Broadband arbitrary wavelength multichannel laser source
A multi-channel laser source, including: a bus waveguide coupled, at an output end of the bus waveguide, to an output of the multi-channel laser source; a first semiconductor optical amplifier; a first back mirror; a first wavelength-dependent coupler, having a first resonant wavelength, on the bus waveguide; a second semiconductor optical amplifier; a second back mirror; and a second wavelength-dependent coupler, on the bus waveguide, having a second resonant wavelength, different from the first resonant wavelength. In some embodiments the first semiconductor optical amplifier is coupled to the bus waveguide by the first wavelength-dependent coupler, which is nearer to the output end of the bus waveguide than the second wavelength-dependent coupler, the second semiconductor optical amplifier is coupled to the bus waveguide by the second wavelength-dependent coupler, and the first wavelength-dependent coupler is configured to transmit light, at the second resonant wavelength, along the bus waveguide.
1. A multi-channel laser source, comprising:
a bus waveguide coupled, at an output end of the bus waveguide, to an output of the multi-channel laser source;
a first semiconductor optical amplifier;
a first back mirror;
a first wavelength-dependent coupler having a first resonant wavelength;
a second semiconductor optical amplifier;
a second back mirror;
a second wavelength-dependent coupler having a second resonant wavelength, different from the first resonant wavelength;
a third wavelength-dependent coupler having a third resonant wavelength, different from the first and second resonant wavelengths; and
an output mirror at the output end of the bus waveguide,
the first semiconductor optical amplifier including inhomogeneously broadened gain material and comprising:
a first end coupled to the first back mirror, and
a second end,
the first wavelength-dependent coupler comprising:
a channel port connected to the second end of the first semiconductor optical amplifier;
a bus output connected to a first portion of the bus waveguide;
a bus input, connected to a second portion of the bus waveguide more distant from the output end of the bus waveguide than the first portion of the bus waveguide; and
a fourth port,
the third wavelength-dependent coupler comprising:
a channel port connected to the fourth port of the first wavelength-dependent coupler;
a bus input, connected to the first portion of the bus waveguide; and
a bus output, connected to a third portion of the bus waveguide nearer the output end of the bus waveguide than the first portion of the bus waveguide,
the second semiconductor optical amplifier being coupled to the second portion of the bus waveguide through the second wavelength-dependent coupler,
the first wavelength-dependent coupler being nearer to the output end of the bus waveguide than the second wavelength-dependent coupler,
the first wavelength-dependent coupler being configured to transmit light, at the second resonant wavelength, from the bus input of the first wavelength-dependent coupler to the bus output of the first wavelength-dependent coupler, and
the output mirror having a first reflectance at the first resonant wavelength and a second reflectance at the second resonant wavelength, the first reflectance differing from the second reflectance by no more than 10%.
2. The multi-channel laser source of claim 1 , wherein the output mirror has a reflectance that is constant, over a wavelength range spanning 150 nm, to 10%.
3. The multi-channel laser source of claim 1 , wherein the output mirror has a reflectance that is constant, over a wavelength range spanning 500 nm, to 10%.
4. The multi-channel laser source of claim 1 , wherein the output mirror has a reflectance that is constant, over a wavelength range spanning 1000 nm, to 10%.
5. The multi-channel laser source of claim 1 , wherein:
the output mirror comprises a transverse slot in the bus waveguide,
the transverse slot extends at least half-way through the total height of the bus waveguide,
the transverse slot is tapered, and
a facet on a side of the transverse slot nearer the output of the multi-channel laser source is oblique to the bus waveguide at the output mirror.
6. The multi-channel laser source of claim 1 , wherein the output mirror comprises a directional coupler and a waveguide loop.
7. The multi-channel laser source of claim 1 , wherein the output mirror is at an edge of a silicon photonics chip and the output mirror is configured to launch light into free space.
8. The multi-channel laser source of claim 1 , wherein the output mirror comprises a chirped distributed Bragg reflector.
9. The multi-channel laser source of claim 1 , wherein:
the first wavelength-dependent coupler is configured:
to reflect a first portion of light received at the first resonant wavelength at the channel port of the first wavelength-dependent coupler, and
to transmit, to the bus output of the first wavelength-dependent coupler, a second portion of light received at the first resonant wavelength at the channel port of the first wavelength-dependent coupler;
the first portion is at least 10% of the light received; and
the second portion is at least 40% of the light received.
10. The multi-channel laser source of claim 1 , wherein the first wavelength-dependent coupler comprises a first ring resonator and a second ring resonator, the first ring resonator and the second ring resonator being configured to operate as a vernier ring resonator filter, or
wherein the first wavelength-dependent coupler comprises a grating assisted co-directional coupler.
11. The multi-channel laser source of claim 1 , wherein the first wavelength-dependent coupler comprises a grating assisted co-directional coupler, and
wherein the first wavelength-dependent coupler further comprises a distributed Bragg reflector connected in cascade with the grating assisted co-directional coupler.
12. The multi-channel laser source of claim 1 , wherein the first wavelength-dependent coupler comprises a wavelength actuator for adjusting the first resonant wavelength.
13. The multi-channel laser source of claim 1 , further comprising an amplitude modulator between the first back mirror and the first wavelength-dependent coupler.
14. The multi-channel laser source of claim 1 , wherein the first semiconductor optical amplifier is the same semiconductor optical amplifier as the second semiconductor optical amplifier.
15. The multi-channel laser source of claim 1 , wherein the first semiconductor optical amplifier comprises a first waveguide in a first semiconductor chip and the second semiconductor optical amplifier comprises a second waveguide in the first semiconductor chip.
16. The multi-channel laser source of claim 1 , wherein the first semiconductor optical amplifier comprises a waveguide in a first semiconductor chip, and the second semiconductor optical amplifier comprises a waveguide in a second semiconductor chip, different from the first semiconductor chip.
17. The multi-channel laser source of claim 1 , further comprising:
a wavelength sensor configured to receive a portion of, and to sense a wavelength of, light emitted by the first semiconductor optical amplifier; and
a control system configured:
to receive a wavelength sensing signal from the wavelength sensor,
to calculate a difference between the wavelength sensing signal and a wavelength setpoint, and
to apply a wavelength correction signal to a wavelength actuator, to reduce the difference between the wavelength sensing signal and the wavelength setpoint,
wherein:
the first wavelength-dependent coupler comprises a coupler wavelength actuator for adjusting the first resonant wavelength,
the wavelength actuator comprises the coupler wavelength actuator, and
the wavelength sensor is configured to receive light from a fourth port of the first wavelength-dependent coupler.
18. The multi-channel laser source of claim 17 , wherein:
the first semiconductor optical amplifier comprises a waveguide in a first semiconductor chip; and
the wavelength sensor comprises a photodiode, the photodiode being in the first semiconductor chip.
19. A multiplexed multi-channel laser source comprising:
a first multi-channel laser source according to claim 1 ,
a second first multi-channel laser source according to claim 1 , and
a multiplexer,
the multiplexer comprising:
a first input,
a second input, and
an output,
the multiplexer being configured:
to transmit light from first input to the output, and
to transmit light from second input to the output.
20. The multi-channel laser source of claim 1 , further comprising:
an amplitude modulator between the first back mirror and the first wavelength-dependent coupler;
a wavelength sensor; and
a control system,
the third wavelength-dependent coupler comprising a grating assisted co-directional coupler and a fourth port connected to the wavelength sensor,
the third wavelength-dependent coupler being configured:
to reflect a first portion of light received at the third resonant wavelength at the channel port of the third wavelength-dependent coupler;
to transmit, to the bus output of the third wavelength-dependent coupler, a second portion of light received at the third resonant wavelength at the channel port of the third wavelength-dependent coupler; and
to transmit, to the fourth port of the third wavelength-dependent coupler, a third portion of light received at the third resonant wavelength at the channel port of the third wavelength-dependent coupler,
the wavelength sensor being configured to receive the third portion of, and to sense a wavelength of, light from the third wavelength-dependent coupler,
the third wavelength-dependent coupler comprising a coupler wavelength actuator for adjusting the third resonant wavelength,
the control system being configured:
to receive a wavelength sensing signal from the wavelength sensor;
to calculate a difference between the wavelength sensing signal and a wavelength setpoint; and
to apply a wavelength correction signal to the coupler wavelength actuator, to reduce the difference between the wavelength sensing signal and the wavelength setpoint,
the output mirror comprising:
a 2×2 directional coupler directional coupler comprising:
first and second waveguides that are parallel to each other within a coupling region and evanescently coupled to each other across a gap therebetween, a width of the gap and a length of the coupling region being set to control the bandwidth of the output coupler and a coupling ratio of the of the 2×2 directional coupler, the width of the gap being between 250 nm and 3 microns wide, and the length of the coupling region being up to 50 microns long,
a first port coupling a first end of the first waveguide to the laser cavity,
a second port coupling a first end of the second waveguide to the output; and
and a waveguide loop coupling a second end of the first waveguide to a second end of the second waveguide.