Wavelength Selective Element Research Articles

16 × 1 Packaged MUX/DEMUX for Flexible-Grid Optical Networks

A comprehensive experimental study on the performance of a packaged flexible-grid compliant 16 × 1 packaged MUX/DEMUX device is presented. The device relies on a bandwidth and wavelength selective filtering element array integrated on an SOI platform, equipped with on-chip polarization multiplexing functionality. Multilateral operating credentials are demonstrated through the evaluation of the device in 2 × 1 MUX, 1 × 2 DEMUX and PolMUX configurations scenarios under realistic data traffic conditions, thus confirming its suitability for next-generation flexible-grid optical networks.

Highly efficient soft X-ray spectrometer based on a reflection zone plate for resonant inelastic X-ray scattering measurements.

We present a newly designed compact and flexible soft X-ray spectrometer for resonant inelastic X-ray scattering (RIXS) studies within an energy range from 380 eV to 410 eV, which would include the K alpha emission lines of vital elements like nitrogen. We utilized an off-axis reflection zone plate (RZP) as the wavelength selective element with a maximum line density of 10000 l/mm. A higher energy resolution over a broader range of ± 15 eV around the designed energy was achieved by displacing the RZP. Additionally, for the first time, an actual optical side effect, the so-called comatic aberration was exploited to increase the energy resolution. First results show a resolving power in the order of 1300 for photon energy of 395 eV, which is comparable to a commercial varied line spacing grating (VLS).

Optimization of excitation of fiber Fabry-Perot tunable filters used in swept lasers using a phase-correction method.

In this paper we investigate a phase-correction method for compensation of the nonlinearity of conventional wavelength-swept laser sources based on a fiber Fabry-Perot tunable filter as a wavelength selective element. A triangular waveform signal is commonly used to drive the filter. We, however, extract the zero crossings from the interferograms and modify the shape of the triangular signal accordingly. This algorithm was tested for different values of the optical path length difference in the interferometer setup. Significant compensation for the nonlinearity of the filter was obtained.

Monolithic single mode interband cascade lasers with wide wavelength tunability

Monolithic two-section interband cascade lasers offering a wide wavelength tunability in the wavelength range around 3.7 μm are presented. Stable single mode emission in several wavelength channels was realized using the concept of binary superimposed gratings and two-segment Vernier-tuning. The wavelength selective elements in the two segments were based on specially designed lateral metal grating structures defined by electron beam lithography. A dual-step dry etch process provided electrical separation between the segments. Individual current control of the segments allowed wavelength channel selection as well as continuous wavelength tuning within channels. A discontinuous tuning range extending over 158 nm in up to six discrete wavelength channels was achieved. Mode hop free wavelength tuning up to 14 nm was observed within one channel. The devices can be operated in continuous wave mode up to 30 °C with the output powers of 3.5 mW around room temperature.

Silicon-based microring resonators for multi-solitons generation for THz communication

Silicon-based microring resonator (SMRR) is required to select the specific channels in a wavelength division multiplexing systems. SMRRs also have applications in optical filters, data storages and bio-sensors, due to their significant advantages such as versatile wavelength-selective elements, compact size, fast operation and compatibility with current optical infrastructure, as well as being able to divert groups of inputs light and synthesize a wide class of filter functions. Here, we proposed a system for multiple mode-locked soliton generation, where the photonic circuits simulator PICWave software made by photon design based on the time-domain travelling wave method is used for modeling passive and active photonic circuits. A mode-locked spectrum possessing a spacing of 30 ps and a full width at half maximum (FWHM) of 10 ps was generated and input into the ring system. The subsequent multiple mode-locked soliton pulses had a free spectral range of 25 GHz and FWHM of 630 MHz, which corresponded to 0.2 nm and 5 pm respectively, with a 40 ps pulse duration and 200 GHz repetition. The obtained finesse was approximately 39.7, and the Q-factor was approximately 3 × 105.

A Numerical Analysis for Optimizing the Gratings Length and Coupling Coefficient for High Reflectivity and Low Cavity Loss in Fiber Grating Fabry-Perot Laser Model

The effects of gratings length (kLFG) and amplitude coupling (Co) coefficients on the effective reflectivity (Reff) and the total cavity loss (αtot) of an external cavity laser source (ECLS) based fiber Bragg gratings (FBGs) are numerically analyzed for designing a laser source operating in strong feedback regime (Regime V). In this study, FBG is used as a wavelength selective element to control the properties of the laser output by controlling the fiber gratings reflectivity level. The study is performed by modifying full analytical expressions for the Reff and the αtot based on laser coupled-wave equations. Results show that Reff is strongly dependent on kLg and Co. Also, it is found that αtot has been reduced significantly with increasing Co, especially at high value for kLG (kLFG> 1.5).

Diode laser using narrow bandwidth interference filter at 852 nm and its application in Faraday anomalous dispersion optical filter**Project supported by the National Natural Science Foundation of China (Grant No. 91436210) and the International Science and Technology Cooperation Program of China (Grant No. 2010DFR10900).

We demonstrate an 852-nm external cavity diode laser (ECDL) system whose wavelength is mainly determined by an interference filter instead of other wavelength selective elements. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 28.3 kHz. Moreover, we test the application of the ECDL in the Faraday atomic filter. Besides saturated absorption spectrum, the transmission spectrum of the Faraday atomic filter at 852 nm is measured by using the ECDL. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.

300 W-level, wavelength-widely-tunable, all-fiber integrated thulium-doped fiber laser.

A high-power, wavelength-tunable, all-fiber integrated thulium-doped fiber laser (TDFL) at 2 μm is presented. The TDFL has a compact configuration which only consists of a low power seed oscillator and a stage of fiber power amplifier. The seed oscillator adopts a tunable band-pass filter as the wavelength selective element, matching the gain spectrum of thulium-doped fiber. It can provide ~5 W single-mode seed laser with superb spectral characteristics, and the lasing wavelength is adjustable from 1890 to 2050 nm. The fiber power amplifier provides a total gain of ~17 dB at 2 μm which boosts the signal power to the 300 W-level. The maximum average power reaches 327.5 W at 1930 nm with the highest slope efficiency of 57.4%. This TDFL can afford >270 W lasing operation over the whole tuning range of 140 nm spanning from 1910 to 2050 nm, together with high spectral quality and power stability. This is the first demonstration, to the best of our knowledge, on an all-fiber integrated wavelength-widely-tunable TDFL at 2 μm with output power at the 300 W-level. The results are of great interest for many applications.

Compact dual-wavelength thulium-doped fiber laser employing a double-ring filter

In this paper, we report on stable dual-wavelength operation of a thulium-doped compact all-fiber laser using a double-ring filter as the wavelength selective element. Simultaneously lasing at 2014.4 and 2018.4nm has been obtained via tuning the polarization controllers to adjust the relative gain and loss of the laser cavity. The side mode suppression ratios are greater than 52dB and the output power difference between the two lasing lines is less than 0.08dB under 2.6W of incident pump power.

Wavelength-tunable, passively Q-switched Yb3+:Ca3Y2(BO3)4 solid state laser using MoS2 saturable absorber

We demonstrate a passively Q-switched Yb3+:Ca3Y2(BO3)4 solid state laser using a hydrothermal prepared MoS2 nanosheets as saturable absorber. The single pulse energy up to 0.75μJ is obtained. The corresponding shortest pulse duration and largest pulse repetition rate are 420ns and 140.4kHz, respectively. By using an etalon as the wavelength selection element, the output wavelength of the Q-switched pulse with a tunable range from 1030.5 to 1050.4nm has been achieved, covering a continuous tuning range of about 20nm. Our experimental results suggest that MoS2 saturable absorber shows great potential as a broadband passive Q-switcher for solid state wavelength tunable lasers at 1.0μm.

Coherence‐selectable operation of external‐cavity semiconductor diode laser by intracavity polarisation control

The operation of an external-cavity semiconductor diode laser with selectable coherence and a tunable wavelength has been successfully demonstrated through the control of the intracavity polarisation state. The laser has an intracavity half-wave plate that is able to rotate the orientation of the polarisation axis with regard to diffraction grating, where the grating acts as a polarisation- and wavelength-selective element. As a result, it was possible to continuously sweep the correlation widths from 230 kHz to 2.0 MHz by simply rotating the half-wave plate.

Wideband tunable graphene-based passively Q-switched Tm:YAP laser

We investigate the characteristics of a graphene Q-switched Tm:YAP laser operating in a wavelength tunable regime. By using a volume Bragg grating (VBG) as the intra-cavity wavelength selection element, and graphene as the saturable absorber (SA), a tunable Q-switched Tm:YAP laser was realized with a continuous tunable wavelength range from 1965.2 to 2000.7 nm. Through careful alignment of the VBG and the graphene SA in coordination, stable pulsed laser operations were achieved at this wavelength range. A maximum output power of 920 mW was obtained at a wavelength of 1989.3 nm, corresponding to a pulse duration of 2.1 μs, a repetition rate of 91.6 kHz and a single pulse energy of 10.1 μJ.

Optimizing the external optical cavity parameters for performance improvement of a fiber grating Fabry–Perot laser

The effects of the external optical cavity parameters (external optical cavity length (L ext), amplitude coupling (C o) and anti-reflection coating (ARC) reflectivity coefficients) on the noise and modulation spectra of a fiber grating Fabry–Perot laser are numerically analyzed for designing a laser that operates in strong feedback regime (Regime V). Fiber Bragg grating (FBG) is used as a wavelength selective element to control the properties of the laser output by controlling the external optical feedback (OFB) level. The study is performed by modifying a set of rate equations that are solved by considering the effects of external OFB and ambient temperature (T) variations. We proposed a model to calculate the temperature dependence (TD) of laser characteristics according to the TD of laser parameters. An accurate analytical expression for the TD of threshold carrier density (N th,fe) has been derived. The TD of N th,fe was calculated according to the TD of laser cavity parameters instead of using well-known empirical Pankove relationship via the use of characteristics temperature (T o) and current (I o). Results show that the optimum external fiber length (L ext) is 3.1 cm. Also, it is shown that ARC with reflectivity value of 1 × 10−2 is sufficient for the laser to operate at low noise, good modulation response, and low fabrication complexity.

Design and construction of a tunable pulsed Ti:sapphire laser

In this paper, design and constr uction of a tunable pulsed Ti:sapphire laser and numerical solution of the corresponding rate equations are reported. Rate equations for a four-level system are written and their numerical solution is examined. Furthermore, an optical setup is introduced. In this setup, a Ti:sapphire crystal is longitudinally pumped by the second harmonics of a Q-Switched Nd:YAG laser, and a prism is used as a wavelength-selective element as well. This setup is established for two 10 and 50 % transmission output couplers. In case of using the 10 % coupler, the output energy of the laser, for the pump energy of 36 mJ, is pulses with 3.5 mJ energy and for the 50 % coupler, with 50 mJ of pump energy, pulses with 10 mJ energy are generated. A wavelength tuning range of more than 160 nm is possible. The repetition rate of this laser is 10 Hz and the temporal duration of the pulses is about 30 ns.

Numerical Analysis of the Effect of Temperature and External Optical Feedback Variation on the Output Characteristics of External Cavity Semiconductor Laser Based Fiber Bragg Gratings

The temperature and external optical feedback (OFB) effects on power characteristics of external cavity semiconductor laser model based fiber Bragg gratings (FBGs) are numerically analyzed. In this model, fiber Bragg grating (FBG) is used as a wavelength selective element to control the properties of the laser output by controlling the external OFB level. The study is performed by modifying output laser equations that are solved by considering the effects of ambient temperature (T) variations and external OFB. In this study, the temperature dependence (TD) of laser characteristics is calculated according to TD of laser parameters instead of using the well-known Pankove relationship. Results show that by increasing the external OFB level, the laser output power improves significantly. Also, results show that by changing the operating temperature 15℃ (from 15℃ to 30℃), there is no great impact on the output characteristics. The obtained results can provide an important idea for the practical fabrication for this type of lasers.

Tapered-EDF-Based Mach–Zehnder Interferometer for Dual-Wavelength Fiber Laser

An all-fiber comb filter using a tapered-erbium-doped fiber in a Mach-Zehnder interferometer structure is presented. The free spectral range, extinction ratio, bandwidth, and interference pattern of the comb filter can be shaped by controlling the taper waist length and the length of up and down taper transition regions. By varying the taper waist length from 5 to 25 mm, the free spectral range changes from 14.7 to 1.0 nm, and the linewidth varies from 3.3 to 0.3 nm, respectively. We demonstrate a tunable dual-wavelength laser by using the tapered-erbium-doped fiber as a gain medium as well as a wavelength-selective element. The laser can be tuned at a resolution of 0.2 nm with a side-mode suppression ratio of up to 46.88 dB and a linewidth of 0.09 nm.

Tunable erbium-doped fiber ring laser based on thermo-optic polymer waveguide Bragg grating

A tunable erbium-doped fiber ring laser incorporating a tunable thermo-optic polymer waveguide Bragg grating is proposed. Nano-imprinting technique was used to fabricate the polymer waveguide Bragg grating whose reflectivity and 3dB bandwidth are 25dB and 0.8nm, respectively. The polymer waveguide Bragg grating was used as wavelength selective element in the ring laser system and the center wavelength can be tuned by controlling the electrical power on the micro-heater. The fabricated tunable laser exhibits an output of 4.1dBm, side-mode suppression ratio of 55dB, 3dB bandwidth less than 16pm, and wavelength tuning range of 8.4nm.

Plasmonic external cavity laser refractometric sensor.

Combining the high sensitivity properties of surface plasmon resonance refractive index sensing with a tunable external cavity laser, we demonstrate a plasmonic external cavity laser (ECL) for high resolution refractometric sensing. The plasmonic ECL utilizes a plasmonic crystal with extraordinary optical transmission (EOT) as the wavelength-selective element, and achieves single mode lasing at the transmission peak of the EOT resonance. The plasmonic ECL refractometric sensor maintains the high sensitivity of a plasmonic crystal sensor, while simultaneously providing a narrow spectral linewidth through lasing emission, resulting in a record high figure of merit for refractometric sensing with an active or passive optical resonator. We demonstrate single-mode and continuous-wave operation of the electrically-pumped laser system, and show the ability to measure refractive index changes with a 3σ detection limit of 1.79 × 10(-6) RIU. The demonstrated approach is a promising path towards label-free optical biosensing with enhanced signal-to-noise ratios for challenging applications in small molecule drug discovery and pathogen sensing.

Frequency modulation response due to the intensity modulation of fiber-grating Fabry–Perot lasers

A comprehensive study on the small-signal frequency modulation (FM) characteristics of a fiber-grating Fabry–Perot (FGFP) laser is numerically conducted. Fiber Bragg grating (FBG) is used as a wavelength selective element to control the properties of the laser output by controlling the external optical feedback (OFB) level. In addition to the external OFB level, the effect of other parameters such as temperature, injection current, cavity volume, nonlinear gain compression factor, linewidth enhancement factor, and fiber-grating (FG) parameters on FM characteristics of the laser are investigated. The study is performed by modifying a set of rate equations that are solved by considering the effects of external OFB and ambient temperature (T) variations. The temperature dependence (TD) of FM characteristics is calculated according to TD of laser parameters instead of using well-known Pankove relationship. Results show that the optimum external fiber length (Lext) is 3.1 cm and the optimum range of working temperature for FGFP laser is within ± 2 °C from the FBG reference temperature (To). Also, it is shown that antireflection (AR) coating reflectivity and the linewidth enhancement factor have no significant effect on the FM response. The FM spectra peak amplitude is less than 5 dB with 5 mW output power. Good temperature stability is also obtained.

Monomode Interband Cascade Lasers at 5.2 $\mu{\rm m}$ for Nitric Oxide Sensing

We demonstrate application-grade monomode distributed feedback (DFB) laser devices with emission wavelength around 5.2 μm; suitable for nitric oxide sensing. The devices are based on interband cascade laser material that enables continuous wave operation in the midinfrared spectral region when mounted on a standard thermoelectrically cooled TO-style header. With etched vertical sidewall DFB gratings as wavelength selective elements, signal to noise ratios around 30 dB and typical tuning ranges greater than 12 nm were achieved, making the devices suitable for applications based on tunable laser absorption spectroscopy.