| 摘要 |
PURPOSE:To provide a grating coupler with which countermeasures to wavelength fluctuation of a light source of incident light can be taken solely without using a wavelength fluctuation compensation element. CONSTITUTION:A coupler part is formed in a multi-layer waveguide layer structure, DELTAlambdaorg is a wavelength fluctuation range of incident light, lambdamax is the maximum wavelength in the wavelength fluctuation range, and the wavelength fluctuation range DELTAlambdaorg equally parted by a total mode number M is set as a possible coupling wavelength range DELTAlambda, where a coupling center wavelength lambdam for an order of (m) (m=0, 1,..., M-1) for M modes is defined as the center of the possible coupling wavelength range DELTAlambda. The coupling center wavelength lambdam of the waveguide mode of the order of (m) is lambdam=lambdamax-(2m+1).(DELTAlambdaorg/2.M), and when thetai is an incident angle of the incident light to a grating coupler, with set as a periodic cycle of grating, then an effective refraction index Nm for the waveguide mode or the order of (m) is Nm=sinthetai+lambdam/LAMBDA. In this constitution, the effective refraction indexes of the respective wave modes become close values to each other, and the incident light of the wavelength within the set wavelength fluctuation range is coupled with one waveguide mode. |
