Electro-optic Comb Research Articles

Fully Adaptable Electro-Optic Dual-Comb Generation

In this letter, an all-electronic method that provides a precise control over the number of spectral lines of an electro-optic frequency comb is presented and experimentally validated. This feature, in conjunction with the straightforward configuration of the optical resolution (repetition frequency) inherent to electro-optic combs, enables the generation of optical comb sources with the unique capability of a complete adaptability to the targeted spectral feature/s that could ultimately maximize the SNR of any electro-optic comb-based spectroscopic measurement.

Tunable insertion of multiple lines into a Kerr frequency comb using electro-optical modulators.

We experimentally insert a flexible number of electro-optical (EO) comb lines into a Kerr frequency comb via EO modulation and demonstrate the use of combined Kerr and EO combs as light sources in coherent communications. The number of EO lines inserted into the Kerr comb can be varied by changing the modulation frequency. Additionally, the inserted EO comb is found to have similar coherence to that of the Kerr comb, as indicated by their linewidths. The high coherence of both the Kerr and EO combs has further been demonstrated in a communication experiment in which the comb lines are encoded with 10 Gbaud quadrature phase-shift-keyed signals. The increased number of comb lines after EO modulation indicates the possibility of obtaining more data channels in optical communications.

Fully Frequency-Locked Multiheterodyne Architecture for Remote Optical Frequency Comb Rapid Detection

In this paper, a new approach to optical frequency comb (OFC) detection based on a multiheterodyne arrangement is presented. The architecture relies on optical injection locking as a mechanism to induce coherence between an incoming remote OFC and a local oscillator comb with slightly different repetition frequency to retrieve the information encoded in the former. An additional RF locking technique between combs is also implemented, cancelling any frequency drifts and ensuring the temporal stability of the detection scheme while preserving its autonomy from any remote comb. The detection system is validated by recording the coherently averaged transmission spectra of a fibre Bragg grating sensor imprinted into an electro-optic comb around 1540 nm within 100 μs integration time. While maintaining the range of advantages of dual-comb architectures, such as simultaneous access to manifold spectral points, high resolution, and ultrafast measurement times, the presented system holds promise for being employed as a remote comb detector for different field applications.

Electro-optic comb based real time ultra-high sensitivity phase noise measurement system for high frequency microwaves

Recent progress in ultra low phase noise microwave generation indispensably depends on ultra low phase noise characterization systems. However, achieving high sensitivity currently relies on time consuming averaging via cross correlation, which sometimes even underestimates phase noise because of residual correlations. Moreover, extending high sensitivity phase noise measurements to microwaves beyond 10 GHz is very difficult because of the lack of suitable high frequency microwave components. In this work, we introduce a delayed self-heterodyne method in conjunction with sensitivity enhancement via the use of higher order comb modes from an electro-optic comb for ultra-high sensitivity phase noise measurements. The method obviates the need for any high frequency RF components and has a frequency measurement range limited only by the bandwidth (100 GHz) of current electro-optic modulators. The estimated noise floor is as low as −133 dBc/Hz, −155 dBc/Hz, −170 dBc/Hz and −171 dBc/Hz without cross correlation at 1 kHz, 10 kHz, 100 kHz and 1 MHz Fourier offset frequency for a 10 GHz carrier, respectively. Moreover, since no cross correlation is necessary, RF oscillator phase noise can be directly suppressed via feedback up to 100 kHz frequency offset.

Low noise electro-optic comb generation by fully stabilizing to a mode-locked fiber comb.

A fully stabilized EO comb is demonstrated by phase locking the two degrees of freedom of an EO comb to a low noise mode-locked fiber comb. Division/magnification of residual phase noise of locked beats is observed by measuring an out-of-loop beat. By phase locking the 200 th harmonics of the EO comb and a driving cw frequency to a fiber comb, a record low phase noise EO comb across +/- 200 harmonics (from 1544.8 nm to 1577.3 nm) is demonstrated.

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Hybrid Electro-Optically Modulated Microcombs

Optical frequency combs based on mode-locked lasers have proven to be invaluable tools for a wide range of applications in precision spectroscopy and metrology. A novel principle of optical frequency comb generation in whispering-gallery mode microresonators ("microcombs") has been developed recently, which represents a promising route towards chip-level integration and out-of-the-lab use of these devices. Presently, two families of microcombs have been demonstrated: Combs with electronically detectable mode spacing that can be directly stabilized, and broadband combs with up to octave-spanning spectra but mode spacings beyond electronic detection limits. However, it has not yet been possible to achieve these two key requirements simultaneously, as will be critical for most microcomb applications. Here we present a route to overcome this problem by interleaving an electro-optic comb with the spectrum from a parametric microcomb. This allows, for the first time, direct control and stabilization of a microcomb spectrum with large mode spacing (>140 GHz) with no need for an additional mode-locked laser frequency comb. The attained residual 1-sec instability of the microcomb comb spacing is 10(-15), with a microwave reference limited absolute instability of 10(-12) at a 140 GHz mode spacing.