An optical apparatus comprising: a light source to provide a light signal; a modulator to modulate the light signal according to a data signal to be transmitted and output a modulated optical signal; and an optical coupling assembly comprising a silicon waveguide to receive the modulated optical signal and a single mode optical coupler to transform the modulated optical signal (1420, 1444) propagating through the silicon waveguide into an optical signal to couple with a single mode fiber, the single mode optical coupler comprising: a multi-stage optical tapered waveguide to convert the modulated optical signal (1420, 1444) taken from the silicon waveguide from a first mode field diameter to a second mode field diameter larger than the first mode field diameter adiabatically; and a total-internal-reflection mirror formed in a dielectric layer under an approximately 45 degree angle with respect to a plane of the dielectric layer to reflect the modulated optical signal (1420, 1444) from the multi-stage optical tapered waveguide substantially perpendicularly and direct the reflected modulated optical signal, as the optical signal, for coupling to the single mode fiber, wherein the multi-stage optical tapered waveguide includes an inverse tapered waveguide as a first stage and a rib tapered waveguide as a second stage, and wherein the single mode optical coupler comprises, in a propagation direction of the modulated optical signal (1420, 1444), a silicon waveguide region, an inverse taper region, an output waveguide region and a final waveguide region, the silicon waveguide region including an input-side slope with respect to a plane perpendicular to the propagation direction, the inverse tapered waveguide being included in the inverse taper region, the rib tapered waveguide being included in the inverse taper region and the output waveguide region, and the mirror being included in the final waveguide region. a light source to provide a light signal; a modulator to modulate the light signal according to a data signal to be transmitted and output a modulated optical signal; and an optical coupling assembly comprising a silicon waveguide to receive the modulated optical signal and a single mode optical coupler to transform the modulated optical signal (1420, 1444) propagating through the silicon waveguide into an optical signal to couple with a single mode fiber, the single mode optical coupler comprising: a multi-stage optical tapered waveguide to convert the modulated optical signal (1420, 1444) taken from the silicon waveguide from a first mode field diameter to a second mode field diameter larger than the first mode field diameter adiabatically; and a total-internal-reflection mirror formed in a dielectric layer under an approximately 45 degree angle with respect to a plane of the dielectric layer to reflect the modulated optical signal (1420, 1444) from the multi-stage optical tapered waveguide substantially perpendicularly and direct the reflected modulated optical signal, as the optical signal, for coupling to the single mode fiber, a multi-stage optical tapered waveguide to convert the modulated optical signal (1420, 1444) taken from the silicon waveguide from a first mode field diameter to a second mode field diameter larger than the first mode field diameter adiabatically; and a total-internal-reflection mirror formed in a dielectric layer under an approximately 45 degree angle with respect to a plane of the dielectric layer to reflect the modulated optical signal (1420, 1444) from the multi-stage optical tapered waveguide substantially perpendicularly and direct the reflected modulated optical signal, as the optical signal, for coupling to the single mode fiber, wherein the multi-stage optical tapered waveguide includes an inverse tapered waveguide as a first stage and a rib tapered waveguide as a second stage, and wherein the single mode optical coupler comprises, in a propagation direction of the modulated optical signal (1420, 1444), a silicon waveguide region, an inverse taper region, an output waveguide region and a final waveguide region, the silicon waveguide region including an input-side slope with respect to a plane perpendicular to the propagation direction, the inverse tapered waveguide being included in the inverse taper region, the rib tapered waveguide being included in the inverse taper region and the output waveguide region, and the mirror being included in the final waveguide region.