Investigation of frequency noise and spectrum linewidth in semiconductor optical amplifier

The characteristics of FM noise and linewidth of semiconductor optical amplifier without facet mirrors were theoretically analyzed and experimentally confirmed. The concept of discrete longitudinal mode for the spontaneous emission was introduced as the basis of quantum mechanical characteristics, allowing the quantitative examination of noise sources. The continuously broaden output spectrum profile of the amplified spontaneous emission (ASE) was well explained as a spectrum broadening of each longitudinal mode. We found that the linewidth of the inputted signal light hardly changes by the optical amplification in the SOA. The FM noise increases proportional to square value of the noise frequency and less affected by the electron density fluctuation, the linewidth enhancement factor and the ASE. The higher FM noise in the higher noise frequency is caused by the intrinsic phase fluctuation on the optical emission. The characteristics of the linewidth and the noise frequency dependency were experimentally confirmed

Optical humidity sensor based on tapered fiber with multi-walled carbon nanotubes slurry

We demonstrated performance comparison of optical humidity sensor for bare and Multi-walled carbon nanotubes (MWCNTs) slurry coated tapered optical fiber. The starting material for MWCNTs slurry is MWCNTs- acrylonitrile butadiene styrene (ABS) based fused deposition modeling (FDM) 3D printer filament. The ABS was dissolved using acetone to produce MWCNTs-acetone suspension. The MWCNTs-acetone suspension was drop-casted on the tapered fiber to produce MWCNTs slurry by evaporation process at room temperature, which resulted the MWCNTs slurry attach to the tapered fiber. The MWCNTs slurry acts as the cladding for humidity changes measurement. The experimental works showed improvement of sensitivity from 3.811 μW/% of bare tapered fiber to 5.17 μW/% for the coated tapered fiber with MWCNTs slurry when the humidity varied from 45% to 80%

Investigation on Double Pass Amplification by employing Zr-EDF as a gain medium with different types of reflectors

In this paper, the amplification for double-pass operation is demonstrated by using a newly doped fiber namely as Zirconia based erbium doped fiber (Zr-EDF) with a different type of reflectors which are optical circulator and a broadband fiber mirror (BFM). The concept of double pass amplification is based on the forwarded and amplified spontaneous emission (ASE) signal that will propagate twice into the gain medium and thus will increase the gain performance in the C- and L- band region. Optical circulator and BFM are placed at the end of the cavity and used as the signal reflector to ensure that the signal will be reflected back into the gain medium, Zr-EDF. The amplification performance of single and double pass Zr-EDFA by utilizing optical circulator and BFM as signal reflectors are investigated at high and low input signal powers, -10 and -30 dBm, respectively. The double pass approach shows a better amplification performance at low input signal power of -30 dBm, compared to the high input signal power of -10 dBm. At low input signal power of -30 dBm, the maximum gain of 40.3 dB is achieved for double pass amplification at a wavelength of 1560 nm. The gain enhancement of 12.30 dB is observed between the single and double pass amplification with BFM as the reflector with the low input signal power. Instead of that, the performance analysis of double pass amplification by utilizing the optical circulator for varying the length of gain medium from 0.5 m to 2 m and pump power from 67 mW to 130 mW is further investigated. From the results, it shows that with the length of 1m Zr-EDF and 130 mW of pump power shows the optimum length and pump power due to the highest gain with lowest noise figure performance

Metallic Cylinder Reflected Power Measurement For 93.1GHz Frequency Modulated Continuous Wave Radar Calibration

A metallic cylinder is one of the best materials and shapes to calibrate a radar system performance. The measurement of a 4cm diameter and 3cm-height metallic cylinder as a target has been presented for the analysis at the millimeter-wave (mm-wave) spectrum. This experiment was conducted in a real airport environment at Kuala Lumpur International Airport considering clear sky conditions. The measurement was carried out at 93.1 GHz which uses Frequency Modulated Continuous Wave (FMCW) radar to consistently detect the target. The radar cross-section (RCS) of the metallic cylinder is measured with respect to the angle of runway pavement. It is found that the measurements exhibited smaller RCS value with an average of –43.47 dBsm at a longer range compared to –30.16 dBsm at a shorter range with a total change of 13.31 dBsm. The reflectivity characteristics of the radar target, theoretical measurement of the metallic cylinder, its incident angle from the radar target, and measurement evaluation are presented in this paper

Metallic Cylinder Reflected Power Measurement For 93.1GHz Frequency Modulated Continuous Wave Radar Calibration

A metallic cylinder is one of the best materials and shapes to calibrate a radar system performance. The measurement of a 4cm diameter and 3cm-height metallic cylinder as a target has been presented for the analysis at the millimeter-wave (mm-wave) spectrum. This experiment was conducted in a real airport environment at Kuala Lumpur International Airport considering clear sky conditions. The measurement was carried out at 93.1 GHz which uses Frequency Modulated Continuous Wave (FMCW) radar to consistently detect the target. The radar cross-section (RCS) of the metallic cylinder is measured with respect to the angle of runway pavement. It is found that the measurements exhibited smaller RCS value with an average of –43.47 dBsm at a longer range compared to –30.16 dBsm at a shorter range with a total change of 13.31 dBsm. The reflectivity characteristics of the radar target, theoretical measurement of the metallic cylinder, its incident angle from the radar target, and measurement evaluation are presented in this paper

UV-written Bragg gratings in a flat-fiber platform as a bending and twisting sensor

High demand on structural health monitoring has encouraged the development of smart structure geometries to be more effective and competitive [1]. One of the technologies that has been integrated into these structures is the fiber Bragg grating (FBG) [2]. The FBG is a mature technology that has seen many applications, particularly the field of sensing where it has many advantages such as immunity to electromagnetic field, long lifetime, high sensitivity, lightweight and low loss. There are several types of optically based physical sensors. Most of which are fabricated in a standard dimension silica optical fiber which due to its cylindrical structure are unable to independently measure twist. Here we demonstrate a bending and twist sensor fabricated in a flat-fiber substrate. A Y-splitter and a series of Bragg gratings along the 50 mm length provides a differential signal providing distinction between bend and twist within the sample

Line of sight visibility analysis for foreign object debris detection system

It is challenging to monitor busy airports' runway through visual inspection to precisely detect foreign object debris. Currently, many technologies for the detection of foreign object debris are available. It has been investigated that millimeter-wave radar technology's detection capability can be one of the most effective techniques for detecting foreign object debris as it is weather-resilient. However, the positioning and height of a millimeter-wave radar pole covering the runway area, considering the existing runway infrastructure, are challenging. The task involves finding the appropriate placement and optimum height. This paper presents a novel method of line of sight visibility for placement and height of radar pole using human factor research to ensure that each point on the runway is visible from various heights of the millimeter-wave radar pole to the runway locations. Kuala Lumpur International Airport, Malaysia runway 32L/14R, has used a case study to test the visibility analysis. The visual analytic test's successful results for different millimeter-wave radar pole locations and viewing heights under a visible and invisible line of sight conditions on the runway have been verified in the field experiment

Passively Q-switched Erbium-doped fiber laser with brass-based saturable absorber

The operating wavelength in the 1.5 µm region is made accessible through an Erbium-doped fiber as a gain medium. The minimum optical loss of this region has proven beneficial in the application of pulsed fiber lasers. However, the ideal material to act as passive modulator for the system is yet to be found. Therefore, this research proposed the generation of pulsed fiber laser using metal based passive saturable absorber by utilizing brass-based 3D printer filament. A free-standing film was fabricated using chitin as host polymer for ease of integration in the laser ring cavity. The Erbium-doped fiber laser with brass-chitin based polymer composite film generated Q-switched pulses within the input pump power of 135.7 mW to 172.3 mW. The repetition rate was increased from 55.80 kHz to 68.03 kHz. Meanwhile the pulse width was reduced from 3.06 µs to 2.24 µs, with corresponding maximum instantaneous pulse energy and peak power of 2.10 nJ and 882.71 µW, respectively. The signal-to-noise ratio was measured at 67 dB, indicating a highly stable pulse generation

Optical fiber proximity sensor for micro distance measurement

This paper demonstrates an optical fiber proximity sensor for micro distance measurement. The optical fiber was used to detect a silver plate which acted as an obstacle. A flat end of a standard single mode optical fiber was functioned to emit the broadband light at near infrared wavelength region and receive the reflected light from the obstacle. The distance between the optical fiber and the obstacle was varied from 0μm to 400 μm. We experimentally characterized the sensor sensitivity based on their free spectral range. The optical fiber tip has shown its potential for proximity sensing application with sensitivity value of 0.0199 nm μm and regression value up to 0.9126

Micromachined multimode interference device in flat-fiber

A novel flat-fiber platform is presented for fabricating integrated optical multimode interference (MMI) devices. Fabrication is achieved by modifying a standard optical fiber drawing process and applying a micromachining technique. The fabricated structure consists of an MMI region within the flat-fiber that is defined by micromachined trenches, illustrated in Figure 1(a). A 1×3 splitter has been demonstrated, with a spatial output mode that be tuned by placing refractive index oils within the micromachined trenches. MMI devices have been demonstrated in different planar platforms such as silicon-on-insulator and silica-on-silicon. However, many of these materials are potentially expensive, high loss or have a complex fabrication process. The desire to have a fiber-like platform, capable of supporting multiple waveguides in a planar format, led us to develop a novel silica optical flat-fiber technology. This allows us to overcome the limitations of existing planar technologies by offering a low cost, low loss substrate with fiber-like flexibility, long lengths and the ability to make integrated devices. The flat-fiber substrate is fabricated using standard silica fiber fabrication but differs by collapsing the preform during the fiber drawing stage by using a vacuum. The trenches of the device were diced using an ultra-precision micromachining technique