Tunable VCSEL with strain compensated semiconductor DBR
Tunable VCSELs (TVCSELs) employing expanded material systems with expanded mechanical/optical design space for semiconductor DBR mirrors on GaAs substrates. One is the InGaAs/AlGaAsP material system. It adds indium In to decrease InGaAs H-layer bandgap for higher refractive index and higher DBR layer refractive index contrast. Adding phosphorus P gives independent control of bandgap and strain of AlGaAsP low refractive index L-layers. The tensile strain of AlGaAsP L-layer compensates compressive strain of InGaAs H-layer and lowers the cumulative strain of the multilayer DBR structure. Another option is the InGaAsN(Sb)/AlGaAsP material system, where both types of layers can be lattice matched to GaAs. It uses indium In and nitrogen N, and possibly antimony Sb, to get independent control of strain and bandgap, and thus refractive index, of dilute nitride InGaAsN(Sb) H-layers, with lower bandgap and higher refractive index than starting GaAs. Using expanded material system enables reliable DBR mirrors with higher reflectivity and spectral bandwidth and tunable VCSELs with wider tuning range.
1. A laser including a semiconductor distributed Bragg reflector mirror, wherein the mirror comprises:
a GaAs substrate; and
a plurality of layers disposed on the GaAs substrate, the plurality of layers comprising layers of compressive InGaAs alternating with layers of tensile AlAsP or GaAlAsP.
2. The laser as claimed in claim 1 , wherein the layers of compressive InGaAs alternating with the layers of tensile AlAsP or GaAlAsP produce substantially low cumulative combined strain on the GaAs substrate.
3. The laser as claimed in claim 1 , further comprising quantum well layers for providing gain.
4. The laser as claimed in claim 3 , wherein the quantum well layers are interspersed with the InGaAs and AlAsP or GaAlAsP layers.
5. The laser as claimed in claim 1 , wherein the laser is a vertical cavity surface emitting laser.
6. The laser as claimed in claim 5 , wherein the laser is a tunable vertical cavity surface emitting laser.
7. The laser as claimed in claim 6 , wherein the laser includes a MEMS membrane including a reflective coating defining an end of the laser cavity.
8. A semiconductor distributed Bragg reflector mirror, wherein the mirror comprises:
a GaAs substrate; and
a plurality of layers disposed on the GaAs substrate, the plurality of layers comprising layers of compressive InGaAs alternating with layers of tensile AlAsP or GaAlAsP.
9. The mirror as claimed in claim 8 , wherein the layers of compressive InGaAs alternating with the layers of tensile AlAsP or GaAlAsP produce substantially low cumulative combined strain on the GaAs substrate.
10. A laser including a semiconductor distributed Bragg reflector mirror, wherein the mirror comprises:
a GaAs substrate; and
a plurality of layers disposed on the GaAs substrate, the plurality of layers comprising layers of compressive InGaAs or InGaAsN (Sb) alternating with layers of tensile AlAsP or GaAlAsP.