Vertically and laterally waveguide-coupled cylindrical microresonators in Si3N4 on SiO2 technology

High-finesse laterally and vertically waveguide-coupled cylindrical microresonators have been designed and realized in Si₃N₄ on SiO₂ technology using conventional optical lithography. Based on the experimental results and detailed simulations, a comparison between the lateral and vertical coupling schemes is made. Received: 16 May 2001 / Revised version: 13 August 2001 / Published online: 2 November 2001     

Intensity modulation in two Mach–Zehnder interferometers using plasma dispersion in silicon-on-insulator

We present comparative measurements of two Mach–Zehnder interferometers, one with Y-junction couplers and the other with MMI couplers, both developed in silicon-on-insulator technology and using plasma dispersion effect for light phase modulation. Measurements of fiber-to-fiber losses, absorption coefficient, output intensity vs. time and extinction ratio vs. frequency have been performed at λ=1.3 μm and at λ=1.55 μm. Results are reported and discussed in this paper. Received: 18 May 2001 / Revised version: 24 September2001 / Published online: 30 October 2001     

Analysis of optical crosstalk within optoelectronic integrated circuits including lasers and photodetectors

Optical crosstalk from a 1.3 μm laser to a 1.55 μm photodiode on a single InP substrate, and its suppression within 1.3 μm/1.5 μm Y-junction transceiver OEICs, has been analyzed experimentally. The results indicate that the optical crosstalk suppression is limited by the accumulated light in the OEIC substrate coming mainly from the spontaneous emission of the integrated laser and from stray light at the laser–waveguide butt joint interface. For OEICs, integrating lasers and photodetectors, the achievable optical intra-chip crosstalk at present will be in the range of 30–40 dB at the required small die dimensions. Received: 16 May 2001 / / Published online: 23 October 2001     

Femtosecond waveguide writing: a new avenue to three-dimensional integrated optics

Using tightly focussed femtosecond laser pulses, waveguides can be fabricated inside various glasses and crystals. This technique has the potential to generate not only planar but three-dimensional photonic devices. In this paper we present, to the best of our knowledge, the first true three-dimensional integrated optical device, a 1×3 splitter fabricated in pure fused silica. The optical properties of this device and possibilities for the fabrication of complex high-density integrated optical elements are discussed. Received: 23 December 2002 / Accepted: 6 January 2003 / Published online: 28 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-3641/65-7680, E-mail: nolte@iap.uni-jena.de     

An in-depth analysis of reflections in MMI couplers using optical low-coherence reflectometry: design optimization and performance evaluation

This paper describes a comprehensive report on the high potential of optical low-coherence reflectometry (OLCR) measurements to assist the design optimization and performance evaluation of symmetric MMI couplers. Using three sets of deep-ridge InGaAsP–InP couplers on InP and by performing OLCR measurements simultaneously in reflection and transmission modes, the nature and origin of all reflections in MMI have first been identified with respect to a deliberately chosen design parameter, namely, the coupler length. In addition, and in total agreement with the self-imaging principle and also the BPM simulations, the back reflections in combiner mode are shown to be prominent even in fully optimized devices. Finally, a simple design artifact has been proposed and demonstrated experimentally for the first time to suppress back reflections. Received: 16 May 2001 / Published online: 2 November 2001     

Design, Fabrication, and Measurement of Two-Dimensional Photonic Crystal Slab Waveguides

Two-dimensional photonic crystal slab waveguides on SOI wafer are designed and fabricated. Photonic band gap, band gap guided mode, and index guided mode are observed by measuring the transmission spectra. The experimental results are in good agreement with the theoretical ones.     

Design of optical polarization splitters in a single-section deeply etched MMI waveguide

The design of a single-section polarization splitter in a deeply etched semiconductor MMI waveguide is presented. Numerically simulated results indicate that the semiconductor MMI exhibits considerable polarization dependence and, utilizing this effect, a compact 1.6-mm-long polarization splitter may be fabricated to yield more than 8-dB polarization separation and only 0.11-dB optical loss, using a very simple design-approach. Received: 16 May 2001 / Revised version: 14 August 2001 / Published online: 2 November 2001     

Optimization of TE–TM mode converters on X-cut, Y-propagation LiNbO3 used for PMD compensation

Two-phase and three-phase TE–TM mode converters for integrated optic polarization mode dispersion compensation are compared, and the latter are found to have a slightly better electro-optic efficiency. If a small differential group delay is needed, compensation performance can be drastically improved by a waveguide tilt in the YZ plane. Received: 16 May 2001 / Published online: 23 October 2001     

Fabrication of Triplexers Based on Flattop SOI AWG

A triplexer is fabricated based on SOI arrayed waveguide gratings （AWGs）. Three wavelengths of the triplexer operate at different diffraction orders of an arrayed waveguide grating. The signals of 1490nm and 1550nm, which are input from central input waveguide of an AWG, are demultiplexed and the signal of 131Onto, which is input from central output waveguide of an AWG, is uploaded. The tested results show that the downloaded and uploaded signals have fiat-top response. The insertion loss is 9 dB on chip, the nonadjacent crosstalk is less than -30 dB for 1490nm and 1301 nm, and is less than -25 dB for 1550nm, the 3dB bandwidth equates that of the input light source.     

Modeling of InGaAsP–InP 1.55 μm lasers with integrated mode expanders using fiber-matched leaky waveguides

A new concept for InGaAsP–InP 1.55 μm lasers integrated with spot size converters using leaky waveguides is presented. The large fundamental mode size and the high discrimination of the higher order modes make ARROWs (Antiresonant Reflecting Optical Waveguides) and antiguided waveguides useful for fiber coupling functions. Three-dimensional (3-D) beam propagation method (BPM) results show that the devices have transformation losses lower than 0.22 dB. Fiber-coupling efficiencies of 60% are possible with standard cleaved single-mode fibers (SMF). The horizontal and vertical FWHM can be efficiently reduced to 9.70° (horizontal) and 17.80° (vertical). The fabrication of such devices avoids the growth of thick layers of quaternary material with a low Ga and As fraction, and simplifies the fabrication to one planar epitaxial growth step and one non-critical conventional etch. Received: 16 May 2001 / Published online: 30 October 2001     

Fabrication of sol-gel-derived optical waveguide on InP for hybridized photonics applications

In this paper, we report on the first successful fabrication, using spin-coating and low-temperature (200 °C) annealing, of organically modified sol-gel planar optical waveguides on InP substrates. Considering the fact that the sol-gel technique is simple and cheap, and III-V compound semiconductors are the essential substrate materials for manufacturing data communication devices, we believe that our demonstration of optical waveguiding in sol-gel-derived waveguides on III-V compound semoconductors is interesting. It opens the possibility of hybridizating traditional glass or optical-crystal-based integrated optics with III-V compound semiconductor-based optoelectronics. Received: 4 August1999 / Accepted: 6 August 1999 / Published online: 16 September 1999     

Multi-layer cladding leaky planar waveguide for high-power applications

We design a multi-layer cladding large-core planar waveguide that supports a single guided mode. The waveguide works on the principle of higher-order mode discrimination. The cladding of the waveguide is formed by alternate low- and high- index regions, which helps leaking out of higher-order modes while retaining the fundamental mode over the entire length of the waveguide. The structure is analyzed by the transfer-matrix method and the leakage losses of the modes have been calculated. We show that a waveguide formed in silica with numerical aperture 0.24 and core width 10 μm can be designed to exhibit single-mode operation at 1550-nm wavelength. Such a structure should find applications in high-power planar waveguide lasers and amplifiers.     

Talbot Effect in Three Waveguide Arrays

By taking the coupling between the non-neighbourhood waveguides into account, the coupling characteristic of three waveguide arrays is analysed. The strong coupling equation of three waveguides is dealt with Laplace transform and LU decomposition. The general field evolution equation is obtained by inversion of the Laplace transform. The results show that the self-imaging conditions （Talbot effect） do not satisfy in general. The theoretical predictions are in good agreement with the BPM simulations.     

Bending Efficiency of Bent Multiple-Slot Waveguides

The bending efficiency of three-dimensional bent multiple-slot waveguides is studied by applying a combined method of effective-index and modified transfer-matrix methods. The effects of asymmetric structure, asymmetric slots, and asymmetric middle strips on the bending efficiency are investigated. We show that the bending efficiency can be improved by the use of asymmetric structures and asymmetric middle strips. The bending efficiency of different slot waveguides （up to quintuple-slot structure） is compared. It is revealed that although the single-slot waveguide in general provides the lowest bending loss for the same waveguide parameters, it is possible that the multiple-slot waveguide can present a lower bending loss than the single-slot one.     

Devices and architectures for photonic chip-scale integration

Silicon nanophotonics holds the promise of dramatically advancing the state of the art in computing by enabling parallel architectures that combine unprecedented performance and ease of use with affordable power consumption. This paper presents a design study for a many-core architecture called Corona which utilizes dense wavelength division multiplexing (DWDM) for on- and off-chip communication together with the devices which will be needed to implement such a communication infrastructure.     

CdTe epilayers for uses in optical waveguides

CdTe epilayers have been grown by vapor phase epitaxy (VPE) on glass, MgO, sapphire, LiNbO₃ and mica substrates. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show the good structural quality of the epilayers. In these epilayers, a few optical modes were excited with a 1.33-μm laser. The measured propagation losses were in the range between 5 dB/cm and less than 0.5 dB/cm. From dark-mode m-lines, the epilayer thickness was found to be in the 1–3 μm range, in good accord with that obtained by SEM measurements. The refractive index obtained from the fitting is also in good accord with that of bulk CdTe. Received: 7 October 1999 / Accepted: 13 March 2000 / Published online: 5 July 2000     

Multiple-order adaptive dispersion compensation using polynomially-chirped grating devices

Devices such as the planar arrayed-waveguide grating or the distributed Bragg reflector (AWG and DBR, respectively) are assuming increasing importance in the areas of fibre point-to-point communication and networking. In the particular context of dense wavelength-division multiplexing (DWDM), these devices play a well-established role as wavelength-selective elements. More recently, chirped variants have found use as dispersion compensators, offering wideband reduction of both basic and higher-order departures from constant group delay. However, up to the present time, the existence of a systematic approach to higher-order dispersion compensation has not been recognised. Additionally, we have identified a comprehensive isomorphism between AWG and DBR devices that allows the design characteristics of the former transverse geometry to be mapped on to the latter longitudinal structure. Here, we present a systematic study of these important passive optical grating-based devices which considers, firstly, analytic solutions for 2nd-order dispersion compensation (DC), and then 3rd- and 4th-order dispersion compensators with 100 GHz bandwidth. We then review optimisation strategies for DC, 3 dB bandwidth, and passband dispersion ripple, as determined by device chirp, apodisation, coupling strength and polyphase transfer function superposition. We conclude with a preliminary discussion of grating parametric sensitivity as evidenced by Monte Carlo analysis. Received: 22 May 2001 / Revised version: 31 July 2001 / Published online: 2 November 2001     

Experimental observation and numerical simulation of guided modes in Nd:YLiF4 channel waveguides produced by carbon ion implantation

We report on, to our knowledge the first time, the channel waveguide formation in Nd:YLiF₄ laser crystal produced by 6 MeV carbon ion implantation. The guided modes are observed by using an end‐face arrangement. We construct the two‐dimensional (2D) refractive index profile of the channel waveguide cross section, which is based on the related planar waveguide index distribution as well as the rectangular shape of the waveguide cross sections. The modal intensity distribution is numerically calculated by using the beam propagation method according to the reconstructed index profile, which shows a reasonable agreement with the experimental result. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Origin of reciprocal circular birefringence observed in X-cut, Z-propagation LiNbO3 polarization transformers

Polarimetric investigation reveals up to ≈ 2 rad of reciprocal circular retardation present in 10 commercial X-cut, Z-propagation LiNbO₃ polarization transformers from two suppliers. A recent experiment confirms the static polarization mode coupling observed in polarization transformers which are fabricated in-house using either off-axis or principal-axis propagation. Optical activity is responsible for the nonideal behavior of the integrated electro-optic waveplates. This phenomenon is explained and accurately modelled using LiNbO₃ anisotropy. Furthermore the procedure required to make the polarization transformers ideal is given. Received: 16 May 2001 / Revised version: 9 August 2001 / Published online: 23 October 2001     

Er-Yb co-doped glass waveguide amplifiers using ion exchange and field-assisted annealing

Er³⁺-Yb³⁺ co-doped waveguide amplifiers fabricated using thermal two-step ion-exchange are demonstrated. K⁺-Na⁺ ion-exchange process was first carried out in pure KNO₃ molten bath, and then field-assisted annealing (FAA) was used to make the buried waveguides. The effective buried depth is estimated to be ∼3.4 μm for the buried FAA waveguides. With the use of cut-back method, the fiber-to-guide coupling loss of ∼4.38 dB, the waveguide loss of ∼2.27 dB/cm, and Er³⁺ absorption loss ∼5.7 dB were measured for a ∼1.24-cm-long waveguide. Peak relative gain of ∼7.0 dB is obtained for a ∼1.24-cm-long waveguide. The potential for the fabrication of compact optical amplifiers operating in the range of 1520-1580 nm is also demonstrated.