20-GHz broadly tunable and stable mode-locked semiconductor amplifier fiber ring laser

Abstract

We present an actively mode-locked fiber ring laser that uses a single active semiconductor optical amplifier device to provide both gain and gain modulation from an external optical pulse train. The laser source generated 4.3-ps pulses at 20 GHz over a 16-nm tuning range and is stable against environmental changes and simple to build.

Numerical Modeling of a High Repetition Rate Fiber Laser, Mode — Locked by External Optical Modulation of a Semiconductor Optical Amplifier

“…The parameters used for the simulations were chosen to agree with the values in the experimental configuration [16]. Specifically, the width of the external pulses was 8 ps, the cavity loss was 15 dB and the full width at half maximum of the spectral limiting filter was 5 nm for both frequencies.…”

“…Note that if the same value of small signal gain as for the 10 GHz operation is used, the mode -locked pulses are longer, 7 ps, with lower energy, Uo = 0.22. In order to assess the ability of the model for quantitative prediction, the parameter values from the experimental set up were substituted in equations (11), (14), (15) and (16). At 10 GHz, with an experimental value for gss 1.53 and using a filter of 5 nm spectral bandwidth and external modulating pulses of 8 ps width, the model predicts mode -locked pulses of 4.5 ps duration with normalized energy 0.45 and external pulses with normalized energy 0.46.…”

“…These subsystems are crucial for the implementation of high speed telecommunication transmission and network systems that are based on WDM and OTDM techniques. More specifically, these subsystems include (a) a 4.3 ps stable 20 GHz fiber ring laser source with 16 nm tuning range [16], (b) a IOx30 GHz source which generates 10 synchronized wavelength channels, each mode-locked at 30 GHz, producing nearly transform limited 7 ps pulses with less than 5% power variation across them [17], (c) an optical clock repetition rate multiplier circuit which has achieved a factor of 6 frequency multiplication and up to 34.68 GHz [18] and (d) an optical clock recovery and division circuit capable to recover clock from a data pattern up to 20 Gb/s and to perform clock division from the 20 Gb/s stream to 10 and 5 GHz [19]. The four subsystems allow the efficient solution of the following problems that are encountered in WDM and OTDM networks: (a) The generation of ultrashort pulses from a stable tunable source at 40 GHz (fiber ring laser source) to provide the necessary optical power in the ultrafast WDM and OTDM networks, (b) The existence of simultaneous, synchronized wavelength channels (lOx30 GHz source).…”

Ultrafast Semiconductor-Based Fiber Laser Sources

“…As the mode-locked pulse transits the SOA, its gain depletes again below the loss line, to recover slowly before the next external or mode-lock pulse enters it. This mechanism results in a temporal displacement between the external and mode-locked pulses in the SOA [40]. From Fig.…”

“…2, it can be seen that after two recirculations, the mode-locked pulses are on average equally amplified due to the temporal displacement, resulting in no pulse-to-pulse pattern distortion. A decrease of the external-pulse energy or an increase in the SOA gain results in higher gain in front of the mode-locked pulse that consequently shifts it toward the first external pulse [40]. Similarly, an increase in the external-pulse energy or a decrease of the SOA gain has the opposite effect, with the mode-locked pulse trailing toward the second external pulse.…”