shown in Fig.16;the modes have been identified,and suitable lens system,alignment was possible.The observa- these are tabulated in Table 2.Preferential excitation is tion of modes has been achieved. swept frequency source wavemeter theoretical M:0-695 X0▣090 isolator level-setting attenuato 8 surface-wave resonator 05 amplifier 10 15 2-0 mode c.r.o. mode loss transducer transducer as function of无 Fig.11 Microwave measuring equipment Fig.13 Radiation loss as a function of L/(HE mode) -llmit of experimental accuracy experimental points 20 fo -9Gc/s X=0-04 B :1013 Ko 1-0 “4 theoretical 8 radius,ft 0.6 Fig.14 Experimental bending loss of a fibre carrying the Eo mode at a frequency of9 GHz 06 Table 2:Details of modes photographed 04 Photo- Mode Fibre Corrected Corrected Approximate graph in core wavelength input spot Fig.16 diameter diameter 0+2 m um um 1.80 0.590 1.15 b EHt 4.50 0.560 3.00 TMo2 or TE02 8.45 0.553 3.00 20 40 60 80 d 0 3.05 0.550 3.00 KoL TEo1+HE21 HE12+EH11 H 8,45 0.580 3.00 12 TE02+HE22 or H 8.45 0.545 3.00 Fig.12 Radiation loss as a function of koL(Eo mode) TMo2+HE22 9 EH+HE H 8.45 0.630 3.00 achieved by the positioning of the light spot and the rota- tion of the light polarisation.The cutoff of some of the higher-order modes may be observed by using a white- A preliminary experiment on the butt jointing of two light source through a monochromator.The use of a fibres has been carried out.It was observed that,when the gallium arsenide laser was aimed at discovering methods fibres were placed with a gap of less than 1 mm,the energy of aligning a near infrared system when visual observation transfer was not less than 10%if a matching fluid was cannot be made.With the aid of an image convertor and a placed in the gap.The first fibre acted as the light source monochromotor x 95 oil-immersion objectives fibre onolyser He-Ne or en pin hole Fig.15 Schematic diagram of the experimental optical apparatus IEE PROCEEDINGS,Vol.133,Pt.J,No.3,JUNE 1986 197shown in Fig. 16; the modes have been identified, and suitable lens system, alignment was possible. The observa￾these are tabulated in Table 2. Preferential excitation is tion of modes has been achieved. swept frequency source trigger isolator wavemeter levs)-setting attenuator surface - wave resonator c.r.o. ornplifier mods transducer mode transducer Fig. 11 Microwave measuring equipment 5 10 1-5 2 0 radiation loss as function of -L Xo Fig. 13 Radiation loss as afunction of L/Xo {HEl{ mode) T.— limit of experimental accuracy jexperimental points O.Ci attenuation, dt 6 \ \ \ \ \ TO =9oC/5" i =,0,3 \ 3 4 5 radius, ft Fig. 14 Experimental bending loss of a fibre carrying the Eo mode at a frequency of 9 GHz Table 2: Details of modes photographed KOL 12 Fig. 12 Radiation loss as afunction ofko L (Eo mode) achieved by the positioning of the light spot and the rota￾tion of the light polarisation. The cutoff of some of the higher-order modes may be observed by using a white￾light source through a monochromator. The use of a gallium arsenide laser was aimed at discovering methods of aligning a near infrared system when visual observation cannot be made. With the aid of an image convertor and a Photo- Mode graph in Fig. 16 Fibre Corrected Corrected Approximate core wavelength input spot diameter diameter a b c d e f 9 HE,, EH,, TM0 2 or TE02 TE0 ,+HE2 1 HE,2 + EH,, TE02 + HE22 or TMO2 + HE22 EH + HE E C H D H H H fjm 1.80 4.50 8.45 3.05 8.45 8.45 8.45 //m 0.590 0.560 0.553 0.550 0.580 0.545 0.630 /i/m 1.15 3.00 3.00 3.00 3.00 3.00 3.00 A preliminary experiment on the butt jointing of two fibres has been carried out. It was observed that, when the fibres were placed with a gap of less than 1 mm, the energy transfer was not less than 10% if a matching fluid was placed in the gap. The first fibre acted as the light source monochromator x 95 oil-immersion objectives fibre laser He-Ne or GaAs lens Pin hol e polariser " eyepieces Fig. 15 Schematic diagram of the experimental optical apparatus analyser IEE PROCEEDINGS, Vol. 133, Pt. J, No. 3, JUNE 1986 197