Single-mode Output Waveguides Research Articles

Engineering Chiral Light-Matter Interactions in a Waveguide-Coupled Nanocavity.

Spin-dependent, directional light–matter interactions form the basis of chiral quantum networks. In the solid state, quantum emitters commonly possess circularly polarized optical transitions with spin-dependent handedness. We demonstrate numerically that spin-dependent chiral coupling can be realized by embedding such an emitter in a waveguide-coupled nanocavity, which supports two near-degenerate, orthogonally polarized cavity modes. The chiral behavior arises due to direction-dependent interference between the cavity modes upon coupling to two single-mode output waveguides. Notably, an experimentally realistic cavity design simultaneously supports near-unity chiral contrast, efficient (>95%) cavity-waveguide coupling and enhanced light–matter interaction strength (Purcell factor FP > 70). In combination, these parameters enable the development of highly coherent spin–photon interfaces ready for integration into nanophotonic circuits.

Numerical analysis of planar multimode optical sensor with active nanolayer

In the paper, numerical studies of the model of an optical sensor, based on interference of modes in a planar one-dimensional step-index configuration, are presented. Calculations are performed using the method of mode field analysis. The structure consists of the single-mode input waveguide, the multimode waveguide that guides only a few modes and the single-mode output waveguide. The structure is covered by a nanometer active sensor layer of a high refractive index, which changes its optical properties in contact with the measured external surrounding. The refractive index variation of an active sensor layer affects the modal properties of the multimode waveguide and the output optical field distribution. By the proper selection of the active layer, the considered configuration can be used for gas detection.

Plasmonic Modulators for Near-Infrared Photonics on a Silicon-on-Insulator Platform

A CMOS compatible interference-based Mach-Zehnder modulator with each arm comprising a metal-insulator-silicon-insulator-metal structure and a simpler, single-arm variant is considered for electro-optic and electroabsorption modulation, respectively, using finite-element electromagnetic simulations. In the calculation of electron density profiles in bias-induced accumulation layers, the size-quantization effects at oxide-silicon interfaces are considered. These are then used to find the complex refractive index profiles across the structure, in its biased and unbiased states, and eventually the modulator insertion loss and extinction ratio, as they depend on various structural parameters. Furthermore, an alternative modulator, comprising a metalized stub filled with SiGe/Ge multiple quantum wells or quantum dots in a silicon matrix, coupled to a dielectric waveguide structure is also investigated using 3-D finite-element simulations. The principle behind its modulation is the change of electromagnetic field profile after the stub, relative to the incoming mode, which happens when the absorption of the stub material varies. This affects the field coupling into a single-mode output waveguide, resulting in a controllable transmission.

Plasmonic enhanced electro-optic stub modulator on a SOI platform

Abstract The performance of a plasmonic enhanced stub modulator coupled to an underlying Si-waveguide was investigated using finite element simulations. The transmission of the system is controlled by changing the absorption coefficient of the material filling the stub, which modifies both the power transmitted by the stub itself and the field profile, and hence the coupling of this field into the single-mode output waveguide. An extinction ratio of 8.5 dB with an insertion loss of 8.5 dB can be achieved via electro-absorption derived from the quantum confined Stark effect (QCSE), assuming that the stub is filled with Ge/SiGe multiple quantum wells (MQWs) or Ge quantum dots (QDs) in a silicon matrix. The effect is of potential interest for application in electro-absorption modulators for integrated photonics, since the sub-wavelength dimensions of the device offer low power operation and high switching speeds.

Tapered multi-mode interference couplers for high order mode power extraction

Tapered 1 × 1 multi-mode interference (MMI) devices are proposed for high order to fundamental modeconversion. Like adiabatic tapers, the device provides a down-tapered image of theinput fundamental mode, while acting as a short taper for higher even-orderedmodes. This is the first tapering scheme capable of near 100% transmission ofthe input fundamental mode, as well as mode conversion for the input higherorder modes. When directly excited by diode lasers, the tapered MMI couplerpresented can convert the fundamental and second-order transverse modes ofdifferent wavelengths into the fundamental mode signals of a single-mode outputwaveguide.

Ultrasmall optical logic gates based on silicon periodic dielectric waveguides

An ultrasmall silicon periodic dielectric waveguides-based multimode interference all-optical logic gate has been proposed. The device consists of three 205 nm wide single-mode input waveguides, a 1.1 μm wide and 5.5 μm long multimode interference waveguide, and three 205 nm wide single-mode output waveguides. The total length and width of the device are 13.7 μm and 3.2 μm, respectively. By changing the states of the input optical signals and/or control signals launched into the device, multifunctional logic functions including OR, NAND, NOR, and NOT gates are performed, and each logic function can be realized at a specific output waveguide in accordance with the launched control signals. The ultrasmall multifunctional logic device has potential applications in high density photonic integrated circuits.

SPR waveguide sensor based on transition of modes at abrupt discontinuity

This paper describes a new scheme of enhanced sensitivity based on transition of modes at abrupt discontinuity using combined amplitude and phase sensing. The design consists of a single SPR waveguide structure supporting two modes acting as sensor section. The two modes are made to interfere by an abrupt discontinuity of the sensing waveguide into a single-mode output waveguide. The geometrical parameters of the entire scheme are chosen as to produce almost total cancellation of the field propagating into the output waveguide. This delicate balance is very sensitive to small changes in the waveguide's environment. Calculated values show sensitivities of an order of magnitude higher compared to previously reported waveguide SPR sensors. Additional sensitivity and extended working range can be gained by allowing external control of the differential phase between the propagating modes.

Demonstration of systematic photonic crystal device design and optimization by low-rank adjustments: an extremely compact mode separator

We present a powerful design and optimization method for devices in a photonic crystal. The method is based on a Wannier basis field expansion and efficient matrix analysis techniques for searching through a vast number of designs. The method permits the design of many compact optical devices with complex and novel functions. We present a design example of a very compact mode separator that is 8.2 microm x 13.3 microm in size that demultiplexes the three modes of an input photonic crystal multimode waveguide into three single-mode output waveguides. We verify the method with finite-difference time-domain calculations.

Ultra-compact multimode interference InGaAsP multiple quantum well modulator

We propose a new structure for an ultra-compact multimode interference (MMI) InGaAsP multiple quantum well modulator. The operating principle is based on restricting the coupling of the self-image produced by the MMI region into a single mode output waveguide. The key is to excite only the even modes within the MMI region, and this is achieved by operating the MMI waveguide under the condition of restricted symmetric interference. By asymmetrically inducing a phase change of π along a selected area within the MMI region, mode conversion of all the even modes to odd modes is achieved. Since only the fundamental mode can be coupled to the output waveguide, neither an individual mode, nor any combination of the modes will be coupled, and therefore the injected light is fully attenuated. The modulation characteristics are analyzed using the finite-difference beam propagation method. Extinction ratios as low as −37 dB are demonstrated without electro-absorption effects. For the case of low electro-absorption, which corresponds to a more realistic situation, this value is only increased to −35 dB.

Single-mode tapered waveguide laser in Er-doped glass with multimode-diode pumping

We report on a demonstration of a planar waveguide laser configuration for single-mode operation around 1550 nm using cost-effective multimode diode pumping. The laser was fabricated by Ag film ion exchange in a hybrid phosphate glass which has active and passive regions monolithically integrated in a single glass chip. Power of 54 mW at 1538 nm was measured from the single-mode output waveguide.

All-active InGaAsP-InP optical tapered-amplifier 1 x N power splitters

All-active tapered-amplifier power splitters (TAPS) consisting of a single-mode input waveguide, which acts as a preamplifier, a two-dimensional (2-D) diffraction section, which amplifies the signal during the splitting process, and N single-mode output waveguides, which act as post-amplifiers, were fabricated in 1.3-μm InGaAsP quantum-well material. Gains in each output guide (power out of guide/input power) of greater than 10 dB with a uniformity of better than 0.5 dB from guide to guide were measured on a 1×8 TAPS device.

High-power broad-area tapered amplifier with a monolithically integrated output focusing lens at 0.98-μm wavelength

We have demonstrated a 0.98-/spl mu/m wavelength tapered broad-area amplifier with a monolithically integrated aspherical waveguide lens. CW output exceeding 1 W from the amplifier-lens chip was measured with 10 mW input from a 0.98-/spl mu/m diode laser. The integrated semiconductor waveguide lens focused the amplifier output to a 8 /spl mu/m/spl times/3 /spl mu/m spot, which was measured at output power up to about 0.5 W, corresponding to 2.5 times the diffraction limit The beam propagation method was used to model the integrated amplifier-lens chip, and the calculated focal distances agree with the experiment to within 5%. The integrated lens may be used for output coupling to a single mode fiber with the requirement that the focal point should be positioned on the output facet. Based on BPM simulation, however, the focal point position becomes uncritical if a single mode output waveguide is integrated. Our results indicate that the waveguiding lens is a useful component for the design of high-power photonic integrated circuits. >