Laser Diode Optical Switches Research Articles

LD optical switch with polarization insensitivity over a wide wavelength range

A double-heterostructure (DH) laser with TM mode lasing has been achieved with a narrow active-layer width, and a laser-diode optical switch (LDSW) module with less than a 0.35-dB gain difference between the TE and TM modes over a wide wavelength range has been constructed by introducing a square bulk active layer formed by dry etching and regrowth. The polarization-insensitive width of a 0.3-/spl mu/m-thick DH laser is clarified to be between 0.30 and 0.35 /spl mu/m, since the 0.30- and 0.35-/spl mu/m-wide DH lasers lase in the TM mode and TE mode, respectively. The polarization-insensitive width of the fabricated 0.3-/spl mu/m-thick LDSW is estimated to be about 0.32 /spl mu/m for the fabricated LDSW with a trapezoidal active layer by measuring the single-pass gain and the gain difference between the TE and TM modes. This must be to within 0.01 /spl mu/m. A 0.35-/spl mu/m-wide, 300-/spl mu/m-long LDSW module has lossless gain in the wavelength range of 1.31 to 1.36 /spl mu/m at 20 mA. The gain difference between the TE and TM modes is as low as 0.35 dB, The rise and fall times are 1.0 and 0.55 ns, respectively. The bulk active-layer LDSW module is promising for use as a polarization-insensitive optical-gate switch in optical information systems.

Lossless operation of 4 × 4 laser diode optical gate switches using Y reflection type branching/combining circuits for large-scale integration

The paper describes a 4 × 4 laser diode optical gate switch made on an InGaAs/GaAs single quantum well GRIN-SCH wafer. The switches were made very compact (only 1.1 × 1.6 mm) by using a Y reflection type optical branching/combining circuit with wide-angle splitting. The light signal launched into an input port is transmitted to an output port through seven gate waveguides and six Y branching circuits. All of the paths between the input and output ports exhibit lossless switching operations when a current of 16 mA (average value) is injected into one gate. The excess loss of the Y branching circuit is estimated to be 0 dB for through coupling and 4 dB for crosscoupling. Good fabrication uniformity of the individual device elements (i.e. the gate waveguide and Y reflection type branching circuit) were confirmed in an area of 10 mm × 10 mm, which was one unit of the photolithography process used in the experiments. However, a significant difference in gain characteristics between the input–output paths in the 4 × 4 switches was observed. The disagreement between the uniformity of the individual elements and the scattering of the path gain characteristics can be explained by the zigzag propagation of the light beam eccentrically launched into the waveguides through the Y reflection type branching circuit.

Isolation spectra for InGaAs/GaAs strained single quantum well laser diode optical switches

The spectral dependence of gain and loss for an InGaAs/GaAs strained single quantum well laser diode were measured. High gain and high isolation at the second quantized transition wavelength can be obtained with a low injection current. A strained single quantum well structure is suitable for construction of an integrated optical matrix switch with low power consumption.

Lossless 1*4 laser diode optical gate switch

The fabrication of a compact 1*4 laser diode (LD) optical gate switch for the 1.3 mu m band, comprising five LD optical gate submodules and a 1*4 planar lightwave circuit, is described. The switch exhibited a lossless switching function and polarization sensitivities of 0.5-1.1 dB, with operation currents of 45 to 55 mA. At operation currents of 120 mA, the switch exhibited positive gains of 9.0 to 10.2 dB. No power penalty was detected for nonreturn-to-zero (NRZ) transmissions of up to 2 Gb/s at -10 dBm input levels, when a narrowband optical filter for spontaneous emission reduction was used.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Isolation spectra for quantum-well laser diode optical switches

The spectral dependence of isolation characteristics for quantum-well laser diode optical switches, which are the level difference between the ON and OFF state attenuation, are calculated for p- and n-type quantum-well InGaAsP/InP using a semiclassical density-matrix analysis. The results show that p-type materials, which have rather large background carrier concentration, are suitable for large gain and high isolation optical switches. Broadband laser diode optical switches with a gain region of 1.3–1.55 μm can be obtained.

Novel assembly method for laser-diode optical switch module

A novel assembly method for laser-diode optical switch modules with a single-mode fibre pigtailed structure has been developed. A chip is aligned with fibres fixed in a package, using the chip itself as a detector. Very compact modules as small as 11 × 8 × 2.6 (mm) are realised, with a gain of 7dB and an isolation of 39 dB observed in the fabricated device. This type of module has good thermal stability in the temperature range 0 to 50°C.

Maximum number of connectable laser diode optical switch (LDSW) systems

The maximum number of connectable laser diode optical switches (LDSWs) was studied through the baseband signal-to-noise ratio calculation. For an NRZ 100 Mbits−1 PCM-IM signal, 60 stages of LDSWs can be connected with a 6-nm optical bandpass filter inserted after the last stage at an input signal level of −30 dB m and an internal gain of 16 dB. A PCM-IM signal of 10 Gbits−1 can be transmitted through 130 stages of LDSWs at an internal gain of 8 dB and an input signal level of −20 dB m.

Fiber-optic digital video distribution system for using high-definition television signals using laser-diode optical switch

A fiber-optic high-definition television (HDTV) distribution system is discussed, which economically distributes HDTV signals to customers at a bit rate of about 100 Mb/s. The subscriber network is formed in a star topology to facilitate bidirectional connection. The distribution system uses digital video transmission at 1.3 mu m wavelength using single-mode fiber. The video channel selection is made by an optical video selector. The optical selector consists of laser diode optical switch modules, which have a gain in the 'ON' state and two-input, two-output 3 dB couplers. The authors describe the bit error rate characteristics of a signal-mode fiber digital distribution system using a four-input, one-output optical selector.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical self-routing switch using integrated laser diode optical switch

A 2*2 optical self-routing switch using integrated laser diode optical switches is proposed. The switch is composed of a Benes network, which can perform large-scale switching functions using less hardware than a crossbar switch. The path each data stream takes through the interconnection network is determined by the binary bits of its destination address, and self-routing is accomplished by monitoring terminal voltage changes in gain guides induced by input optical signals which are injected into a p-n junction. Concentrated control is not necessary, and large optical multistage switches can be easily constructed because complicated electrode patterns are not necessary. >

Tandem transmission characteristics of laser diode optical switches measured by a circular pulse method

Tandem transmission characteristics of laser diode optical switches have been measured using the circular pulse method. With an input optical signal power level of −18 dBm, output optical signal pulses have been observed to recirculate 50 times without a filter, and more than 80 times with an optical bandpass filter inserted in front of a photodetector.

Tandem switching characteristics for laser diode optical switches

The switching characteristics of three laser diode optical switch modules connected in tandem were measured. The measured isolation characteristics were coincident with the sum of the individual isolation characteristics. The transmitted optical pulse waveform was not distorted through the three connected LDSW modules.

Signal-monitoring characteristics for laser-diode optical switches

Signal-monitoring characteristics of terminal voltage change across laser-diode optical switches (LDSW) have been studied. The terminal voltage changes are caused by the photovoltaic effect in the OFF state and by the quasi-Fermi level change in the ON state. The baseband frequency response characteristics are analyzed by small-signal analysis and coincide well with the measured characteristics. The 6-dB down frequency response bandwidths are verified to be very wide in both the ON and OFF states.

Isolation characteristics for laser diode optical switches

The isolation spectra for laser diode optical switches, which are the level difference between the on and off state attenuation, are calculated for n- and p-type GaAlAs and InGaAsP using a Gaussian fit to the Halperin–Lax band tails and Stern’s matrix element model. The measured and calculated isolation spectra for a GaAlAs laser diode are closely coincident with one another. The calculated results show that p-type materials, which contain small background carrier concentrations, are suitable for high isolation laser diode optical switches. Especially, it becomes clear that p-type In0.533Ga0.467As laser diode optical switches, whose operating wavelength is 1.65 μm, give the best isolation characteristics.

Laser-diode optical switch module

A pigtail structure laser-diode optical switch module was first fabricated. A 6 dB gain in the `on? state and 82 dB isolation were obtained.

Reduction of turn-on delay in laser diode optical switch

Switching response time of a semiconductor laser diode (LD) switch is studied. Turn-on delay of the LD switches was reduced to about 1 ns by applying a preshaped gate pulse. Fall time was less than 1 ns.

Isolation spectra for laser diode optical switch

Isolation spectra for a GaAlAs laser diode optical switch were measured directly by using a tunable light source. Isolation was higher than 60 dB in the 200 A wavelength region. Theoretical isolation spectra, calculated by the GHLB-SME model, were coincident with the measured isolation spectra.

Optical properties for an antireflection-coated LD optical switch

Measured optical properties for an antireflection-coated laser-diode optical switch are described. With antireflection coatings, output level stability for injection current and temperature are much improved. The input and output signal spectra are the same.