Tunable laser
Examples of the present disclosure include a tunable laser comprising a waveguide including gain section. The waveguide overlies and is optically coupled to another waveguide. The another waveguide has a reflector at one end. A laser cavity is formed in the waveguides.
1. A tunable laser comprising:
a first waveguide comprising a first III-V semiconductor material and including a first gain section;
a second waveguide comprising a second III-V semiconductor material and including a second gain section;
an optical coupler to couple light between the first waveguide and the second waveguide;
wherein the first waveguide overlies and is optically coupled to a third waveguide which comprises a third III-V semiconductor material, the third waveguide having a width which is greater than a largest width of the first gain section of the first waveguide;
wherein the second waveguide overlies and is optically coupled to a fourth waveguide which comprises a fourth III-V semiconductor material, the fourth waveguide having a width which is greater than a largest width of the second gain section of the second waveguide; and
wherein a first laser cavity is formed between the optical coupler and a reflector of the third waveguide and a second laser cavity is formed between the optical coupler and a reflector of the fourth waveguide.
2. The tunable laser of claim 1 wherein the first waveguide includes a first taper transition tip to couple light from the first waveguide to the third waveguide and the second waveguide includes a second taper transition tip to couple light from the second waveguide to the fourth waveguide.
3. The tunable laser of claim 1 wherein the effective refractive index of the first gain section of the first waveguide is higher than an effective refractive index of the third waveguide.
4. The tunable laser of claim 3 wherein the third waveguide is a diluted waveguide including a plurality of alternating layers, a first one of said alternating layers comprising the third III-V semiconductor material and the second one of said alternating layers comprising a fifth III-V semiconductor material, wherein the third semiconductor material has a higher refractive index than the fifth semiconductor material.
5. The tunable laser of claim 1 wherein reflectors of the third and fourth waveguides are respective facets of the third and fourth waveguides.
6. The tunable laser of claim 1 wherein the reflector of the third waveguide has a lower reflectance than a reflectance of the reflector of the fourth waveguide, said reflector of the third waveguide forming an output of the tunable laser.
7. The tunable laser of claim 1 wherein the second waveguide includes an amplitude modulator.
8. The tunable laser of claim 1 wherein the second waveguide includes at least one bend of more than 60 degrees.
9. The tunable laser of claim 1 wherein the first laser cavity has a free spectral range (FSR) which is different to a FSR of the second laser cavity and wherein a resonance wavelength of at least one of the first laser cavity and the second laser cavity is tunable to provide wavelength tuning of the tunable laser via Vernier effect.
10. The tunable laser of claim 1 comprising a first electrical contact overlying the first gain section, a second electrical contact overlying the second gain section, and a third electrical contact positioned such that a potential difference applied between the first electrical contact and the third electrical contact causes an electrical current to flow in the first gain section.
11. The tunable laser of claim 1 wherein the first waveguide includes a cladding layer and a multi-quantum well layer, the multi quantum well layer being positioned between the cladding layer and the third waveguide and wherein the second waveguide includes a cladding layer and a multi-quantum well layer positioned between a cladding layer of the second waveguide and the fourth waveguide.
12. The tunable laser of claim 1 in combination with a silicon photonic integrated circuit (PIC) comprising a mode converter that is optically butt-coupled to an output of the third waveguide of the tunable laser; the mode converter of the silicon PIC comprising silicon in a lower refractive index material, wherein the lower refractive index material has a width similar to the width of the third waveguide and the silicon includes a tapered section having a width that reduces in the direction towards the tunable laser.