the optical waveguide fiber having the novel thin carbon coating is characterized by : ease of coloring similar to that of a polymer coated waveguide having no carbon layer . thus , a strength benefit of a carbon coated waveguide is realized , while essentially none of the drawbacks associated with a hermetic coating need be dealt with . in addition to the ease of coloring , it is believed the thin carbon coat may be applied at higher draw speeds than that of a hermetic coating process . no additional on line measurements coupled to the draw control loop are required and quality control can be maintained by making a statistically significant number of off line measurements of coating electrical resistance . these statements are based upon the results , discussed below , which show that resistance per unit length of the order of mega - ohms provide a suitable thin coating . in sharp contrast , the resistance requirement for a hermetic carbon coating , i . e ., a coating having a thickness no less than about 500 ° a , is in the kilo - ohm range , three orders of magnitude lower . the end view illustration of the novel waveguide is shown in fig1 . the clad glass layer 2 is surrounded by and adhered to thin carbon layer 4 . the outer layer 6 represents the protective polymer coating , which may comprise one or more layers . note that the carbon layer is formed directly onto the glass surface of the waveguide fiber . a method of forming the coating comprises pyrolytic deposition of carbon onto the waveguide fiber as the fiber emerges from the hot zone of the draw furnace . the fiber passes from the hot zone into a controlled environment chamber where a carbon containing compound reacts to produce a carbon layer on the waveguide surface . the reaction may be driven by the heat from the waveguide fiber . a process suitable for applying a hermetic coating or the thin carbon coating of this application is found in u . s . pat . no . 5 , 346 , 520 , meabon , et al (&# 39 ; 520 patent ). because the concentration of the carbon containing compound in the reactor is low in the thin coating process , the pyrolytic reaction tended to be somewhat unstable . the pyrolytic reaction was stabilized by introducing a relatively inert gas into the flow . a gas such as argon was used . depending upon the thickness of the carbon coated layer , the flow rate of the argon was in the range of 0 to 75 % by volume of the total flow of gas into the reactor vessel . a waveguide fibers was prepared having a thin carbon coating on the clad glass surface . a polymer coating was applied over the carbon coating . the waveguide was strength tested to determine a weibull strength distribution and a dynamic fatigue constant . the weibull plots shown in fig2 show the failure probability of the fiber versus applied stress . the steep slope , straight line appearance of the plots is markedly similar to those characteristic of hermetic coated waveguides . the data was generated by applying linear tension to break the fiber in 20 meter gauge lengths . the environment was controlled to a temperature of 30 ° c . and a relative humidity of 100 %. curve 10 is the failure probability vs . stress using a strain rate of 0 . 004 %/ min . curve 8 represents a strain rate of 4 . 0 %/ min . the shift to the right of the higher strain rate curve is expected because the higher rate does not allow time for certain of the waveguide surface flaws to grow to failure . in effect , the higher strain rate acts upon a smaller distribution of flaws , i . e . faster growing flaws . the dynamic fatigue constant was determined by fitting a line on a chart of break strength vs . stress rate , multiple readings of strength at failure were taken at each of the two stress rates and n d , the dynamic fatigue constant , was found by fitting a line to the data . the method is known in the art and detailed in fiber optic test procedure ( fotp ) 76 , published by a u . s . standards group . the 20 meter gauge test is more reliable than the 0 . 5 meter gauge test . it is not unusual for the shorter gauge test to yield a lower value of n d . however , the data point which gives an n d of 23 . 3 may indicate that the carbon coating resistance of about 4 m / cm is near the limit of how thin the carbon coating may be . to test this hypothesis , the testing of three additional fibers was carried out at the shorter gauge length . the data is significant and does show the carbon coating is effective to increase n d to about 25 as compared to a waveguide having no carbon coating for which n d is typically about 20 . by comparison , a thicker , hermetic carbon coating provides an n value of 200 or greater . a second waveguide fiber having a thin carbon layer on the clad glass surface was prepared . in this case the electrical resistance per unit length was 1 . 28 m / cm , about a factor of three lower than the previous example , indicative of a thicker carbon layer . the data is given in table 2 . the data again shows the effectiveness of the thin carbon layer in greatly improving the fatigue constant . the two data sets taken together suggest that a target thickness of about 4 m / cm may be appropriate . turning now to the effect of the carbon layer on polymer coating adhesion , it is noted that both of the waveguide fibers described in the examples performed well . table 3 shows the test waveguides had essentially no degradation in coating adhesion or waveguide function under severe environmental testing . the absence of delamination of the coating from the carbon coated waveguide is unusual . more unusual is the very small change in attenuation of the waveguide in these severe environments . the results of the testing of the b samples are of particular import . the b samples had no adhesion promoter , so that the lack of delamination is quite unusual and unexpected . such a coating applied to a silica surface would have delaminated very quickly , i . e ., in no more than a few hours . coating delamination causes strength degradation as well as increased attenuation . a typical environmental testing data set is shown charted in fig3 . the chart is a plot of attenuation vs . time for waveguide fiber a immersed in 65 ° c . water . curve 12 shows the essentially continuous data readout of waveguide a attenuation at 1310 nm over the 128 day time period . curve 14 is a plot of 1550 nm attenuation for waveguide a . the small attenuation increase is , for essentially all applications , not sufficient to degrade performance of a system comprised of this waveguide fiber . the required thickness of the novel carbon coating may be determined by : measurement of electrical resistance or another electrical property related to carbon thickness ; this last characteristic affords another benefit of the novel thin carbon coating . hermetic coated fiber requires a thicker carbon layer and thus appears black . the polymer coating may be somewhat transparent so that a color added to the polymer coat may be changed in appearance by the underlying black layer . in point of fact , considerable difficulty has been encountered in manufacture of yellow , white , green , and red polymer coated hermetic fibers because of the black layer . the light gray color of the carbon coated waveguide fiber disclosed herein does not interfere with the color added or applied to the polymer . furthermore , the colors remain within specification , as determined by a standard muncell color chart , when subjected to standard environmental testing . although particular embodiments of the invention have herein been disclosed and described , the invention is nonetheless limited only by the following claims .