Devices and methods for coherent detection using chirped laser pulses

Inventors

Vakhshoori, Daryoosh • Blanchard, Romain • Mansuripur, Tobias

Assignees

Pendar Technologies LLC

Abstract

We present here systems and methods for generating a heterodyne signal using the naturally occurring chirp of a pulsed single-mode laser. The electrical square-wave pulse used to drive the laser heats the laser cavity, causing the laser frequency to change or chirp during the emission of the optical pulse. This chirped optical pulse can be split into a chirped signal pulse that interacts with a sample and a chirped reference pulse that interferes with the chirped signal pulse on a detector to produce a heterodyne modulation whose instantaneous phase and amplitude depend on the sample's dispersion and absorption, respectively. The chirp is reproducible, so the heterodyne modulation, instantaneous phase, and/or instantaneous amplitude can be average over many measurements, either with multiple pulses from the same laser or multiple pulses from different lasers, each emitting at a different wavelength.

Core Innovation

The invention performs a spectroscopic measurement of a sample by generating a chirped signal with at least one single-mode laser and illuminating the sample so that the chirped signal interacts with the sample. A chirped reference is provided such that interference occurs between the chirped signal and the chirped reference, producing a heterodyne modulation. The heterodyne modulation depends on dispersion and/or absorption of the sample, linking the measured modulation directly to the sample optical properties.

The invention determines the dispersion and/or the absorption of the sample from the detected heterodyne modulation, where the interference is characterized by the chirped signal interacting coherently with the reference. In described embodiments, the chirped reference and chirped signal are generated in an arrangement that can include a single-mode laser through an optical communication path and a lens that focuses the chirped signal onto a reflective surface disposed in a focal plane to reflect the chirped signal back through the lens. The chirped signal may also be produced using laser arrays and pulse sequencing to support time multiplexing and coherent extraction.

The innovation further includes approaches where a single-mode laser is driven with an electrical signal to emit chirped signals, and detection is based on heterodyne modulation created by interference of chirped signals. In other described architectures, a first chirped pulse and a second chirped pulse are emitted from the single-mode laser, the sample is illuminated with the first chirped pulse, and heterodyne modulation caused by interference between the first and second chirped pulses is detected to determine dispersion and/or absorption. The chirped signal may jitter in phase with respect to the chirped reference, and the described heterodyne modulation and phase behavior are used for robust time-resolved retrieval via envelope/analytic signal approaches such as Hilbert transform.

Claims Coverage

The provided independent claims describe four core inventive approaches that all rely on chirped signals from single-mode lasers and heterodyne detection from interference with a chirped reference to determine sample dispersion and/or absorption. Across the independent claims, at least four inventive-feature sets are present: chirp-signal/reference heterodyne spectroscopic determination, an optical-lens reflective-path configuration, electrical-pulse-driven chirped signal with phase-jitter behavior, and sequential first/second chirped pulses with interference-based heterodyne modulation.

Across the independent claims, the central claim coverage is the use of heterodyne modulation created by interference between a chirped signal and a chirped reference (or between first and second chirped pulses) to determine sample dispersion and/or absorption. Additional independent-claim-specific coverage is provided by an optical arrangement using a lens and reflective surface to send a chirped signal back through the sample, and electrical-pulse-driven emission with phase-jitter behavior relative to the reference, while still using interference-dependent modulation for dispersion/absorption retrieval.

Stated Advantages

Documented Applications