Hamed Dalir

29 GHz directly modulated 980 nm vertical-cavity surface emitting lasers with bow-tie shape transverse coupled cavity

A concept for the bandwidth enhancement of directly modulated vertical-cavity surface emitting lasers (VCSELs) using a transverse-coupled-cavity (TCC) scheme is proposed, which enables us to tailor the modulation-transfer function. A bow-tie shaped oxide aperture forms the transverse-coupled cavity resulting in optical feedback to boost the modulation speed. While the bandwidth of conventional VCSELs is 9–10 GHz, the 3 dB-bandwidth of the TCC VCSEL is increased by a factor of 3 far beyond the relaxation-oscillation frequency. The maximum bandwidth is currently limited by the photo-detector used in the experiment. Clear 36 Gbps eye opening was attained with an extinction ratio of 4 dB.

Bandwidth enhancement of single-mode VCSEL with lateral optical feedback of slow light

In this paper a novel method to increase the modulation bandwidth of vertical-cavity surface-emitting lasers (VCSEL) is proposed. The modeling predicts that the modulation bandwidth can be enhanced by 60% with lateral optical feedback. Even if the relaxation oscillation frequency is below 15GHz without optical feedback, the modulation bandwidth can reach at 40GHz beyond the limit of a relaxation oscillation frequency. Small and large-signal-modulation analysis is carried out. The result shows a potential of high-speed modulation beyond 40Gbps for use in low-power consumption optical interconnects.

High-speed operation of bow-tie-shaped oxide aperture VCSELs with photon?photon resonance

This paper presents experimental and modeling results for extending the 3-dB modulation bandwidth of a 980-nm quasi-single-mode (QSM) vertical-cavity surface-emitting laser (VCSEL) with a passive transverse-coupled cavity (TCC). While the bandwidth of a conventional VCSEL is 9 GHz, the 3-dB modulation bandwidth of a QSM TCC VCSEL with the same epi-wafer structure can reach 27 GHz, which is three times larger than the conventional VCSEL without optical feedback. A clear eye opening is obtained for large-signal modulations at 36 Gbps. A numerical simulation for further enhancement of the bandwidth is also conducted.

Enhancing the modulation bandwidth of VCSELs to the millimeter-waveband using strong transverse slow-light feedback

We present modeling on the millimeter (mm)-wave modulation of vertical-cavity surface-emitting laser (VCSEL) with a transverse coupled cavity (TCC). We show that strong slow-light feedback can induce 300% boosting of the modulation bandwidth of the TCC-VCSEL. Also, the strong lateral feedback can induce resonance modulation over passbands centered on frequencies as high as 3.8 times the VCSEL bandwidth. The slow-light feedback is modeled by a time-delay rate equation model that takes into account the multiple round trips as well as the optical loss and phase delay in each round trip in the feedback cavity.

High Frequency Modulation of Transverse-Coupled-Cavity VCSELs for Radio Over Fiber Applications

We demonstrate a high-speed and efficient direct modulation of a novel transverse-coupled-cavity vertical cavity surface emitting laser for radio over fiber applications. A bow-tie joint connection between two oxide apertures results in a leaky traveling wave in the lateral direction between the two cavities. The measured L/I characteristics and lasing spectra demonstrate coherent coupling of the two cavities. The small signal response of the fabricated device shows a large enhancement of over 30 dB in the modulation amplitude at frequencies . The resonantly enhanced modulation response is suitable for efficient narrow-band modulation in the millimeter wave range over 25 GHz far beyond the intrinsic modulation bandwidth of the laser without optical feedback.

Spatial mode multiplexer/demultiplexer based on tapered hollow waveguide

A spatial-mode multiplexer/demultiplexer using a Bragg reflector tapered hollow waveguide is proposed. Depending on each spatial mode, vertical radiation takes place at a cut-off condition, which shows low wavelength-dependence and polarization- independence.

Compact electro-absorption modulator integrated with vertical-cavity surface-emitting laser for highly efficient millimeter-wave modulation

We demonstrate a compact electro-absorption slow-light modulator laterally-integrated with an 850 nm vertical-cavity surface-emitting laser (VCSEL), which enables highly efficient millimeter-wave modulation. We found a strong leaky travelling wave in the lateral direction between the two cavities via widening the waveguide width with a taper shape. The small signal response of the fabricated device shows a large enhancement of over 55 dB in the modulation amplitude at frequencies beyond 35 GHz; thanks to the photon-photon resonance. A large group index of over 150 in a Bragg reflector waveguide enables the resonance at millimeter wave frequencies for 25 μm long compact modulator. Based on the modeling, we expect a resonant modulation at a higher frequency of 70 GHz. The resonant modulation in a compact slow-light modulator plays a significant key role for high efficient narrow-band modulation in the millimeter wave range far beyond the intrinsic modulation bandwidth of VCSELs.

Attojoule-efficient graphene optical modulators

Electro-optic modulation is a technology-relevant function for signal keying, beam steering, or neuromorphic computing through providing the nonlinear activation function of a perceptron. With silicon-based modulators being bulky and inefficient, here we discuss graphene-based devices heterogeneously integrated. This study provides a critical and encompassing discussion of the physics and performance of graphene. We provide a holistic analysis of the underlying physics of modulators including graphenes index tunability, the underlying optical mode, and discuss resulting performance vectors for this novel class of hybrid modulators. Our results show that reducing the modal area and reducing the effective broadening of the active material are key to improving device performance defined by the ratio of energy-bandwidth and footprint. We further show how the waveguides polarization must be in-plane with graphene, such as given by plasmonic-slot structures, for performance improvements. A high device performance can be obtained by introducing multi- or bi-layer graphene modulator designs. Lastly, we present recent results of a graphene-based hybrid-photon-plasmon modulator on a silicon platform and discuss electron beam lithography treatments for transferred graphene for the relevant Fermi level tuning. Being physically compact, this 100  aJ/bit modulator opens the path towards a novel class of attojoule efficient opto-electronics.

Highly efficient out-of-plane optical coupler based on tapered hollow waveguide

We proposed a highly efficient out-of-plane optical coupler based on a tapered hollow waveguide. Modeling shows low polarization and wavelength dependences in a 35 nm wavelength window (C-band). The relative lateral displacements per spot size of the vertical output for the entire C-band are less than 0.13 and 0.38 for TE and TM input modes, respectively. At the same time, the polarization-dependent insertion loss is below 1.35 dB for both TE and TM input modes. Our device functions as a spot size converter, via taper angle modification, which can be used for a variety of applications such as out-of-plane coupling of vertical cavity surface emitting lasers (VCSELs), detectors, and so on.

40 Gbps modulation of transverse coupled cavity VCSEL with push–pull modulation scheme

The push–pull modulation of a transverse coupled cavity VCSEL with a bow-tie-shaped oxide aperture is demonstrated. We experimentally show the transverse-mode switching of laterally coupled VCSELs, which potentially offers a novel push–pull modulation concept. The calculated results of small-signal responses indicate an extreme expansion of the modulation bandwidth regardless of the relaxation oscillation frequency. The small-signal response was measured by tuning the RF phase of the modulation current in one cavity. A clear eye opening up to 40 Gbps with push–pull modulation has been obtained, whereas the eye pattern with the single-cavity modulation is completely closed.