HRP980428A2 - Laser-based railroad signal light - Google Patents

Description

This invention relates to railway signal lights.

Such signal lights can be used for road crossings over railroad tracks, pedestrian crossings, flashing warning lights, and for railroad control signals that determine the right of way. Until now, incandescent lamps have been the light source for all railway signal applications. It is common for incandescent lamps to have colorless light, and for the desired color of light to be obtained through a colored filter. For example, ramps and other warning devices typically use a red color filter, light collection device, and diverging lenses. For priority-determining signals, where red, yellow and green are the conventional colors, there will be filters to ensure that the appropriate color of light is obtained through the appropriate aperture.

A laser light source has many advantages over an incandescent lamp as a light source. Longer lifespan is probably the biggest advantage. For example, the estimated lifetime of existing incandescent signal lights used on railways is around 2,000 hours, with it being more common and realistic for them to last around 1,000 hours. The duration of the laser light source is estimated to be at least 10,000 hours, and the accompanying electronics have a much longer lifespan. Moreover, a laser light source can consist of a beam of multiple lasers or multiple sources, and since the simultaneous timing of all such lasers is very unlikely, a gradual attenuation of the light source can realistically be expected, which can be internally monitored as a signal sent by a railway personnel, and when the light source reaches a predetermined level of illumination, the laser beam can be replaced.

Another important advantage is that multiplying a laser into a filament is much more efficient than multiplying an incoherent source such as an incandescent lamp or a light-emitting diode.

Furthermore, the laser light source is much easier to direct and its amplitude can be easily controlled using cheap and accessible semiconductor electronics. Laser light sources will work at significantly higher electrical-light efficiency than current incandescent lamps.

According to the present invention, a railway light signaling device is provided which includes a housing, a signal light opening on the housing, lenses covering the opening, and a light source inside the housing, to provide light that is directed through the lenses, with the light source being provided by a laser which gives light within a certain light spectrum.

The laser can emit light in the red color spectrum at a wavelength in the range of 630 - 680 nanometers, light in the green color spectrum at a wavelength in the range of 555 nanometers, or light in the yellow color spectrum at a wavelength in the range of 588 nanometers.

The laser can be connected by a light guide to a place opposite the lens. In this case, the laser can be located far from the housing, for example using a light guide, namely an optical cable (for example an optical cable with the addition of a metal oxide that is difficult to reduce, such as praseodymium) as a light guide.

Another option is to place the laser inside the housing.

The laser can be a laser diode that emits light within a certain light spectrum. In that case, the laser diode can be one of such diodes in the beam. Each laser diode can be connected by a suitable light guide to a common location opposite the lens.

A signal light device can function, for example, as a warning light at intersections or as a railway control signal.

There may be a plurality of such light housings, each having an opening for a signal light and a lens covering the opening, and such an illumination source within each housing as to provide light directed through the lens of the housing, the illumination source in each housing originating from at least one laser providing light within the color spectrum that is specific to that housing.

In the case of a laser diode, since its wavelength is actually independent of the supply current, its input or output power, the chromatic coordinates (or colors) will not be a function of the current. An incandescent lamp produces light due to the high temperature of the filament in accordance with the law of black body radiation and therefore the content of its spectrum is a strict function of the power used to heat the filament.

Another advantage is that when using a laser, it is not necessary to use a filter in front of the light source, since the source itself gives the desired color.

This invention will now be described by way of example with reference to the accompanying figures, in which:

Figure 1 shows a typical older railway crossing warning light,

Figure 2 is a diagrammatic illustration of a typical housing of an early railway signal light using an incandescent source,

Fig. 3 appearance of a beam of laser diodes connected to an optical cable,

Figure 4 is a clip showing a railway signal that determines the right of way, using laser diodes as a light source,

Figure 5 is a section, similar to Figure 4, showing an array of laser diodes directly abutting a diffusion lens,

Figure 6 is a layout of the array of laser diodes shown in Figure 5 i

Figure 7 shows a railway signal that determines the right of way, and has three touch laser signal lights that emit light with three different wavelengths.

In the embodiments of the present invention that will be described, laser diodes are used as a light source for railway signals, namely for flashing signaling devices at road crossings and for railway signaling devices that determine the right of way, in the form of a beam of such diodes as a light source. This beam can be located directly at the point of illumination, or it can be located far away, in which case it is connected to the point of illumination inside the housing by optical cables.

Compared to red as the color used on ramps at road-rail crossings, and as one of the colors on railway light devices that determine the right-of-way, such a beam of laser diodes can operate within the red color spectrum of 630-680 nanometers (nm). In that spectrum, laser diodes will not all emit light of the same wavelength, but can emit many different wavelengths within this particular spectrum. For railway signals that determine the right of way, a beam of laser diodes can operate near the wavelength of 588 nm for yellow light and 555 nm for green light. In the case of the need for "white light, a combination of these colors can be used to obtain "white" or the use of two "complementary" colors, that is, those whose wavelengths are connected by a straight line through the white point on the chromatic diagram of the "Commission Internationale d' Eclairege" (CIE). For example, 495 and 670 nm as well as 474 and 569 nm are complementary colors.

In addition to the use of a beam of laser diodes of certain wavelengths mentioned above, the purpose of the invention is also to use an optical cable with the addition of a metal oxide that is difficult to reduce, which can be excited by very efficient near-ultra-red lasers, in order to obtain visible light of the appropriate wavelengths. This is achieved by the gradual absorption of two infrared photons from working lasers and the emission of visible photons from excited atoms of metal oxides. A suitable metal oxide that is difficult to reduce is praseodymium. An optical cable with the addition of this material would use lasers at 1.01 μm and 835 nm to produce light wavelengths of 635 nm (red), 520 nm (green-blue), and 492 (blue). Other metal oxides and different threads can be used to obtain different colors. Importantly, fiber optic cable with accessories used in conjunction with lasers operating at specific wavelengths can provide any color found useful in a railway environment. For further instructions on the use of lasers in combination with fiber optic cable with accessories, see The Journal of Quantum Electronics, Vol. 33, No. 6, July 1977 and the article on p. 905 entitled "Theory of Pr - Doped Fluoride Fiber Upconversion Lasers" by Yuxing Zhao and Simon Fleming.

Figure 1 shows a typical early railway flashing signal light device at rail-road crossings. There is an outer housing 10 which may have an inner mirror layer 12. The layer is placed on the parabolic reflector 14, and there is a color filter and a diverging lens 16 covering the opening of the housing 10. An incandescent light source 18 is located inside the housing and directs the light along the lines of the arrows 20 out through a filter and a diverging lens 16. Such a light source is common and can be seen throughout the United States wherever there are road or railroad crossings.

Figure 2 shows a typical railway signaling device that determines the right of way. There is a housing 30 whose interior can be blackened to avoid light reflection. The housing 30 has an opening 32 and a light source 34 located inside the housing. There is a lens system consisting of an inner lens 36 and an outer lens 38, with the combination of the two lenses in such a way that it is possible to direct the light from the signal source along a predetermined line with very little divergence of the beam in its useful length. This is important because the signal light must be visible from a greater distance, and this can only be achieved if the light from the source is concentrated along the desired direction.

A railroad signal light source from a laser diode according to an example of the present invention is shown in Figures 3 and 4. It may be useful in warning light conditions or as a right-of-way signal. There is a housing 40 having a signal light opening 42. Figure 4 uses a lens system consisting of an inner lens 44 and an outer lens 46, similar to the previous lens structure shown in Figure 2.

A plurality of laser diodes labeled 48, 50, 52, 54 and 56 are used as the light source, which are fed via a cable 90 connected to the power source. The number is illustrative, and concretely there can be from 15 to 20 such diodes and they can be spread in the spectrum of wavelengths from 630 to 680 nanometers, if we use red as an example of railway color. Laser diodes of other spectra should be used for yellow and green signal lights. The laser diodes designated 48 and further are all connected in a light source beam as shown in Figure 3 and located at an opening 58 within the wall 60 of the housing 40. Optical light guides designated 62 connect each light source from the laser diode to the light source beam. shown in Figure 3. One of the advantages of using laser diodes is that they can be located far from the signal enclosure taking advantage of the multiplexing of the laser into the fiber optic cable and the low loss characteristic of existing fiber optic cables available. For example, the loss for a length of ten meters of optical cable can be only 0.04 dB, giving a transmission factor of 99.08%.

There may also be a ring 64 which holds together the light sources in a closed beam so as to give the effect of a point light source, emitting with a characteristic cone of radiation, as indicated by its numerical aperture, and emitting at one or more wavelengths, and can be located to the focus of the collimation optics. Although the laser diodes, as shown in Figure 4, are inside the signal housing, they must be located far from it, if for example in a control box along a right-of-way signal or next to a road and railway crossing.

A particular advantage in using laser diodes as a light source is the longer duration, which is attributed to the diodes themselves as a source, as well as the fact that even if one or more diodes in the beam fail, enough light remains from the beam as a whole. Moreover, solid state sources for electronic controls will contribute to the long life of such a signal light. A further advantage of laser diodes is that each diode is wavelength specific and therefore all light originating from the laser diode is of that wavelength. In contrast, in an incandescent lamp, the light is spread over a large part of the light spectrum. As a specific example of laser diodes that can be satisfactorily used in the present invention, there are laser diodes with nominal wavelengths of 635, 650, 670 and 640 nanometers.

Figure 5 shows the use of an array of laser diodes at 70, with corresponding electrical leads 72, located at an opening 74 inside a signal light housing 76. In this embodiment of the invention there are no optical cables, but a diverging lens 78 is placed in front of the array of laser diodes 70, after which the beam will which originates from the diverging lenses to be collimated by the lens 80. The end result will be a beam of light along the line of arrows 82. Figure 6 is a view of the laser assembly 70 and shows a plurality of individual light sources of laser diodes 84, all within a sheath or sleeve 86.

Fig. 7 shows the multiple housings 76 of Fig. 5 to provide a three-signal light source suitable for railway traffic control with right-of-way devices. For example, in a three-signal light mold there may be typical red, green, and yellow lights, which are produced by individual sets of laser diodes, with the laser diodes operating at the wavelengths described earlier. Of course the invention may include more than three individual signal lights and colors other than red, yellow and green, as required for train control.

The use of laser diodes as a light source makes it possible to modulate the amplitude of the light source with simple and reliable electronic devices. This could have a particular advantage in train control, as the receiver on the locomotive could be tuned to a certain level of modulation, providing electronic feedback for train control, all while the driver's perception of the visible signal.

Claims (16)

1. A railway light signaling device which is characterized by including: a housing, a signal light opening on the housing, lenses covering the opening and a light source inside the housing, to obtain light that is directed through the lenses, the light source being obtained through laser that emits light within a certain light spectrum. 2. Signal light device according to claim 1, characterized in that the laser emits light in the red color spectrum at a wavelength in the range of 630-680 nanometers. 3. Signal light device according to claim 1, characterized in that the laser emits light in the green color spectrum at a wavelength in the range of 555 nanometers. 4. Signal light device according to claim 1, characterized in that the laser emits light in the yellow color spectrum at a wavelength in the range of 588 nanometers. 5. A signal light device according to any preceding claim, characterized in that the laser is connected by a light guide to a location opposite the lens. 6. A signal light device according to claim 5, characterized in that the laser is located away from the housing 7. Signal light device according to claim 6, characterized in that the light guide is an optical cable. 8. A signal light device according to claim 7, characterized in that the optical cable is supplemented with a hard-to-reduce metal oxide. 9. A signal light device according to claim 8, characterized in that the hard-to-reduce metal oxide is praseodymium. 10. A signal light device according to any one of claims 1 to 5, characterized in that the laser is located inside the housing. 11. A signal light device according to any one of claims 1 to 7, characterized in that the laser is a laser diode that emits light within a certain color spectrum. 12. Signal light device according to claim 11, characterized in that the laser diode is one of a beam of such laser diodes. 13. A signal light device according to claim 12, depending on claims 5, 6 or 7, characterized in that each laser diode is connected by a respective light guide to a common location located opposite the lens. 14. A signal light device according to any preceding claim, characterized in that the device acts as a warning light at intersections. 15. A signal light device according to any one of claims 1 to 13, characterized in that the device acts as a train control signal. 16. A signal light device according to any preceding claim, characterized in that there are a plurality of such signal light housings, each having a signal light opening and a lens covering the opening, and there is such a light source within each of said housings as to provide light which is directed through the housing lens, and the light source in each housing originates from at least one laser that provides light within the color spectrum specific to that housing.