| http://www.w3.org/ns/prov#value | - to feed a part of the output light back to the semiconductor laser; and an i-th light feedback element each arranged at an optical distance Li from the front facet on the optical path of the output light (where i=2 to n, n is a positive integer not less than 2, and Li>L1), the i-th light feedback element each having a reflection center wavelength substantially equal to the reflection center wavele
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