgap nonlinear crystals for the mid‐infrared

Biaxial BaGa₄S₇ and BaGa₄Se₇ crystals transparent in the mid‐IR have been grown by the Bridgman–Stockbarger technique in sufficiently large sizes and with good optical quality to measure the refractive indices and analyze phase‐matching properties. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)