Nayara Jornod

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

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.

Frequency comb metrology with an optical parametric oscillator

We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser.

Carrier-envelope offset frequency stabilization of an ultrafast semiconductor laser

We present the self-referenced stabilization of the carrier-envelope offset (CEO) frequency of a semiconductor disk laser. The laser is a SESAM-modelocked VECSEL emitting at a wavelength of 1034 nm with a repetition frequency of 1.8 GHz. The 270-fs pulses are amplified to 3 W and compressed to 120 fs for the generation of a coherent octavespanning supercontinuum spectrum. A quasi-common-path f-to-2f interferometer enables the detection of the CEO beat with a signal-to-noise ratio of ~30 dB sufficient for its frequency stabilization. The CEO frequency is phase-locked to an external reference with a feedback signal applied to the pump current.

Optical frequency comb stabilization of a gigahertz semiconductor disk laser

Semiconductor lasers are a promising technology to make optical comb systems more accessible and cost-efficient. We stabilized the carrier-envelope offset (CEO) frequency of a semiconductor disk laser. The laser was modelocked by a SESAM and generates pulses at a wavelength of 1034 nm. It operates at a repetition frequency of 1.8 GHz. The 270-fs pulses are amplified to 3 W and compressed to 120 fs. A coherent octave-spanning supercontinuum spectrum is generated in a highly nonlinear fiber. Using a standard f-to-2f interferometer, we detect the CEO beat with a signal-to-noise ratio of ~30 dB. By applying a feedback signal to the pump current, the CEO frequency is phase-locked to an external reference.

Novel techniques for stabilizing fiber laser frequency combs

We present the carrier envelope offset (CEO) frequency stabilization of a fiber laser using two novel methods. The first one is based on cross gain modulation (XGM) implemented with a low-power auxiliary light sharing the laser gain medium. The second method is based on opto-optical-modulation (OOM) of a semiconductor absorber mirror in the laser cavity, used for the first time in a fiber laser. We achieved CEO stabilization with feedback bandwidths of up to 600 kHz using these two easy-to-integrate methods. A tight CEO lock was achieved with a residual integrated phase noise of less than 400 mrad.

Towards self-referencing of a VECSEL frequency comb

Optical frequency combs from ultrafast lasers have revolutionized the field of optical metrology and photonics. However, todays commercial frequency combs are still based on complex and expensive ultrafast laser systems, which prevent applications for cost-sensitive areas. Among emerging technologies, modelocked semiconductor lasers are highly promising for future low-cost high-volume production owing to the benefits of semiconductor manufacturing. Vertical external-cavity surface-emitting lasers (VECSELs) are one of the most promising technologies for this purpose. However, the carrier-envelope offset (CEO) frequency of an ultrafast VECSEL has never been stabilized yet because of the demanding combination of high peak power and short pulse duration required for the generation of a coherent, octave-spanning supercontinuum (SC) spectrum for CEO detection. In 2014, the first CEO beat signal from a VECSEL has been recorded after external pulse amplification and compression, but a high noise prevented a detailed analysis and stabilization [1]. In 2016, we presented the first characterization of the noise properties and modulation response of a VECSEL CEO frequency based on an indirect method using a beating signal with an auxiliary continuous-wave laser [2].

Ultrafast optical parametric oscillator pumped by a vertical external-cavity surface-emitting laser (VECSEL)

We report the first optical parametric oscillator synchronously pumped by a SESAM modelocked vertical external-cavity surface-emitting laser (VECSEL). As a nonlinear medium, we use a periodically poled MgO:PPLN crystal. The VECSEL operates at a wavelength of 982 nm and a repetition rate of 198 MHz. The pump radiation is converted to signal and idler wavelengths tunable in the ranges of 1.4-1.8 µm and 2.2-3.5 μm, respectively, simply by a change of the poling period and crystal temperature. The signal pulses have a duration between 2 ps to 4 ps and an average output power up to 100 mW.

High-power amplification of a femtosecond vertical external-cavity surface-emitting laser in an Yb:YAG waveguide

We present the amplification of a mode-locked vertical external-cavity surface-emitting laser (VECSEL) using an Yb:YAG crystalline waveguide as gain medium. The VECSEL seed laser operates at a center wavelength of 1030 nm and generates 300-fs pulses at a repetition rate of 1.77 GHz. An average seed power of 60 mW was launched onto a 8.3 mm long fs-laser written Yb:YAG waveguide pumped by 7.7 W from a 969-nm continuous-wave VECSEL. The amplifier achieves an average output power of up to 2.9 W, corresponding to an amplification factor of 17 dB. Due to gain narrowing, the pulse duration increases to 629 fs. Our results show that crystalline waveguides are a promising technique for the realization of compact multi-watt ultrafast amplifier systems.

Frequency comb metrology with a near-infrared optical parametric oscillator

We show the first absolute optical frequency metrology demonstration performed with an OPO. The OPO frequency comb shows ∼300-mrad integrated CEO phase noise and ∼70-kHz optical linewidth at 1557-nm when fully-stabilized to a radio-frequency reference.

First Investigation of the Noise and Modulation Properties of the Carrier Envelope Offset Frequency in a Semiconductor Modelocked Laser

We report the first characterization of the CEO-frequency in a modelocked semiconductor laser, in terms of noise and modulation bandwidth, performed using a novel approach that does not require an octave-spanning spectrum and a self-referencing scheme.