We present the development of a transportable laser frequency stabilization system with application to both optical clocks and a next-generation gravity mission (NGGM) in space. This effort leverages a 5-cm long cubic cavity with crystalline coatings operating at room temperature and with a center wavelength of 1064 nm. The cavity is integrated in a custom vacuum chamber with dedicated low-noise locking electronics. Our vacuum-mounted cavity and control system are well suited for space applications, exhibiting state-of-the-art noise performance while being resilient to radiation exposure, vibration, shock, and temperature variations. Furthermore, we demonstrate a robust means of automatically (re)locking the laser to the cavity when resonance is lost. We show that the mounted cavity is capable of reaching technology readiness level (TRL) 6, paving the way for high-performance ultrastable laser systems and eventually optical atomic clocks amenable to future satellite platforms.

The rubidium two-photon optical atomic clock is a promising technology for applications that require a compact yet stable timekeeping device. However, its long-term frequency stability is often limited by the light shift (or AC Stark effect). In a rubidium two-photon frequency standard, we demonstrate in experiment that the light shift of the 778.1 nm wavelength probe beam can be mitigated with another, 1556.2 nm wavelength beam.

The performance of a two-photon atomic clock currently developed at CSEM in partnership with Rolex is reported. This clock, designed in view of its integration in a 19-inch rack-mount enclosure, is intended for 24/7 operation as Rolex timescales master clock. Its design, based on a standard architecture, takes advantage of the high-reliability and high-availability of telecom C-band components. Long-term stability limited to a few 10 -15 by the cell helium permeation drift is demonstrated. A drift-removed relative frequency stability in the 10 -15 range at 10 5 s and beyond is achieved, limited by the residual AC Stark-shift.

The Laser Interferometer Space Antenna (LISA), with its extreme distance measurement requirements (pm over arm lengths of 2.5 Mio km), imposes many stringent requirements on the laser sources used for interferometry. Frequency and power stability, as well as the side band phase noise represent considerable technological challenges, that must be maintained over the full 12.5 years mission duration. These constraints demand a streamlined laser design and a particular attention to reliability and procurement strategy, which poses a significant challenge. The main requirements for the laser critical sub-system have been analyzed. The Centre Suisse d’Electronique et de Microtechnique (CSEM), in the frame of a European Space Agency activity, was mandated to demonstrate a laser head for the LISA mission based on an alternative laser oscillator approach that does not rely on the LISA-baseline technology (i.e. Nd:YAG NPRO laser). The activity was named MONALISA. After a presentation of the key laser head requirements, the laser head design is described. A comprehensive test campaign was performed, and test results are presented.

A digital optical phase-locked loop (OPLL) has been implemented to develop a distributed Brillouin sensing system in optical fibers. In our experiment, two commercial semiconductor lasers are phase-locked to each other with a highly flexible offset frequency using field programmable gate array (FPGA)-based electronics. Then, the difference frequency between the two lasers is highly stabilized and scanned by a desired step frequency in the vicinity of the Brillouin frequency of standard single-mode optical fibers. Consequently, the distribution of Brillouin frequency shift over a 50 km-long sensing fiber has been successfully measured by a very simple and low-cost Brillouin optical time-domain reflectometry (BOTDR) sensing system without any penalty in the sensing performance. The measurement repeatability at 50 km position of sensing fiber with a 5 m spatial resolution was measured be 4.5 MHz under fast measurement conditions: the number of trace averaging of 2000 and the frequency scan step of 12.8 MHz, showing the figure-of-merit of 3.0.

Optical frequency combs have become a very powerful tool in metrology and beyond, thanks to their ability to link radio frequencies with optical frequencies via a process known as self-referencing. Typical self-referencing is accomplished in two steps: the generation of an octave-spanning supercontinuum spectrum and the frequency-doubling of one part of that spectrum. Traditionally, these two steps have been performed by two separate optical components. With the advent of photonic integrated circuits, the combination of these two steps has become possible in a single small and monolithic chip. One photonic integrated circuit platform very well suited for on-chip self-referencing is lithium niobate on insulator—a platform characterized by high second and third order nonlinearities. Here, we show that combining a lithium niobate on insulator waveguide with a silicon photodiode results in a very compact and direct low-noise path toward self-referencing of mode-locked lasers. Using digital servo electronics, the resulting frequency comb is fully stabilized. Its high degree of stability is verified with an independent out-of-loop measurement and is quantified to be 6.8 mHz. Furthermore, we show that the spectrum generated inside the lithium niobate waveguide remains stable over many hours.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text C. Greve, K. Dahl, G. Barwood, J. Bennès, C. Braxmaier, P. Cebeci, C. Deutsch, O. Fitzau, M. Ghulinyan, M. Giesberts, P. Gill, B. Kassner, S. Koller, E. Kovalchuk, M. Krutzik, S. Kundermann, S. Lecomte, R. Le Goff, C. Meier, M. Oswald, A. Peters, S. A. Pyka, J. Sanjuan, M. Schiemangk, S. Schilt, T. Schuldt, A. Sell, C. Stenzel, K. Voss, A. Wicht, and A. Zhukov, "Space based lasers for gravitational wave detection," in Laser Congress 2019 (ASSL, LAC, LS&C), OSA Technical Digest (Optica Publishing Group, 2019), paper CM3C.4. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Laser frequency combs (LFC) have been shown to provide exquisite precision that can be used in astronomical spectrograph calibration [1–5], for research fields such as exoplanets, cosmology and fundamental physics.

European Space Agency (ESA) considers picosecond mode-locked semi-conductor laser technology as a promising candidate for space applications in precision optical metrology systems. However, very challenging performance requirements should be met by such laser without additional amplification stages. In order to address this challenge, we realized two types of mode-locked edge emitting lasers operating at 990 nm wavelength. In particular, we demonstrate a very-long (13.5 mm) monolithic multi-section tapered laser reaching 201 pJ mode-locked pulses at low repetition frequency of 2.89 GHz with the pulse width that can be compressed down to 2.4 ps. We also report on a multi-section inverse how-tie external cavity laser producing mode-locked pulses of 70 pJ energy and 6 ps width (0.73 fs atter compressor) at 1.65 GHz pulse repetition frequency (PRF). The laser operates in an 80-mm-long external cavity. The PRFs of the two lasers can be continuously tuned over 9.8 and 9.1 MHz ranges, respectively. Active stabilization with a phase locking loop actuating on the driving current has allowed us to reach PRF relative stabilities of 1.15-10(-10) and 2.9.10(-10) on 1 s intervals for the two lasers. These performances fulfill the requirements of ESA for inter-satellite long distance measurements.

Earth-like planets, dark energy and variability of fundamental physical constants can be discovered by observing wavelength shifts in the optical spectra of astronomical objects1–5. These wavelength shifts are so tiny that exquisitely accurate and precise wavelength calibration of astronomical spectrometers is required. Laser frequency combs, broadband spectra of laser lines with absolutely known optical frequencies, are uniquely suited for this purpose6–13, provided their lines are resolved by the spectrometer. Generating such astronomical laser frequency combs ('astrocombs') remains challenging. Here, a microphotonic astrocomb is demonstrated via temporal dissipative Kerr solitons14–16 in photonic-chip-based silicon nitride microresonators17, directly providing a spurious-free spectrum of resolvable calibration lines. Sub-harmonically driven by temporally structured light18, the astrocomb is stabilized to a frequency standard, resulting in absolute calibration with a precision of 25 cm s–1 (radial velocity equivalent), relevant for Earth-like planet detection and cosmological research. The microphotonic technology can be extended in spectral span17,19–24, further boosting the calibration precision. A microphotonic astrocomb is demonstrated via temporal dissipative Kerr solitons in photonic-chip-based silicon nitride microresonators with a precision of 25 cm s–1 (radial velocity equivalent), useful for Earth-like planet detection and cosmological research.

Wavelength tuneable lasers for 40G and 100G coherent optical communications systems need to meet stringent requirements on narrow linewidth emission across the entire tuning range, with typical values of 300-500 kHz required in commercial systems. Higher capacities can be achieved in next generation systems by employing higher order modulation formats such as 16QAM or 64QAM. However, such systems have even more stringent linewidth requirements [1]. For example, square 64QAM transmission at data rate 40Gbit/s (the baud rate is 6.7G symbols / second) demands a laser with 1 kHz linewidth. Although linewidths as low as 70 kHz and even lower have been demonstrated in free-running Discrete Mode Laser Diodes (DMLD), further (active) linewidth reduction is required. This can be achieved by introducing a phase modulator on chip and applying a Pound-Drever-Hall (PDH) technique to stabilize on an optical reference cavity for instance. In the usual implementation of the PDH technique an external acousto-optic modulator (AOM) is used for active phase noise correction (Figure 1 (a), compare blue and red curves). This worsens significantly the intensity noise (Figure 1 (b)) rendering the laser unsuitable for QAM applications. In this talk we will report a DMLD laser with on-chip integrated frequency modulator based on Joule heating and showing zero residual amplitude modulation (RAM) (Figure 1 (a) and (b) green curves show preliminary stabilization results). DMLDs with integrated phase modulators are highly interesting for coherent optical communications and other applications demanding actively narrowed linewidth emission while offering an economic approach with a focus on high volume manufacturability of monolithic semiconductor lasers [2].

The repetition rate stabilization of an optical frequency comb based on diode-pumped solid-state laser technology is demonstrated using an intra-cavity electro-optic modulator. The large feedback bandwidth of such modulators allows disciplining the comb repetition rate on a cavity-stabilized continuous-wave laser with a locking bandwidth up to 700 kHz. This surpasses what can be achieved with any other type of actuator reported so far. An in-loop integrated phase noise of 133 mrad has been measured and the PM-to-AM coupling of the electro-optic modulator has been investigated as well.

We report ground-level gamma and proton radiation tests of a passively mode-locked diode-pumped solid-state laser (DPSSL) with Yb:KYW gain medium. A total gamma dose of 170 krad(H(2)O) applied in 5 days generates minor changes in performances while maintaining solitonic regime. Pre-irradiation specifications are fully recovered over a day to a few weeks timescale. A proton fluence of 9.76·10(10) cm(-2) applied in few minutes shows no alteration of the laser performances. Furthermore, complete stabilization of the laser shows excellent noise properties. From our results, we claim that the investigated femtosecond DPSSL technology can be considered rad-hard and would be suitable for generating frequency combs compatible with long duration space missions.

We report ultra-low phase-noise microwave generation at a 9.6 GHz carrier frequency from optical frequency combs based on diode-pumped solid-state lasers emitting at telecom wavelength and referenced to a common cavity-stabilized continuous-wave laser. Using a novel fibered polarization-maintaining pulse interleaver, a single-oscillator phase-noise floor of -171 dBc/Hz at 10 MHz offset frequency has been measured with commercial PIN InGaAs photodiodes, constituting a record for this type of detector. Also, a direct optical measurement of the stabilized frequency combs' timing jitter was performed using a balanced optical cross correlator, allowing for an identification of the origin of the phase-noise limitations in the system.

Carrier envelope frequency (f CEO ) stabilization of frequency combs is traditionally achieved via power modulation of the pump of the comb oscillator. A further possibility is to shift the laser f CEO using an external acousto-optic frequency shifter (AOFS). In this case the optical frequency comb spectrum is shifted exactly by the RF modulation frequency of the AOFS. In this work different stabilization schemes in self-referenced frequency comb system architecture are compared. It is shown that AOFS frequency shifting represents a high performance alternative to the standard feedback control via pump power modulation.

We present ultra-low phase noise microwave generation based on a photonics oscillator. By using an ultra-narrow linewidth continuous-wave laser stabilized on a high-finesse optical cavity as a frequency reference, an optical frequency comb as an optical-to-microwave frequency divider and a photodiode for optical-to-electrical conversion, a 9.6 GHz carrier frequency signal has been generated with residual phase noise of -110 dBc/Hz and absolute phase noise below -165 dBc/Hz at 1 Hz and 1 MHz offset frequencies respectively. Further improvements of the system are under way.

Optical frequency combs are key instruments that have revolutionized many fields like frequency metrology and spectroscopy. Traditionally based on fiber lasers or Ti:Sapphire lasers they have been widely studied. Here we demonstrate a 1-micron optical frequency comb based on passively mode-locked diode-pumped solid-state laser technology with low-noise properties and high-reliability.

Increasing the compactness and robustness of laser stabilization systems is a critical need for the development of industrial applications of ultra-narrow linewidth lasers. In this aim, a compact optical setup based on the Pound-Drever-Hall scheme with a high finesse cavity was built with overall dimensions of L × W × H = 45 × 35 × 13 cm3. An external cavity diode laser (PLANEX™, RIO Inc.) as well as a distributed-feedback fiber laser (Koheras Adjustik, NKT photonics) were stabilized using this system. The frequency stability was evaluated using a similar setup as reference. The combined relative stability of the systems reached 7·10-15 at 1s.

We present carrier envelope offset (CEO) frequency detection of a diode-pumped Yb:KGW (ytterbium-doped potassium gadolinium tungstate) laser with a repetition rate of 1 GHz. The SESAM-soliton-modelocked laser delivers 2.2-W average power in 290-fs pulses. This corresponds to a peak power of 6.7 kW and the optical-to-optical efficiency is 38%. With a passive pulse compression the duration is reduced to 100 fs at an average power of 1.1 W. Coherent supercontinuum (SC) generation in a highly nonlinear photonic crystal fiber (PCF) is achieved without additional amplification. Furthermore we have demonstrated that pulse compression towards lower soliton orders of approximately 10 was required for coherent SC generation and CEO detection. Additional numerical simulations further confirm these experimental results.