B. Glance

Digitally tunable channel dropping filter/equalizer based on waveguide grating router and optical amplifier integration

We demonstrate a novel and powerful device that permits individual and simultaneous control of all the wavelength channels in a WDM system. The device is based on the monolithic integration of two identical waveguide grating routers with semiconductor optical amplifiers. By biasing appropriately the individual amplifier, each WDM channel can be amplified, detected or modulated. The device exhibits a channel bandwidth of 60 GHz, a channel spacing of 195 GHz and a crosstalk of /spl minus/19 dB.<<ETX>>

Fast optical packet switching based on WDM

An optical switch capable of routing a 3-Gb/s bit stream in 10-ns packets between ten different destinations is demonstrated. Switching time between destinations is 2 ns. The switch is based on wavelength division multiplexing (WDM) technology. It uses a fast tunable laser capable of addressing 24 discrete optical frequencies spaced by 40 GHz.<<ETX>>

Cascadability and fanout of semiconductor optical amplifier wavelength shifter

Data at bit rates of 1 or 2 Gb/s are transferred through two cascaded, broadband wavelength shifters, which operate using gain saturation in semiconductor optical amplifiers. Such devices copy data from a modulated pump signal, in which the intensity of the marks is sufficient to significantly compress the gain of the amplifier, to a CW probe signal, producing the complement of the data. Furthermore, fanout (multicasting) is demonstrated in a single device by using two input CW probe signals. Such devices may find importance in wavelength division multiplexed systems requiring wavelength reuse and reassignment.<<ETX>>

Switching-time limitation in tunable multisection lasers

The impact of the thermal transient on the frequency switching of multisection tunable lasers is studied. A simple thermal model is used to calculate the amplitude and time evolution of the frequency transient due to the thermal properties of both the laser chip and its mount. Transient time constants as large as 200 mu s for the laser chip and several hundred milliseconds for the diode mount are measured, limiting the applicability of these devices to systems where the frequency is switched at low rates. A method to compensate electrically for this transient by means of a passive net work is demonstrated.<<ETX>>

Wavelength-tunable add/drop optical filter

A new type of add/drop optical filter discretely tunable along equally spaced channels is presented. This device may have very useful applications in WDM optical networks.

Monolithic balanced p-i-n/HBT photoreceiver for coherent optical heterodyne communications

Two InGaAs p-i-n photodetectors connected in a balanced configuration have been monolithically integrated with a transimpedance preamplifier made from InP-InGaAs heterojunction bipolar transistors (HBTs) to realize a balanced optoelectronic integrated circuit (OEIC) receiver. The receiver, with a bandwidth of 3 GHz and a common mode rejection of 25 dB, has a sensitivity of -49 dBm at a bit error rate of 10/sup 9/ under NRZ FSK reception at 200 Mb/s. >

Large capacity multiaccess optical packet network

A multiaccess optical packet network capable of providing multigigabit-per-second transmission per user is presented. The proposed system is based on wavelength division multiplexing and frequency routing. It is optically transparent, has no internal blocking, and is optically self-routing. Users freely transmit their packets. Collision-free reception is achieved by means of a novel fast-tunable optical filter that controls the packet flow. Reception acknowledgments are passively generated without the use of optical sources and are transported on the same packet network. Assuming a single transmitter per user, and either one or two receivers (each with its own fiber) per user, the system throughput can approach 60% and 90% (per wavelength), respectively.<<ETX>>

Densely spaced FDM coherent optical system with random access digitally tuned receiver

The authors report the results obtained with a densely spaced FDM (frequency division multiplexing) coherent optical fiber star network utilizing monolithic frequency-tunable lasers to generate optical signals frequency-shift-keyed at 200 Mb/s, which provides an optical receiver sensitivity of 74 photons/b at a bit error rate of 10/sup -9/ and random access channel selection by a computer-controlled digitally tuned receiver. The demonstration system consists of six optical channels spaced by 2.2 GHz, the minimum frequency interval possible without adjacent channel interference. The channels are generated by multiple-quantum-well distributed-Bragg-reflector lasers operating at a wavelength of 1.53 mu m. These lasers provide a narrow linewidth (2-4 MHz) that is small enough for coherent detection application.<<ETX>>

Computer-controlled multichannel heterodyne optical communication system

The described system consists of eight frequency-shift-keying (FSK) modulated channels multiplexed by a 16*16 optical star coupler. Six of these channels are generated by individual digitally tuned optical frequency synthesizers. The frequency of these six channels can be randomly selected from a set of equispaced frequencies (2.2 GHz). Two of the 16 multichannel signals coming out of the star coupler are demultiplexed by their individual digitally tuned heterodyne receivers. Each receiver can randomly select, from the computer keyboard, a desired channel. The computer can identify missing channels. More importantly, the digital tuning of the frequency synthesizers and of the receivers is insensitive to variations of the frequency-tuning current relationship of the lasers. These results show that the digital tuning capability of todays radio systems can be transposed to the optical domain.<<ETX>>

One-THz digital random access high resolution optical frequency synthesizer providing cold-start operation from a frequency reference

The operation of a second-generation optical frequency synthesizer that provides digital random access to every frequency of the 1-THz tuning range of the laser with a resolution of 20 MHz is discussed. The synthesizers insensitivity to frequency drifts of the laser and its cold-start operation from an optical frequency reference are described.<<ETX>>