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In this study, we explore the effect of integrated auxiliary rods at varying angles to the primary cavity rod on the dispersion characteristics of the photonic crystal coupled cavity waveguide (PC CCW). Here, it is intended to break the symmetry of the cavity region by introducing auxiliary rods which gives the degree of freedom for tuning effective index of the PC waveguide. Furthermore, rotational angle variations of auxiliary rods reveal slow light operation of the PC CCW where the group index is maximized and group velocity dispersion, as well as the third-order dispersion, are minimized. In addition, auxiliary rods with a broken symmetry increase not only group index but also operating bandwidth and accordingly increase group bandwidth product by 675%. Leveraging these results, we demonstrate effective rainbow trapping by manipulating the auxiliary rod angles in photonic crystal coupled cavity waveguides. Our results have encouraging implications for optical buffering, multiplexing, demultiplexing, advanced time-domain and spatial signal processing. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method to design an ultra-small photonic integrated biosensor to detect cancerous cells. The proposed biosensor is based on the self-phase modulation in PhC-SOA, inducing a frequency shift on a pulse traveling through the device. The amount of the frequency chirp depends on the group velocity of the active medium waveguide being determined by the refractive index of the microfluidic infiltrating the holes around the waveguide. The refractive index of the microfluidic is also determined by the cell type that can be normal or cancerous. Since the refractive index of a cancerous cell is higher than that of a normal one, the group index of the waveguide and the output chirp will decrease. By measuring the amount of the output chirp, we can detect the cell type. The Simulation results showed that for a 0.02 change in the refractive index of the cell, a 3.71 nm central wavelength shift occurred for a 10-ps 7-mW gaussian pulse input with a central wavelength of 1533.53 nm. In terms of the wavelength shift, the sensitivity and figure of merit are 185.5 and 530, respectively. To detect the cell type, we integrated a PhC channel drop filter to drop the chirped signal due to the cancerous cell infiltration. Designing an appropriate PhC-CDF leads to achieving an ultra-small cancerous detection cell biosensor with more than 97% precision. [ABSTRACT FROM AUTHOR]

In this study, an optical switch based on two-dimensional photonic crystals is presented for the slow light regime. This regime enhances light–matter interaction and can be used to design low-power all-optical devices. Due to slow light properties in photonic crystals, the maximum flat band for the group index of 8 was obtained. The threshold light intensity was reduced to 16 mW/µm2 in comparison with other works. The maximum rise and fall times were calculated about 1 ps, which means the switching frequency is about 1 THz. The total footprint of the proposed switch is 5.5 × 9 µm2, which makes the possibility for optical integration. [ABSTRACT FROM AUTHOR]

In this paper, we present two new photonic crystal designs, giving the free space of the slabs around the cavities as well as the possibility of further absorption for the active layer of quantum dots. In the second design, the radius of the cavities gradually increases and the distance between them becomes smaller. Here, the removal of 4 small holes and replacing them with larger cavities are employed. The band structure is also presented because the presence of bands can be related to absorptions due to the defect structure. Because of the presence of bands that delay the movement of the wavelength of light, it is a plan for high absorption of its defect structure. The dielectric function of the quantum dots with a GaAs slab is calculated from the Maxwell–Garnet model and then replaced in Maxwell equations. The phenomena, namely slow light in the photonic crystal, cause increasing characteristics of optical structure. [ABSTRACT FROM AUTHOR]

Slow light propagation through photonic crystal (PhC) slab devices has great potential to reduce the size and power consumption of silicon photonic optical circuits. Most commonly, slow light routing through photonic crystals is achieved by using W1 waveguide bends operating near their cutoff frequencies. Unfortunately, this leads to optical pulse distortion due the high group velocity dispersion (GVD) associated with these designs. In this letter, however, we study the coupling between slow light waveguides optimized for near-zero GVD and 60° PhC bends. Using numerical methods and the temporal coupled mode theory, we assess the performance of single bends coupled to input/output waveguides, and S-bends composed of two cascaded bends. In this latter, we observe that the bend-waveguide quality factor has great impact over transmission and dispersion. We propose a novel 60° PhC bend design for routing optical modes while maintained reduced dispersion. This is achieved over a -3 dB bandwidth of around 50 nm in devices with slowdown factor up to 40. We show that this 60° PhC bend has good stability under changes in S-bend length and fabrication induced disorder. These results can lead to great improvements in the design of monolithically integrated modulators, switches, (de)multiplexers, and filters based on photonic crystals, as well as on the routing of long optical buffers and delay lines.

Üçgen örgülü GaAs fotonik kristal yapısı kullanılarak sayısal ortamda bir sıcaklık algılayıcısı önerilmiş ve algılayıcının duyarlılığı kavite çevresinde yapısal değişimler yapılarak ve yavaş ışık özelliği kullanılarak iyileştirilmiştir. Fotonik kristal dalga kılavuzunun bir sıra ilerisinde bir noktasal kusur oluşturularak kavite rezonans frekanslarındaki ışık bu noktasal boşluğa bağlaştırılmış ve sıcaklığa bağlı olarak rezonans frekansın değişimi incelenmiştir. Duyarlılığın artırılması için kavitenin yanlarındaki deliklerin yarıçapı ve kavite alanı değiştirilmiştir. 0.1001 nm/ºC olan sıcaklık algılayıcısının duyarlılığı yapısal iyileştirmeler ile 1.4%±0.1% artırılmıştır. Dalga kılavuzu çevresindeki ilk sıra deliklerin yarıçapı değiştirilerek ve dalga kılavuzuna paralel doğrultuda kaydırılarak kavite rezonans dalga boyunu da içeren 20.23 nm'lik aralıkta ışık 14 kat yavaşlatılmıştır. Yavaş ışık etkisi ile kipin kavite ile daha fazla optiksel olarak örtüşmesi sonucu algılayıcının duyarlılığı %2.8±%0.1 artmıştır.

A temperature sensor is proposed in the computational environment using triangular lattice GaAs photonic crystal structure and the sensitivity of the sensor is enhanced by employing structural improvements around the cavity and by using slow light feature. By creating a point defect one row ahead from the photonic crystal waveguide, light in the cavity resonance frequencies is coupled to this point defect and the change of the resonance frequency related to the temperature is investigated. The radius of the holes around the cavity and the cavity area are changed to enhance the sensitivity. 0.1001 nm/ºC sensitivity of the temperature sensor is increased by 1.4%±0.1% with structural optimizations. Light is slowed down by 14 times in a 20.23 nm range including the cavity resonance wavelength by changing the radius of the first rows of holes surrounding the waveguide and shifting them in a direction parallel to the waveguide. The sensitivity of the sensor is increased by 2.8%±0.1% as a result of increasing optical overlap of the mode with the cavity by slow light effect.

In this paper, a novel type of slow light photonic crystal waveguide obtained by enlarging the entire holes of the PhC and shifting the first and second rows of the air holes adjacent to the waveguide center in the longitudinal direction, the designed structure provided a nearly constant group index over a large bandwidth. A flexible control of ng (18.24 < ng < 41.7) with large bandwidth (11.7 nm < Δ λ < 24 nm) has been achieved. As well, a large normalized delay-bandwidth NDBP products ranging from 0.282 to 0.465 have obtained. [ABSTRACT FROM AUTHOR]

Slow light propagation through photonic crystal (PhC) slab devices has great potential to reduce the size and power consumption of silicon photonic optical circuits. Most commonly, slow light routing through photonic crystals is achieved by using W1 waveguide bends operating near their cutoff frequencies. Unfortunately, this leads to optical pulse distortion due the high group velocity dispersion (GVD) associated with these designs. In this letter, however, we study the coupling between slow light waveguides optimized for near-zero GVD and 60 $^{\circ }$ PhC bends. Using numerical methods and the temporal coupled mode theory, we assess the performance of single bends coupled to input/output waveguides, and S-bends composed of two cascaded bends. In this latter, we observe that the bend-waveguide quality factor has great impact over transmission and dispersion. We propose a novel 60 $^{\circ }$ PhC bend design for routing optical modes while maintained reduced dispersion. This is achieved over a -3 dB bandwidth of around 50 nm in devices with slowdown factor up to 40. We show that this 60 $^{\circ }$ PhC bend has good stability under changes in S-bend length and fabrication induced disorder. These results can lead to great improvements in the design of monolithically integrated modulators, switches, (de)multiplexers, and filters based on photonic crystals, as well as on the routing of long optical buffers and delay lines. [ABSTRACT FROM AUTHOR]

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In this paper,we experimentally demonstrate a highly sensitive on-chip photonic electromagnetic wave sensor operating at 14.1 GHz with a 3 dB bandwidth of 4.84 GHz. The demonstrated electromagnetic sensor has several important advantages over conventional electrical electromagnetic sensors, including high sensitivity, compact in size, and strong immunity to electromagnetic interference. The sensor is comprised of a bowtie antenna and an asymmetric Mach-Zehnder interferometer (MZI). One arm of the MZI is an electro-optic polymer infiltrated one-dimensional slot photonic crystal waveguide (SPCW) and the other is a strip waveguide with teeth of subwavelength pitch. Bowtie antennas are designed and optimized to effectively collect 14.1 GHz microwave signal and applies it across theSPCW. The phase of the light guided in the SPCW therefore changes, and so does the amplitude of the output end of the MZI. The sensor is only 4.6 mm × 4.8 mm in size and has a low insertion loss of ~10 dB. Experimental results show the limit of detection at 14.1 GHz is 4.31 mW/m2, which is corresponding to a minimum detectable electric field of 1.8 V/m [ABSTRACT FROM AUTHOR]

Slow light with high group index and wideband is achieved in photonic crystal coupled-resonator optical waveguides (PC-CROWs). According to the eye-shaped scatterers and various microcavities, saddle-like curves between the normalized frequency f and wave number k can be obtained by adjusting the parameters of the scatterers, parameters of the coupling microcavities, and positions of the scatterers. Slow light with decent flat band and group index can then be achieved by optimizing the parameters. Simulations prove that the maximal value of the group index is > 10, and the normalized delay bandwidth product within a new varying range of n > 10 or n > 10 can be a new and effective criterion of evaluation for the slow light in PC-CROWs. [ABSTRACT FROM AUTHOR]

In conventional slow light waveguide, the delay time of signal in a waveguide is inversely proportional to its bandwidth. As a measure of storage density of optical pulse, the delay-bandwidth product is limited to a small constant depending on waveguiding approach. Breaking the limit is fundamental problem in optical signal and quantum information processing fields. The solution to this problem is becoming increasingly important, especially with high-speed signal processing system. So far, there have been neither practical nor realizable techniques that can solve this problem. In this paper, we propose a mechanism to explore the possibility for breaking the delay-bandwidth limit by using ultra-flat photonic band cluster. We show that based on multiple micro-cavities having corresponding multiple ultra-flat photonic bands, a slow light with arbitrary bandwidth in frequency can be achieved with ultraslow group velocity and ultralow group velocity dispersion, leading to a broken delay-bandwidth limit. This work demonstrates that arbitrary bandwidth dispersionless slow light can be realized with a two-dimensional multiple-microcavity photonic-crystal line-defect waveguide. [ABSTRACT FROM AUTHOR]

A high output transmission and high quality factor, compact LiNbO3-based Fabry-Perot-type photonic crystal cavity is reported that can be used in electro-optical modulators at optical communication wavelengths. The electro-optic effect is 123 times enhanced as compared to the bulk material as a result of the slow light effect. The transmission wavelength is found to depend linearly on the applied voltage with 1.2 nm/V modulation sensitivity. Moreover, an externally switchable dual mode regime with high quality factors and transmissions is realized. High transmissions and high quality factors are also obtained for both transverse-electric and transverse-magnetic polarizations simultaneously. [ABSTRACT FROM AUTHOR]

A tunable slow light with low group velocity, high buffer performance and high sensitivity is realized in photonic crystal coupled resonator optical waveguide (PC-CROW) with elliptical rod around cavity. By adjusting the long axis and short axis of the elliptical rods, the slow light and buffer performance of PC-CROW are optimized. As a e =0.42 a , b e =0.20 a , the group velocity is below 2.3053×10 −4 c , simultaneously, the buffer capacity C and delay time T s reach the optimum value of 9.8214 bit and 354.8 ps. Then the dynamic modulation of the slow light and buffer performance based on this optimized structure has been discussed systematically. Thanks to the electro-optic effect of the polystyrene substrate, the guided mode shifts linearly to short wavelength in sensitivity of 3.0 nm/mV around 1550 nm, as the applied voltage increases. The modulation sensitivities of delay time and buffer capacity are 0.445 ns/mV and 0.051 bit/mV, respectively. These results show a considerable potential for this structure that can be dynamically controlled according to the practical requirements by electro-optic effect in PC-CROW. [ABSTRACT FROM AUTHOR]

We theoretically optimized and demonstrated the periodic p–n junction in silicon photonic crystal slow-light modulators to balance the efficiency and speed of phase shifters and reduce the power consumption compared with those of previous linear and interleaved p–n junctions. In particular, sawtooth and wavy junctions, whose profiles match with the distribution of the slow-light mode, theoretically prove effective in achieving these objectives. However, the sawtooth junction requires a high-resolution process. Therefore, we finally employed the wavy junction and obtained 25- and 32-Gb/s operations in a 200-μm device with extinction ratios of 4 and 3 dB, respectively, for an excess modulation loss of 1 dB. [ABSTRACT FROM PUBLISHER]

A photonic free-electron laser (pFEL) produces coherent Cerenkov radiation from a set of parallel electron beams streaming through a photonic crystal. The function of the crystal is to slow down the phase velocity of a copropagating electromagnetic wave, such that also mildly relativistic electrons (of about 10-keV energy) can emit coherent Cerenkov radiation. Starting from spontaneous emission, the feedback of the radiation on the electrons results in bunching of the electrons on the scale of the radiation wavelength, and consequently, coherent radiation can build up. The frequency of the coherent mode is set by the electron velocity and wave dispersion of the photonic crystal and can, a priori, be continuously varied by varying the electron energy. The scale invariance of Maxwell's equation allows operation from Gigahertz to Terahertz and possible infrared (IR) frequencies without the need to increase the electron beam energy. Therefore, the pFEL is a very attractive, compact, and coherent radiation source that has the potential to significantly enhance the power available in the THz domain.

We design two novel air-hole-array strip waveguides: one with elliptic air holes and the other with sandglass-shaped ones. Simulation results prove that flatband modes with low group velocity and low dispersion can be obtained. Each waveguide has its merits; one can choose waveguides with a low group velocity of $2.52\times 10^{-3}\ \hbox{c}$ and a narrow bandwidth of 2.71 nm (one with elliptic air holes) or a high group velocity of $1.2\times 10^{-2}\ \hbox{c}$ and a wide bandwidth of 13.6 nm (one with sandglass-shaped air holes), according to the application. Numerical simulation by finite-difference time domain (FDTD) demonstrates the propagation of the broadband pulse.

Future communication networks require the entire communication system to be all-optical to overcome the bandwidth constraints of electronics. All-optical devices play a vital role in supporting future networks, which demand a high speed of up to Tbps. An all-optical gray code converter operation was demonstrated numerically using a photonic crystal semiconductor optical amplifier (PhC-SOA) in a Mach–Zehnder interferometric (MZI) configuration at 1 Tbps for M-ary differential phase shift keying modulated binary and BCD inputs. The design achieved a very high extinction ratio of about 123.8 dB with a good quality factor value of about 45. The results show that PhC-SOA-based XOR and OR gates in the gray code converter design exhibits improved modulation features compared with traditional SOAs in our previous works. [ABSTRACT FROM AUTHOR]

Photonic crystal waveguides are known to support C-points--point-like polarization singularities with local chirality. Such points can couple with dipole-like emitters to produce highly directional emission, from which spin-photon entanglers can be built. Much is made of the promise of using slow-light modes to enhance this light-matter coupling. Here we explore the transition from travelling to standing waves for two different photonic crystal waveguide designs. We find that time-reversal symmetry and the reciprocal nature of light places constraints on using C-points in the slow-light regime. We observe two distinctly different mechanisms through which this condition is satisfied in the two waveguides. In the waveguide designs, we consider a modest group velocity of vg≈c/10 is found to be the optimum for slow-light coupling to the C-points. [ABSTRACT FROM AUTHOR]

Ultra-slow light can enhance light–matter interactions and effectively realize all-optical buffering and modulation. In this paper, we present an efficient design for a two-dimensional square-lattice photonic crystal coupled-cavity waveguide, which can realize multi-frequency band slow-light transmission in the near-infrared band (1500–1640 nm).Through adjusting intercavity spacing N and structural parameters of elliptical air holes, high group index n g (202.46) within the bandwidth of 5.04 nm and improved normalized delay–bandwidth​ product of 0.6583 can be obtained at the wavelength of 1550.05 nm. Moreover, the designed devices can effectively function as a slow light sensor with the wavelength sensitivity of 585 nm/RIU. Multiple functions can be achieved synchronously in only one structure, which is essential in complex optical integrated circuits. • Multi-frequency band slow-light transmission is achieved in the near-infrared band (1500–1640 nm). • Both high group index (ultra-slow light) and high NDBP values can be obtained at the wavelength of 1550.05 nm. • The designed devices can effectively function as a slow light sensor with the wavelength sensitivity of 585 nm/RIU. [ABSTRACT FROM AUTHOR]

We comprehensively calculated the photonic bands of the waveguide modes in practical lattice-shifted photonic crystal waveguides, which are completely cladded by silica. We assumed various lattice shifts and found that the shift of the second rows and the mixed shift of the first and third rows along the waveguide generate low-dispersion slow light with group indices of 34–36, which is higher than those with a conventional shift of the third rows, maintaining a wide bandwidth over 10 nm at telecom wavelengths. We fabricated the waveguides using a CMOS-compatible process and confirmed correspondence with the calculation results. We also compared 25-Gb/s photonic crystal slow light Mach–Zehnder modulators and confirmed the improvement of the modulation efficiency by second-row shifts. [ABSTRACT FROM PUBLISHER]

The light transmission characteristics through the coupled-resonator optical waveguides (CROWs) based on the two-dimensional square-lattice photonic crystal with rectangular microcavities are systematically studied by the finite-difference time-domain method. Owing to the multiple spatial symmetries of the defective modes localized by the rectangular microcavities, the guiding bands can be adjusted by changing the coupling region between the CROW and the traditional W1-typed input and output channels, and their corresponding group velocities can be quite different from each other through the same CROW structure. Through optimizing the coupling regions between the CROW and three output channels, a kind of device with both the abilities of light beam splitting and frequency selection can be obtained, which has potential applications in the future complex all-optical circuits. [ABSTRACT FROM AUTHOR]

Recently, majority of current research in the field of designing Phonic Crystal Waveguides (PCW) focus in extracting the relations between output slow light properties of PCW and structural parameters through a huge number of tedious non-systematic simulations in order to introduce better designs. This paper proposes a novel systematic approach which can be considered as a shortcut to alleviate the difficulties and human involvements in designing PCWs. In the proposed method, the problem of PCW design is first formulated as an optimization problem. Then, an optimizer is employed in order to automatically find the optimum design for the formulated PCWs. Meanwhile, different constraints are also considered during optimization with the purpose of applying physical limitations to the final optimum structure. As a case study, the structure of a Bragg-like Corrugation Slotted PCWs (BCSPCW) is optimized by using the proposed method. One of the most computationally powerful techniques in Computational Intelligence (CI) called Particle Swarm Optimization (PSO) is employed as an optimizer to automatically find the optimum structure for BCSPCW. The optimization process is done by considering five constraints to guarantee the feasibility of the final optimized structures and avoid band mixing. Numerical results demonstrate that the proposed method is able to find an optimum structure for BCSPCW with 172% and 100% substantial improvements in the bandwidth and Normalized Delay-Bandwidth Product (NDBP) respectively compared to the best current structure in the literature. Moreover, there is a time domain analysis at the end of the paper which verifies the performance of the optimized structure and proves that this structure has low distortion and attenuation simultaneously. [ABSTRACT FROM AUTHOR]

Through shifting the rows adjacent to the line-defect along the waveguide direction, slow light photonic crystal slab waveguides with electro-optic polymer filled holes that show average group indices of 123 and 61.5 are obtained by three-dimensional plane-wave expansion method calculations. It is shown that the slow light properties and the buffering performance are enhanced by using an efficient method based on retreating the anti-crossing point with enlarging the lattice constant. This method has been shown to improve not only the bandwidth and flatten dispersion but also to reduce the variations in slow light properties that could occur due to fabrication inaccuracies. The performance of electro-optic modulation is drastically enhanced by exploiting local field enhancement induced by slow light effect. The buffering performance of the photonic crystal based buffer configurations are investigated and compared in terms of application needs. Since the modulation sensitivities of center wavelength and delay time change linearly with the applied voltage while remaining the buffer capacity and bit length almost constant, the investigated photonic crystal structures show promise for flexible and convenient buffering application in optical communication systems. [ABSTRACT FROM AUTHOR]

This work designs a type of line-defect photonic crystal waveguide (PCW) called hypoellipse PCW (HPCW) that considers two conflicting issues: group index and bandwidth. To do so, the recent multi objective framework called MoMIR is employed. A wide range of designs obtained demonstrates the advantage of considering group index and bandwidth simultaneously when designing HPCWs. Comparison of the proposed HPCW with the current best PCWs shows a nearly 7% improvement over the latter in terms of normalized delay-bandwidth product (NDBP). Analysis of the results reveals some of the physical rules about the structure of the HPCW. Finally, optical pulse propagation in obtained HPCWs and the process of designing an optical buffer by using an obtained design are explained. [ABSTRACT FROM AUTHOR]