Cutoff-mesa isolated rib optical waveguide for III-V heterostructure photonic integrated circuits
First Claim
1. A composite optical waveguide for use within a photonic integrated circuit with light of a particular wavelength comprising:
- a cutoff mesa waveguide structure comprising a slab layer of thickness t at the upper surface of the mesa, said slab layer being underlain by a lower cladding layer, the mesa waveguide structure having a vertically asymmetric refractive index profile that is controlled by the thickness t and the chemical composition of the slab and the lower cladding layer such that the light does not propagate in a guided mode in the cutoff mesa waveguide structure by itself, the cutoff mesa being further defined by two parallel lateral walls to form an elongated structure; and
an elongated rib waveguide structure formed atop the cutoff mesa waveguide structure and aligned therewith, the rib waveguide structure having a width less than the width of the cutoff mesa with the width and the chemical composition of the rib waveguide being such that only the TE00 and TM00 modes of the light are guided by the combination of the cutoff mesa waveguide structure and the rib waveguide structure in the region beneath the rib waveguide structure and no modes of the light are permitted in other regions of the cutoff mesa waveguide.
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Abstract
A cutoff mesa rib waveguide provides single-mode performance regardless of any deep etches that might be used for electrical isolation between integrated electrooptic devices. Utilizing a principle of a cutoff slab waveguide with an asymmetrical refractive index profile, single mode operation is achievable with a wide range of rib widths and does not require demanding etch depth tolerances. This new waveguide design eliminates reflection effects, or self-interference, commonly seen when conventional rib waveguides are combined with deep isolation etches and thereby reduces high order mode propagation and crosstalk compared to the conventional rib waveguides.
48 Citations
19 Claims
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1. A composite optical waveguide for use within a photonic integrated circuit with light of a particular wavelength comprising:
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a cutoff mesa waveguide structure comprising a slab layer of thickness t at the upper surface of the mesa, said slab layer being underlain by a lower cladding layer, the mesa waveguide structure having a vertically asymmetric refractive index profile that is controlled by the thickness t and the chemical composition of the slab and the lower cladding layer such that the light does not propagate in a guided mode in the cutoff mesa waveguide structure by itself, the cutoff mesa being further defined by two parallel lateral walls to form an elongated structure; and an elongated rib waveguide structure formed atop the cutoff mesa waveguide structure and aligned therewith, the rib waveguide structure having a width less than the width of the cutoff mesa with the width and the chemical composition of the rib waveguide being such that only the TE00 and TM00 modes of the light are guided by the combination of the cutoff mesa waveguide structure and the rib waveguide structure in the region beneath the rib waveguide structure and no modes of the light are permitted in other regions of the cutoff mesa waveguide. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A composite optical waveguide for use within a photonic integrated circuit with light of a particular wavelength comprising:
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an elongated cutoff mesa structure of width w1 defined by lateral walls with the cutoff mesa structure comprising a base layer capped by a lower cladding layer of refractive index n0 in turn capped by a slab layer of refractive index n1 and thickness t; and an elongated rib waveguide structure of width w2 approximately centered atop the cutoff mesa structure and aligned therewith and comprising an upper cladding layer adjacent to the slab layer, the upper cladding layer having a refractive index of n3, wherein w1 >
w2 and the refractive index, n2, of the material present above the slab layer in the regions other than where the upper cladding layer is present satisfies the condition n1 >
n0 >
n2, such that only the fundamental modes of the light are guided by the composite optical waveguide structure comprising the cutoff mesa structure and the rib waveguide structure. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification