We propose and analyze a new type of a resonant high-Q cavity for lasing, sensing or filtering applications, which is based on a surface states of a finite photonic crystal. We demonstrate that such the cavity can have a Q factor comparable with that one of conventional photonic band-gap defect mode cavities. At the same time, the distinguished feature of the surface mode cavity is that it is situated directly at the surface of the photonic crystal. This might open up new possibilities for design of novel photonic devices and integration of photonic circuits.
We develop a class of supercell photonic crystals supporting complete photonic bandgaps based on breaking spatial symmetries of the underlying primitive photonic crystal. One member of this class based on a two-dimensional honeycomb structure supports a complete bandgap for an index-contrast ratio as low as $n_{high}/n_{low} = 2.1$, making this the first such 2D photonic crystal to support a complete bandgap in lossless materials at visible frequencies. The complete bandgaps found in such supercell photonic crystals do not necessarily monotonically increase as the index-contrast in the system …
We introduce a small-core air-guiding photonic crystal fiber whose cladding is made of improved air-silica photonic crystal with non-circular air holes placed in triangular lattice. The fiber achieves un-disturbed bandgap guidance over 350nm wavelength range.
We present the design of mid-infrared and THz quantum cascade laser cavities formed from planar photonic crystals with a complete in-plane photonic bandgap. The design is based on a honeycomb lattice, and achieves a full in-plane photonic gap for transverse-magnetic polarized light while preserving a connected pattern for efficient electrical injection. Candidate defects modes for lasing are identified. This lattice is then used as a model system to demonstrate a novel effect: under certain conditions - that are typically satisfied in the THz range - a complete photonic gap can be obtained by …
We have measured the photonic bandgap in the transmission of microwaves through a two-dimensional photonic crystal slab. The structure was constructed by cementing acrylic rods in a hexagonal closed-packed array to form rectangular stacks. We find a bandgap centered at approximately 11 GHz, whose depth, width and center frequency vary with the number of layers in the slab, angle of incidence and microwave polarization.
We report a planar 1D photonic bandgap waveguide exhibiting four second-order exceptional points (EP2s). The interactions between the selective pairs of supported quasi-guided TE modes are modulated by spatial distribution of transverse in-homogeneous gain-loss profile.
We present an algorithm for the maximization of photonic bandgaps in two-dimensional crystals. Once the translational symmetries of the underlying structure have been imposed, our algorithm finds a global maximal (and complete, if one exists) bandgap. Additionally, we prove two remarkable results related to maximal bandgaps: the so-called `maximum contrast' rule, and about the location in the Brillouin zone of band edges.
Three-dimensional complete photonic bandgap materials or photonic crystals block light propagation in all directions. The rod-connected diamond structure exhibits the largest photonic bandgap known to date and supports a complete bandgap for the lowest refractive index contrast ratio down to $n_{high}/n_{low} \sim 1.9$. We confirm this threshold by measuring a complete photonic bandgap in the infrared region in Sn--S--O $(n\sim1.9)$ and Ge--Sb--S--O $(n\sim2)$ inverse rod-connected diamond structures. The structures were fabricated using a low-temperature chemical vapor deposition process via …
We report generation of broadband low divergent supercontinuum over the entire wavelength window of 1.5 to 3.5 μm from a 2.25 meter long effective single moded photonic bandgap fiber with mode area of 1100 μm2.
Since the forward and backward waves are coupled with each other and a standing wave with no net propagation of energy is formed in the photonic bandgap, it is a commonsense of basic physics that, any kinds of effects associated with wave propagation including four-wave-mixing (FWM) are thought to be impossible. However, we lay great emphasis here on explaining that this commonsense could be broken under specific circumstances. In this article, we report with the first experimental observation of the energy conversion in the photonic bandgap into other channel via FWM. Owing to the phase manip…
In this paper we study and design quasi-2D optomechanical crystals, waveguides, and resonant cavities formed from patterned slabs. Two-dimensional periodicity allows for in-plane pseudo-bandgaps in frequency where resonant optical and mechanical excitations localized to the slab are forbidden. By tailoring the unit cell geometry, we show that it is possible to have a slab crystal with simultaneous optical and mechanical pseudo-bandgaps, and for which optical waveguiding is not compromised. We then use these crystals to design optomechanical cavities in which strongly interacting, co-localized …
The supercell method is used to study the variation of the photonic bandgaps in one-dimensional photonic crystals under random perturbations to thicknesses of the layers. The results of both plane wave and analytical band structure and density of states calculations are presented along with the transmission cofficient as the level of randomness and the supercell size is increased. It is found that higher bandgaps disappear first as the randomness is gradually increased. The lowest bandgap is found to persist up to a randomness level of 55 percent.
Birefringent magnetophotonic crystals are found to exhibit degeneracy breaking for asymmetric contradirectional coupling in planar waveguides. Fundamental to high-order local normal mode coupling leads to partially overlapping gyrotropic bandgaps inside the Brillouin zone and partial suppression of Bloch mode propagation. A large magneto-optically active reorientation in polarization state is found for allowed Bloch modes at bandgap edges.
We numerically analyze, using Finite Difference Time Domain simulations, the bandgap properties of photonic quasicrystals with a low index contrast. We compared 8-, 10- and 12-fold symmetry aperiodically ordered lattices with different spatial tiling. Our results show that tiling design, more than symmetry, determines the transmission properties of these structures.
We present a formal analogy between the eigenvalue problem for guided scalar modes in a low-contrast photonic bandgap fiber and quasi-stationary TM modes of a two-dimensional (2D) photonic structure. Using this analogy, we numerically study the confinement losses of disordered microstructured fibers through the leakage rate of an open 2D system with high refractive index inclusions. Our results show that for large values of the disorder, the confinement losses increase. However, they also suggest that losses might be improved in strongly disordered fibers by exploring ranges of physical parame…
We study the bandgap properties of two-dimensional photonic crystals created by a lattice of rods or holes conformed in a symmetric or asymmetric triangular structure. Using the plane-wave analysis, we calculate a minimum value of the refractive index contrast for opening both partial and full two-dimensional spectral gaps for both TM and TE polarized waves. We also analyze the effect of ellipticity of rods and holes and their orientation on the threshold value and the relative size of the bandgap.
The field energy distributions and effective mode areas of silica-based photonic bandgap fibers with a honeycomb airhole structure in the cladding and an extra airhole defining the core are investigated. We present a generalization of the common effective area definition, suitable for the problem at hand, and compare the results for the photonic bandgap fibers with those of index-guiding microstructured fibers. While the majority of the field energy in the honeycomb photonic bandgap fibers is found to reside in the silica, a substantial fraction (up to ~30%) can be located in the airholes. Thi…
A novel type of a plasmonic waveguide has been proposed featuring an "open" design that is easy to manufacture, simple to excite and that offers a convenient access to a plasmonic mode. Optical properties of photonic bandgap (PBG) plasmonic waveguides are investigated experimentally by leakage radiation microscopy and numerically using the finite element method confirming photonic bandgap guidance in a broad spectral range. Propagation and localization characteristics of a PBG plasmonic waveguide have been discussed as a function of the wavelength of operation, waveguide core size and the numb…
We present two novel hybrid photonic structures made of silica that possess two well-separated frequency bandgaps. The addition of interstitial air holes in a precise location and size allows these bandgaps to open up with a ratio of ${\sim3}$ between their central frequencies at the air line ${ck_z/w=1}$, thus fulfilling the basic guidance condition for third harmonic generation in hollow-core fibers. In addition, these designs may serve as high-power laser delivery of two well-separated wavelengths, such as visible and near infrared.
The polarization properties of perfectly periodical and defective one-dimensional photonic bandgap structures with nonreciprocal chiral (bi-isotropic) layers are studied. The method of solution is based on the 2x2-block-representation transfer-matrix formulation. Numerical simulations are carried out for different type of structures (symmetrical or asymmetrical) in order to reveal the dependence of the reflection and transmission coefficients on frequency, chirality, nonreciprocity parameters, and the angle of wave incidence.
A silicon-compatible light source is the final missing piece for completing high-speed, low-power on-chip optical interconnects. In this paper, we present a germanium-based light emitter that encompasses all the aspects of potential low-threshold lasers: highly strained germanium gain medium, strain-induced pseudo-heterostructure, and high-Q optical cavity. Our light emitting structure presents greatly enhanced photoluminescence into cavity modes with measured quality factors of up to 2,000. The emission wavelength is tuned over more than 400 nm with a single lithography step. We find increase…
A gyroid structure is a distinct morphology that is triply periodic and consists of minimal isosurfaces containing no straight lines. We have designed and synthesized amorphous silicon (a-Si) mid-infrared gyroid photonic crystals that exhibit a complete bandgap in infrared spectroscopy measurements. Photonic crystals were synthesized by deposition of a-Si/Al2O3 coatings onto a sacrificial polymer scaffold defined by two-photon lithography. We observed a 100% reflectance at 7.5 \mum for single gyroids with a unit cell size of 4.5 \mum, in agreement with the photonic bandgap position predicted f…
We present the first observations of zero-n bandgaps in photonic crystal superlattices consisting of alternating stacks of negative index photonic crystals and positive index dielectric materials in the near-infrared. Guided by ab initio three-dimensional numerical simulations, the fabricated nanostructured superlattices demonstrate the presence of zero-order gaps in remarkable agreement with theoretical predictions across a range of different superlattice periods and unit cell variations. These volume-averaged zero-index superlattice structures present a new type of photonic band gap, with po…
Nonreciprocal electromagnetic devices play an important role in modern optical and microwave technologies. Conventional methods for realizing such systems are incompatible with integrated circuits. With recent advances in integrated photonics, the need for efficient on-chip magnetless nonreciprocal devices is more urgent than ever. This paper leverages space-time engineered asymmetric photonic bandgaps to generate optical isolation. It is shown that a properly designed space-time modulated slab is highly reflective/transparent for opposite directions of propagation. The proposed method require…
We present the fabrication and characterization of an artificial crystal structure formed from a thin-film of silicon which has a full phononic bandgap for microwave X-band phonons and a two-dimensional pseudo-bandgap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the bandgap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large vacuum coupling rate of 220kHz between the fundamental optical cavity resonance at 195THz and a co-localized mechanical resonanc…
We report for the first time the bandgap engineering of Tamm plasmon photonic crystals - Tamm plasmon structures of which the metalic layer is periodically patterned into lattice of subwavelength period. By adopting a double period design, we evidenced experimentally a complete photonic bandgap up to $150\,nm$ in the telecom range. Moreover, such design offers a great flexibility to tailor on-demand, and independently, the band-gap size from $30\,nm$ to $150\,nm$ and its spectral position within $50\,nm$. Finally, by implementing a defect cavity within the Tamm plasmon photonic crystal, an ult…
We demonstrate second harmonic generation at telecommunications wavelengths in L3 photonic crystal cavities in (111)-oriented GaAs. The second harmonic power from photonic crystal cavities fabricated in (111)-oriented GaAs is significantly increased compared to those fabricated in conventional (001)-oriented GaAs.
The role of a prominent photonic bandgap (PBG) on the phenomenon of transverse localization of light in a semi-infinite lossless waveguide lattice consisting of evanescently coupled disordered one-dimensional optical waveguides has been investigated numerically. The interplay between the underlying photonic bandgap due to inherent periodicity of the optical system and various levels of deliberately induced transverse disorder in its refractive index periodicity has been studied. We show that the PBG indeed plays an important role and its simultaneous presence could catalyze realization of loca…
We present the simulation, fabrication, and optical characterization of low-index polymeric rod-connected diamond (RCD) structures. Such complex three-dimensional photonic crystal structures are created via direct laser writing by two-photon polymerization. To our knowledge, this is the first measurement at near-infrared wavelengths, showing partial photonic bandgaps for this structure. We characterize structures in transmission and reflection using angular resolved Fourier image spectroscopy to visualize the band structure. Comparison of the numerical simulations of such structures with the e…
The waveguiding properties of two silica-based airguiding photonic bandgap fiber designs are investigated with special emphasis on material effects. The nonlinear coefficients are found to be 1-2 orders of magnitude smaller than those obtained in index-guiding microstructured fibers with large mode areas. The material dispersion of silica makes a significant contribution to the total chromatic dispersion although less than 10% of the field energy is located in the silica regions of the fibers. These findings suggest that dispersion engineering through the choice of base material may be a possi…
We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal cavities to the facets of optical fibers. Passive Si cavities were measured via fiber taper coupling as well as direct transmission from the fiber facet. Active quantum dot containing GaAs cavities showed photoluminescence that was collected both in free space and back through the original fiber. Cavities maintain a high quality factor (2000-4000) in both material systems. This new design architecture provides a practical mechanically stable platform for the integration of photonic crystal cavities with macr…
We demonstrate high optical quality factors in aluminum nitride (AlN) photonic crystal nanobeam cavities. Suspended AlN photonic crystal nanobeams are fabricated in sputter-deposited AlN-on-insulator substrates using a self-protecting release process. Employing one-dimensional photonic crystal cavities coupled to integrated optical circuits we measure quality factors up to 146,000. By varying the waveguide-cavity coupling gap, extinction ratios in excess of 15 dB are obtained. Our results open the door for integrated photonic bandgap structures made from a low loss, wide-transparency, nonlinea…
The minimal refractive index contrast to obtain a complete photonic bandgap (CPBG) in structured media was not identified so far. We address this problem by considering distributed quasicrystals in with arbitrary number and positions of Bragg peaks in reciprocal space. For these structures an analytical estimation is derived which predicts that there is an optimal number of Bragg peaks for any refractive index contrast and finite CPBGs for an arbitrarily small refractive index contrast in 2D and 3D. Results of numerical simulations of dipole emission in 2D structures support our estimation. In…
We experimentally demonstrate an all-fiber spectrometer consisting of a photonic bandgap fiber bundle and a black and white CCD camera. Photonic crystal fibers used in this work are the large solid core all-plastic Bragg fibers designed for operation in the visible spectral range and featuring bandgaps of 60nm - 180nm-wide. 100 Bragg fibers were chosen to have complimentary and partially overlapping bandgaps covering a 400nm-840nm spectral range. The fiber bundle used in our work is equivalent in its function to a set of 100 optical filters densely packed in the area of ~1cm2. Black and white …
We demonstrate an amplitude-based micro-displacement sensor that uses a plastic photonic bandgap Bragg fiber with one end coated with a silver layer. The reflection intensity of the Bragg fiber is characterized in response to different displacements (or bending curvatures). We note that the Bragg reflector of the fiber acts as an efficient mode stripper for the wavelengths near the edge of the fiber bandgap, which makes the sensor extremely sensitive to bending or displacements at these wavelengths. Besides, by comparison of the Bragg fiber sensor to a sensor based on a regular multimode fiber…
We demonstrate second harmonic generation in photonic crystal cavities in (001) and (111)B oriented GaAs. The fundamental resonance is at 1800 nm, leading to second harmonic below the GaAs bandgap. Below-bandgap operation minimizes absorption of the second harmonic and two photon absorption of the pump. Photonic crystal cavities were fabricated in both orientations at various in-plane rotations of the GaAs substrate. The rotation dependence and farfield patterns of the second harmonic match simulation. We observe similar maximum efficiencies of 1.2 %/W in (001) and (111)B oriented GaAs.
One dimensional nano-beam photonic crystal cavities fabricated in silicon dioxide are considered in both simulation and experiment. Quality factors of over 10^4 are found via simulation, while quality factors of over 5*10^3 are found in experiment, for cavities with mode volumes of 2.0 cubic wavelengths (in oxide) and in the visible wavelength range (600-716nm). The dependences of the cavity quality factor and mode volume for different design parameters are also considered.
We demonstrate fast (up to 20 GHz), low power (5 $μW$) modulation of photonic crystal (PC) cavities in GaAs containing InAs quantum dots. Rapid modulation through blue-shifting of the cavity resonance is achieved via free carrier injection by an above-band picosecond laser pulse. Slow tuning by several linewidths due to laser-induced heating is also demonstrated.
Surface modes (SM) are highly spatially localized modes existing at the core-cladding interface of photonic-bandgap hollow-core fiber (PBG-HCF). When coupling with SM, the air modes (AM) in the core would suffer a higher loss despite being spectrally within the cladding photonic bandgap, and would be highly dispersive around the avoided crossing (anti-crossing) wavelength. In this paper, we numerically demonstrate that such avoided crossings can play an important role in the tuning of the temperature dependence of group delay of AM of PBG-HCF. At higher temperatures, both the thermal-optic eff…
We propose supercritical xenon in a hollow-core photonic bandgap fiber as a highly nonlinear medium, and demonstrate 200 nm control over the guidance window of the fiber as the xenon goes through its supercritical phase transition. The large optical polarizability and monoatomic nature of xenon are predicted to allow large optical nonlinearity, on the same order as that of fused silica, while maintaining greatly reduced Raman scattering, offering benefits for nonlinear and quantum optics.
In this paper we study thermo-optical effects in gallium phosphite photonic crystal cavities in the visible. By measuring the shift of narrow resonances we derive the temperature dependency of the local refractive index of gallium phosphide in attoliter volumina over a temperature range between 5 K and 300 K at a wavelength of about 605 nm. Additionally, the potential of photonic crystal cavities for thermo-optical switching of visible light is investigated. As an example we demonstrate thermo-optical switching with 13 dB contrast.
The famous vanishing of the density of states (DOS) in a band gap, be it photonic or electronic, pertains to the infinite-crystal limit. In contrast, all experiments and device applications refer to finite crystals, which raises the question: Upon increasing the linear size $L$ of a crystal, how fast does the DOS approach the infinite-crystal limit? We present a theory for finite crystals that includes Bloch-mode broadening due to the presence of crystal boundaries. Our results demonstrate that the DOS for frequencies inside a band gap has a $1/L$ scale dependence for crystals in one, two and …
We investigate the design, fabrication and experimental characterization of high Quality factor photonic crystal nanobeam cavities in silicon. Using a five-hole tapered 1D photonic crystal mirror and precise control of the cavity length, we designed cavities with theoretical Quality factors as high as 14 million. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a Quality factor of nearly 750,000. The effect of cavity size on mode frequency and Quality factor was simulated and then verified experimentally.
We investigate optical parametric oscillations through four-wave mixing in resonant cavities and photonic crystals. The theoretical analysis underlines the relevant features of the phenomenon and the role of the density of states. Using fully vectorial 3D time-domain simulations, including both dispersion and nonlinear polarization, for the first time we address this process in a face centered cubic lattice and in a photonic crystal slab. The results lead the way to the development of novel parametric sources in isotropic media.
We experimentally demonstrate high Quality factor dual-polarized TE-TM photonic crystal nanobeam cavities. The free-standing nanobeams are fabricated in a 500 nm thick silicon layer, and are probed using both tapered optical fiber and free-space resonant scattering set-ups. We measure Q-factors greater than 10^4 for both TM and TE modes, and observe large fiber transmission drops (0.3 -- 0.4) at the TM mode resonances.
We present the integrated chip-scale tuning of multiple photonic crystal cavities. The optimized implementation allows effective and precise tuning of multiple cavity resonances (up to ~1.60 nm/mW) and inter-cavity phase (~ 0.038 pi/mW) by direct local temperature tuning on silicon nanomembranes. Through designing the serpentine metal electrodes and careful electron-beam alignment to avoid cavity mode overlap, the coupled photonic crystal L3 cavities preserve their high quality factors. The deterministic resonance and phase control enables switching between the all-optical analogue of electrom…
One dimensional nanobeam photonic crystal cavities are fabricated in silicon dioxide with silicon nanocrystals. Quality factors of over 9 x 10^3 are found in experiment, matching theoretical predictions, with mode volumes of 1.5(lambda/n)^3 . Photoluminescence from the cavity modes is observed in the visible wavelength range 600-820 nm. Studies of the lossy characteristics of the cavities are conducted at varying temperatures and pump powers. Free carrier absorption effects are found to be significant at pump powers as low as a few hundred nanowatts.
We present design guidelines for realizing side-coupled photonic crystal nanobeam (PCN) cavities with efficient coupling to low order resonances through adjusting the overlap of the PCN cavity mode and a feeding bus waveguide in both physical and k-space. We show that optimal side-coupled configurations function at a non-zero k-vector offset between the bus waveguide and PCN cavity modes. The straightforward design of side-coupled PCNs with high contrast resonances opens the door to their practical implementation in multiplexed, on-chip photonic devices.
A Bragg waveguide-based resonant fluidic sensor operating in THz band is studied. A fused deposition modeling 3D printing technique is employed to fabricate the sensor where the liquid analyte is flowing in the microfluidic channel integrated into the waveguide cladding. The analyte refractive index-dependent resonant defect state supported by the fluidic channel is probed by tracking the resulting absorption dip and phase change of the core-guided mode on waveguide transmission spectra. The proposed fluidic sensor can open new opportunities in applied chemical and biological sensing as it off…
We report the observation of optical bistability in Si-based photonic crystal cavities operating around 4.5 \mum. Time domain measurements indicate that the source of this optical bistability is thermal, with a time constant on the order of 5 \mus. Quality (Q) factor improvement is shown by the use of surface treatments (wet processes and annealing), resulting in an increase of Q-factor from 11,500 to 29,300 at 4.48 \mum. After annealing in a N2 environment, optical bistability is no longer seen in our cavities.
We demonstrate an add-drop filter based on a dual photonic crystal nanobeam cavity system that emulates the operation of a traveling-wave resonator and drops light on resonance to a single output port. Realized on an advanced SOI CMOS (IBM 45nm SOI) chip without any foundry process modifications, the device shows 16dB extinction in through port and 1dB loss in drop port with a 3dB bandwidth of 64GHz. To the best of our knowledge, this is the first implementation of a four-port add-drop filter based on photonic crystal nanobeam cavities.
