Bülent A. Franke

Photonic crystal microcavities in SOI waveguides produced in a CMOS environment

We have investigated microcavities in Silicon-on-Insolator (SOI) waveguides. The rectangular waveguides with 500 nm width are fabricated in the 220 nm silicon device layer. The microcavities are formed by one-dimensional photonic crystals in Fabry-Perot structure directly written in the waveguides. The SOI photonic structures are produced in a CMOS environment using 248 nm DUV lithography, where the waveguides as well as the photonic crystals are created in the same step using a single mask. In order to achieve a desired spectral shape of the filter function capable for several applications, a number of different cavities were investigated, e.g. single cavities of first and higher order as well as multi-cavity filters. The experimental results are compared with simulations of photonic crystal microcavities in strip waveguides. The spectral transmission function of such filters dependent on the design parameters are calculated by an analysis based on Finite-Difference-Time-Domain (FDTD) method.

High-Speed Fabry–Pérot Optical Modulator in Silicon With 3-μm Diode

A silicon optical modulator using a novel node-matched-diode geometry inside a Fabry-Pérot nanowaveguide resonator is presented. The diode length is only 3 μm. An analysis of the dynamic spectral transmission behavior is given. Non-return-to-zero data transmission of 10 Gb/s is demonstrated.

Method for comprehensive dynamic spectral characterization of wavelength dependent modulators

We present a method to simultaneously determine the temporal and spectral dynamics of modulator devices that utilize spectral changes during modulation operation. For this purpose, a series of signal traces at different wavelengths is recorded.

Spontaneous and stimulated Raman scattering in planar silicon waveguides

Raman scattering in planar silicon on insulator (SOI) waveguides with 2 μm width, 220 nm height and 2 cm length is investigated. A cw Nd:YAP laser at 1340.6 nm with 7 GHz FWHM spectral width is used as the pump source. A lensed fiber of 2.5 μm focus diameter is used to couple the pump laser into the waveguide. The coupling efficiency is estimated to be around 10%. Spontaneous Raman scattering is observed with as low as 2.5 mW pump power inside the waveguide. The spontaneous Raman spectrum is measured by an optical spectrum analyzer. The first order Raman peak is measured at around 1441.4 nm corresponding to a Raman shift of 15.6 THz, while the FWHM of Raman spectrum is measured as around 100 GHz. Maximum Raman output of around 90 pW is obtained by around 22 mW pump. The stimulated Raman gain coefficient is estimated as around 56 cm/GW from the relationship between spontaneous Raman output power and pump power. A temperature dependence of Raman frequency shift of about 0.6 GHz/K is measured. The spontaneous anti-Stokes Raman scattering output peak at 1253 nm is also observed with around 35 mW pump. Stimulated Raman amplification measurement is carried out with a SLED white light source as probe signal. With 35 mW pump power, around 0.6 dB gain has been determined with both pump and probe being TE polarized.

Single cavity filters on end-faces of optical fibers

We have developed thin film Fabry-Perot filters directly coated on optical fibers to archive a high level of integration with a reduction of optical elements. Such band-pass filters can be used in fiber optical sensor systems, and for fiber communication, e.g. CWDM applications. The filters cavities consist of a single spacer and two dielectric mirrors. The dielectric mirrors are deposited by PVD directly on end-faces of single-mode optical fibers. Dielectric as well as polymeric materials were applied as the spacer layer. Polymeric spacer layers were deposited by dip coating. The influence of the mirror reflectivity on the transmission band of the Fabry-Perot filters was investigated. Furthermore, the optical performance of filters with first order (λ/2) as well as higher order spacers was analyzed. The experimental results are compared with numerical analysis of Fabry-Perot cavities on the end-face of cylindrical waveguides. The spectral characteristic of the filters are calculated using a software solving Maxwell´s equations by a FDTD method. The layer design of the filters and the deposition process were optimized for maximum transmission and narrow bandwidth of the transmission peak. Passive band-pass filters on fiber end-faces were designed, fabricated and characterized for transmission wavelengths of 945 nm, 1300 nm, as well as 1550 nm. Bandwidths as narrow as 1 nm could be achieved for 945 nm.

18 dB cw Raman on-off Gain in Silicon-On-Insulator Nanowire Waveguide Laser Amplifiers

Optical cw Raman gain of 18.4dB in SOI-nano-rib waveguides was obtained at 45mW internal pump power. Nonlinear on-off-gain increase at about 30mW pump power indicates that the Raman amplifier approaches the lasing threshold.

Silicon optical modulator with 3 µm diode

A silicon optical modulator using a novel node-matched-diode geometry is presented. The diode length is only 3 μm. NRZ data transmission of 10 Gb/s is demonstrated. According to the frequency response, 28 Gb/s are feasible.

Integrated Silicon E/O Waveguide Platform for Advanced Optoelectronic Signal Processing

We review a Si E/O waveguide technology for low-loss integrated optics, highly efficient nonlinear devices & modulators. The platform opens the possibility of integrated photonic signal processing combining linear & nonlinear optics & electronics.

Frequency-to-Time Conversion based Delay and Dispersion Generators in a CMOS Compatible SOI Platform: Prospects and Limitations

Footprint limitations of an electrically tunable delay and dispersion generator in the CMOS compatible platform based on ring resonators as well as maximum producible delay and group velocity dispersion are studied.

RAMAN SCATTERING AND GAIN IN SILICON-ON-INSULATOR NANOWIRE WAVEGUIDES

Raman scattering in air-covered and SiO2-covered Silicon-on-insulator waveguides of 1.25 cm length, 220 nm height and two widths of 2 μm or 0.45 μm was investigated. A continuous wave (CW) Raman fiber laser at 1454.8 nm with linewidth of <0.1 nm was used as a pump source. The coupling efficiency was estimated to be around 10% for one end facet. Spontaneous Raman shift of 521 cm-1 (1574.2 THz) scattering was observed at 1573.8 nm for SOI waveguides in air and 1574.2 nm for waveguides covered with SiO2 at pump power of <1.5 mW inside both waveguides of 2 and 0.45 μm. Anti-Stokes scattering was observed at 1352.8 nm with pump power of 16 mW. The stimulated Raman gain was calculated from spontaneous Raman efficiency. Total Raman on-off gain was determined to be 0.6 dB for waveguide with width of 2 μm and 1 dB for waveguide with width of 0.45 μm.