We present the introduction of high-speed phase modulators based on the quantum-confined Stark effect to the generic InP foundry platform at Fraunhofer HHI. An overview of the technological integration of the high-speed phase Mach-Zehnder modulators (MZM) to the existing generic foundry process is described. In addition, an electro-optical behavioral model for the high speed MZM, which gives insight into the influence of design parameters on performance, is discussed. The presented MZM structure with a traveling wave electrode length of 5 mm has a $V_\pi$ of 1.4 V and a small signal electro-optic 3 dB bandwidth of 32 GHz. Large signal RF operation up to 80 Gbps is demonstrated. To the best of our knowledge, these are the highest-performance MZMs in an InP open access integrated photonics foundry platform.

This paper describes a fabrication process for realizing Indium-Phosphide-based photonic-integrated circuits (PICs) with a high level of integration to target a wide variety of optical applications. To show the diversity in PICs achievable with our open-access foundry process, we illustrate two examples: a fully-integrated 20 Gb/s dual-polarization electro-absorption-modulated laser, and a balanced detector composed of avalanche photodiodes for detection of 28 Gb/s optical signals. On another note, datacenters are increasingly relying on hybrid integration of PICs from different technology platforms to increase transmission capacity, while simultaneously lowering cost, size, and power consumption. Several technology platforms require surface coupling rather than the traditional edge coupling to couple the light from one PIC to another. To accommodate the surface-coupling approach in our integration platform, we have developed a strategy to transfer the following optical Input/Output devices into our fabrication process: grating couplers, and vertical mirrors. In addition, we introduced etched facets into the process to improve the usability of our edge-coupling elements. We believe that the additional flexibility in Input/Output interfacing combined with the integration of multiple devices onto one PIC to reduce the number of PIC-to-PIC alignments can contribute significantly to the development of compact, low-cost, and high-performance datacenter modules.

A fabrication tolerant polarization rotator (PR) building block is added to our generic photonic integration technology. Using asymmetric waveguides, we propose a PR with guided modes that do not enclose a 45 degrees angle with the substrate. Rather, we find that polarization performance and loss can be improved substantially by allowing the mode angles to vary along the device. We numerically optimize PR designs, targeting at high extinction and high fabrication tolerance. The optimization makes use of the Jones formalism and the fact that Jones calculus is numerically much faster than beam propagation methods. A comparison of our Jones model and commercial simulation software shows excellent agreement. Fabricated devices show a polarization extinction between 10 and 14 dB across different wafers, at an excess lass of 1 dB. Compared to PR designs without tapers, the loss is 3 dB lower and the polarization extinction is now reproducible from wafer to wafer.

We propose and demonstrate a transmit-type photonic integrated circuit (PIC) for polarization multiplexing applications. With a single integrated DFB laser source, the PIC generates two independently modulated states of polarization. The PIC is used for 40 Gbit/s transmission.

We have achieved monolithic integration of photodetectors, DFB- and DBR lasers, SOAs, spot-size converters, polarization-rotators and splitters, EAMs, and passive-waveguide devices on InP technology. This generic foundry process provides endless possibilities for PIC designers.

A schematic of our DP-EAM PIC is shown in fig. 1(a). For incident light, only the TE component will be modulated by the signal applied to the first EAM. The entire polarization state is then turned by 90°, effectively swapping the TE and TM components. The second EAM will only modulate the previously unmodulated component and leave the already modulated component unaffected. The serial nature of this design brings two advantages: no splitters or combiners are needed, and there is no routing which requires bends. All this makes the design more compact and reliable. Most critical in this concept is a polarization converter (PC) with a high polarizationconversion efficiency. We reported on PCs in [2] recently. With respect to [2], here we introduced tapers to the design to lower the PC insertion loss. The PC is oriented perpendicular to the large flat of the wafer (as opposed to parallel to the large flat in [2]), resulting in a circular sidewall instead of a slanted one, see fig. 1(c). This enables an identical orientation of the PCs and the EAMs.

In this work, we report on experimental results of a fully integrated polarization converter made in InP. The device relies on slanted side wall waveguides. Using a novel design, we are able to demonstrate 15 dB of polarization extinction ratio (PER) for a fabrication tolerance of > 250 nm with respect to the critical waveguide width. The design of the device was derived using a new fully analytical model. No active tuning is required.

Selective area growth (SAG) technology has been added to an established InP monolithic integration platform to fabricate arrays of multi-wavelength distributed feedback (DFB) lasers. The local epitaxy growth rate is controlled by the SiO 2 mask width, and different quantum well (QW) thicknesses can be obtained in one run. The laser wavelengths span from 1447 nm to 1602 nm. The DFB lasers may include amplifying sections at the front and/or rear side. Output power up to 18 mW is achieved. This technology opens up possibilities to integrate various passive and active components such as lasers, modulators, detectors with different operating wavelengths monolithically on one wafer with less regrowth steps and reduced fabrication complexity.

This paper describes the development of a very-versatile InP-Based Photonic-Integration platform by Butt-Joint integration of the passive waveguides to active waveguides across a relatively high mesa of 34μm. The Butt-Joint losses are currently around 1dB.

We demonstrate a fully integrated polarization beam splitter with a polarization extinction ratio above 25dB for both polarization states and an insertion loss of 2.5dB. The footprint of the device including electrical contacts is 0.4×2mm2. A Mach-Zehnder configuration is used, the birefringence in both arms differs due to different waveguide widths. Fabrication tolerances can be compensated with thermal tuning. The device is realized in our generic integration platform, making it viable to provide monolithically integrated solutions for polarization diversity applications.

A directly modulated 1.55-μm buried-heterostructure passive feedback laser exhibits a high modulation bandwidth of up to 34 GHz at moderate distributed-feedback (DFB) section currents between 20 and 60 mA. A very flat frequency response and a low alpha parameter have been demonstrated in the small signal modulation analysis. The device has open eyes at data rates of 25 and 40 Gb/s with reduced frequency chirp.

An electroabsorption modulator (EAM) was integrated with a distributed feedback laser and a spot-size expander forming an electro-modulated laser (EML) device. The EMLs are based on the conventional InP/InGaAsP material system and are designed for flip-chip mounting. They rely on a buried heterostructure with Fe-doped blocking layers, and the EAM section is optically butt-joint-coupled. The performance of EMLs with two different EAM lengths is reported. 150 μm long EAM sections can be operated with an f3dB bandwidth of 25 GHz allowing an error-free large signal modulation at 25 Gb/s with a dynamic extinction ratio (ER) of 11 dB. With 100 μm long EAM sections, the f3dB bandwidth increases up to 33 GHz. Large signal modulation at 40 Gb/s is achieved with a dynamic ER of more than 8 dB. Transmission of 40 Gb/s over 2 km is demonstrated.

An electroabsorption modulator (EAM) was integrated with a distributed feedback laser and a spot-size expander forming an electro-modulated laser (EML) device. The EMLs are based on the conventional InP/InGaAsP material system and are designed for flip-chip mounting. They rely on a buried heterostructure with Fe-doped blocking layers, and the EAM section is optically butt-joint-coupled. The performance of EMLs with two different EAM lengths is reported. 150 mu m long EAM sections can be operated with an f3dB bandwidth of 25 GHz allowing an error-free large signal modulation at 25 Gb/s with a dynamic extinction ratio (ER) of 11 dB. With 100 mu m long EAM sections, the f3dB bandwidth increases up to 33 GHz. Large signal modulation at 40 Gb/s is achieved with a dynamic ER of more than 8 dB. Transmission of 40 Gb/s over 2 km is demonstrated.

1.55μm electroabsorption-modulated laser (EML) devices designed for flip-chip mounting have been developed including a DFB laser, a butt joint coupled electroabsorption modulator (EAM), and a spot-size expander. Flip-chip mounting enables array-like arrangements of individually optimized discrete chips to be placed on optical PLC platforms like Silicon-on-Insulator (SOI) boards. The EMLs are based on the conventional InP/InGaAsP material system and rely on a buried heterostructure with Fe doped InP blocking. Large signal modulation at 25 Gb/s and 40Gb/s with high extinction ratio is demonstrated.

The integration potential of waveguide-integrated photodiodes is demonstrated by a novel broadband self-powered photodetector with 72 GHz bandwidth, >55 dBd. dynamical range, and a packaged pin-antenna chip for sub-THz applications suitable as transmitter and receiver.

40 Gbit/s open eyes are demonstrated for a passive feedback laser transmitter with complex coupled DFB section. The transmitter shows superior single mode emission in combination with chirp tuning capability and high reliability.

Complex-coupled and index-coupled DFB lasers are fabricated and characterized regarding their feedback sensitivity. The feedback stability is improved by 15 dB using the complex coupling. BER measurements demonstrate the potential for isolator-free transmitter application.