One of the biggest challenges of silicon photonics is the efficient coupling of light between the sub-micron SiP waveguides and a standard optical fiber (SMF-28). We recently proposed a novel approach based on a spot-size converter (SSC) that fulfills this need. The SSC integrates a tapered silicon waveguide and a superimposed structure made of a plurality of rods of high index material, disposed in an array-like configuration and embedded in a cladding of lower index material. This superimposed structure defines a waveguide designed to provide an efficient adiabatic transfer, through evanescent coupling, to a 220 nm thick Si waveguide tapered down to a narrow tip on one side, while providing a large mode overlap to the optical fiber on the other side. An initial demonstration was made using a SSC fabricated with post-processing steps. Great coupling to a SMF-28 fiber with a loss of 0.6 dB was obtained for TEpolarized light at 1550 nm with minimum wavelength dependence. In this paper, SSCs designed for operation at 1310 and 1550 nm for TE/TM polarizations and entirely fabricated in a CMOS fab are presented.
We present a compact four-laser source based on low-noise, high-bandwidth Pound-Drever-Hall method and optical phase-locked loops for sensing narrow spectral features. Four semiconductor external cavity lasers in butterfly packages are mounted on a shared electronics control board and all other optical functions are integrated on a single silicon photonics chip. This high performance source is compact, automated, robust, operates over a wide temperature range and remains locked for days. A laser to resonance frequency noise of 0.25 Hz/rt-Hz is demonstrated.
TeraXion started silicon photonics activities aiming at developing building blocks for new products and customized
solutions. Passive and active devices have been developed including MMI couplers, power splitters, Bragg grating
filters, high responsivity photodetectors, high speed modulators and variable optical attenuators. Packaging solutions
including fiber attachment and hybrid integration using flip-chip were also developed. More specifically, a compact
packaged integrated coherent receiver has been realized. Good performances were obtained as demonstrated by our
system tests results showing transmission up to 4800 km with BER below hard FEC threshold. The package size is small
but still limited by the electrical interface. Migrating to more compact RF interface would allow realizing the full benefit
of this technology.
Sensing systems for defense and security operate in evermore demanding environments, increasingly leaving the comfort
zone of fiber laser technology. Efficient and rugged laser sources are required that maintain a high level performance
under large temperature excursions and sizable vibrations. This paper first presents a sample of defense and security
sensing applications requiring laser sources with a narrow emission spectrum. Laser specifications of interest for defense
and security sensing applications are reviewed. The effect of the laser frequency noise in interferometric sensing systems
is discussed and techniques implemented to reduce phase noise while maintaining the relative intensity noise
performance of these sources are reviewed. Developments towards the size reduction of acoustically isolated narrow-linewidth
semiconductor lasers are presented. The performance of a narrow-linewidth semiconductor laser subjected to
vibrations is characterized. Simulation results of interferometric sensing systems are also presented, taking into account
both the intensity and phase noise of the laser.
We review the improved performances of a narrow linewidth laser using negative electrical feedback obtained through
advances on narrowband FBG filters. Noteworthy, the tolerance of the laser to vibrations is significantly improved. As
an extension of this work, these narrow filters are proposed for filtering optical signals in RF photonics systems.
Semiconductor lasers are of great interest in high performance optical fiber sensing systems because of their high
reliability, lifetime, low cost and size. However, their linewidth and phase noise are often a limitation. Using
frequency discrimination based on a specially designed fiber Bragg grating, we decrease the linewidth of a
semiconductor laser to the kHz level, with phase noise reduction up to 1 MHz. Using a phase modulator in a second
feedback loop to correct fast phase fluctuations, we demonstrate that the bandwidth can be pushed above 10 MHz.
Frequency noise reduction of semiconductor lasers using electrical feedback from an optical frequency
discriminator is an efficient and simple approach to realize narrow linewidth lasers. These lasers are of great
interest for applications such as LIDAR, RF photonics and interferometric sensing. In this paper, we review
the technological choices made by TeraXion for the realization of its Narrow Linewidth Laser modules. The
method enables to decrease the linewidth of DFB lasers from several hundreds of kHz to a few kHz. We
present the work in progress to integrate such system into a miniature package and to incorporate advanced
functionalities such as multi-laser phase locking.
This is a progress report on the realization of a compact and transportable frequency standard at 1556 nm based on a two-photon transition in rubidium at 778 nm. These hyperfine transitions present great metrological interest. They have a narrow theoretical linewidth of 150 kHz when observed with a 1556 nm laser, and their absolute frequency is known with an uncertainty of 5.2 X 10-12. In this experiment, we use a high power 1556 nm DFB laser and reduce its linewidth to the 10 kHz level using optical feedback from a confocal cavity. We generate its second harmonic in a periodically poled LiNbO3 crystal and use this signal to injection-lock a Fabry-Perot laser emitting 42 mW at 778 nm. The slave laser is used to observe the Doppler-free two- photon transitions: two counter-propagating beams excite rubidium atoms which emit a blue fluorescence on resonance. This 420 nm light is detected on the side of the Rb cell with a photomultiplier. Such an optical frequency standard at 1556 nm, standing in the multiwavelength telecommunications systems window, becomes an attractive source for absolute frequency calibration of WDM components, optical spectrum analyzers and wavemeters.
We have undertaken a research directed to the realization of frequency-stabilized lasers for multifrequency optical communications in the 375 THz, 229 THz, and 193 THz (0.8, 1.3, and 1.55 micrometers ) bands. In this paper, we present an overview of our latest results in the 1.55 micrometers band. We compare the performance of optical frequency references based on lasers frequency-locked to acetylene molecules and rubidium atoms. The absolute vales and the frequency stability improvements are discussed. We also present techniques to transfer those performance to multiple frequencies for multifrequency communication systems. We study the use of an absolutely calibrated multimode Fabry-Perot optical resonator with transmission peals set at exact multiples of 100 GHz. We also study the use of a calibrated wavemeter based on a sum-frequency surface emitting multilayered nonlinear crystal to allow the precise tuning at any frequency in the vicinity of an absolute optical frequency standard.
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