Photonic Packaging Sourcebook

In the last 20 years, fiber optic systems show a huge development in terms of expanded data rates of 40–160 Gb/s in the telecom core network. Additionally, the data rates in the consumer PC segment such as internal front side bus or external bus structures such as USB 3.0 or Thunderbolt (Intel_Corporation 2011) are also expanding extremely. In automotive applications, the bus speed becomes also in the region of several hundred megabits (MOST 3.0). The advantage of optical fibers depends on its almost infinite transmission bandwidth, but still has strong disadvantages in the field of handling of the fibers and in the fiber–chip coupling, respectively. In this work, the fiber-chip coupling technology will be analyzed, while new coupling techniques and cost optimization basics are presented. Thus, at the beginning, an overview of the technology drivers of optical communications systems will be discussed. Further, many examples of photonic packaging and interconnection technology are presented in depth. All actual adjustment and fixation techniques are focused. A deeper analysis of the optical interconnection technology with basic theory of waveguide coupling and loss mechanisms concludes the introductory part of work. Then, an overview on the modular technology of major photonic components in the field of high-rate fiber optic networks is presented, followed by the analysis of the fiber–chip coupling in these different applications. In the conclusions, a summary and an outlook on the further development of the technology of photonic packaging and interconnection technology will be given.

This section describes the characteristics of optical waveguides in various material systems. The main focus will be on the properties of glass fiber whose different types and production methods will be described. The material systems of optical waveguides, which are described in this chapter, are displayed in the following: (1) in fibers, (2) in SiO₂, (3) in Polymethylmethacrylate (PMMA), (4) in GaAs, and (5) in InP.

The optical coupling between the various optical components requires low coupling loss and low reflection. Very often is the application of ray optics not useful, but the wave observation of light must be used. In most cases, the optical modes of the components (laser, fiber, waveguide) will be described in the form of a Gaussian distribution, and all coupling efficiencies will be calculated with the aid of an overlap integral. The biggest problem occurs by mechanical adjustment of the components and the long-term stability of the coupling.

In modern optical communication systems, it is of the highest importance to transmit as much optical power from the transmitter to the receiver. It seems that future systems will not be that strongly dependent on good optical waveguides. Actually, even after 25 years of existence of low-loss glass fibers, the coupling efficiency remains the biggest concern of the system engineers. In this chapter, the most important principles of the optical coupling that are relevant for engineers working with this topic are discussed.

The wide use of integrated microwave and millimeter-wave circuits requires a packaging and interconnection technology, which keeps in mind on the one hand the specific circumstances of the case materials and on the other hand meets the special requirements of high-frequency connection to the chip. The necessary structures are typically implemented as microstrip line or coplanar line. For particularly high-frequency connections to more than 100-GHz semirigid coaxial cables are used. In this chapter, the basic principles of the coaxial and coplanar lines are represented.

This chapter discusses and analyzes the bonding of OEIC and its electrical and thermal environment. First, the bonding interface between the OEIC and the heat sink would be investigated. In the following, failure mechanisms and reliability tests are discussed. Adhesive bonding takes more and more place in the electrical packaging especially for flexfoil and thermal sensitive chips. An overview of different gluing mechanisms is given. Finally, the different types of wire bonding techniques are depicted and compared in conjunction with practical examples for the application with RF connections.

Optical connectors are used in a widespread application range, from low-cost automotive networks with polymeric fibers to multi-fiber single-mode connectors in optical glass fiber core networks. In this chapter, either single-fiber or multi-fiber connectors are described. Different types of single-mode and multi-mode connectors are currently available on the market. A description about the used types is included. In the second section of the chapter, the production and quality control of optical fiber tapers are represented.

In this chapter, basic components of active adjustment tools will be introduced. Here, the advantages, disadvantages, and applications of mechanical carriage systems are described for micropositioning and afterward deeply analyzed. Furthermore, an overview of existing possibilities of fiber-chip fixation in regard to the long-term stable welding process is shown. At the end of the chapter an example of the application of microwelds is illustrated and described in detail for the use in modules for optical communications systems. A coupling machine in combination with laser welding performs the fixing of the fiber-chip connection. Hereby, an adjusting welding technique, which is called “strain-reducing” welding, is introduced.

In the course of the book, methods for optical coupling have been described that realize an active adjustment of the fiber by micromechanical actuator elements. In the present chapter, however, several methods are described that allow a passive fiber–chip connection. These methods include the flip chip (FC) technology and the LIGA technique (lithography, electroplating, molding technique). FC technique has also the great advantage of allowing a batch processing of the optical and electrical connection structure for a mass production of future optoelectronic communication engineering applications.

In this chapter, the hybrid integration of optoelectronic components on a suitable substrate such as silicon, ceramic, glass, or PCB is set out in detail. So far, this technology is succeeded only in approaches to produce a wide range of applications with this technology. The large number of additional technologies such as flip chip technology, vapor deposition, and silica etching makes the production of complex component groups very expensive and complex. A potential approach to lower the complexity and hence the fabrication costs is the integration of optics into printed circuit boards. The key for wide adoption of optics on board-level is the development of compatible processes for integration and assembly. The chapter addresses these developments and shows the supremacy of PCB-integrated optics for applications where high energy efficiency and bandwidth density are particularly in demand.

In this chapter, different module structures are presented which are applied in commercial modules. Usually, module assemblies are classified into the following categories: (1) transmitter modules (laser) with and without cooling; (2) receiver module (photodiode); (3) mixed modules (transmitter or receiver); (4) multi-fiber modules (arrays). For each category, an example is shown in more detail in the following. Previously, however, it is necessary to provide some explanation of the used coupling method.

In this chapter, the construction way of mechanical and optical design of photonic modules is described in detail. First, an overview of the general requirements of photonic packaging techniques is given followed by an exact example of the mechanical design of a laser module, which is shown in Chap. 11. Afterward, several optical simulation tools are described, which are important to apply for the fiber–chip coupling and the design of the waveguides on an optoelectronic integrated chip (OEIC).

At the end of the development of a module, the question about the stability of the fiber-chip coupling and electrical and mechanical stability always stands. The following test runs are essential to modules, which must be tested for the datacom industry (DUT, device under test): (1) Temperature cycles. (2) Test at high dampness and high temperature. (3) Mechanical oscillations. (4) Mechanical shock. The environmental influences on products and their effects are numerous and from most different kind. The necessity for device and component manufacturers to bring long-lived products on the market requires suitable examinations under operating conditions. The goals of the environmental checks are the uncovering of cause-and-effects connections, the qualification of environmental conditions and the optimization of a long-term-stable product development. With aging and decomposition processes and with reliability studies, one mostly uses time lapse and artificial aging. The tests are accomplished in suitable environmental simulators, whereby commercial climate chambers are available from interior of some liters up to 100 m² large areas for automobile tests. A typical climatic chamber with an interior of 200 L and a usable temperature range between −40 and +280 °C is represented in Fig. 13.1. Basis of the audits provides international testing standards. In the specific case, the stress values must be adapted to the standards, which manifests itself, e.g., in the different procedures of the various standards for telecommunications goods.