In recent years, the research work regarding an optical device using a photonic crystal has been active, and a Non-Patent Document 1 discloses a technique regarding the surface emitting laser formed by a two-dimensional photonic crystal and a multilayer mirror.
Specifically, as shown in FIG. 17, a multilayer mirror 3100 made of a laminated body of Si and SiO2 and a two-dimensional photonic crystal slab 3300 are provided on a Si substrate 3000 through a clad layer 3200 made of SiO2.
This two-dimensional photonic crystal slab is made of In0.53Ga0.47As, a barrier layer of InP, and a quantum well layer of InAs0.65P0.35. In this configuration, an average refractive-index of the slab is presumed to be approximately 3.2.
The two-dimensional photonic crystal slab 3300 at the side opposite to the substrate 3000 contacts an air (refractive-index 1.0).
Further, the refractive-index of the clad layer (lower clad layer) 3200 made of SiO2 adjacent to the two-dimensional photonic crystal slab 3300 at the substrate side is approximately 1.4.
In this manner, since the air, which is a refractive-index medium lower than the slab, and the clad layer 3200 are provided at both sides of the slab, the slab forms a slab waveguide.
In this slab waveguide, a light emitting active layer is buried, and by a DFB action of the two-dimensional photonic crystal, the light generated by the active layer resonates in the in-plane direction of the slab, and performs a laser oscillation.
Since a secondary diffracted light of the light laser-oscillated by the two-dimensional photonic crystal is extracted in the vertical direction to the substrate, the surface emitting laser can be realized.
Further, between the slab and the substrate, the multilayer mirror in which an optical thickness of each layer is formed by λ/4 (λ indicates a resonance wavelength) is installed. Here, the optical thickness means a thickness of a certain layer multiplied by a refractive-index of the material configuring that layer.
This multilayer mirror 3100 not only improves light extraction efficiency by returning the light radiated to the substrate side from the slab, but also controls an oscillation mode in the slab resonator.
By appropriately taking the distance between the slab 3300 and the multilayer mirror 3100, a Q value of the resonator can be controlled. For example, it is disclosed that by increasing the Q value, the threshold value of the laser can be decreased.    [Non-Patent Document 1] APPLIED PHYSICS LETTERS 88, 081113 (2006)
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