First investigation of the noise and modulation properties of the carrier-envelope offset in a modelocked semiconductor laser

Abstract

We present the first characterization of the noise properties and modulation response of the carrier-envelope offset (CEO) frequency in a semiconductor modelocked laser. The CEO beat of an optically-pumped vertical external-cavity surface-emitting laser (VECSEL) at 1030 nm was characterized without standard f -to-2f interferometry. Instead, we used an appropriate combination of signals obtained from the modelocked oscillator and an auxiliary continuous-wave laser to extract information about the CEO signal. The estimated linewidth of the free-running CEO beat is approximately 1.5 MHz at 1-s observation time, and the feedback bandwidth to enable a tight CEO phase lock to be achieved in a future stabilization loop is in the order of 300 kHz. We also characterized the amplitude and phase of the pump current to CEO-frequency transfer function, which showed a 3-dB bandwidth of ∼300 kHz for the CEO frequency modulation. This fulfills the estimated required bandwidth and indicates that the first self-referenced phase-stabilization of a modelocked semiconductor laser should be feasible in the near future. Optical frequency combs from modelocked solid-state lasers have been a revolution in the field of high precision metrology by directly and coherently linking the optical and microwave parts of the electromagnetic spectrum [1][2][3]. Such stabilized frequency combs enable the measurement of optical frequencies with an extreme precision [4,5] and constitute a key element of novel optical atomic clocks that have surpassed the best microwave frequency standards in terms of fractional frequency stability [6,7]. Most comb applications today require self-referencing, i.e., the detection and stabilization of the carrier envelope offset (CEO) frequency f CEO [1,8]. This has been achieved in various fiber laser systems [9] and solid-state lasers (Ti:sapphire [2] or diode-pumped solid-state lasers-DPSSLs [10,11]). Electronic feedback modulating the pump power of the femtosecond laser is the most common approach to phase-stabilize f CEO to an external reference frequency [3]. Alternative methods have been demonstrated, which make use of an intracavity loss modulator enabling the modulation bandwidth to be extended beyond the gain lifetime limitation, such as a graphene electro-optic modulator [12] or an opto-optical modulation of a semiconductor saturable absorber mirror (SESAM) [13]. Other solutions are based on feedforward corrections applied to the CEO frequency [14] or passive CEO cancellation using a difference frequency generation (DFG) process [15].Self-referencing modelocked lasers with a high repetition rate in the GHz range is much more challenging, as the CEO noise typically scales with the repetition rate [16], therefore requiring larger feedback bandwidths. In addition, the standard self-referencing method most often involves f -to-2f interferometry to detect the CEO frequency [1]. This requires a coherent supercontinuum (SC) spectrum that covers at least one frequency octave, which is fairly challenging to achieve fo...

Carrier-envelope offset frequency stabilization of a gigahertz semiconductor disk laser

“…5(b)]. This result is in good agreement with our previous measurement performed indirectly in a similar laser without detecting the CEO beat by f -to-2f interferometry [25]. In addition, we also measured the transfer function of the optical power of the pump diode [see orange curves in Fig.…”

“…The pump laser is driven in parallel by a high DC current source (Delta Elektronika SM 7.5-80) and a home-built voltageto-current converter, providing a high bandwidth modulation channel of the pump power for CEO frequency stabilization. We previously measured a modulation bandwidth in the range of 300 kHz (cutoff at −3 dB amplitude or −90°phase shift) for the CEO frequency modulated by the pump power in a similar laser using an indirect method [25]. In addition, a low-pass electrical filter is implemented between the DC current source and the pump diode to filter out the driver noise and to furthermore avoid any cross-talk between the two current drivers.…”

“…The insufficient signal-to-noise ratio (SNR) of the CEO beat hindered detailed noise characterization or frequency stabilization of this system. In 2016, we used an indirect method based on an appropriate combination of different signals from a VECSEL and a continuous-wave laser to characterize both the frequency noise and the modulation bandwidth of the CEO beat for direct pump current modulation [25], without detecting the CEO beat by a standard nonlinear interferometry method [1]. Here we present the first self-referenced stabilization of the CEO frequency of a modelocked semiconductor disk laser with a repetition frequency (f rep ) of 1.8 GHz.…”

Optically pumped VECSELs: review of technology and progress

“…The resulting > 10 kW of peak power was also sufficient for generating an octave-spanning supercontinuum using a highly nonlinear photonic crystal fiber, and enabled the first carrier envelope offset (CEO) frequency measurement of a mode-locked VECSEL. Later, this work was extended with the first characterization of noise properties and modulation response of CEO frequency in mode-locked VECSELs [403].…”

“…for highprecision spectroscopy, frequency metrology, ultra-stable optical clocks, and ultra-high-speed optical communication (see [402,434] and the references therein). Again, the specific interest arises from the possibility of fabricating compact and cost-effective ultrashort pulse sources [403]. In addition, the high repetition rates can prove useful in relation to frequency combs leading to lines with a larger frequency spacing and more power per mode, and in turn higher signal-to-noise ratios [362,390].…”