Optical two-way communication systemusing a rotary coupler

Noboru Ito and Toshiaki Numazaki

As one of the media of automation, a two-way communication system between stationary and moving parts

has been effectively accomplished by making use of a line of optical fibers, a specially designed rotary cou-

plers and two-way communication modules.

1. Introduction

For the purpose of communication between station-ary and moving parts (which can be changed into a ro-tary motion), it is effective to make use of a line of op-tical fibers and lenses mounted on the axis of a rotarycoupler. Specially designed rotary couplers and two-way communication modules in line with optical fiberswere developed during 1981-1982 and a system usingthese devices was constructed and tested during1982-1983.

According to the tests, the system ran well and therotary coupler was found to match it effectively.

II. Optical Rotary Coupler

In the rotary coupler on each axis of the stator(right-hand side) and rotator (left-hand side) in Fig. 1,a fiber and a lens are placed to connect both sides op-tically. The rotating part is fixed to the ball bearingswith the bushing; the ball bearing housing is fixed to thestator with screws, where the rotator can turn in eitherdirection.

A gap (Z) between the two Selfoc lenses (SLS, 2.0 X

0.25) and a gap (11) between each lens and fiber are ofimportance in this device. Several characteristics ofthis coupler are discussed within these parameters.

Figure 2 depicts the coupler insertion loss against gapZ in millimeters with a parameter 11 in millimeters foran optical fiber, SI 80/125 (step index with an 80-Mmcore and 125-Mm cladding diam, N.A., 0.24); where the865-nm wavelength is used for the measurement.

The authors are with Oi Electric Company, Ltd., 7-3-16 Kikuna,Kohoku-ku, Yokohama 222, Japan.

Received 24 September 1984.0003-6935/85/142221-04$02.00/0.© 1985 Optical Society of America.

As shown in the figure, the curves are so insensitiveto the variation of gap Z that this device is easy tohandle. This means it can easily be modified for eitherthrustable or plug-in type by selecting 11 adequately,where 11 can be fixed with glue. Other than variationsof gap Z, however, the offset and slanting between eachaxis of the rotator and the stator caused by wear andtear must be considered.

Figures 3 and 4 depict coupler insertion loss incre-ments against the offset A, and slanting angle AO be-tween the axes. According to running tests, the influ-ence of offset and slanting was found to be negligible forthe structure shown in Fig. 1.

Figure 5 depicts the coupler insertion loss variationagainst its rotating angle caused by the above-men-tioned misalignments and shows the coupler is in goodalignment. Other curves in Fig. 2-7, except Fig. 5, aremeasured at the state of zero variation in Fig. 5. Figure6 depicts the coupler loss deviation against ambienttemperatures and Fig. 7 depicts its loss deviation againstthe total number of rotations, which means it is insen-sitive to ambient temperatures and mechanical dete-rioration.

According to the various measurements shown inFigs. 2-7, this type of rotary coupler is clearly useful insevere conditions.

Figure 8 shows the rotary coupler unit and Fig. 9,shows the test set of the couplers, where two couplerunits are connected back to back in the opposite direc-tion with a flexible joint. In addition, ball lenses canbe used instead of Selfoc lenses for the coupler units.Similar characteristics have been obtained in our lab-oratory for ball lenses (borosilicate Crown 7).

111. Optical Two-Way Communication System

To transform electrical signals to optical signals orvice versa, an optical two-way communication modulewas developed. Figure 10 depicts a structure in whichlight emitting diodes (LED) with center wavelengthsof XA (730 nm on one side) and X2 (865 nm on the other

15 July 1985 / Vol. 24, No. 14 / APPLIED OPTICS 2221

c

C._

Et

z_2

C,)

coco

Fig. 1. Optical rotary coupler.

Fiber Lenses FiberI-a z- 4

1.0

0.5

0

-, Lens Fiber

Lens ~ _

Fiber

1 = 0. 3 mmZ =4 Omm1 = 865 nm /

0.2 0.4 0.6

SLANTING ANGLE -O in DEGREE

Fig. 4. Coupler loss increment vs slanting angle AO in fiber-lensaxes.

8

2

0 ?(.0 60 d

DISTANCE Z in mm

Fig. 2. Coupler insertion loss vs distance Z between two Selfoc lenses(SLS, 2.0 X 0.25) with parameter 11 in millimeters for an optical fiber;

SI 80/125.

0.1

0

2:0

C.) 0.1I

Lenses Fiber

FiberFiber L x =~~~~In1 - ) - - -

1.0 _.

0.5

1/27 7C 3/2

ROTATION in RADIAN

Fig. 5. Coupler loss variation vs its rotating angle.

+0051.L= 0. 3 mmZ=4 0mmA = 865 nm

0

2:c0

E-

C/)0- 0.1

0 0.05 0.1 0.15 0.2

OFFSET x in mm

Fig. 3. Coupler loss increments vs offset Ax in fiber-lens axes.

4= O. 3mmZ= 4 0mm2 = 865 nm

AMBIENT TEMPERATURE in 0C

Fig. 6. Coupler loss deviation vs ambient temperatures.

2222 APPLIED OPTICS / Vol. 24, No. 14 / 15 July 1985

c._

a:

E-'z.

C.

0

I

I I I

4= 0. 3 mmZ= 4 0 mm

t ing Speed :2.5 Hz= 8 6 5 nm

Fig. 10. Optical two-way communication module.

0 0.5 1.0 1.5 2.0

TOTAL NUMBER OF ROTATION (MILLION)

Fig. 7. Coupler loss deviation vs total number of rotations at roomtemperature.

Table 1. Some Characteristics of the Optical Two-WayCommunication Module

S P F L P F

2 center 7 3 0 nm 8 6 5 nm

Fibre Output not less than not less than( S I - 8 0 ) - 1 0 dBm - 1 0 dBm

Fi l ter P I N 0.2 8 dB 0.5 6 dBI n s e rt i onLoss LED 0.5 dB 0.3 6 dB

Near End not more than not more thanCross Talk 4 5 dB -4 3 dB

VIDEO

ffi'qA

I Il

c DATA' 2VOICES DATA

4.2 5.3 6.0 MHz

(a)

Fig .10

Fig. 8. Rotary coupler unit.

Fig. 9. Test set of couplers.

(b)

Fig. 11. Optical two-way communication system: (a) frequencyallocation; (b) block diagram.

side) are used. A pair of filters, short pass (SPF) andlong pass (LPF), is mounted with a slanting angle of 730to the optical beams. A spatial filter is placed to reducecross talk caused by dispersion beams leaking directlyfrom the LED to the PIN photodiode.

Fresnel reflections of the transmission beam againstthe surface of the fiber end reflects six times betweenthe pair of filters placed face to face so that they satis-factorily lower cross talk. The two filters in parallel areof the same kind, so assembly of this module is easy andthe module can be made small in size. Some charac-teristics of the module are shown in Table I.

An experimental two-way communication system setwas constructed using a pair of rotary couplers (con-nected back to back) and a pair of two-way communi-cation modules. Figure 11 depicts its (a) frequencyallocation and (b) block diagram. In the system a totalof 2-km long SI 80/125 fiber is connected, where thetotal loss of the optical pass is 13 dB.

15 July 1985 / Vol. 24, No. 14 / APPLIED OPTICS 2223

+ 0.1 5

0

-0.1 5

-0.3

SPF(LPF)

_

This system accommodates a one-way base bandvideo channel (from 60 Hz to 4.2 MHz), a two-way voicechannel (0.3-3.4 kHz) frequency modulated by ±25 kHzat a carrier frequency of 5.3 MHz, and a two-way datachannel of 9600 bit/sec frequency modulated by 25kHz at a carrier frequency of 6 MHz.

According to the overall test, the system proved toclear the specifications, CCITT for voices and JEMJapan Electrical Manufacturers Association) forvideo.

IV. Conclusion

This system is one of the special and distinctive ap-plications of optical communication media. Accordingto the test, this system proved to be useful in practicalareas such as the joints of robots and other controlmachines.

Further development for this system is planned onsingle-mode optical rotary couplers and two-way com-munication modules.

IMPROVED MEASUREMENT OF ELECTRON ATTENUATION LENGTHSNBS researchers have developed an improved technique formeasuring the mean distance that electrons travel in solidmaterials before they are scattered by an atom. The techniquecan be used over a wide range of electron energies and with awide variety of condensed molecular solids. Electronattenuation lengths are important for understanding the effectsof radiation on such things as biological systems andsemiconductors. They also are used to calculate the depth ofpenetration of a variety of electron and photon probes used insurface science research. These attenuation lengths can bemeasured by generating photoelectrons in a substrate such ascopper, and measuring the percentage of them that penetrate--without loss of energy--a layer of a solid condensed on thesubstrate, as the condensed layer is gradually thickened.Until now, difficulties in knowing just how thick the condensedlayer is have led to errors as great as 100 percent in theattenuation lengths. The NBS team developed a microcapillaryarray that can deliver a calibrated flow of gas-phase moleculesto the substrate, where they condense into a layer ofcomparatively well-known thickness. The researchers estimatethe error in their technique to be about 35 percent, and expectto reduce it to 25 percent or less. Initial measurements havebeen made on H 0 CH OH, and C H in the electron kineticenergy range from 18-68 eV (where there are almost no previousdata) and have shown a mass-dependent variation in attenuationlength larger than that predicted by present theory.

2224 APPLIED OPTICS / Vol. 24, No. 14 / 15 July 1985