Silica-based Arrayed Waveguide Grating Research Articles

Silica-Based Hybrid-Integrated Receiver Optical Subassembly for 400 Gbps Ethernet

A silica-based hybrid-integrated receiver optical subassembly (ROSA) for 400 Gbps Ethernet (400GbE) is demonstrated, which consists of an 8-channel silica-based arrayed waveguide grating (AWG), two 4-channel InP-based surface-illuminated photodetector (PD) arrays, two 4-channel transimpedance amplifier (TIA) arrays, and a high-frequency flexible printed circuit (FPC). All lanes of the ROSA exhibit responsivities of over 0.539 A/W, 3-dB bandwidths of greater than 30.86 GHz, and receiver sensitivities of less than −11.7 dBm. The ROSA has achieved a transmission rate of 8 × 50 Gbps for data center interconnect.

Compact Hybrid-Integrated 4 × 80-Gbps TROSA Module Using Optical Butt-Coupling of DML/SI-PD and Silica AWG Chips

We have developed a compact 4 × 80-Gbps transmitter-receiver optical subassembly (TROSA) module using a chip-to-chip optical butt-coupling method. For a Tx submodule, four directly modulated laser (DML) chips precisely bonded on a silicon DML-carrier are simultaneously butt-coupled to a vertically polished silica-based arrayed waveguide grating (AWG) chip, revealing good optical characteristics insensitive to external optical feedback. A Rx submodule is realized by passive alignment between a 45°-polished AWG and four surface-illuminated (SI)-PD chips, and subsequently integrated with the Tx submodule into a single package case to form the compact TROSA module whose size is only 25 mm × 15 mm × 6.4 mm and compliant to fit into the QSFP-DD/OSFP transceiver. The fabricated TROSA module shows clear Tx optical eye patterns at 80-Gbps PAM4 signals for all channels, achieving the Rx sensitivities within −7.1∼−6 dBm at a bit error rate (BER) of 2.4 × 10−4.

4?×?20 GHz silica-based AWG hybrid integrated receiver optical sub-assemblies

Both the 4×20 GHz coarse wavelength division multiplexing and LAN-WDM receiver optical sub-assemblies (ROSAs) were developed. The ROSA package was hybrid integrated with a planar lightwave circuit arrayed waveguide grating (AWG) with 2% refractive index difference and a four-channel top-illuminated positive-intrinsic-negative photodetector (PD) array. The output waveguides of the AWG were designed in a multimode structure to provide flat-top optical spectra, and their end facet was angle-polished to form a total internal reflection interface to realize vertical coupling with a PD array. The maximum responsivity of ROSA was about 0.4 A/W, and its 3 dB bandwidth of frequency response was up to 20 GHz for each transmission lane. The hybrid integrated ROSA would be a cost-effective and easy-assembling solution for 100 GbE data center interconnections.

Generation and manipulation of entangled photons on silicon chips

AbstractIntegrated quantum photonics is now seen as one of the promising approaches to realize scalable quantum information systems. With optical waveguides based on silicon photonics technologies, we can realize quantum optical circuits with a higher degree of integration than with silica waveguides. In addition, thanks to the large nonlinearity observed in silicon nanophotonic waveguides, we can implement active components such as entangled photon sources on a chip. In this paper, we report recent progress in integrated quantum photonic circuits based on silicon photonics. We review our work on correlated and entangled photon-pair sources on silicon chips, using nanoscale silicon waveguides and silicon photonic crystal waveguides. We also describe an on-chip quantum buffer realized using the slow-light effect in a silicon photonic crystal waveguide. As an approach to combine the merits of different waveguide platforms, a hybrid quantum circuit that integrates a silicon-based photon-pair source and a silica-based arrayed waveguide grating is also presented.

Compact Hybrid-Integrated 100-Gb/s TOSA Using EADFB Laser Array and AWG Multiplexer

We have developed a compact hybrid-integrated four-lane $\times 25.8$ Gb/s transmitter optical sub-assembly (TOSA) for a 100 Gb/s transceiver for 40-km transmission. The TOSA has a simple configuration in which a four-channel electroabsorption modulator integrated distributed feedback (EADFB) laser array is directly attached to the input waveguide end-faces of a silica-based arrayed waveguide grating (AWG) multiplexer. We integrated a lateral tapered spot-size converter for the EADFB laser to achieve a high optical butt coupling efficiency between the EADFB lasers array and the AWG multiplexer. We confirmed that the TOSA, which is $19.9~\text {mm} \,\times \, 6~\text {mm} \,\times \, 5.8$ mm, achieved error-free operation for a 40-km transmission with a high average optical output power of over 0.3 dBm at an operating temperature of 55 °C.

Compact Hybrid Integrated 100-Gb/s Transmitter Optical Sub-Assembly Using Optical Butt-Coupling Between EADFB Lasers and Silica-Based AWG Multiplexer

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.

Monolithic integration of a silica-based 16-channel VMUX/VDMUX on quartz substrate

A monolithic integrated variable attenuator multiplexer/demultiplexer is demonstrated. It is composed of a 16-channel 200 GHz silica-based arrayed waveguide grating and an array of Mach—Zehnder interferometer thermo-optic variable optical attenuators. The integrated device is fabricated on a quartz substrate, which eliminates the process of depositing the undercladding layer and reduces the power consumption compared with a device fabricated on a silicon substrate. The insertion loss and crosstalk of the integrated device are −5 dB and less than −22 dB, respectively. The power consumption is only 110 mW at the attenuation of 20 dB per channel.

Experimental Demonstration of Birefringence Compensation Using Angled Star Couplers in Silica-Based Arrayed Waveguide Grating

A birefringence compensation technique based on angled star couplers in arrayed waveguide grating (AWG) is experimentally investigated in silica-on-silicon waveguide with B–Ge codoped upper cladding. A 16-channel AWG with 100-GHz channel spacing is designed and fabricated. The star couplers are designed according to Rowland circle construction with an oblique incident/diffraction angle. Five different polarization compensation parameters corresponding to different incident/diffraction angles are employed to investigate the stress-induced birefringence. The experimental results confirm that the polarization-dependent wavelength shift <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $(\hbox{PD}\lambda)$</tex></formula> can be tuned by varying the incident/diffraction angle at the star couplers, and a birefringence-free AWG can be achieved without any additional fabrication process.

Monolithic integration of a silica AWG and Ge photodiodes on Si photonic platform for one-chip WDM receiver

On the silicon (Si) photonic platform, we monolithically integrated a silica-based arrayed-waveguide grating (AWG) and germanium (Ge) photodiodes (PDs) using low-temperature fabrication technology. We confirmed demultiplexing by the AWG, optical-electrical signal conversion by Ge PDs, and high-speed signal detection at all channels. In addition, we mounted a multichannel transimpedance amplifier/limiting amplifier (TIA/LA) circuit on the fabricated AWG-PD device using flip-chip bonding technology. The results show the promising potential of our Si photonic platform as a photonics-electronics convergence.

Reduction of Second-Order Temperature Dependence of Silica-Based Athermal AWG by Using Two Resin-Filled Grooves

We devise a novel design for an athermal silica-based arrayed-waveguide grating (AWG) to reduce the residual second-order temperature dependence of conventional athermal AWGs with a silicone-filled groove. This athermal AWG has two grooves filled with silicone and polyolefin that compensate for the first- and second-order temperature dependence, respectively. The passband wavelength variation is successfully reduced from 80 to 16 pm in a -40°C ~ +80°C temperature range.

Loss Uniformity Improvement of Arrayed-Waveguide Grating With Mode-Field Converters Designed by Wavefront Matching Method

We describe a silica-based arrayed-waveguide grating (AWG) with low channel-dependent loss variation achieved by using mode-field converters designed with the wavefront matching method. This mode-field converter converts the fundamental mode of the arrayed waveguide into the field distribution with a flat-top far field at the interface between the slab and output waveguides. We applied our mode-field converters to an AWG with a 100-GHz channel spacing and reduced the loss deviations experimentally from 2.4 to 0.7 dB over one free spectral range. Moreover, we confirmed that the introduction of our mode-field converters had no adverse effects on the AWG demultiplexing characteristics. It is notable that the loss uniformity was improved solely by replacing the conventional tapered waveguide between the arrayed waveguides and output slab waveguide with our mode-field converter without sacrificing the fabrication manageability or AWG design flexibility.

Compensation for Second-Order Temperature Dependence in Athermal Arrayed-Waveguide Grating Realizing Wide Temperature Range Operation

We propose a new compensation technique for the second-order temperature dependence in a silica-based arrayed-waveguide grating (AWG) multi/demultiplexer with a resin-filled groove that realizes a wide operating temperature range. We newly employ an additional interferometer in the input port and control the optical field perturbation by using a first-mode lightwave at the entrance to the first slab waveguide. We employ the design to fabricate a 32-channel 100-GHz-spacing athermal AWG that is as compact as a conventional AWG, and demonstrate a reduction in the passband wavelength variation from 70 to 22 pm over an extended - 40degC to 80degC temperature range.

50-GHz-Spacing Athermal Mach–Zehnder Interferometer-Synchronized Arrayed-Waveguide Grating With Improved Temperature Insensitivity

We describe a technique designed to compensate for the residual temperature sensitivity of an athermal silica-based arrayed-waveguide grating (AWG) and its application to a 50-GHz-spacing multi/demultiplexer with a low loss and a wide passband. The device has a Mach-Zehnder interferometer (MZI)-synchronized configuration, in which the AWG and the MZI are athermalized with resin-filled grooves. The point is that we employ a temperature-dependent phase-generating coupler (TD-PGC) in the MZI to compensate for the second-order temperature dependence of the AWG passband wavelength. The fabricated device exhibits practical characteristics including a low loss of less than 3.5 dB and a wide 0.5-dB bandwidth of 24.1 GHz as well as a reduced wavelength variation of less than 10 pm in a - 5degC to 65degC temperature range.

Estimated optimization parameters of arrayed waveguide grating (AWG) for C-band applications

In the present paper, we will investigate theoretically the basic design parameters of silica-based arrayed waveguide grating (AWG) in the C-band’s spectral range (from 1.528 to 1.56 μm). We have demonstrated theoretically that the minimum the diffraction order m, the maximum the number of the input/output wavelength channels, and the maximum the number of the arrayed waveguides. Also, we have investigated the optimization design parameters of AWG for C-band applications. Key words: Silica-based AWG, wavelength multiplexer, wavelength demultiplexer, dense wavelength division multiplexing (DWDM), free spectral range (FSR).

Flat-top silica-based arrayed waveguide grating with 40-channels

A flat response silica-based arrayed waveguide grating (AWG) with 40-channels and 0.8 nm (100 GHz) channel spacing has been designed and fabricated using multimode interferometer (MMI) at the end of input waveguide. Proper width of MMI is theoretically optimized using beam propagation method (BPM). An AWG with a 16 μm width MMI is fabricated experimentally. The measurement results show that the 3 dB bandwidth is 0.62 nm, insertion loss (IS) ranges from 5.2 dB to 7.5 dB, and the crosstalk is less than —20 dB. The 3dB bandwidth, channel numbers and channel spacing of the AWG agree well with the simulation values.

Flat-top arrayed waveguide grating using a tapered multimode interferometer

A 40-channel 0.8-nm-spaced flat-top silica-based arrayed waveguide grating (AWG) with a tapered multimode interferometer (MMI) at the end of its input waveguide has been experimentally demonstrated for the first time. By adding the MMI, the 1-dB and 3-dB bandwidths are increased to 0.45 and 0.62 nm, respectively. The insertion loss (IS) of the device ranges from 3.8 to 6.8 dB. The IS uniformity is better than 3.0 dB. The crosstalk is better than –25 dB. Compared to the AWG with a rectangular MMI, the AWG with a tapered MMI shows better IS, crosstalk, and ripple.

Dispersion resulting from wide passband shape in 50-GHz-spaced wavelength router

We report dispersions resulting from a slot device (SD) in silica-based arrayed-waveguide grating (AWG). A SD is used to produce flattened passbands and we show the dependence on the bandwidth, the crosstalk, the ripple, and the chromatic dispersion (CD) of the passband in the presence of such a device. A comparison with other known techniques is also given. The device has been developed on a high index silica-based PLC platform but can be implemented on higher index contrast platforms.

Elimination of PD- at all output ports of silica-based AWG

It is shown that the polarisation dependent wavelength shift (PD-λ) of a silica-based arrayed waveguide grating (AWG) is proportional to its output port location as a result of the birefringence in a slab waveguide. This PD-λ was eliminated to less than 0.01 nm by inserting a half waveplate across the slab waveguide.

A key component in optical systems: the silica-based arrayed waveguide grating (de)multiplexer. Overview and perspectives

In the ten past years, the telecommunication industry has experienced an unprecedented growth rate. To follow the exponential Bandwidth demand, new transmission technologies have emerged. Amongst them, we find Wavelength Division Multiplexing (WDM) technology. Its appearance coinciding with the emergence of key optical functions.

Reduction in dispersion of silica-based AWG using photosensitive phase trimming technique

The dispersion of a 25 GHz-spaced 64-channel silica-based arrayed waveguide grating (AWG) is reduced using a photosensitive phase trimming technique. The dispersion at the centre wavelength was reduced from about 170 to 30 ps/nm. Furthermore, we confirmed the same improvement in the dispersion for all 64 ports. The trimming technique is useful for realising fine AWGs with low crosstalk and dispersion.