Analysis of diffraction characteristics for arrayed-waveguide grating multiplexer

We present a basic configuration of an unique integrated-optic arrayed-waveguide grating (AWG) multiplexer with loop-back optical paths and demonstrate an add-drop multiplexer (ADM), a network access terminal, and a wavelength channel selector for dense-WDM ring or bus networks, as three useful examples of its attractive applications. A key device in these components is a silica-glass based 1.55 /spl mu/m polarization-insensitive 32/spl times/32 AWG multiplexer chip with 0.8 nm channel spacing which is fabricated using planar lightwave circuit (PLC) technologies. Fine operation in their new functional components is achieved by using the AWG multiplexer module having low insertion loss of 3.9 dB and low interchannel crosstalk of less than -28 dB.

A 32 × 32 arrayed waveguide grating (AWG) multiplexer operating around the 1550 nm wavelength has been designed and fabricated using fluorinated poly (ether ether ketone). The schematic layout is about 3.2×1.7 cm². For our AWG, the total loss of designed AWG multiplexer is calculated to be 4.5 dB. We fabricated the AWG multiplexer by spin coating, photolithographic patterning and reactive ion etching (RIE). The core size is 5×5 μm². The roughness of polymer surface was reduced by 20 nm using a remelting technique. The measured wavelength channel spacing of the fabricated AWG multiplexer is 0.796 nm and center wavelength is 1548 nm. The inserting loss of the AWG is 9.5 dB and crosstalk less than -20 dB.

A compact hybrid-integrated 100 Gb/s (4 lane × 25.78125 Gb/s) transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s transceiver for 40-km transmission over a single-mode fiber. The TOSA has a simple configuration in which four electro-absorption modulator-integrated distributed feedback (EADFB) lasers are directly attached to the input waveguide end-face of a silica-based arrayed waveguide grating (AWG) multiplexer without bulk lenses. To achieve a high optical butt coupling efficiency between the EADFB lasers and the AWG multiplexer, we integrated a laterally tapered spot-size converter (SSC) for the EADFB laser and employed a waveguide with a high refractive index difference of 2.0% for the AWG multiplexer. By optimizing the laterally tapered SSC structure, we achieved a butt-coupling loss of less than 3 dB, which is an improvement of around 2 dB compared with a laser without an SSC structure. We also developed an ultracompact AWG multiplexer, which was 6.7 mm × 3.5 mm in size with an insertion loss of less than 1.9 dB. We achieved this by using a Mach–Zehnder interferometer-synchronized configuration to obtain a low loss and wide flat-top transmission filter spectra. The TOSA body size was 19.9 mm (L) × 6.0 mm (W) × 5.8 mm (H). Error-free operation was demonstrated for a 40-km transmission when all the lanes were driven simultaneously with a low EA modulator driving voltage of 1.5 V at an operating temperature of 55 °C.

A multichannel optical wavelength selective switch is investigated, which can switch signals at arbitrary wavelengths between multichannels in wavelength division multiplexing systems. It is based on the combination of an arrayed-waveguide grating (AWG) multiplexer and an array of optical space-division switches. A monolithically integrated 2/spl times/2 optical wavelength selective switch is successfully fabricated for four multiplexed signals in the 1.55 /spl mu/m wavelength region. Here, an AWG and four 2/spl times/2 thermooptic switches are laid out on a 30/spl times/60 mm/sup 2/ chip. Wavelength selective switching operations for four wavelength signals between two lines are demonstrated in a time slot of 40 ms with a switching speed of 1 ms.

In this article, a polymeric 41‐channel array‐waveguide grating (AWG) multiplexer was fabricated by simple direct Ultraviolet photolithography process. We try to use a cross‐linkable negative photoresist as core material and an optically clear UV curable epoxy as cladding material. Once exposed to Ultraviolet light through a photomask, the polymeric waveguide stripes were obtained upon development. Because of the superiority of UV resist in microelectro mechanical systems, the characteristic of the optical waveguide is better than that fabricated by steam‐redissolution technique of polymeric waveguide. The propagation loss is low as 2.03 dB/cm at 1550‐nm wavelength. The AWG multiplexer has channel spacing of 0.789 nm and the center wavelength is close to 1550 nm. The new technique will be well suited for fabricating optical integrated circuits. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3040–3044, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22965

PHASARs or Arrayed Waveguide Grating (AWG) multiplexers for application in Dense Wavelength Division Multiplexing optical networks have been realized using silica-waveguide technology. Using waveguide tapers, a flat-top passband characteristic is obtained. Using Fourier transform spectroscopy employing a low coherence interferometer, the power-distribution coefficients and the phase error distribution in such components is evaluated. Because of the coherence length of the used light source being smaller than the optical path length difference in the PHASAR, it is possible to resolve individual waveguides of the array. Thus, the transfer functions of the individual optical paths are accessible to the measurement, enabling the full simulation of the PHASAR transmission spectrum. It is demonstrated that the measured phase error distribution in tapered PHASAR devices consists of contributions from both tapered waveguides and arrayed waveguide grating regions. An evaluation method suitable for investigating both contributions separately is developed. Phase shift introduced by the waveguide tapers is in good agreement with simulation calculations based on the Beam Propagation Method. An analytic transmission calculation based on measured phase and power-distribution coefficients enables a full simulation of PHASARs including insertion loss, bandwidth and crosstalk performance. Excellent agreement with transmission measurements is performed.

Quadratic electro-optic shift of central wavelength in boron-phosphorous-doped folded Arrayed Waveguide Grating (AWG) multiplexer has been demonstrated. A spectral shift of ~1-GHz/KV was obtained with virtually zero power consumption.

In this paper, the basic principle, details of fabricating process and measuring results were described for a polymer/Si arrayed waveguide grating (AWG) multiplexer around the central wavelength of 1.550 micron with the wavelength spacing of 1.6nm. The fluorinated polymer was used to fabricate AWG to reduce the optical loss, but the fluorinated material was expensive, so we initially adopted the polymer of polymethylmethacrylate(PMMA) type to go on technologic research. The regulated curve of refractive index was given for the core polymer. In order to obtain better shape of the waveguide after the reactive ion etching (RIE) using oxygen, an aluminum film as mask was used on polymer instead of conventional photoresist as mask. In order to reduce radiation loss of underciadding layer to Si substrate, the underciadding layer thickness was increased to 11 micron through two times of spin-coating, thus the radiation loss was reduced to the order of 0.001dB. The measuring results indicates fabricated optical waveguide achieved single-mode transmission.

Optical dense wavelength division multiplexing (WDM) systems have been investigated in order to enlarge transmission capacity and improve network flexibility. Arrayed-waveguide grating (AWG) multiplexers are key components in such systems because they can process plural wavelengths simultaneously. This paper reviews recent work on AWGs based on silica-based planar lightwave circuits and their applications to dense-WDM systems. An AWG consists of plural input/output waveguides, two focal slab waveguides and a waveguide array. Applications investigated include optical add/drop multiplexers, wavelength routers and multi-channel light sources.

Multistage WDM access architecture employing cascaded AWGs

We describe the use of a reflective arrayed waveguide grating multiplexer in conjunction with a digital micromirror device to modulate the electric field distribution in the grating. Modulation of the electric field is accomplished by turning individual digital mirrors on and off. By imposing a reconfigurable grating superstructure on the digital mirror array, we can change the free-spectral range of the device and alter the overall transmission spectra. The experimental results are in excellent agreement with model calculations. This type of a device is expected to be useful in generation of reconfigurable sequences of ultrashort pulses.

A linear tapered double S-shaped arrayed waveguide grating (AWG) was designed as an alternative to a U-shaped AWG, and a complete transmission spectrum for 18 channels of coarse wavelength-division multiplexing (CWDM) was demonstrated. The silicon-on-insulator based AWG with a rib waveguide structure with a broad channel spacing of 20 nm was designed to serve as a multiplexer/demultiplexer. A beam propagation method modeling simulation under transverse electric mode polarization over a free spectrum range of 700 nm was used for the design process. The geometrical dimensions of the AWG rib structure were optimized to achieve the lowest reported insertion loss of 1.07 dB and adjacent crosstalk of −38.83 dB. The influence of different etching depths on the top Si layer of the AWG for a constant core width of 0.6 μm as well as birefringence effects were also investigated. A transmission spectrum response at the output port close to the standard CWDM wavelength grid range of 1271 to 1611 nm with an average channel spacing of 2485 GHz was obtained.

The crosstalk performance of an arrayed-waveguide grating (AWG) multiplexer or demultiplexer is primarily caused by random optical phase errors introduced in the arrayed waveguides. Because the layout of waveguides on a wafer is patterned via photomask through the photolithography process, the resolution of a photomask has a direct influence on the phase errors of an AWG. The paper presents a theoretical analysis on the phase error caused by photomask resolution and other basic design parameters. Both calculation and measurement results show that a high-resolution photomask (better than 25 nm) is a critical requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigate the effect of nonideal power distribution in the arrayed waveguides because it contributes considerable phase errors when material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation, number of grating waveguides, and material index variation are also summarized.

Utilizing T-band (1000 nm to 1260 nm) for optical communications is promising for short reach, and large capacity networks, such as data centers or access networks. It is feasible to use this with low-cost coarse wavelength division multiplexing (WDM). However, a tunable wavelength light source is necessary for such applications. In this paper, we propose a new configuration for an external cavity laser, which uses a silica-based arrayed waveguide grating (AWG) for the wavelength selecting element. The external cavity laser consists of a gain chip with high reflection (HR) and anti-reflection (AR) coated facets, coupling lenses, an AWG with AR/HR coatings, and an output fiber. The AWG has 17 connection ports, which correspond to 17 wavelengths with a channel spacing of 1.67 nm. The width of the connection port waveguides was optimized to achieve high coupling efficiency. The AWG chip size is 15 mm x 30 mm. The active layer in the gain chip has InAs quantum dots. The spontaneous emission 3-dB bandwidth was 48 nm (1108 nm to 1156 nm) when a current of 150 mA was injected into the gain chip. The lasing wavelength of the external cavity laser was successfully tuned from 1129.9 nm to 1154.4 nm by selecting the connection ports of the AWG. The typical threshold current was about 130 mA.

A slot waveguide structure is used in the part of arrayed waveguides in AWG instead of silicon waveguides. It is filled with high negative thermo-optic coefficient polymer in the narrow slot. The arrayed slot structure can remarkably reduce the center wavelength shift when the temperature changes. In this study, we use the polymer WIR30-490 and ZP49 to be filled in the slot. The thermo-optic coefficients of WIR30-490 and ZP49 are negative, and have the same order of magnitude with silicon. In our simulations, by adjusting several variables of the slot structure, such as the width of the slot between the pair of silicon wires, the width of the silicon waveguide, and the height of the silicon waveguide, we can get the athermal condition of AWG for each polymer. Even if there is an acceptable error on fabrication, temperature-dependent center wavelength shift of AWG can still be reduced down to 1 pm/°C. It makes the fabrication of athermal silicon AWG possible.