Waveguide Loss Measurements Research Articles

Reflection Airy distribution of a Fabry-Pérot resonator and its application in waveguide loss measurement.

The reflection Airy distribution (RAD) of a Fabry-Pérot (F-P) resonator is deduced with the consideration of the mode coupling between the cavity resonance field and the initial back-reflected field at the input F-P resonator facet, as well as the influence of the loss/gain factor. A waveguide loss/gain measurement method is proposed based on the measurement of the finesse of the RAD, which is intrinsically free from the influence of the coupling loss and the substrate scattering noise. The waveguide loss can be measured with a simple single-facet coupling setup, considerably reducing the coupling difficulty and the complexity of the measurement system while achieving the same or better measurement accuracy as that of the transmission F-P method.

Ultrahigh Index and Low-loss Silicon Rich Nitride Thin film for NIR HAMR Optics

Ultrahigh index and low-loss silicon rich nitride (SiNx) thin-film material is developed and studied for application in heat-assisted magnetic recording (HAMR) as light delivery system operating in the near infrared (NIR) wavelength range. The film is deposited by low-temperature inductively coupled plasma chemical vapour deposition and developed through the tuning of SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar gases ratio. Film characterization of SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , including material composition, optical properties, and thermal-optics is presented. X-ray photoelectron spectroscopy shows the spectrum of binding energy and a material composition of x = 0.6. The refractive index of developed film is >3.0 with an optical bandgap around 656 nm according to ellipsometery and photospectrometery measurement. Characterization of ultra-low optical absorption is addressed with the use of ellipsometry and prism coupler waveguide loss measurement and the developed film has an absorption coefficient of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> in the NIR. The thermal optic characterization shows a thermal optical coefficient of 2.66 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with a stable optical absorption at temperature up to 200 °C. The use of the developed SiNx film for HAMR as high-index contrast nanowaveguide and enabling to integrate III-V semiconductor laser for a fully integrated light delivery system is discussed.

Deposited amorphous silicon-on-insulator technology for nano-photonic integrated circuits

Low-loss deposited amorphous silicon (α-Si:H) layers for nano-photonic integrated circuit have been prepared using complementary-metal-oxide-semiconductor (CMOS) compatible technology. Waveguide loss as low as 3.45dB/cm is reported for films deposited at a low temperature (300°C) using plasma enhanced chemical vapour deposition process. The influence of the deposition parameters such as gas dilution, plasma power and pressure on the quality of the deposited material is thoroughly characterized using Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry, X-ray diffraction and atomic force microscopy. We show that the optical quality of the deposited film can be directly assessed from distinct frequency bands (2090, 2000 and 840cm−1) using FTIR, without the need for further waveguide loss measurements.

Modified Fabry-Perot interferometric method for waveguide loss measurement

An extension to the Fabry-Perot interferometric method is demonstrated to calculate the optical loss and the reflectivity for optical waveguides simultaneously. The method uses an excitation of the waveguide with a broadband amplified spontaneous emission source (a superluminescent diode in our case) and curve fitting to account for the change of input power, thereby simplifying the measurement procedure. The use of a broadband source as opposed to tunable lasers allows for simultaneous measurements over multiple wavelengths and decreased sensitivity to reflections in the cavity. Further, waveguides of different lengths are measured to calculate the optical loss and the reflectivity simultaneously. It is shown that, if the value for reflectivity is assumed, there could be a large error in the measurement of loss especially for short waveguides. Optical loss for ridge waveguides is measured and compared by using a tunable laser as the input source. The method can be used for a generic case where it is suspected that the input power changes during the measurement.

Waveguide Loss Measurement Using the Reflection Spectrum

A method for waveguide loss measurement purely based on the reflection spectrum is proposed. Using the Fourier series expansion of the single longitudinal mode in the reflection spectrum, the ratio between the second and first harmonics gives the round-trip loss even when the reflection coefficient of the launching optical field directly reflected by the waveguide facet is unknown. The internal loss of a Fabry-Perot laser diode was measured by the proposed method with results which compare well with those estimated from the amplified spontaneous emission spectrum.

Characterization of organic multi‐mode optical waveguides for electro‐optical printed circuit boards (EOPCB)

Purpose – To characterise the optical performance of organic multi‐mode optical waveguides integrated with printed circuit board (PCB) and to demonstrate the feasibility of 2.5 and 10 Gbps optical interconnection in board‐level, respectively.Design/methodology/approach – This paper provides both qualitative and quantitative approaches for the characterization the wave guide performance, i.e. using loss measurement, optical beam profiling, ethernet verification, and eye‐diagram testing. In addition to wave guide loss measurement, the most significance part of the work reported in this paper is to evaluate optical wave guides with coupled VCSELs, by which a 3 dB coupling design budget can thus be identified. Furthermore, by artificially manipulating coupling conditions, practical concerns of EOPCB integration, including waveguide geometry, VCSEL driving power, alignment tolerance, coupling spacing, etc. are studied.Findings – Thermal stability studies related to PCB lamination processes show the feasibility...

Performance comparison of optically pumped type-II midinfrared lasers

We report a comparative study on the performance of three optically pumped, type-II quantum well lasers with differing quantum well (QW) confinement. One of the active regions emphasized hole confinement, another emphasized electron confinement, while the third incorporated both electron and hole confinements. In all cases the wells were inserted in a thick InxGa1−xAsySb1−y waveguide/absorber region. The lasing wavelengths at 84K were 2.26, 3.44, and 2.37μm, respectively. The maximum peak output powers and differential quantum efficiencies η at 84K were similar for the hole well and W lasers (≈13W,η≈0.55), but significantly reduced in the electron-well-only laser (2.3W,η=0.14). Waveguide loss measurements via the traditional quantum efficiency versus cavity length method and by a Hakki-Paoli method revealed that all three lasers had low waveguide loss that either increased slowly or not at all with increasing temperature. However, the laser’s internal efficiency, ηi, showed a linear decline with increasing temperature, with the ηi of the electron-well-only laser significantly less than the other two. The data suggest that for antimonide-based type-II designs, strong hole confinement is essential for improved performance. The data further suggest that it is hole leakage from the QW and/or hole dilution that is largely responsible for the degradation in laser performance.

Vertically tapered epilayers for low-loss waveguide-fiber coupling achieved in a single epitaxial growth run

Next-generation optical-communications systems require on-wafer integration of active and passive opto-electronic components to increase operating speed and reduce packaging costs. Increased coupling efficiencies between semiconductor waveguides and optical fibers are of particular interest. A simple and cost-effective method of fabricating a mode-size converter monolithically integrated with a semiconductor waveguide is presented. An on-wafer mode-size converter reduces the number of interfaces in an opto-electronic circuit and improves the coupling efficiency between semiconductor waveguide and optical fiber. Vertically tapered epilayers are deposited in a single epitaxial growth run using shadow-masked growth by chemical-beam epitaxy, avoiding complex and expensive processing and regrowth stages. Waveguides that taper vertically and horizontally over /spl sim/1 mm for gradual expansion of the mode size are demonstrated. Waveguide loss measurements showed that there was negligible loss across the tapered regions. A loss of <2 dB/interface was achieved compared with /spl sim/8 dB/interface for a butt-coupled discrete device.

Planar and Channel Optical Waveguide Loss Measurement Using Optical Phase Conjugation in BaTiO 3

A new methodology of the propagation loss coefficient measurement with an accuracy of at least 10 -3 cm -1 is demonstrated using a single-pass transmission measurement method and beam coupling based on a self-pumped phase conjugation process in a single BaTiO 3 crystal. A new, high-precision optical "bridge system" for routine measurement of the planar waveguide propagation loss coefficient is designed.

Measurement of far-infrared waveguide loss using a multisection single-pass technique

Waveguide loss measurements based on a multisection single-pass technique have been performed for both mid-infrared and far-infrared quantum cascade structures. The far-infrared quantum cascade structures are based on a vertical transition active region emitting at λ≈76 μm, embedded in a double-plasmon waveguide. The measured waveguide loss of 42±20 cm−1 agrees well with the calculated one based on free carrier absorption.

Electrically pumped Terahertz quantum well sources

Far infrared emission from quantum cascade structures is presented. Surface emission from a grating coupler show that the intersubband luminescence of our vertical transition structure is limited at low temperature by electron–electron scattering. As the temperature is increased, the limitation comes from the emission of optical phonons. In order to check for material gain, waveguide loss and differential gain measurements have been performed using a single-pass-type measurement. We report waveguide losses of 110 cm −1 and differential gain of 23 cm −1 . Our results strongly suggest the possibility of far-infrared lasers using the quantum cascade technology coupled to double plasmon waveguides.

New techniques for optical absorption measurement of implanted nanoparticles in float glass

New techniques are reported for optical absorption and waveguide loss measurement of copper, gold and silver implanted float glass. Implantations were carried out on the tin face of the float glass since this face is an optical waveguide. Specially made triangle shape masks were used during implantation to study the optical loss–implant length relation. Absorption coefficients were extracted as 2.4 and 1 cm −1 for the gold and silver implants at 633 nm, respectively. These values were found to be implant condition dependent. To analyse the shape of nanoparticles a sandwiched structure was used in an optical absorption measurement set-up in which two guiding faces were put in contact. The sandwiched structure places the colloids at the centre of the optical field distribution rather than on the boundary zone. These experiments have revealed that the copper and the gold particles may have non-spherical shapes, whereas for silver, the formation of spherical nanoparticles is more likely.

Surface emitted second-harmonic generation from a quasi-phase matched waveguide in an Al_xGa_1-xAs/Al_2O_3 microcavity

A nonlinear Al(x)Ga(1-x)As waveguide consisting of a quasi-phase matched heterostructure embedded in a microcavity has been designed and fabricated. The microcavity resonator is formed by Al(2)O(3)/Al(0.32)Ga(0.68)As multilayer mirrors located above and below the waveguide core. The cavity resonantly enhances the surface emitting second-harmonic generation. The SH conversion efficiency has been measured for wavelengths between l = 1525 and 1575 nm. A simple waveguide loss measurement technique based on the SH autocorrelation of short optical pulses in a III-V waveguide is also demonstrated.

Characterization of poly(phenylsilsesquioxane) thin-film planar optical waveguides

Characterization results of thin-film poly(phenylsilsesquioxane) (PPSQ) planar-optical waveguides are presented. Results of absorption spectrum, refractive index, thermal stress effect, and waveguide loss measurements performed on 1-2 /spl mu/m PPSQ films indicate this silicon backbone polymer to be a strong potential candidate for optical waveguide integration within microelectronic systems. PPSQ films are shown to exhibit thermal stability with respect to volume, refractive index, and optical loss for temperatures up to 400/spl deg/C. The first TE mode of PPSQ planar optical waveguides between 1.32 and 1.72 /spl mu/m in thickness fabricated on 5-/spl mu/m HiPOX Si wafers exhibited optical loss of 0.16 dB/cm at 632.8 mn.

Laser spectral linewidth dependence on waveguide loss measurements using the Fabry–Perot method

The critical role of the optical source spectral linewidth in semiconductor low loss waveguide measurements using the Fabry–Perot resonance method is analyzed. For 5-mm-long GaAs/AlGaAs waveguides with losses in the 1 dB/cm range, a frequency stabilized single mode laser with a linewidth of less than 0.01 Å is required to obtain a loss value accurate to within 5%.

A fully automated stage for loss measurements of optical waveguides

A novel test setup for making three-prism or out-of-plane scattering loss measurements for thin-film optical waveguides is described. The test structure is automated and provides quick, convenient and repeatable measurements. The setup is relatively easy to fabricate and employs several unique features which improve the accuracy and repeatability of the measurements including real-time coupling force monitoring.

Measurement of distributed losses in optical waveguides: a new technique

An accurate measurement method for waveguide loss measurement is reported which is suitable for the determination of low values of distributed loss in integrated optical waveguides. The technique is insensitive to the values of other circuit characteristics such as splitter loss and splitting ratio; indeed it provides a means of evaluating most relevant circuit parameters. The concept is demonstrated through the use of discrete single-mode fiber optical components, and it is shown that the method is capable of generating repeatable measurements of waveguide loss with good accuracy.

Monolithic integrated external cavity GaAs/AlGaAs lasers with selectively disordered quantum well passive waveguides

The authors report on selectively disordered integrated external cavity GaAs/AlGaAs lasers, where the passive waveguide length is in the millimeter range. Partial disordering of the single QW (quantum well) was achieved by selective silicon ion implantation and subsequent lamp annealing. Lasers with 2.07-mm-long passive and 0.48-mm-long active sections had threshold currents of 33 mA, compared to 9.8 mA for lasers without passive cavities. Lasing data indicate a residual modal loss of 11 cm/sup 11/ in the passive section, consistent with direct waveguide loss measurements. Control samples of external cavity laser structures in which the QW in the passive section was not disordered showed significantly higher threshold currents and a large red shift (as much as 11.4 nm) of the lasing wavelength compared to lasers without a passive cavity. It is shown that the red shift results from the wavelength-dependent losses in the passive section; the net cavity losses are hence minimized by the red shift to lower threshold currents of the integrated laser structures. Loss measurements inferred from amplified spontaneous emission spectra show that without the red shift, the laser would have to overcome a large absorption of approximately 50 cm/sup -1/. A much smaller red shift (4.2 nm at L/sub p/=2.07 mm) was observed for the implanted samples. The results clearly demonstrate that partial disordering of the QW in the passive section leads to reduced cavity losses and hence to lower threshold currents of the integrated laser structures.

Integrated external cavity GaAs/AlGaAs lasers using selective quantum well disordering

Integrated external cavity GaAs/AlGaAs single quantum well lasers were fabricated by selective quantum well disordering. Lasers with 2.07-mm-long passive sections and 0.48-mm-long active sections had threshold currents of 33 mA, compared to 9.8 mA for lasers without passive sections. Lasing data indicate a residual modal loss of 11 cm−1 in the passive sections, consistent with direct waveguide loss measurements. Control composite structures with a nondisordered quantum well in the passive sections showed significantly higher threshold currents and a large red shift of as much as 11.4 nm in the lasing wavelength compared to lasers without a passive cavity. This red shift is the main reason for the reduced resonant losses in integrated external cavity lasers with a nondisordered quantum well in the passive section.

Reduced optical waveguide losses of a partially disordered GaAs/AlGaAs single quantum well laser structure for photonic integrated circuits

We present TE and TM waveguide loss measurements of partially disordered GaAs/AlGaAs quantum well separate confinement laser structures. Disordering is accomplished by silicon ion implanation and subsequent annealing. Propagation losses as low as 9 cm−1 are observed at the lasing wavelength of the corresponding untreated laser wafer. The waveguides are shown to be compatible with fabrication and dimensional requirements of high quality semiconductor lasers; ridge waveguide lasers fabricated in unimplanted portions of the same wafer exhibit threshold currents of only 8 mA. The results show that impurity-induced quantum well disordering is suitable for monolithic integration of low-threshold quantum well lasers and transparent optical waveguides.