An ultra-low intensity and beatnote phase noise dual-frequency vertical-external-cavity surface-emitting laser is built at telecom wavelength. The pump laser is realized by polarization combining two single-mode fibered laser diodes in a single-mode fiber, leading to a 100% in-phase correlation of the pump noises for the two modes. The relative intensity noise is lower than -140 dB/Hz, and the beatnote phase noise is suppressed by 30 dB, getting close to the spontaneous emission limit. The role of the imperfect cancellation of the thermal effect resulting from unbalanced pumping of the two modes in the residual phase noise is evidenced.
We built a 1-watt cw singly resonant optical parametric oscillator operating at an idler wavelength of 1.65 µm for application to quantum interfaces. The non resonant idler is frequency stabilized by side-fringe locking on a relatively high-finesse Fabry-Perot cavity, and the influence of intensity noise is carefully analyzed. A relative linewidth down to the sub-kHz level (about 30 Hz over 2 s) is achieved. A very good long term stability is obtained for both frequency and intensity.
for pumping at (π/2) 2 times above the oscillation threshold. This theoretical limit was almost reached with a CW SRO based on a periodically poled lithium niobate (PPLN) crystal for which the authors reported 93 % of pump depletion [7]. In most cases, the optimization of the output power depends on the choices of the crystal length and mirror reflectivities for a given available pump power. A recent example shows that a low threshold is not necessarily the best way to obtain a high output power, even for the nonresonant beam (idler) [8].Besides, SROs are also extremely attractive for their frequency noise properties. In particular, it has been shown that the frequency noise of the pump can be dumped to the wave which is not resonant inside the cavity [9]. By locking the frequency of the resonant wave at resonance with a high-finesse resonator, this has allowed to stabilize this frequency down to the kHz level [10, 11], i. e., well below the linewidth of the pump laser. The problem then is that the output power obtained from the resonant wavelength is usually quite small, i. e., well below 1 W for pump powers of several Watts. Indeed, the converted pump power is mostly extracted by the non-resonant wave which carries the pump noise. This problem has received quite some attention. For example, extracting some power from the wave resonant in the cavity can be performed by using an optimized output coupler such as a dielectric coating mirror [2, 13] or a volume Bragg grating [14]. Another method consists in inserting a plate inside the cavity at an incidence angle close to the Brewster angle in order to ensure a small but adjustable amount of output coupling [15].However, in spite of the partial success of these demonstrations, it would be extremely desirable to be able to stabilize the frequency of the non-resonating wave. This would allow us to benefit from the two main advantages of SROs-efficient conversion and extremely small Abstract We present an experimental technique allowing to stabilize the frequency of the non-resonant wave in a singly resonant optical parametric oscillator (SRO) down to the kHz level, much below the pump frequency noise level. By comparing the frequency of the non-resonant wave with a reference cavity, the pump frequency noise is imposed to the frequency of the resonant wave and is thus subtracted from the frequency of the non-resonant wave. This permits the non-resonant wave obtained from such a SRO to be simultaneously powerful and frequency stable, which is usually impossible to obtain when the resonant wave frequency is stabilized.
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