Veli Heikkinen

Single-mode tuning of a 1540-nm diode laser using a Fabry-Pe/spl acute/rot interferometer

We realized a wavelength-tunable laser using a 1540-nm Fabry-Pe/spl acute/rot diode laser and a silicon surface micromachined Fabry-Pe/spl acute/rot interferometer device in the short external cavity configuration. This hybrid-integrated system enables the use of standard laser chips and potentially has a low cost. We obtained single-mode tuning of 13 nm, a sidemode suppression ratio of better than 25 dB, and an average single-mode fiber-coupled power of 100 /spl mu/W. The emitter can be employed in optical communication and fiber-optic sensor applications.

Wavelength-tunable laser module using low-temperature cofired ceramic substrates

We realized a prototype series of the 1550-nm band wavelength-tunable laser module. The edge-emitting Fabry-Perot diode laser operates in the short external cavity configuration and is tuned by a silicon surface micromachined Fabry-Peacuterot interferometer device. Low-temperature cofired ceramic (LTCC) substrate technology was used in the module packaging to enable the passive alignment of the photonic components. Low conductor resistance and dielectric loss, multilayer structures with fine-line capability, compatibility with hermetic sealing, and the ability to integrate passive electrical components (resistors, capacitors, and inductors) into the substrate make LTCC a useful technology for telecommunication applications. In addition, the fair match of the thermal expansion coefficient to optoelectronic chips reduces packaging-induced thermomechanical stresses. The precision three-dimensional (3-D) structures, such as cavities, holes, and channels manufactured in the ceramic parts, ease the packaging process via the passive assembly. The wavelength tuning range of the realized modules ranged from 8 to 19 nm and single-mode fiber-coupled output power was between 100 and 570 muW. The hybrid arrangement uses standard laser chips and, therefore, potentially provides a cost-effective and easily configurable solution for last-mile fiber optic communications

Fiber-optic transceivers for high-speed intra-satellite links

High-bit-rate fiber-optic transmitter and receiver components were developed for intra-satellite data links, which will benefit from reduced EMI and savings in mass and volume. The ceramic-based fiber-optic packages enable robustness for harsh environments. Two kinds of components were introduced: “SpaceFibre” transceivers (>;6 Gbps) and parallel optic transceivers with fiber ribbon cables (4+4 x 10 Gbps), both based on 850-nm VCSEL sources and multimode fibers. The transceivers are expected suitable also for other harsh environment applications.

Inexpensive packaging techniques of fiber pigtailed laser diodes

Commercial single heterojunction GaAs laser diode chips have been fiber pigtailed with a 100/140 micrometers fiber. These lasers, producing 5 ... 10 W peak pulse power, are used in time-of-flight distance measurement instruments. The laser chips were purchased mounted on a coaxial TO-5 base. Two different types of packaging constructions were tested: a sleeve construction and a butt construction. In the sleeve construction the fiber was aligned with the laser chip using a loose sleeve and a fiber ferrule. In the butt construction the fiber ferrule was butt coupled to the laser submount. The fiber ferrule was actively aligned with the laser and fixed with an adhesive or with an adhesive and laser welding. Silicone gel potting was tested to improve the module stability in outdoor applications. The pigtailed laser modules and commercial laser modules were temperature cycled and results were compared. The measurements show that the properties of the adhesive are crucial to the temperature stability of the module. The tests show that optical output variation of the module was 6 dB in the temperature range of -20 ... 55 degree(s)C when the peak power was 3.7 W at room temperature. The stability of poor adhesive joints can be improved utilizing laser welding. However, the drawback is the high investment cost of equipment required. The results show that simple and inexpensive fiber pigtailed modules can be made using properly selected adhesives.

Packaging considerations of fiber-optic laser sources

The continuous progress in material and component technology has generated new laser-based applications that require special packaging techniques. Hybrid integration offers a flexible method to accomplish custom design needs. This paper discusses several aspects in fiber optic packaging including optical, thermal, and mechanical issues. Special emphasis is on optical coupling between a laser diode and a single-mode fiber.

MEMS, MOEMS, RF-MEMS and photonics packaging based on LTCC technology

In order to fulfill the specifications of photonic systems, various optoelectronic chips, MEMS, MOEMS and RF-MEMS devices, micro-optical elements and integrated circuits needs to be integrated into functional components, modules and systems. The sub-systems of the photonic system must be fabricated by the use of cost-efficient, reproducible, well-established, high-volume manufacturing technologies. The functionality of the system is outlined by the combination of the functionalities of individual devices. The performance of the system, however, is defined by packaging and integration methods and configurations. Low temperature cofired ceramics (LTCC) is one of our key technology assets for photonics and MEMS/MOEMS/RF-MEMS packaging. In photonics integration, the tolerance of device alignment is the key issue of integration. In order to be able to use mass-manufacturing tools, the primary aim is to process 3D structures, such as, grooves, cavities, holes, bumps and alignment fiducials, which can be used for the passive alignment of devices. The tolerances of LTCC structures are typically ±5μm and in some specific cases ±2μm. Therefore, LTCC provides means for the passive alignment of multimode fiber as well as MOEMS devices. Thermal management by the use of thermal vias in LTCC is a well-established technique, and liquid cooling channels in the LTCC substrate provide efficient additional means for high-power laser cooling. When targeting for thermally controlled systems, thermal bridge structures can be used to isolate critical devices from main structures. LTCC provides inherently hermetic substrate allowing for the possibility to hermetic encapsulation. Hermetic fiber feed throughs and transparent windows can be integrated in LTCC structures. Cavities, channels and sealed gas cells can be fabricated, also. RF antennas and coil structures for electro-magnetic field control can be integrated in the LTCC substrate. Therefore, 3D packaging of MEMS, MOEMS and photonic devices is enabled by LTCC.

High-throughput optical inter-board interconnects for next-generation on-board digital transparent processors

The satellite telecommunication sector is continuously facing new challenges. Operators turn towards increasing capacity payloads with higher number of beams and broader bandwidth, in order to cope with exhausting orbital positions and to lower the cost of in-orbit delivery of bit. Only satellites able to provide high data rate connections to numerous users are expected to achieve affordable communication prices. On the other hand, as the telecom market grows and the range of offered services (HDTV, Video On Demand, Triple Play), operators call for more versatile solutions to quickly grasp new markets and to adapt to these evolutions over the average 15 years of a satellite lifetime. Flexible payloads have found an increasing interest for a number of years. Flexibility is considered as a means for a better commercial exploitation of a satellite fleet and a better allocation of resource in response to traffic evolution and/or changing business plans, with potential advantages such as a wider range of applications, less customization for specific missions, increased production runs of equipment, enhancement of reliability, reduction of equipment cost, reduction of program schedules [1]. Flexibility is expected to be offered in spectrum management and frequency plan, in coverage, or in the repeater power allocation. The industry is taking up the challenge both by improving current telecom satellites and offering new payload technology, more flexible and able to address the new markets. From a system integrator perspective, flexibility is as an opportunity to design more generic payloads, that can be customized during or after fabrication only, thus shortening the design-to-manufacturing cycle, and improving the industry competitiveness.

High-speed ADC and DAC modules with fibre optic interconnections for telecom satellites

The flexibility required for future telecom payloads calls for the introduction of more and more digital processing capabilities. Aggregate data throughputs of several Tbps will have to be handled onboard, thus creating the need for effective, ADCDSP and DACDSP highspeed links. ADC and DAC modules with optical interconnections is an attractive option as it can solve easily the transmission and routing of the expected huge amount of data. This technique will enable to increase the bandwidth and/or the number of beams/channels to be treated, or to support advanced digital processing architectures including beam forming. We realised electrooptic ADC and DAC modules containing an 8 bit, 2 GSa/s A/D converter and a 12 bit, 2 GSa/s D/A converter. The 4channel parallel fibre optic link employs 850nm VCSELs and GaAs PIN photodiodes coupled to 50/125μm fibre ribbon cable. ADCDSP and DSPDAC links both have an aggregate data rate of 25 Gbps. The paper presents the current status of this development.

The European project Merlin on multi-gigabit, energy-efficient, ruggedized lightwave engines for advanced on-board digital processors

Modern broadband communication networks rely on satellites to complement the terrestrial telecommunication infrastructure. Satellites accommodate global reach and enable world-wide direct broadcasting by facilitating wide access to the backbone network from remote sites or areas where the installation of ground segment infrastructure is not economically viable. At the same time the new broadband applications increase the bandwidth demands in every part of the network - and satellites are no exception. Modern telecom satellites incorporate On-Board Processors (OBP) having analogue-to-digital (ADC) and digital-to-analogue converters (DAC) at their inputs/outputs and making use of digital processing to handle hundreds of signals; as the amount of information exchanged increases, so do the physical size, mass and power consumption of the interconnects required to transfer massive amounts of data through bulk electric wires.

Integration of 150 Gbps/fiber optical engines based on multicore fibers and 6-channel VCSELs and PDs

Multicore fiber enables a parallel optic data link with a single optical fiber, thus providing an attractive way to increase the total throughput and the integration density of the interconnections. We study and present photonics integration technologies and optical coupling approaches for multicore transmitter and receiver subassemblies. Such optical engines are implemented and characterized using multimode 6-core fibers and multicore-optimized active devices: 850-nm VCSEL and PD arrays with circular layout and multi-channel driver and receiver ICs. They are developed for bit-rates of 25 Gbps/channel and beyond, i.e. <150 Gbps per fiber, and also optimized for ruggedized transceivers with extended operation temperature range, for harsh environment applications, including space.