Electro-Optically Tunable Folded Arrayed Waveguide Grating Multiplexer

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.

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.

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.

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

A 17 × 17 polymer arrayed waveguide grating (AWG) multiplexer with flat spectral response have been designed and fabricated by using FPE polymer materials.The measured results are as: the center wavelength is 1550.83 nm, wavelength channel spacing is 0.8 nm, 3-dB bandwidth is about 0.476 nm, insertion loss is 13∼15 dB, and crosstalk is about −21 dB. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1653–1655, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25277

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.

Multistage WDM access architecture employing cascaded AWGs

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.

As the need for greater bandwidth in local-area networks grows, wavelength-division multiplexing (WDM) is gathering attention as a viable successor to Gigabit Ethernet technologies. In this paper we introduce a new WDM optical LAN architecture based on the waveguide grating multiplexer (WGM) rather than the traditional passive star coupler (PSC). An N-port WGM allows N2 × N2 connectivity via only N physical wavelengths, due to its inherent space-division multiplexing property. Wavelength-routed networks based on the WGM promise to be significant components of future LAN and WAN technologies not only because of their efficient use of wavelengths, but also because they have been implemented as integrated devices. We propose simple, low-complexity TDM schedules for interconnecting MN nodes (M nodes per port) with a WGM in a local environment. Each node is equipped with a single tunable transmitter and a single tunable receiver (both of which can access all N wavelengths). Various transmitter and receiver tuning latencies are considered. We show that, for negligible tuning latencies, aggregate network throughput approaching min(MN, N2) can be achieved, and for tuning latencies on the order of a packet length or more, throughput on the order of N can be achieved. Since these performance metrics are vastly superior to that of an equivalent PSC-based system (whose maximum throughput is limited by the number of wavelengths, N), we propose that the WGM be considered as an alternative to the PSC for enabling WDM LANs and multiprocessor interconnects.

The diffraction characteristics are analyzed for a polymer arrayed-waveguide grating (AWG) multiplexer around the central wavelength of 1.55 μm with the wavelength spacing of 1.6 nm. The diffraction loss and diffraction efficiency in the input and the output slab waveguide are investigated and discussed for different values of parameters, such as the core width, pitch of adjacent waveguides, the number of arrayed waveguides, taper end width of waveguides, and number of output wavelength. Finally, we give a set of parameters which have been optimized in this device.

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.

Monolithic integration of an InP-based O-band 4-channel arrayed waveguide grating (AWG) to a uni-traveling carrier photodiode (UTC-PD) array is realized by the selective area growth (SAG) technique. The passive-active buttjoint design is introduced and experimentally proved to ensure both good compatibility between the PD fabrication process and the SAG technique, and high photodiode quantum efficiency under the complex butt-joint geometry. An extended coupling layer is adopted between the AWG output waveguides and the PD mesa. The extended coupling layer length, the regrowth boundary edge position and the AWG etching edge position relative to the heterogeneous butt-joint boundary, and the refractive indices of the PD collector and coupling layer are optically simulated and optimized by a finite-difference time-domain method. It is found that the extended coupling layer, compared with the un-extended situation, ensures a good matched optical field from AWG to PD and could reduce nearly 30% quantum efficiency loss when connecting seamlessly to the regrown InP AWG top cladding layer. A stable high efficiency around 80% is maintained within an extended layer length from 7.5 m to 15.0 m. The regrowth boundary edge into the coupling region will cause a drastic efficiency oscillation up to 20% period with the increase of distance. The efficiency drop is also attributed to the light scattering at the regrowth boundary edge, caused by the optical field mismatch, while the oscillation comes from the alternative light power concentration between the coupling layer and the core layer, for the light scattering is only obvious when the light power is well concentrated in the coupling layer. The AWG etching edge position deviation from the butt-joint boundary, however, exerts little influence on the PD quantum efficiency, which is believed not to bring obvious coupling loss during device fabrication. The higher UTC-PD collector refractive index is proved to be crucial for further better optical coupling from the coupling layer to the PD, with quantum efficiency rapidly increasing from around 0.1 to 0.8 when the index is increased from 3.20 to 3.42. By comparison, the efficiency is little affected by the coupling layer refractive index from 3.34 to 3.42.All things considered, we select a 10 m extended coupling layer, the refractive indices of both PD collector and the coupling layer to be 3.42, and align both the regrowth boundary edge and the AWG etching edge to the heterogeneous butt-joint boundary, and a PD quantum efficiency of 80% is expected. Owing to the extended coupling layer at the butt-joint, the SAG technique facilitates the PD fabrication process. The overgrown AWG top cladding layer ridge stretches out 4.67 m toward the PD, but not over the mesa yet, hence has little influence on the PD fabrication accuracy. The monolithic chip presents a uniform photodiode quantum efficiency of 76%, which accords well with theoretical value and confirms the butt-joint design. Central wavelengths for the four channels are 1347.0 nm, 1325.0 nm, 1308.0 nm, and 1286.5 nm, respectively. The low crosstalk level (below -22 dB) also indicates a good de-multiplexer performance.

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.

Arrayed waveguide gratings (AWG) are widely used as wavelength division multiplexers (MUX) and demultiplexers (DEMUX) in optical networks. Here we propose and demonstrate that conventional AWGs can also be used as integrated spectral filters to realize a Fast Fourier transform (FFT) and its inverse form (IFFT). More specifically, we point out that the wavelength selection conditions of AWGs when used as wavelength MUX/DEMUX also enable them to perform FFT/IFFT functions. Therefore, previous research on AWGs can now be applied to optical FFT/IFFT circuit design. Compared with other FFT/IFFT optical circuits, AWGs have less structural complexity, especially for a large number of inputs and outputs. As an important application, AWGs can be used in optical OFDM systems. We propose an all-optical OFDM system with AWGs and demonstrate the simulation results. Overall, the AWG provides a feasible solution for all-optical OFDM systems, especially with a large number of optical subcarriers.