High-performance on-chip spectrometers and spectrum analyzers
We disclose an on-chip photonic spectroscopy system capable of dramatically improving the signal-to-noise ratio (SNR), dynamic range, and reconstruction quality of Fourier transform spectrometers. Secondly, we disclose a system of components that makes up a complete on-chip RF spectrum analyzer with low-cost and high-performance.
1. A method of operating a spectrometer, the method comprising:
splitting incident light into a first portion and a second portion;
transmitting the first portion through at least one delay stage switchable between a first waveguide having a first optical path length and a second waveguide have a second optical path length different than the first optical path length;
transmitting the second portion through a reference waveguide;
attenuating at least one of the first portion or the second portion to compensate for loss imbalance between the at least one delay stage and the reference waveguide;
detecting interference between the first portion with the second portion; and
determining a spectrum of the incident light based on the interference of the first portion and the second portion,
wherein attenuating the first portion comprises modulating a relative phase between the first portion and the second portion such that the interference of the first portion with the second portion has a null at a desired frequency.
2. The method of claim 1 , wherein transmitting the first portion through the at least one delay stage comprises transmitting the first portion through a plurality of cascaded delay stages.
3. The method of claim 1 , wherein transmitting the first portion through the at least one delay stage comprises transmitting a first fraction of the first portion through the first waveguide and a second fraction of the first portion through the second waveguide.
4. The method of claim 1 , wherein transmitting the first portion through the at least one delay stage comprises transmitting the first portion through the first waveguide and further comprising:
switching the at least one delay stage from the first waveguide to the second waveguide; and
transmitting the first portion along the second waveguide.
5. The method of claim 1 , wherein attenuating the first portion increases an extinction ratio of the interference between the first portion and the second portion.
6. The method of claim 1 , further comprising, before detecting the interference:
coupling a fraction of the first portion out of the at least one delay stage;
detecting an intensity of the fraction of the first portion; and
adjusting a setting of the at least one delay stage based on the intensity.
7. A spectrometer comprising:
a beam splitter to split incident light into a first portion and a second portion;
a delay stage, in optical communication with a first output of the beam splitter and switchable between a first waveguide having a first optical path length and a second waveguide have a second optical path length different than the first optical path length, to delay the first portion with respect to the second portion;
a reference waveguide, in optical communication with a second output of the beam splitter, to guide the second portion;
an attenuator, in optical communication with at least one of the delay stage and the reference waveguide, to attenuate at least one of the first portion or the second portion;
a detector, in optical communication, via the attenuator, with the delay stage and the reference waveguide, to detect interference of the first portion with the second portion;
a processor, operably coupled to the detector, to determine a spectrum of the incident light based on the interference of the first portion and the second portion;
a tap, in optical communication with the delay stage, to couple a fraction of the first portion out of the delay stage; and
a monitor photodetector, in optical communication with the tap, to monitor an intensity of the fraction of the first portion.
8. The spectrometer of claim 7 , wherein the delay stage is a first delay stage and further comprising:
a second delay stage, concatenated with the first delay stage and switchable between a third waveguide having a third optical path length and a fourth waveguide having a fourth optical path length different than the third optical path length, to further delay the first portion with respect to the second portion.
9. The spectrometer of claim 7 , wherein the delay stage is configured to guide a first fraction of the first portion through the first waveguide and, simultaneously, to guide a second fraction of the first portion through the second waveguide.
10. The spectrometer of claim 7 , wherein the delay stage is configured to be switched between a first state in which the first portion propagates through the first waveguide and a second state in which the first portion propagates through the second waveguide.
11. The spectrometer of claim 7 , wherein the attenuator is configured to increase an extinction ratio of the interference between the first portion and the second portion.
12. The spectrometer of claim 7 , wherein the attenuator is configured to adjust a relative phase between the first portion and the second portion.
13. The spectrometer of claim 7 , further comprising:
a phase modulator, in optical communication with the beam splitter, to modulate a relative phase between the first portion and the second portion such that interference of the first portion with the second portion creates a null at a desired frequency.
14. A spectrometer comprising:
a beam splitter to split incident light into a first portion and a second portion;
a delay stage, in optical communication with a first output of the beam splitter and switchable between a first waveguide having a first optical path length and a second waveguide have a second optical path length different than the first optical path length, to delay the first portion with respect to the second portion;
a reference waveguide, in optical communication with a second output of the beam splitter, to guide the second portion;
an attenuator, in optical communication with at least one of the delay stage and the reference waveguide, to attenuate at least one of the first portion or the second portion;
a detector, in optical communication, via the attenuator, with the delay stage and the reference waveguide, to detect interference of the first portion with the second portion;
a processor, operably coupled to the detector, to determine a spectrum of the incident light based on the interference of the first portion and the second portion; and
a phase modulator, in optical communication with the beam splitter, to modulate a relative phase between the first portion and the second portion such that interference of the first portion with the second portion creates a null at a desired frequency.
15. The spectrometer of claim 14 , wherein the delay stage is a first delay stage and further comprising:
a second delay stage, concatenated with the first delay stage and switchable between a third waveguide having a third optical path length and a fourth waveguide having a fourth optical path length different than the third optical path length, to further delay the first portion with respect to the second portion.
16. The spectrometer of claim 14 , wherein the delay stage is configured to guide a first fraction of the first portion through the first waveguide and, simultaneously, to guide a second fraction of the first portion through the second waveguide.
17. The spectrometer of claim 14 , wherein the delay stage is configured to be switched between a first state in which the first portion propagates through the first waveguide and a second state in which the first portion propagates through the second waveguide.
18. The spectrometer of claim 14 , wherein the attenuator is configured to increase an extinction ratio of the interference between the first portion and the second portion.