Programmable broadband optical field spectral shaping with megahertz resolution using a simple frequency shifting loop

Abstract

Controlling the temporal and spectral properties of light is crucial for many applications. Current state-of-the-art techniques for shaping the time- and/or frequency-domain field of an optical waveform are based on amplitude and phase linear spectral filtering of a broadband laser pulse, e.g., using a programmable pulse shaper. A well-known fundamental constraint of these techniques is that they can be hardly scaled to offer a frequency resolution better than a few GHz. Here, we report an approach for user-defined optical field spectral shaping using a simple scheme based on a frequency shifting optical loop. The proposed scheme uses a single monochromatic (CW) laser, standard fiber-optics components and low-frequency electronics. This technique enables efficient synthesis of hundreds of optical spectral components, controlled both in phase and in amplitude, with a reconfigurable spectral resolution from a few MHz to several tens of MHz. The technique is applied to direct generation of arbitrary radio-frequency waveforms with time durations exceeding 100 ns and a detection-limited frequency bandwidth above 25 GHz.

Radial Structure of OAM-Carrying Fundamental X-Waves

“…The recent technological advances in spectral shaping [36], realization of long-range Bessel beams [37], and the control of the spatiotemporal structure of electromagnetic waves [15,16] envisions the possibility to achieve great control over the spectral structure of Bessel-X pulses, and, possibly, to realize fundamental X-waves with different values of the spectral index n, thus being able to exploit this extra degree of freedom encoded in their spectral structure. With this at hand, OAM-carrying X-waves could be used for a number of different applications, ranging from communication (where they could be coupled with OAM-carrying waves in optical fibers to realize long-range diffraction-resilient communication systems [38]), sensing (where the spectral index could be used as a means to tune the central frequency of the X-wave spectrum to a specific compound/specimen that needs to be detected), and material processing (where the different field configurations obtained by controlling the spectrum of the X-wave could result in different geometries and possibilities for, e.g., laser drilling, and quantum information).…”

11‐GHz‐Bandwidth Photonic Radar using MHz Electronics

“…In the radar transmitter, a continuous‐wave laser (LD1) centered at a frequency of $$f_{\rm c}$$ is chopped into a train of rectangular pulses with a pulse duration of $$\tau _{\text{p}}$$ and a repetition rate of $$f_{\rm p}$$ using an optical switch driven by an electronic pulsed signal generator. A $$10\%$$ tap of the seed pulses is injected to a fiber‐based optical frequency‐shifted cavity [ 38,39 ] through an optical coupler (OC1), in which an acousto‐optic modulator (AOM) is used to progressively shift the pulse center frequency by a fixed frequency step. The frequency step $$\Delta f$$ can be positive or negative, depending on the frequency shift direction of the AOM.…”

Photonic Generation of 30 GHz Bandwidth Stepped-Frequency Signals for Radar Applications

“…The SF waveforms are generated through recirculating a rectangular optical pulse signal in a frequency-shifting loop (FSL) [36], [37], [41], as diagrammed in Fig. 1(a).…”

“…Another widely-used signal format in radars relies on steppedfrequency (SF) waveforms that can exhibit high time-frequency linearity and small spontaneous processing bandwidth while sustaining the same range resolution for the same bandwidth with the LFM signals [35]. Photonic generation of SF signal using frequency shifting modulation has been recently demonstrated [36]- [39], showing advantages of bandwidth flexibly while sustaining a high time-frequency linearity in radar ranging and imaging system demonstrations. In principle, the SF signal bandwidth can be adjusted by tuning the passband of an optical filter [37], [39], modifying the RF frequency applied to the EOM [38], and electronically controlled in-loop switch [40].…”