Photonic devices and new functions based on HHI’s hybrid integration platform PolyBoard are presented providing lowloss thin-film-element-based light routing, an on-chip micro-optical bench and flexible chips comprising optical and electrical waveguides. The newly developed transfer and integration of graphene layers enables the fabrication of active optoelectronic devices in the intrinsically passive polymer waveguide networks with bandwidths in the GHz range. These novel functionalities in combination with the mature thermo-optic components of the PolyBoard platform such as tunable lasers, switches and variable attenuators pave the way towards new applications of photonic integrated circuits in communications and sensors.
A hybrid polymer/InP dual DBR laser at 1.5μm is presented as an optical source for heterodyne generation and detection of cw-THz signals. The device consists of an active InP chip as an active gain element, end-fire coupled to a polymer chip with thermo-optically tunable phase shifters and Bragg gratings. Mode-hop-free tuning of 1.1 THz has been achieved on the single DBR lasers. The usability of such sources for heterodyne cw-THz generation has been demonstrated in a coherent cw-THz setup. Scans in the THz range show a resolution of the H<sub>2</sub>O absorption lines comparable to the results achievable with commercially-available external-cavity diode lasers.
Recent progress on polymer-based photonic devices and hybrid photonic integration
technology using InP-based active components is presented. High performance thermo-optic
components, including compact polymer variable optical attenuators and switches are powerful
tools to regulate and control the light flow in the optical backbone. Polymer arrayed waveguide
gratings integrated with InP laser and detector arrays function as low-cost optical line terminals
(OLTs) in the WDM-PON network. External cavity tunable lasers combined with C/L band thinfilm
filter, on-chip U-groove and 45° mirrors construct a compact, bi-directional and color-less
optical network unit (ONU). A tunable laser integrated with VOAs, TFEs and two 90° hybrids
builds the optical front-end of a colorless, dual-polarization coherent receiver. Multicore polymer
waveguides and multi-step 45°mirrors are demonstrated as bridging devices between the spatialdivision-
multiplexing transmission technology using multi-core fibers and the conventional PLCbased
photonic platforms, appealing to the fast development of dense 3D photonic integration.
Electro-absorption modulated 10G and 25G DFB lasers (EML) are key components in transmission systems for long reach (up to 10 km) and extended reach (up to 80 km) applications. The next generation Ethernet will most likely be 400 Gb/s which will require components with even higher bandwidth. Commercially available EMLs are regarded as high-cost components due to their separate epitaxial butt-coupling growth process to separately optimize the DFB laser and the electro-absorption modulator (EAM). Alternatively the selective area growth (SAG) technique is used to achieve different MQW bandgaps in the DFB and EAM section of an EML. However for a lot of applications an emission wavelength within a narrow wavelength window is required enforcing a temperature controlled operation. All these applications can be covered with the developed EML devices that use a single InGaAlAs MQW waveguide for both the DFB and the EAM enabling a low-cost fabrication process similar to a conventional DFB laser diode. It will be shown that such devices can be used for 25Gb/s and 40Gb/s applications with excellent performance. By an additional monolithic integration of an impedance matching circuit the module fabrication costs can be reduced but also the modulation bandwidth of the devices can be further enhanced. Up to 70Gb/s modulation with excellent eye openings can be achieved. This novel approach opens the possibility for 100Gb/s NRZ EMLs and thus 4x100Gb/s NRZ EML-based transmitters in future. Also even higher bitrates seem feasible using more complex modulation formats such as e.g. DMT and PAM.
In the European projects EuroPIC and PARADIGM development of an InP based generic photonic integration technology is being undertaken to implement complex InP based application-specific photonic integrated circuits (ASPIC) with transmit and receive functionalities from a set of basic building blocks. The integration platform pursued at Fraunhofer HHI is building on semi-insulating substrate. Recently a variety of receiver-type PIC with up to 40 GHz bandwidth capability designed by external users was fabricated in multi-project wafer runs. Examples are demonstrated. Extension of this platform to include transmit functionalities is underway using an MOVPE based butt-coupling approach.
We have developed electroabsorption modulated ridge waveguide-based DFB Lasers for 4x25Gbit/s that comply with
the IEEE 100GBASE-ER4 Standard for 100Gbit-Ethernet. An identical InGaAlAs MQW layer stack is used in the DFB
and the EAM section. Devices from a single wafer show excellent 25Gbit/s modulation performance at all four
wavelengths with dynamic extinction ratios exceeding 9dB. All devices have facet output powers over +2.5dBm and are
operated semi-cooled at 45°C.
Low cost and compact transmitters are key components for short reach and datacom applications in fiber communication
systems. Bit rates of 40 Gbit/s are beyond the speed limitation of conventional directly modulated lasers. Lasers with an
integrated electro-absorption modulator (EML) represent one possible solution. An attractive alternative are Passive
Feedback Lasers (PFL). Here, the modulation bandwidth is significantly increased by an integrated feedback section.
Underlying physics and functionality of the PFL are presented as well as the successful realization at wavelengths in the
1300 nm and 1550 nm regions. The performance of these PFLs is demonstrated in system experiments.
Compound semiconductors provide state-of-the-art performance in optoelectronics, while silicon-on-insulator (SOI) is an ideal platform for many passive functions in integrated optics. By combining them one can realise optical devices with high performance and low cost. This paper discusses the various applications and technologies for integrating InP chips with SOI waveguides. Bonding of lasers, SOA arrays and detectors for practical applications is described. Experimental results are given for visually aligned thermo-compression bonding and self-aligned flip-chip bonding with Indium bumps. Flip-chip bonding is reported directly on SOI chips, as well as on a separate silicon-optical-bench.
A novel DFB laser structure, referred to as CSDFB, is presented that, different from conventional designs, simultaneously allows to obtain very high yield single mode behaviour even without applying facet coatings, high slope efficiency, and low beam divergence. These advantages result from the incorporation of a curved and tapered laser waveguide designed such that a constant period DFB grating can be utilized. Preliminary feedback measurements have indicated enhanced immunity to optical back-reflection in comparison to a conventional DFB structure. The CSDFB design has large potential of reducing transmitter costs due to both reduced chip and module fabrication costs.
"Berlin Access", a regional R&D project carried out by six companies and Heinrich Hertz Institute, Fraunhofer
Society, is geared towards low cost solutions for fibre access network architectures (PON and CWDM-PON), ONU
transceivers, and passive fibre components. Close communication with system manufacturers, non-incumbent
carriers, and a city services supplier implementing a local FTTH network supports orientation towards market
demands. In this paper we report on a new FTTH transceiver based on an all-polymer PLC motherboard. The
waveguides exhibit high transmission, strong optical confinement, and large operation temperature range. Low loss
passively adjusted fibre/PLC coupling is achieved by employing a waveguide taper. Downstream/upstream
wavelength separation is accomplished by a directional coupler, or, alternatively, a thin film filter inserted into the
input/output waveguide (the latter approach also allowing for the provisioning of an overlay broadcasting channel).
The horizontal-cavity surface-emitting laser diode, the pin-photodiode (equipped with a thin film filter for improved
crosstalk suppression), and the monitor diode are all flip-chip surface mounted; the light being coupled via 45°
waveguide mirrors. Chip mounting can be done with a commercial fineplacer using semi-active automatic
alignment. Micro-strip lines with impedances adapted to both laser and photodiode are fabricated on the basis of the
PLC films. The polymer motherboard integration scheme offers compact transceiver optical subassemblies and lends
itself favourably to highly automized, low cost manufacturing with high yield. Extended functionalities like loss of
light alarm or concepts for colourless CWDM ONUs can be easily realized with this concept.
Recent development trends in InP-based optoelectronic devices are illustrated by means of selected examples. These include lasers for uncooled operation and direct modulation at 10 Gbit/s, complex-coupled lasers, which exhibit particularly low sensitivity to back reflections as well as monolithic mode-locked semiconductor lasers as ps-pulse sources for OTDM applications. Furthermore, a Mach-Zehnder interferometer modulator for high bit rate applications (40 Gbit/s and beyond) is described, and finally, photoreceivers and ultra high-speed waveguide-integrated photodiodes with > 100 GHz bandwidth are presented, which are key component for high bit rate systems, advanced modulation format transmission links, and for high speed measurement equipment as well.
InGaAs/InGaAsP-multi-quantum--well-layers are preferably used as the active region in long-wavelength semiconductor lasers. In this work we present calculations of their optical gain in dependence of the carrier density . These calculations are compared with measurements of electrically and optically excited gain spectra of such laser structures for 1. SSim emission wavelength with different numbers of wells. In contrast to conventional double heterostructure lasers a distinct sublinear increase of the gain g with increasing carrier densities N is observed which is well pronounced for low well numbers and can be described approximately with a logarithmic equation g''''ln(N) quite in accordance with theoretical predictions.