Patent ID: 12197006

DESCRIPTION OF EMBODIMENTS

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. An RGB coupler that multiplexes wavelengths of three primary colors of light is described as an example, but it goes without saying that the present invention can be applied to optical multiplexing circuits that multiplex a plurality of other wavelengths.

First Embodiment

FIG.4is a diagram illustrating a light source with a monitoring function according to a first example of a first embodiment of the present invention. A light source with a monitoring function includes first to third LDs2011to2013that respectively output light of respective colors of R, G, and B, a PLC-type RGB coupler210, and first to third PDs2021to2023optically connected to the RGB coupler210.

The PLC-type RGB coupler210includes first to third input waveguides2111to2113optically connected to the first to third LDs2011to2013, first to third branching units2121to2123that divide light propagating through the waveguide into two, a multiplexing unit214that multiplexes one beam of the light divided by each of the first to third branching units2121to2123, first to third monitoring waveguides2131to2133that output the other beam of the light divided by each of the first to third branching units2121to2123to the first to third PDs2021to2023, and an output waveguide215that outputs the light multiplexed by the multiplexing unit214.

In the PLC-type RGB coupler210, light incident on each of the first to third input waveguides2111to2113is divided into two by each of the first to third branching units2121to2123. One beam of the divided light is output to the first to third PDs2021to2023via the first to third monitoring waveguides2131to2133, and the other beam of the divided light is multiplexed by the multiplexing unit214and output to the output waveguide215.

An optical multiplexing circuit using the directional coupler illustrated inFIG.3can be used as the multiplexing unit214. In this case, the first to third input waveguides2111to2113are coupled to the first to third input waveguides101to103illustrated inFIG.3, respectively, and the output waveguide215is coupled to the output waveguide106illustrated inFIG.3. However, the multiplexing unit214is 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.

As illustrated inFIG.4, when light propagating through the first to third input waveguides2111to2113is divided by the first to third branching units2121to2123, respectively, a coupling characteristic between the first to third LDs2011to2013and the first to third input waveguides2111to2113can 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 PDs2021to2023by recognizing a multiplexing characteristic of the multiplexing unit214in advance.

Second Embodiment

According to the first example of the first embodiment, the first to third PDs2021to2023can respectively monitor light of the respective colors of R, G, and B. Thus, even if, for example, deviation from a design value of an RGB coupler is different between the short wavelength side (B) and the long wavelength side (R) due to an error in manufacturing, a white balance can be adjusted with high accuracy since feedback control can be performed individually. However, in a case where it is out of a range for feedback control due to the error in manufacturing, accurate white balance adjustment cannot be made. Thus, in a second embodiment, a configuration is employed in which individual accurate monitoring is possible even at a time of actual operation of a light source without setting a small allowable error in manufacturing.

First Example

FIG.5is a diagram illustrating a light source with a monitoring function according to a first example of the second embodiment of the present invention. The light source of the first example can be said to have a configuration in which three of the RGB coupler210of the first embodiment are integrated into an RGB coupler310on the same PLC substrate. A light source with a monitoring function includes first to third LDs3011to3013that respectively output light of respective colors R, G, and B, a PLC-type RGB coupler310, and first to third PDs3021to3023optically connected to the RGB coupler310.

The PLC-type RGB coupler310includes first to third input waveguides3111to3113, first to third branching units3121to3123, multiplexing units3141to3143, first to third monitoring waveguides3131to3133, and output waveguides315. The first to third input waveguides3111to3113are optically connected to the first to third LDs3011to3013. The first to third branching units3121to3123divide light propagating through the first to third input waveguides3111to3113into two. The multiplexing units3141to3143multiplex one beam of the light divided by the first to third branching units3121to3123. The other beam of the light divided by the first to third branching units3121to3123propagates through the first to third monitoring waveguides3131to3133and is output to the first to third PDs3021to3023. The light multiplexed by the multiplexing unit214propagates through the output waveguide315and is output to an output port316.

The multiplexing units3141to3143may use, for example, an RGB coupler illustrated inFIG.3, and are multiplexing units with the same circuit format. However, the multiplexing units are designed such that the wavelength at which the transmittance of the multiplexing units is greatest is shifted toward the long wavelength side at the multiplexing unit3143and shifted toward the short wavelength side at the multiplexing unit3141with respect to the multiplexing unit3142. For example, for the waveguide length, the waveguide width, and the gap between the waveguides of the RGB coupler310, the multiplexing unit3142in accordance with the design values and the multiplexing units3141and3143with the design values ±0.05 μm are fabricated on the same substrate.

In the state illustrated inFIG.5, the first to third LDs3011to3013and the output port316are connected to the multiplexing unit3141, and the first to third PDs3021to3023respectively monitor the outputs of the first to third LDs3011to3013. In a case where it is out of a range for feedback control when the light source is in actual operation, as illustrated inFIG.5, the fixed position of the RGB coupler310can be changed relative to the LDs and PDs, and can be switched from the multiplexing unit3141to the multiplexing unit3142or the multiplexing unit3143.

With such a configuration, it is possible to easily switch between multiplexing units with different characteristics, and thus even an RGB coupler having a small allowable error in manufacturing is capable of individual accurate monitoring even in a case of being in actual operation without reducing the yield. Because optical circuits are fabricated on the same wafer or chip, there is no increase in manufacturing cost and no additional components are needed because it can be made simultaneously in a single process.

Second Example

FIG.6illustrates a light source with a monitoring function according to a second example of the second embodiment of the present invention. The configuration of the light source with a monitoring function is the same as that of the first example, except that the light source is different from that of the first example in that three outputs from the multiplexing units3141to3143are multiplexed by a multiplexer317and output to the output port316, and three outputs of the respective first to third monitoring waveguides3131to3133are multiplexed by multiplexing units3181to3183and output to the first to third PDs3021to3023. The first to third LDs3011to3013are fixed to an LD mount319, and by changing the fixed position of the LD mount319relative to the RGB coupler310, it is possible to switch from the multiplexing unit3141to the multiplexing unit3142or the multiplexing unit3143.

With such a configuration, it is possible to easily switch between multiplexing units with different characteristics, and thus even an RGB coupler having a small allowable error in manufacturing is capable of individual accurate monitoring even in a case of being in actual operation without reducing the yield. Compared to the first example, the circuit size of the optical circuit of the RGB coupler is slightly larger, but required locations of alignment between the RGB coupler and external optical elements can be reduced.

FIG.7illustrates an example of a multiplexer according to the second example of the second embodiment. A single mode needs to be maintained in order to output light of each of colors of R, G, and B multiplexed by the multiplexing units3141to3143to the output port316. Thus, an optical circuit in which Y branch circuits illustrated inFIG.7(a)are connected in two stages, a three-branch circuit illustrated inFIG.7(b), or an optical circuit combining a Multi-mode Interference (MMI) with a mode converter illustrated inFIG.7(c)is applied to the multiplexer317.

Third Example

FIG.8is a diagram illustrating a light source with a monitoring function according to a third example of the second embodiment of the present invention. The light source of the third example differs in the connecting order of the branching units and the multiplexing units of the RGB coupler310. The PLC-type RGB coupler310includes first to third input waveguides3111to3113optically connected to the first to third LDs3011to3013, multiplexing units3141to3143that respectively multiplex light of the respective colors input to the first to third input waveguides3111to3113, first to third branching units3121to3123that divide the outputs of the multiplexing units3141to3143into two, a multiplexer317that multiplexes beams each being one beam of the light divided by each of the first to third branching units3121to3123, and first to third monitoring waveguides3131to3133that output the other beam of the light divided by each of the first to third branching units3121to3123to the first to third PDs3021to3023.

In the third example, light in which light of the respective colors R, G, and B is multiplexed is output to the first to third monitoring waveguides3131to3133. Thus, in a case where light of the respective colors of R, G, and B is monitored, it is necessary to use a wavelength filter or the like in a preceding stage of the first to third PDs3021to3023to separate. The multiplexer317uses the multiplexer ofFIG.7illustrated in the second example.

Note that, in the RGB coupler, the branching units for monitoring, the multiplexing units, and the multiplexer that multiplexes the outputs of the plurality of multiplexing units have various connection configurations as illustrated in the first to third examples, and the present invention is not limited to these examples.

Fourth Example

FIG.9illustrates a light source with a monitoring function according to a fourth example of the second embodiment of the present invention. The configuration of the light source with the monitoring function is the same as that of the first and second examples, except that the RGB coupler320is divided into two PLC substrates of an RGB coupler320A and an RGB coupler320B.

The RGB coupler320A includes first to third input waveguides3211to3213optically connected to first to third LDs3011to3013, and first to third branching units3221to3223that divide light propagating in the waveguide into two. Then, one beam of the light that is divided by each of the first to third branching units3221to3223is output to the RGB coupler320B. The other beam of the light is output to the first to third PDs3021to3023via a plurality of monitoring waveguides3131to3133.

The RGB coupler320B includes three sets of multiplexing units3241to3243that multiplex beams each being one beam of light that is divided by the first to third branching units3221to3223. By changing the fixed position of the RGB coupler320B relative to the RGB coupler320A, it is possible to switch from the multiplexing unit3241to the multiplexing unit3242or the multiplexing unit3243.

With such a configuration, it is possible to easily switch between multiplexing units with different characteristics, and thus even an RGB coupler having a small allowable error in manufacturing is capable of individual accurate monitoring even in a case of being in actual operation without reducing the yield. Compared to the first example, the number and intersection of the waveguides in the RGB coupler320A and320B can be reduced, and the circuit size of the optical circuit can be reduced.

In the third example, the emission direction of the light from the LD301is configured to be generally perpendicular to the incident direction of the light at the PD302, and thus it is possible to avoid stray light entering PD302. Stray light is light that has leaked into the RGB coupler310without the output of the LD301being able to couple to the input waveguide311, or the like.

Other Examples

In the second example, three outputs of the first to third monitoring waveguides3131to3133are multiplexed by the multiplexers3181to3183and output to the first to third PDs3021to3023. In a case where the effective light-receiving area in the light-receiving surface of each PD is wide, the light emitted from all of the three monitoring waveguides can also be received by the PDs by disposing the three monitoring waveguides at 5 to 20 μm intervals at the end surface of the RGB coupler310. In other words, the multiplexers3181to3183can be omitted. Similarly, for optical coupling from the output waveguide315to the output port316, in a case where the three output waveguides315are disposed at 5 to 20 μm intervals, a spatial optical system of the output port316may be fine tuned, and the multiplexer317can be omitted.

In the first example as well, in a case where the first to third monitoring waveguides3131to3133and the three output waveguides315can be arranged as described above, the multiplexing units3141to3143can be switched by changing only the relative positional relationship between the RGB coupler and the LDs.

In the third example, the emission direction of the light from the LD301is configured to be generally perpendicular to the incident direction of the light at the PD302. In the first and second example as well, in a case where the output ends of the first to third monitoring waveguides3131to3133are disposed on the end surface of the side orthogonal to the side coupled to the LD301, it is possible to avoid stray light from entering the PD202or302. At this time, it is also possible to remove light that is not multiplexed by the multiplexing unit314or stray light that has leaked out therefrom or stray light that has leaked out to the interior of the RGB coupler310via a disposal port of the multiplexing unit314.

REFERENCE SIGNS LIST

1to3,21to23,201,301LD4to6Lens7to9Half mirror10to12Dichroic mirror13to15,202,302Photodiode (PD)16MEMS17Screen30,100,210,310,320A,320B RGB coupler31to33Waveguide34,35Multiplexer101to103,211,311,321Input waveguide104,105Directional coupler106,215,315,325Output waveguide212,312,322Branching unit213,313Monitoring waveguide214,314,324Multiplexing unit316Output port