Silicon-photonics multi-wavelength common-gain tunable laser providing both source and pump for an amplified transceiver.

We propose and demonstrate a silicon-photonics-based laser that outputs multiple independently tunable wavelengths using a single InP gain element. We use it to generate a C-band tunable source for a coherent transceiver and simultaneously a 1480-nm source to pump an Er-doped fiber amplifier on the transmitter output.

Silicon-photonic laser emitting tunable dual wavelengths with highly correlated phase noise.

A silicon-photonic tunable laser emitting two tunable wavelengths simultaneously is demonstrated. The laser consists of a single semiconductor optical amplifier that provides shared gain and a silicon-photonic chip that provides wavelength selections. A total optical power of 29.3 mW is shown, with 300 mA of gain current at 40°C. Continuous tuning of frequency spacing from 69.5 GHz to 114.1 GHz is demonstrated. The two simultaneous laser channels show highly correlated phase noise, with a phase noise correlation coefficient of 90.7%.

Compact ultrabroad-bandwidth cascaded arrayed waveguide gratings.

Here, we present a compact, high-resolution, and ultrabroad-bandwidth arrayed waveguide grating (AWG) realized in a silicon nitride (Si3N4) platform. The AWG has a cascaded configuration with a 1×3 flat-passband AWG as the primary filter and three 1×70 AWGs as secondary filters (i.e. 210 output channels in total). The primary AWG has 0.5-dB bandwidth of 45 nm over 190 nm spectral range. The ultrabroad-bandwidth is achieved by using an innovative design that is based on a multiple-input multi-mode interference (MMI) coupler placed at the entrance of the first free propagation region of the primary AWG. The optical bandwidth of the cascaded AWG is 190 nm, and the spectral resolution is 1 nm. The overall device size is only 1.1 × 1.0 cm2. Optical loss at the central channel is 4 dB, which is 3 dB less than a conventional design with the same bandwidth and resolution values but using a primary filter with Gaussian transfer function. To the best of our knowledge, this is the first demonstration of an ultrabroad-bandwidth cascaded AWG on a small footprint. We also propose a novel low-loss (∼ 0.8 dB) design using a small AWG instead of an MMI coupler in the primary filter part, which can be used in applications where the light intensity is very weak, such as Raman spectroscopy.

Aluminum nitride grating couplers.

Grating couplers in sputtered aluminum nitride, a piezoelectric material with low loss in the C band, are demonstrated. Gratings and a waveguide micromachined on a silicon wafer with 600 nm minimum feature size were defined in a single lithography step without partial etching. Silicon dioxide (SiO(2)) was used for cladding layers. Peak coupling efficiency of -6.6 dB and a 1 dB bandwidth of 60 nm have been measured. This demonstration of wire waveguides and wideband grating couplers in a material that also has piezoelectric and elasto-optic properties will enable new functions for integrated photonics and optomechanics.

A photonic spectral processor employing two-dimensional WDM channel separation and a phase LCoS modulator.

We present a Photonic Spectral Processor (PSP) that provides both fine spectral resolution and broad bandwidth support by dispersing light over two-dimensional space using the crossed-grating approach. The PSP uses a hybrid guided wave/free-space optics arrangement, where a waveguide grating router implemented in silica waveguides disperses the light in one dimension with a 100 GHz FSR and a bulk 1200 gr/mm diffraction grating disperses the light along the second (crossed) dimension. The diffracted light is focused by a lens onto a liquid-crystal on silicon, two-dimensional, phase-only, spatial light modulator, which we use to prescribe phase and amplitude to the signal's spectral components. With the 2-D PSP arrangement we are able to address frequency components at 0.2 GHz/column with an optical resolution of 3.3 GHz covering 40 C-band channels.

Monolithic silicon chip with 10 modulator channels at 25 Gbps and 100-GHz spacing.

We demonstrate a chip containing ten low-chirp silicon modulators, each operating at 25 Gbps, multiplexed by a SiN arrayed-waveguide grating with 100-GHz spacing, showing the potential for 250 Gbps aggregated capacity on a 5×8 mm(2) footprint.

Compact polarization rotator on silicon for polarization-diversified circuits.

We demonstrate a polarization rotator based on adiabatic mode evolution on silicon for polarization-diversified circuits. The rotator has a device length of 420 µm, a polarization-conversion efficiency of more than 90%, and an insertion loss less than 1 dB for a wavelength range of 80 nm. Combining the rotator with a compact, broadband polarization beam splitter based on cascaded directional couplers enhances the polarization conversion extinction ratio to over 30 dB with less than 1.5 dB total insertion loss over a 60 nm spectral range.

Circular grating coupler for creating focused azimuthally and radially polarized beams.

We show a planar optical circuit design that takes light from an input waveguide and creates a focused azimuthally or radially polarized beam emanating from the surface of the substrate. It is implemented in silicon-on-insulator waveguides and does not require any external components to focus the beam. The focal spot size can be subwavelength and is potentially useful for lithography, imaging, optical data storage, optical trapping, optical excitation of molecules, or coupling to optical fibers.

Optical isolator using two tandem phase modulators.

We propose and demonstrate an integrated optical isolator in InP using two phase modulators in series. The phase modulators are driven with a single-frequency signal in quadrature. Theoretically there is no effect on the forward signal, and the carrier of the backward signal can be eliminated, the energy distributed to other frequencies. We achieve a carrier isolation of 11 dB and an excess insertion loss of 2.3 dB. Such an isolator can be monolithically integrated with a laser without extra materials or magnetic fields.

All-channel tunable optical dispersion compensator based on linear translation of a waveguide grating router.

We propose and demonstrate a compact tunable optical dispersion compensation (TODC) device with a 100 GHz free spectral range capable of mitigating chromatic dispersion impairments. The TODC is based on longitudinal movement of a waveguide grating router, resulting in chromatic dispersion compensation of ±1000 ps/nm. We employed our TODC device for compensating 42.8 Gbit/sec differential phase-shifting keying signal, transmitted over 50 km fiber with a -2 dB power penalty at 10⁻9.

Comment on "Nonreciprocal light propagation in a silicon photonic circuit".

We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function.