Fano resonance in a multimode tapered fiber coupled with a microspherical cavity

Chiba, Akito; Fujiwara, Hideki; Hotta, Jun‐ichi; Takeuchi, Shigeki; Sasaki, Keiji

doi:10.1063/1.1951049

Cited by 80 publications

(43 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…13,14 The transmittance of the fiber was about 90% ͑when fablicated͒ and flat for the wavelength region from 1500 to 1620 nm, indicating single mode operation at 1550 nm. 14 The experimental setup for acquiring the lasing spectrum is shown in Fig.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Fiber-microsphere laser with a submicrometer sol-gel silica glass layer codoped with erbium, aluminum, and phosphorus

Takashima

Fujiwara

Takeuchi

et al. 2007

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

Lasing of a taper-microsphere system with a gain layer of submicrometer thickness is demonstrated. For the gain layer, an Er 3+ -doped P 2 O 5 -Al 2 O 3 -SiO 2 thin film with a thickness of 200 nm was fabricated using the sol-gel method on a silica microsphere. The demonstration of single-mode lasing with the thin gain layer suggests the improved dispersion of Er ions in the P codoped gain layer. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2711384͔Microsphere resonators coupled with a tapered optical fiber have been attracting considerable attention recently as ideal cavity systems having ultrahigh Q factors and single spatial mode input-outputs. After pioneering demonstrations of coupling between a silica glass microsphere and a tapered fiber, 1,2 demonstrations of lasing phenomena have been reported. [3][4][5][6][7][8] One concern has been to improve the coupling parameter ͑␤͒ between the spontaneous emission of the gain medium and the cavity mode in the microsphere in order to realize ultralow threshold lasers. 9 Realization of a submicrometer thick gain layer is essential for achieving better coupling between the gain layer and a cavity mode in the microsphere, since the spatial distribution of the mode is about 1 m.The first demonstration of a fiber-microsphere laser was reported by Cai et al. using an erbium:ytterbium-codoped phosphate glass microsphere. 3 Later, demonstrations using tellurite glass microspheres with doped Er ions 4 and with doped Tm ions 5 were also reported. In those experiments, however, the whole spheres were filled with the gain media. Yang and Vahala applied erbium-doped sol-gel films to the surface of a silica microsphere. 6 The thickness of the gain region was varied from 1 m to more than 5 m. They observed continuous wave operation for microspheres having thin gain layers ͑1 m͒, while pulse mode operation was observed in microspheres having thicker ͑ജ5 m͒ gain layers. Recently, Hoi et al. adopted erbium-doped sol-gel silicaalumina glasses as the gain layer. 7 They succeeded in increasing the concentration of Er ions upto 15 000 ppm by aluminum codoping. However, the thickness of the gain medium was still more than 1 m. In earlier studies, 6,7 the spheres were repeatedly dipped into the coating sol, heated and irradiated by a laser beam even for gain layers having a 1 m thickness since the buildup rate was 0.3 m / cycle. 6 Recently, an ion implantation technique was used to control the position and thickness of the gain region; 8 however, an ion accelerator is required for such a process.In this letter, we report single-mode lasing of a tapermicrosphere system having a gain layer of a thickness of a few hundred nanometers using phosphorus codoped sol-gel erbium silica-aluminum glass. Our trial of phosphorus doping is motivated by a recent electron spin resonance study 10 that reported a striking difference between Al and P codopings for the local structure near Er ions, suggesting a better dispersion of highly doped Er ions with P codoping. We consider that the improved d...

show abstract

mentioning

confidence: 99%

“…The microsphere and the tapered fiber were in a plastic box, which was filled with dry air. 13 Unabsorbed pump light ͑975 nm͒ was removed from the laser emission light ͑about 1550 nm͒ using two 980/ 1550 nm WDM couplers. Then, the laser emission light was analyzed using an optical spectrum analyzer ͑Anritsu, MS9001A͒.…”

mentioning

confidence: 99%

Fiber-microsphere laser with a submicrometer sol-gel silica glass layer codoped with erbium, aluminum, and phosphorus

Takashima

Fujiwara

Takeuchi

et al. 2007

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

show abstract

“…17,18 The transmittance of the fiber was about 90% ͑when fabricated͒ and flat for the wavelength region from 1500 to 1620 nm, indicating single-mode operation at 1550 nm. 18 A single-mode laser diode operating at 975 nm ͑Thor-labs, PL980P200͒ with single-mode optical fiber output was used for pumping.…”

mentioning

confidence: 99%

“…During the experiments, the microspheres were in contact with the tapered fiber inside a plastic box filled with dry air. 17 Unabsorbed pump light ͑975 nm͒ was removed from the laser emission light ͑about 1550 nm͒ using two 980/ 1550 nm wave division multiplexing couplers. Then, the laser emission light was analyzed using a spectrometer ͑Oriel, MS257͒ equipped with an InGaAs multichannel detector head ͑Hamamatsu, C8062-01͒.…”

mentioning

confidence: 99%

Control of spontaneous emission coupling factor β in fiber-coupled microsphere resonators

Takashima

Fujiwara

Takeuchi

et al. 2008

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

The spontaneous emission coupling factor ␤ is studied for fiber-coupled microspheres with a thin gain layer of phosphorus codoped sol-gel erbium silica-aluminum glass. From the input-output characteristics of the lasing, ␤ = 0.039 is estimated for a sample with a gain layer on the sphere surface. ␤ is estimated to increase to 0.19 when an additional silica glass thin layer is overcoated to improve the overlap between the gain layer and the optical mode of the lasing inside the sphere. [4][5][6][7][8][9] In addition to Q values and coupling efficiency, a crucial parameter for its applications is the spontaneous emission coupling factor ␤, defined as the fraction of spontaneous emission coupled into a cavity mode with respect to the spontaneous emission into all modes. 10 To realize microsphere lasers with a low lasing threshold, it is essential to improve ␤. Moreover, ␤ is important for the realization of optical quantum information devices, such as single photon sources 11 and quantum phase gates. 12,13 The ␤ factor has been investigated in sole liquid microdroplets and polymer microspheres ͑without tapered-fiber coupling͒. Chang and Campillo measured the stimulated Raman scattering in carbon disulfide microdroplets of 8 m diameter. 14 They observed an absence of a clear threshold and estimated ␤ to be about 0.42. Kuwata-Gonokami and Takeda demonstrated lasing in a 5 m diameter polystyrene microsphere with a dye doped surface layer. 15 From the input and output characteristics near the lasing threshold, they estimated ␤ to be 0.3. However, these studies were for sole microspheres using free-space laser pumping and ␤ factors for fiber-coupled microspheres have not been fully investigated.In this letter, we report the estimation of ␤ factors for fiber-coupled microspheres. We also study the change of ␤ factor according to the location of the gain layer inside the sphere. For this study, the thickness of the gain layer has to be sufficiently smaller than the distribution of the optical mode in the sphere. For this purpose, we used a method to fabricate a fiber-coupled microsphere laser with a submicron thickness gain layer. 9 By overcoating an undoped sol-gel silica glass thin layer to improve the overlap between the gain layer and the optical mode in the sphere, ␤ of a sample with a gain layer on the sphere surface was increased from 0.039 to 0.19.Overcoating of an undoped sol-gel silica glass on a precoated gain layer produces optimal coupling between the gain layer and the optical mode in a microsphere. Figure 1 shows the calculated distribution of the thin gain layer and the optical mode in a 40 m diameter microsphere at 1535.7 nm wavelength, corresponding to the emission wavelength of Er. The calculation of the optical mode was based on the Lorenz-Mie theory. 16 The optical mode is confined in the region about 600 nm inside from the surface with full width at half maximum of about 1000 nm. To realize a large ␤, it is essential to locate the gain layer at the peak of the optical mode. Considering the thickness...

show abstract

“…Toward complete PL-LSP coupling, which means that all power of PL can couple into a single LSP antenna * sasaki@es.hokudai.ac.jp without loss, we employ a tapered-fiber-coupled microspherical cavity. Microspherical cavities possess ultra-high-quality factors (>10 8 ) and small mode volumes (<10 3 μm 3 ) [22][23][24][25], which can provide sufficiently high intracavity enhancement for strong PL-LSP coupling. Because the whispering gallery mode forms an evanescent field around the microsphere, a metal nanostructure placed on or near the sphere surface can be coupled with the cavity mode.…”

mentioning

confidence: 99%

Efficient optical coupling into a single plasmonic nanostructure using a fiber-coupled microspherical cavity

et al. 2014

Self Cite

View full text Add to dashboard Cite

Toward complete coupling between propagating light (PL) and a single localized-surface-plasmon (LSP) nanostructure, we propose a tapered-fiber-coupled microspherical cavity system combining an Au-coated probe tip. This system possesses the unique characteristic of precise adjustability for the fiber-cavity coupling rate and the cavity-plasmon coupling rate, which is indispensable for achieving the critical coupling conditions. We successfully demonstrate the 93% PL coupling into the LSP antenna with an effective area of a 58 nm circle, exceeding the diffraction limit. Localized surface plasmons (LSPs) of metal nanostructures have attracted considerable attention because of the unique enhancement of the exciton-photon coupling by strong localization of the optical field [1][2][3][4][5][6][7][8][9][10][11]. The LSP polaritons have the ability to confine the optical field into nanometer-scale areas, exceeding the diffraction limit, using the so-called optical antenna effect [1][2][3]. LSP fields with the small mode volumes strongly enhance the interactions between light and matter [4][5][6][7][8]. Recently, vacuum Rabi splitting was observed in exciton-plasmon coupling systems at room temperature [9][10][11]. This effect demonstrates that a single photon harvested by the LSP antenna can couple into a single-exciton state with high efficiency, which will be applicable to highly efficient photonic devices. One of the ultimate goals is a single-photon switching gate for quantum information [12,13].Although the strong-coupling regime can be obtained within the LSP field, the coupling efficiency between a single LSP antenna and propagating light (PL) in free space or in optical waveguides is extremely low. The harvesting antenna size, which corresponds to the extinction cross section of a single metal nanostructure, is typically ß10 3 nm 2 for visible light [14], which is comparable to the actual geometrical cross section of the structure. The desired size of a single antenna structure is on the order of tens of nanometers, which is determined from the LSP resonance wavelength. Conversely, the cross section of the PL mode is ß10 5 nm 2 for a diffraction-limited spot and ß10 7 nm 2 for a single-mode optical fiber. This size mismatch between the LSP antenna and the PL mode results in a low coupling efficiency on the order of ß10 −4 −10 −2 , which limits the total throughput of the exciton-photon coupling via the LSP polariton.The use of microcavities can drastically improve the efficiency of the optical coupling with metal nanostructures. There are some reports on the cavity-LSP coupling systems and their applications to highly sensitive biosensors and efficient photon emitters [15][16][17][18][19]. Those works, however, have not paid attention to ultimate optimization of the coupling between the PL mode and the LSP antenna via the microcavity mode [20,21]. Toward complete PL-LSP coupling, which means that all power of PL can couple into a single LSP antenna * sasaki@es.hokudai.ac.jp without loss, we employ a tapered-fibe...

show abstract

Fano resonance in a multimode tapered fiber coupled with a microspherical cavity

Cited by 80 publications

References 14 publications

Fiber-microsphere laser with a submicrometer sol-gel silica glass layer codoped with erbium, aluminum, and phosphorus

Fiber-microsphere laser with a submicrometer sol-gel silica glass layer codoped with erbium, aluminum, and phosphorus

Control of spontaneous emission coupling factor β in fiber-coupled microsphere resonators

Efficient optical coupling into a single plasmonic nanostructure using a fiber-coupled microspherical cavity

Contact Info

Product

Resources

About