Visible Light Source

Abstract

A visible light source capable of preventing degradation of a laser diode and accurately monitoring light of a plurality of wavelengths without hermetic sealing is provided. The visible light source includes a laser diode that is configured to output visible light, and a planar lightwave circuit (PLC) including an input waveguide optically coupled to the laser diode. A space is provided between an emission end face of the laser diode and the input waveguide, and is filled with an inorganic material.

Claims

1. A visible light source, comprising: a laser diode that is configured to output visible light; and a planar lightwave circuit (PLC) including an input waveguide optically coupled to the laser diode, wherein a space is provided between an emission end face of the laser diode and the input waveguide, and is filled with an inorganic material.

2. A visible light source, comprising: a plurality of laser diodes that are configured to output visible light; a plurality of input waveguides each optically coupled to a corresponding one of the plurality of laser diodes; a multiplexing unit that is configured to multiplex light from the plurality of input waveguides; and an output waveguide that is configured to output light multiplexed by the multiplexing unit, wherein a space is provided between an emission end face of the plurality of laser diodes and the plurality of input waveguides, and is filled with an inorganic material.

3. The visible light source according to claim 2, further comprising: a plurality of branching units that are each inserted into a corresponding one of the plurality of input waveguides, and each configured to divide light from a corresponding one of the plurality of input waveguides, output one beam of the divided light to the multiplexing unit, and output another beam of the divided light to a monitoring waveguide; and a plurality of photodiodes each optically coupled to a corresponding one of the plurality of monitoring waveguides.

4. The visible light source according to claim 2, further comprising a spot size converter at an emission end face of the output waveguide.

5. The visible light source according to claim 2, wherein the plurality of laser diodes are three laser diodes that are configured to output three primary colors of red light (R), green light (G), and blue light (B).

6. The visible light source according to claim 3, further comprising a spot size converter at an emission end face of the output waveguide.

7. The visible light source according to claim 3, wherein the plurality of laser diodes are three laser diodes that are configured to output three primary colors of red light (R), green light (G), and blue light (B).

8. The visible light source according to claim 4, wherein the plurality of laser diodes are three laser diodes that are configured to output three primary colors of red light (R), green light (G), and blue light (B).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0019] FIG. 1 is a diagram illustrating a typical light source of a projector using an LD.

[0020] FIG. 2 is a diagram illustrating a basic structure of an RGB coupler using a PLC.

[0021] FIG. 3 is a diagram illustrating a configuration of an RGB coupler using two directional couplers.

[0022] FIG. 4 is a diagram illustrating a light source with a monitoring function according to a first embodiment of the present invention.

[0023] FIG. 5 is a diagram illustrating a state of coupling of an LD and an RGB coupler of a light source with a monitoring function according to a second embodiment of the present invention.

[0024] FIG. 6 is a diagram illustrating another example of the coupling of the LD and the RGB coupler according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

[0025] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the present embodiment, description is given for the case of a method using a directional coupler as a multiplexer, but the present invention is not limited to a multiplexing method.

First Embodiment

[0026] In the optical connection between the LDs 21 to 23 and the RGB coupler 20 illustrated in FIG. 2, optical axes are generally aligned with each other through a space. However, the LDs 21 to 23 for visible light used in the light source have a wavelength shorter and also have a mode field diameter smaller than those of an LD in a communication wavelength band. Therefore, even when the LDs 21 to 23 have the same light output power as that of the communication wavelength band, a power density thereof is higher by one order of magnitude. Furthermore, since the energy of the ultraviolet light from the visible light is higher than the energy of the light in the communication wavelength band, an emission end face is severely degraded due to a dust collection effect of the light, and the life of the LD is shortened. Thus, deterioration is suppressed by hermetically sealing the LD and the RGB coupler in a housing made of a metal or a resin.

[0027] FIG. 4 illustrates a light source with a monitoring function according to a first embodiment of the present invention. A light source 200 with a monitoring function includes first to third LDs 201.sub.1 to 201.sub.3 that respectively output light of respective colors of G, B, and R, a PLC-type RGB coupler 210, and first to third PDs 202.sub.1 to 202.sub.3 optically connected to the RGB coupler 210. An output of the RGB coupler 210 is taken out of a window 203 provided in a housing, and, for example, when the output is applied to a projector, a MEMS mirror is irradiated with the output.

[0028] Furthermore, the light source 200 with a monitoring function includes a thermistor 204. Since an oscillation wavelength of each of the LDs 201 fluctuates due to a change in temperature, feedback control is performed on the LDs 201 in accordance with the change in temperature.

[0029] The PLC-type RGB coupler 210 includes first to third input waveguides 211.sub.1 to 211.sub.3 optically connected to the first to third LDs 201.sub.1 to 201.sub.3, first to third branching units 212.sub.1 to 212.sub.3 that divide light propagating through the waveguide into two, a multiplexing unit 214 that multiplexes one beam of the light divided by each of the first to third branching units 212.sub.1 to 212.sub.3, first to third monitoring waveguides 213.sub.1 to 213.sub.3 that output the other beam of the light divided by each of the first to third branching units 212.sub.1 to 212.sub.3 to the first to third PDs 202.sub.1 to 202.sub.3, and an output waveguide 215 that outputs the light multiplexed by the multiplexing unit 214.

[0030] In the PLC-type RGB coupler 210, light incident on each of the first to third input waveguides 211.sub.1 to 211.sub.3 is divided into two by each of the first to third branching units 212.sub.1 to 212.sub.3. One beam of the divided light is output to the first to third PDs 202.sub.1 to 202.sub.3 via the first to third monitoring waveguides 213.sub.1 to 213.sub.3, and the other beam of the divided light is multiplexed by the multiplexing unit 214 and output to the output waveguide 215.

[0031] An optical multiplexing circuit using the directional coupler illustrated in FIG. 3 can be used as the multiplexing unit 214. In this case, the first to third input waveguides 211.sub.1 to 211.sub.3 are coupled to the first to third input waveguides 101 to 103 illustrated in FIG. 3, respectively, and the output waveguide 215 is coupled to the output waveguide 106 illustrated in FIG. 3. However, the multiplexing unit 214 is not limited thereto, and another multiplexing unit of a waveguide type (for example, a Mach-Zehnder interferometer, a mode coupler, or the like) may be used.

[0032] As illustrated in FIG. 4, when light propagating through the first to third input waveguides 211.sub.1 to 211.sub.3 is divided by the first to third branching units 212.sub.1 to 212.sub.3, respectively, a coupling characteristic between the first to third LDs 201.sub.1 to 201.sub.3 and the first to third input waveguides 211.sub.1 to 211.sub.3 can be monitored. In addition, it is possible to adjust white balance as a light source by using a monitoring value of the first to third PDs 202.sub.1 to 202.sub.3 by recognizing a multiplexing characteristic of the multiplexing unit 214 in advance.

Second Embodiment

[0033] On the other hand, hermetic sealing by a housing made of a metal or a resin increases a production process of a visible light source and increases a manufacturing cost. Thus, an optical connection between the LD and the RGB coupler 20 that does not require hermetic sealing is achieved. A configuration of a light source with a monitoring function according to a second embodiment is the same as that according to the first embodiment, and the method of optically coupling the first to third LDs 201.sub.1 to 201.sub.3 and the RGB coupler 210 is different.

[0034] FIG. 5 illustrates a state of coupling of an LD and an RGB coupler of the light source with the monitoring function according to the second embodiment of the present invention. As illustrated in FIG. 5(a), the RGB coupler is acquired by forming an optical circuit in a SiO.sub.2 layer 402 formed on a Si substrate 401, and being fixed to a bottom portion of a housing 403 made of a metal. An LD 405 of each color of R, G, and B together with a chip 406 including a drive circuit are mounted on a mounting 404 for heat radiation, and are fixed to a bottom portion of the housing 403.

[0035] As described above, optical connection between the LD 405 and an input waveguide 407 formed in the SiO.sub.2 layer 402 is performed through a space. As illustrated in FIG. 5(b), a width W of the waveguide 407 is approximately several μm, and a width S of the space is also approximately several μm. The size of the chip of the LD 405 is approximately 150 μm square, but an active layer has a width of approximately several μm, and is aligned so as to face the input waveguide 407. In the second embodiment, an inorganic material 408 such as polysilazane fills the space and is sintered.

[0036] FIG. 6 illustrates another example of the coupling of the LD and the RGB coupler according to the second embodiment. The inorganic material 408 may cover a space between an emission end of the LD 405 and the input waveguide 407. Thus, grooves 409a and 409b are formed on both sides of the input waveguide 407 formed in the RGB coupler such that the inorganic material 408 does not spread out along the space.

[0037] With such a configuration, an emission end of the LD of each color of R, G, and B is covered by an inorganic material, and thus it is possible to prevent an organic substance from adhering to an emission end face due to a dust collection effect of light or the like. As a result, degradation of the LD can be prevented and a long life can be achieved, and white balance as a light source can also be accurately adjusted without hermetic sealing.

Third Embodiment

[0038] An emission end of the first to third monitoring waveguides 213.sub.1 to 213.sub.3 of the RGB coupler 210 illustrated in FIG. 4 may emit light having a power lower than that of the output of the first to third LDs 201.sub.1 to 201.sub.3, but the light has a short wavelength, and thus degradation of the emission end face may occur due to light with a short wavelength. Further, an emission end of the output waveguide 215 emits light that is in a broad wavelength range in which light of each color of R, G, and B is multiplexed, but has a high power, and degradation of an emission end face may still occur. Thus, it is preferable that the mode field diameter be increased by providing a spot size convertor (SSC) at the emission end of the first to third monitoring waveguides 213.sub.1 to 213.sub.3 and the output waveguide 215 to reduce a power density at the emission end face.