Residual Phase Jitter Research Articles

Phase Noise of Fourier Domain Mode Locked Laser Based Coherent Detection Systems

Swept source based coherent detection system (CDS) is a common method to measure weak signals in optical sensing and imaging systems. The nature of the phase noise of swept source based CDS however has attracted little attention. In this paper, the statistical properties of the phase noise in a CDS based on Fourier domain mode locked (FDML) laser are investigated theoretical and experimental. The fast spectral evolution of the FDML laser is characterized by using the time-varying phase. The probability density function (PDF) of the measured residual phase jitter (RPJ) is found to be close to the Gaussian distribution. The variance of the RPJ increases quadratically with the optical path difference of the CDS. The PDF of the RPJ and the variation of the variance of the RPJ and the frequency-noise power spectral density are studied numerically using stationary white noise. The experimental results agree well with simulations. The study provides insight into the noise property of FDML laser based CDS and evaluates the temporal coherence of swept lasers.

Phase-coherent asynchronous optical sampling system.

Mutual phase coherence is the utmost crucial factor in an asynchronous optical sampling system. The enhancement is commonly achieved by phase-locking dual femtosecond lasers to a shared narrow-linewidth cavity-stabilized laser. Here we report such a system with a low residual optical phase jitter at a level of 0.04 rad in a Fourier frequency band from 1 Hz to 5 MHz around 1.55 µm, corresponding to a timing jitter of 30 as. The residual phase jitter reaches 1 rad at a Fourier frequency between 0.06 Hz and 0.1 Hz, from which the phase-coherence time is inferred to be at least 10 s. The multi-heterodyne beats experimentally reveal a hardware-limited phase coherence time of ∼8.155 s throughout the direct lasing spectral band.

A fully stabilized low-phase-noise Kerr-lens mode-locked Yb:CYA laser frequency comb with an average power of 1.5 W

We report a fully stabilized self-referenced all-solid-state-laser frequency comb based on a home-built Kerr-lens mode-locked Yb:CaYAlO4 oscillator, which delivers ultrafast pulses with a pulse duration of 54 fs and an average power of 1.5 W. Free running carrier-envelope phase offset frequency (fceo) is observed with a signal to noise ratio of 40 dB at 100 kHz resolution bandwidth, which is phase-locked to a microwave frequency synthesizer with a residual phase jitter of 370 mrad [1 Hz–1 MHz] and with a standard frequency deviation of 0.8 mHz at 1-s gate time within 3-h, corresponding to the relative frequency instability of 2.9 × 10−18 at 1-s average time. It is the lowest phase noise and the highest frequency stability of fceo obtained in a watt-level all-solid-state bulk laser frequency comb to the best of our knowledge. A 13th repetition rate is simultaneously phase-locked to the same microwave standard with a frequency instability level of 10−12 at 1 s average time. Such fully stabilized power scaling Yb: CaYAlO4 laser frequency combs have great potential for applications in broadband dual comb spectroscopy as well as high loss cases such as long-distance time and frequency transfer.

A full-path phasing technique based on the far-field interference fringe for tiled-aperture coherent beam combining

We propose a new phase error measurement and control technique based on the far-field interference fringe (FFIF) for a coherent beam combined with a tiled-aperture design. By using this method, the phase error can be directly measured at the focal plane, enabling a visual monitor of full-path measurement without introducing extra optical elements before focusing. The analytical expression of the relation between far-field distributions and phase errors is derived, which gives a theory guidance by the phase extraction from the FFIF. A proof of the principle experiment is demonstrated and a residual phase jitter of 0.157 rad (approximately 1/40 λ) is achieved, which is adequate for a coherent beam combined with femtosecond pulses.

Passive-Compensation-Based Stable RF Phase Dissemination for Multiaccess Trunk Fiber Link With Anti-GVD and Anti-Backscattering Function

We propose and demonstrate a scheme of stable radio frequency (RF) phase dissemination for multiaccess trunk fiber link by passive frequency mixing with anti-group velocity dispersion (GVD) and anti-backscattering function. The propagation delay of the entire fiber link is detected by a round-trip probe signal. After converting the frequency of the precompensated signal to the same frequency as the backward probe signal, the phase drifts can be eliminated automatically by frequency mixing at an arbitrary receiving node. Signals with different radio frequencies at the same wavelength are employed in the forward and backward transmissions to efficiently suppress the effect of the GVD and Rayleigh backscattering at the same time. In the experiment, a 2.4-GHz RF signal is delivered through a 50.2-km single mode fiber with autophase correction. The residual phase jitter of the recovered signals is no more than 0.031 rd at two points along the trunk fiber link.

Carrier-envelope frequency stabilization of a Ti:sapphire oscillator using different pump lasers: part II

Complementing an earlier report (Vernaleken et al. in Opt Exp 20:18387, 2012), we investigate the residual phase jitter of a carrier-envelope frequency stabilized Ti:sapphire oscillator when pumped by additional commercially available pump lasers that were not part of the first study. We find that all tested pump lasers allow stabilization of the oscillator with a residual rms phase noise (integrated between 2 Hz and 5 MHz) of less than 150 mrad despite their different design and properties. Possible sources of technical noise and their elimination for specific models are discussed.

Direct carrier-envelope phase control of an amplified laser system

Direct carrier-envelope phase stabilization of an Yb:KGW MOPA laser system is demonstrated with a residual phase jitter reduced to below 100mrad, which compares favorably with previous stabilization reports, both of amplified laser systems as well as of ytterbium-based oscillators. This novel stabilization scheme relies on a frequency synthesis scheme and a feed-forward approach. The direct stabilization of a sub-MHz frequency comb from a CPA amplifier not only reduces the phase noise but also greatly simplifies the stabilization setup.

Long-term carrier-envelope-phase-stable few-cycle pulses by use of the feed-forward method

The feed-forward technique has recently revolutionized carrier-envelope phase (CEP) stabilization, enabling unprecedented values of residual phase jitter. Nevertheless, its demonstrations have hitherto remained in a proof-of-principle state. Here we show that pulse quality and power issues can be solved, leading to few-cycle pulses with good beam quality. Making use of stable interferometers, we achieve day-long CEP-stable operation of the setup. Out-of-loop RMS phase noise amounts to less than 30 mrad in 20 s, with more than 24 h of CEP-locked operation being demonstrated.

Combining Decision-Feedback Equalization and Carrier Recovery for Two-Dimensional Signal Constellations

In this paper, the combination of decision feedback equalizer and digital phase-locked loop (DPLL) is investigated in detail in channels impaired by intersymbol interference and phase noise. Various methods for carrier phase recovery in several system configurations are analyzed and compared. Two cases of phase noise are considered. In the first one, the significant phase noise is in the receiver side, whereas in the second case, the significant noise is in the transmitter side. We select the best estimation schemes for the two cases and analyze them in terms of residual phase jitter, optimal loop gain, and complexity of implementation. Their performances relative to the other schemes are verified by simulations under both high and low signal-to-noise ratio conditions, where in the latter, the mean time to lose lock criterion is used. We show the relevance of knowing the source of the phase noise. We also treat the special case of one-dimensional signal constellations, such as binary phase-shift keying and gaussian minimum-shift keying (GMSK), where further optimizations are employed. Finally, the more general case of phase noise, which originates both in the transmitter and the receiver in the same order of magnitude is introduced. For this case, the new transmitter phase noise loop is combined with the receiver loop to a double DPLL.

High-quality photonic sampling streams from a semiconductor diode ring laser

We report on the development of an ultralow-noise, external-cavity, actively mode-locked semiconductor diode laser for application in next-generation photonic sampling systems. A summary of harmonically mode-locked noise characteristics in a 65-MHz ring cavity is presented through the range of pulse repetition frequencies between 130 MHz and 8.3 GHz (2nd-128th harmonic). Important implications regarding the use of gain-versus-loss modulation as the active modelocking mechanisms are discussed. We also report what are, to our knowledge, the lowest noise characteristics achieved to date for a semiconductor diode laser operating at 10 GHz. Individually optimized results of 0.12% rms amplitude noise (10 Hz-10 MHz), and 43 fs rms residual phase jitter (10 Hz-10 MHz) provide a theoretical resolution of 8.6 bits in a 10-GSPS optical analog-to-digital converter. We have also achieved dispersion-compensated pulsewidths; as short as 1.2 ps, and shown successful operation of a novel phase-locked-loop capable of reducing the rms; residual phase noise by as much as 91% within its response bandwidth. Finally, the first measurements of residual phase noise out to the Nyquist frequency (5 GHz) are presented, providing an upper bound on the rms residual phase jitter of 121 fs (10 Hz-5 GHz).