Coarse Wavelength Division Multiplexing Applications Research Articles

Ultra-Compact Low Loss Polymer Wavelength (De)Multiplexer With Spot-Size Convertor Using Topology Optimization

Polymer waveguides are considered to be good candidates for optical interconnects application due to their advantages such as flexibility, good compatibility, and versatility for realizing 3D and micro structures. However, constrained by the limited degrees of freedom provided by template-based design approaches, there lacks a satisfying solution which achieves small footprint and low loss simultaneously. Inverse design has been proposed to improve the performance. However, most inverse design methods target at silicon-based optical devices optimization which has a relatively high refractive index difference. In this paper, we demonstrate an ultra-compact low loss polymer wavelength (de)multiplexer with spot-size conversion structure to interposing Si and optical fiber using gradient-based topology optimization and downhill simplex method. The 2-channel wavelength (de)multiplexer displays an excess propagation loss of 0.84 dB and 1.06 dB at 1310 nm and 1550 nm, respectively, with a total footprint of 245 × 35 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The 4-channel wavelength (de)multiplexer for coarse wavelength division multiplexing applications with 20 nm spacing (1270, 1290, 1310, and 1330 nm) with an excess waveguide propagation loss of 1.72 dB within 271 × 50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has also been demonstrated and all the output ports of the polymer wavelength demultiplexing structure achieved a conversion efficiency over 90%.

1.3-µm 4×25-Gb/s hybrid integrated TOSA and ROSA

The design and fabrication of a compact and low-cost 4×25-Gb/s transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA) using a hybrid integrated technique are reported. TOSA and ROSA are developed without thermoelectric cooler for coarse wavelength division multiplexing applications. Physical dimension of the packaged optical subassembly is limited to 11.5 mm×5.4 mm×5.4 mm. The design of TOSA and ROSA is employed using a silica-based arrayed waveguide grating chip to select the specific channel wavelength at O-band. In TOSA, the wavelength of four 1.3-µm discrete directly modulated laser chips is well controlled based on the reconstruction equivalent chirp technique. In the back-to-back transmission test, bit error rates for all lanes of cascade of the TOSA and ROSA are small. A clear opening eye diagram is obtained.

Compact, silicon-on-insulator, series-cascaded, contradirectional-coupling-based filters with >50 dB adjacent channel isolation.

In this work, we present optical add/drop multiplexer (OADM) filters for coarse wavelength-division-multiplexing (CWDM) systems with high sidelobe suppressions that result in high adjacent channel isolations (Ai). The filters are realized by using a compact, series-cascaded configuration of apodized, contradirectional-coupling-based filters. We experimentally demonstrate a device with a measured Ai of 53dB (these devices hold the promise of achieving even higher Ais). While having large Ais, our devices have the wide bandwidths and low insertion losses required for CWDM applications. In addition, our demonstrated OADM has a nearly constant group delay, which results in low dispersion in the passband.

Monolithic quantum-dot distributed feedback laser array on silicon

Electrically-pumped lasers directly grown on silicon are key devices interfacing silicon microelectronics and photonics. We report here, for the first time, an electrically-pumped, room-temperature, continuous-wave (CW) and single-mode distributed feedback (DFB) laser array fabricated in InAs/GaAs quantum-dot (QD) gain material epitaxially grown on silicon. CW threshold currents as low as 12 mA and single-mode side mode suppression ratios (SMSRs) as high as 50 dB have been achieved from individual devices in the array. The laser array, compatible with state-of-the-art coarse wavelength division multiplexing (CWDM) systems, has a well-aligned channel spacing of 20 0.2 nm and exhibits a record wavelength coverage range of 100 nm, the full span of the O-band. These results indicate that, for the first time, the performance of lasers epitaxially grown on silicon is elevated to a point approaching real-world CWDM applications, demonstrating the great potential of this technology.

Demonstration and Fabrication Tolerance Study of Temperature-Insensitive Silicon-Photonic MZI Tunable by a Metal Heater

We present a temperature-insensitive tunable silicon-photonic Mach–Zehnder interferometer (MZI) filter fabricated by deep ultraviolet lithography. The wavelength shift of the MZI filter depending on temperature is reduced down to −4 pm/°C at ∼1480 nm using a design with waveguide narrowing and widening, and the MZI filter is tunable with a thermal heater at an efficiency of 24 mW/free spectral range (FSR). The FSR of the MZI is about 5.8 nm, which corresponds to a channel spacing of 2.9 nm for a two-channel MZI. We discuss the fabrication tolerance of the fabricated MZI according to experimental and simulation results and show design parameters for a fabrication-tolerant temperature-insensitive MZI with a 20-nm channel spacing for coarse wavelength-division multiplexing application.

Benchmarking Si, SiGe, and III–V/Si Hybrid SIS Optical Modulators for Datacenter Applications

Recently, Si-photonics received a growing interest and started to move from laboratories to industrial product development, mainly for the applications inside data-centers. One of the weaknesses of Si is its relatively low plasma dispersion efficiency, making the size of phase modulator large. This efficiency can be improved by using the heterogeneous integration of material such as InP, InGaAsP, or SiGe to fabricate hybrid semiconductor–insulator–semiconductor (SIS) optical phase modulators. At the same time, the standard figure of merit for modulator benchmarking $V_{\pi }L_{\pi }$ does not consider the dynamic behavior of the SIS devices, nor is making the link with the system level specifications such as optical modulation amplitude (OMA), widely used in 100G to 400G parallel single mode or coarse wavelength division multiplexing applications. In this paper, we propose to simply link the modulator performance to the OMA, to derive a compact model for SIS devices and to compare hybrid device performances for various materials.

Improved dropping efficiency in two-dimensional photonic crystal-based channel drop filter for coarse wavelength division multiplexing application

We study the two-dimensional photonic crystal (PC) square lattice structure to design a channel drop filter. The channel drop filter (CDF) is designed using a PC ring resonator structure because of its better response. The variation in the shape of scatterer rods causes the shift in resonant wavelength and also shows an improvement in quality factor as well as dropping efficiency. The dropping efficiency is improved from 92.7% to 99.5% for a particular wavelength at 1531 nm, which is especially used in telecommunication. The designed CDF structure is useful for coarse wavelength division multiplexer. The size of the device is very small, so these devices can play an important role in optical communication networks and photonic integrated circuits.

Investigation of AWG demultiplexer based SOI for CWDM application

9-channel Arrayed Waveguide Grating (AWG) demultiplexer for conventional and tapered structure were simulated using beam propagation method (BPM) with channel spacing of 20 nm. The AWG demultiplexer was design using high refractive index (n~3.47) material namely silicon-on-insulator (SOI) with rib waveguide structure. The characteristics of insertion loss, adjacent crosstalk and output spectrum response at central wavelength of 1.55 μm for both designs were compared and analyzed. The conventional AWG produced a minimum insertion loss of 6.64 dB whereas the tapered AWG design reduced the insertion loss by 2.66 dB. The lowest adjacent crosstalk value of -16.96 dB was obtained in the conventional AWG design and this was much smaller compared to the tapered AWG design where the lowest crosstalk value is -17.23 dB. Hence, a tapered AWG design significantly reduces the insertion loss but has a slightly higher adjacent crosstalk compared to the conventional AWG design. On the other hand, the output spectrum responses that are obtained from both designs were close to the Coarse Wavelength Division Multiplexing (CWDM) wavelength grid.

Quantum well intermixed waveguide grating

A waveguide grating have been designed suitable for Coarse Wavelength Division Multiplexing applications in which the refractive index is perturbed by the spatial tailoring of the band gap with fluorine ion implanted quantum well intermixing of the In0.95Ga0.05As0.10P0.90/InP multi quantum well structure. The gratings have been modeled using coupled mode theory and diffusion equations and Schrodinger wave equations are used to model quantum well energy while interdiffusion. A four channel waveguide grating from 1,550 to 1,610 nm at a span of 20 nm have been simulated with a channel bandwidth of 13 nm and a cross talk of −5 to −10 dB.

The temperature dependence of InGaAs single-wavelength quantum well and multi-wavelength quantum dot square resonator microlasers

In this paper, we examine the performance of distinct InGaAs quantum well and quantum dot square resonator microlasers at different temperatures (−20, 20 and 50 °C) under optical pumping. The quantum well laser operates at a single wavelength (single-mode operation is achieved by the introduction of air trenches at the nodes of a selected mode) while the quantum dot laser array operates at three distinct wavelengths 1140, 1160 and 1180 nm, which makes it suitable for coarse wavelength division multiplexing applications. We show not only multi-wavelength lasing operation on the same quantum dot chip, but also the relatively stable operation of quantum dot devices over a wide range of temperatures.

Design of an arrayed waveguide grating optical demultiplexer for CWDM applications

A proposed arrayed waveguide grating (AWG) demultiplexer (DEMUX) design for coarse wavelength division multiplexing (CWDM) networks is described in which two cascaded AWG are used to obtain a flat-top passband with steep roll-off and wide channel bandwidth. Scalar electromagnetic simulations are used to verify the operation of four-and eight-channel devices satisfying the standard International Telecommunication Union (ITU) grid for CWDM. The devices show good channel uniformity with very low crosstalk in the range of −60 dB in the case of the four-channel demultiplexer.

Experimental assessment of some Raman fiber amplifiers solutions for coarse wavelength division multiplexing applications

Raman amplification will, in a closer future, penetrate into the access network, bringing new challenges and difficulties to be overcome. In this article, we present the performance assessment of Raman amplification solutions suitable for Coarse Wavelength Division Multiplexing (CWDM) access networks applications. For this purpose, a pumping scheme with three lasers allows a bandwidth of 78 nm which is suitable for four CWDM channels. For this scheme, the gain and noise figure dependence with the pumping configuration was evaluated. The gain equalization was experimentally obtained based on a previously developed model using the Genetic Algorithm (GA) for pump allocation. A comparative study of Raman amplification in different types of Raman fibers (single mode fiber and dispersion shifted fiber) is also presented as well as the use of composite links. Those applications were tested in a local network and the obtained results comply with the modeling foreknowledge, showing the feasibility of Raman amplification over CWDM networks.

Manufacturing of laser diodes grown by molecular beam epitaxy for coarse wavelength division multiplexing systems

Molecular beam epitaxy (MBE) was used to grow ridge-waveguide distributed feedback (DFB) lasers for uncooled coarse wavelength division multiplexing applications. The lasers covered a wavelength range from 1270to1610nm and a temperature range of at least −20to85°C. The MBE growth includes atomic hydrogen cleaning of exposed InGaAsP surfaces for regrowth over a DFB grating. The devices show good performance over the whole wavelength range, with 85°C median threshold currents from 25to40mA depending on the wavelength. Accelerated lifetime testing indicates minimal degradation with TO packaged devices showing less than a 1% increase in operating current after 4000h at 85°C.

S-C-L triple-band double-pass erbium-doped silica fiber amplifier with an embedded DCF module for CWDM applications

In this paper, the authors present a double-pass triple-band doped fiber amplifier including an embedded dispersion-compensating fiber. The amplifier employs only silica-based erbium-doped fibers to achieve signal amplification over S-, C-, and L-bands. Experimental characterization is carried out in terms gain and noise figure over the coarse-wavelength-division-multiplexing (CWDM) wavelength grid. By providing optical gain to seven CWDM channels spectrally located between 1490 and 1610 nm, the amplifier can extend the reach of a CWDM optical bus well beyond the 100-km limit