Low-power phototransceiver arrays with vertically integratedresonant-cavity LEDs and heterostructure phototransistors

Low-power phototransceivers and phototransceiver arrays, with vertically integrated high-gain heterojunction phototransistors (HPTs) and resonant-cavity light-emitting diodes (RCLEDs), are demonstrated. A tunnel junction was used as a low resistance interconnect between the two devices. The input and output wavelengths are 0.63-0.85 and 0.98 μm, respectively. The phototransceiver exhibits an optical gain of 13 dB and power dissipation of 400 μW for an input power of 5 μW. The phototransceiver arrays demonstrate good uniformity, low optical crosstalk, and imaging capabilities     

Parallel optical interconnection for uncoded data transmission with1 Gb/s-per-channel capacity, high dynamic range, and low powerconsumption

The design, realization, and characterization of a multichannel dc-coupled ECL-voltage compatible parallel optical interconnection with a bit rate of up to 1 Gb/s-per-channel is reported. The transmitter module consists of an array of laser diodes with low threshold currents and the 50 Ω matching network, the receiver module of a photo diode array and an amplifier array. All the opto-electronic and electronic components are fabricated as arrays with a pitch of 250 μm. The total power consumption is 110 mW per channel, For a BER <10¹⁴ the dynamic range is 15 dB for a bit rate per channel of 200 Mb/s, 13 dB for 630 Mb/s, and 8 dB for 1 Gb/s. The channel crosstalk is below -48 dB (electrical). The size of the opto-electronic parts (12 channels, without electrical connectors) is only 10 mm (length)×5 mm (width)×4 mm (height)     

Low-threshold, highly reliable 630 nm-band AlGaIP visible laserdiodes with AlInP buried waveguide

Low-threshold, highly reliable 630 nm-band AlGaInP visible laser diodes have been developed by employing a low-loss optical waveguide buried in the AlInP layer. A low-threshold current of 19 mA at 25°C is obtained with a cavity length of 310 μm. This current is the lowest value for 630 nm-band AlGaInP visible laser diodes, to our knowledge. Our AlInP-buried laser diodes with a cavity length of 500 μm operated over 7000 h without significant degradation at 60°C and 5 mW     

Description and evaluation of the FAST-Net smart pixel-basedoptical interconnection prototype

The design, packaging approach, and experimental evaluation of the free-space accelerator for switching terabit networks (FAST-Net) smart-pixel-based optical interconnection prototype are described. FAST-Net is a high-throughput data-switching concept that uses a reflective optical system to globally interconnect a multichip array of smart pixel devices. The three-dimensional optical system links each chip directly to every other with a dedicated bidirectional parallel data path. in the experiments, several prototype smart-pixel devices were packaged on a common multichip module (MCM) with interchip registration accuracies of 5-10 μm. The smart-pixel arrays (SPAs) consist of clusters of oxide-confined vertical-cavity surface-emitting lasers and photodetectors that are solder bump-bonded to Si integrated circuits. The optoelectronic elements are arranged within each cluster on a checkerboard pattern with 125-μm pitch. The experimental global optical interconnection module consists of a mirror and lens array that are precisely aligned to achieve the required interchip parallel connections between up to 16 SPAs. Five prototype SPAs were placed on the MCM to allow the evaluation of a variety of interchip links. Measurements verified the global link pattern across several devices on the MCM with high optical resolution and registration. No crosstalk between adjacent channels was observed after alignment. The I/O density and efficiency results suggest that a multi-terabit switch module that incorporates global optical interconnection to overcome conventional interconnection bottlenecks is feasible     

Gigabit-per-second cryogenic optical link using optimizedlow-temperature AlGaAs-GaAs vertical-cavity surface-emitting lasers

We describe the design of GaAs-AlGaAs vertical-cavity surface-emitting lasers (VCSELs) that are optimized for operation at very low temperatures and the experimental demonstration of a free-space optical interconnect for cryogenic electronic systems using a VCSEL. We demonstrate high-speed modulation of the optical link at a data rate of up to 2 Gb/s at 77 K, with a very low bit-error rate of <10^-13 , and thermally stable operation is achieved over a wide range of cryogenic temperatures without laser bias current compensation. Cryogenic VCSELs with excellent lasing characteristics have been achieved over the entire temperature range from 150 K to 6 K, including high output power (22 mW), high power-conversion efficiency (32%), high slope efficiency (~100%), low threshold voltage (1.75 V) and current (1.7 mA), as well as a high-modulation bandwidth (12 GHz) for a 16 μm diameter device at 80 K     

Channel cross-coupling in a polymer-based single-mode bus array

In this paper, a crosstalk model is developed to study the packing density and interconnect distance limitations of an optical interconnect system employing polymer-based single-mode bus arrays. The upper limit of channel packing density (1250 channels/cm at interconnect distance of 5 cm) is determined for the first time using the crosstalk model, in which channel cross-coupling among an infinite number of waveguides is considered. Computer simulations are provided together with the proven experimental results. It is shown that there is a threshold of channel separation due to channel cross-coupling, which results in a tradeoff between channel packing density and interconnect distance. Waveguide dimension closer to the cutoff boundary of second mode (E₁₂ ^x) is preferred for an optimum design     

InxGa1-xAs-AlyGa1-yAs-GaAs strained-layer quantum-well heterostructure circular ringlasers

The growth, processing, and optical characterization of a single Y-junction In_xGa_1-xAs-Al_yGa_1-y As-GaAs strained-layer quantum-well heterostructure circular ring laser (6 μm width, 11~251 μm outer radius) are described. The circular ring lasers have been grown by metalorganic chemical vapor deposition, etched by SiCl₄ reactive ion etching, and planarized by polyimide. The dependences of laser threshold current density and peak emission wavelength (950~1015 nm) on outer radius are presented. The emission spectra show that the circular ring lasers lase mainly in high-order whispering gallery modes, with smaller outer radius ring lasers operating in low-order whispering gallery modes     

15 Gb/s multichannel optical interconnect laser array transmitteroperating at λ=1.3 μm

We have fabricated and measured detailed bit error rate experiments on a 12 channel optical interconnect transmitter operating at rates up to 1.25 Gb/s per channel, using InGaAsP/InP λ=1.3 μm lasers. The lasers are highly uniform, the channel crosstalk is less than 1 dB, and the mode selective losses are low (<1 dB). This transmitter has been demonstrated in an architecture which would allow the transmission of 120 channels of 100-Mb/s uncompressed video signals     

Power minimization and technology comparisons for digitalfree-space optoelectronic interconnections

This paper investigates the design optimization of digital free-space optoelectronic interconnections with a specific goal of minimizing the power dissipation of the overall link, and maximizing the interconnect density. To this end, we discuss a method of minimizing the total power dissipation of an interconnect link at a given bit rate. We examine the impact on the link performance of two competing transmitter technologies, vertical cavity surface emitting lasers (VCSELs) and multiple quantum-well (MQW) modulators and their associated driver-receiver circuits including complementary metal-oxide-semiconductor (CMOS) and bipolar transmitter driver circuits, and p-n junction photodetectors with multistage transimpedance receiver circuits. We use the operating bit-rate and on-chip power dissipation as the main performance measures. Presently, at high bit rates (>800 Mb/s), optimized links based on VCSELs and MQW modulators are comparable in terms of power dissipation. At low bit rates, the VCSEL threshold power dominates. In systems with high bit rates and/or high fan-out, a high slope efficiency is more important for a VCSEL than a low threshold current. The transmitter driver circuit is an important component in a link design, and it dissipates about the same amount of power as that of the transmitter itself. Scaling the CMOS technology from 0.5 μm down to 0.1 μm brings a 50% improvement in the maximum operating bit rate, which is around 4 Gb/s with 0.1 μm CMOS driver and receiver circuits. Transmitter driver circuits implemented with bipolar technology support a much higher operating bandwidth than CMOS technology; they dissipate, however, about twice the electrical power. An aggregate bandwidth in excess of 1 Tb/s-cm² can be achieved in an optimized free-space optical interconnect system using either VCSELs or MQW modulators as its transmitters     

高密度封装中互连结构差分串扰建模与分析

针对传统模型存在较大分析误差的问题,提出高密度封装中互连结构差分串扰建模与分析.在对互连结构差分传输线耦合关系分析的基础上,建立了四线差分结构串扰模型.运用该模型对互连结构差分串扰中的电阻、电容以及电感进行等效分析,解决高密度封装中互连结构差分串扰问题.经试验证明,此次建立模型平均误差为0.042,满足抑制高密度封装中...     

Integrated four-wavelength DFB laser array with 10 Gb/s speed and 5nm continuous tuning range

A 1.5 μm, four-wavelength DFB (distributed feedback) laser array operating at a speed of 10 Gb/s and with a continuous tuning range of 5 nm for each laser has been demonstrated. An adjacent channel electrical crosstalk penalty of 0.6 dB was measured, and the thermal tuning limitation was identified. Each laser could be modulated at a speed of 10 Gb/s with moderate electrical crosstalk penalty (~0.6 dB) from the adjacent laser. The high-speed performance was not degraded by thermal tuning up to 3.2 nm     

Accurate determination of waveguide-fed p-i-n photodiode absorption

Experimental and theoretical determinations of the absorption of a waveguide fed GaInAs photodiode are presented. The absorption is determined as a function of the propagation length using μ-p-i-n diodes regularly spaced along the GaInAs absorbing layer. The detector absorption is as high as 2060 dB/cm. However, for propagation lengths longer than ~200 μm it falls to about 120 dB/cm. The results are analyzed using two different approaches. The first consists in determining the eigenmodes of both the passive waveguide and the detector/waveguide structure. The second is the beam propagation method (BPM). Both methods demonstrate that the absorption curve can be fully explained by the existence of two modes, of which the one with the lowest absorption is induced by the presence of an undoped InP buffer layer. Both eigenmode decomposition and BPM are in quantitative agreement with the experimental data     

Design optimization of one-turn helix: a novel compliant off-chip interconnect

As the rapid advances in integrated circuit (IC) design and fabrication continue to challenge and push the electronic packaging technology, in terms of fine pitch, high performance, low cost, and good reliability, compliant interconnects show great potential for next-generation packaging. One-turn helix (OTH) interconnect, a compliant chip-to-next level substrate or off-chip interconnect, is proposed in this work, and this interconnect can facilitate wafer-level probing as well as wafer-level packaging without the need for an underfill. The interconnect has high mechanical compliance in the three orthogonal directions, and can accommodate the differential displacement induced by the coefficient of thermal expansion (CTE) mismatch between the silicon die and an organic substrate. The fabrication of the helix interconnect is similar to the standard IC fabrication, and the wafer-level packaging makes it cost effective. In this paper, we report the fabrication of an area array of helix interconnects on a silicon wafer. Also, we have studied the effect of interconnect geometry parameters on its mechanical compliance and electrical parasitics. Thinner and narrower arcuate beams with larger radius and taller post are found to have better mechanical compliance. However, it is found that structures with excellent mechanical compliance cannot have good electrical performance. Therefore, a trade off is needed for the design of OTH interconnect. An optimization technique using response surface methodology has been applied to select the optimal structure parameters. The optimal compliant OTH interconnect will have a total standoff height of about 100 /spl mu/m, a radius of about 35 /spl mu/m and a cross section area of about 430 /spl mu/m/sup 2/.     

Monolithic serial InGaAs-GaAs-AlGaAs laser diode arrays

Top-contact monolithic serially-biased InGaAs-GaAs-AlGaAs (λ~0.93 μm) broad area strained-layer quantum well laser arrays have been fabricated on a semi-insulating GaAs substrate. The laser array consists of four individual laser diodes and operates up to 2.8 W at 3.6 A (supply limited) per uncoated facet under pulsed conditions (15 kHz, 2 μs). The threshold current is ~0.5 A, and the peak slope efficiency and the peak electrical-to-optical conversion efficiency of an individual laser element are ~0.53 W/A and 14%, respectively. The near-field intensity distribution is shown to be broad enough to fill the entire active region under the p-metal stripe (125 μm) of the individual laser diodes at high current levels     

Vertical integration of a GaAs/AlGaAs quantum-well laser and along-wavelength quantum-well infra-red photodetector

A short-wavelength (~0.8 μm) GaAs/AlGaAs graded-index separate-confinement heterostructure quantum-well laser has been monolithically integrated with a long-wavelength (~8 μm) GaAs/AlGaAs multiple-quantum-well infra-red photodetector on a semi-insulating GaAs substrate by molecular beam epitaxy. The vertical integration method is used and the combined structure is a pinin structure. Both the laser and detector exhibit excellent characteristics. At room temperature, the ridge waveguide laser has an extremely low threshold current of 25 mA and a differential quantum efficiency above 65% with a stripe width of 20 μm. The quantum-well detector has a peak response at 8 μm and a responsivity of 0.7 A/W     

Wavelength Sensing With Subpicometer Resolution Using Ultrahigh Order Modes

The ultrahigh order modes of a symmetrical metal-cladding optical waveguide, which exhibit strong wavelength dispersion characteristics, are used to track small wavelength changes of the light output of laser diodes. In the case of free-space coupling, the wavelength shift is transformed into an intensity variation of the light reflected on a surface of the waveguide. The sensitivity considering the divergence of the incident light and the thickness of the upper cladding is analyzed. A wavelength resolution of 0.5 pm at a center wavelength of 859.8 nm is demonstrated experimentally     

Analysis of optical crosstalk in coherence multiplexed systemsemploying a short coherence laser diode with arbitrary power spectrum

It is shown that the crosstalk level in coherence multiplexed systems is closely dependent on the profile of the emission spectrum of the laser diodes used. The cases of Gaussian, Lorentzian, and cos² power spectra are considered. The results demonstrate that crosstalk may very by several tens of decibels when using laser diodes operating with the same coherence length but exhibiting different spectral profiles. Illustrations in the area of optical communications are given for superluminescent diodes and multimode laser diodes with a Lorentzian and a cos² power spectrum. Results indicate that Gaussian sources are preferable     

A study of laser emission wavelength variations in 1.5 μmInGaAsP/InP BRS laser diodes: theoretical model and experiment

This is a study of the dependence of the emission wavelength on the cavity length observed in laser diodes with InGaAsP/InP buried ridge stripe (BRS) structure. Theoretical calculations were made taking into account the variation of the threshold gain due to the influence of the cavity length on the total optical loss and, therefore, on the level of the carrier density at the threshold. This density affects the spectral position of the gain peak thus creating the regular dependence of the emission wavelength on the cavity length. The band-shrinkage effect and the free carrier absorption effect are also considered. In samples covering the spectral range of 1.46-1.53 μm, the calculated and experimental results agree satisfactorily     

An eight-channel add-drop filter using vertically coupled microringresonators over a cross grid

An eight-channel add-drop cross-grid vertically coupled microring resonator (VCMRR) filter is proposed and demonstrated. The cross grid comprises a grid-like array of buried channel waveguides which perpendicularly cross through each other, VCMRRs at each of the cross-grid nodes serve as the wavelength selective add-drop filters. Measured crosstalk levels at the crossings are typically less than -30 dB. Rings with a nominal radius of 10 μm are used to achieve a free-spectral range of 20 nm and optical bandwidths of 1 nm, while changes of the radii in increments of 50 nm lead to a nominal channel spacing of 5.7 nm     

An InGaAs/GaAs MQW optical switch based on field-induced waveguides

A novel optical waveguide switch containing InGaAs/GaAs multiple-quantum wells (MQW) is proposed. In this structure, a large field-induced refractive index increase (0.1%) due to the quantum-confined Stark effect (QCSE) is utilized to generate electrically controllable waveguides. Switching operation of a first fabricated device has been investigated at wavelengths of about 1 μm. A crosstalk ratio of -18.8 dB and an extinction ratio of 20.9 dB was achieved at a reverse voltage of -7 V. Within an operational wavelength region of 9 nm, crosstalk was found to be less than -13 dB for both switching conditions. Further, the proposed switch structure seems to be well suited for monolithic integration with laser diodes and exhibits the potential for high-speed operation