Pump and probe experiments on Er3+ ions coupled to Si nanoclusters have been performed in rib-loaded waveguides to investigate optical amplification at 1.5μm. Rib-loaded waveguides were obtained by photolithographic and reactive ion etching of Er-doped silica layers containing Si nanoclusters grown by reactive sputtering. Insertion losses measurements in the infrared erbium absorption region allowed to gauge an Er3+ absorption cross section of about 5×10−21cm2 at 1534nm. Signal transmission under optical pumping at 1310nm shows confined carrier absorption of the Si nanoclusters. Amplification experiments at 1535nm evidence two pump power regimes: Losses due to confined carrier absorption in the Si nanoclusters at low pump powers and signal enhancement at high pump powers. For strong optical pumping, signal enhancement of about 1.2dB∕cm was obtained.
Si 3 N 4 ∕ SiO 2 waveguides have been fabricated by low pressure chemical vapor deposition within a complementary metal–oxide–semiconductor fabrication pilot line. Propagation losses for different waveguide geometries (channel and rib loaded) have been measured in the near infrared as a function of polarization, waveguide width, and light wavelength. A maximum thickness of single Si3N4 of 250 nm is allowed by the large stress between Si3N4 and SiO2. This small thickness turns into significant propagation losses at 1544 nm of about 4.5dB∕cm because of the poor optical mode confinement factor. Strain release and control is possible by using multilayer waveguides by alternating Si3N4 and SiO2 layers. In this way, propagation losses of about 1.5dB∕cm have been demonstrated thanks to an improved optical mode confinement factor and the good quality of the interfaces in the waveguide.
In this contribution, new developments on the silicon photomultipliers (SiPM) fabricated at FBK-irst (Trento, Italy) are reported. With respect to the first series of devices produced in 2005/2006, there have been major improvements on both the the layout and the technology. Concerning the first aspect we fabricated SiPMs with increased fill factor and with different geometries (square/circular devices, arrays and matrices of SiPMs) to meet the requirements of different applications. Concerning the technology, we identified a process technique able to reduce significantly the dark count rate. In this paper we will describe the main electro-optical characteristics of these devices.
I. INTRODUCTIONN the past few years a growing attention has been devoted to a solid state version of the photo-multiplier tube (PMT), generally referred to as the silicon photomultiplier (SiPM). Compared to PMTs it presents important advantages, such as: compactness, ruggedness, low operational voltage, insensitivity to magnetic fields and low cost. On the other hand, a lot of development is still needed to reach both the noise level (dark count rate) of a PMT as well as to increase the area covered by the device. FBK-irst (former ITC-irst, Trento) have been developing this device in its own fabrication laboratory since 2005 [1,2]. This is done in collaboration with INFN, which is mainly interested in the application of the sensor in high-energy physics, nuclear medicine and astro physics. At the 2006 IEEE Nuclear Science Symposium we presented the electro-optical characteristics of the first prototypes of Silicon Photomultipliers produced at FBK-irst, (see [3]). The devices under test had an area of 1x1mm 2 with 625 microcells. The fill factor was not optimized yet and its maximum value was about 30%. The electrical characteristics of such devices can be summarized as follows:• Breakdown voltage of about 30V;Manuscript received November 21, 2007.
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