도파로공진을 이용한 슬롯도파로 포화흡수체 반사기

김명환,김상인,Kim, Myung-Hwan,Kim, Sang-In 한국광학회 2011 한국광학회지 Vol.22 No.3

본 논문에서는 도파모드공진을 이용한 포화흡수체 반사기를 제안하였다. 포화흡수체로는 탄소나노튜브(CNT)를 사용하였다. 제안된 반사기는 CNT의 두께 변화 없이 modulation depth를 키울 수 있다는 장점이 있다. 제안하는 반사기의 fill factor(F)와 CNT의 두께변화에 따른 modulation depth, 대역폭, 포화되었을 때의 최대 반사율의 특징을 알아보았다. 제안된 반사기는 포화에너지를 줄일 수 있다는 장점이 있고, 100~200nm 얇은 CNT박막에서 50배정도 줄어드는 것을 확인 하였다. We propose a saturable absorber reflector based on guided-mode resonance. A carbon nanotube is used as a saturable absorber. By tuning the fill factor, modulation depth can be increased without a change of height of the CNT. We investigate the reflector properties such as modulation depth, bandwidth and peak reflectance as a function of the height of the CNT and the fill factor. The advantage of the proposed reflector is that it can reduce saturation energy by 50 times compared with CNT thin film of 100~200nm.

Mode-Locked All-Fiber Lasers at Both Anomalous and Normal Dispersion Regimes Based on Spin-Coated <named-content content-type='math' xlink:type='simple'> <tex> $\hbox{MoS}_{2}$ </tex></named-content> Nano-Sheets on a Side-Polished Fiber

Khazaeinezhad, Reza,Kassani, Sahar Hosseinzadeh,Hwanseong Jeong,Nazari, Tavakol,Dong-Il Yeom,Kyunghwan Oh IEEE 2015 IEEE photonics journal Vol.7 No.1

<P>We demonstrate an all-fiberized mode-locked laser by employing Molybdenum Disulfide (MoS<SUB>2</SUB>) spin-coated onto a side-polished fiber (SPF) as an in-line saturable absorber. Single crystal MoS<SUB>2</SUB> has been exfoliated via the Li intercalation method and then dispersed with large population of few-layer MoS<SUB>2</SUB> nano-sheets in ethanol. Subsequently, a saturable absorber has been prepared using a relatively simple method: spin-coating the uniform MoS<SUB>2</SUB> solution on the fabricated SPF without using any polymer or toxic procedure. Power-dependent transmission property of the prepared MoS<SUB>2</SUB> nano-sheets on the SPF was experimentally analyzed, providing the feasibility to apply it as an efficient in-line saturable absorption behavior. By deploying the MoS<SUB>2</SUB> SPF into a fiber laser cavity with finely tuned laser pump power and cavity dispersion, mode-locked pulses were obtained at anomalous and normal dispersion of the laser cavity. The self-started soliton pulses at the anomalous dispersion regime were generated with a spectral bandwidth of 9.96 nm at 1584 nm and a pulse duration of 521 fs. Moreover, by managing the dispersion to the normal regime, stable pulses at net-normal intra-cavity dispersion with 11.9 ps pulse duration were obtained with a spectral bandwidth of 18.2 nm at 1570 nm. The results prove the effectiveness of developing MoS<SUB>2</SUB> saturable absorbers and applications for pulsed laser operation.</P>

포화흡수체를 이용한 극미세선폭 FBG 공동 DFB 레이저

김준원,진용옥,최규남,Kim, Jun-Won,Jin, Yong-Ok,Choe, Gyu-Nam 대한전자공학회 2002 電子工學會論文誌-SD (Semiconductor and devices) Vol.39 No.5

DFB 레이저를 이용하여 긴 FBG 공동에서 극미세선폭 레이저광을 발생시키는 새로운 방법을 제시하였다 63㎞의 광섬유 지연선로를 사용한 자기헤테로다인 측정장치를 사용하여 레이저 선폭을 측정한 결과 3㏈ 선폭으로 20㎑를 얻었다. 이 레이저에 포화흡수체로 Er/sup +3/ 이 도핑된 광섬유를 사용하여 다시 선폭을 압축한 결과 자기헤테로다인 측정장치의 해상도 한계인 3㎑ 이하의 선폭을 얻었다. 이는 2×10/sup -8/㎚의 선폭에 해당한다. A novel ultra-narrow linewidth single longtudinal mode DFB semiconductor laser in the extended FBG cavity is proposed. The 3㏈ linewidth of 20KHz was demonstrated by using self-heterodyne measurement set-up with a fiber delay line of 63km. And this linewidth was further compressed to less than 3KHz, which is resolution limited performance, by inserting E $r^{+3}$ doped fiber saturable absorber. This is equivalent to 3㏈ linewidth of 2$\times$10$^{-8}$ nm.

다이오드로 펌핑하고 V3+:YAG포화흡수체를 이용한 수동형 Q-스위칭된1.34 μm-Nd:GdVO4 레이저의 출력 특성

추한태,박차곤,김규욱,변성욱 한국물리학회 2013 새물리 Vol.63 No.2

We investigated the output characteristics of a diode-pumped passively Q-switched 1.34 μm-Nd:GdVO4 laser with V3+:YAG as a saturable absorber. The laser had a concave-plane cavity configuration. The focal length of the thermal lens in the diode-end-pumped Nd:GdVO4 laser was experimentally investigated for the 1.34-μm transition. The measured proportionality constant was estimated to be 8.1 × 103 W/mm. For the Q-switching operation, an output coupler of T = 15%was used with a cavity length of 63 mm. A maximum average output power of 1.45 W was achieved when the incident pump power was 18.5 W, corresponding to an optical conversion of 7.8% and a slope efficiency of 20%. The minimum pulse width obtained was 65 ns when the pulse repetition frequency was 39 kHz. The single-pulse energy and peak power were estimated to be 0.037 mJ and 570 W, respectively. The measured values of M2 about the x-axis and the y-axis were 1.09 and 1.13respectively. V3+:YAG 포화흡수체를 이용하고 다이오드로 펌핑하는 수동형Q-스위칭된1.34 μm-Nd:GdVO4 레이저의 출력 특성을조사하였다. 오목-평면 형태의 공진기 구조를 갖고 다이오드로 단면펌핑하는 Nd:GdVO4 레이저의 1.34 μm 천이에 대한 열초점 거리를실험적으로 조사하였으며, 비례상수가 8.1 × 103 W/mm로측정되었다. 공진기 길이가 63 mm이고 출력거울의 투과율 T = 15%인Q-스위칭 동작에 대하여 18.5 W의 입사 펌프 파워에 대한 최대 평균출력은 1.45 W 이었으며 이에 대응되는 광변환 및 기울기 효율은 각각7.8% 및 20%이었다. 또한 펄스 반복률이 39 kHz인 65 ns의 최소펄스폭을 얻어 그때의 단일 펄스 에너지 및 피크 파워는 각각 0.037 mJ 및 570 W로 계산되었고, x-축 및 y-축에 대한 M2 값은 각각 1.09 및1.13으로 측정되었다.

수동 큐스위칭 Nd:YAG 레이저에서 포화흡수체 Cr⁴⁺:YAG의 초기 광흡수 효과와 출력 특성

최영수,윤주홍,김기홍,Choi, Young-Soo,Yoon, Joo-Hong,Kim, Ki-Hong 한국광학회 2002 한국광학회지 Vol.13 No.4

To understand the characteristics of the passively Q-switched Nd:YAG laser output energy with $Cr^{4+}$:YAG saturable absorbers, the transmissions of $Cr^{4+}$:YAG and the inversion population densities of Nd:YAG at the onset of Q-switch were experimentally analysed. The measured transmissions at the onset of Q-switch were 0.70$\pm$0.02 and 0.62$\pm$0.02 for the 0.48 and 0.38 of initial transmission, respectively. It means that the initial transmission loss of $Cr^{4+}$:YAG absorber is reduced in a low Q-state due to the initial absorbing effect of $Cr^{4+}$:YAG. In pumping stage, $Cr^{4+}$:YAG has absorbing processes due to the fluorescence and amplified spontaneous emissions of the Nd:YAG even if there is no laser oscillation. The minimum population inversion densities for Qswitch were approximately 3.7${\times}{10^{17}}$ and 4.0${\times}{10^{17}}$ $cm^{-3}$, respectively. At the beginning of Q-switch, the number density of $Cr^{4+}$ions in the ground state of $Cr^{4+}$:YAG was approximately 1.4${\times}{10^{17}}$ $cm^{-3}$ and the ratio of the ground to the excited state of absorbing $Cr^{4+}$ions was 0.44 both. The modified theoretical output energies with the initial absorbing effect were 18 and 18.5 mJ. The measured output energies were 17$\pm$1 and 18$\pm$1.5 mJ, respectively. The quantum extraction efficiencies of Q-switch were 0.32 both. The theoretical Q-switched output results with the initial absorbing effect of the saturable absorber are a good agreement with the experimental results. 초기투과도 0.48과 0.38인 포화흡수체 $Cr^{4+}$: YAG를 사용한 수동 큐스위칭 Nd:YAG 공진기에서 포화흡수의 초기 광흡수 효과로 낮은 Q-상태에서 나타나는 포화흡수체의 투과 광손실 변화와 더불어 레이저 매질의 펌핑된 밀도반전 상태를 분석하였다. 포화흡수체의 초기 광흡수로 수동 큐스위칭 열림동작때 나타나는 포화흡수체의 투과도는 각각 0.70$\pm$0.01과 0.62$\pm$0.01이었다. 이는 큐스위칭 레이저 공진기의 초기 광손실이 간소함을 의미한다. 큐스위칭 열림동작 시점에서 측정된 두 $Cr^{4+}$:YAG의 기저상태 $Cr^{4+}$ 밀도수는 약 1.4${\times}{10^{17}}$$cm^{-3}$이고 기저상태에 대한 여기상태의 $Cr^{4+}$이온밀도수의 비는 약 44%이었다. 또, 큐스위칭 펄스 발생을 위해 펌핑된 최소 반전밀도수는 각각 3.6${\times}{10^{17}}$과 3.9${\times}{10^{17}}$ $cm^{-3}$이고 양자추출효율은 두 경우 모두 약 0.32였다. 낮은 Q-상태에서 나타나는 포화흡수체의 광흡수 효과를 고려한 수동 큐스위칭 레이저 출력에너지의 수정 이론값은 각각 18과 18.5 mJ로 측정된 실험값 약 17$\pm$1과 18$\pm$1.5mJ과 잘 일치함을 보였다.

솔리톤 전송용 InGaAsP MQW Saturable Absorber

송주빈 慶熙大學校 레이저 工學硏究所 2003 레이저공학 Vol.14 No.-

This paper describes InGaAsP multiple quanhum well(MQW) saturable absorbers to increase amplifier span of soliton transmission systems by reducing recovery time of soliton pulses. Achieved recovery time was less than 6ps in case of carrier sweep-out method and 2ps when ion implanted MQW was involved. Due to the long carrier life in MQW carrier sweep-out method shows limited results on reducing the recovery time. Clearly, ion implanted MQW could be a resonable candidate for high speed soliton transmission systems.

다이오드로 펌핑하고 V³+:YAG 포화흡수체를 이용한 수동형 Q-스위칭 및 내부공진기 주파수 배가된 Nd:GdVO₄/LBO 적색 레이저의 출력 특성

박차곤,추한태,김규욱,이상호 한국물리학회 2014 새물리 Vol.64 No.3

We investigated the output characteristics of a diode-pumped, passively Q-switched, intracavity frequency-doubled Nd:GdVO₄/LBO red laser with V³+:YAG as a saturable absorber and LBO as a nonlinear crystal. The laser had a V-type cavity configuration with two concave mirrors and one flat mirror. We searched for a suitable position for the saturable absorber by using ABCD transfer matrix method to calculate the radius of the TEM_{00} mode. The calculation considered the thermal lensing effect of the gain medium. We calculated not only the radii of TEM_{00} modes in the gain medium and the saturable absorber but also the ratio of the cross-sectional areas of the mode in those regions. Comparing these results with those for the passive Q-switching condition, we were able to investigate the possibility of a Q-switched red laser oscillation. The maximum average power, repetition rates, pulse widths, single-pulse energies, and peak powers of a Q-switched 670 nm red laser were 32 mW, 18.4 ~ 162 kHz, 113 ~ 158 ns, 0.20 ~ 0.65 μJ, and 1.25 ~ 5.26 W, respectively. 다이오드로 펌핑하고 V³+:YAG 포화흡수체와 LBO 비선형 결정을 이용하여 수동형 Q-스위칭 및 내부공진기 주파수 배가된 670 nm Nd:GdVO₄/LBO 적색 레이저의 출력 특성에 관해 조사하였다. 레이저 공진기는 두 장의 오목거울과 한 장의 평면거울을 이용하여 V-자 형태로 구성하였다. 이득 매질의 열렌즈 효과를 고려한 ABCD 전파행렬 방법을 이용하여 공진기를 분석하여 포화흡수체의 위치를 적절히 결정하였다. 또한 이득 매질 및 포화흡수체 내의 TEM_00 모드 반지름뿐만 아니라 모드 단면적 비를 계산하고 Q-스위칭 이론과 비교하여 적색 레이저의 발진 가능성을 확인할 수 있었다. Q-스위칭된 670 nm 적색 레이저의 출력 특성 결과로 최대 32 mW의 평균 출력, 18.4 $\sim$ 162 kHz의 펄스 반복률, 113 ~ 158 ns의 펄스폭, 0.20 ~ 0.65 μJ의 단일 펄스 에너지 및 1.25 ~ 5.26 W의 첨두 출력을 얻었다.

Solid-State Laser Mode-Locking Near 1.25 µm Employing a Carbon Nanotube Saturable Absorber Mirror

Won Bae Cho,Sun Young Choi,김준완,Dong-Il Yeom,김기홍,Fabian Rotermund,Hanjo Lim 한국광학회 2011 Current Optics and Photonics Vol.15 No.1

We demonstrate passive mode-locking of a Cr:forsterite laser with a single-walled carbon nanotube saturable absorber mirror (SWCNT-SAM). Without compensation of intra-cavity dispersion, the self-mode-locked laser generates 11.7 ps pulses at a repetition rate of 86 MHz. The dispersion-compensated laser yields ultrashort pulses as short as 80 fs near 1.25 µm at 78 MHz with average output powers up to 295 mW, representing the highest power ever reported for mode-locked solid-state lasers based on saturable absorption of SWCNTs in this spectral region.

A Thermo-optically controllable saturable absorber for switchable operation of a fiber laser between Q-switching and harmonic mode-locking

Koo, Joonhoi,Kim, Jihwan,Lee, Ju Han Elsevier 2019 Journal of luminescence Vol.205 No.-

<P><B>Abstract</B></P> <P>A thermo-optically controllable fiberized saturable absorber (SA) that is based on a combination of graphene oxide (GO), a thermo-optic polymer adhesive, and a thermo-electric temperature controller (TEC), is proposed and experimentally demonstrated. By incorporating the SA into an all-fiberized erbium-doped fiber (EDF) ring cavity, an operation-state-switchable fiber laser is successfully implemented. The operation state of the laser is shown to be switchable from a continuous wave (CW) to the Q-switching state to the harmonic mode-locking state depending on the current that is applied to the TEC under a fixed pump-power condition. As a function of the applied current, the temporal width and the repetition rate of the Q-switched pulses varied from ~5.54 μs to ~12.35 μs and from ~ 31.02 kHz to ~17.25 kHz, respectively. The maximum pulse energy is ~52.8 nJ. In the harmonic-mode-locking state, the 19th order of the harmonic-mode-locked pulses was generated. The pulse width was measured as ~595 fs with a pulse-repetition rate of ~237.5 MHz. It is believed that the operation-mode change is due to the variations of the insertion loss and the beam-polarization status of the implemented SA that are due to the temperature-variation-induced refractive-index changes of the thermo-optic polymer.</P>

Femtosecond Mid-IR Cr:ZnS Laser with Transmitting Graphene-ZnSe Saturable Absorber

조원배,배지은,이승철,명노성,이상민 한국광학회 2023 Current Optics and Photonics Vol.7 No.6

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF 2 and ZnSe. Using the graphene-SA based on CaF 2 , a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF 2 with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.