Reducing back reflection in hybrid lasers
In conventional hybrid lasers large back refection may lead to a degradation of relative intensity noise (RIN), linewidth broadening, mode hopping, etc. To solve the aforementioned problem a hybrid laser includes a mode converter for converting a higher-back-reflection mode of the light to a mode providing less back reflection to the gain chip. The mode converter may comprise a polarization rotator, a waveguide converter, or high-order mode converter. A routing waveguide may be provided including a phase shifter, e.g. a doped waveguide, for adjusting a cavity length of the laser cavity.
1. A hybrid laser comprising:
a gain chip including a gain medium for generating and amplifying light;
a first reflector optically coupled to the gain medium for reflecting at least a first portion of the light back through the gain medium;
a photonic integrated circuit (PIC) chip comprising:
an edge coupler for transmitting the light between the gain chip and a device layer on the PIC chip;
a mode converter for converting a mode of the light to a mode providing less back reflection for light traveling back and forth within the PIC chip;
a routing waveguide extending from the mode converter; and
a second reflector coupled to the routing waveguide for reflecting at least a second portion of the light back to the gain medium forming a laser cavity with the first reflector; and
an output port coupled to the first or second reflector for outputting laser light;
wherein the mode converter comprises a waveguide converter for converting a ridge waveguide to a rib waveguide; and
wherein the routing waveguide comprises the rib waveguide, comprising a wider lower slab region and a narrower upper ridge region.
2. The hybrid laser according to claim 1 , wherein the routing waveguide includes a phase shifter for adjusting a laser cavity length of the laser cavity.
3. The hybrid laser according to claim 2 , wherein the phase shifter comprises a doped waveguide; and
further comprising a controller capable of applying a bias voltage to the doped waveguide.
4. The hybrid laser according to claim 1 , wherein the edge coupler comprises a spot-size converter extending from the gain medium for reducing a mode size of the light exiting the gain medium.
5. The hybrid laser according to claim 4 , wherein the edge coupler extends at an acute angled from a normal from the gain chip to reduce back reflection into the gain medium.
6. A hybrid laser comprising:
a gain chip including a gain medium for generating and amplifying light;
a first reflector optically coupled to the gain medium for reflecting at least a first portion of the light back through the gain medium;
a photonic integrated circuit (PIC) chip comprising:
an edge coupler for transmitting the light between the gain chip and a device layer on the PIC chip;
a mode converter for converting a mode of the light to a mode providing less back reflection for light traveling back and forth within the PIC chip;
a routing waveguide extending from the mode converter;
a second reflector coupled to the routing waveguide for reflecting at least a second portion of the light back to the gain medium forming a laser cavity with the first reflector; and
an output port coupled to the first or second reflector for outputting laser light;
wherein the mode converter comprises a polarization rotator comprising a bent and tapered optical waveguide polarization rotator.
7. The hybrid laser according to claim 6 , wherein the polarization rotator is for converting between a TE0 mode and a TM0 mode.
8. The hybrid laser according to claim 6 , wherein the polarization rotator comprises a high-order mode converter selected from the group consisting of a TM0-to-TE1 mode converter, and a TE0-to-TE1 mode converter.
9. A hybrid laser comprising:
a gain chip including a gain medium for generating and amplifying light;
a first reflector optically coupled to the gain medium for reflecting at least a first portion of the light back through the gain medium;
a photonic integrated circuit (PIC) chip comprising:
an edge coupler for transmitting the light between the gain chip and a device layer on the PIC chip;
a mode converter for converting a mode of the light to a mode providing less back reflection for light traveling back and forth within the PIC chip;
a routing waveguide extending from the mode converter;
a second reflector coupled to the routing waveguide for reflecting at least a second portion of the light back to the gain medium forming a laser cavity with the first reflector; and
an output port coupled to the first or second reflector for outputting laser light;
wherein the mode converter comprises a waveguide converter for converting a ridge waveguide to a bus waveguide; and
wherein the routing waveguide comprises the a bus waveguide.
10. The hybrid laser according to claim 9 , wherein the waveguide converter expands in width from a first end having a first width a same as the ridge waveguide to a second end having a second width a same as the bus waveguide, which is at least twice the first width of the first end.
11. The hybrid laser according to claim 9 , wherein the waveguide converter comprises a gradually tapering waveguide which expands from 400 μm to 500 μm wide to between 800 μm to 1200 μm wide.
12. The hybrid laser according to claim 1 , wherein the waveguide converter includes a slab region expanding in width from a first end having a first width a same as the ridge waveguide to a second end having a second width a same as the slab region of the routing waveguide, which is at least twice the first width of the first end.
13. The hybrid laser according to claim 1 , wherein the waveguide converter comprises a tapering slab region, which gradually expands from 400 μm to 500 μm wide to between 800 μm to 1200 μm wide.
14. The hybrid laser according to claim 1 , wherein the PIC chip includes a trench for receiving the gain chip.
15. The hybrid laser according to claim 1 , wherein the first reflector comprises a reflective facet of the gain chip.
16. The hybrid laser according to claim 1 , wherein the first reflector is <95% reflective to selected wavelengths in the light.
17. The hybrid laser according to claim 1 , wherein the second reflector is between 30% and 90% reflective to selected wavelengths in the light.
18. The hybrid laser according to claim 17 , wherein the second reflector comprises a reflector selected from the group consisting of a single ring reflector, a Sagnac loop mirror, a Vernier ring reflector, a distributed Bragg reflector, and a distributed feedback reflector.
19. The hybrid laser according to claim 17 , wherein the output port is coupled to the second reflector.