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Proposed distributed-Bragg-reflector (DBR) semiconductor laser has wide curved gratings favoring single-mode operation, even with relatively wide laser stripe, enabling use of higher power. Consists of semiconductor double heterostructure laser bounded at each end by region of passive waveguide.
The linewidth of a distributed feedback semiconductor laser or a distributed Bragg reflector laser having one or more second order gratings is reduced by using an external cavity to couple the vertical emission back into the laser. This method and device prevent disturbance of the main laser beam. provide unobstructed access to laser emission for the formation of the external cavity. and do not require a very narrow heat sink. Any distributed Bragg reflector semiconductor laser or distributed feedback semiconductor laser that can produce a vertical emission through the epitaxial material and through a window in the top metallization can be used. The external cavity can be formed with an optical fiber or with a lens and a mirror of grating.
The linewidth of a distributed feedback semiconductor laser or a distributed Bragg reflector laser having one or more second order gratings is reduced by using an external cavity to couple the vertical emission back into the laser. This method and device prevent disturbance of the main laser beam, provide unobstructed access to laser emission for the formation of the external cavity, and do not require a very narrow heat sink. Any distributed Bragg reflector semiconductor laser or distributed feedback semiconductor laser that can produce a vertical emission through the epitaxial material and through a window in the top metallization can be used. The external cavity can be formed with an optical fiber or with a lens and a mirror or grating.
The performance of a GaAs/GaAlAs distributed Bragg reflector (DBR) laser using a focused ion beam implanted grating (FIB-DBR) is reported for the first time. Stripes of Si(2+) with a period of 2300 A and a dose about 10 to the 14th/sq cm are directly implanted into the passive large optical cavity layer to provide the distributed feedback. Surface-emitting light from the second-order grating is observed. Threshold current of 110 mA and single DBR mode operation from 20 to 40 C are obtained. The wavelength tuning rate with temperature is 0.8 A/C. The coupling coefficient is estimated to be 15/cm. The results show that FIB technology is practical for distributed feedback and DBR lasers and optoelectronic integrated circuits.
High power singlemode strained GaInAs lasers have been fabricated which use buried second order gratings as distributed Bragg reflectors. The lasers operate in an edge emitting fashion with CW powers in excess of 110 mW with single longitudinal and transverse mode operation at 971.9 nm up to 42 mW.
Single-mode strained-layer lasers have been fabricated which use buried second-order gratings for distributed Bragg reflectors. The lasers contain a strained GaInAs quantum well in the active region and operate in an edge emitting fashion with CW powers in excess of 110 mW. Single longitudinal and transverse mode operation is maintained at about 971.9 nm up to 42 mW. Total power conversion efficiencies as high as 28 percent have been observed. The longitudinal and transverse mode behavior is stable under 90 percent amplitude modulation with 50 percent duty cycle pulses at 10 kHz and 10 MHz. Preliminary life-test data at 40 C also indicate room temperature lifetimes in excess of 45,000 hours.
There is a growing interest in the fabrication of semiconductor optical group delay lines for the development of phased arrays of Vertical-Cavity Surface-Emitting Lasers (VCSELs). We present a novel structure incorporating In(x)GA(1-x)As quantum wells in the GaAs quarter-wave layers of a GaAs/AlAs distributed Bragg reflector (DBR). Application of an electric field across the quantum wells leads to red shifting and peak broadening of the el-hhl exciton peak via the quantum-confined Stark effect. Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. We discuss the tradeoffs between the maximum amount of change in group delay versus absorption losses for such a device. We also compare a simple theoretical model to experimental results, and discuss both angle and position tuning of the BDR band edge resonance relative to the exciton absorption peak. The advantages of such monolithically grown devices for phased-array VCSEL applications will be detailed.
The first demonstration, to the best of our knowledge, of distributed Bragg reflector (DBR) and monolithic distributed feedback (DFB) lasers in photothermorefractive glass doped with rare-earth ions is reported. The lasers were produced by incorporation of the volume Bragg gratings into the laser gain elements. A monolithic single-frequency solid-state laser with a line width of 250 kHz and output power of 150 mW at 1066 nm is demonstrated.
A static plasma grating has been demonstrated experimentally (Wu et al., 1988) in a large-optical-cavity focused-ion-beam-distributed-Bragg-reflector (FIB-DBR) GaAlAs/GaAs laser diode. The grating is formed by implanting stripes of dopants with a focused ion beam. The dopants ionize to form periodic fluctuations in the carrier concentration which, through the Kramers-Kronig relations, form an index grating. A model of the grating strength for optimizaton of the laser design is developed and presented. The computed results show that the coupling coefficient k can be increased by more than an order of magnitude over the 15/cm experimentally. Therefore, FIB-DBR or FIB-distributed-feedback (DFB) lasers with performance comparable to that of conventional DBR (or DFB) lasers can be expected.
We describe and analyze a novel approach to implementing an Optical Backplane Interconnect Technology (OBIT) that is capable of optically connecting any row of a 32x32 backplane array to any row of a second 32x32 array. Each backplane array is formed monolithically on a wafer. The technology is based on the use of Grating Surface Emitting (GSE) waveguides formed on a wafer containing quantum-well and separate confinement waveguide layers. These layers are used for transverse guiding, gain, modulation, detection, and for the formation of wavelength tunable distributed-Bragg reflector lasers. The required surface structures are formed photolithographically. The GSE waveguides act as efficient antennae that radiate light at angles selected by tuning the wavelength of the lasers. The same waveguides may be used as the receiving antennae when the array is used in the receiving mode. Thus, wavelength tuning is used to direct each row of the transmitting array to the desired row of the receiving array. In summary: The optical backplane array will have the following characteristics: Any row of a 32x32 GSE array may be optically connected to any row of a second 32x32 array. Only one switch decision is required to switch 32 parallel connections to any one of 32 positions. Each monolithic array can be used as both transmitter and receiver by switching the bias on the quantum-well switch-detectors. Separate transmitting and receiving structures could be provided for duplex operation. For a bit error rate of 10 sup 9 at 100-MHz data rate, a required laser power of 12 mW is calculated based on an estimated total optical loss of 40 dB.
Phased locked arrays of multiple AlGaAs diode laser emitters were investigated both in edge emitting and surface emitting configurations. CSP edge emitter structures, coupled by either evanescent waves or Y-guides, could not achieve the required powers (greater than or similar to 500 mW) while maintaining a diffraction limited, single lobed output beam. Indeed, although the diffraction limit was achieved in this type of device, it was at low powers and in the double lobed radiation pattern characteristic of out-of-phase coupling. Grating surface emitting (GSE) arrays were, therefore, investigated with more promising results. The incorporation of second order gratings in distribute Bragg reflector (DBR) structures allows surface emission, and can be configured to allow injection locking and lateral coupling to populate 2-D arrays that should be able to reach power levels commensurate with the needs of high performance, free space optical communications levels. Also, a new amplitude modulation scheme was developed for GSE array operation.
A design for a monolithic narrow-linewidth InGaAsP diode laser has been developed using a multiple-quantum-well (MQW) extended-passive-cavity distributed-Bragg-reflector (DBR) laser design. Theoretical results indicate that this structure has the potential for a linewidth of 100 kHz or less. To realize this device, a number of the fabrication techniques required to integrate low-loss passive waveguides with active regions have been developed using a DBR laser structure. In addition, the MOCVD growth of InGaAs MQW laser structures has been developed, and threshold current densities as low as 1.6 kA/sq cm have been obtained from broad-stripe InGaAs/InGaAsP separate-confinement-heterostructure MQW lasers.
An optically controlled reflection modulator has been demonstrated that consists of a combination of a GaAs-AlGaAs n-i-p-i doping structure with a multiple-quantum-well structures on top of a distributed Bragg reflector, all grown by MBE. A modulation of approximately 60 percent is obtained on the test structure, corresponding to a differential change of absorption coefficient in the quantum wells of approximately 7500/cm. Changes in reflectance can be observed with a control beam power as low as 1.5 microW. This device structure has the potential of being developed as an optically addressed spatial light modulator for optical information processing.
The variation in the center wavelength of distributed Bragg reflectors used in optoelectronic devices, such as surface emitting lasers and Fabry-Perot modulators, is measured as the temperature of the mirrors changes over the range 25 C to 105 C. An analytic expression for the shift in center wavelength with temperature is presented. The mirrors measured are made of InP/InGaAsP, GaAs/AlAs, and Si/SiN(x). The linear shifts in center wavelength are 0.110 +/- 0.003 nm/C, 0.087 +/- 0.003 nm/C, and 0.067 +/- 0.007 nm/C for the InP/InGaAsP, GaAs/AlAs, and Si/SiN mirrors, respectively. Based on these data, the change in penetration depth with temperature is calculated.
An edge-emitting monolithically integrated master oscillator power amplifier (M-MOPA) has been fabricated by integrating a distributed Bragg reflector laser with a 500 microns long single mode amplifier. The M-MOPA contains a strained InGaAs quantum well in the active region and operates at about 981.5 nm in an edge-emitting fashion with maximum powers in excess of 175 mW. Single longitudinal and transverse mode operation is maintained to powers in excess of 110 mW CW.
This report describes work performed by SDL in the development of monolithically-integrated master oscillator power amplifiers under the NASA-SCAR research contract. The goals of the program were to demonstrate high power diffraction-limited operation from a semiconductor laser with the following characteristics: (1) Output power of 0.5 to 1.0 W continuous-wave (cw); (2) Single spectral mode with greater than 20 dB of side mode suppression; (3) Single spatial mode operation; (4) Modulation capability of 0.5 GHz; and (5) Operating wavelength between 830-860 nm. Cw diffraction-limited output powers as high as 2.2 W were achieved while maintaining a single longitudinal mode. Side mode suppression ratios greater than 20 dB are typically obtained. The single spatial mode output has a Strehl ratio estimated at 0.85, and a high-speed modulation capability was demonstrated with a small-signal 3-dB roll-off at 1.0 GHz. Finally, all of this performance was obtained in the 860 nm wavelength band, which corresponds to the peak sensitivity of Si detectors. During the first option period, three deliverables were fabricated and delivered that included 1 distributed Bragg reflector (DBR) laser operating at 970 nm, 1 DBR laser operating at 860 nm, and one monolithic flared amplifier master oscillator power amplifier (MFA-MOPA) providing 0.5 W cw diffraction-limited output. During the second option period, a total of 5 MFA-MOPA devices were delivered, each operating to better than 1 W cw diffraction-limited at 860 nm.
The design and operation of InGaAs-GaAs-AlGaAs asymmetric cladding ridge waveguide distributed Bragg reflector lasers is presented. Targeted for the remote sensing of water vapor with absorption lines in the lambda approximately 930 nm region, these devices operate CW with threshold currents as low as 11 MA and slope efficiencies as high as 0.37 W/A. Tbey also operate with over 30-dB side-mode suppression, and the typical CW characteristic temperature, T(sub o), is 95 K.
Optical intersubband response of a multiple quantum well (MQW)-embedded microcavity driven by a coherent pump field is studied theoretically. The n-type doped MQW structure with three subbands in the conduction band is sandwiched between a semi-infinite medium and a distributed Bragg reflector (DBR). A strong pump field couples the two upper subbands and a weak field probes the two lower subbands. To describe the optical response of the MQW-embedded microcavity, we adopt a semi-classical nonlocal response theory. Taking into account the pump-probe interaction, we derive the probe-induced current density associated with intersubband transitions from the single-particle density-matrix formalism. By incorporating the current density into the Maxwell equation, we solve the probe local field exactly by means of Green's function technique and the transfer-matrix method. We obtain an exact expression for the probe absorption coefficient of the microcavity. For a GaAs/Al(sub x)Ga(sub 1-x)As MQW structure sandwiched between a GaAs/AlAs DBR and vacuum, we performed numerical calculations of the probe absorption spectra for different parameters such as pump intensity, pump detuning, and cavity length. We find that the probe spectrum is strongly dependent on these parameters. In particular, we find that the combination of the cavity effect and the Autler-Townes effect results in a triplet in the optical spectrum of the MQW system. The optical absorption peak value and its location can be feasibly controlled by varying the pump intensity and detuning.