AU7184798A - Laser-based railroad signal light - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE

SPECIFICATION

(ORIGINAL)

Class Int. Glass Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Safetran Systems Corporation Actual Inventor(s): joseph T Verdeyen Ronald W Snee Address for Service: PHILLIPS ORMONDE

FITZPATRICK

Patent and Trade mark Attorneys 367 Collins Street Melbourne 3004) AUSTRALIA invention Title: LASER-BASED RAILROAD SIGNAL

LIGHT

our Ref: 532629 POF Code: 73726/338300 The ollwin sttemnt s aful decritio ofthis invention, including the best phefo rfor satmn toafl esrpinO method of pefrigit known~t applicant(s);

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LASBR-

-r, BASED RAILROAD

SIGNALLIGHT

THE FIELD OF THE INVENTION The present invention relates to railroad signal lights both for use at railroad highway and pedestrian grade crossings, as flashing warning lights, and for railroad right-ofway control signals. For many years, incandescent lamps have provided the light source for all railroad signal applications. Conventionally, the incandescent lamp will have essentially uncolored illumination, with the desired color being provided by a color filter. For example, for crossing gates and other warning devices there is typically a red color filter, light collecting device and a diverging lens. For right-of-way signals in which red, yellow and green are the conveniti colors, there will be filters to insure that the proper color of illumination is provided through the proper opening.

A laser light source has many advantages over incandescent lamps as a source of light. Longer life is perhaps the most significant advantage. For example, present incandescent signal lights used by the railroad have a rated lifetime of approximately 2,000 hours, with 1,000 hours being a more common, realistic period of use. A laser light source may be rated at least as long as 10,000 hours and the accompanying electronics will have a much longer life. Moreover, a laser light source will be composed of an array of multiple lasers or multiple sources and since it is extremely unlikely that there would be a simultaneous failure of all such lasers, a more realistic situation would involve a slow la degradation of the light source which can be monitored internally and a signal sent to railroad personnel and when thelight source reaches a predetermined level of illumination, the laser array can be replaced.

Another important advantage is that the coupling of a laser to a fiber is far more efficient than such a coupling to an incoherent source suchas an incandescent lamp or an LED.

Further, a laser light source is more easily directionalized and its amplitude canbe easily controlled with low cost available semiconductor electronics. Laser light sources will operate at substantially higher electrical-tight efficiencies than current, S0. preent-day incandescent lamps.

Since the wavelength of a laser diode is virtually independent of the drive current its input or output power, and hence its chromaticity coordinates (or color) will not be a function of the current. An incandescent lamp produces light by virtue of the high Stemperature of the filament according to the blackbody radiation law and thus its spectral content is a strong function of the power used to heat the filament.

As a further advantage, it is not necessary to use a filter in front of a laser light source, as the source itself will provide the desired color.

Preferably, the laser light source will be an array of lasers within a particular wavelength range common to a specific desired color. This light source may be located directly at the point of illumination within the signal housing or it may be remotely located and coupled to the signal housing by an array of fiber optic cables. A further method of obtaining the desired wavelength is to use an infrared laser to excite the rare earth atoms of a v. -ii .2 f :r doped fiber.

SUMMARY OFTE IVENTON The present invention relates to railroad signals and particularly to a railroad signal using laser diodes as the light source.

A primary purpos of the invention is a simple, reliable railroad signal using an array of laser diodes as the light source.

Another purpose of the invention is to provide a railroad signal as described in which the diodes have a range of wavelengths corresponding to the desired colors such as red, yellow and green.

SAnother purpose of the invention is a railroad signal as described in which the laser diodes are coupled by fiber optic cables to the point of illumination within the signal housing.

Another purpose of the invention is a railroad signal as described in which the fiber optic cable may be doped with a rare earth that can be excited by one or more infrared lasers so as to generate red, yellow or green light.

Other purposes will appear in the ensuing specification, drawings and claims.

BRIEF DESCRIPTION OF THE

DRAWINGS

SThe invention is illustrated diagrammatically in the following drawings wherein: Fig. 1 is a prior art disclosure of a typical railroad crossing warning light; Fig. 2 is a diagrammatical illustration of a typical prior art railroad signal housing using an incandescent lamp source; 3 _1 rs;ii Fig. 3 is a perspective illustrating an array of laser diodes connected to fiber L blre 0 i. *Do 5..

2O SFig. 4 is a section illustrating a right-of-way railroad signal using laser diodes as the light source; Fig. 5 is a section, similar to Fig. 4, showing a bundle of laser diodes directly adjacent a diffusing lens; Fig. 6 is a perspective of the bundle of laser diodes shon in Fig. 5; and Fig. 7 illustrates a railroad right-of-way signal having three adjacent laser signals to provide light at three different wavelengths.

DESCRIPTION OF THE REFERRED

EMBODIMENT

The present invention, which utilizes laser diodes as the light source for railway signals, both highway crossing flashing signal fixtures and railroad right-of-ay train control fitures, uses an array of such diodes as the light source. The array may be located control fixtures, uses an array oopc directly at the point of illumination or it may be remotely located and coupled by fiber optic cables to the point of illumination within the signal housing.

Focusing on red as the color used in highway crossing gate flashing lights and as one of the signals for right-of-way train control, the array of laser diodes may operate S within the red color spectrum of 630-680 nanometers. Within this spectrum the laser diodes will not all emit light at the same wavelength, but may emit a plurality of different wavelengths within this specific spectrum. For railroad ight-of-way signals the array of laser diodes may-operate near a wavelength of 588 nm for a yellow light and 555 nm for a requirement, one could use combinations of these green light. In the case of a "white" light requirement one 4 i

N.:

r; colors to produce "white" or use two "complementary" colors, e.g. those wavelengths connected by a straight line through the white point on the IE chromaticity diagram. As an example, 494 and 670 nm, as well as 474 and 568 nm are complementary colors.

In addition to using an array of lasers at the specific wavelengths set forth above, it is also within the scope of the invention to utilize a fiber optic cable doped with a rare earth which can be excited by very efficient near-infrared lasers to produce visible light of the appropriate wavelengths. This is accomplished by the sequential absorption of two infrared photons from the pumping lasers and the emission of visible photons from the excited rare earth atom. A particular appropriate rare earth is praseodymium. A fiber optic 0 cable doped with this material would utilize lasers at 1.0t1pm and 835 nm to generate either 635 un (red), 520 nr (green-blue), or 492 nm (blue) wavelengths of light. Other rare earths and different fibers can be utilized to produce different colors. What is important is that a doped fiber optic cable used in combination with lasers operating at particular wavelengths can provide any necessary color which would find utility in the railroad environment. For further details on the use of lasers in combination with doped fiber optic cable, see The Journal of Qantum Electronics, Vol. 33, No. 6, June 1977, and the article at page 905, entitled "Theory of Pr" Doped Fluoride Fiber Upconversion Lasers" by Yuxing Zhao and Simon Fleming.

Fig. 1 shows a typical prior art highway crossing flashing light signal fixture.

S There is an outer housing 10 which may have an inner mirror coating 12. The coating is placed on a parabolic reflector 14 and there is a color filter and diverging lens 16 closing the aperture o the housing 0- An incandescent light source 18 is positioned within the housing the filter and diverging lens and will direct light along the paths of the arrows 20 out through 16. Such a light source is conventional and can be found throughout the United States wherever there are highway or pedestrian crossings of railroad tracks.

Fig. 2 illustrates a typical railroad right-of-way signal fixture. There is a housing 30 which may be blackened on the inside so as to avoid light reflection. The housing 30 has an aperture 32 and a light source 34 positioed within the housing. There is a lens system which consists of an inner lens 36 and an outer lens 38, with the combination of the two lenses providing a means to direct the light from the signal source along a predetermined path, with only slight divergence in the beam over its useful length. this is S important in that the signal light must be visible from a great distance and this can only come impo.

about if the light from the source is concentrated along a desired path.

The laser diode railroad signal light source of the present invention is shown i Figs. 3 and 4. It may be useful in either a warning light environment or as a right-of-way Ssignal. There is a housing 40 which has a signal light aperture 42. A lens system comprising an inner lens 44 and an outer lens 46, similar to the prior art lens structure of Fig. 2 is used in Fig. 4.

The illumination source may be provided by a plurality of laser diodes indicated at 48, 50, 52, 54 and 56. the number is only illustrative and specifically there may be anywhere from 15 to 20 such laser diodes and they may be spread in the wavelength spectrum, using red as an example of the desired color, from 630-680 nanometers For a green or yellow signal light, laser diodes in other spectrums wold be utilized. The laser Sconnected into a light source array such as diodes indicated at 48 and fo wing are r at:cr~ illustrated in Fig. 3 and located at an opening 58 within a wall 60of the housing 40. Fiber optic light transmissive conduits indicated at 62 will connect each of the laser diode light sources into the bundle of light sources illustrated in Fig. 3. One of the advantages of using lasers as the light source is that the source can be located remotely from the signal housing by taking advantage of the superior coupling of a laser to a fiber optic cable and by the low loss characteristics of readily available fiber optic cables. For example, the loss for a ten meter length of fiber optic cable may be as low as 0.04 dB yielding a transmission factor of 99.08%.

There may be an enclosure 64 which binds the light sources together in a closed array so that the effect is effectively a point source of light,which emits with a characteristic cone of radiation, as indicated by its numerical aperture, and emits at one or multiple wavelengths and which can be located at the focal point of the collimating optics.

Although the laser diodes as illustrated in Fig. 4 are within the signal housing, they may be remotely located therefrom, such as in a control box along the signal right-of-way or adjacent to a railroad highway crossing.

Of particular advantage in the use of laser diodes as a light source is the y e a n d t h e fa ct h a t e v ecn i f one i te longer life attributed both to the diode itself as"a source and the fact that even if one or more S of the individual diodes within an array should go out, there is still adequate light from the array as a whole. Moreover, solid state sourcesfor the electronic controls will contribute to 0 the long life of such a signal light. A further advantage to lasers is that each laser is specific to a particular wavelength and thus all of the light which emaatesfrom the laser diode is at that wavelength. In contrast, in an incandescent lamp the light is spread throughout a wide ir; 'i -i 1 e4 *B e, o 5..

e 4 b 20 1.' f ,oq ee o j portion of the light spectrum- As a specific example of laser diodes which may be satisfactorily used in the present invention, laser diodes are available with nominal wavelengths of 635, 650, 670, 640 nanometers.

Fig. 5 illustrates the use of a bundle of laser diodes at 70, each with appropriate electrical connections 72, positioned in an aperture 74 within a signal light housing 76. There are no fiber optic cables in this embodiment of the invention, however, a diverging lens 78 is placed in front of the laser bundle 70, after which the beam emanating from the diverging lens will be collimated by a lens 80. The end result will be a light beam along the path of arrows 82. Fig. 6 is a perspective of the laser bundle 70 and shows a plurality of individual laser light sources 84, all within the sheath or sleeve 86.

Fig. 7 shows a multiple of the housing 76 of Fig. 5 so as to provide a threesignal light source suitable for railroad right-of-way train control. For example, in a threesignal light matrix, there may be the typical red, green and yellow lights provided by the individual bundles of lasers, with the lasers functioning at the wavelengths described above.

Clearly, the invention can encompass more than three specific signal lights and colors other than red, green and yellow, as required for train control.

The use of laser diodes as a light source also permits the light source to be amplitude-modulated with simple and reliable electronics. This would have particular advante in train control, as a receiver on a locomotive could be tuned to a particular modulation rate providing an electronic backup connection for train control in addition to the engineer's sighting of the visible signal.

Whereas the preferred form of the invention has been shown and described oiherein, it should be realied that there may be many modifications, substitutions and alterations thereto.

*1*

Claims (12)

1. A railroad signal light fixture including a housing, a signal light aperture in said housing, lens means covering said aperture, a light source positioned within said housing to provide light directed through said lens means, said light source including an array of laser diodes, at least some of which provide light within a specific color spectrum.

2. The signal light fixture of claim I wherein the laser diodes provide light in the red color spectrum with a plurality of different wavelengths within the range of 630-680 S nanomters.

3. The signal light fixture of claim 1 wherein the laser diodes provide light in the green color spectruma a wavelength in the range of 555 nanometers.

4. The signal light fixtureof claim 1 w hediesli S the yellow color spectrum at a wavelength in the range of 588 nanometers The signal light fixture of claim wherein each of said laser diodes is connected y a light conduit to a common location posiioned opposite said lens means.

6. The signal light fixture of claim 5 wherein said laser diodes are located remote from said housing.

7. The signal light fixture of claim 6 wherein said light conduits are fiber optic cables.

8. The signal light fixture of claim 7 wherein said fiber optic cables are doped with a rare earth material.

9. The signal light fixture of claim 8 wherein said rare earth material is I'll PraseodyiiuM. The signal light fixture of claim 1 wherein each of said laser diodes is positioned within said housing.

11. The signal light fixture of claim 1 wherein the fixture functions as a crossing warning light.

12. The signal light fixture of claim 1 wherein the fixture functions as a train control signal. i- i: i 1 1-- ;i i I I; 31: I

13. The signal light fixture of claim 1 wherein there are a plurality of signal light housings, each having a signal light aperture and lens means covering said aperture, a light source positioned within each of said housings to provide light directed through said lens means, the light source in each housing including an array of laser diodes, with the diodes in each array within a specific housing providing light within a specific color spectrum.

14. The signal light fixture of claim 13 wherein the laser diodes for each signal light housing are located remote from the housing. The signal light fixture of claim 13 wherein each of the laser diodes is positioned within a housing. positioned within a housing. S Dated: 12th June 1998 PHI: LLIPS ORMONDE FITZPATRICK Attorneys For; safetrari Systems Corporation i; 4-IC L-i i;