Design of Low-Loss Surface-Plasmon Quantum Cascade Lasers

National Research Projects of China 60525406 60736031 60806018 60906026 2006CB604903 2007AA03Z446 2009AA03Z403

A 2x2 optical switch based on plasma dispersion effect in silicon-on-insulator

Based on Mach-Zehnder interferometer (MZI) structure, a 2 x 2 optical switch is fabricated on SOI wafer. Modulation of the refractive index of MZI arms is achieved through free carriers plasma dispersion effect of silicon. The device presents an insertion loss as low as 3.44 dB and a response time as small as 300 ns. The crosstalk and extinction ratio are -15.54 and 14.9 dB, respectively. Detailed analysis and explanation of the operating behaviors are also presented. (C) 2005 Elsevier B.V. All rights reserved.

Electroabsorption modulated semiconductor optical amplifier monolithically integrated with spot-size converters

We have demonstrated an electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) monolithically integrated with novel dual-waveguide spot-size converters (SSCs) at the input and output ports for low-loss coupling to planar light-guide circuit silica waveguide or cleaved single-mode optical fiber. The device is fabricated by means of selective-area MOVPE growth (SAG), quantum well intermixing (QWI) and asymmetric twin waveguide (ATG) technologies with only three steps low-pressure MOVPE growth. For the device structure, in SOA/EAM section, double ridge structure was employed to reduce the EAM capacitances and enable high bit-rate operation. In the SSC sections, buried ridge stripe (BRS) were incorporated. Such a combination of ridge, ATG and BRS structure is reported for the first time in which it can take advantage of both easy processing of ridge structure and the excellent mode characteristic of BRS. At the wavelength range of 1550-1600 nm, lossless operation with extinction ratios of 25 dB DC and more than 10 GHz 3-dB bandwidth is successfully achieved. The beam divergence angles of the input and output ports of the device are as small as 8.0 degrees x 12.6 degrees, resulting in 3.0 dB coupling loss with cleaved single-mode optical fiber. (c) 2005 Elsevier B.V. All rights reserved.

Multimode-interference-type thermo-optic variable optical attenuator with a response frequency of 10 kHz

A thermo-optic variable optical attenuator based on a multimode interference coupler principle is fabricated. The propagation loss of the fabricated device is 1.6 to 3.8 dB at the wavelength range 1510 to 1610 nm, which is very near the calculated value (1.2 dB) by the finite difference beam propagation method. The maximum power consumption is 363 mW and the dynamic attenuation range is 0 to 26 dB. The response frequency of the fabricated attenuator is about 10 kHz. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Semiconductor optical amplifier optical gate with graded strained bulk-like active structure

A novel semiconductor optical amplifier (SOA) optical gate with a graded strained bulk-like active structure is proposed. A fiber-to-fiber gain of 10 dB when the coupling loss reaches 7 dB/factet and a polarization insensitivity of less than 0.9 dB for multiwavelength and different power input signals over the whole operation current are obtained. Moreover, for our SOA optical gate, a no-loss current of 50 to 70 mA and an extinction ratio of more than 50 dB are realized when the injection current is more than no-loss current, and the maximum extinction ratio reaches 71 dB, which is critical for crosstalk suppression. (C) 2003 society of Photo-Optical Instrumentation Engineers.

Investigation progress on key photonic integration for application in optical communication network

Proceeding from the consideration of the demands from the functional architecture of high speed, high capacity optical communication network, this paper points out that photonic integrated devices, including high speed response laser source, narrow band response photodetector high speed wavelength converter, dense wavelength multi/demultiplexer, low loss high speed response photo-switch and multi-beam coupler are the key components in the system. The, investigation progress in the laboratory will be introduced.

Simulation and fabrication of thermo-optic variable optical attenuators based on multimode interference coupler

A type of thermo-optic variable optical attenuator based on multimode interference coupler is proposed. The optical field propagation properties of the devices are simulated using finite difference beam propagation method. The propagation loss of the fabricated device is 2-4.2 dB at the wavelength range 1510-1610 nm. The total power consumption is 370 mW and the maximum attenuation is more than 25 dB, which almost can meet the requirements of optical fiber communication systems.

Resonant frequencies and quality factors for optical equilateral triangle resonators calculated by FDTD technique and the Pade approximation

The mode wavelength and quality factor (Q-factor) for resonant modes in optical equilateral triangle resonators (ETR's) are calculated by the finite-difference time-domain (FDTD) technique and the Pade approximation, For an ETR with the side length of 3 mu m and the refractive index of 3.2, we get the mode wavelength interval of about 70 nm and the Q-factor of the fundamental mode over 10(3), The results show that the ETR is suitable to realize single-mode operation, and that the radiation loss in the corner regions of ETR is rather low, In addition, the numerical results of the mode wavelength agree very well with our analytical formula.

Numerical evaluation of energy loss rate for hot carriers in quantum wells

Using the Frohlich potential associated with realistic optical phonon modes in quantum well systems, the energy loss rates of hot electrons, holes, and electron-hole pairs are calculated, with special emphasis on the effects of carrier density, hot phonon population, quantum well width, and phonon dispersion on the hot-carrier relaxation process in quasi-two-dimensional systems. (C) 1998 Academic Press Limited.

High energy ion implantation enhanced intermixed quantum well structures and their absorption characteristics in passive optical waveguides

We have shown that high energy ion implantation enhanced intermixing (HE-IIEI) technology for quantum well (QW) structures is a powerful technique which can be used to blue shift the band gap energy of a QW structure and therefore decrease its band gap absorption. Room temperature (RT) photoluminescence (PL) and guided-wave transmission measurements have been employed to investigate the amount of blue shift of the band gap energy of an intermixed QW structure and the reduction of band gap absorption, Record large blue shifts in PL peaks of 132 nm for a 4-QW InGaAs/InGaAsP/InP structure have been demonstrated in the intermixed regions of the QW wafers, on whose non-intermixed regions, a shift as small as 5 nm is observed. This feature makes this technology very attractive for selective intermixing in selected areas of an MQW structure. The dramatical reduction in band gap absorption for the InP based MQW structure has been investigated experimentally. It is found that the intensity attenuation for the blue shifted structure is decreased by 242.8 dB/cm for the TE mode and 119 dB/cm for the TM mode with respect to the control samples. Electro-absorption characteristics have also been clearly observed in the intermixed structure. Current-Voltage characteristics were employed to investigate the degradation of the p-n junction in the intermixed region. We have achieved a successful fabrication and operation of Y-junction optical switches (JOS) based on MQW semiconductor optical amplifiers using HE-IIEI technology to fabricate the low loss passive waveguide. (C) 1997 Published by Elsevier Science B.V.

Electronic, structural, and optical properties of crystalline yttria

The electronic structure of crystalline Y2O3 is investigated by first-principles calculations within the local-density approximation (LDA) of the density-functional theory. Results are presented for the band structure, the total density of states (DOS), the atom-and orbital-resolved partial DOS. effective charges, bond order, and charge-density distributions. Partial covalent character in the Y-O bonding is shown, and the nonequivalency of the two Y sites is demonstrated. The calculated electronic structure is compared with a variety of available experimental data. The total energy of the crystal is calculated as a function of crystal volume. A bulk modulus B of 183 Gpa and a pressure coefficient B' of 4.01 are obtained, which are in good agreement with compression data. An LDA band gap of 4.54 eV at Gamma is obtained which increases with pressure at a rate of dE(g)/dP = 0.012 eV/Gpa at the equilibrium volume. Also investigated are the optical properties of Y2O3 up to a photon energy of 20 eV. The calculated complex dielectric function and electron-energy-loss function are in good agreement with experimental data. A static dielectric constant of epsilon(O)= 3.20 is obtained. It is also found that the bottom of the conduction band consists of a single band, and direct optical transition at Gamma between the top of the valence band and the bottom of the conduction band may be symmetry forbidden.

Realization of SOI submicrometer optical waveguide components - art. no. 68380L

Submicrometer channel and rib waveguides based on SOI (Silicon-On-Insulator) have been designed and fabricated with electron-beam lithography and inductively coupled plasma dry etching. Propagation loss of 8.39dB/mm was measured using the cut-back method. Based on these so-called nanowire waveguides, we have also demonstrated some functional components with small dimensions, including sharp 90 degrees bends with radius of a few micrometers, T-branches, directional couplers and multimode interferometer couplers.

High efficiency fiber to waveguide optical coupler in silicon-on-insulator-based slot waveguides - art. no. 68310R

We propose a novel optical fiber-to-waveguide coupler for integrated optical circuits. The proper materials and structural parameters of the coupler, which is based on a slot waveguide, are carefully analyzed using a full-vectorial three dimensional mode solver. Because the effective refractive index of the mode in a silicon-on-insulator-based slot waveguide can be extremely close to that of the fiber, a highly efficient fiber-to-waveguide coupling application can be realized. For a TE-like mode, the calculated minimum mismatch loss is about 1.8dB at 1550nm, and the mode conversion loss can be less than 0.5dB. The discussion of the present state-of-the-art is also involved. The proposed coupler can be used in chip-to-chip communication.

High speed silicon optical switches based on carrier depletion - art. no. 67812D

The novel design of a silicon optical switch on the mechanism of a reverse p-n junction is proposed. The figuration of contact regions at slab waveguides and the ion implantation technology for creation of junctions are employed in the new design. The two-layer rib structure is helpful for reduction of optical absorption losses induced by metal and heavily-doped contact. And more, simulation results show that the index modulation efficiency of Mach-Zehnder interferometer enhances as the concentrations of dopants in junctions increase, while the trade-off of absorption loss is less than 3 dB/mu m. The phase shift reaches about 5 x 10(-4) pi/mu m at a reverse bias of 10V with the response time of about 0.2ns. The preliminary experimental results are presented. The frequency bandwidth of modulation operation can arrive in the range of GHz. However, heavily-doped contacts have an important effect on pulse response of these switches. While the contact region is not heavily-doped, that means metal electrodes have schottky contacts with p-n junctions, the operation bandwidth of the switch is limited to about 1GHz. For faster response, the heavily-doped contacts must be considered in the design.

SOI optical switch matrix integrated with spot size converter (SSC) and total internal reflection (TIR) mirrors

SOI (Silicon on Insulator) based photonic devices has attracted more and more attention in the recent years. Integration of SOI optical switch matrix with isolating grooves, total internal reflection (TIR) mirrors and spot size converter (SSC) was studied. A folding re-arrangeable non-blocking 4x4 optical switch matrix and a blocking 16x16 matrix with TIR mirrors and SSC were fabricated on SOI wafer. The performaces, including extinction ratio and the crosstalk, are better than before. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length, more bend and intersecting waveguides. The insertion losses decrease 2 similar to 3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.