**6. Passive adjusting techniques**

#### **6.1. Flip-chip-technique**

The flip-chip (FC) bond technology was developed in 1964 by IBM for high dense packages for hybrid modules. At that time it was called C4-technology or Controlled Collapse Chip Connection [11]. Its main goal was to replace the uneconomical wire bonds. The FC-techni‐ que allows the highest density of connections on the chip scale. For this reason this techni‐ que is a possible candidate for high volume production in the micro electronic industry.[1, 12] and [13] have shown that the FC-technique could meet the precision needed for optical fiber-chip coupling (± 3μm). Figure 12 shows the working principle of the optical FC-con‐ nection. The OEIC is connected bottom up to the substrate. Bonding is performed by a ther‐ mal reflow process which isdepicted in figure 13. The surface forces of the melted solder trek the OEIC into a preferred position, that differs very little from connection to connection. This is called "self-alignment". [14], [15]and [16] had developed a fluxless FC-bonding tech‐ nique which allows a self-alignment of better than 1μm. Additionally, the short bond-dis‐ tances promise very good RF-features up to 100GHz bandwidth. Today this progress allows the introduction of batch processing for the optical and electrical part of the optoelectronic packaging of OEICs. This benefit opens the market for high volume production of devices for optical communications systems that allows cost effective production of low budget products for the consumer market.

**Figure 12.** Flip-chip set-up.

For fiber-chip-alignment mostly all six degrees of freedom must be moved. Several commer‐ cial six axes motion systems have been developed with translatoric resolution of better then 0.02μm and angular resolution of better then one arc second. As an example, a mechanical/ piezoelectric driven system with six degrees of freedom is shown in figure 11. Software tools are also included for automated coupling for one fiber and fiber arrays. Most of the software

The flip-chip (FC) bond technology was developed in 1964 by IBM for high dense packages for hybrid modules. At that time it was called C4-technology or Controlled Collapse Chip Connection [11]. Its main goal was to replace the uneconomical wire bonds. The FC-techni‐ que allows the highest density of connections on the chip scale. For this reason this techni‐ que is a possible candidate for high volume production in the micro electronic industry.[1, 12] and [13] have shown that the FC-technique could meet the precision needed for optical fiber-chip coupling (± 3μm). Figure 12 shows the working principle of the optical FC-con‐ nection. The OEIC is connected bottom up to the substrate. Bonding is performed by a ther‐ mal reflow process which isdepicted in figure 13. The surface forces of the melted solder trek the OEIC into a preferred position, that differs very little from connection to connection. This is called "self-alignment". [14], [15]and [16] had developed a fluxless FC-bonding tech‐ nique which allows a self-alignment of better than 1μm. Additionally, the short bond-dis‐

applications are available as a Labview virtual Instrument (VI).

**Figure 11.** Six axes Nano-positioning system.

428 Optoelectronics - Advanced Materials and Devices

**6. Passive adjusting techniques**

**6.1. Flip-chip-technique**

**Figure 13.** Flip-chip self-alignment.

#### **6.2. Optical board technology**

The progress in mechanical precision of the FC-bonds makes it possible to align one or mul‐ tiple optical fibers direct to OEICs. Firstly, the OEIC will be FC-bonded as shown in figure 14. In the next step the fibers are inserted into V-grooves, fabricated by an anisotropic wet etching of the silica substrate. After insertion, the fiber must be fixed mostly by UV-hard‐ ened glue. Here more than 100 fibers can be arranged passively in one single fabrication step to the OEIC. An example of the connection of four lasers to an array of single mode fibers is shown in photograph 15.

In the next development step additional electrical amplifiers, multiplexers, modulators etc. can also be located on the substrate. This kind of hybrid integration is called optical mother‐ board or photonic lightwave circuit (PLC) depicted in figure 16. This type of integration is the most promising technique today for reaching an adequate price level of optical commu‐ nications products for the consumer market.

**7. Optical connectors**

**7.1. Single fiber connectors**

**11.** Polarization maintaining fibers

**15.** Automated light shutter function

**cut**

**12.** Matching gel/coating

**13.** Physical contact

**16.** Duplex connectors

**Name losses Straight**

**Table 1.** Optical connectors summary.

**14.** Air gap

Diamond E2000

connectors are used in various applications including:

This chapter will give a summary of the optical connectors used today. There are several dif‐ ferent types of connectors used for single mode and for multimode operation. Additionally, there are straight polished types and slant polished ones, which are used in high speed opti‐ cal communication systems because of their high reflection loss characteristics. Further on,

**Slant cut Single (SM)**

Mini BNC 0.21dB -20dB MM "/500 low ST 0.28dB -20dB SM,MM "/500 med FC/PC 0.35dB -30dB SM,MM "/500 low FC/APC 0.4dB -55dB SM "/500 med SMA 0.38dB -20dB MM "/500 low Radiall VFO 0.4dB -30dB SM yes "/250 high

Radiall EC 0.2dB -50dB MM "/250 med

SC 0.5dB -30dB SM "/1000 low

HRL-10 0.3dB -60dB SM "/1000 High LC-Duplex 0.2dB -30dB SM/MM "/10.000 low

**Multi (MM) mode**

0.7dB -55dB SM "/250 high

0.5dB -60dB SM yes "/250 med

0.18dB -30dB SM "/1000 low

0.18dB -55dB SM yes "/1000 low

0.5dB -60dB SM yes "/1000 low

**Polarization maintaining** **Durability (insertions)**

Opto-Electronic Packaging http://dx.doi.org/10.5772/51626 431

**Price**

**Figure 14.** Fiber-chip connection with flip-chip.

**Figure 15.** Photograph of flip-chip bonded laser array(Heinrich-Hertz-Institute, Berlin).

**Figure 16.** Concept for a complete optical motherboard [1], [17].
