Side-pumped WGM milled microstub resonator laser

Whispering Gallery Mode (WGM) resonators are promising candidates for realization of ultra-small micro lasers. Conventional 3D resonators such as micro toroids [1], micro spheres [2, 3] and microbottles [4] are well studied as both passive and active devices. The excitation and signal collection are mostly done using evanescently coupled micro-sized fibers [5], integrated waveguides [3] and\or collecting the scattered light [6]. As the spectrum and coupling efficiency highly depend on the excitation position, the coupling system requires precise alignment, and packaging is complex. Here, we demonstrate a completely new micro laser based on WGM generated in an Yb3+-doped stub resonator side-pumped at 976nm wavelength

Coupling between waveguides and microresonators:The local approach

Coupling between optical microresonators and waveguides is a critical characteristic of resonant photonic devices that has complex behavior that is not well understood. When the characteristic variation length of the microresonator modes is much larger than the waveguide width, local coupling parameters emerge that are independent of the resonator mode distributions and offer a simplified description of coupling behavior. We develop a robust numerical-fitting-based methodology for experimental determination of the local coupling parameters in all coupling regimes and demonstrate their characterization along a microfiber waveguide coupled to an elongated bottle microresonator

WGM microrod laser fabricated by pulsed CO₂ laser micromilling

Fabrication of high Q milled microrod resonators using a pulsed CO2 laser, directly on Yb3+-doped fibers, is demonstrated. Evanescently pumped WGM microlaser with ~9µW output power has been achieved

Optik yönlü bağlaşım temelli dalgaboyu-altı mesafe ölçüm sensörlerinin tasarımı, imalatı ve karakterizasyonu

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2013Bu tezde ozellikle nano-boyutlu sensor ve telekomunikasyon uygulamalar. icin, yal.tkan uzeri silisyum (Silicon-on-insulator, SOI) pul uzerinde ultra-kompakt silisyum-tel Optik Yonlu Ba.la.t.r.c.lar f.n (Optical Directional Couplers, ODCs) teorik ve deneysel cal..malar. sunulmaktad.r. Silisyum nano-teller taraf.ndan s.n.rland.r.lan bolgede, guclu bir .ekilde s.n.rland.r.lm.. kontrol edilebilen kaybolan .....n varl...n.n, dalgak.lavuzlar. aras.ndaki optik guc ba.la..m. uzerinde buyuk bir etkiye sahip oldu.u bulunmu.tur. Mesafe, dalgaboyu, dalgak.lavuzu geometrisi ve ...k alan ilerleme mesafesine ba.l. olarak Optik yonlu Ba.la.t.r.c.lar fda (ODCs) guc iletimi ve ba.la.ma uzunlu.unun karakterizasyonu, Ba.la.m.. Mod Teorisi (Coupled Mode Theory, CMT), Sonlu-Fark Zaman-Alan. (Finite-Difference Time-Domain, FDTD) Analizi ve I..n .lerleme Yontemi (Beam Propogation Method, BPM) ile ac.klanm.. ve deneysel olarak do.rulanm..t.r. BPM metodu kullan.larak, 300nm geni.lik ve 340nm kal.nl..a sahip SOI ODC flerin simetrik ve antisimetrik elektriksel mod profilleri ve bu profillere kar..l.k gelen elektriksel gucler bulunmu.tur. Ayr.ca, iki dalgak.lavuzu aras.ndaki ayr.m mesafesinin bir fonksiyonu olarak sozkonusu ODC geometrilerinin ba.la.ma uzunlu.u hesaplanm..t.r. Ba.la.m.. dalgak.lavuzlar. aras.ndaki mesafenin ve dalgaboyunun ba.la..m uzunlu.una olan ustel etkisi dikkate de.er yuksek-hassasiyetli optik alg.lama ve anahtarlama ozellikleri gostermektedir. Dalgak.lavuzu geometrisinin ve olas. imalat hatalar.n.n ba.la.ma uzunlu.u uzerindeki etkisi, birkac mikrometrelik de.i.imlere sebep olabilmektedir. Ayr.ca, ...k alan.n.n dalgaboyu de.i.tirilirken ba.la.ma uzunlu.unun da de.i.ece.i anla..lm..t.r. Mesafenin 5?Êm-uzunluklu bir optik yonlu ba.la.t.r.c.n.n dalgaboyuna ba.l.l..., uc boyutlu FDTD simulasyonu kullan.larak gosterilmi.tir, ve ayr.ca farkl. ba.la.ma uzunluklar.na sahip dalgak.lavuzlar. ile 100nm, 200nm ve 300nm mesafeli ODC flerin dalgaboyu cevaplar. hesaplanm..t.r. .htiyaca ozel spektral ozellikler, ba.la.m.. nano-tel dalgak.lavuzlar.n.n mesafe ve uzunluklar.na ba.l. olarak konfigurasyonu ile elde edilebilir oldu.u anla..lm..t.r. Yonlu ba.la.t.r.c.lar, donu. dalgak.lavuzlar. ve optik guc boluculer gibi Optik Yonlu Ba.la.t.r.c.lar f.n imalat. icin tasarlanm.. bile.enlerin tumu, deneysel karakterizasyon ve imalat surecindeki hata olas.l...n. azaltmak icin FDTD simulasyonlar. kullan.larak numerik olarak cal...lm..lard.r. Optik Yonlu Ba.la.t.r.c.lar SOI pul platformu kullan.larak uretilmi.lerdir. .lk olarak, SOI pullar.n uzeri 50nm kal.nl..a sahip Elektron Huzme Litografi rezist tabakas. (Electron Beam Lithography Resist, PMMA) ile kaplanm.., ve daha sonra istenilen desen Elektron Huzme Litografi (Electron Beam Lithography) ile rezist tabakas.na aktar.lm..t.r. Daha sonra, yap.n.n tumu Elektron Huzme Buharla.t.rma (Electron Beam Evaporation) i.lemi yard.m.yla krom ile kaplanm.., ve kalan PMMA rezist katman. istenilen silisyum yuzeyinden kald.r.lm..t.r. Ard.ndan kromla kaplanm.. silisyum katman.n istenmeyen bolgesi Enduktif-E.le.mi.-Plazma Derin-Reaktif-.yon-Kaz.ma (Inductively-Coupled-Plasma Deep-Reactive-Ion-Etching, ICP-DRIE) prosesi kullan.larak kaz.nm.. ve tum pul cihaz uzerinden krom katman.n kald.r.lmas.ndan sonra iki parcaya bolunerek mekanik ve optik karakterizasyona haz.r hale getirilmi.tir. xxvi Son olarak, ultra-kompakt yuksek-hassasiyetli optomekanik sensorler, anahtarlar ve Dalgaboyu Bolmeli Coklay.c. (Wavelength Division Multiplexer, WDM) cihazlar.n optimizasyonu ile ilgili eri.ilen prensipler belirlenerek sunulmu.tur. Fabrikasyon parametrelerinin yap.y. nas.l etkiledi.ini anlamak ve en iyi receteleri bulmak icin herbir uretim a.amas.ndan sonra uretilen cihazlar.n bir k.sm. Taramal. Elektron Mikroskobu (SEM) f nda cal...lm..t.r. Herbir ODC cihaz.nda dalgak.lavuzu ciftlerinin geni.lik, uzunluk ve ayr.m mesafesini kapsayan tum geometrik ozellikleri SEM alt.nda olculmu.tur. Uretilen cihazlar ayarlanabilir lazer kayna.. kullanarak karakterize edilmi.tir. ODC fnin hem paralel hem de carpraz portlar.ndaki c.k.. gucu bir InGaAs NIR kamera kullan.larak tespit edilmi. ve daha sonra bu goruntuler bilgisayara aktar.larak analizleri gercekle.tirilmi.tir. Sonuclar gostermi.tir ki ...k c.k.. gucu, ba.la.t.r.c. uzunlu.u ile sinusoidal olarak de.i.mektedir. .ki dalgak.lavuzu aras.ndaki gradyen alan. yuksek oranda mesafeye ba.l.d.r, oyle ki daha kucuk ayr.m mesafeleri c.k.. gucunde keskin farkl.l.klara neden olan daha kucuk ba.la.ma uzunluklar.na yolacmaktad.r. Bu yuzden, daha yuksek hareket aral... ya da du.uk-hassasiyet gerektiren uygulamalarda uzunluktaki de.i.imlerden faydalan.labiliyorken, optomekanik anahtarlar ya da dedektor cihazlar icin ise farkl. mesafeye sahip ODC flerde yuksek-duyarl.kl. kullan.labilecektir. ODC flerin filtre ve dalgaboyu secici cihazlar olarak kullan.m.na yonelik .ekilde simulasyonlar. da yap.lm.., uretilmi. ve karakterize edilmi.lerdir. ODC flerin ayr.m mesafesi ve boyu istenilen filtre tayf. icin en uygun hale getirilebilir. ODC flerin iletim spektrumunun ayr.m mesafeleri ve ba.la.ma boylar. yard.m.yla ayarlanabilir oldu.u bulunmu.tur, oyle ki orne.in; 1578nm dalgaboyundaki 10?Êm-uzunlu.a sahip bir ODC icin ayr.m mesafesinin 150nm fden 200nm fye c.kar.lmas. ba.lant. noktas. uzerinden iletimi neredeyse %100 fden %0 fa du.urebilmektedir. Daha uzun ODC fler sayesinde eri.ilen ayarlanabilir geni. Serbest Spektrum Aral... (Free spectral Range, FSR), daha yuksek kanal-du.urme ozelliklerine sahip filtrelerin tasar.m. icin uygun k.lmaktad.rlar. Bu tezde gercekle.tirilen tum cal..malarda, teorik ve deneysel sonuclar aras.nda iyi bir uyum elde edilmi.tir. Bir sonraki ad.m, ODC fnin bir mesafe sensoru olarak performans.n. gormek icin gerceklenmesi olmu.tur. Mesafe sensoru uygulamalar.nda ODC fnin mesafe ve boyut parametrelerinin etkilerini gozlemlemek ve analiz etmek icin bir dizi cihaz yap.s. onerilmi.tir. Bu amacla, sistemde dalgaboyu-alt. hareketleri uretmek icin ihtiyac duyulan yerde.i.tirme de.erleri esas al.narak mikro-tarak (micro-comb) eyleyicilerin hesaplamalar. ve karakterizasyonlar. gerceklenmi.tir. Tasarlanan tarak-eyleyicinin yerde.i.tirme c.kt.s., giri. voltaj.n.n bir fonksiyonudur. Bir ODC fde hareketli dalgak.lavuzu ile mekanik eyleyici aras.ndaki ba.lant., sistemde ek carpraz-konu.maya (cross-talk) sebep olaca.. icin, dalgak.lavuzu du.uk-kay.pl. eliptik dalga k.lavuzlar. yard.m.yla merkezinden tutularak neredeyse e.de.er fonksiyon kalitesine sahip carpraz-konu.man.n onune gecilebilecek olan iki ODC bolume ayr..t.r.lm..t.r. ODC boyunca optik guc de.i.imi, daha yuksek hareket aral.klar. icin kullan.labilir, fakat uretim s.n.rlar.na gore 200nm fden daha k.sa mesafeli ODC flerin deneysel olarak gerceklenmesi zor ve yuksek maliyetlidir. Di.er taraftan, daha uzun ayr.m mesafelerinde cihaz. test etmek icin eyleyici cok fazla say.da tahrik parmaklar.na ihtiyac duyan en az 3?Êm hareket uretmelidir. Cunku Elektron Huzme Litografi Sistemi kullan.m. nedeniyle bir alt-alan (subfield) fda fabrikasyon bolgesi 50?Êm ~50?Êm ile s.n.rl. olmaktad.r ve parmak say.lar.n.n artt.r.labilmesi de ayn. nedenden oturu mumkun de.ildir. Alternatif olarak, iki kolundan birinde bir optik yonlu ba.la.t.r.c.ya sahip Mach-Zehnder .nterferometresi fne dayanan yeni bir cihaz numerik olarak xxvii cal...lm.. ve tasar.m. tamamlanm..t.r. CMT fye gore bir optik yonlu ba.la.t.r.c., mesafe ve uzakl..a ba.l. olarak c.k.. ...k faz.n. de.i.tirebilir. Bu nedenle, MZI fn.n c.k...ndaki faz fark. alg.lama amac.yla kullan.labilir. FDTD simulasyonlar., cihazlar.n k.sa ve uzun mesafelerde yuksek ve du.uk hassasiyetli sensor olarak kullan.labileceklerini gostermi.tir. Cihazlar bir SOI pul uzerine kaplanan PMMA katman. uzerine desenlenmi.tir. Do.ru litografi dozu birkac kontrollu yazma denemesi ile bulunmu.tur. Daha sonra, giri. ba.la.t.r.c. dalgak.lavuzu, c.k.. dalgak.lavuzu, tarak tahrik eleman. ve elektriksel ba.lant.lar. iceren komple bir cihaza sahip olmak icin birkac alt-alan ayr. ayr. PMMA uzerine desenlenmi. ve dikkatli bir .ekilde ba..l olarak hizalanm..t.r. Desen yazma suresince tasar.mdaki birkac modifikasyon ile Elektron Huzme Litografisi sonuclar.na ba.l. olarak yap.lm..t.r. Cihaz imalatlar.n. yapmakta oldu.umuz temizodadaki Elektron Huzme Buharla.t.r.c.s., ICP-DRIE ekipman. ve Kalem Yuzey Profilometre (Stylus Surface Profilometry) makinas.ndaki ar.zalar nedeniyle uretimin bu son bolumu henuz tamamlanamam..t.rThis thesis presents theoretical and experimental study of ultra-compact Si-wire Optical Directional Couplers (ODCs) on Silicon-on-Insulator (SOI) wafer for telecommunication and sensory applications especially in nanoscale sensing. The presence of the controllable evanescent light strongly confined in the region bounded by the Si nano-wires is found to have a large impact on the optical power coupling between waveguides. The characteristics of coupling length and power transmission in ODCs based on separation, wavelength, light field propagation distance and geometry of waveguides are described by the Coupled Mode Theory (CMT), 3D Finite-Difference Time-Domain (FDTD) Analysis and Beam Propagation Method (BPM), and are confirmed by experiments. Using BPM method the symmetric and antisymmetric electric mode profiles of a 300nm-wide and 340nm-thick SOI ODC and the corresponding electrical powers are found. The coupling length of the aforementioned ODC geometry as a function of separation distance between the two waveguides is also calculated. The exponential dependency of coupling length on the separation of coupled waveguides and wavelength shows interesting high-sensitivity optical sensing and switching properties. The effects of the geometry of the waveguides on the coupling length and possible fabrication imperfections can cause several micrometers change in coupling length. Also the coupling length is found to be changeable as the wavelength of the light field changes. The wavelength dependency of a 5ìm-long ODC on separation distance using 3D FDTD simulations is shown, and the wavelength responses of 100nm, 200nm and 300nm-separated ODCs with changeable coupled-waveguide lengths are also calculated. Custom spectral properties can be achieved by the configuration of coupled nano-wire waveguides based on their separation and lengths. All of the components designed for ODC fabrication, such as directional couplers, bending waveguides and optical power splitters are simulated using an FDTD simulations order to reduce the failure possibilities in fabrication process and experimental characterization. ODCs are fabricated utilizing SOI wafer platform. First, a 50nm-thick layer of electron beam lithography resist (PMMA) is coated on the SOI wafer, and then desired pattern is transferred to the resist by electron beam lithography. The entire structure is then coated by chromium in electron beam evaporation process and the remaining PMMA resist is lifted-off the desired silicon surface. Then, using the ICP- DRIE etching process undesired regions of the silicon layer, which are not coated by chromium are etched, and the whole wafer is diced into two parts after removal of the chromium layer on the device. Ultimately, guidelines on optimization of ultra compact high-sensitivity optomechanical sensors, switches and WDM devices are provided. several SEM micrographs of the fabricated devices after each fabrication stage are studied in order to find the best recipe and understand how the fabrication parameters affect the structures. All of the geometries including width, length and separation distance of waveguide pairs in each ODC device are measured under SEM. xxiii Fabricated devices are characterized using a tunable laser source. Output powers from both of the parallel and cross port of the ODCs are detected using an InGaAs NIR camera and then transferred to computer. Results show that the output light power changes sinusoidally with the length of the coupler. The gradient field between two waveguides is highly dependent on their separation such that smaller separation distances yield smaller coupling lengths causing sharper variations at the output power. Hence, ODCs with variable separation can be exploited for high-sensitivity optomechanical switches or sensor devices while changes in length can be utilized in applications requiring higher range of motion or low-sensitivity. ODCs as filters and wavelength-selective devices are also simulated, fabricated and characterized. The separation and length of the ODCs can be optimized for the desired filter spectrum. The transmission spectra of ODCs are found to be tunable by their separation and length such that, for instance, increasing the separation distance from 150nm to 200nm for a 10ìm-long ODC at 1578nm wavelength will drop the transmission from almost 100% down to about 0% at through port. Longer ODCs have more channel dropping characteristics making them suitable for the design of tunable wide-FSR channel-dropping filters. In all experiments results show a good agreement between theory and experiment. The next step is the realization of ODCs to see their performance as a displacement sensor. Structures are proposed to observe and analyze the effects of separation and length parameters of the ODCs in displacement sensing applications. For this pupose, in order to generate subwavelength motions in the system, micro-comb actuators are simulated and characterized based on the desired displacement values. The output displacement of the designed com-actuator is given as a function of input voltage. Since the connection between the movable waveguide in an ODC to the mechanical actuator may cause additional cross-talk in the system the waveguide is splitted into sections constructing two ODCs with almost the same functionality but capable to be handled from the center using low-loss elliptical waveguides. Using the optical power change along the ODC can be utilized for higher ranges of motions, but according to the limits of fabrication, ODCs with less than 200nm constant separation are hard and expensive to fabricate, on the other hand, for longer separation distances, in order to test the device the actuator should at least generate motions more than 3ìm which needs a very large number of actuation fingers. Since the fabrication area for a subfield is limited (induced by the e-beam lithography system), the enlargement of the numbers of the fingers is not possible. Alternatively, a new device based on Mach-Zehnder Interferometry in which one of the arms includes an ODC is simulated. According to the CMT an ODC can change the phase of the output light with respect to the separation and length. Hence, having the phase difference at the output of the MZI can be used for sensing. FDTD simulations show that the device can be used as both high and low-sensitivity sensors at short or long distances. Devices are patterned on a layer of PMMA coated on a SOI wafer. The correct dose is found by several controlled trials of writings. Then, in order to have a complete device including input coupler waveguide, output waveguide, comb actuator and electrical connections several subfields are patterned individually on the PMMA and aligned carefully together. Then, a layer of 30nm-thick Cr is coated on top of the PMMA and the rest of the PMMA is lifted off the wafer. Si device is then etched down to the SiO2 layer using Inductively Coupled Plasma (ICP), and the Cr layer is removed from the top of the devices. In order to release the mechanical parts floating in the air, devices are exposed to the vapor HF. Various devices connected to micro-comb actuators as the source of motion are fabricated. MZ based devices with length of xxiv 10ìm, 12.5ìm and 17.5 ìm, and ODCs with 10ìm and 15ìm are tested. For MZ devices a distinction ratio of 4dB at 1550nm wavelength at less than 60nm displacement is acheived. For a 15ìm-long ODC more than 15dB attenuation in the output signal can be acheived for less than 25nm displacement around 70nm separation. The specraal response of the devices is measured to be very sensitive to the changes of separation. For instance, dips in the spectra of an MZ device with 12.5ìm coupler length can be red-shifted for 17nm by changing the separation from 60nm to 110nm. ODCs also show interesting spectral characteristics. If the length of the ODC is kept long while working at the small separations, small changes (few nanometers) in the separation can cause large attenuation or boost in the output signal. It is shown that for a 15ìm-long ODC at 125nm separation more than 25dB attenuation can be achieved by decreasing the separation to 90nm at 1540nm wavelength.Yüksek LisansM.Sc

Theoretical and experimental investigation of novel passive and active optical microresonators

The scope of this thesis is to develop and investigate novel “fiberised” microresonator lasers suitable for side/remote pumping and signal collection. Several resonator configurations (stub, bottle, rod and sphere) made from normal optical fibres are studied in detail towards development of all-in-fibre microlasers.A theoretical model for tapered fibre-coupled microspheres based on general coupled mode theory is developed, describing the excitation of multimode WGMs. By precisely designing the taper coupling condition, excitation of specific mode or group of modes is possible. Simulations show coupling induced cross-coupling between frequency degenerate WGMs in a perfect microsphere, and provide their intra-cavity intensity distribution which is important in lasing and nonlinear applications. Lasing characteristics of Yb3+-doped microbottle lasers are theoretically investigated. Along with the experiment, it is demonstrated that desired lasing characteristics for a specific WGM is achievable by precisely setting the taper-resonator coupling condition, intrinsic Q factors and dopant concentration. Yb3+-doped MBLs are experimentally demonstrated to be promising devices in realization of selective WGM microlasers. Such cavities naturally exhibit multimode lasing. Precise, fast and low cost spectral cleaning methods are employed towards developing robust, stable and single mode lasers. It is observed that by further improving the quality factor of such resonators, cascaded Stimulated Raman Scattering (SRS) lasing is enabled, that together with Yb3+-lasing, extend the spectra beyond the emission band of Yb ions, well in the O-band of the telecom spectrum. It is also demonstrated that pumping and signal collection in such laser cavities can be achieved without the complex and sensitive tapered fibre coupling mechanism. In this study, microtaper-free side-pumped laser-milled microrod and microstub lasers are developed as robust, stand-alone and compact devices towards the realization of ultra-short all-in-fibre microlasers

Yb³⁺-doped silica WGM milled microrod laser

A fast and versatile fabrication method for high Q milled microrod resonators, directly on rare-earth doped fibers, is demonstrated using a pulsed CO2 laser. Evanescently pumped WGM microlaser with ~9µW output power has been achieved

Microrod resonator laser with versatile pumping configurations

A new Yb3+-doped silica WGM microrod resonator laser is demonstrated using different pump-delivery and signal-collection configurations, which include evanescently-coupled microtapers or direct side-pumping

Polarisation effects in optical microresonators

Polarization effects in different types of optical microresonators are studied in detail. It is observed that microresonators with tighter axial power confinement, such as MBRs and micro-milled resonators, show larger cross-polarization coupling efficiencies

Yb-doped and Raman Microbottle Lasers (Invited)

We present our recent works on Microbottle Resonator (MBR) lasers. Wavelength selective and single mode lasing from Ytterbium-doped MBRs and nonlinear processes such as Raman amplification in such resonators are studied

Long range Raman-Amplified Distributed Acoustic Sensor based on spontaneous Brillouin Scattering for large strain sensing

A Brillouin distributed acoustic sensor (DAS) based on optical time-domain refractometry exhibiting a maximum detectible strain of 8.7 mε and a low signal fading is developed. Strain waves with frequencies of up to 120 Hz are measured with an accuracy of 12 µε at a sampling rate of 1.2 kHz and a spatial resolution of 4 m over a sensing range of 8.5 km. The sensing range is further extended by using a modified inline Raman amplifier configuration. Using 80 ns Raman pump pulses, the signal-to-noise ratio is improved by 3.5 dB, while the accuracy of the measurement is enhanced by a factor of 2.5 to 62 µε at the far-end of a 20 km fibe