On-chip lateral Si:Te PIN photodiodes for room-temperature detection in the telecom optical wavelength bands.

Photonic integrated circuits require photodetectors that operate at room temperature with sensitivity at telecom wavelengths and are suitable for integration with planar complementary-metal-oxide-semiconductor (CMOS) technology. Silicon hyperdoped with deep-level impurities is a promising material for silicon infrared detectors because of its strong room-temperature photoresponse in the short-wavelength infrared region caused by the creation of an impurity band within the silicon band gap. In this work, we present the first experimental demonstration of lateral Te-hyperdoped Si PIN photodetectors operating at room temperature in the optical telecom bands. We provide a detailed description of the fabrication process, working principle, and performance of the photodiodes, including their key figure of merits. Our results are promising for the integration of active and passive photonic elements on a single Si chip, leveraging the advantages of planar CMOS technology.

Theoretical investigation of a photonic-assisted instantaneous frequency measurement with a tunable measurement range and resolution by adjusting the chirp parameter of an optical intensity modulator.

The chromatic dispersion-based frequency-to-power mapping approach is often used in microwave photonic (MWP) instantaneous frequency measurement (IFM) receivers. A mechanism to tune the measurement range and resolution of these MWP IFM receivers by adjusting the chirp parameter of their optical intensity modulators is proposed and demonstrated. In particular, an MWP IFM receiver with a tunable measurement range and resolution based on a chirp-adjustable dual-drive Mach-Zehnder modulator (DDMZM) and two dispersive mediums is proposed and theoretically investigated. In the proposed MWP IFM receiver, a radio frequency (RF) signal whose unknown frequency is intended to be measured is applied to the two arms of a DDMZM with an appropriate power ratio. By adjusting the ratio of the two applied RF signals, the chirp parameter of the DDMZM and consequently, the measurement range and resolution of the MWP IFM receiver, can be tuned. The analytical results are verified by simulation results using commercial software. The proposed method also can be used in most of the previously reported MWP IFM receivers based on the chromatic dispersion and frequency-to-power mapping approach to tune their measurement ranges and resolutions.

Optical single sideband polarization modulator with tunable optical carrier-to-sideband ratio and its applications in microwave photonic phase shifter and optical frequency shifter.

In this paper, a novel scheme to implement an optical single sideband (OSSB) polarization modulator (PolM) is proposed and theoretically investigated. The proposed structure contains two dual-drive Mach-Zehnder modulators inside a Mach-Zehnder interferometer whose input/output optical Y-couplers are replaced by two optical polarization beam splitters/polarization beam combiners. It is shown that by applying four equal power radio-frequency signals with appropriate phases, an OSSB polarization-modulated signal is generated. In addition, $(4n+3)$(4n+3)th-order sidebands, where ${n}$n is an integer, are suppressed without the need for an optical filter. The proposed OSSB PolM can find many applications in microwave photonic (MWP) systems. For instance, by using the proposed OSSB PolM, an OSSB modulator with tunable optical carrier-to-sideband ratio (OCSR), an OSSB-suppressed carrier modulator/optical frequency shifter with ultralow spurious sidebands, and an MWP phase shifter with 360° tunable phase shifts, are proposed and theoretically investigated. Simulation results using commercial software are also presented, which are in good agreement with analytical results.

Tunable microwave-photonic filter using frequency-to-time mapping-based delay lines.

A new implementation of microwave-photonic filters (MPFs) based on tunable optical delay lines is proposed and demonstrated. The variable delay is based on mapping of the spectral components of an incoming waveform onto the time domain, the application of linearly-varying temporal phase offsets, and an inverse mapping back to the frequency domain. The linear phase correction is equivalent to a frequency offset, and realized though suppressed-carrier single-sideband modulation by a radio-frequency sine wave. The variable delay element, controlled by the selected frequency, is used in one arm of a two-tap MPF. In a proof-of-concept experiment, the free spectral range (FSR) of the MPF was varied by over a factor of four: between 1.2 GHz and 5.3 GHz.

Fully-tunable microwave photonic filter with complex coefficients using tunable delay lines based on frequency-time conversions.

A fully electrically tunable microwave photonic filter is realized by the implementation of delay lines based on frequency-time conversion. The frequency response and free spectral range (FSR) of the filter can be engineered by a simple electrical tuning of the delay lines. The method has the capability of being integrated on a silicon photonic platform. In the experiment, a 2-tap tunable microwave photonic filter with a 3-dB bandwidth of 2.55 GHz, a FSR of 4.016 GHz, a FSR maximum tuning range from -354 MHz to 354 MHz and a full FSR translation range is achieved.

Frequency domain aperture for the gain bandwidth reduction of stimulated Brillouin scattering.

In this Letter, we propose a novel method based on the inhomogeneous Brillouin gain saturation to reduce the gain bandwidth significantly below its natural value. Based on our first experiments, we report a decrease of the bandwidth in a standard single mode fiber down to 3 MHz.

Continuously variable long microwave-photonic delay of arbitrary frequency-chirped signals.

A generic method for the continuously variable, long microwave-photonic delay of the impulse response of arbitrarily chirped waveforms is proposed and demonstrated. Nonlinear-frequency-modulated waveforms of 500 MHz bandwidth are delayed by tens of nanoseconds. The principle relies on the specific phase-time relations of the waveforms, and is applicable to chirped pulses of arbitrary durations, central radio frequencies, and bandwidths. The approach is suitable for beam steering in large phased-array antennas.

Brillouin scattering gain bandwidth reduction down to 3.4MHz.

We present a simple method for the stimulated Brillouin scattering (SBS) gain bandwidth reduction in an optical fiber. We were able to reduce the natural bandwidth of 20 MHz to around 3.4 MHz by a superposition of the gain with two losses produced by the same source. This reduced bandwidth can drastically enhance the performance of many different applications which up to now were limited by the minimum of the natural SBS bandwidth.

Quasi-light-storage enhancement by reducing the Brillouin gain bandwidth.

The quasi-light-storage (QLS) is a method for the variable and almost distortion free storage of optical data which is based on stimulated Brillouin scattering (SBS). The natural gain bandwidth of SBS limits the storage time of this method to up to 100 ns. We overcome this limit by the superposition of the SBS gain bandwidth with two losses. With this narrowed gain bandwidth, we were able to enhance the storage time for the QLS by 40%.

Quasi-Light-Storage based on time-frequency coherence.

We show a method for distortion-free quasi storage of light which is based on the coherence between the spectrum and the time representation of pulse sequences. The whole system can be considered as a black box that stores the light until it will be extracted. In the experiment we delayed several 5 bit patterns with bit durations of 500ps up to 38ns. The delay can be tuned in fine and coarse range. The method works in the entire transparency range of optical fibers and only uses standard components of optical telecommunications. Hence, it can easily be integrated into existing systems.