Rapid, k-space linear wavelength scanning laser source based on recirculating frequency shifter

Abstract

We propose and successfully demonstrate a k-space linear and self-clocked wavelength scanning fiber laser source based on recirculating frequency shifting (RFS). The RFS is realized with a high speed electro-optic dual parallel Mach-Zehnder modulator operating at the state of carrier suppressed single sideband modulation. A gated short pulse is injected into an amplified RFS loop to generate the wavelength scanning pulse train. We find that the accumulation of in-band amplified spontaneous emission (ASE) noise over multiple scanning periods will saturate the erbium-doped fiber amplifier and impede the amplification to the pulse signal in the RFS loop. To overcome the degradation of temporal signal due to the accumulation of ASE noise over multiple scanning periods, we insert a modulated optical switch into the RFS loop to completely attenuate the in-band ASE noise at the end of each scanning period. The signal to noise ratio of the temporal pulsed signal is greatly enhanced. K-space linear and self-clocked wavelength scanning fiber laser sources in 6.1 nm/7.2 nm scanning range with 20 GHz/30 GHz frequency shifting are successfully demonstrated.

Frequency Quasi-Linear Swept Light Source Based on Multi-Frequency Time-Matched Spectrum Stitching

“…Some attempt has been studied to suppress the ASE noise by inserting additional optical switches in the RFSL such as the modulated semiconductor optical amplifier (SOA) [14]. However, the switch needs to be turned off for a long time (several microseconds) to achieve effective noise suppression, which is difficult to realize the stitching of swept pulses in time-domain.…”

Ultrafast Wavenumber Linear-Step-Swept Source Based on Synchronous Lightwave Synthesized Frequency Sweeper

“…The lightwave synthesized frequency sweeper (LSFS) is another effective scheme that realizes linear swept output in k-space [20]- [22]. The LSFS consists two main parts: (i) a frequency-stabilized optical seed source; (ii) an optical loop including a frequency shifter and an optical amplifier.…”

“…Generally, the signal to noise ratio (SNR) of the output decreases with the circulation number increasing due to the noise accumulation induced by the optical amplifier. In [22], a wavelength band-pass filter is used to control the circulation number and an extra optical switch is used to suppress the noise in each circulation. The swept range is 6.1 nm/7.2 nm with a 20 GHz/30 GHz swept step.…”

Wavelength-swept fiber laser based on bidirectional used linear chirped fiber Bragg grating

“…Wavelength-swept fiber lasers have attracted much interest due to their wide potential applications in optical coherence tomography (OCT), distributed fiber sensing based on the optical frequency domain reflection (OFDR) technique, continuous wave terahertz generation, and optical communication systems [1][2][3][4]. Many technologies have been proposed to build wavelength-swept fiber lasers [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The most straightforward realization of a swept laser is composed of the gain medium and a tunable bandpass filter in the laser cavity [5,6].…”

“…By using the FDML scheme, sweep rate has been significantly improved [9,10]. Other methods such as dispersion tuning or dispersion mode-locking techniques [11][12][13], rapid, k-space linear wavelength scanning based on recirculating frequency shifter [14,15] also have been demonstrated, benefiting from the tunable-filter-free configuration. Time-division multiplexing of ultrashort pulses with broad spectrum by incorporation of dispersion outside mode-locked laser sources also were reported [16][17][18] but with relatively low output power.…”