Terabaud Optical Coherent Transmitter Based on Spectral Modulation

In the new era of digital intelligence, the exponential growth of global data traffic poses a defining challenge to modern optical communication infrastructure. While conventional time‐domain quadrature‐amplitude‐modulation (QAM) schemes support high‐order modulation for significant spectral efficiency gains, they are constrained by limited single‐channel electro‐optic (E/O) bandwidth, which impedes efficient and cost‐effective architectural design. Here, we propose a terabaud‐accessible optical transmitter based on spectral‐domain QAM encoding, implemented using a 20‐GHz commercial in‐phase/quadrature (I/Q) modulator and a complementary pair of chirped fiber Bragg gratings. Unlike wavelength‐division multiplexing (WDM) multi‐tributary solutions, this transmitter enables real‐time full‐field shaping of a broad optical spectrum. In a high‐speed coherent communication demonstration, we generate 11 λ × 100‐gigabaud WDM channels carrying QAM symbols, along with dual terabaud‐class channels achieving a bit rate up to 3 Tb/s in a Fourier‐domain transceiver configuration. The proposed scheme opens a new pathway to overcome the bandwidth limitations in optical arbitrary waveform generation, offering promising prospects for broadband applications such as high‐speed telecommunication, advanced device testing, and high‐resolution ranging.