Erbium doped materials are of great interest in thin film integrated optoelectronic technology, due to their Er3+ intra-4f emission at 1.54 μm, a standard telecommunication wavelength. Er-doped dielectric thin films can be used to fabricate planar optical amplifiers or lasers that can be integrated with other devices on the same chip. Semiconductors, such as silicon, can also be doped with erbium. In this case the Er may be excited through optically or electrically generated charge carriers. Er-doped Si light-emitting diodes may find applications in Si-based optoelectronic circuits. In this article, the synthesis, characterization, and application of several different Er-doped thin film photonic materials is described. It focuses on oxide glasses (pure SiO2, phosphosilicate, borosilicate, and soda-lime glasses), ceramic thin films (Al2O3, Y2O3, LiNbO3), and amorphous and crystalline silicon, all doped with Er by ion implantation. MeV ion implantation is a technique that is ideally suited to dope these materials with Er as the ion range corresponds to the typical micron dimensions of these optical materials. The role of implantation defects, the effect of annealing, concentration dependent effects, and optical activation are discussed and compared for the various materials.

Erbium implanted thin film photonic materials

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Nanotube–Polymer Composites for Ultrafast Photonics

Recent developments in rare-earth doped materials for optoelectronics

Organic dye-doped polymers have been widely investigated as gain media in solid-state dye lasers. Dye molecules which have large absorption and induced emission cross sections due to allowed π-π transitions are ideal active dopants for the generation and amplification of intense light pulses. However, continuous wave operation is not feasible with organic dyes because of the triplet losses. On the other hand, lanthanide ions that have long metastable state lifetimes are widely used in silica glass-based fiber amplifiers and for both continuous and pulsed lasers. It has been more than 30 years since the first lanthanide lasers were reported.1-3 During this period a wide variety of lanthanide lasers and amplifiers have been investigated, and extensive progress has been made by many researchers. Many reviews have been written concentrating primarily on the physical and chemical properties of lanthanides in many matrices for laser action.4-8 Recently, several books have focused on lanthanide-doped fiber amplifiers for optical communications.9-11 The success of lanthanide-doped fiber amplifiers has inspired thousands of publications and continues to motivate research on the many diverse components that are required in these systems. Optical links are now used primarily in applications such as telecommunications with single-mode silica optical fibers, which have the ability to provide high-bandwidth and long-distance communications. However, as the demand for bandwidth increases in the office and home, it has become increasingly important to develop very low cost optical links that can be readily installed by users. Plastic optical fibers (POF) have received increasing attention because of their clear technical advantages over glass fibers, such as flexibility and a large core diameter, which enables efficient connection and coupling resulting in a low-cost system for a local area network. Recently a low-loss (100 db/km), highbandwidth 5.12 GHz for 100 m transmission graded index plastic optical fiber (GI-POF) has been developed.12 Also, an all fluorinated POF, whose low loss region is extended to the visible and near-infrared, has been successfully prepared.13 Plastic optical fiber amplifiers (POFA) that generate signal light in the visible and near-infrared are potentially important because of their adaptability for POF-based short span optical local distribution networks. This review describes recent progress on plastic optical fiber lasers and amplifiers with lanthanides. We focus especially on the design and selection of plastic optical fiber and chelate materials.

Plastic optical fiber lasers and amplifiers containing lanthanide complexes.

Lithium niobate on insulator (LNOI) technology is revolutionizing the lithium niobate industry, enabling higher performance, lower cost and entirely new devices and applications. The availability of LNOI wafers has sparked significant interest in the platform for integrated optical applications, as LNOI offers the attractive material properties of lithium niobate, while also offering the stronger optical confinement and a high optical element integration density that has driven the success of more mature silicon and silicon nitride (SiN) photonics platforms. Due to some similarities between LNOI and SiN, established techniques and standards can readily be adapted to the LNOI platform including a significant array of interface approaches, device designs and also heterogeneous integration techniques for laser sources and photodetectors. In this contribution, we review the latest developments in this platform, examine where further development is necessary to achieve more functionalities in LNOI integrated optical circuits and make a few suggestions of interesting applications that could be realized in this platform. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Status and Potential of Lithium Niobate on Insulator (LNOI) for Photonic Integrated Circuits

The first integrated optical laser in LiNbO3, doped by an indiffusion of Er3+ prior to channel-guide fabrication by Ti diffusion is reported. Pumped by a colour centre laser (λp = 1.477 μm), CW operation at λ = 1.532 μm (Δ~0.3 nm) with a threshold of ~8 mW absorbed power was achieved.

Continuous-wave erbium-diffused LiNbO3 waveguide laser

The first continuous wave (cw) and pulsed mode operation of an Er‐diffused Ti:LiNbO3 monomode waveguide laser at 1563 nm (E⊥ c) and 1576 nm (E∥ c) wavelengths is reported. A tunable Tl:KCl color center laser was used as a pump source. With π‐polarized (Ep∥ c) pump radiation of 1479 nm wavelength an oscillation threshold of 13 mW coupled pump power was achieved for the 1576 nm emission line. Above 25 mW pump power additional lasing at 1563 nm wavelength was observed. σ‐polarized (Ep⊥ c) pumping led to a single line emission at 1563 nm throughout with the highest cw output power of 3 mW and a slope efficiency of 3%. Time averaged emission linewidths of about 0.6 nm were measured for both wavelengths at about two times the threshold pump power level. With pulsed excitation of about 1 W coupled peak power output pulses of up to 200 mW peak power were measured.

Er‐diffused Ti:LiNbO3 waveguide laser of 1563 and 1576 nm emission wavelengths

The erbium incorporation into LiNbO3 by diffusion doping is investigated in detail by means of Secondary Ion Mass Spectrometry, Secondary Neutral Mass Spectrometry, Rutherford Backscattering, Atomic Force Microscopy, X-ray Standing Wave technique and optical site-selective spectroscopy. The diffusion of erbium in LiNbO3 can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient. The diffusion constants and activation energies for Z-cut (X-cut) LiNbO3 are 4.8×10-5 cm2/s (12.0×10-5 cm2/s) and 2.28 eV (2.44 eV), respectively. A limited solubility of erbium in LiNbO3 has to be taken into account increasing exponentially with rising temperature. During the first step of diffusion an Er
 x
 Nb
 y
 -oxide layer is formed at the surface of the sample acting as diffusion reservoir. Erbium is incorporated into LiNbO3 on vacant Li-sites slightly shifted from the original Li-position along the (-c)-direction. Site-selective spectroscopy found four distinguishable energetically different erbium centres at this lattice site resulting from locally different symmetries of the crystal field.

Erbium incorporation in LiNbO3 by diffusion-doping

Single-pass and double-pass Er-diffused Z- and X-cut Ti:LiNbO/sub 3/ waveguide amplifiers, optically pumped at /spl lambda//sub p//spl ap/1484 nm, have been investigated. With a 48 mm long Z-cut amplifier device, Er-diffusion doped at 1100/spl deg/C, 6.7 dB (coupled pump power P/sub p,c/=170 mW) and 14.7 dB (P/sub p,c/=90 mW) net small-signal gain have been achieved with a single-pass and a double-pass configuration, respectively, at the signal wavelength /spl lambda//sub s/=1531 nm. A Z-cut sample doped at 1135/spl deg/C showed a considerably improved behavior. 11.3 dB single-pass net small-signal gain has been obtained (P/sub p,c/=170 mW; sample length 5.7 cm). Theoretical calculations predict gain figures up to 20 dB in single-pass and 40 dB in double-pass Er:Ti:LiNbO/sub 3/ amplifiers with increased (realistic) lengths of 10 cm. >

Erbium-doped single- and double-pass Ti:LiNbO/sub 3/ waveguide amplifiers

The development of a Fabry-Perot-type Ti,Er:LiNbO/sub 3/ waveguide laser of optimized CW output power up to 63 mW (/spl lambda//sub s/=1561 nm) at a pump power level of 210 mW (/spl lambda//sub p/=1480 nm) and a slope efficiency of up to 37% is reported. The theoretical model for the waveguide laser is presented and applied to determine the optimum resonator configuration using waveguide parameters obtained from a detailed characterization of the laser sample. With pulsed pumping, waveguide laser pulses of up to 6.2 W peak power were observed. Apart from residual relaxation oscillations, the laser emission proved to be shot-noise limited.

R. Brinkmann

Papers

Continuous-wave erbium-diffused LiNbO3 waveguide laser

Er‐diffused Ti:LiNbO3 waveguide laser of 1563 and 1576 nm emission wavelengths

Erbium incorporation in LiNbO3 by diffusion-doping

Erbium-doped single- and double-pass Ti:LiNbO/sub 3/ waveguide amplifiers

Ti:Er:LiNbO/sub 3/ waveguide laser of optimized efficiency