A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

We review the family of optoelectronic devices whose performance is enhanced by placing the active device structure inside a Fabry‐Perot resonantmicrocavity. Such resonantcavity enhanced (RCE) devices benefit from the wavelength selectivity and the large increase of the resonant optical field introduced by the cavity. The increased optical field allows RCE photodetector structures to be thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. Off‐resonance wavelengths are rejected by the cavity making RCE photodetectors promising for low crosstalk wavelength division multiplexing(WDM) applications. RCE optical modulators require fewer quantum wells so are capable of reduced voltage operation. The spontaneous emission spectrum of RCE light emitting diodes(LED) is drastically altered, improving the spectral purity and directivity. RCE devices are also highly suitable for integrated detectors and emitters with applications as in optical logic and in communication networks. This review attempts an encyclopedic overview of RCE photonicdevices and systems. Considerable attention is devoted to the theoretical formulation and calculation of important RCE device parameters. Materials criteria are outlined and the suitability of common heteroepitaxial systems for RCE devices is examined. Arguments for the improved bandwidth in RCE detectors are presented intuitively, and results from advanced numerical simulations confirming the simple model are provided. An overview of experimental results on discrete RCE photodiodes, phototransistors, modulators, and LEDs is given. Work aimed at integrated RCE devices,optical logic and WDM systems is also covered. We conclude by speculating what remains to be accomplished to implement a practical RCE WDM system.

Resonant cavity enhanced photonic devices

It is anticipated that more than 75 Mb/s per subscriber is required for the convergence service such as triple-play service (TPS) Among several types of high-speed access network technologies, wavelength-division-multiplexing passive optical network (WDM-PON) is the most favorable for the required bandwidth in the near future Furthermore, WDM technologies, such as athermal arrayed-waveguide grating (AWG) and low-cost light source, have matured enough to be applied in the access network In this paper, the authors propose and implement a WDM-PON system as a platform for TPS The system employs an amplified spontaneous emission (ASE)-injected Fabry-Pe/spl acute/rot laser diode scheme It has 32 channels of 125 Mb/s and adopts Ethernet as Layer 2 Multicast and virtual local area network features are used for the integration of services such as Internet protocol high-definition broadcast, voice-over Internet protocol, video on demand, and video telephone The services were demonstrated using the WDM-PON system

Fiber-to-the-home services based on wavelength-division-multiplexing passive optical network

The photosensitivity characteristics of resonant cavity-enhanced (RCE) photodetectors are investigated. The photodetectors were formed by integrating the active absorption region into a resonant cavity composed of top and bottom (buried) mirrors. A general expression for quantum efficiency for RCE photodetectors was derived taking the external losses into account. Drastic enhancement in quantum efficiency is demonstrated at resonant wavelengths for a high quality factor Q cavity with a very thin absorption layer. An improvement by a factor of four in the bandwidth-efficiency product for RCE p-i-n detectors is predicted. Molecular beam epitaxy grown RCE-heterojunction phototransistors (RCE-HPT) were fabricated and measured demonstrating good agreement between experiment and theory. >

Resonant cavity-enhanced (RCE) photodetectors

Aspects of the subject disclosure may include, for example, receiving, by a feed point of a dielectric antenna, electromagnetic waves from a dielectric core coupled to the feed point without an electrical return path, where at least a portion of the dielectric antenna comprises a conductive surface, directing, by the feed point, the electromagnetic waves to a proximal portion of the dielectric antenna, and radiating, via an aperture of the dielectric antenna, a wireless signal responsive to the electromagnetic waves being received at the aperture. Other embodiments are disclosed.

Method and apparatus for coupling an antenna to a device

A guided-wave optical multi/demultiplexer is capable of providing a wide wavelength band freely. Each of two directional couplers is constructed so that the coupling ratio of light intensity in the wavelength λ2 is at least 50% and the coupling ratio of light intensity in the wavelength λ3 having a wavelength band in close proximity to the wavelength λ1 is 0% or 100%, the light in the wave band containing the wavelength λ1 and the wavelength λ3 and the light in the wave band containing the wavelength λ2 being multiplexed and demultiplexed.

Guided-wave optical multi/demultiplexer

This paper reviews the recent technologies supporting arrayed waveguide gratings (AWGs) based on planar lightwave circuits. From the practical point of view, I describe new technologies such as an athermalization and the high-contrast waveguide that includes the mode field transfer needed for low connection loss with conventional optical fiber. As AWG applications, I present new types of AWG modules such as a dynamic gain equalizer and a variable optical attenuator (VOA) MUX/DEMUX. Both of these will play an important role for next-generation wavelength-division multiplexing networks.

AWG technologies for dense WDM applications

An optical device having a switching function has a waveguide filter for switching an input signal light including at least one specific wavelength to be either transmitted or reflected. The input signal lights of wavelengths .lambda.1 to .lambda.n are transmitted to the input waveguide. When the waveguide filter is off, the signal lights of all wavelengths are transmitted to the output port. when the waveguide filter is on, the signal lights of wavelengths .lambda.2 to .lambda.n are transmitted, but the signal light of wavelength .lambda.1 is reversed and output to the drop port. If the thin film heaters are off, a signal light of wavelength .lambda.1 is output (dropped) from the drop port. If the thin film heaters are on, it is reversed and transmitted to the output port.

Optical Device Having Switching Function

We demonstrate multi/demultiplexers with a very flat passband and small excess loss using a multi-input arrayed waveguide grating combined with a cascaded Mach-Zehnder interferometer structure. We also analyze the impact of coupling between input waveguides just before the input slab on chromatic dispersion and investigate a waveguide structure for reducing the chromatic dispersion. We fabricated flat-passband multi/ demultiplexers with 100-GHz channel spacing using 2.5%-Delta silica waveguides and experimentally investigated the dependence of their optical characteristics on design parameters to demonstrate the effectiveness of the proposed theoretical model. We obtained a very flat passband response having a 1-dB bandwidth of 0.645-0.658 nm and 20-dB bandwidth of 0.944-0.960 nm with a loss penalty due to the passband-flattening of 0.9-1.0 dB and chromatic dispersion of -22.1-17.5 ps/nm over 0.5 nm in the passband. The measured passband shape and chromatic dispersion generally agreed with the simulation results.

Demonstration of Flat-Passband Multi/Demultiplexer Using Multi-Input Arrayed Waveguide Grating Combined With Cascaded Mach–Zehnder Interferometers

We describe a novel structure for super-high-/spl Delta/ athermal arrayed waveguide gratings (AWGs) employing spot-size converters based on a segmented core formed in the slab region, to reduce the diffraction loss in resin-filled trenches This structure requires no depth-tapering process We demonstrated a compact 16-channel athermal AWG based on the 25%-/spl Delta/ silica waveguides The excess loss due to athermalization was reduced to 09 dB with the proposed structure, whereas the excess loss was 24 dB using a conventional one The measured results of the proposed structure show no degradation of the crosstalk and passband shape

Hisato Uetsuka

Papers

Guided-wave optical multi/demultiplexer

AWG technologies for dense WDM applications

Optical Device Having Switching Function

Demonstration of Flat-Passband Multi/Demultiplexer Using Multi-Input Arrayed Waveguide Grating Combined With Cascaded Mach–Zehnder Interferometers

2.5%-/spl Delta/ silica-based athermal arrayed waveguide grating employing spot-size converters based on segmented core