Coupled Bragg Gratings Research Articles

On the Technology of a Laterally Coupled Bragg Grating of Single-Mode Distributed Feedback Laser Diodes

On the Technology of a Laterally Coupled Bragg Grating of Single-Mode Distributed Feedback Laser Diodes

Narrowband Bragg filters based on subwavelength grating waveguides for silicon photonic sensing.

Subwavelength grating (SWG) waveguides have been shown to provide enhanced light-matter interaction resulting in superior sensitivity in integrated photonics sensors. Narrowband integrated optical filters can be made by combining SWG waveguides with evanescently coupled Bragg gratings. In this paper, we assess the sensing capabilities of this novel filtering component with rigorous electromagnetic simulations. Our design is optimized for an operating wavelength of 1310 nm to benefit from lower water absorption and achieve narrower bandwidths than at the conventional wavelength of 1550 nm. Results show that the sensor achieves a sensitivity of 507 nm/RIU and a quality factor of 4.9 × 104, over a large dynamic range circumventing the free spectral range limit of conventional devices. Furthermore, the intrinsic limit of detection, 5.1 × 10-5 RIU constitutes a 10-fold enhancement compared to state-of-the-art resonant waveguide sensors.

Dynamics of colliding counterpropagating solitons in coupled Bragg gratings with cubic-quintic nonlinearity

ABSTRACTThe collisions of moving gap solitons in a system of two linearly coupled identical Bragg gratings with cubic-quintic nonlinearity are investigated systematically. In a previous work, it was found that the model supports two disjoint families of solitons, referred to as Type 1 and Type 2 moving gap solitons. It was also shown that within each of these categories there exist both symmetric and asymmetric moving gap soliton solutions. The collisions of the π-out-of-phase Type 1 asymmetric solitons generally leads to the mutual repulsion of both solitons. However, in the case of π-out-of-phase Type 2 asymmetric solitons, the low velocity solitons repel each other, but the collision of high velocity ones results in the destruction of both solitons. Collisions of the in-phase Type 1 asymmetric moving gap solitons exhibit rich dynamics and a range of outcomes, such as the separation of solitons with identical, reduced, increased, asymmetric velocities, destruction of both solitons, and formation of a quiescent soliton, either through a merger or through transformation. We have identified the outcome regions in the plane of quintic nonlinearity vs. frequency for different coupling coefficients and velocities. The interplay between the coupling coefficient and the velocity on the outcome regions is investigated. Also, the effect of the initial phase difference on the formation of quiescent solitons and the transformation is analysed.

High-Efficiency Silicon Photonic Modulator Using Coupled Bragg Grating Resonators

In this, we propose a novel design of a silicon photonic modulator that has a high modulation efficiency and that is tolerant to temperature variations. A series of phase-shifted Bragg gratings are placed in each arm of a Mach–Zehnder interferometer in order to provide enhanced phase modulation. The slow light effect in these ultra-compact coupled resonators improves phase modulation efficiency compared to conventional silicon phase shifters. These Bragg grating cavities are designed such that the optical bandwidth is increased compared to other coupled resonators, such as micro-rings. This improved bandwidth reduces the temperature sensitivity of the devices. We present in detail how to optimize these modulators considering properties, such as modulation efficiency ( Vπ × L ), optical modulation amplitude, and optical bandwidth ( $\Delta \lambda _{BW}$ ); the latter property determines the operating temperature range (Δ T ). As examples, we present two designs that meet different target specifications for short-reach or long-haul applications. We further provide a model, based on the coupled mode theory, to investigate the dynamic response of the proposed modulators. A large signal analysis is performed using finite-difference time domain in order to simulate on/off keying modulation and eye diagrams up to 110 Gb/s.

Stability of moving gap solitons in linearly coupled Bragg gratings with cubic–quintic nonlinearity

The existence and stability of moving gap solitons in coupled Bragg gratings with cubic–quintic nonlinearity are investigated. It is shown that the model supports two disjoint families of solitons, known as Type 1 and Type 2 solitons, which fill the entire bandgap. There exist symmetric and asymmetric moving gap solitons within each family of solitons. By means of systematic numerical stability analysis, the stability regions in the plane of the coefficient of quintic nonlinearity versus frequency have been identified. We have analyzed the effects and interplay of quintic nonlinearity, coupling coefficient, and velocity on the stability of solitons and the stability regions.

Dynamics of moving gap solitons in linearly coupled Bragg gratings with dispersive reflectivity

We investigate the existence, stability, and collision dynamics of moving gap solitons in a model of two linearly coupled Bragg gratings with dispersive reflectivity. It is shown that the model supports both symmetric and asymmetric moving solitons that fill the entire bandgap. It is found that beyond a certain value of the dispersive reflectivity parameter, the moving solitons develop sidelobes. To analyze the sidelobes, exact analytical expressions for the tails of the symmetric solitons are found and it is shown that they are in excellent agreement with the numerical solutions. By means of numerical stability analysis, we have identified stability regions within the bandgap for various values of dispersive reflectivity, coupling coefficient, and velocity. It is found that dispersive reflectivity has a stabilizing effect. We have also systematically investigated the collisions of in-phase and π-out-of-phase counterpropagating solitons. In-phase collisions lead to various outcomes such as separation of solitons with reduced, increased, or unchanged velocities; merger into a single quiescent soliton; and generation of three solitons (one quiescent and two moving solitons). A key finding is that depending on the velocity and coupling coefficient, collisions may lead to the formation of three solitons even in the absence of dispersive reflectivity. In the out-of-phase case, it is found that colliding solitons generally bounce off each other.

Single-mode high-power interband cascade lasers for mid-infrared absorption spectroscopy.

For high-sensitivity absorption spectroscopy, single-mode light sources capable of emitting high optical output power in the 3 to 5 µm wavelength range are vital. Here, we report on interband cascade lasers that emit 20 mW of optical power in a single spectral mode at room temperature and up to 40 mW at 0 °C using second-order laterally coupled Bragg gratings for distributed feedback. The lasers employ a double-ridge design with a narrow 3-µm-wide top ridge to confine the optical mode and a 9-µm-wide ridge for current confinement. The lasers were developed for an integrated cavity output spectroscopy instrument for stratospheric detection of hydrogen chloride at a wavelength of 3.3746 µm and emit at the target wavelength with more than 34 mW of single-mode power.

Stability of gap solitons in dual-core Bragg gratings with cubic-quintic nonlinearity

We investigate the existence and stability of quiescent gap solitons in a system of two linearly coupled Bragg gratings with cubic-quintic nonlinearity. It is found that the model supports two disjoint families of solitons that fill the entire bandgap. There exist symmetric and asymmetric solitons in each family. Exact analytical solutions of symmetric solitons for both families are found. The stability of solitons is investigated by means of systematic numerical stability analysis. The effect of quintic nonlinearity and coupling coefficient on the stability of solitons and the stability regions are analyzed.

Gap solitons in dual-core Bragg gratings with dispersive reflectivity

We investigate the existence and stability of gap solitons in a system of two linearly coupled Bragg gratings with dispersive reflectivity. It is found that families of symmetric and asymmetric solitons fill the entire bandgap and that above a certain value of the dispersive reflectivity parameter the solitons develop sidelobes. Exact analytical expressions for the tails of symmetric and asymmetric solitons are presented and found to be in excellent agreement with the numerical results. We also derive analytical conditions for the appearance of the sidelobes. The stability of symmetric and asymmetric solitons is investigated numerically. A key finding is that dispersive reflectivity has a stabilizing effect and results in the expansion of the stability region for the asymmetric solitons. It is also shown that the stabilization effect due to dispersive reflectivity is more pronounced for smaller coupling coefficients.

Quasisymmetric and asymmetric gap solitons in linearly coupled Bragg gratings with a phase shift

We introduce a model including two linearly coupled Bragg gratings, with a mismatch (phase shift theta) between them. The model may be realized as parallel-coupled fiber Bragg gratings (FBGs), or, in the spatial domain, as two parallel planar waveguides carrying diffraction gratings. The phase shift induced by a shear stress may be used to design a different type of FBG sensor. In the absence of the mismatch, the symmetry-breaking bifurcation of gap solitons (GSs) in this model was investigated before. Our objective is to study how mismatch theta affects families of symmetric and asymmetric GSs, and the bifurcation between them. We find that the system's band gap is always filled with solitons (for theta not equal to 0, the gap's width does not depend on coupling constant lambda if it exceeds some minimum value). The largest velocity of the moving soliton, cmax, is found as a function of theta and lambda (cmax grows with theta). The mismatch transforms symmetric GSs into quasisymmetric (QS) ones, in which the two components are not identical, but their peak powers and energies are equal. The mismatch also breaks the spatial symmetry of the GSs. The QS solitons are stable against symmetry-breaking perturbations as long as asymmetric (AS) solutions do not exist. If theta is small, AS solitons emerge from their QS counterparts through a supercritical bifurcation. However, the bifurcation may become subcritical at larger theta. The condition for the stability against oscillatory perturbations (unrelated to the symmetry breaking) is essentially the same as in the ordinary FBG model: both QS and AS solitons are stable if their intrinsic frequency is positive (i.e., in a half of the band gap).

Reflective Display Configurations Based on Total Internal Reflection and Grating-Grating Coupling of Holographic Polymer Dispersed Liquid Crystals (H-PDLC)

ABSTRACT We report on a novel electro-optical reflective configuration based on total internal reflection and grating-grating coupling fabricated in Holographic Polymer Dispersed Liquid Crystals (H-PDLC) materials. In this device, two symmetric slanted gratings are temporally multiplexed into a single film. A narrowband light is selected and diffracted from two coupled Bragg gratings creating a reflected image. These reflective configurations have switching voltages that are at least one-half that of H-PDLC reflective displays reported in the literature, and therefore have potential as low power, reflective display devices.

Symmetric and asymmetric solitons in linearly coupled Bragg gratings.

We demonstrate that a symmetric system of two linearly coupled waveguides, with Kerr nonlinearity and resonant grating in both of them, gives rise to a family of symmetric and antisymmetric solitons in an exact analytical form, a part of which exists outside of the bandgap in the system's spectrum, i.e., they may be regarded as embedded solitons (ES's, i.e., the ones partly overlapping with the continuous spectrum). Parameters of the family are the soliton's amplitude and velocity. Asymmetric ES's, unlike the regular (nonembedded) gap solitons (GS's), do not exist in the system. Moreover, ES's exist even in the case when the system's spectrum contains no bandgap. The main issue is the stability of the solitons. We demonstrate that some symmetric ES's are stable, while all the antisymmetric solitons are unstable; an explanation is given to the latter property, based on the consideration of the system's Hamiltonian. We produce a full stability diagram, which comprises both embedded and regular solitons, quiescent and moving. A stability region for ES's is found around the point where the constant of the linear coupling between the two cores is equal to the Bragg-reflectivity coefficient accounting for the linear conversion between the right- and left-traveling waves in each core, i.e., the ES's are the "most endemic" solitary solitons in this system. The stability region quickly shrinks with the increase of the soliton's velocity c, and completely disappears when c exceeds half the maximum velocity. Collisions between stable moving solitons of various types are also considered, with a conclusion that the collisions are always quasielastic.

P‐111: Reflective Display Based on Total Internal Reflection and Grating‐Grating Coupling

AbstractWe report on a novel reflection‐type display based on total internal reflection and grating‐grating coupling fabricated in H‐PDLC materials. In this display, two symmetric slanted gratings are temporally multiplexed into a single film. A narrowband light is selected and diffracted from two coupled Bragg gratings creating a reflected image. These holographic pixels have switching voltages that are at least one‐half that of H‐PDLC reflective displays reported in the literature.