Patents by Inventor Radhakrishnan Nagarajan

Radhakrishnan Nagarajan has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Publication number: 20060023992
    Abstract: A method of in-wafer testing is provided for a monolithic photonic integrated circuit (PIC) formed in a semiconductor wafer where each such in-wafer circuit comprises two or more integrated electro-optic components, one of each in tandem forming a signal channel in the circuit. The method includes the provision of a first integrated photodetector at a rear end of each signal channel and a second integrated photodetector at forward end of each signal channel. Then, the testing is accomplished, first, by sequentially operating a first of a selected channel electro-optic component in a selected circuit to monitor light output from a channel via its first corresponding channel photodetector and adjusting its operating characteristics by detecting that channel electro-optic component output via its second corresponding channel photodetector to provide first calibration data.
    Type: Application
    Filed: October 3, 2005
    Publication date: February 2, 2006
    Applicant: Infinera Corporation
    Inventors: Fred Kish, Charles Joyner, Mark Missey, Frank Peters, Radhakrishnan Nagarajan, Richard Schneider
  • Publication number: 20050249509
    Abstract: A coolerless photonic integrated circuit (PIC), such as a semiconductor electro-absorption modulator/laser (EML) or a coolerless optical transmitter photonic integrated circuit (TxPIC), may be operated over a wide temperature range at temperatures higher then room temperature without the need for ambient cooling or hermetic packaging. Since there is large scale integration of N optical transmission signal WDM channels on a TxPIC chip, a new DWDM system approach with novel sensing schemes and adaptive algorithms provides intelligent control of the PIC to optimize its performance and to allow optical transmitter and receiver modules in DWDM systems to operate uncooled. Moreover, the wavelength grid of the on-chip channel laser sources may thermally float within a WDM wavelength band where the individual emission wavelengths of the laser sources are not fixed to wavelength peaks along a standardized wavelength grid but rather may move about with changes in ambient temperature.
    Type: Application
    Filed: April 14, 2005
    Publication date: November 10, 2005
    Applicant: Infinera Corporation
    Inventors: Radhakrishnan Nagarajan, Fred Kish,, David Welch, Drew Perkins, Masaki Kato
  • Publication number: 20050213883
    Abstract: A method is disclosed for optimizing optical channel signal demultiplexing in a monolithic receiver photonic integrated circuit (RXPIC) chip by providing an integrated channel signal demultiplexing with multiple waveguide input verniers provided to an WDM signal demultiplexer. The RxPIC chip may optionally include an integrated amplifier in at least some of the waveguide input verniers. The RxPIC chip may be comprised of, in monolithic form, a plurality of optional semiconductor optical amplifiers (SOAs) at the input of the chip to receive a WDM signal from an optical link which is provided along a plurality of waveguide input verniers to an integrated optical demultiplexer, such as, but not limited to, an arrayed waveguide grating (AWG), as a WDM signal demultiplexer. Thus, optical outputs from the respective semiconductor laser amplifiers are provided as vernier inputs to the optical demultiplexer forming a plurality of input verniers at the input to the optical demultiplexer.
    Type: Application
    Filed: May 24, 2005
    Publication date: September 29, 2005
    Applicant: Infinera Corporation
    Inventors: David Welch, Radhakrishnan Nagarajan, Fred Kish, Mark Missey, Vincent Dominic, Atul Mathur, Frank Peters, Charles Joyner
  • Publication number: 20050207696
    Abstract: An optical-to-electrical-to-optical converter comprises a monolithic receiver photonic integrated circuit (RxPIC) InP-based chip comprising an optical waveguide formed in the chip from a chip input to receive a first multiplexed channel signal from an optical link and provide them to an arrayed waveguide grating (AWG) which demultiplexes the multiplexed channel signals and provides a plurality of electrical channel signals to an electronic regenerator. The regenerator regenerates the electrical channel signals to an original signal waveform and provides the reformed electrical signals to a monolithic transmitter photonic integrated circuit (TxPIC) InP-based chip having an array of modulated sources formed in the chip that are coupled as inputs to an arrayed waveguide grating (AWG). The TxPIC modulates the reformed electrical signals to form a plurality of optical channel sign which are combined to form a second first multiplexed channel signal for transmission on an optical link.
    Type: Application
    Filed: May 5, 2005
    Publication date: September 22, 2005
    Applicant: Infinera Corporation
    Inventors: David Welch, Radhakrishnan Nagarajan, Fred Kish, Mark Missey, Vincent Dominic, Atul Mathur, Frank Peters, Charles Joyner, Richard Schneider, Ting-Kuang Chiang
  • Publication number: 20050201669
    Abstract: An optical transport network comprises a monolithic transmitter photonic integrated circuit (TxPIC) InP-based chip and a monolithic receiver photonic integrated circuit (RxPIC) InP-based chip.
    Type: Application
    Filed: May 5, 2005
    Publication date: September 15, 2005
    Applicant: Infinera Corporation
    Inventors: David Welch, Radhakrishnan Nagarajan, Fred Kish, Mark Missey, Vincent Dominic, Atul Mathur, Frank Peters, Charles Joyner, Richard Schneider, Ting-Kuang Chiang
  • Publication number: 20050135730
    Abstract: A method is disclosed for monitoring and controlling the bit error rate (BER) in an optical communication network where an optical receiver in the optical transmission network is a monolithic photonic integrated circuit (RxPIC) chip. The method includes the steps of decombining on-chip a combined channel signal received from the network and then monitoring a real time bit error rate (BER) of a decombined channel signal. The determined BER is then communicated, such as through an optical service channel (OSC) to an optical transmitter source that is the source of origin of the channel signal. Based upon the determined BER, the chirp of a channel signal modulator at the optical transmitter source that generated the monitored channel signal is adjusted by, for example, adjusting its bias. The same channel signal received at the RxPIC chip can be monitored again to determine if an acceptable level for the BER has been achieved by the previous chirp adjustment.
    Type: Application
    Filed: January 7, 2005
    Publication date: June 23, 2005
    Applicant: Infinera Corporation
    Inventors: David Welch, Radhakrishnan Nagarajan, Fred Kish, Mark Missey, Vincent Dominic, Atul Mathur, Frank Peters, Charles Joyner, Richard Schneider, Ting-Kuang Chiang
  • Publication number: 20050135729
    Abstract: An optical receiver photonic integrated circuit (RxPIC) comprises a semiconductor monolithic chip having an input to receive from an optical transmission link a combined channel signal originating from an optical transmitter source and comprising a plurality of channel signals having different wavelengths forming a wavelength grid. An optical decombiner is integrated in the chip and optically coupled to the input to receive the multiplexed channel signal and provide a decombined individual channel signal on an output waveguide of a plurality of such output waveguides provided from the optical decombiner. A plurality of photodetectors are also integrated in the chip and each photodetector is optically coupled to one of the output waveguides to receive a decombined channel signal and convert the channel signal to an electrical signal.
    Type: Application
    Filed: January 6, 2005
    Publication date: June 23, 2005
    Inventors: David Welch, Radhakrishnan Nagarajan, Fred Kish, Mark Missey, Vincent Dominic, Atul Mathur, Frank Peters, Charles Joyner, Richard Schneider, Ting-Kuang Chiang
  • Publication number: 20050129350
    Abstract: An optical transmitter photonic integrated circuit (TxPIC) comprises a semiconductor monolithic chip with a plurality of optical signal channels where each channel comprises a modulated signal source. The output from the modulated signal sources are coupled to an input of an integrated optical combiner to form a WDM output signal for transmission off the TxPIC chip to an optical transmission link. An optical service channel (OSC) is also integrated on the TxPIC chip to receive a service signal from the optical receiver source which is also coupled the optical transmission link.
    Type: Application
    Filed: January 7, 2005
    Publication date: June 16, 2005
    Applicant: Infinera Corporation
    Inventors: David Welch, Radhakrishnan Nagarajan, Fred Kish, Vincent Dominic, Ting-Kuang Chiang
  • Publication number: 20050117834
    Abstract: A photonic integrated circuit (PIC) comprises a plurality of integrated optically coupled components formed in a surface of the PIC and a passivating layer overlies at least a portion of the PIC surface. The overlying passivating layer comprises a material selected from the group consisting of BCB, ZnS and ZnSe. Also, when the circuits are PIC chips are die in the semiconductor wafer, a plurality of linear cleave streets are formed in a wafer passivation layer where a pattern of the cleave streets define separate PIC chips in the wafer for their subsequent singulation from the wafer.
    Type: Application
    Filed: December 21, 2004
    Publication date: June 2, 2005
    Applicant: Infinera Corporation
    Inventors: Charles Joyner, Mark Missey, Radhakrishnan Nagarajan, Fred Kish
  • Publication number: 20050111779
    Abstract: Disclosed is a method of in-wafer testing of integrated optical components and in-wafer chips with photonic integrated circuits (PICs).
    Type: Application
    Filed: December 16, 2004
    Publication date: May 26, 2005
    Applicant: Infinera Corporation
    Inventors: Charles Joyner, Mark Missey, Radhakrishnan Nagarajan, Frank Peters, Mehrdad Ziari, Fred Kish
  • Publication number: 20050111780
    Abstract: A method for reducing insertion loss in a transition region between a plurality of input or output waveguides to a free space coupler region in a photonic integrated circuit (PIC) includes the steps of forming a passivation layer over the waveguides and region and forming the passivation overlayer such that it monotonically increases in thickness through the transition region to the free space coupler region.
    Type: Application
    Filed: December 21, 2004
    Publication date: May 26, 2005
    Applicant: Infinera Corporation
    Inventors: Charles Joyner, Mark Missey, Radhakrishnan Nagarajan, Fred Kish
  • Publication number: 20050100278
    Abstract: An arrayed waveguide grating (AWG) comprises at least two free space regions, a plurality of grating arms extending between the two space regions, a passivation layer formed over the arrayed waveguide grating and a plurality of inputs at least to one of the free space regions to receive a plurality of channel signals separated by a predetermined channel spacing. A depth of the passivation layer chosen by providing a TE to TM wavelength shift between TE and TM modes propagating through the arrayed waveguide grating being approximately less than or equal to 20% of a magnitude of the channel spacing.
    Type: Application
    Filed: December 17, 2004
    Publication date: May 12, 2005
    Applicant: Infinera Corporation
    Inventors: Charles Joyner, Mark Missey, Radhakrishnan Nagarajan, Fred Kish
  • Publication number: 20050100300
    Abstract: A method for forming and apparatus comprising a free space coupler region having a plurality of optical waveguides coupled to the space coupler region at an interface region, the waveguides converging with one another to the interface region, and a trench formed between adjacent waveguides, the depth of the trench or trenches extending from an outer point to the interface region and monotonically decreasing in depth from the outer point to the interface region.
    Type: Application
    Filed: December 21, 2004
    Publication date: May 12, 2005
    Applicant: Infinera Corporation
    Inventors: Charles Joyner, Mark Missey, Radhakrishnan Nagarajan, Frank Peters, Mehrdad Ziari, Fred Kish
  • Publication number: 20050094926
    Abstract: A method of calibrating a monolithic transmitter photonic integrated circuit (TxPIC) chip is disclosed where the chip contains integrated arrays of laser sources and electro-optic modulators forming a plurality of different wavelength signal channels where each laser source on the chip is sequentially selected and tested for the output power and operational wavelength. Calibration data is initially determined by checking an amount of output power of each laser output and any offset of each laser operational wavelength from a desired predetermined value. Then, adjustment of the operational wavelength of each laser source is accomplished to substantially match the desired predetermined value. The laser source output power and operational wavelength may then be rechecked to determine if there is any remaining offset of each laser operational wavelength from the desired predetermined value.
    Type: Application
    Filed: November 16, 2004
    Publication date: May 5, 2005
    Applicant: Infinera Corporation
    Inventors: Vincent Dominic, Fred Kish, Radhakrishnan Nagarajan, Richard Schneider, Charles Joyner
  • Publication number: 20050094927
    Abstract: Method and apparatus for utilizing a probe card for testing in-wafer photonic integrated circuits (PICs) comprising a plurality of in-wafer photonic integrated circuit (PIC) die formed in the surface of a semiconductor wafer where each PIC comprises one or more electro-optic components with formed wafer-surface electrical contacts. The probe card has a probe card body with at least one row of downwardly dependent, electrically conductive contact probes. The probe body is transversely translated over the surface of the wafer to a selected in-wafer photonic integrated circuit (PIC) die. Then, the contact probes of the probe card are brought into engagement with surface electrical contacts of the selected photonic integrated circuit (PIC) die for testing the operation of electro-optic components in the selected in-wafer photonic integrated circuit (PIC) die.
    Type: Application
    Filed: November 16, 2004
    Publication date: May 5, 2005
    Applicant: Infinera Corporation
    Inventors: Fred Kish, Radhakrishnan Nagarajan, Frank Peters, Richard Schneider
  • Publication number: 20050094925
    Abstract: A method of in-wafer testing is provided for a monolithic photonic integrated circuit (PIC) formed in a semiconductor wafer where each such in-wafer circuit comprises two or more integrated electro-optic components, one of each in tandem forming a signal channel in the circuit. The method includes the provision of a first integrated photodetector at a rear end of each signal channel and a second integrated photodetector at forward end of each signal channel. Then, the testing is accomplished, first, by sequentially operating a first of a selected channel electro-optic component in a selected circuit to monitor light output from a channel via its first corresponding channel photodetector and adjusting its operating characteristics by detecting that channel electro-optic component output via its second corresponding channel photodetector to provide first calibration data.
    Type: Application
    Filed: November 12, 2004
    Publication date: May 5, 2005
    Applicant: Infinera Corporation
    Inventors: Fred Kish, Mark Missey, Radhakrishnan Nagarajan, Frank Peters, Richard Schneider, Charles Joyner
  • Publication number: 20050025409
    Abstract: A photonic integrated circuit (PIC) chip with a plurality of electro-optic components formed on a major surface of the chip and a submount that includes a substrate that extends over the major surface of the chip forming an air gap between the substrate and the major surface, the substrate to support electrical leads for electrical connection to some of the electro-optic components on the chip major surface.
    Type: Application
    Filed: May 25, 2004
    Publication date: February 3, 2005
    Applicant: Infinera Corporation
    Inventors: David Welch, Vincent Dominic, Fred Kish, Mark Missey, Radhakrishnan Nagarajan, Atul Mathur, Frank Peters, Robert Taylor, Matthew Mitchell, Alan Nilsson, Stephen Grubb, Richard Schneider, Charles Joyner, Jonas Webjorn, Ting-Kuang Chiang, Robert Grencavich, Vinh Nguyen, Donald Pavinski, Marco Sosa
  • Publication number: 20020106156
    Abstract: An optical gain apparatus has a pump source providing pump energy at a pump wavelength to a gain medium that generates optical energy at a signal wavelength. To minimize disturbance from signal wavelengths appearing in a coupling path between the pump source and the gain medium, an optical attenuator is located in the coupling path that provides a significant degree of attenuation to signal wavelengths, while providing negligible attenuation of pump wavelengths. The attenuator may comprise a grating structure, such as a long period grating or a blazed grating. It may also comprise an angled coupling fiber that is oriented to reflect signal wavelengths out of the coupling path. The end of such a fiber would typically be formed into a microlens, such as a wedge-shaped lens or a biconic lens, and would preferably be coated with a material that is highly reflective at the signal wavelength, but anti-reflective at the pump wavelength. The microlens may also be angled relative to a longitudinal axis of the fiber.
    Type: Application
    Filed: February 2, 2001
    Publication date: August 8, 2002
    Inventors: Edward Vail, Radhakrishnan Nagarajan, Harrison Ransom, Ian Booth, Tae Jim Kim, Edmund Wolak, Jo Major, Stuart MacCormack, Tanya Oleskevich
  • Patent number: 5933265
    Abstract: An optical transmission link has both a transmitter module and a receiver module operable under uncooled conditions, i.e., without the need of costly cooling equipment, such as thermoelectric coolers. The optical transmission system includes both a semiconductor laser diode source and an optical receiver module that are both designed to operate uncooled under high frequencies (e.g., GHz range) over a wide temperature range without significant changes in signal bandwidth and at temperatures in excess of 125.degree. C. Compensation is provided to reduce the effect of photodiode noise and amplifier noise. In addition, temperature compensation can be provided that provides for overall reduction in receiver noise across the bandwidth of the receiver module through maintenance of a temperature environment optimizing receiver performance.
    Type: Grant
    Filed: April 22, 1998
    Date of Patent: August 3, 1999
    Assignee: SDL, Inc.
    Inventor: Radhakrishnan Nagarajan
  • Patent number: 5760939
    Abstract: An optical transmission link has both a transmitter module and a receiver module operable under uncooled conditions, i.e., without the need of costly cooling equipment, such as thermoelectric coolers. The optical transmission system includes both a semiconductor laser diode source and an optical receiver module that are both designed to operate uncooled under high frequencies (e.g., GHz range) over a wide temperature range without significant changes in signal bandwidth and at temperatures in excess of 125.degree. C. Compensation is provided to reduce the effect of photodiode noise and amplifier noise. In addition, temperature compensation can be provided that provides for overall reduction in receiver noise across the bandwidth of the receiver module through maintenance of a temperature environment optimizing receiver performance.
    Type: Grant
    Filed: October 23, 1995
    Date of Patent: June 2, 1998
    Assignee: SDL, Inc.
    Inventors: Radhakrishnan Nagarajan, Jo S. Major, Jr.