JP2013252440A - Optical fiber illumination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber illumination device suitable for use for an endoscope.SOLUTION: An optical fiber illumination device includes: a semiconductor laser 10 emitting exciting light 100; a single fiber 20 guiding the exciting light 100 emitted from the semiconductor laser 10; a phosphor unit 30 receiving the exciting light 100 emitted from the single fiber 20, and emitting fluorescence having a wavelength different from the exciting light 100; and a fiber bundle 40 guiding at least a part of the fluorescence emitted from the phosphor unit 30. The phosphor unit 30 can be selected from a plurality of wavelength conversion parts each emitting light having a different spectrum.

Description

  The present invention relates to an optical fiber lighting device.

  There has been proposed an optical fiber illuminating device in which a plurality of LEDs are arranged at the proximal portion of the endoscope and guided by a fiber bundle to the light emitting portion at the distal end of the endoscope via the insertion portion. The fiber bundles are bundled together on the endoscope distal side, but are divided into three on the light source side, and are optically coupled to LEDs that emit red light, green light, and blue light, respectively. .

JP 2006-314686 A

  In this optical fiber illuminating device, illumination light is guided by a fiber bundle from the proximal portion of the endoscope to the light emitting portion at the distal end of the endoscope. Generally, since the waveguide efficiency of the optical fiber has wavelength dependence, The RGB output ratio at and the RGB output ratio at the exit end differ depending on the waveguide length of the fiber bundle. For this reason, in order to obtain a desired RGB output ratio at the exit end, the RGB output ratio at the entrance end must be adjusted according to the length of the fiber bundle.

  The objective of this invention is providing the optical fiber illuminating device suitable for the use to an endoscope.

  An optical fiber lighting device according to the present invention includes an excitation light source that emits excitation light, a first optical fiber that guides the excitation light emitted from the excitation light source, and the emission light that is emitted from the first optical fiber. A wavelength converter that receives the excitation light and emits wavelength-converted light having a wavelength different from that of the excitation light; and a second optical fiber that guides at least a part of the wavelength-converted light emitted from the wavelength converter. It has. The wavelength converter can be selected from a plurality of wavelength converters that emit light with different spectra.

  According to the present invention, an optical fiber illumination device suitable for use in an endoscope is provided.

1 schematically shows an optical fiber lighting device according to a first embodiment of the present invention. The spectrum of the illumination light inject | emitted from the optical fiber illuminating device of FIG. 1 is shown. The transmission loss characteristic of the general optical fiber for guiding the light of visible region is shown. The peripheral part of the fluorescence unit of the optical fiber illuminating device by 2nd embodiment of this invention is shown. Fig. 5 shows a spectrum of fluorescence emitted from the phosphor unit shown in Fig. 4. 3 schematically shows an optical fiber lighting device according to a third embodiment of the invention. 7 shows an enlarged view of the periphery of the phosphor unit of the optical fiber illuminating device in FIG. 6. The spectrum of the illumination light inject | emitted from the optical fiber illuminating device of FIG. 6 is shown. 6 schematically shows an optical fiber lighting device according to a fourth embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First embodiment>
FIG. 1 shows an optical fiber lighting device according to a first embodiment of the present invention. As shown in FIG. 1, the optical fiber illumination device includes a semiconductor laser 10 that emits a laser beam that is an excitation light source that emits the excitation light 100, and a first waveguide that guides the excitation light 100 emitted from the semiconductor laser 10. A single fiber 20 that is an optical fiber; a phosphor unit 30 that is a wavelength conversion unit that receives the excitation light 100 emitted from the single fiber 20 and emits fluorescence that is wavelength-converted light having a wavelength different from that of the excitation light 100; It has the fiber bundle 40 which bundled the several single fiber which is the 2nd optical fiber which guides the wavelength conversion light emitted from the fluorescent substance unit 30, ie, a part of fluorescence, at least. A condensing lens 80 that condenses the excitation light 100 emitted from the semiconductor laser 10 in the incident region of the single fiber 20 is disposed between the semiconductor laser 10 and the single fiber 20.

  In FIG. 1, the excitation light 100 emitted from the semiconductor laser 10 is collected by the condenser lens 80 and enters the single fiber 20. The excitation light 100 incident on the single fiber 20 is guided by the single fiber 20 and is emitted from the exit end of the single fiber 20. The excitation light 100 emitted from the single fiber 20 enters the phosphor unit 30, a part of the excitation light 100 enters the phosphor unit 30, and is longer than the excitation light 100 by the phosphor in the phosphor unit 30. Converted to wavelength fluorescence. A part of the fluorescence and a part of the excitation light 100 enter the fiber bundle 40 and are emitted as illumination light 110 from the exit end of the fiber bundle 40.

  When this optical fiber illuminating device is used for an endoscope, the length of the single fiber 20 can be arbitrarily selected as necessary. However, the length of the fiber bundle 40 is generated at the distal end of the endoscope. It is necessary to select in consideration. That is, when a brightness of about 20 lm is realized, the heat generation in the phosphor unit 30 increases by about 40 ° C. compared to the ambient temperature, particularly when no heat dissipation mechanism is provided. For this reason, it is necessary to determine the length of the fiber bundle 40 in consideration of the configuration around the phosphor unit 30 and the influence of heat to the outside. Considering the influence on the device provided inside the imaging element or the like integrated at the distal end portion of the endoscope and the influence on the human body as the observation target, the phosphor unit 30 is 10 cm or more from the distal end of the endoscope insertion portion. It is necessary to keep away. That is, the length of the fiber bundle 40 is desirably 10 cm or more. Thereby, it is possible to reduce heat generation from the distal end portion of the endoscope.

  The semiconductor laser 10 is a blue semiconductor laser light source having a peak at a wavelength of 480 nm or less, for example, a blue semiconductor laser that emits light in a blue band of 440 nm. The phosphor unit 30 includes a phosphor that emits fluorescence having a peak at least at 540 nm or more. This phosphor is, for example, a cerium-added YAG phosphor that emits light having a spectrum having a peak at 560 nm and extending to a wavelength region of 700 nm or more with respect to excitation by excitation light of 440 nm. The spectrum of the illumination light 110 emitted from the fiber bundle 40 is shown in FIG. In the case of white light having such a spectrum, the blue component is only about 440 nm laser light. Therefore, the waveguide loss of blue light can be represented by the waveguide loss having the peak value of 440 nm. it can.

  Both the single fiber 20 and the fiber bundle 40 are general optical fibers for guiding light in the visible light region, and have transmission loss characteristics as shown in FIG. The dotted line in FIG. 3 is that of a normal optical fiber, and the solid line is that of a high-quality optical fiber. As shown in the figure, when a high-quality optical fiber is used, the characteristics in the infrared region and the ultraviolet region are improved, but in the visible region, the characteristics are almost similar. As shown in FIG. 3, the transmission loss at 440 nm is about 0.2 dB / m, the transmission loss at 560 nm band is about 0.1 dB / m, and the difference is only about 0.1 dB. This means that, in terms of transmittance, 440 nm light has a 2.3% decrease in light components in the 440 nm band per meter compared to 560 nm light. Therefore, when this optical fiber is used, if the light emitted from the phosphor unit is guided, the blue component decreases according to the distance. Therefore, if the length L2 of the fiber bundle 40 is excessively increased, the light is emitted from the emission end. The illuminating light 110 to be applied has a strong yellow to reddish taste. That is, the spectrum of light emitted from the exit end of the fiber bundle 40 becomes smaller in the blue region than the desired RGB output ratio. In other words, the difference between the spectral pattern corresponding to the desired RGB output ratio and the spectral pattern of the actually emitted light is larger than the predetermined value in the 400 to 500 nm band as compared with the wavelength region longer than that. .

  For this reason, in this embodiment, the length L2 of the fiber bundle 40 is 1 m, and the length L1 of the single fiber 20 is 3 m. According to this, the excitation light emitted from the excitation light source is incident on the single fiber 20 and guided to the phosphor unit 30 by being guided by 3 m. Assuming that the amount of light at the incident end of the single fiber 20 is 1, this optical fiber has a loss of 0.2 dB / m in the 440 nm band, and thus decreases to 0.87 at the time when the phosphor unit 30 is irradiated. However, at this time, since it is a monochromatic waveguide, it is merely a loss of the waveguide and does not affect the spectrum of the illumination light 110.

  Next, the phosphor unit 30 is irradiated with this excitation light. The light emitted from the phosphor unit 30 has a spectrum as shown in FIG. 2, and the peak intensity of the excitation light having a wavelength of 440 nm is slightly larger than the peak intensity of the fluorescence having a wavelength of 560 nm. It has been adjusted to be. Here, assuming that the peak intensity of each wavelength at the incident end of the fiber bundle 40 is 1, the intensity of 440 nm blue light at the exit end after 1 m transmission by the fiber bundle 40 is 0.955, which is 560 nm. The intensity of fluorescence is 0.977. Therefore, the difference between the two is about 2.2%. Therefore, according to this embodiment, when a light source unit that transmits 4 m is used, as compared with the 9% difference in intensity between 440 nm light and 560 nm light when each color is guided by 4 m as in the conventional technique, The difference can be reduced to 2.2%. That is, the difference between the spectrum of light emitted from the exit end of the fiber bundle 40 and the spectrum pattern corresponding to the desired RGB output ratio can be set within a predetermined range.

  Thus, in this embodiment, the light guided by the fiber bundle 40 is white light and has a wavelength spread, and the length of the fiber bundle 40 is in the wavelength region of the light guided by the fiber bundle 40. It is set on the basis of the waveguide loss. Specifically, the length of the fiber bundle 40 is selected to be 1 m so that the difference in waveguide efficiency with respect to the wavelength region of light guided by the fiber bundle 40 is 2.2% or less.

  With this configuration, a 2 m long optical fiber illuminating device, a 4 m long optical fiber illuminating device, and a 10 m long optical fiber illuminating device are manufactured using the same phosphor unit and the same excitation light source. In this case, it is possible to provide a stable optical fiber illumination device in which the emission spectrum of the illumination light 110 emitted from the exit end of the fiber bundle 40 does not change by adjusting the length of the single fiber 20. It becomes possible. Furthermore, even when only a single-length optical fiber illumination device is produced, the spectrum adjusted with the phosphor unit 30 alone is not greatly changed, and therefore, spectrum evaluation with the second optical fiber attached becomes unnecessary. It is also possible to reduce the load in the manufacturing steps. Furthermore, even when multiple types of optical fibers are used for the second optical fiber, the longest length is calculated from the waveguide loss characteristics, so that the phosphor unit for each type of optical fiber. There is no need to adjust 30 and even if only the second optical fiber is replaced, there is no significant change in color.

  As described above, according to the present embodiment, it is possible to reduce the influence of the change in the length of the fiber bundle 40 on the color of the illumination light, and a stable optical fiber whose color does not change in the wavelength region of the illumination light. An illumination device can be provided.

<Second embodiment>
FIG. 4 shows the periphery of the fluorescent unit of the optical fiber illuminating device according to the second embodiment of the present invention. The optical fiber illuminating device of the present embodiment has the same basic structure as that of the first embodiment, but as shown in FIG. 4, the phosphor unit 30 corresponds to red (R), green (G), and blue (B). A plurality of RGB phosphors 30a, 30b, and 30c that emit the respective fluorescence are mixed and sealed with resin.

  In this embodiment, the semiconductor laser 10 which is an excitation light source is a 405 nm blue-violet laser light source, and the phosphor unit 30 includes general RGB phosphors 30a, 30b and 30c which are excited in this wavelength band. Yes. The RGB phosphors 30a, 30b, and 30c are excited by 405 nm excitation light and emit 460 nm blue, 540 nm green, and 630 nm red fluorescence, respectively. The spectrum of the fluorescence emitted from the phosphor unit 30 is shown in FIG. As shown in FIG. 5, the excitation light of 405 nm is converted into almost RGB fluorescence by the phosphor unit 30, and the light intensity of the excitation light is smaller than the spectrum of the first embodiment shown in FIG. It has become. Since this excitation light hardly affects the color of the illumination light 110, only the light emission from the RGB phosphors 30a, 30b, 30c may be considered here. Therefore, it can be seen from FIG. 3 that transmission losses at wavelengths of 460 nm, 540 nm, and 630 nm are about 0.2 dB / m, 0.1 dB / m, and 0.05 dB / m. In addition, the light of each wavelength emitted from the phosphor is broader than the excitation light, and both light having a wavelength shorter than the peak and light having a longer wavelength exist, but the half-value width is about several tens of nm. The transmission loss may be obtained approximately using the value of the transmission loss at the peak wavelength. According to this, the difference Δα between the maximum value and the minimum value of transmission loss is the difference in transmission loss between 450 nm and 650 nm, and Δα = 0.15 dB / m. That is, it shifts by 3.4% per meter.

  In the case of using this light source, calculation is performed using Lmax = Δλ / ((1-10 (−Δα / 10)) × 100) where the allowable value Δλ of the difference in intensity of the spectrum of each wavelength component is 10%. The length range of the fiber bundle 40 which is the second optical fiber is 3 m. In other words, if the difference between the longest and shortest optical fibers is 3 m or less, Δλ can be 10% or less.

  In other words, the range of the length of the fiber bundle 40 is the difference between the maximum value and the minimum value of the waveguide loss due to the fiber bundle 40 in the wavelength region of the illumination light 110 emitted from the fiber bundle 40, Δα [dB / m]. And Lmax [m] = Δλ / ((1-10 (−Δα / 10)) × 100, where Δλ [%] is the allowable difference in spectral intensity change of each wavelength component in the wavelength region of the illumination light 110. ) It should be the following.

  The light guided by the fiber bundle 40 has a plurality of peaks in its intensity spectrum, and the difference Δα between the maximum value and the minimum value of the waveguide loss is based on the maximum value of the waveguide loss at the wavelengths of the plurality of peaks. The minimum value is subtracted.

  The light guided by the fiber bundle 40 has a wavelength spread, and the length of the fiber bundle 40 is such that the spectrum of the light emitted from the exit end of the optical fiber bundle 40 is a desired RGB at the exit end. The predetermined pattern corresponding to the output ratio is determined.

  The allowable value Δλ of the difference in spectral intensity change of each wavelength component varies depending on the purpose of use of the illumination device. It is desirable to make it smaller than about 10% for general lighting applications and about 5% for medical applications. That is, it is desirable that the difference between the spectral pattern corresponding to the desired RGB output ratio and the spectral pattern of the light emitted from the exit end of the fiber bundle 40 be a predetermined value or less. In other words, this allowable range is desirably 10% or less for general lighting applications and 5% or less for medical applications. For example, in medical applications, it is possible to realize more desirable illumination light by suppressing the length within 1.5 m.

  As described above, according to the present embodiment, it is possible to reduce the influence of the change in the length of the fiber bundle 40 on the RGB output ratio, and stable optical fiber illumination that does not change in color in the wavelength range of illumination light. An apparatus can be provided.

<Third embodiment>
FIG. 6 shows an optical fiber lighting device according to a third embodiment of the present invention. The optical fiber illuminating device of the present embodiment has the same basic structure as that of the first embodiment, but, as shown in FIG. 6, instead of the semiconductor laser 10, a plurality of semiconductor lasers 10-1 and 10 that respectively emit excitation light. −2 and 10−3, and instead of the single fiber 20, a plurality of single fibers 20− that respectively guide pumping lights respectively emitted from the plurality of semiconductor lasers 10-1, 10-2, and 10-3. 1, 20-2, 20-3, and instead of the phosphor unit 30, the excitation light emitted from each of the plurality of single fibers 20-1, 20-2, and 20-3 is received and has different wavelengths. The plurality of phosphor units 30-1, 30-2, and 30-3 that respectively emit the wavelength-converted light. Further, instead of the condensing lens 80, the semiconductor lasers 10-1, 10-2, 10-3 and the single fibers 20-1, 20-2, 20-3 are respectively disposed between the semiconductor lasers 10-1, 10-2. Condensing lenses 80-1, 80-2, and 80-3 for condensing excitation light emitted from −2, 10-3 in the incident areas of the single fibers 20-1, 20-2, and 20-3, respectively. Has been.

  The phosphor units 30-1, 30-2, and 30-3 include phosphors that emit fluorescence in a red region of 630 nm, a green region of 540 nm, and a blue region of 460 nm, respectively. The wavelengths of the light emitted from the semiconductor lasers 10-1, 10-2, and 10-3 are preferably selected in accordance with the excitation efficiencies of these phosphors.

  FIG. 7 is an enlarged view of the periphery of the phosphor units 30-1, 30-2, and 30-3. As shown in FIG. 7, a light shielding plate 92 is provided between the phosphor units 30-1, 30-2, and 30-3. The fiber bundle 40 is composed of partial fiber bundles 40-1, 40-2, 40-3 connected to the phosphor units 30-1, 30-2, 30-3, respectively. The arrangement of the single fibers constituting the fiber bundle 40 is different between the incident end and the emission end, and the single fibers constituting the partial fiber bundles 40-1, 40-2, 40-3 are the fluorescence emitted by them. Are substantially uniformly mixed at the exit end of the fiber bundle 40. Further, at the emission end of the fiber bundle 40, the center of gravity of the output intensity of each of the fluorescence emitted through the partial fiber bundles 40-1, 40-2, and 40-3 is substantially the same as the center of the effective emission region of the fiber bundle 40. Configured to match. The number of single fibers constituting the partial fiber bundles 40-1, 40-2, 40-3 may be equal to each other. The number of single fibers constituting the partial fiber bundles 40-1, 40-2, and 40-3 is determined through the partial fiber bundles 40-1, 40-2, and 40-3 according to the emission intensity of each fluorescent light. You may adjust so that it may become a desired color, for example, white, when each emitted fluorescence mixes.

  In FIG. 6 and FIG. 7, the excitation light emitted from the plurality of semiconductor lasers 10-1, 10-2, 10-3 respectively passes through the corresponding single fibers 20-1, 20-2, 20-3. Then, the light enters the corresponding plurality of phosphor units 30-1, 30-2, and 30-3. The plurality of phosphor units 30-1, 30-2, 30-3 receive excitation light emitted from the plurality of single fibers 20-1, 20-2, 20-3, respectively, and receive red and green regions. And emits fluorescence in the blue region. The fluorescence emitted from the plurality of phosphor units 30-1, 30-2, 30-3 is white from the exit end of the fiber bundle 40 via the partial fiber bundles 40-1, 40-2, 40-3, respectively. Is emitted as illumination light 110.

  In the present embodiment, as shown in FIG. 8, in the selection of the phosphors, those that emit fluorescence having a broader spectrum than those in the second embodiment are selected. In such a case, it is desirable to calculate not only the peak of the fluorescence emitted from each phosphor but also its base in calculating the transmission loss. The calculation is performed over the entire visible light region that can be seen by a typical human being, that is, the region from 400 nm to 700 nm. In other words, it is desirable to consider the desired RGB output ratio from the red region, which is the visible region, to the purple region, rather than considering only the R region, G region, and B region. That is, from FIG. 3, the difference Δα between the maximum value and the minimum value of transmission loss is 0.25−0.05 = 0.2 dB / m, which corresponds to 4.5% / m. As a result, if the range of the length of the fiber bundle 40, that is, the difference between the longest and the shortest is 1.1 m or less, the allowable value Δλ of the difference in the intensity of the spectrum of each wavelength component should be 10% or less. Can do. That is, for a Δλ of 10%, the length range of the fiber bundle 40 may be 1.1 m or less. For example, if Δλ is set to 5%, for example, for medical use, where the change in color needs to be reduced, the length range of the fiber bundle 40 needs to be about 50 cm.

  Further, when the color is adjusted only with the phosphor units 30-1, 30-2, and 30-3, the length of the fiber bundle 40 is 1.1 m with respect to Δλ of 10% and 5%, What is necessary is just to be 0.55 m or less. That is, when the color is adjusted only with the phosphor units 30-1, 30-2, and 30-3, the shortest of the length range of the fiber bundle 40 is 0 m, so the longest is relative to Δλ. Thus, 1.1 m and 0.55 m may be used, respectively.

  In this embodiment, the light guided by the fiber bundle 40 has a plurality of peaks in its intensity spectrum, and the difference Δα between the maximum value and the minimum value of the waveguide loss is the plurality of phosphor units 30-1. , 30-2, 30-3, and subtracting the minimum value from the maximum value of the waveguide loss for the light emitted from the plurality of semiconductor lasers 10-1, 10-2, 10-3. Value.

  As described above, according to the present embodiment, it is possible to reduce the influence of the change in the length of the fiber bundle 40 on the RGB output ratio, and stable optical fiber illumination that does not change in color in the wavelength range of illumination light. An apparatus can be provided.

<Fourth embodiment>
FIG. 9 shows an optical fiber lighting device according to a fourth embodiment of the present invention. The optical fiber illuminating device of the present embodiment has the same basic structure as that of the first embodiment, but includes an LED 12 that emits LED light instead of the semiconductor laser 10 as an excitation light source as shown in FIG. Instead of the single fiber 20, an optical fiber has a fiber bundle 24 in which a plurality of single fibers are bundled. By using the LED 12 as the excitation light source, it is possible to simultaneously realize low cost and eye safe. In addition, the system can be simplified such that a feedback circuit for optical output is not required. Further, by using the fiber bundle 24 as the first optical fiber that guides the excitation light, the LED light can be efficiently guided to irradiate the phosphor unit 30.

  In the present embodiment, the excitation light source is configured by the lamp-type LED 12 having a dome lens, but is not limited thereto. The excitation light source may be composed of, for example, a current confinement type LED light source or an SLD light source. By using a current confinement type LED light source or SLD light source, it becomes possible to improve the coupling with the optical fiber as compared with normal LED light, and it is possible to improve the utilization efficiency of the excitation light.

  As described above, according to the present embodiment, it is possible to provide a stable optical fiber illumination device that does not change in color in the wavelength region of illumination light.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these embodiments, and various modifications and changes can be made without departing from the scope of the present invention. Also good.

  DESCRIPTION OF SYMBOLS 10,10-1,10-2,10-3 ... Semiconductor laser, 12 ... LED, 20, 20-1, 20-2, 20-3 ... Single fiber, 24 ... Fiber bundle, 30, 30-1, 30 -2, 30-3 ... phosphor unit, 30a, 30b, 30c ... RGB phosphor, 40 ... fiber bundle, 40-1, 40-2, 40-3 ... partial fiber bundle, 80, 80-1, 80- 2, 80-3 ... Condensing lens, 92 ... Light shielding plate, 100 ... Excitation light, 110 ... Illumination light.

Claims (13)

An excitation light source that emits excitation light;
A first optical fiber that guides the excitation light emitted from the excitation light source;
A wavelength converter that receives the excitation light emitted from the first optical fiber and emits wavelength-converted light having a wavelength different from that of the excitation light;
A second optical fiber that guides at least a part of the wavelength-converted light emitted from the wavelength converter;
The said wavelength converter is an optical fiber illuminating device which can be selected from the several wavelength converter which light-emits by a different spectrum.   The optical fiber illuminating apparatus according to claim 1, wherein the plurality of wavelength conversion units include a wavelength conversion unit containing one or more phosphors.   The optical fiber illumination device according to claim 2, wherein the wavelength conversion unit containing a plurality of phosphors is a mixture of a plurality of phosphors or an adjacent arrangement. A semiconductor laser light source is selected as the excitation light source,
The at least one of the plurality of wavelength conversion units transmits or scatters a part of the laser light emitted from the semiconductor laser light source without wavelength conversion and radiates the laser light toward the second optical fiber. The optical fiber lighting device described.   The optical fiber illumination device according to claim 2, wherein the plurality of wavelength conversion units include a phosphor that emits light in any one of a blue region, a green region, a red region, and a white region.   The optical fiber illumination device according to claim 1, wherein the second optical fiber is a fiber bundle, and an arrangement of the plurality of single fibers constituting the fiber bundle is different between the incident end and the exit end.   The incident end of the fiber bundle is a plurality of partial fiber bundles separated into a plurality, and the fiber bundle is configured such that light incident on each partial fiber bundle is mixed almost uniformly at the exit end. Item 7. The optical fiber lighting device according to Item 6. There are a plurality of combinations of the excitation light source, the first optical fiber, and the wavelength conversion member,
The plurality of wavelength conversion members have different wavelength conversion characteristics from each other,
The optical fiber illuminating device according to claim 1 or 7, wherein each is incident from an incident end of the second optical fiber and is emitted from an illumination light emitting end.   The second optical fiber has a plurality of separated incident ends and one illumination light exit end, and the plurality of wavelength conversion members are respectively arranged to face the plurality of separated incident ends. The optical fiber lighting device according to claim 8.   The optical fiber lighting device according to claim 1, wherein the second optical fiber is shorter than the first optical fiber.   The optical fiber lighting device according to claim 10, wherein the first optical fiber can be selected from a plurality of types of optical fibers having different lengths.   The optical fiber illumination device according to claim 11, wherein the plurality of types of first optical fibers have substantially equal waveguide loss characteristics.   An endoscope comprising the optical fiber illuminator according to any one of claims 1 to 12.

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