KEYWORDS: Sum frequency generation, Resonators, Emission wavelengths, Gallium arsenide, Optical resonators, Electric fields, Signal detection, Nonlinear optics, Near field optics, Microresonators
III-V semiconductors, such as Aluminium Gallium Arsenide (AlGaAs), are known for their high refractive index and strong non-resonant second-order optical nonlinearity making them useful for building active nonlinear photonic devices. AlGaAs-based nanophotonic structures supporting anapole resonances can significantly boost the internal electric fields resulting in enhanced nonlinear optical response. However, low-quality factors of these anapolar resonances can result in poor conversion efficiency for the nonlinear optical process. Here we report enhanced sum frequency generation (SFG) from vertically stacked three-disk AlGaAs-based nanoresonators supporting anapole type resonance that exhibit an order of magnitude increase in field enhancement compared to a single-disk resonator system at the SFG wavelength. The vertically stacked resonators consist of three individual AlGaAs layers separated vertically by an under-cut Gallium Arsenide (GaAs) stem. Finite difference time domain (FDTD) simulations of the scattering cross sections were performed to optimize the dimensions of AlGaAs resonator. The optimal structure consists of three vertically stacked AlGaAs nanodisks (550 nm diameter, 50 nm height) separated by a 100 nm GaAs stem. This design ensures anapole type resonance overlap at SFG wavelength (600-670 nm). Multi-spectral SFG images were acquired by varying the input signal wavelength in the range of 1400-1800 nm, keeping the pump wavelength fixed at 1040 nm. The experimental results show a maximum SFG enhancement of approximately 50-times near the resonance wavelength of 645 nm in comparison to unpatterned multilayer samples. Optical nanostructures based on stacked AlGaAs resonators provide a very exciting platform to tailor the light-matter interactions for linear and non-linear optical applications.
TiO2 nanoparticles dispersion was used to fabricate three dimensional (3D) composite structures on the surface of various substrate materials as well as on the surface of nitride light emitting diodes (LEDs). Optical power enhancements in the range of ~1.4-2.1 were measured.
The fabrication and characterization of a compact InP-based polarization beamsplitter (PBS) is presented. A multimode interference (MMI) coupler with an internal air hole photonic crystal (PhC) section is utilized to separate the two polarizations. The PhC structure in the middle of the MMI is polarization dependent, so that one polarization is reflected and the other one is transmitted; both are collected by the respective output ports of the MMI coupler. The obtained experimental results show that the PBS as short as ~400 µm has an extinction ratio as large as 15 dB.
In this work variations of the carrier lifetime in a GaInAsP/InP quantum well in two-dimensional PhC structures etched
by Ar/Cl2 chemically assisted ion beam etching as a function of the processing parameters is investigated. It is shown
that the deposition conditions of the SiO2 mask material and its coverage as well as other process steps such as annealing
affect the carrier lifetimes. However the impact of patterning the semiconductor on the carrier lifetime is dominant,
showing over an order of magnitude reduction. For given PhC lattice parameters, the sidewall damage is shown to be
directly related to the measured carrier lifetimes. A simple qualitative model based on sputtering theory and assuming a
conical hole-shape development during etching is used to explain the experimental results.
This work addresses feature size effects (the lag-effect and roughness development) in chemically assisted ion beam etching (CAIBE) etching of InP based photonic crystals. Photonic crystal fields with varying hole size and periods were etched with different etching times. The slope of the etch depth versus diameter curves (lag-curves) reveals a hole size dependence, with a critical aspect ratio higher than 25. A model for the etch rate specific to Ar/Cl2 CAIBE is proposed. We calculate the etch rate using a physico-chemical model which takes in to account the effect of Ar-ion sputtering and surface chemical reactions. In addition, it combines the aspect ratio dependence of the gas conductance of the etched holes. The origin and evolution of the bottom roughness of the etched holes is examined. The impact of the feature size dependence of the etching on the photonic crystal optical properties is then assessed by measuring the quality-factor of one dimensional Fabry Perot cavities using the Internal Light Source method, and discussed in terms of hole shape and depth. A systematic trend between the determined quality factor (Q) and the lag-effect is evidenced: Q decreases from about 250 to 60 when the hole depth drops from 5 μm to 2 μm.
This work investigates the current transport across two-dimensional PhCs dry etched into InP-based low-index-contrast
vertical structures using Ar/Cl2 chemically assisted ion beam etching. The electrical conduction through the PhC field is
influenced by the surface potential at the hole sidewalls, which is modified by dry etching. The measured current-voltage
(I-V) characteristics are linear before but show a current saturation at higher voltages. This behaviour is confirmed by
simulations performed by ISE-TCAD software. We investigate the dependence of the conductance of the PhC area as a
function of the geometry of the photonic crystal as well as the material parameters. By comparing the experimental and
simulated conductance of the PhC, we deduce that the Fermi level is pinned at 0.1 eV below the conduction band edge.
The method presented here can be used for evaluating etching processes and surface passivation methods. It is also
applicable for other material systems and sheds new light on current driven PhC tuning.
We have investigated the dispersion properties of photonic crystal waveguide resonators. A passive InGaAsP/InP slab waveguide structure was used for the fabrication of the samples. The PhC waveguide resonators were defined by the omission of several rows of holes along the ΓΚ or ΓΜ direction of a triangular photonic crystal lattice. In addition, mirrors with a thickness of 1 to 4 rows of holes were inserted into the waveguide. An optimized dry etch process was used to etch the patterns to a depth of 3.5 µm through the waveguide layer. The group delay of the PhC devices was measured using the phase shift technique. The signal of a tunable laser was modulated at 3 GHz using a LiNbO3 Mach-Zehnder modulator and detected with a high-frequency lightwave receiver. A phase sensitive detection with a network analyer measured the phase shift of the transmitted signal, which is proportional to the group delay. Close to the center of the resonances, the chromatic dispersion reaches values of -250 ps/nm and 250 ps/nm. This corresponds to the chromatic dispersion of 15 km standard fiber.
One of the most distinctive features of photonic crystals (PhCs) is their unique wavelength dispersion allowing novel device concepts for enhancement of photonic functionality and performance. Here, we present examples of our design and demonstrations utilizing dispersion properties of 1D and 2D photonic crystals. This includes the demonstration of negative refraction in 2D PhC at optical wavelengths, filters based on 1D and 2D PhC waveguides, and the design of a widely tunable filter involving 1D PhC.
Recently there has been a growing amount of attention devoted to tuneable photonic crystals (PhCs) where the optical response of PhC structures can be dynamically modified. We will show how infiltrating planar PhCs with a synthetic organic material allows the trimming and tuning of their optical properties. The potential of PhC infiltration
will be demonstrated for InP-based planar PhCs consisting of a hexagonal array of air holes (hole diameter = 200 − 400 nm; air filling factor = 0.40-0.50) etched through a planar waveguide in which light emitters (i.e. quantum wells) were embedded to enable optical measurements. The PhC pores were infiltrated with LC-K15 (5CB) nematic liquid crystals (LCs) in a specifically designed vacuum chamber, thereby changing the refractive index contrast between the holes and the semiconductor (trimming). Moreover, the possibility of tuning the optical response of PhCs by an external perturbation (i.e. temperature) was demonstrated. The change of the PhC optical properties due to infiltration and temperature tuning was studied both experimentally and theoretically. Experimental measurements were compared to theoretical calculations in order to obtain information on the in-filling efficiency, the LC refractive index, and the molecule orientation inside the holes. In the first case, optical measurements were performed as a function of
temperature, whilst the average LC director configuration was determined by comparing transmission spectra in the transverse electric and magnetic polarization directions.
We report on low-loss light propagation at the communication wavelength of 1.55 µm through straight two-dimensional photonic crystal waveguides patterned into InGaAsP/InP heterostructures. The linear defect waveguides along the ΓK direction of a triangular lattice of air holes were etched deeply into the semiconductor by Cl2/Ar electron cyclotron resonance reactive ion etching. Efficient waveguiding was observed for both polarization directions, although a photonic band gap exists for only one of the polarization states. Propagation losses, determined by the Fabry-Perot resonance method, are as low as 0.2 dB/mm and 1.5 dB/mm for waveguides based on seven and three missing rows of holes, respectively. Waveguide resonators with 100 GHz channel spacing and quality factors up to 15,000 have been realized by inserting photonic crystal mirrors into the waveguides. The dispersion of the resonators was measured using a phase shift technique. Values for the group velocity dispersion range from -250 ps/nm to +250 ps/nm at wavelengths around 1.55 μm, which is sufficient to compensate for the dispersion of 15 km standard single-mode fiber. Controlling the device temperature allows to tune the dispersive properties of the devices.
The coupling efficiency between external plane waves and the Bloch waves in photonic crystals are investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air n=1 and a photonic crystal with effective index -1. It is also shown that, for point imaging by a photonic crystal slab owing to the negative refraction, the influence of the surface termination to the transmission and the imaging quality is significant. Finally, we present results demonstrating experimentally negative refraction in a two-dimensional photonic crystal.
We have investigated tunable photonic crystal waveguide lasers and their integration with a photonic crystal based combiner. The devices were fabricated on a layer structure with active and passive sections. The lasers are formed in the active part and consist of two longitudinally coupled photonic crystal waveguide segments. Photonic crystals based waveguides and a combiner, both defined in the passive sections, are used to direct the light of the two sources into a single output waveguide. Tuning over a 30 nm range is demonstrated. The two sources can be operated independently, allowing the simutaneous transmission of two freely selectable wavelengths.
We report on the temperature tuning of the optical properties of planar Photonic Crystal (PhC) microcavities. Studies were made on one and two dimensional PhCs that were etched in InP and GaAs vertical waveguides. Two dimensional (hexagonal) and one-dimensional (Fabry-Perot) cavities were optically investigated by an internal light source technique. The samples were mounted on a Peltier-stage which allowed temperature variation from T = 20 °C up to T = 76 °C. A linear dependence of the resonance wavelengths with respect to temperature is observed. A gradient of dλ/dT = 0.09 nm/°C and 0.1 nm/°C for the GaAs and InP based cavities was observed, respectively. These results are in agreement with the theoretical calculations based on the thermal dependence of the refractive index of the PhC semiconductor component.
Practical realizations of 2D (planar) photonics crystal (PhC) are either on a membrane or etched through a conventional heterostructure. While fascinating objects can emerge from the first approach, only the latter approach lends itself to a progressive integration of more compact PhC's towards monolithic PICs based on InP. We describe in this talk the various aspects from technology to functions and devices, as emerged from the European collaboration "PCIC." The main technology tour de force is deep-etching with aspect ratio of about 10 and vertical sidewall, achieved by three techniques (CAIBE, ICP-RIE, ECR-RIE). The basic functions explored are bends, splitters/combiners, mirrors, tapers, and the devices are filters and lasers. At the end of the talk, I will emphasize some positive aspects of "broad" multimode PhC waveguides, in view of compact add-drop filtering action, notably.
Optical add/drop filters using two-dimensional photonic crystals (PC’s) are presented for different designs. In-plane channel add/drop filter composed of two waveguides and an optical resonator system is very compact, but sensitive to the losses. While add/drop filter based on a contra-directional PC waveguide coupler is much more robust to the losses, and reasonable compactness is possible with careful designs. The possibility to utilize the PC dispersion properties to design optical filters is also discussed briefly.
We report on the fabrication and characterization of 2D photonic crystals (PhCs) in InP/InGaAsP/InP heterostructures. It is demonstrated that Ar/Cl2 based chemically assisted ion beam etching (CAIBE) is a very promising method to obtain high aspect ratio etching of PhCs in the InP-based materials. With this process, it is possible to obtain PC-holes as deep as 3 microns even for feature (PhC-hole) sizes as small as 200-250 nm. The optical characteristic of the fabricated PhC-based elements/devices such as line-defect waveguides, in-plane resonant cavities and drop-filter based on contra-directional coupling will be reported. The devices were measured using end-fire coupling and the obtained results were simulated using the 2D finite difference time domain (FDTD) method including an effective loss-approximation. The etched PhC-waveguides show low transmission losses, less than 1 dB/100 μm. A quality factor of 400 for a 6 micron long cavity with 6-hole mirrors is obtained. Finally, drop-functionality in a PhC-based filter using contra-directional coupling is demonstrated.
Photonic crystal waveguides in InP-based heterostructures are studied experimentally and theoretically. The waveguides are fabricated in an InP/GaInAsP/InP low index contrast heterostructure using Ar/Cl2 Chemical Assisted Ion Beam Etching, and characterized using the end-fire method. The obtained experimental near-infrared transmission spectra are further analyzed by comparing with theoretical results calculated by the finite-difference time-domain method. A loss of 1 dB/100 μm in the photonic crystal waveguides is demonstrated. The mini-stop bands, positioned in agreement with our theory, are observed. In-plane cavities with photonic crystal boundaries inside the waveguide are also realized. A quality factor of 400 for a 6 mm long cavity is obtained.
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