An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

This Review discusses the emerging field of mid-infrared frequency comb generation, including technologies based on novel laser gain media, nonlinear frequency conversion and microresonators, as well as the applications of these combs in precision spectroscopy and direct frequency comb spectroscopy. Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science.

Mid-infrared frequency combs

Fibre lasers in the mid-infrared regime are useful for a diverse range of fields, including chemical and biomedical sensing, military applications and materials processing. This Review summarizes the different rare-earth cations and host materials used in mid-infrared fibre laser technology, and discusses the future applications and challenges for the field.

Towards high-power mid-infrared emission from a fibre laser

Optical Waveguide Theory

We review photonic applications of dielectric whispering-gallery mode (WGM) resonators-tracing the growth of the technology from experiments with levitating droplets of aerosols to ultrahigh-Q solid state crystalline and integrated on-chip microresonators.

Optical resonators with whispering-gallery modes-part II: applications

We present a compact integrated fiber laser with more than 200 mW of output power. It combines polarized fiber output with very narrow linewidth of less than 2 kHz. The coherence length of the laser is measured to be longer than 5 km. The laser features high mode stability of less than /spl plusmn/10 MHz over hours. The relative intensity noise (RIN) spectrum is dominated by a peak at the relaxation oscillation frequency and is shot-noise limited otherwise. The RIN peak at 1 MHz is reduced to /spl sim/-130 dB/Hz by integrating a negative feedback circuit. In addition to thermal wavelength tuning, the laser frequency can be modulated at a bandwidth of up to 10 kHz via the piezoelectric effect.

Low-noise narrow-linewidth fiber laser at 1550 nm (June 2003)

The effect of the types of alkaline earth metal ions (Mg2+, Ca2+ and Ba2+) and concentration of Al2O3 and BaO on the refractive index and the effective emission linewidths of the 4I13/2−4I15/2 transition of Er3+ ions in phosphate glasses, 64P2O5 · 12Al2O3 ·  3.5( Er 2 O 3 + La 2 O 3 )·20.5 MO ( M = Mg , Ca , Ba ) and 64P2O5 · 3.5(Er2O3+La2O3) · (21.5 − x)Al2O3 ·  (11+x) BaO (x=0,3.5,6.5 and 9.5) , were investigated. A single mode Er3+ doped phosphate glass fiber with a core diameter of 4 μm was fabricated by the rod-in-tube technique. A new Er3+ doped fiber amplifier is demonstrated pumping with a 980 nm fiber pigtailed-laser diode. A gain per unit length greater than 2 dB/cm is demonstrated, which is the largest gain per unit length for fiber amplifiers to our knowledge.

Er3+-doped phosphate glasses for fiber amplifiers with high gain per unit length

Systematic studies of cooperative upconversion and Yb3+–Er3+ energy transfer in newly developed phosphate glasses were performed by a rate-equation formalism. The cooperative-upconversion coefficients of the  4I13/2 level for different Er3+ concentrations were determined from the luminescence-decay curves for high pump intensities. A small cooperative-upconversion coefficient of 1.1×10-18 cm3/s was obtained for a high Er3+ concentration of 4×1020 ions/cm3.Yb3+–Er3+ energy-transfer coefficients for an Er3+ concentration of 2×1020 ions/cm3 codoped with different Yb3+ concentrations were calculated from the lifetime measurements of the  2F5/2 level of Yb3+ ions. For Er3+ codoped with an Yb3+ concentration of 6×1020 ions/cm3, an energy-transfer coefficient of 1.1×10-16 cm3/s and an energy-transfer efficiency higher than 95% were determined from our measurements under weak excitation. The cooperative-upconversion coefficients of Yb3+–Er3+-doped samples were found to be consistent with that of an Er3+-doped sample with the same Er3+ concentration. The weak cooperative-upconversion effect of high Er3+ concentrations and efficient Yb3+–Er3+ energy transfer indicate that these newly developed Er3+- and Yb3+–Er3+-doped phosphate glasses are excellent for active device applications.

Cooperative upconversion and energy transfer of new high Er 3+ - and Yb 3+ –Er 3+ -doped phosphate glasses

Er3+ doped Nb2O5–TeO2 (NT) glass suitable for developing optical fiber laser and amplifier has been fabricated and characterized. Intense and broad 1.53 μm infrared fluorescence and visible upconversion luminescence were observed under 975 nm diode laser and 798 nm laser excitation. For 1.53 μm emission band, the full width at half-maximum is 51 nm, the fluorescence lifetime is 2.6 ms, and the quantum efficiency is ∼100%. The maximum emission cross section is 8.52×10−21 cm2 at 1.532 μm, and is higher than the values in silicon and phosphate glasses. Under 798 nm excitation, efficient 531, 553, and 670 nm upconversion emissions are due to two-photon absorption processes. The “standardized” efficiency for the green upconversion light is 9.5×10−4, and this value is comparable to that reported for Er3+/Yb3+ codoped fluoride glasses. Intense visible upconversion fluorescence in Er3+ doped NT glass can be used in color display, undersea communication, and infrared sensor.

Optical transitions and visible upconversion in Er3+ doped niobic tellurite glass

A 64 W fiber laser at 1.9 μm with a slope efficiency of 68% with respect to the launching pump power at 800 nm was demonstrated in a one-end pump configuration using a piece of 20 cm long newly developed thulium-doped germanate glass double-cladding single-mode fiber. A quantum efficiency of 1.8 was achieved. An output laser power of 104 W at 1.9 μm was demonstrated from a piece of 40 cm long fiber with a dual-end pump configuration.

Shibin Jiang

Papers

Low-noise narrow-linewidth fiber laser at 1550 nm (June 2003)

Er3+-doped phosphate glasses for fiber amplifiers with high gain per unit length

Cooperative upconversion and energy transfer of new high Er 3+ - and Yb 3+ –Er 3+ -doped phosphate glasses

Optical transitions and visible upconversion in Er3+ doped niobic tellurite glass

Highly efficient high-power thulium-doped germanate glass fiber laser