Browsing by Author "Lin, K"

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Characteristics of MOCVD- and MBE-grown InGa(N)As VCSELs
(2005-08-01)
Yang, HPD
;
Lu, C
;
Hsiao, R
;
Chiou, C
;
Lee, C
We report our results on InGaNAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) in the 1.3 mu m range. The epitaxial structures were grown on (10 0) GaAs substrates by metalorganic chemical vapour deposition (MOCVD) or molecular beam epitaxy (MBE). The nitrogen composition of the InGa(N)As/GaAs quantum-well (QW) active region is 0-0.02. The long-wavelength (up to 1.3 mu m) room-temperature continuous-wave (RT CW) lasing operation was achieved for MBE- and MOCVD-grown VCSELs. For MOCVD-grown devices with n- and p-doped distributed Bragg reflectors (DBRs), a maximum optical output power of 0.74 mW was measured for In(0.36)Ga(0.64)N(0.006)AS(0.994)/GaAs VCSELs. A very low J(th) of 2.55 kA cm(-2) was obtained for the InGaNAs/GaAs VCSELs. The MBE-grown devices were made with an intracavity structure. Top-emitting multi-mode 1.3 mu m In0.35Ga0.65N0.02As0.98/GaAs VCSELs with 1 mW output power have been achieved under RT CW operation. A J(th) of 1.52 kA cm-2 has been obtained for the MBE-grown In0.35Ga0.65N0.02As0.98/GaAs VCSELs, which is the lowest threshold current density reported. The emission characteristics of the InGaNAs/GaAs VCSELs were measured and analysed.
Code compression by register operand dependency
(2002)
Lin, K
;
Shann, JJJ
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
This paper proposes a dictionary-based code compression technique that maps the source register operands to the nearest occurrence of a destination register in the predecessor instructions. The key idea is that most destination registers have a great possibility to be used as source registers in the following instructions. The dependent registers can be removed from the dictionary if this information can be specified otherwise. As a result, the compression ratio benefits from the decreased dictionary size. A set of programs has been compressed using this feature. The compression results show that the average compression ratio is reduced to 38.6% on average for MediaBench benchmarks compiled for MIPS R2000 processor.
Code compression techniques using operand field remapping
(2002-01-01)
Lin, K
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
Dictionary-based code compression stores the most frequently used instruction sequences in a dictionary, and replaces the occurrences of these sequences in the program with codewords. The large dictionary size is due mainly to many instruction sequences which are different only in operands, but are otherwise the same. The operand factorisation technique divides the expression tree into tree-pattern (opcode sequence) and operand-pattern (operand sequence) to reduce this redundancy; instruction sequences with the same opcodes but different operands may thus share the same tree-pattern dictionary entry. The paper proposes an operand field remapping method to further reduce dictionary size. The key idea is to explore the relations between the current operand to be compressed with those already compressed. The operand-pattern dictionary is therefore divided into an operand remapping dictionary and an operand list dictionary. Each entry in the operand remapping dictionary indicates whether the operand (register or immediate value) to be compressed is the most used operand, the same as the destination register of the previous instructions, or otherwise. With this remapping technique, the operand dictionary size is greatly reduced. An average 46% compression ratio can be achieved where compression ratio = (dictionary size + compressed code size)/(original program size).