Analysis and demonstration of single-passband response and tuning characteristics in a chirped ladder interferometric filter for a widely tunable laser diode

We have designed and demonstrated a chirped ladder-type tunable filter and discussed its potential application for a tunable diode laser. A ladder interferometric filter normally has a periodic passband, which makes it impossible to stabilize laser oscillation frequency. To overcome this drawback, we have designed, fabricated, and characterized a novel chirped tunable ladder filter. We have successfully demonstrated a single-passband response in the fabricated device. Furthermore, a tuning operation of more than 30 nm was achieved by introducing a current injection structure and optimizing electrode lengths at each single-stage ladder interferometer.     

Stable and fast 100 GHz-spaced 30-channel digitally tunable operation in monolithically integrated semiconductor laser employing chirped ladder filter

Stable and fast 100 GHz-spaced 30-channel digital tuning operation with single longitudinal-mode oscillation in a monolithically integrated semiconductor diode laser has been achieved. It is experimentally demonstrated that the oscillation frequencies of the tunable laser were stabilised using the chirped ladder interferometric filter.     

Degradation behavior of narrow-spectral-linewidth DFB lasers forsuper-wide-band FM conversion

The feasibility of using narrow-spectral-linewidth distributed-feedback lasers as subcarrier multiplexing video distribution sources in optical heterodyne FM converters is shown by investigating degradation modes of the lasers. There is no change in the dynamic properties, such as the FM response and the composite second-order and composite triple-beat figures, though spectral linewidth is increased by degradation. The main degradation appears as an increase in spectral linewidth due to 1/f noise caused by buried heterointerface degradation. The FM response, composite second-order, and composite triple-beat, however, hardly change in the degradation process     

Optimal aggregation factor and clustering under delay constraints in aggregate sequential group paging schemes

This paper considers several optimization problems of sequential paging with aggregation mechanism which has been shown to reduce significantly the paging cost of a wireless communication system. An important problem is to find the optimal aggregation factor subject to a constraint on the average paging delay. Another problem is, given a cost function that depends on both paging cost and paging delay, how to find the optimal aggregation factor to minimize that cost function. We have formulated and shown that these can be solved nicely due to the monotonicity and convexity of the average paging cost function and paging delay function. We demonstrate that the optimization problems of the aggregate factor and subnet clustering are not separable. This leads to joint optimization problems of aggregation factor and clustering that are investigated in this paper. The paper presents different algorithms to solve these joint optimization problems using the monotonicity in the aggregation factor and the number of clusters of the average paging cost and delay with the unconstrained optimal clustering and the structures of the constrained optimal clustering.     

200-GHz FSR periodic multi/demultiplexer with flattenedtransmission and rejection band by using a Mach-Zehnder interferometerwith a ring resonator

A periodic multi/demultiplexer that has a square spectrum response with a 200-GHz free spectrum range was fabricated using a modified Mach-Zehnder interferometer with MMI couplers, a delay line, and a ring resonator. A large enhancement of the FSR is obtained by using a deep ridge waveguide. The transmission bandwidths of 1 dB down and -15-dB rejection are about 75 GHz and over 50 GHz, respectively     

Chirped ladder-type interferometric filter for widely tunable laser diode

A dominant passband response has been achieved by chirping a ladder-type interferometric filter. This response is indispensable for obtaining a single lasing wavelength in a widely tunable laser diode employing a ladder-type filter. Chirping the device is not accompanied by any excess loss nor does it require any additional fabrication processes.     

Mode stabilization method for superstructure-grating DBR lasers

A wavelength stabilization method for widely tunable superstructure-grating (SSG) distributed Bragg reflector (DBR) laser is described. The output characteristics under tuning are studied theoretically and experimentally. It is found that peak reflectivity states, in which the lasing mode is just aligned with the reflection peaks of both DBR's, are obtained at saddle points in the output characteristics while changing the two SSG-DBR currents. Based on these results, a method for the Bragg frequency control of the two SSG-DBRs is proposed. The feedback control circuit keeps the lasing mode at a peak reflectivity state, and it suppresses mode hopping. Additionally, the oscillation mode is locked to arbitrary reference wavelengths of an optical filter. Stabilization at 200 GHz (1.6 nm)-spaced 16 wavelengths was achieved within the wide tuning range of the SSG-DBR laser. Control was maintained under a laser temperature variation of ±5°C as a result of the Bragg frequency control of the two DBR's     

Impact of Power Control Strategy and Cell Classification on Hierarchical Cellular System's Reverse Link

1IntroductionRecelltly,theCDMAtechniquehasdrawntheattentionfrommanyresearchersforitsapplicationinglobalPersonnelmobilesystemsl'1'l'].UsingCDMAscheme,combiningmacrocellwithmicrocellhierarchicalsystemsmayprovidehighcapacityradioaccesstOthecellularsystem.InCDMAsystem,themoStimpo~problemissaidtobeaso-called"near-farproblem"I'l'I'I,generally,thisproblemcanbeovercomebyintroducingtheperfecttransmitterPOwercontrol(TPC).TheTPCiscomprisedofreverselinkandfonvardlinkTPCS.Butinpracticalsystems…     

CO2 reduction effect of the utilization of waste heat and solar heat in a city gas system

We evaluated total energy consumption and CO₂ emissions in the phases of a city gas utilization system from obtaining raw materials to consuming the product. Assuming monthly and hourly demand figures for electricity, heat for space heating, and hot water in a typical hospital, we explore the optimal size and operation of a city gas system that minimizes the life cycle CO₂ emissions or total cost. The cost‐effectiveness of conventional cogeneration, a solar heating system, and hybrid cogeneration utilizing solar heat is compared. We formulate a problem of mixed integer programming that includes integral parameters that express the state of system devices such as the on/off condition of switches. As a result of optimization, the hybrid cogeneration can reduce annual CO₂ emissions by 43% compared with the system without cogeneration. The sensitivity of CO₂ reduction and cost to the scale of the CGS is also analyzed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 22–32, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10369