Low-loss Passive Waveguide Research Articles

High-efficiency mid-infrared InGaAs/InP arrayed waveguide gratings.

Photonic integrated circuits and mid-infrared quantum cascade lasers have attracted significant attention over the years because of the numerous applications enabled by these compact semiconductor chips. In this paper, we demonstrate low loss passive waveguides and highly efficient arrayed waveguide gratings that can be used, for example, to beam combine infrared (IR) laser arrays. The waveguide structure used consists of an In0.53Ga0.47As core and InP cladding layers. This material system was chosen because of its compatibility with future monolithic integration with quantum cascade lasers. Different photonic circuits were fabricated using standard semiconductor processes, and experiments conducted with these chips demonstrated low-loss waveguides with an estimated propagation loss of ∼ 1.2 dB/cm as well as micro-ring resonators with an intrinsic Q-factor of 174,000. Arrayed waveguide gratings operating in the 5.15-5.34 µm range feature low insertion loss and non-uniformity of ∼ 0.9 dB and ∼ 0.6 dB, respectively. The demonstration of the present photonic circuits paves the path toward monolithic fabrication of compact infrared light sources with advanced functionalities beneficial to many chemical sensing and high-power applications.

Feasibility of chipscale integration of single-photon switched digital loop buffer

A strategy for realizing a microchip-scale single-photon digital loop buffer controlled by low-voltage electronic signals is studied in the context of integrated photonics. A potential implementation for bridging a gap between other technologies uses a recirculating loop architecture based on advances in low-loss passive waveguides and a fast electro-optic add-drop switch. Though the requirements of single-photon buffers are demanding, our analysis suggests that a voltage-controlled, room-temperature catch-and-store short-term quantum memory for light on a chip may be feasible in certain regimes.

Homogeneous photonic integration of mid-infrared quantum cascade lasers with low-loss passive waveguides on an InP platform

Mid-infrared (mid-IR, λ≈3–12 μm) photonic integrated circuits on low-loss passive waveguide platforms are of significant interest for a wide range of mid-IR applications. Quantum cascade lasers (QCLs) are currently the only room-temperature electrically pumped semiconductor light sources that can operate in a continuous-wave at room temperature over the entire mid-IR spectral range. Given very high thermal dissipation in QCL active regions, achieving long-term reliability and continuous-wave operation of heterogeneously integrated devices on silicon platforms is challenging. Here we experimentally demonstrate homogeneous integration of mid-IR QCLs with low-loss In0.53Ga0.47As passive waveguides epitaxially grown on InP substrates. The homogeneous integration approach uses materials, growth, and processing steps nearly identical to those used for conventional high-performance mid-IR QCLs, which offers superior reliability and performance of photonic integrated circuits. Over 0.57 W of peak-pulsed optical power was coupled to the passive waveguide from a homogeneously integrated λ≈4.6 μm QCL, which represents an order of magnitude improvement in optical power compared to the best results obtained with heterogeneously integrated QCLs.

A III-V-on-Si ultra-dense comb laser

Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution. The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz). However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth. In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization. The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate. The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines. The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (<400 kHz) indicate notably stable mode-locking. Such integrated dense comb lasers are very promising, for example, for high-resolution and real-time spectroscopy applications.

Low-loss passive waveguides in a generic InP foundry process via local diffusion of zinc.

Generic InP foundry processes allow monolithic integration of active and passive elements into a common p-n doped layerstack. The passive loss can be greatly reduced by restricting the p-dopant to active regions. We report on a localized Zn-diffusion process based on MOVPE, which allows to reduce waveguide loss from 2 dB/cm to below 0.4 dB/cm. We confirm this value by fabrication of a 73 mm long spiral ring resonator, with a record quality factor of 1.2 million and an extinction ratio of 9.7 dB.

Reconfigurable Delay Time Polymer Planar Lightwave Circuit for an X-band Phased-Array Antenna Demonstration

A 4-bit polymer optoelectronic true-time delay (TTD) device is demonstrated. The planar lightwave circuit (PLC) is composed of monolithically integrated low-loss passive polymer waveguide delay lines and five cascaded 2 times 2 polymer thermooptic switches. Waveguide junction offsets and air trenches simultaneously reduce the bending loss and device area. Simulations are used to optimize the trench and offset structures for fabrication. The 16 time delays generated by the device are measured to be in the range from 0 to 177 ps in 11.8-ps increments. The packaged PLC has an insertion loss of up to 14.9 dB, and the delay switching speed is 2 ms. An eight-element X-band phased-array antenna system is constructed to demonstrate the beam-steering capabilities of the 4-bit-delay devices. The TTD devices are shown to steer the far-field radiation pattern between 0deg and -14.5deg

Integration of an InGaAs quantum-dot laser with a low-loss passive waveguide using selective-area epitaxy

An InGaAs quantum-dot (QD) laser integrated with a low-loss waveguide is demonstrated. Selective-area epitaxy is used to simultaneously form the QDs that form the active region of the laser and quantum wells (QWs) that form the waveguide section of the integrated devices. The losses in the active and passive sections of the integrated devices are 6 and 3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. Very low losses in the waveguide section are due to a large difference of 200meV in the bandgap energies of the selectively grown QDs and QWs

Synthesis and Characterization of Tunable and Highly Transparent Thick Layers of Nanocomposites Based on Methacrylates and Silica Nanoparticles

ABSTRACTWe present a nanocomposite material based on functionalized silica nanoparticles in a methacrylate matrix. The nanocomposite material is synthesized without addition of a co-solvent, which enables the spin-coating of thick and defect-free layers of several tens of micrometers with smooth surfaces. SEM analysis indicates uniform distribution of the nanoparticles in the methacrylate matrix, and pinhole-free surfaces suitable for applications in optics. For optical characterization, the refractive index of the material for different silica concentrations is reported, and propagation losses in the UV/VIS range discussed. The tuning of the refractive indices can be applied towards the realization of low-loss passive optical waveguides. As a first step towards this goal, the processibility of the nanocomposite material for microfluidic applications, and the realization of a planar optical waveguide are demonstrated.

Low-loss interconnection between electrooptic and passive polymer waveguides with a vertical taper

To enable the hybrid integration of electrooptic (EO) polymer and low-loss passive waveguides, a low-loss interconnection between the two waveguides is demonstrated based upon adiabatic coupling in a vertically tapered waveguide. Fluorinated passive polymers incorporated in this device exhibit 0.35 dB/cm of propagation loss, and the EO polymer has an EO coefficient of 35 pm/V and high thermal stability with a glass transition temperature of 200/spl deg/C. According to a beam propagation method simulation, the interconnection loss could be negligible if the taper length is longer than 300 μm. From the fabricated device, an interconnection loss of 0.4 dB is demonstrated by cutback measurement of the waveguide loss.

Synthesis of fluorinated polyimides and their application to passive optical waveguides

Fluorinated and chlorofluorinated polyimides with high thermal stability and low optical absorption loss in the optical communication wavelengths of 1.3 and 1.55 μm were investigated for low-loss passive waveguide applications. These polyimides were prepared from pyromellitic dianhydride (PMDA) with 1,4-bis-[4-amino-2-(trifluoromethyl)phenoxy]tetrafluorobenzene (ATPT), 1,4-bis-[4-amino-2-(trifluoromethyl)phenoxy]benzene (ATPB), and 1,3-bis-[4-amino-2-(trifluoromethyl)phenoxy]-4,6-dichlorobenzene (ATPD). Control of the refractive indices of the polymers was achieved from 1.5397–1.5671 for TE polarization and 1.5239–1.5513 for TM polarization at 1.55 μm by copolymerization of PMDA/ATPT and PMDA/ATPB. As the amount of PMDA/ATPT was increased, the refractive indices of the polymers were decreased. Rib-type optical waveguides were fabricated using these fluorinated polyimides. These waveguides exhibited a low propagation loss of less than 0.5 dB/cm at 1.55 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2172–2177, 2000

Low-loss passive polymer waveguides by using chlorofluorinated polyimides

Chlorofluorinated polyimides were prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 2,2′-dichloro-4,4′-diaminobiphenyl (DCB) for optical waveguide applications. The resulting optical polymers exhibited good thermal stability, controllable refractive index, and low optical loss in the optical communication wavelengths of 1.3 and 1.55 µm. The control of refractive indices of the polymers was achieved by copolymerization of 6FDA/PFMB and 6FDA/DCB. As the amount of DCB was increased, the refractive indices of polymer were increased. The effect of addition of chlorine on optical properties of polymers such as absorption loss in the near-IR region were also investigated. Rib-type optical waveguides were fabricated using these chlorofluorinated polyimides. These waveguides exhibited low loss of less than 0.4 dB/cm for both TE and TM polarizations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 107–112, 1999

Passive modelocking in semiconductor lasers with monolithically integrated passive waveguides

A low-loss passive waveguide, fabricated by quantum well intermixing (QWI), has been integrated with an active region to form a modelocked semiconductor laser with an extended passive cavity (ECL). The 4 mm-long device has a threshold current of 18 mA and, modelocking at 9.3 GHz, generates 3.5 ps wide optical pulses with jitter levels as low as 9.3 ps (1 kHz–1 MHz). The variation of the modelocking frequency with the biasing conditions of such devices is also measured and a tuning range of ~1% of the modelocking frequency is observed.

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.

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).

Novel fabrication-tolerant twin-guide laser structurewith an external passivewaveguide

The authors propose a novel quasi-symmetrical twin guide GaAs/AlGaAs laser structure (QSTGL) with a low-loss external passive waveguide. The device is tolerant to fabrication misalignment and therefore well suited for monolithic integration. Threshold current densities of less than 1.1 kA/cm 2 and a coupling efficiency between 70 and 80% into the low-loss passive waveguide are achieved

Multi-quantum well distributed feedback and distributed Bragg reflector lasers

Unlike bulk semiconductors, quantum well (QW) structures exhibit unique optical features, because their band structure is completely different. In this paper, the authors review the applications of multi-quantum well (MQW) structures to AlGaAs/GaAs distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. Theoretical and experimental results on the lasing characteristics of MQW DFB lasers are described, mainly focusing on linewidth. Reduction in the chirp and the alpha -parameter were measured, and a linewidth as narrow as 1.5 MHz was obtained. Next they review various characteristics of MQW DBR lasers. In these lasers, MQW structures were used both as an active layer and as a low loss passive waveguide. Highly efficient surface emission from the second-order grating was observed. They also measured the fast bistable switching and beam switching characteristics. In the last part they review the fabrication and characterisation of AlGaAs/GaAs quantum well wires grown on corrugated substrates.

Edge- and surface-emitting distributed Bragg reflector laser with multiquantum well active/passive waveguides

A novel AlGaAs/GaAs distributed Bragg reflector laser utilizing a multiquantum well structure both as an active waveguide and as a low loss passive waveguide was fabricated. The threshold current was 102 mA at room temperature, and the differential quantum efficiency for the edge- and surface-emitted light was 16% and 3.7%, respectively. No mode hopping was observed in a temperature range of 35 K. A 0.17°×17° far-field pattern was obtained for the surface-emitted light.

IIIA-3 monolithic integrated coupling of an AlxGa1-xAs laser to a low-loss passive AlyGa1-xAs waveguide

IIIA-3 monolithic integrated coupling of an Al_xGa_1-xAs laser to a low-loss passive Al_yGa_1-xAs waveguide