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Stimulation emission (SE) in high-quality single-crystal thin GaN films grown on sapphire and SiC substrates at temperatures as high as 700 K is analyzed. The temperature dependence of the energy position for spontaneous and SE peaks was determined and empirical equations were provided. By measuring the temperature sensitivity of the SE threshold, a characteristic temperature was obtained. Prospects for the development of GaN-based high-temperature optoelectronic equipment are discussed. The results are presented.

Novel applications in optical coherence tomography (OCT) and LiDAR systems have become possible due to performance characteristics of a state-of-the-art silica-on-silicon planar lightwave circuit (PLC) platform. We have achieved ultra-low propagation losses of

Machine learning has opened a new realm of possibilities in photonic circuit design and manufacturing. First, we describe our approach of using deep learning to optimize the multi-dimensional parameter space for hundreds of optical chips on a mask, resulting in homogeneity of performance in high volume applications. Second, we present our approach of using a support vector machine to predict the performance of optical devices by wafer probing. This approach eliminates the expensive and labour-intensive process of optical chip testing, and allows unprecedented control over the fabrication process, including in-situ monitoring of wafer fabrication and real-time process adjustments. The combination of these two approaches paves the way for accelerated adoption of photonics in high volume applications.

Further increase in the density of integrated planar lightwave circuits (PLCs) depends on the introduction of compact guided-wave layout solutions. We describe a novel architecture for coiling multistage interferometric devices with densities reaching the theoretical limit. Our approach is validated by the design, fabrication, and deployment of state-of-the-art PLCs based on the proposed architecture for use in datacom and telecom applications.

We propose an all optical switch in a dual-core photonic crystal fiber (PCF) that has the core region consisting of soft glass and has nematic liquid crystal filled holes in the cladding region. Light waves are guided in this PCF by total internal reflection (TIR) due to the refractive index contrast between soft glass and liquid crystal (LC). Its wavelength dependent coupling, birefringence and dispersion are calculated and later use these parameters to evaluate the switching characteristics of short pulses propagating through this optical waveguide. The switch demonstrates tunability with external perturbation such as applying external heat source or electric field. Refractive index sensitivity of LC with these perturbation as well as polarization of the light signal determines the coupling, birefringence and dispersion properties of the overall waveguide and its switching characteristics. [ABSTRACT FROM AUTHOR]

Abstract: We have successfully designed, fabricated, and tested an optical filter based on cascaded planar reflective gratings. The device uses a combination of two grating elements arranged in a subtractive dispersion configuration. The first grating demultiplexes a 300nm wide band and drops optical channels at 1490 and 1550nm, commonly used in passive optical networks. The second grating completely counter-balances the dispersion properties of the first grating and ultimately yields zero dispersion in the output waveguide. Such a configuration allows the transmission of optical signals though the device in an ultra-wide band spanning 1250–1410nm. The filter was manufactured using an industry standard silica-on-silicon process which was augmented with grating facet formation and metallization. In spite of using low refractive index contrast waveguides (0.82%), the device had a remarkably low footprint of only 0.21cm2. Applications of the device in passive optical networks are discussed. [Copyright &y& Elsevier]

Abstract: Configurable coarse wavelength division multiplexing filters were realized using a planar reflective grating architecture utilizing small diffraction angles. The novel architecture yielded a 10-fold reduction in the chip size compared to previously reported filter configurations. The proposed design was manufactured using a standard silica-on-silicon process with a waveguide refractive index contrast of 0.82%. Polarization dependent losses of less than 0.2dB were achieved without any post-processing steps. Fabricated filters showed insertion losses of 2.4dB and remarkably broad free spectral ranges of more than 500nm. The combination of single-mode input and multi-mode output guides resulted in box-like passband responses with bandwidth of 14.2nm. Applications of the filters for integrated coarse wavelength division receivers and monitors are discussed. [Copyright &y& Elsevier]

This paper reports a novel architecture for the design of dense wavelength-division multiplexing interleavers based on planar echelle gratings. Double astigmatic point design of the echelle grating is discussed. The important and inherent limitation of aberrations associated with the echelle grating has been eliminated by the introduction of aberration free elliptical facets. A mechanism for compensating the variations of the refractive index with wavelength is also described. The theoretical analysis was used to design and manufacture remarkably low footprint 50/100 and 100/200 GHz interleavers in silica-on-silicon with the waveguide refractive index contrast of 0.62%. The comparison between the theoretical and experimental results shows an excellent agreement. The fabricated devices based on the proposed approach showed low nonuniformity in insertion loss, high dynamic range, and precise channel periodicity over the entire C band. [ABSTRACT FROM PUBLISHER]

A new approach for eliminating aberration effects through introduction of elliptical grating facets in optical comb filters is presented. Simulation results show remarkable improvements of comb filter performance for aberration-free elliptical facets compared to traditional flat facet designs. The proposed theory was validated through design and fabrication of 100-GHz-period planar silica-on-silicon comb filters for use in multiwavelength optical sources. Multimode interference structures were used to achieve both flat-top and Gaussian spectral comb filter responses. All devices showed high extinction ratio, low nonuniformity in insertion loss, and high degree of passband shape control. [ABSTRACT FROM PUBLISHER]

A novel design of a silicon-on-insulator (SOI) filter for passive optical network applications is described. The SOI filter comprises a monolithically integrated planar reflective grating and a multistage Mach-Zehnder interferometer. The fabricated device showed low insertion losses and high optical isolation. To the best of our knowledge, this letter describes the first demonstration of an SOI circuit comprising monolithically integrated planar reflective grating and cascaded Mach-Zehnder interferometer [ABSTRACT FROM PUBLISHER]

We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low-pressure metalorganic chemical vapor deposition. The SCH wells are unstrained and lattice-matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Details an experimental study on efficient laser action in an optically pumped GaN/AlGaN separate-confinement heterostructure in the temperature range of 10 to 300 degrees Kelvin. Measurement of lasing threshold; Polarized lasing peaks observed over a wavelength range; High-finesse lasing models that originate from self-formed microcavities in the AlGaN and GaN layers.

Presents a technique for evaluating optical confinement in GaN-based lasing structures by studying their spectrally resolved near-field pattern under high optical excitation. Dependence of emission spectra on the position of the collection optics; Modulation signature contained in the spatially resolved spectra; Evaluation of the degree of optical confinement in GaN epilayers.

Studies near-threshold gain mechanisms in GaN thin films in the temperature range of 20-700 K. Use of high-quality single-crystal GaN films; Band-filling phenomena; Shift between simulated and band-edge-related emission.

Examines a spatially resolved surface-emitted stimulated emission in gallium nitride (GaN) crystal films under conditions of strong optical pumping. Effect of defects on GaN lasing; Variation of emission spectra near defect region; Dependence of the integrated stimulated emission on the position of the sample surface.

We report the results of an experimental study of the stimulated emission (SE) properties of AlGaN epilayers grown by metalorganic chemical vapor deposition under high optical excitation conditions in the temperature range of 30-300 K. The band gap and energy position of spontaneous and SE peaks were measured over the entire temperature range studied. Through an analysis of the temperature dependence of the relative energy positions and the SE threshold, combined with absorption and time-resolved photoluminescence measurements, we estimated the carrier density at threshold to be ∼10[sup 19] cm[sup -3] throughout the temperature range studied. Such a high carrier density indicates that an electron-hole plasma is responsible for the generation of gain in this material system from 30 to 300 K. Issues related to the development of short-wavelength AlGaN-based light emitting devices are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation length (L[sub exc]). Two distinct SE peaks were observed from these structures: one that originates at 425 nm at 10 K (430 nm at 300 K) and another that originates at 434 nm at 10 K (438 nm at 300 K). The SE threshold for the high-energy peak was observed to always be lower than that of the low-energy peak, but the difference was found to decrease greatly with increasing L[sub exc]. A detailed study of the emission intensity of these two SE peaks as a function of excitation density shows that the two peaks compete for gain in the MQW active region. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Stimulated emission (SE) in optically pumped InGaN/GaN multiquantum well (MQW) structures grown by metalorganic chemical vapor deposition was experimentally studied in the temperature range of 175–575 K. The GaN barriers were intentionally doped with a different Si concentration ranging from 1×10[sup 17] to 3×10[sup 19] cm[sup -3] and the effects of Si doping of GaN barriers on the optical properties of InGaN/GaN MQWs were investigated. The SE threshold was measured as a function of temperature and compared with bulk GaN. We observed that the SE threshold had a low value and a weak temperature dependence: for example, ∼25 kW/cm[sup 2] at 175 K, ∼55 kW/cm[sup 2] at 300 K, and ∼300 kW/cm[sup 2] at 575 K for one of the samples. Low SE thresholds are attributed to the high-quantum efficiency of the MQWs, possibly associated with the large localization of excitons. The characteristic temperature of 162 K was derived from the temperature dependence of the SE threshold. The integrated emission intensity versus pumping density was examined for different temperatures. This study shows that InGaN/GaN MQWs are suitable for development of laser diodes that can operate well above room temperature. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Laser action was observed in GaN pyramids under strong optical pumping at room temperature. The pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal–organic chemical vapor deposition. Each pyramid had a 15-μm-wide hexagonal base and was on average 15 μm in height. The pyramids were individually pumped, imaged, and spectrally analyzed through a high-magnification telescope system using a high-density pulsed excitation source. Under high levels of optical pumping, multimode laser at room temperature was observed. The integrated emission intensity for both spontaneous and lasing peaks was studied as a function of excitation power density. The effects of pyramid geometry and short-pulse excitation on the multimode nature of laser oscillations inside of the pyramids is discussed. This study suggests that GaN microstructures could potentially be used as pixel elements and high-density two-dimensional laser arrays. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Broadband low-resolution near-infrared spectrographs in a compact form are crucial for ground- and space-based astronomy and other fields of sensing. Astronomical spectroscopy poses stringent requirements including high efficiency, broad band operation (> 300 nm), and in some cases, polarization insensitivity. We present and compare experimental results from the design, fabrication, and characterization of broadband (1200 - 1650 nm) arrayed waveguide grating (AWG) spectrographs built using the two most promising low-loss platforms - Si 3 N 4 (rectangular waveguides) and doped-SiO 2 (square waveguides). These AWGs have a resolving power (λ/Δλ) of ∼200, free spectral range of ∼ 200-350 nm, and a small footprint of ∼ 50-100 mm 2 . The peak overall (fiber-chip-fiber) efficiency of the doped-SiO 2 AWG was ∼ 79% (1 dB), and it exhibited a negligible polarization-dependent shift compared to the channel spacing. For Si 3 N 4 AWGs, the peak overall efficiency in TE mode was ∼ 50% (3 dB), and the main loss component was found to be fiber-to-chip coupling losses. These broadband AWGs are key to enabling compact integrations such as multi-object spectrographs or dispersion back-ends for other astrophotonic devices such as photonic lanterns or nulling interferometers.