A new optical read-out system based on three groups of L-shape 3-axis interferometer is proposed to measure 6-degrees-of-freedom (6-DoF) of the test mass (TM) in the gravitational wave (GW) detection missions. In this system, the source laser is firstly divided into three parts to detect the displacement of the three perpendicular planes of the TM. To decouple the translations and rotations with respect to the XYZ axis, each part of the laser is further applied as the source of the L-shape 3-axis interferometer for the posture detection of each plane. The results of the numerical simulation showed that the solution accuracy of the translation and rotation are better than ±2×10-2 pm and ±3×10-5 nrad respectively, proving the computational accuracy is sufficient for the project requirements. The works above will provide a theoretical basis of the optical read-out system for the space-based GW detection mission.
The lack of compact and low-cost multi-comb sources has been a hindrance to the development of multi-comb metrology. The multidimensional multiplexing, a new multi-comb generation method, gives consideration to both comb quantity and spectral bandwidth and thus attracts extensive attentions. In this paper, a subring-wavelength multidimensional multiplexing scheme has been proposed. Four optical frequency combs with spectral bandwidths of at least 1.3 nm have been simultaneously generated in one integrated dual-ring mode-locked laser. A dual-ring structure of optical path separation is constructed for the subring multiplexing, while wavelength-dependent spectral filters are made up for the wavelength multiplexing. With necessary adjustment of both the spectral filters and the net-gain balance between subrings, cooperative operation of multiplexing between the two dimensions has implemented the subringwavelength multidimensional multiplexing. In this case, quadruple combs are detected with stable intensity. And the bandwidths of the generated combs are up to 2.8 nm, broader than the schemes with pure wavelength-dimensional multiplexing. Based on the previous research of polarization-wavelength multidimensional multiplexing, this work has proved the extendibility of multidimensional multiplexing schemes. We are convinced that multiplexing of triple or more dimensions could be further developed, promoting potential multi-comb applications.
The stability of output power, as a crucial evaluation index of erbium-doped fiber amplifiers, extremely affects the precision in metrology applications. Semiconductor laser diodes, which are commonly used as pump in erbium-doped fiber amplifiers, attracts extensive researches on stabilization due to the excellent characteristics and wide applications. In this paper, a highly stable erbium-doped fiber amplifier pumped with a constant-current-driven semiconductor laser diode is proposed. The stability of the output power is 0.92% in backward pumping structure and 0.71% in forward pumping structure. A constant current circuit operating in deep negative feedback mode ensures the driving current stabilized with the jitter range of 100 μA. Over-current protection and soft start are leveraged to protect the pump laser diode from inrush currents. In this case, the power stability of the pump laser diode is 0.1%, at the operating temperature with a fluctuation of 0.002℃. Without a complicated power-constant driving scheme, the relatively simple currentconstant driving system still performs remarkably for driving the pumping semiconductor laser diodes. We are convinced that the highly stable erbium-doped fiber amplifiers with simple and stable current-constant pump driving schemes, would be extensively employed, and thus promoting related applications.
Dual-comb generation with bidirectional fiber ring laser is highly prospective for its compactness and coherency. In this paper, we propose a dual-ring hybrid mode-locked fiber laser for dual-comb generation. The dual-ring laser contains elements of hybrid mode-locking for each sub-ring individually, while sharing the bidirectionally pumped erbium-doped fiber (EDF). The hybrid mode-locking is realized by transmission semiconductor saturable absorber (SESA) and nonlinear polarization evolution (NPE). With the help of two three-port optical circulators, non-ideal reflection of two SESAs are eliminated. Accordingly, two series of short pules are generated in each sub-ring with different direction individually. Experimental observations and analyses demonstrate that dual comb of about 300 kHz difference in repetition rates are generated by inserting a 10 cm cavity length difference between the two sub-rings. With the help of hybrid mode-locking and large power bidirectional pumping, the mode-locking of dual combs are stable and self-starting.
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