Abstract
The penalty of extending the cavity length of a laser diode when seeking a linewidth reduction is normally revealed by poor side mode suppression, which prevents the laser from operating purely in a single mode of the external cavity. A hybrid laser, based on a C-band semiconductor optical amplifier combined with a long erbium doped fiber external cavity, is carefully engineered to operate with high spectral purity and outstanding stability. For the first time, a side-mode suppression ratio of ≥42 dB, measured at a resolution of 1.16 pm (149 MHz) at all intra-cavity powers above the lasing threshold, is reported. The output power at the peak lasing wavelength is 13.3 dBm. Also, the ability to lock such a hybrid laser to a particular external-cavity mode is realized for the first time. Excluding the effect of mechanical and thermal drifts on the cavity length, the long-term frequency stability is demonstrated to be within ± 11 Hz while the long-term linewidth is 2.26 kHz, measured using the self-beating technique under free running conditions.
Highlights
Cost-effective, simple structure and compact laser sources with high spectral quality are sought by many segments of industry
The linewidth of a commercial distributed feedback (DFB) laser diode, for example, was reduced from 200 kHz to 2 kHz by optimizing an electrical feed-back loop [1]. Another method was developed by subtracting the measured phase noise from the phase of the laser in an electro-optical feedforward loop, by which a 6-MHz linewidth of a DFB laser diode was reduced to 250 kHz [2]
We report a hybrid semiconductor laser, in which the external cavity is made entirely of erbium doped fiber (EDF)
Summary
Cost-effective, simple structure and compact laser sources with high spectral quality are sought by many segments of industry. The presence of the long FBG, self-induced through saturable absorption, enhances the selectivity of a single operating mode and the wavelength stability. The best long-term stability of single-frequency operation with a high SMSR of an erbium doped FECL was measured to be primarily within ± 1.5 pm ( ± 193 MHz) [16]. Special attention is paid to specify the operating parameters for any potential application We believe these results confirm the possibility of a low cost solution for compact lasers with ultra-high performance. The fiber cavity is made of a piece of PM-EDF, PANDA fiber from CorActive with a birefringence of 1.14 × 10−4, whose one end is sculpted into a biconic lens with an FBG directly written on the other end The absorption of this PM fiber is measured at 1528 nm to be ~30 dB/m. The temperature of the fiber cavity and the SOA are stabilized using a laser driver LDC-3900
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