Resolution Of Optical Spectrum Analyzer Research Articles

Resolving Intrinsic Modulation Spectral Lines from Electro-Optic Modulation Spectra Based on Boosted Iterative Deconvolution

Optical spectrum analysis is the most direct and effective method for characterizing electro-optic modulation spectra. According to the Rayleigh criterion, the best resolution of an optical spectrum analysis is limited by the point spread function of an optical spectrum analyzer (OSA) and the relative intensity of closely spaced spectral lines. In this paper, we propose a boosted iterative deconvolution (BID) method to resolve the intrinsic modulation of spectral lines from the measured optical carrier and modulation spectra. In our scheme, the electro-optic modulation spectrum is considered the convolution of the optical carrier spectrum and the intrinsic δ-function modulation spectrum, and the BID method enables fast and accurate extraction of the δ-function spectral lines from the measured modulation spectrum. The proof-of-concept experiment demonstrates that our method can improve the resolution of OSA by 10–30 p.m. at different relative intensities, with a best resolution of 10 p.m. in the iso-intensity case and wavelength errors of less than 2 p.m., which largely improves the measurement resolution and accuracy of the modulation spectrum.

Watt-level, green-pumped optical parametric oscillator based on periodically poled potassium titanyl phosphate with high extraction efficiency

We report a compact, efficient optical parametric oscillator (OPO) based on a periodically poled potassium titanyl phosphate (PPKTP) crystal pumped by a 532 nm laser, which generated 1.51 W of average power at the signal wavelength of 709 nm with the pulse duration of ∼ 1.0 ns. The extraction efficiency was up to 59%. To the best of our knowledge, this is the first report on Watt-level green-pumped PPKTP-based singly resonant oscillator OPO (SRO-OPO). The precise build-up time of OPO was determined to be 1.6 ns benefitting from the characteristic of twin-peak pulse profile of pump beam. The spectrum width of the idler was also measured to be 4.2 nm with the central wavelength of 2134 nm at 0.2 nm spectral resolution of optical spectrum analyzer. In addition, the beam quality of M 2 < 1.9 of generated signal exhibits a good consistency with M 2 < 1.5 for the pump source.

Design and Testing of a 2D Optical Fiber Sensor for Building Tilt Monitoring Based on Fiber Bragg Gratings

In this paper, a new type of optical fiber tilt sensor based on fiber Bragg grating (FBG) is presented for 2D dual-axis tilt angle sensing. The tilt sensor is composed of two cylindrical floats suspended in water, connected with FBG. When the external environment causes the tilting of the sensor, the surface of the liquid within the container will form a new balanced liquid surface plane due to the gravity and change the height of the liquid at different locations in the container. So the buoyancy force of the cylindrical floats of the sensor will vary with the depth of liquid, thus the changed FBG strain will cause the FBG reflection central wavelength shift. According to the measured central wavelength shift by the optical spectral analyzer (OSA), we can obtain the two-axis tilt angle of the sensor. The proposed sensor can detect a tilt angle range of −5 degrees to +5 degrees and achieve a sensitivity of 0.1° with optical spectrum analyzer resolution of 0.01 nm. Due to its good sensing linearity, the proposed sensor can be applied in building tilt measurement.

Calibration of grating based optical spectrum analyzers

In this paper, three methods are used to calibrate a grating-based Optical Spectrum Analyzer (OSA). The first method is used to calibrate OSA over the full spectral range by using a set of well characterized laser sources. These lasers, whose wavelengths cover OSA range, are well characterized using a highly accurate wavemeter. The Accuracy and stability for some lasers are found sufficient to calibrate OSA without the need to have an online measurement with a wavemeter. The second method uses the advantage of phase matching in non-linear crystals to generate frequency doubled light with exactly half the wavelength to measure OSA wavelength scale accuracy, resolution and linearity. In the third method, a Hydrogen Cyanide (H13C14N) gas cell - (HCN) is used as wavelength reference to calibrate OSA in the wavelength range 1533–1557 nm.

Optical phase-shift interrogation method with a single-ended PM-PCF sensor

We propose an optical phase-shift interrogation method that uses optical interferometric signals from a polarization-maintaining photonic crystal fiber (PM-PCF). The interference signal can be achieved using two different polarized beams, which propagate through the PM-PCF and the reflection coating. Since the PM-PCF has negligible thermal sensitivity, it is suitable for remote temperature-insensitive strain sensors when it is single-ended with reflection coating. Because the PM-PCF has a much lower wavelength-strain sensitivity compared with normal polarization-maintaining fibers, we developed an alternative optical phase-shift interrogation method to detect tiny strain deviations below the resolution of optical spectrum analyzer. We also demonstrated dynamic strain measurement using a wavelength-swept laser source.

Stabilized single longitudinal mode fibre ring laser based on an inline dual taper Mach Zehnder interferometer filter coated with graphene oxide

This paper describes a proposal and experimental demonstration of a narrow single longitudinal mode fibre ring laser with high power efficiency and a simple setup. A single longitudinal mode filter was realized by depositing graphene oxide flakes on a dual fibre taper Mach Zehnder interferometer in a loop mirror, wherein the loop structure acted as a passive narrowband reflector with the ability to generate a stable single longitudinal mode. This filter incorporation allowed for the generation of a single longitudinal mode having a side mode suppression ratio of 75dB at 60mW pump power and a 3dB line width of 0.16nm which is limited by the optical spectrum analyzer resolution.

In-Line Single-Mode Optical Fiber Interferometric Refractive Index Sensors

Novel in-line single-mode fiber interferometers- Mach-Zehnder and Michelson-have been designed, fabricated, and tested as refractive index (RI) sensors. Abrupt tapers and connector-offset attenuators are proposed as alternatives to long period gratings (LPGs) as mode-coupling mechanisms to transfer optical power between core and cladding modes in optical fiber. The coupling coefficients between core and cladding modes in the proposed designs were calculated using numerical packages and the devices were subsequently implemented using commercially available fusion splicer. For an abrupt taper, most coupling occurs between the LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> modes, with the first ten modes accounting for 98% of the incident mode energy. For a connector-offset attenuator, coupling mainly occurs between the LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> modes, with the first ten LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> modes and first ten LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> modes accounting for 92% of the incident mode energy. In particular, in the case of connector-offset attenuator, the relative direction between the two connector-offsets was found to be very important to the interference performance. Interference patterns were realized in simulation for the interferometers using both mode-coupling mechanisms. Three interferometers were realized in the experiment using abrupt taper-Mach-Zehnder and Michelson-and connector-offset attenuator-Michelson. They showed large extinction ratios (up to 23 dB) and small insertion losses (smaller than 3 dB). Although it is difficult to make Mach-Zehnder interferometers using connector-offset attenuator pair due to the lack of polarization control in the fusion splicer, some evidence of constructive interference was observed in the experiment. The interferometers were tested as RI sensors using the maximum attenuation wavelength shift. Given that the minimum resolution of optical spectrum analyzer is 10 pm, ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> difference of RI can be detected by the proposed interferometric sensors, providing similar performance as LPG-based interferometers at a lower cost and simpler fabrication process.

BRILLOUIN FIBER LASER WITH SIGNIFICANTLY REDUCED GAIN MEDIUM LENGTH OPERATING IN L-BAND REGION

Brillouin fiber laser (BFL) is demonstrated using a piece of photonic crystal fiber (PCF) in conjunction with a Bismuth-based erbium-doped fiber (Bi-EDF) as the gain media with a simple ring resonator. The proposed BFL operates at wavelength of 1574.08 nm, which is 0.08 nm shifted from the Brillouin pump wavelength with a maximum peak power of 8dBm. The BFL has a side mode suppression ratio and 3dB bandwidth of approximately 23 dB and 0.02 nm respectively limited by the optical spectrum analyzer resolution. The BFL is also stable at room temperature and compact due to the use of only 20 m long of PCF and 215 cm long of Bi-EDF.

Measurement of gain spectrum for semiconductor lasers utilizing integrations of product of emission spectrum and a phase function over one mode interval

A technique based on the integration of the product of amplified spontaneous emission spectrum and a phase function over one mode interval is proposed for measuring the gain spectrum for Fabry-Perot semiconductor lasers, and a gain correction factor related to the response function of the optical spectrum analyzer (OSA) is obtained for improving the accuracy of the measured spectrum. Gain spectra with a difference less than 1.3 cm/sup -1/ from 1500 to 1600 nm are obtained for a 250-μm-long semiconductor laser at an OSA resolution of 0.06, 0.1, 0.2, and 0.5 nm. The corresponding gain correction factor is about 9 cm/sup -1/ at a resolution of 0.5 nm. The gain spectrum measured at a resolution of 0.5 nm has the same accuracy as that obtained by the Hakki-Paoli method at a resolution of 0.06 nm for a laser with a mode interval of 1.3 nm.

Measurement of gain spectrum for fabry-perot semiconductor lasers by the fourier transform method with a deconvolution process

To improve the accuracy of measured gain spectra, which is usually limited by the resolution of the optical spectrum analyzer (OSA), a deconvolution process based on the measured spectrum of a narrow linewidth semiconductor laser is applied in the Fourier transform method. The numerical simulation shows that practical gain spectra can be resumed by the Fourier transform method with the deconvolution process. Taking the OSA resolution to be 0.06, 0.1, and 0.2 nm, the gain-reflectivity product spectra with the difference of about 2% are obtained for a 1550-nm semiconductor laser with the cavity length of 720 /spl mu/m. The spectra obtained by the Fourier transform method without the deconvolution process and the Hakki-Paoli method are presented and compared. The simulation also shows that the Fourier transform method has less sensitivity to noise than the Hakki-Paoli method.