Browsing by Subject "Spectral filtering"

Now showing 1 - 4 of 4

Open Access
High-energy femtosecond photonic crystal fiber laser
(2010) Lecaplain, C.; Ortaç, B.; MacHinet G.; Boullet J.; Baumgart, M.; Schreiber, T.; Cormier, E.; Hideur, A.
We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15:5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1:9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber. © 2010 Optical Society of America.
Open Access
Multilevel diffraction gratings inside silicon towards spectral filtering
(SPIE - International Society for Optical Engineering, 2024-03-12) Bütün, Mehmet; Saylan, Sueda; Sabet, Rana Asgari; Tokel, Onur; Gemini, Laura; Kleinert, Jan; Miyaji, Godai
Silicon-based integrated photonics holds the promise of revolutionizing key technologies, such as telecommunications, computing, and lab-on-chip systems. One can achieve diverse functionalities in two ways: on the wafer surface ("on-chip") or within its bulk ("in-chip"), the latter gaining recognition due to recent advancements in laser lithography. Until recently, 3D in-chip laser writing has only been utilized for single-level devices, leaving a vast potential for monolithic and multilevel functionality within silicon untapped. In our previous research, we successfully designed and fabricated multilevel, high-efficiency diffraction gratings in silicon using nanosecond laser pulses. Their high performance stemmed from effective field enhancement at Talbot self-imaging planes. Our current work takes a theoretical approach, investigating how varying the grating period affects the performance of in-chip multilevel gratings. We demonstrate that the previously achieved 95% diffraction efficiency at a 1550 nm wavelength is also attainable with a reduced period of 3 μm. This smaller period is predicted to allow for spectral filtering, nearly equivalent to commercially available filters in terms of Full Width at Half Maximum (FWHM). Our findings underscore the potential of volumetric Si photonics and mark a significant step towards realizing 3D-integrated monolithic chips.
Open Access
Polarization maintaining and spectral filtering properties of hollow-core optical fibers for near-infrared region
(2024-08) Siddiqui, Muhammad Zain
Negative curvature hollow-core fibers (NCFs) offer attractive properties like ultralow losses, broad bandwidth, low latency, low nonlinearity, and a high damage threshold. Additionally, NCFs can overcome the inherent optical transparency limitations posed by solid-core fibers, which restrict their application to specific wavebands, thus enabling more flexible usage of NCF. These qualities make NCFs suitable for their utilization as polarization-maintaining (PM) fibers. In this thesis, the PM properties of NCFs are investigated through two different design approaches. In the first part of the thesis, a new design of polarization-maintaining and spectral filtering NCF tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates nested tubes anchored radially by pole structures in the vertical direction. Meanwhile, in the horizontal direction, nested tubes without pole anchors are employed, making the fiber structure asymmetric, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through numerical modeling, transmission losses below 0.1 dB/km for spectrally filtered wavelengths are achieved, with birefringence on the order of 10−5 within the spectral range of 1.45 μm to 1.60 μm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmission with specific polarization. The second part of the thesis focuses on the effect of ellipticity on the polarization maintaining performance of NCFs. The nested tube NCF is stretched vertically and compressed horizontally with the same ellipticity of 5%, 8%, and 10% to introduce ellipticity through the entire cross-section of the fiber. Through these modifications, the fiber successfully exhibits orthogonal polarization states compared to the original fiber with no ellipticity. Further investigations into the fiber with 8% ellipticity involve coupling it with bi-thickness (t1 and t2) and a manipulated nested tube diameter (dnx) along the horizontal axis of the fiber. The findings reveal that ellipticity has a limited effect on the improvement of the birefringence and polarization extinction ratio (PER) in NCFs, but it can be used as a complementary fine-tuning process. This suggests that ellipticity has the potential to be utilized as an additional mechanism for enhancing the overall polarization-maintaining characteristics of NCFs.
Open Access
Properties of a microjoule-class fiber oscillator mode-locked with a SESAM
(IEEE, 2011) Lecaplain, C.; Ortac, Bülend; MacHinet G.; Boullet J.; Baumgartl, M.; Schreiber, T.; Cormier, E.; Hideur, A.
Energy scaling of ultrafast Yb-doped fiber oscillators has experienced rapid progress largely driven by many applications that require high average power femtosecond pulses. The fundamental challenge for ultrafast fiber lasers relies on the control of excessive nonlinearity, which limits pulse energy. The development of all-normal dispersion laser cavities based on large-mode-area photonic crystal fibers (PCFs) has enabled significant energy scaling [1-3]. In particular, up to microjoule energy levels have been achieved from rod-type fiber-based oscillators [2-3]. In such lasers, pulse shaping is dominated by the strength of the mode-locking mechanism which determines the pulse properties. In this contribution, we report the generation of high-energy sub-picosecond pulses from a highly normal dispersion fiber laser featuring an Yb-doped rod-type PCF and a large-mode-area PCF [Fig.1(a)]. Passive mode-locking is achieved using saturable absorber mirrors (SAMs). We study the influence of the SAM parameters on performances obtained in this new class of fiber oscillators. The structures exhibit 20 % modulation depths and 500 fs relaxation time with resonant and antiresonant designs. The antiresonant SAM structures ensure absorption bandwidths 45 nm while the resonant structures exhibit 20 nm bandwidths. Stable mode locking with average powers as high as 15 μW at 15 MHz repetition rate, corresponding to microjoule energy level are obtained with all the structures. However, pulse properties and pulse shaping mechanism distinguish between resonant and antiresonant designs. Using a broadband antiresonant SAM leads to generation of highly-chirped pulses with 30 ps duration and 10 nm spectral width [Fig.1(b)]. The output pulses are extra-cavity dechirped down to 550 fs duration. By increasing the strength of the mode-locking mechanism through the combination of the SAM with the NPE process, we obtain shorter pulses with slightly boarder spectra. Indeed, the output pulse duration is decreased from 30 ps to 13 ps by adjusting the wave-plates settings. The dechirped pulse duration is then shortened to 450 fs. We note that the current laser performances are limited to 1 J by the available pump power. Using a resonant SAM structure, the output pulse duration is decreased to 7 ps [Fig.1(b)]. This pulse shortening results from the spectral filtering induced by the limited SAM bandwidth. All these results are in good agreement with numerical simulations which will be discussed in this communication. © 2011 IEEE.