All-silicon terahertz absorbers have attracted considerable interest. We present a design and numerical study of an all-silicon polarization-insensitive terahertz metamaterial absorber. The meta-atoms of the metamaterial absorber are square silicon rings which can be viewed as gratings. By properly optimizing the structure of the meta-atom, we achieve a broadband absorptivity that is above 90% ranging from 0.77 THz to 2.53 THz, with a relative bandwidth of 106.7%. Impedance matching reduces the reflection of the terahertz waves and the (0, ±1)-order diffraction induce the strong absorption. The absorption of this absorber is insensitive to the polarization of the terahertz wave and has a large incident angle tolerance of up to 60 degrees. The all-silicon metamaterial absorber proposed here provides an effective way to obtain broadband absorption in the terahertz regime. Metamaterial absorbers have outstanding applications in terahertz communication and imaging.

A wavelength step-swept light source (WSSL) using a recirculating frequency shifter loop (RFSL) based on a single-side-band (SSB) modulator is proposed, in order to achieve a linear and fast wavelength-sweeping. The swept step can be tuned from 1.2 pm to 128 pm by adjusting a precise and stable radio frequency (RF) signal that is applied to the SSB modulator. The swept rate can be tuned up to 99 kHz in a range of over 5.12 nm. Wavelength-to-time mapping is used to measure static strain-induced or temperature-induced shifting of the reflected central wavelength of a fiber Bragg grating (FBG). Because of the high linearity of the light source, the interrogation linearity of the strain and the temperature are as high as 0.99944 and 0.99946, respectively. When a dynamic periodic strain applied to FBG sensor, the dynamic performance of the FBG sensor is successfully recorded in the time domain and its power spectral density of a fast Fourier transform (FFT) is calculated. The signal-to-noise ratio (SNR) of the power spectral density is over 40 dB for a 100 Hz dynamic strain and the calculated sensitivity is 0.048 με/Hz^1/2. A sharp change in the strain frequency from 100 Hz to 500 Hz is captured in real time.

We present a scheme to broaden the sweeping span of lightwave synthesized frequency sweeper (LSFS) by using self-induced auto-tracking filter (SIATF). It is based on spatial-hole-burning effect in unpumped erbium-doped fiber (EDF), equivalent to introducing a Bragg grating. This Bragg grating works as the SIAFT, tracks the frequency of the incident optical signal automatically. It broadens LSFS’s sweeping span limited by the homogeneous broadening of EDF. The scheme is demonstrated experimentally that the amplified spontaneous emission (ASE) noise is effectively suppressed meanwhile sweeping span of LSFS is enlarged. 12.48nm sweeping span within 3.5dB power change is obtained, which corresponds to 1.56THz sweeping span.

Dissipative soliton resonance (DSR) with multiple stable states has been experimentally demonstrated in a passively mode-locked Yb-doped fiber laser. The generation of the DSR square pulse has been achieved with the nonlinear optical loop mirror technique. The duration of the square pulse varies from 16 to 123 ns, while the amplitude of the pulse remains constant. Experimentally, by fixing the pump power and changing the orientations of the polarization controllers, we have observed three different square pulses that all operate in the DSR regime. At the same time, we have obtained a wavelength-tunable square pulse, which demonstrates that the DSR and operation wavelength are independent of each other. We also analyzed the ideal state in the DSR regime.

A novel scheme of self-oscillation multicarrier light source based on recirculating frequency shift loop (RFSL) is proposed and experimentally demonstrated in this paper. Compared with conventional RFSL-based multicarrier generation schemes, the radio frequency (RF) signal for driving the modulator in RFSL is generated by an internal self-oscillation of the optical carrier instead of the external commercial RF source device. The self-oscillation method significantly reduces the cost of the light source and decreases the phase noise of RF signal and multicarrier signal. In the experiment, we successfully generate a single-mode oscillation RF signal with the phase noise of −85.10 dBc/Hz at 10 kHz offset frequency. A total of 49 multicarrier optical signals from 1550.59 nm to 1554.44 nm with the power fluctuation as low as 3 dB are obtained. The frequency interval is approximately 10.014 GHz, which is equal to the oscillation frequency of the RF signal.