W Weiming Yao

An introduction to InP-based generic integration technology

Photonic integrated circuits (PICs) are considered as the way to make photonic systems or subsystems cheap and ubiquitous. PICs still are several orders of magnitude more expensive than their microelectronic counterparts, which has restricted their application to a few niche markets. Recently, a novel approach in photonic integration is emerging which will reduce the R&D and prototyping costs and the throughput time of PICs by more than an order of magnitude. It will bring the application of PICs that integrate complex and advanced photonic functionality on a single chip within reach for a large number of small and larger companies and initiate a breakthrough in the application of Photonic ICs. The paper explains the concept of generic photonic integration technology using the technology developed by the COBRA research institute of TU Eindhoven as an example, and it describes the current status and prospects of generic InP-based integration technology.

-1 V bias 67GHz bandwidth Si-contacted germanium waveguide p-i-n photodetector for optical links at 56 Gbps and beyond

We demonstrate a 67 GHz bandwidth silicon-contacted germanium waveguide p-i-n photodetector operating at -1 V with 6.8 fF capacitance. The dark current is below 4 nA. The responsivity is 0.74 A/W at 1550 nm and 0.93 A/W at 1310 nm wavelength. 56 Gbps on-off-keying data reception is demonstrated with clear open eye diagrams in both the C-band and O-band.

Experimental and Numerical Study of Electrical Crosstalk in Photonic-Integrated Circuits

This paper presents measurement results on electrical crosstalk between interconnect lines and electro-optical phaseshifters in photonic-integrated circuits. The results indicate that overall crosstalk originates from radiative and substrate coupling between lines and from shared ground connections. The latter is the main noise source in the structures measured in this paper and keeps crosstalk above -25 dB for interconnects and above -20 dB for phase-shifters independent of coupling distance. Measurements on the effect of electrical crosstalk on optical modulation show that -20 dB of coupling degrades modulation performance significantly, leading to at least 2-dB power penalty. A simulation approach is presented that reproduces the experimental results and gives insight into crosstalk mechanisms.

High-bandwidth uni-traveling carrier waveguide photodetector on an InP-membrane-on-silicon platform

A uni-traveling carrier photodetector (UTC-PD), heterogeneously integrated on silicon, is demonstrated. It is fabricated in an InP-based photonic membrane bonded on a silicon wafer, using a novel double-sided processing scheme. A very high 3 dB bandwidth of beyond 67 GHz is obtained, together with a responsivity of 0.7 A/W at 1.55 μm wavelength. In addition, open eye diagrams at 54 Gb/s are observed. These results promise high speed applications using a novel full-functionality photonic platform on silicon.

Substrate thickness effects on thermal crosstalk in InP-based photonic integrated circuits

We experimentally demonstrate the substrate thickness effect on thermal crosstalk between active and passive components in Indium Phosphide based photonic integrated circuits. The thermal crosstalk is quantified by measuring the effects on the electro-optical response of a MZ modulator considered as a test structure. The heat sources are represented by semiconductor optical amplifiers placed at different distances with respect to the position of the MZ. For a fixed substrate thickness (t), the dc switching curve drift reduces exponentially with the increase of distance (d) between MZ and heating source. We show how the amount of drift depends on the ratio between d and t. d/t >1 is the best condition to minimize the thermal effects, while d/t <; 1 heavily affects the MZ dc switching curve resulting in a reduction of its extinction ratio.

Performance degradation of integrated modulator arrays due to electrical crosstalk

This paper reports on the performance degradation of optical modulators in an array due to electrical crosstalk. Bit-Error-Rate measurements reveal that additional power penalties are introduced due to crosstalk noise.

Observation of Dynamic Extinction Ratio and Bit Error Rate Degradation Due to Thermal Effects in Integrated Modulators

We experimentally demonstrate how the thermal crosstalk between active and passive components limits the performance of integrated Mach-Zehnder (MZ) modulators operating in the radiofrequency regime. To evaluate the role of the distance between active and passive components, the MZs are placed at different distances with respect to a semiconductor optical amplifier that represents the heat source. The thermal crosstalk is quantified by measuring the effects on the electro-optical response of MZ modulators considered as the test structure. Both extinction ratio and bit error rate degradation are measured. The proposed investigation allows the introduction of design rules, based on the minimum distance between components to ultimately avoid unwanted thermal effects. According to the result provided by our analysis, we also show how the ER degradation can be recovered.

Performance Degradation of Integrated Optical Modulators Due to Electrical Crosstalk

In this paper, we investigate electrical crosstalk in integrated Mach-Zehnder modulator arrays based on n-doped InP substrate and show that it can be the cause for transmitter performance degradations. In particular, a common ground return path between adjacent modulators can cause high coupling noise up to -20 dB which leads to system power penalties of more than 10 dB at 10 Gb/s OOK modulation. Furthermore, we demonstrate that electrical crosstalk is significantly reduced in the absence of the shared ground and that it varies with modulator separation distance. Experimental results are shown that indicate a crosstalk tolerance of -40 dB for 1 dB power penalty at 10 Gb/s.

Monolithic Tunable Coupled-Cavity WDM Transmitter in a Generic Foundry Platform

We present the monolithic integration of an extended tuning range coupled-cavity laser with traveling-wave Mach–Zehnder modulators in a low-cost generic photonic foundry platform for 10 Gb/s operation. Using an intra-cavity Michelson interferometer combined with on-chip reflectors, the coupled-cavity laser shows a tuning range of 25 nm. The modulator building blocks with optimized traveling wave electrodes exhibit efficient modulation and 8.5-GHz electro-optic bandwidth, enabling 10 Gb/s ON–OFF keying. We demonstrate error-free operation of the tunable transmitter in a full photonic circuit environment. The laser modulator combination neither requires Bragg grating formation for wavelength tuning nor additional growth steps for multiquantum-well material in the modulator section and is therefore well suited for cost effective foundry platforms specifically for low-cost applications.

InP-Based Generic Foundry Platform for Photonic Integrated Circuits

The standardization of photonic integration processes for InP has led to versatile and easily accessible generic integration platforms. The generic integration platforms enable the realization of a broad range of applications and lead to a dramatic cost reduction in the development costs of photonic integrated circuits (PICs). This paper addresses the SMART Photonics generic integration platform developments. The integration technology based on butt joint active-passive epitaxy is shown to achieve a platform without compromising the performance of the different components. The individual components or building blocks are described. A process design kit is established with a comprehensive dataset of simulation and layout information for the building blocks. Latest results on process development and optimization are demonstrated. A big step forward is achieved by applying high-resolution ArF lithography, which leads to increased performance for AWGs and a large increase in reproducibility and yield. The generic nature of the platform is demonstrated by analyzing a number of commercial multiproject wafer runs. It is clear that a large variety of applications is addressed with more than 200 designs from industry as well as academia. A number of examples of PICs are displayed to support this. Finally, the design flow is explained, with focus on layout-aware schematic-driven design flow that is required for complex circuits. It can be concluded that generic integration on InP is maturing fast and with the current developments and infrastructure it is the technology of choice for low cost, densely integrated PICs, ready for high-volume manufacturing.