3.1.

Finger Mechanism

Performing optical cross-connection to a connection board in a high-density mounting requires a finger that can access the whole area of the connection board. A long and thin finger structure is needed so that the finger can maneuver through parts overcrowded with the fiber. We designed such a finger using the finite element method (FEM). The FEM analysis produced a finger shape with enough strength. The analysis model and result are shown in Fig. 4. The stress in the finger part is equal to or less than $1/5$ of the yielding point. We confirmed that the finger has enough strength. Moreover, the displacement is 8 μm, which is within the permissible positioning error. Even, when the maximum force is applied to a plug, the displacement is within the designed tolerance.

Fig. 4

FEM analysis model for designing a long and thin finger and result.

When the finger connects or disconnects, the connector plugs into or from the adaptors, it must remove the overcrowded fibers without cutting the optical jumper cord and move. Therefore, we developed a mechanism for removing entangled fibers, which is shown in Fig. 5. The arm of the mechanism synchronizes with the vertical motion of the finger. The arm swings rotationally, which enables the fiber to be released from the finger. These approaches contribute to the stability of cross-connecting the optical fibers.

Fig. 5

Mechanism for removing entangled fibers.

Next, we explain the fiber-handling mechanism for treating APC optical connectors. Figure 6 shows the state where the fiber-handling mechanism grips an optical connecter plug. As shown in Fig. 6, such a positioning/gripping part can set the posture where optical connection can be done because the optical connector is gripped along with the positioning side using the fiber-handling mechanism. An optical fiber cord is fixed in the body region so that the positioning side becomes parallel to the minor axis of the ellipsoidal section of the optical fiber cord when an optical fiber cord is an ellipsoidal cross section; in other words, the optical fiber cord is at right angles to the major axis of the ellipsoidal section of the optical fiber cord. Further, because the rotational position of the optical connector plug held in the optical connector plug-alignment part can be kept in a predetermined alignment by using the cross sectional shape of the optical fiber cord and the corresponding guide passage in the optical connector plug alignment part, the fiber-handling mechanism can grip the rotational angle reference surface of the optical connector plug easily and reliably.

Fig. 6

Configuration of the optical fiber cord with the APC connector plug.

4.1.

Optical Connection Board

For high density in the optical connection part, we designed the connection board by using a housing in which 25-port optical adaptors are arranged in two steps. Figure 7 shows the configuration of the optical connection part. The adaptors in the housing are arranged in two lines with the adaptors in one line shifted by a half pitch (3 mm) from those in the other. By stacking the housing, each adaptor is arranged in the vertical direction in four steps. The plug and adaptor are based on the miniature-unit connector so that a low-cost and compact optical connector part can be achieved. The offset sensors for the $xyz$-positioning sensing method are installed on both sides of the optical connection board. The width and height of the optical connection board for 200 ports are 330 and 50 mm, respectively.

Fig. 7

Configuration of the optical connection part.

4.2.

Optical Arrangement Board

An arrangement board in the optical connection part is used to arrange the connector plug after an optical fiber cord is rewound into an optical fiber storage unit. The arrangement board aligns optical connecter plugs in a horizontal state at an appointed height position and supports it. Figure 8 shows the configuration of the arrangement board. The arrangement board consists of a pair of flat plates. It is made by stacking an upper plate and a base plate. Multiple through-holes allow connection of the optical connection board side and the rewind mechanism side. A guide part is formed at the arrangement board entrance, and a fiber derivation compartment is formed on the exit side. A groove is formed between the guide part and the fiber derivation compartment. For use in the connection of an APC connector, the shape of the entrance of the guide part is similar to the cross sectional shape of the end of the optical connecter plug. The section of the vertical direction of the guide part assumes a shape that is the as same as the positioning/gripping part of the optical connecter plug. The cross section of the groove and the cross section of the optical fiber cord assume a similar shape.

Fig. 8

Configuration of the arrangement board.

4.3.

Fiber Storage Cartridge

The optical jumper cords are rewound into the fiber storage space to prevent their becoming entangled with other cords during reconnection. The fiber storage cartridge has a function for storing extra lengths of the optical jumper cord. In this optical fiber cross-connection module, it accommodates one of the 200 optical jumper cords, which must be stored into the module. The optical fiber storage cartridge, which is made of plastic molding, was designed so that multiple fibers can be accommodated in one cartridge. This provides compactness and a high packing density and reduces cost. Figure 9 shows the optical fiber storage cartridge. For this cartridge, we developed a structure in which each fiber is aligned and held at four points by the fiber guide parts; therefore, the fibers do not entwine each other. The width and height of the fiber storage cartridges for 200 ports are 310 and 140 mm, respectively.

Fig. 9

Optical fiber storage cartridge.

5.1.

Fundamental Optical Characteristics

We first measured the insertion loss of the prototype. Figure 10 shows the initial insertion and return losses of the equipment and the experimental setup for optical characteristics measurement. The initial insertion loss is 1 dB or less, and the return loss is 40 dB or more. Next, we measured the change in insertion and return losses with repeated connection and disconnection. Figure 11 shows the insertion loss and return loss changes. After 500 cross-connections, the insertion loss and return loss satisfies the requirements. We confirmed that the average switching time of an optical jumper cord pair is $<1\min$. In the experiments, multiple cross-connection tests were done for random connection patterns. We also confirmed that the jumper cords do not become entangled and can be connected and disconnected normally in random cross-connections. We confirmed the good optical characteristics after connections and disconnections of one thousand times.

Fig. 10

Initial insertion and return losses.

Fig. 11

Change in insertion loss and return loss after 500 cross-connections.

Next, we show the results of a cross-connection experiment that was performed to confirm the feasibility of automated optical connection between APC optical connectors. We made prototypes of the optical fiber cords with the APC connector plug, the arrangement boards, and the fingers of fiber-handling robot. These parts are implemented in the $200\times 200$ automated optical fiber cross-connect module. We measured the insertion loss of the prototypes. Figure 12 shows the initial insertion and return losses of the equipment and the experimental setup for optical characteristics measurement. The initial insertion loss is 1 dB or less, and the return loss is 40 dB or more. Next, we measured the change in insertion and return losses with repeated connection and disconnection. Figure 13 shows the insertion loss and return loss changes after 500 cross-connections. After 500 cross-connections, the insertion loss and return loss satisfy the requirements. We also confirmed that the jumper cords do not become entangled and can be connected and disconnected normally in random cross-connections in the same way as the connection of the normal optical connecter.

Fig. 12

Initial insertion and return losses (APC).

Fig. 13

Change in insertion loss and return loss after 500 cross-connections (APC).

5.2.

Reliability Test

We examined the reliability of the optical connector plug and housing. Our reliability metric is the Telcordia standard GR-326. As shown in Fig. 14, we confirmed that the maximum value of insertion loss was 0.5 dB or less, and the return loss was 40 dB or more during the reliability test and after it. In addition, the loss change did not exceeded 0.3 dB during a period of 10 ns in vibration and impact tests. The performance of the optical parts composed of the optical connector plug and the housing is comparable to that of an MU connector and satisfies the Telcordia standard GR-326. Regarding environmental characteristics of the equipment, we confirmed that the equipment operates flawlessly when the temperature in the installation room changes from 5 to 45°C. In telecommunication devices, electromagnetic compatibility (EMC) is demanded. Therefore, we performed an EMC evaluation based on CISPR 22 class A. We confirmed that the equipment satisfies CISPR 22 class A for EMC. The equipment was also found to operate normally after a simulated earthquake of seven in seismic intensity on the first and lower floors (acceleration input: $10\mathrm{m}/{\mathrm{s}}^2$). Table 1 summarizes the environmental and other characteristics. The evaluation results clarify that the automated optical fiber cross-connect equipment is suitable for practical use.

Fig. 14

Insertion and return loss after GR-326 test.

Table 1

Environmental and other characteristics.