Henry M. Daghighian

Single-Channel 50G and 100G Discrete Multitone Transmission With 25G VCSEL Technology

This paper explores the feasibility of single-channel 50G and 100G transmission using 25G VCSEL technology. We show through experiments the practicality of 50G transmission through 100 m of OM3 multi-mode fiber. To address the question of whether single-channel 100G transmission is feasible, we show through simulation the needed reduction in relative intensity noise of 25G VCSELs and present a novel modulation technique which offers improved performance over conventional discrete multitone with little additional computational complexity.

Four 45 Gbps PAM4 VCSEL based transmission through 300 m wideband OM4 fiber over SWDM4 wavelength grid

We demonstrate successful transmission of four 45 Gbps PAM4 single-channels through OM4 multimode fibers (MMFs) and wideband MMF using a PAM4 PHY chip and four vertical cavity surface emitting lasers (VCSELs) with wavelengths ranging over short wavelength division multiplexing (SWDM) grid. Real-time bit error ratios (BERs) < 2 × 10-4 were achieved for all four 45 Gbps PAM4 SWDM grid channels over 100 m, 200 m, and 300 m of wideband OM4 MMFs. All four channel received PAM4 optical eyes are shown after propagating through 100 m, 200 m, and 300 m of wideband OM4 as well as 100 m and 200 m conventional OM4 MMFs. The measured BERs as a function of the inner eye optical modulation amplitudes (OMAs) are shown for all four SWDM grid channels. Inner eye OMAs ranged from -16.2 dBm to -13.5 dBm for different channels over different OM4 MMF types at the KP4 BER threshold of 2 × 10-4.

112 Gb/s transmission with a directly-modulated laser using FFT-based synthesis of orthogonal PAM and DMT signals.

We report the experimental measurement of 112 Gb/s transmission back-to-back and through 12 km of S-SMF with a single directly-modulated laser (DML) using the novel modulation format Orthogonal PAM-DMT. This work demonstrates a record DML-based 112 Gb/s receiver sensitivity of -7.1 dBm at a BER of 10(-3), outperforming conventional PAM and DMT by approximately 2.5 dB.

56 Gb/s transmission over 100m OM3 using 25G-class VCSEL and discrete multi-tone modulation

We report experimental data demonstrating 56 Gb/s VCSEL transmission over 100m OM3, and 40 Gb/s transmission over 200m OM3 using discrete multi-tone modulation. This result is achieved with a conventional 850nm 25G-class VCSEL.

55 GHz Bandwidth Distributed Reflector Laser

We have demonstrated a 1300-nm short-cavity distributed reflector (DR) laser having 55 GHz bandwidth (BW), and successful 112-Gb/s transmission using four-level pulse-amplitude-modulation (PAM-4), without any pre-equalization for the transmitter. Two effects were realized in the design and operation of the DR laser: photon–photon ( P–P) resonance and detuned-loading. The P–P resonance effect was realized between the DFB and distributed Bragg reflector (DBR) modes that coexisted in the cavity of the DR laser. The detuned-loading effect was used to effectively enhance the differential gain through the dynamic change in the mirror reflectivity that occurs on the flank of the DBR mirror due to the frequency chirp under modulation. Despite a limited RC cutoff frequency of 22 GHz, a wide modulation BW of 55 GHz was achieved. It is shown that the RC limitation was counteracted by the combined effects of the detuned-loading, which reduces the damping of relaxation oscillations, and an in-cavity FM–AM conversion effect that created a high-pass filter effect in the modulation response. This will be discussed by way of simulations and experimentally observed eye diagrams for 10 Gb/s NRZ and 28 Gbd PAM-4. The short-cavity DR laser achieved 112-Gb/s PAM-4 transmission over links having a range of dispersions from –28 to +7 ps/nm without precompensation on the transmitter.

A promising new mechanism of ionizing radiation detection for positron emission tomography: modulation of optical properties

Using conventional scintillation detection, the fundamental limit in positron emission tomography (PET) time resolution is strongly dependent on the inherent temporal variances generated during the scintillation process, yielding an intrinsic physical limit for the coincidence time resolution of around 100 ps. On the other hand, modulation mechanisms of the optical properties of a material exploited in the optical telecommunications industry can be orders of magnitude faster. In this paper we borrow from the concept of optics pump-probe measurement to for the first time study whether ionizing radiation can produce modulations of optical properties, which can be utilized as a novel method for radiation detection. We show that a refractive index modulation of approximately [Formula: see text] is induced by interactions in a cadmium telluride (CdTe) crystal from a 511 keV photon source. Furthermore, using additional radionuclide sources, we show that the amplitude of the optical modulation signal varies linearly with both the detected event rate and average photon energy of the radiation source.

100G SWDM4 transmission over 300m wideband MMF

Experimental data is presented demonstrating 100GbE (4 × 25.8 Gb/s) SWDM4 VCSEL technology, and SWDM4 transmission over 200m and 300m of wideband OM4 fiber. All SWDM4 channels achieve error free transmission at 200m, and BER <; 1.e-9 at 300m.

45Gb/s PAM4 VCSEL 850/940nm Transmission over OM3 and OM4 Multimode Fibers

We present experimental data demonstrating 45Gb/s VCSEL transmission over 200m of OM3 and 300m of wideband OM4 fibers at 850/940nm. The measured PAM4 OMA-sensitivity was -15.0 dBm at 2e-4 over 100m OM3 fiber at 850/940nm.

Study of material properties important for an optical property modulation-based radiation detection method for positron emission tomography

Abstract. We compare the performance of two detector materials, cadmium telluride (CdTe) and bismuth silicon oxide (BSO), for optical property modulation-based radiation detection method for positron emission tomography (PET), which is a potential new direction to dramatically improve the annihilation photon pair coincidence time resolution. We have shown that the induced current flow in the detector crystal resulting from ionizing radiation determines the strength of optical modulation signal. A larger resistivity is favorable for reducing the dark current (noise) in the detector crystal, and thus the higher resistivity BSO crystal has a lower (50% lower on average) noise level than CdTe. The CdTe and BSO crystals can achieve the same sensitivity under laser diode illumination at the same crystal bias voltage condition while the BSO crystal is not as sensitive to 511-keV photons as the CdTe crystal under the same crystal bias voltage. The amplitude of the modulation signal induced by 511-keV photons in BSO crystal is around 30% of that induced in CdTe crystal under the same bias condition. In addition, we have found that the optical modulation strength increases linearly with crystal bias voltage before saturation. The modulation signal with CdTe tends to saturate at bias voltages higher than 1500 V due to its lower resistivity (thus larger dark current) while the modulation signal strength with BSO still increases after 3500 V. Further increasing the bias voltage for BSO could potentially further enhance the modulation strength and thus, the sensitivity.

Investigation of electron multiplication effect in optical property modulation-based radiation detection method for PET

In this paper, we further explore the optical property modulation-based method for ionizing radiation photon detection in PET as a potential new direction to dramatically improve the coincidence time resolution. We compare the performance of three detector crystals for this method including two types of cadmium telluride (CdTe) crystals and one bismuth silicon oxide (BSO) crystal under high bias voltages up to 3500V. We first show that the induced current flow in the detector crystal determines the strength of the optical property modulation signal due to ionization. A larger resistivity is favorable for reducing the dark current (noise) in the crystal and facilitates the detection of weak optical property modulation signals. In addition, we show that BSO is a potential candidate detector material. When biased at 3500 V, it has comparable modulation signal sensitivity as CdTe biased at 1000V, but with higher resistivity (lower noise), larger 511 keV photon attenuation coefficient, lower price, better crystal surface finish quality, and less toxicity. By studying the dependence of modulation signal amplitude on crystal bias voltage, we show that the modulation signal amplitude (induced by both UV laser diode and Ge-68 source) is linearly proportional to crystal bias voltage with a linear fit R factor of around 0.95. The modulation signal amplitude induced by UV laser diode irradiation increases from 0% to 2% (normalized to the average signal level) for both CdTe and BSO under crystal bias voltage from 0V to 3500V. The modulation signal amplitude induced by Ge-68 irradiation increases from 0% to 12% for CdTe under crystal bias voltage from 0V to 1500 V, and increases from 0% to 10% for BSO under crystal bias voltage from 0V to 3500 V. Therefore the electron multiplication effect (with high crystal bias) shows promise to significantly boost the modulation signal amplitude with the ultimate goal to achieve single 511 keV photon detection.