An ultrafast electro-optic laser makes a stabilized comb and includes: a comb generator that produces a frequency comb; a dielectric resonant oscillator; a phase modulator in communication with the dielectric resonant oscillator; an intensity modulator in communication with the phase modulator; an optical tailor in communication with the comb generator and that produces tailored light; a filter cavity in communication with the intensity modulator; a pulse shaper in communication with the filter cavity; a highly nonlinear fiber and compressor in communication with the pulse shaper; an interferometer in communication with the optical tailor and that produces a difference frequency from the tailored light; and an electrical stabilizer in communication with the interferometer and the comb generator and that produces the stabilization signal with a stabilized local oscillator cavity that produces a stabilized local oscillator signal that is converted into the stabilization signal and communicated to the dielectric resonant oscillator.
Our invention is for an ultrafast light source that produces femtosecond pulses with sub-cycle timing jitter using electro-optic switching of a continuous-wave (cw) laser. The apparatus is composed of the following key elements: 1) an electro-optic (EO) frequency comb, 2) a microwave-cavity stabilization scheme to suppress electronic oscillator noise, 3) an optical noise filtering cavity, 4) a nanophotonic waveguide for broad spectrum generation, and 5) an electronic feedback loop for microwave noise reduction via f-2f offset stabilization.
The invention works by using EO phase and intensity modulation of a cw laser to create a train of optical pulses driven directly by an electronic oscillator. The resulting frequency comb is spectrally broadened in a nanophotonic waveguide, allowing for the generation of ultrashort few-cycle pulses of light, as well as self-referenced frequency stabilization, which is crucial for suppressing the electronic noise of the comb at frequencies less than ~100 kHz. Electronic noise in the frequency range up to several megahertz is suppressed via locking the electronic oscillator directly to a narrow-linewidth microwave cavity and noise at frequencies extending up to the Nyquist frequency are filtered out using the optical cavity. Together, these components allow sufficient reduction of the microwave noise typically limiting EO comb performance to below the noise of the optical carrier wave, and results in ultrastable timing precision for the pulse train.
Our ultrastable EO comb invention is important because it represents a fundamentally new approach to generating ultrashort pulses of light with extremely low timing and phase noise. To achieve this, the invention relies on several new innovations including the cavity stabilization of the microwave electronic oscillator, the use of a photonic waveguide for pulse compression and spectral broadening, and self-referencing of the comb for microwave phase noise reduction. Moreover, because our invention can produce pulses at rates beyond 10 GHz, it may fulfill the need for stable high-repetition-rate comb sources in areas including communications, spectroscopy, and real-time biological imaging.
The main limitation of our invention is the reduced frequency tunability that results from the microwave and optical filtering devices used for suppression of the electronic phase noise. However, further development of microwave oscillator technology may reduce the requirements on these components and allow a significantly improved tuning range while further encouraging commercialization.
This invention is technically superior to and significantly moves beyond the current state current practice in several metrics: (1) It provides a means to generate few-cycle optical pulses at repetition rates that are in the range of 10 GHz, and the repetition rate is directly synchronized to a microwave drive at the same frequency. (2) The optical phase of these pulses can be controlled relative to the pulse repetition rate with sub-optical-cycle precision. (3) The corresponding frequency domain spectrum of the pulses can be engineered to extend over significant portions of the visible and near infrared spectrum (~600-2400 nm). (4). All of this can be done with user-chosen repetition rate and center wavelength. No such commercial device exists with these properties.