Dynamic Extinction Ratio Research Articles

Low Chirp EMLs Fabricated By Combining SAG and Double Stack Active Layer Techniques

We present electroabsorption modulators integrated with distributed feedback lasers (EMLs) fabricated by a simple method, which combines the advantages of the selective area growth and double stack active layer techniques. The obtained EML device has a threshold current as low as 16 mA and optical power of larger than 10 mW at 85 mA laser current. Quite low chirp parameter of the fabricated EMLs is obtained. Negative chirp parameters can be obtained at only about 0.5 V reverse bias voltage. Open eye diagrams are demonstrated from the EML at both 10 and 20 Gb/s modulations with the driving voltage of only 0.65 V while securing high dynamic extinction ratio. The exhibited performance makes our device a very promising candidate as a simple light source in long distance and cost sensitive applications.

AlGaInAs EML having high extinction ratios fabricated by identical epitaxial layer technique

AlGaInAs electroabsorption-modulated lasers (EMLs) fabricated by identical epitaxial layer technique are demonstrated. The EML device shows an infinite characteristic temperature when the temperature ranges from 20 oC to 30 oC. The integrated modulator has static extinction ratios of larger than 20 dB at a reverse bias voltage of −2 V. The small signal modulation bandwidth of the modulator is larger than 11 GHz. At 10 Gb/s data modulation, the dynamic extinction ratio is about 9.5 dB in a back to back test configuration. Because only a simple fabrication procedure is needed, our EMLs are promising low cost light sources for optical fiber transmission applications.

RF and Thermal Considerations of a Flip-Chip Integrated 40+ Gb/s Silicon Photonic Electro-Optic Transmitter

We demonstrate a flip-chip integrated electro-optic transmitter incorporating a high-swing CMOS driver and silicon photonic Mach–Zehnder modulator, and discuss the RF and thermal characteristics of the assembly. The transmitter showed a dynamic extinction ratio of 8 dB, which is the highest to date for 40+ Gb/s-class transmitters using CMOS drivers with silicon modulators. The input reflection coefficient of the module was mostly determined by the input electrical lines, solder bumps, and driver, while the electro-optic transfer function was mostly set by the Mach–Zehnder modulator. Despite the high power consumption of the driver and modulator (553 mW) and the close proximity between the electronic and photonic dies, the thermal simulations show that heat can be efficiently sunk from the bottom side of the silicon photonic die.

Fast Extinction Ratio Enhancement With a Graphene-Based Device on $1.5~\mu \text{m}$ Optical Signals

Ability of fast intensity discrimination provided by a graphene-based saturable absorber device is demonstrated in the perspective of all-optical signal processing in $1.5~\mu \text{m}$ wavelength range. The dynamic extinction ratio enhancement is measured as more than 3 dB. It is argued that, the device performances are promising enough to be tested further in an efficient all-optical module to reduce crosstalk or intensity noise in high rate signals.

Flip-chip integrated silicon Mach-Zehnder modulator with a 28nm fully depleted silicon-on-insulator CMOS driver.

We present a silicon electro-optic transmitter consisting of a 28nm ultra-thin body and buried oxide fully depleted silicon-on-insulator (UTBB FD-SOI) CMOS driver flip-chip integrated onto a Mach-Zehnder modulator. The Mach-Zehnder silicon optical modulator was optimized to have a 3dB bandwidth of around 25 GHz at -1V bias and a 50 Ω impedance. The UTBB FD-SOI CMOS driver provided a large output voltage swing around 5 Vpp to enable a high dynamic extinction ratio and a low device insertion loss. At 44 Gbps, the transmitter achieved a high extinction ratio of 6.4 dB at the modulator quadrature operation point. This result shows open eye diagrams at the highest bit rates and with the largest extinction ratios for silicon electro-optic transmitter using a CMOS driver.

Over 67 GHz Bandwidth and 1.5 V Vπ InP-Based Optical IQ Modulator With n-i-p-n Heterostructure

We report novel high-bandwidth InP-based Mach–Zehnder modulator and in-phase/quadrature (IQ) modulators that we realized by combining an n-i-p-n heterostructure and a capacitively loaded traveling wave electrode. The extremely low electrical and optical loss structure enhances the 3-dB electro-optic bandwidth of over 67 GHz without degrading other properties such as driving voltage and optical loss. The modulator also exhibits a static extinction ratio of over 24 dB with a V π of less than 1.5 V for the entire C-band. Furthermore, we demonstrate the first 120-Gbaud rate IQ modulation without optical pre equalization, and 100-Gb/s non-return-to-zero on-off keying modulation with a dynamic extinction ratio of over 10 dB.

Hybrid III-V Silicon Photonic Integrated Circuits for Optical Communication Applications

This paper summarizes recent advances of integrated hybrid InP/silicon-on-insulator lasers and transmitters based on a wafer bonding technique. First, directly modulated hybrid III-V/Si tunable lasers integrated with an external ring resonator filter are demonstrated, enabling the improvement of the dynamic extinction ratio. An efficient tunable filter is then reported mainly for access applications. Finally, results on integrated distributed feedback laser and electro-absorption modulator at 1.3 μm are presented, showing the capability of operation up to $\text{32}\,\text{Gb}/\text{s}$ . Meanwhile, an integrated tunable laser with an electro-absorption modulator is demonstrated at 1.5 μm, exhibiting excellent bit-error-rate performance at $\text{10}\,\text{Gb}\text{/s}$ .

Demonstration of Silicon Photonics Push–Pull Modulators Designed for Manufacturability

We demonstrate a single-drive push–pull silicon photonics modulator copackaged with a linear driver upon ON–OFF keying and binary phase-shift keying modulation formats at a speed of 28 Gb/s. The modulator was designed for manufacturability by crossing the signal radio frequency lines and the optical waveguides in the middle of the device, thereby obtaining a dc extinction ratio of up to 40 dB and a dynamic extinction ratio of 12 dB over the whole $C$ -band.

A Photonic-Integrated Transceiver for Data Readout Systems

This study presents a photonic integrated transceiver for application in a data readout unit of a sensor network. The device was realized in a generic InP-based technology. The circuit uses an asymmetric coupler and a PIN photodiode for input signal detection and a Mach–Zehnder amplitude modulator for encoding of output sensor data. Small-signal modulation bandwidth of 11.1 GHz was measured, eye-diagrams with a dynamic extinction ratio of 11 dB were recorded, and transmission of a 10-Gb/s signal over 25 km of SMF fiber with bit error rate below 10−10 was achieved.

High dynamic extinction ratio and pulse modulation of optical signals

The use of a saturable absorber for increasing the extinction ratio at external modulation of optical signals is considered. An erbium doped fiber was used as the saturable absorber in the experiments. A considerable increase in the static extinction ratio (up to 50 dB) was demonstrated. A rather long erbium doped fiber relaxation time (about 10 ms) was a limiting factor in the case of pulse modulation. Ways of overcoming this drawback are discussed.

Multi‐wavelength channel 1.5 μm and 10 Gb/s EMBH DFB‐LD array module using SAG technology

A multi-wavelength channel distributed feedback laser diode array (DFB-LDA) for the low-cost and low-power consumption applications of WDM-based datacentre networks is reported. The gain spectrum and lasing wavelength of each channel are controlled by using selective area growth and E-beam lithography techniques, respectively. To reduce the operation current and parasitic capacitance of the proposed array, an etched mesa buried hetero-structure (EMBH) is introduced. From this study, it was found that an eight-channel 300 μm long λ/4-shifted DFB-LDA has a threshold current of 10 ± 1.5 mA and a side mode suppression ratio of over 50 dB at a current of 50 mA for all channels. A transmission test for this LDA showed a clear eye opening with a dynamic extinction ratio of over 4.5 dB at 10 Gb/s after a 2 km transmission.

56 Gb/s Germanium Waveguide Electro-Absorption Modulator

We report a Germanium waveguide electro-absorption modulator with electro-optic bandwidth substantially beyond 50 GHz. The device is implemented in a fully integrated Si photonics platform on 200 mm silicon-on-insulator wafers with 220 nm top Si thickness. Wide open eye diagrams are demonstrated at 1610 nm operation wavelength for nonreturn-to-zero on-off keying (NRZ-OOK) modulation at data rates as high as 56 Gb/s. Dynamic extinction ratios up to 3.3 dB are obtained by applying drive voltages of 2 V peak-to-peak, along with an optical insertion loss below 5.5 dB. The device has a low junction capacitance of just 12.8 fF, resulting in 12.8 fJ/bit of dynamic and ∼1.2 mW of static power consumption in typical operating conditions. Wafer-scale performance data are presented and confirm the manufacturability of the device. The demonstrated modulator shows great potential for realizing high-density and low-power silicon photonic transceivers targeting short-reach optical interconnects at serial data rates of 56 Gb/s and beyond.

1.5-μm and 10-Gb s−1 etched mesa buried heterostructure DFB-LD for datacenter networks

We report a 1.5 μm and 10 Gb s−1 etched mesa buried heterostructure λ/4-shifted distributed feedback laser diode (DFB-LD) for the low-cost application of WDM–based datacenter networks. To reduce the threshold current and improve the modulation bandwidth in a conventional p-/n-/p-InP current blocking structure, a thin undoped-InP (u-InP) layer was inserted between the side walls of the active region and the p-InP layer (i.e., a u-/p-/n-/p-InP structure), and the region containing the active region and the current blocking structures was etched in a mesa form (i.e., an etched mesa). From this work, it was found that a 300 μm long anti-reflection (AR)-AR DFB-LD with a mesa width of 8 μm is reduced by about 25% while a side mode suppression ratio is >50 dB and a 3 dB bandwidth is >10 GHz at a current of 40 mA; in addition, it shows a clear eye-opening with a dynamic extinction ratio of >4.5 dB at 10 Gb s−1, and a power penalty of <1 dB after a 2 km transmission.

Transmitter Optical Subassembly Using a Polarization Beam Combiner for 100 Gbit/s Ethernet over 40-km Transmission

A transmitter optical subassembly (TOSA) has been developed for a 100-Gbit/s Ethernet system for a long optical transmission distance over a 40-km single-mode fiber (SMF). To obtain a high optical output power and a high dynamic extinction ratio, the TOSA consists of two two-channel distributed feedback laser diode array chips integrated with electro-absorption modulators (EADFB laser array chips) with a 2 × 1 multimode interference (MMI) optical coupler and a polarization beam combiner for wavelength multiplexing. The TOSA is 8.7 mm × 28.7 mm × 6.5 mm including an LC-type receptacle. The TOSA has a twin collimator path for two EADFB laser array chips. The wavelength multiplexer consists of a mirror, a half-wavelength plate, and a polarization beam combiner. The TOSA could improve the optical output power by around 2 dB compared with a TOSA with a four-channel EADFB laser array chip and a 4 × 1 MMI optical coupler. An optical modulation amplitude of over 0.5 dBm and a mask margin exceeding 21% were obtained for each lane when all lanes were operated simultaneously with an EA modulator driving voltage of 1.5 V at a bit rate of 25.78125 Gbit/s, which fully satisfies the 100GBASE-ER4 specifications. We demonstrated error-free operation for an SMF transmission of over 40 km. Moreover, we confirmed that the TOSA was capable of error-free SMF transmission over 60 km with a power penalty of less than 1.4 dB.

Fabrication of 32Gb/s Electroabsorption Modulated Distributed Feedback Lasers by Selective Area Growth Technology**Supported by the National High-Technology Research and Development Program of China under Grant Nos 2011AA010303 and 2012AA012203, the National Basic Research Program of China under Grant No 2011CB301702, and the National Natural Science Foundation of China under Grant Nos 61321063 and 6132010601.

A 32 Gb/s monolithically integrated electroabsorption modulated laser is fabricated by selective area growth technology. The threshold current of the device is below 13 mA. The output power exceeds 10 mW at 0 V bias when the injection current of the distributed feedback laser is 100 mA at 25°C. The side mode suppression ratio is over 50 dB. A 32Gb/s eye diagram is measured with a 3.5Vpp nonreturn-to-zero pseudorandom modulation signal at −2.3 V bias. A clearly opening eyediagram with a dynamic extinction ratio of 8.01 dB is obtained.

Observation of Dynamic Extinction Ratio and Bit Error Rate Degradation Due to Thermal Effects in Integrated Modulators

We experimentally demonstrate how the thermal crosstalk between active and passive components limits the performance of integrated Mach–Zehnder (MZ) modulators operating in the radiofrequency regime. To evaluate the role of the distance between active and passive components, the MZs are placed at different distances with respect to a semiconductor optical amplifier that represents the heat source. The thermal crosstalk is quantified by measuring the effects on the electro–optical response of MZ modulators considered as the test structure. Both extinction ratio and bit error rate degradation are measured. The proposed investigation allows the introduction of design rules, based on the minimum distance between components to ultimately avoid unwanted thermal effects. According to the result provided by our analysis, we also show how the ER degradation can be recovered.

High-efficiency Si optical modulator using Cu travelling-wave electrode.

We demonstrate a high-efficiency and CMOS-compatible silicon Mach-Zehnder Interferometer (MZI) optical modulator with Cu traveling-wave electrode and doping compensation. The measured electro-optic bandwidth at Vbias = -5 V is above 30 GHz when it is operated at 1550 nm. At a data rate of 50 Gbps, the dynamic extinction ratio is more than 7 dB. The phase shifter is composed of a 3 mm-long reverse-biased PN junction with modulation efficiency (Vπ·Lπ) of ~18.5 V·mm. Such a Cu-photonics technology provides an attractive potentiality for integration development of silicon photonics and CMOS circuits on SOI wafer in the future.

A &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;\(10 \times 10\) &lt;/tex-math&gt;&lt;/inline-formula&gt;-Gb/s DFB-LD Array Integrated With PLC-Based AWG for 100-Gb/s Transmission

We describe a hybrid integration module of a 10 × 10-Gb/s distributed feedback laser diode array (DFB-LDA) and a planar light-wave circuit-based arrayed waveguide grating (AWG). For fabrication of the DFB-LDA, we adopted a selective area growth technique to tailor the channel gain properly, and E-beam lithography to accurately control the channel lasing wavelength and grating phase. For implementation of the AWG, we introduced a 2%-Δ structure to reduce the coupling loss between the AWG and DFB-LDA, and designed the tapered and parabolic waveguides at the junctions of the free propagation regions to widen the spectral passband width (i.e., a -1-dB spectral width of 3 nm). The developed module shows a side-mode suppression ratio of >45 dB, a clear eye opening with a dynamic extinction ratio of >4.4 dB at 10 Gb/s, and a power penalty of <;1.5 dB after a 2-km transmission for all channels.

A 10 × 10 Gb/s DFB laser diode array fabricated using a SAG technique.

We present a ten-channel distributed feedback laser diode array (DFB-LDA) developed for the transmission of 100-Gb/s (10 × 10 Gb/s) signals separated by an 8 nm wavelength grid at a center wavelength of 1.55 μm. For the fabrication of this type of laser array, a selective area growth (SAG) technique, electron-beam lithography, and a reverse-mesa ridge waveguide LD processing technique were adopted to offer a tailored gain spectrum to each channel, providing both accurate lasing-wavelength control and excellent single-mode yield over all channels, and reducing the fabrication cost and electrical and thermal resistances. To evaluate the operational performance of the fabricated chip systematically, we also developed a sub-assembly module containing a ten-channel λ/4-shifted DFB-LDA, ten matching resistors, flexible printed circuit board (FPCB) wiring, and a thermistor on a metal optical bench. The static and dynamic properties of all channels of the fabricated array are examined in this paper. The developed sub-assembly module shows a side-mode suppression ratio (SMSR) of > 50 dB, a modulation bandwidth of > 10 GHz, and a clear eye-opening before and after a 2-km transmission with dynamic extinction ratio of > 5 dB.

Quantum dash based directly modulated lasers for long‐reach access networks

An innovative 10 Gbit/s single mode optical transmitter with the capacity of error-free transmission is demonstrated in the range of 0–100 km with constant biasing conditions by using a quantum dash directly modulated laser. A commercially available etalon filter is used as a passive optical filter to achieve penalty-free transmission with a dynamic extinction ratio >6 dB over a large range of fibre spans.