Discovery Semiconductors (United States)

We report integrated coherent optical receivers designed specifically for RF Photonics applications. These receivers may be implemented in either single- or dual-polarization (DP) systems which utilize I/Q (in-phase, quadrature) phase modulation. The integrated receivers incorporate a monolithic 90 degree optical hybrid followed by eight high power-handling InGaAs photodiodes. Linear operation to +27 dBm of total optical input power, 20 mA photocurrent per diode, output third-order intercept (OIP3) > 40 dBm, third-order harmonic distortion 4 GHz is presented. Such photoreceiver power-handling and linearity is required to optimize the photonic system spurious free dynamic range (SFDR), noise figure (NF) and link gain.

As the current handling - bandwidth product of a single photodiode comprised of lattice matched In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/InP material reaches a practical limit, we explore new lattice mismatched material system of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.72</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.28</sub> As/InAsP/InP as a path-forward technology to increase this key parameter.

We report a large-area quad photoreceiver (2 times 2 array) having an equivalent input current noise density of <3.2 pA/radicHz per quadrant up to a 3-dB bandwidth of ~20 MHz. The low-noise photoreceiver performance is enabled by a 1-mm diameter quad p-i-n InGaAs photodiode having 2.5-pF capacitance per quadrant at 5-V reverse bias.

We have demonstrated 22 GHz bandwidth dual photodiodes having high amplitude & phase linearity as well as high power handling in both CW and pulsed operation. The two photodiodes are also well-matched in linear as well as nonlinear performance.

We have manufactured a miniaturized, light weight, high data rate, optical coherent receiver system with weight less than 37 lbs and power consumption less than 70 W. By using a coherent heterodyne method, the bench-top receiver has achieved a link rate of 2.5 Gb/s at a Bit Error Ratio of 1e-9 with a sensitivity of -40 dBm. This receiver could be used as a critical component of a free-space optical link, where the large distances and power limitations necessitate a high sensitivity. Optical communications links provide tremendous bandwidth and can achieve data rates two orders of magnitude higher that an RF communications link. Potential mass and power savings that go with using an optical system over an RF, along with the significantly higher bandwidth and reduced susceptibility to interference make them very attractive in the further development of the space environment.

Heterodyne detection of 10-Gb/s nonreturn-to-zero (NRZ) on-off keying and NRZ differential phase-shift keying is demonstrated. The noise performance of the heterodyne receiver with and without the use of an optical preamplifier is experimentally investigated

We report -31 dBm receiver sensitivity for heterodyne detection of 10 Gb/s OOK without using an optical pre-amplifier. These are the highest receiver sensitivities for unpreamplified heterodyne 10 Gb/s detection. We also show the development of a coherent heterodyne balanced fiber optic receiver. The receiver incorporates a DFB or a solid state laser local oscillator, balanced PIN photodiodes, RF post amplifier, automatic frequency control (AFC), phase locked loop (PLL), polarization control, and precision power supplies in a small instrument case. We will show shot noise limited detection of amplitude modulated signals, cancellation of laser RIN noise, performance improvement using balanced detection at 2.5 and 10 Gb/s, and IF linewidth reduction.

We have manufactured rad-hard, InGaAs photodiodes using our proprietary Dual-Depletion Region (DDR) technology with bandwidths exceeding 10 GHz. The devices demonstrate high reliability and superior RF performance, thus, making them ideal for deployment in space for applications such as LIDAR and optical intersatellite links. The responsivity at 1064 nm is >0.45 A/W with optical return loss of 40 dB. The photodiodes have broad wavelength coverage from 800 nm to 1700 nm, and thus can be used at several wavelengths such as 850 nm, 1064 nm, 1310 nm, 1550 nm, and 1620 nm. The InGaAs photodiodes exhibit very low Polarization Dependence Loss (PDL) of 0.05 dB typical to 0.1 dB maximum. The typical Failure-in-time (FIT) values of these photodiodes are 0.011 and 15.384 at 25°C and 75°C respectively. FIT is defined as the number of failures per billion hours of operation. The photodiodes have been tested for different radiation tests such as 50 kRad gamma (Co 60) and protons with a fluence of 3 x 10¹¹ p/cm², and have passed typical qualification levels of random vibration.

The realization of monolithic optical interconnects by integration of III-V materials with conventional Si circuitry has long been hindered by materials incompatibilities (i.e. lattice mismatch and heterovalent interface) and practical processing constraints. We have demonstrated successful integration of hetero-epitaxially grown InGaAs/Si diodes with an n-well CMOS process on (001) Si offcut 6 degrees towards [110]. The In0.15Ga0.85As/InxGa1- xAs/GaAs/Si diodes were grown by atmospheric pressure organo-metallic chemical vapor deposition (OMCVD) and features a room temperature R0A product of 20,000 ohm-cm2. No degradation of PMOS or NMOS transistor characteristics was detected upon integration of the III-V devices. Further improvement of III-V/Si device characteristics are anticipated in future efforts by incorporating relaxed, compositionally- graded Ge/GexSi1-x/Si with low threading dislocation densities (approximately 2 X 106/cm2) to bridge the gap in lattice constants between Si and GaAs. Recent progress towards this end includes the suppression of antiphase disorder during GaAs growth on Ge/GexSi1-x/Si by OMCVD and strong room temperature photoluminescence from In0.20Ga0.80As QW test structures on GaAs/GexSi1- x/Si at 920 nm.

Microsatellites are fast becoming important scientific and commercial realities. However, most satellites that fall in this class are still fairly large (∼50 Kg, ∼0.5 m). One of the major obstacles in reducing these parameters further is the lack of integration of all the satellite’s functions. Normally, most satellites are constructed from physically separate sub-systems, each of which is composed of some combination of circuit boards and components. This partitioned approach wastes valuable space and weight directly by increasing demands on structure and power resources of the satellite (Payne 1992 and Priedhorsky 1989). This is the problem that Discovery Semiconductors wishes to address. We propose to design and construct an entirely integrated satellite (INT-SAT) that contains all the electronics of a fully functional satellite condensed into one module. This module, which would be very compact and light-weight, would be constructed from specially designed 4 to 8 inches silicon wafer size chips. Through the creative use of semiconductor processing and proprietary crystal growth techniques, all the components required for a state of the art satellite can be implemented on the silicon chips. The INT-SAT’s condensed electronics module will be compact and light weight, and will occupy only 200 cubic centimeters, and will weigh less than 500 grams. Since the electronics are the heart of almost every mission, this integration will produce drastic savings in weight and size, enabling the reduction of satellite mass to well below 10 Kg.