Transmission Electrophotonic Devices Research Articles

Uniformity Improvement of Optical and Electrical Characteristics in Integrated Vertical-to-Surface Transmission Electro-Photonic Device with a Vertical Cavity

We report an improvement in uniformity of both electrical and optical characteristics in an integrated vertical-to-surface transmission electro-photonic device with a vertical cavity. This improvement is due to both highly controlled reactive ion-beam etching and a self-alignment process. Reactive ion-beam etching highly controls etching depth, and leads to uniform electrical and optical characteristics. Self-alignment process makes it possible to fabricate a fine pattern with high accuracy. By using these fabrication processes, the deviations of both the electrical resistance and the optical light-output characteristics are reduced to less than half of those for the wet-etched devices. Furthermore, the remaining deviation in the light-output characteristics is reduced by suppressing light reflection on the surface. As a result, the standard deviation of the threshold current under the CW condition is 0.39 mA. This value is about half of that for the wet-etched devices.

Uniform characteristics with low threshold and high efficiency for a single-transverse-mode vertical-cavity surface-emitting laser-type device array

Vertical-to-surface transmission electrophotonic devices with a vertical-cavity are described. The individually accessed 12/spl times/4 arrays are characterized and demonstrated to have uniform room-temperature continuous-wave operating characteristics for a threshold current of /spl sim/2.8/spl plusmn/0.15 mA and a slope efficiency of /spl sim/0.18/spl plusmn/0.012 W/A with a single transverse mode. Both low threshold and high efficiency with 5% and 7% deviation, respectively, are achieved simultaneously. These devices can be used to constructing two-dimensional massively parallel optical interconnections. >

Light detection sensitivity of a vertical cavity structure used in an optical switch device

The light detection characteristics in a vertical cavity surface-emitting laser-type vertical-to-surface transmission electrophotonic device (VC-VSTEP) have been evaluated. To realize a low energy optical interconnection, not only the switching threshold energy but also the light detection sensitivity must be optimized. Maximum sensitivity is achieved when the input light wavelength and the field distribution coincide with fundamental cavity mode characteristics. Under the best matching condition, the input light energy necessary to switch the VC-VSTEP state is easily lower than 1 pJ.

Effect of sidewall reflector on current versus light output in a pnpn vertical-to-surface transmission electrophotonic device with a vertical cavity

The authors experimentally study the effect of a sidewall reflector on current versus light-output characteristics in a pnpn vertical-to-surface-transmission electrophotonic device with a vertical cavity. The distributed Bragg reflectors that form the vertical cavity for laser oscillation and the sidewall reflector retain spontaneously emitted photons in the optical cavity, and only the photons that have the resonance wavelength of the vertical cavity are emitted. As a result, spontaneously emitted photons are absorbed and the carriers are regenerated; that is, the injected carriers are converted to light, and spontaneous emission is reconverted to carriers. As a result of photon recycling of spontaneous emission, threshold reduction is expected. Threshold reduction by at least a factor of 4 is obtained with a device that has the sidewall reflector. >

A new architecture of photonic ATM switches

A photonic asynchronous transfer mode (ATM) switch architecture for ATM operation at throughputs greater than 1 Tbit/s is proposed. The switch uses vertical-to-surface transmission electrophotonic devices (VSTEPs) for the optical buffer memory, and an optical-header-driven self-routing circuit in contrast with conventional photonic ATM switches using electrically controlled optical matrix switches. The optical buffer memory using massively parallel optical interconnections is an effective solution to achieve ultra-high throughput in the buffer. In the optical-header-driven self-routing circuit, a time difference method for a priority control is proposed. For the optical buffer memory, the write and read operations to and from the VSTEP memory for 1.6 Gbit/s, 8-bit optical signal are confirmed. The optical self-routing operation and priority control operation by the time difference method in the 4*4 self-routing circuit were performed by 1.6-Gbit/s 256-bit data with a 10-ns optical header pulse. >

High electronic-optical conversion efficiency in a vertical-to-surface transmission electro-photonic device with a vertical cavity

Electronic-optical conversion efficiency of 11.4% in a vertical-to-surface-transmission electrophotonic device with a vertical cavity is reported. Reduction of the electrical resistance by the double mesa structure, efficient confinement of carriers in the active region by the proton implanted structure, and photon recycling by sidewall reflectors lead to this high conversion efficiency. Efficiency over 10% is achieved for the first time in surface-emitting devices. >

Double-Mesa-Structure Vertical-to-Surface Transmission Electro-Photonic Device with a Vertical Cavity

We report a high electronic-optical power conversion efficiency of 11.4% in the laser operation of a double-mesa-structure vertical-to-surface transmission electro-photonic device with a vertical cavity. This high conversion efficiency is due to both reduction in the device resistance and increase in light emission efficiency. To reduce electrical resistance, a double mesa structure with a highly doped region is proposed and the resistance reduction is analyzed. To increase light emission efficiency, efficient carrier confinement in the active region by a proton-implanted structure, threshold current reduction by photon recycling, and decreased light absorption by annealing after proton implantation are utilized. Electronic-optical conversion efficiency of over 10% is achieved in surface-emitting devices for the first time to the authors' knowledge.

Indistinct threshold laser operation in a pnpn vertical to surface transmission electrophotonic device with a vertical cavity

The vertical to surface transmission electrophotonic device has a laser cavity covered with plated gold, which has high reflectivity. The laser light is emitted from the distributed Bragg reflector (DBR) with no gold. Consequently, spontaneous emission remains in the laser cavity, and the carriers are regenerated. The injected carriers are converted to light and spontaneous emission is reconverted to carriers. Due to photon recycling, threshold current density decreases and indistinct threshold laser operation is obtained. In the indistinct threshold operation, the light output is linearly polarized. The submode suppression ratio is larger than 25 dB, and the divergence angle of a far field is as narrow as 6.8 degrees . The indistinct threshold laser characteristics lead to high slope efficiency in low current level. To achieve high slope efficiency in the overall current level, DBR mirrors are designed, and high slope efficiency of 0.32 mW/mA is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical fiber loop memory using vertical to surface transmission electro-photonic device

An optical fiber loop memory is proposed, using a photonic switch device of a vertical to surface transmission electro-photonic device. The photonic switch works as an optical pulse repeater. The operation stability as the memory was analyzed, and more than 30 minutes storage time has been realized. The maximum operational clock was as high as 20 MHz. This memory may be a part of the future optical computer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Free-space optical bus using cascaded vertical-to-surface transmission electrophotonic devices

A free-space optical bus, which consists of cascaded optical switch devices, is proposed. The switch devices have multiple functions, such as data transmission, data detection, and data repetition. Basic interconnection characteristics were measured with vertical-to-surface transmission electrophotonic devices. Optical switching energy as low as 150 FJ and up to 4 MHz and a relatively high datatransmission rate, i.e., more than 20 MHz, were obtained. Connection cascadability and extendibility were confirmed.

Electro-photonic devices for gigabit networks

A photonic asynchronous transfer mode (ATM) switch that can achieve very high throughput by using two-dimensional optical functional devices for both optical buffer memories and an optical self-routing circuit is described. The photonic switch uses vertical to surface transmission electrophotonic devices (VSTEPs). It is shown that the optical cell signal speed in the proposed optical buffer memory can reach around 10 Gb/s, and the optical header-driven, self-routing circuit can switch 10 Gb/s optical signals. The maximum input and output port numbers in the self-routing circuit are estimated to be around 100. As a result, the total throughput for the photonic ATM switch can reach as large as the Tb/s level. >

Cascadable optical switching characteristics in vertical-to-surface transmission electrophotonic devices operated as vertical cavity lasers

We examine the optical switching characteristics in vertical cavity surface-emitting laser-type vertical-to-surface transmission electrophotonic devices (VC-VSTEPs) with a pnpn structure. It is theoretically and experimentally demonstrated that both optical input/output characteristics are strongly influenced by the structure of the vertical cavity. With improvements in optical power output due to laser oscillation, optical switching speed is enhanced by two orders of magnitude compared to spontaneous emission-type VSTEPs. A 20-μm-square VSTEP with an optimized vertical cavity structure demonstrates a low optical switching energy of 2.2 pJ with a switching time of 10 ns, as low as spontaneous emission-type VSTEPs.

Cascade-connective optical parallel logic processor using electrophotonic devices

To perform image or arithmetic processing optically, it is necessary that a large number of required optical processors be connected in a series. For such cascade connections, however, coding and decoding processes are undesirable because of the necessity for the complicated hardware that often results. We propose here a new logic algorithm for application to cascade connections, which utilizes, in place of coding and decoding processes, true logic signals and their complements. Its optical implementation is also discussed. A processing module is constructed from electro-photonic devices referred to as vertical to surface transmission electro-photonic devices, a ferroelectrical liquid-crystal spatial light modulator, and a planar microlens array. Its logic operations are successfully demonstrated.

Vertical-to-surface transmission electrophotonic device with a pnpn structure and vertical cavity

Surface emitting laser operation and optical switching operation are demonstrated in vertical-to-surface transmission electrophotonic devices using pnpn structures and vertical cavities. Threshold current density as low as 1.4 kA cm−2 for laser operation and optical switching energy as low as 2.2 pJ for optical switching operation are achieved. It is found that optical switching energy can be lowered by multireflections in the vertical cavity. Growth rate calibration and series resistance in the distributed Bragg reflector mirrors are examined for device fabrication.

Dependence of laser characteristics on distributed Bragg reflector pairs in vertical-to-surface transmission electrophotonic devices

The threshold current dispersion, slope efficiency and lasing wavelength of vertical-to-surface transmission electrophotonic devices with vertical cavities are investigated. The critical number of output distributed Bragg reflectors (DBRs) required to overcome the disturbance due to back-surface reflections for surface-emitting-laser (SEL) structure devices is clarified. >

Surface-emitting laser operation in vertical-to-surface transmission electrophotonic devices with a vertical cavity

We demonstrate the first surface-emitting laser operation in a vertical-to-surface transmission electrophotonic device with a vertical cavity. The thyristor-like current-voltage characteristics, which are required for optical and electrical switching, are achieved. Threshold current during the on state is as low as 1.2 mA. All 100 devices, which were randomly extracted from a grown wafer, emit laser light.

Optical self-routing switch using vertical to surface transmission electrophotonic devices with transmission light amplification function

A unique optical self-routing switch, which uses laser mode vertical to surface transmission electrophotonic (VSTEP) devices, is proposed. This optical self-routing switch, in which the light input itself determines the output port by switching on VSTEPs, has a high internal optical gain of more than 20 dB and a wavelength filtering function. The light extinction ratio for the data signals between the on and off state is larger than 30 dB.

32 × 32 two-dimensional array of vertical to surface transmission electrophotonic devices with a pnpn structure

A novel electrophotonic mode of operation reduces both the memory holding power and the optical switching energy to 26 fJ at a 9 ns writing period in vertical to surface transmission electrophotonic devices with a pnpn structure (pnpn-VSTEPs). An integration of 1024 pnpn elements in a two-dimensional matrix has been demonstrated for these electrophotonic operations by using a thick metal line process and a low temperature dielectric film deposition for improving characteristics uniformity. >

Reconfigurable optical interconnection using a two-dimensional vertical to surface transmission electrophotonic device array

A dynamic reconfiguration of optical interconnections for enhanced flexibility in photonic switching systems is realized using a two-dimensional vertical to surface transmission electrophotonic (VSTEP) device array. A matrix operational scheme for the VSTEP array is proposed and demonstrated. Through this operation, functions for light emission and for electrically programmable spatial light modulation are obtained in a single chip of the VSTEP array and a high-speed electronic addressing of 1 ns per one line for the matrix is also confirmed.

Uniformity in the performance characteristics of an 8×8 vertical to surface transmission electro-photonic device matrix

Characteristic uniformities in a vertical to surface transmission electro-photonic device matrix are studied using a double heterostructure optoelectronic switch as an element device. Uniformity of switching voltage and optical switching energy, which is critical in optical parallel operations, is shown over an entire matrix including 64 monolithically integrated elements.