Patent number 8598673 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Quad photoreceivers typically include a 2.times.2 array of p-i-n photodiodes with each photodiode followed by a transimpedance amplifier (TIA). Such quad photoreceivers are used in many applications, such as long baseline interferometry, free-space optical communication, missile guidance, and biomedical imaging and spectroscopy, which rely on free-space optical propagation with position and/or direction sensing capability. It is desirable to increase the active area of quad photoreceivers (and photodiodes) to enhance the link gain, and therefore sensitivity, of the system. However, the resulting increase in the photodiode capacitance reduces the bandwidth of the photoreceiver and adds to the equivalent input current noise, especially at high frequencies, for a given voltage noise level of the TIA.
"In fact, the capacitance of the photodiode and its excess current noise arising therefrom, scales linearly as the device area, thereby negating the corresponding increase in the link gain. Owing to this contradiction, the front-end quad photoreceiver can limit the sensitivity of the overall system. An example of such an application is the Laser Interferometry Space Antenna (LISA), which proposes to detect gravity waves in space by measuring distance with .about.10 .mu.m/ Hz accuracy over a baseline of five million kilometers. The present invention, as described herein relative to quad photoreceivers, is applicable for use in LISA which requires use of low-noise large-area photoreceivers, based on low-capacitance large-area photodiodes, for free space applications.
"In LISA, the optical local oscillator (LO) power incident on each photoreceiver quadrant will be restricted to 100 .mu.W to minimize the power requirements and thermal fluctuations for high pathlength stability. Assuming a photodiode responsivity of 0.7 A/W at 1064-nm wavelength, the desired shot noise-limited system operation requires the photoreceiver to display an equivalent input current noise density of
"Accordingly, there is a need for photoreceivers having associated low capacitance photodiodes to achieve enhanced sensitivity. There is also a need for low capacitance photodiodes for many other applications that can be provided individually or in an array. The present inventors urge that such applications include systems relying on coherent optical detection, such as LISA, as well as those utilizing direct detection."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "A quad photoreceiver for a first embodiment of the invention includes four p-i-n photodiodes formed on a common n.sup.+ doped InP (100) substrate serving as a buffer layer with a bottom metal layer contact providing a common cathode for receiving a bias voltage, a first i-InP drift layer is deposited on the buffer layer, followed by an i-InGaAs absorption layer, followed by an InP cap layer divided into four spaced apart p.sup.+-doped sections, with the p.sup.+ doping extending into a top most underlying portion of the absorption layer. Each cap section quadrant has p.sup.+ metal contacts deposited on top outermost portions thereof to serve as respective output terminals, and the top portions of each quadrant providing an active region responsive to light signals. Four transimpedance amplifiers have individual input terminals electrically connected to the output terminals of each cap section quadrant, respectively.
"A second embodiment of the invention includes an individual p-i-n photodiode formed as in the above-described first embodiment of the invention, for applications requiring low capacitance photodiodes.
"A third embodiment of the invention includes a photoreceiver comprising a single p-i-n photodiode of the second embodiment driving a TIA.
"A fourth embodiment of the invention includes an array of at least two of the low capacitance p-i-n photodiodes of the first embodiment."
URL and more information on this patent, see:
Keywords for this news article include: Electronics,
Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2013, NewsRx LLC
Most Popular Stories
- 5 Notable Hispanic Technology Executives
- Top Hispanic Tech Companies Push for the Top
- Visa, MasterCard Team Up to Focus on Payment Security
- Russia, Crimea Discuss Referendum
- China Urges Malaysia Flight Emergency Response
- Taco Bell Rings Up Breakfast Menu
- Sunday Starts Daylight Saving Time
- For Obama, a Last Stab at Improving Ties with Capitol Hill
- Three Americans on Missing Malaysia Airlines Plane: State Department
- California Establishes Center for Coffee Study