SQL Join vs NoSQL Wide column
I would go with option 3, and have a many to many mapping table to associate Books and Authors.  What if you have a book with more than one author? I've included an example for you below.

Your second approach could work for you.  But the answer as to what's best is how will you be querying for the information?  If you are going to query for data inside the Wide Column Store, that's going to be slow through SQL.

CREATE TABLE dbo.Author
    (
    AuthorID INT NOT NULL PRIMARY KEY IDENTITY(1,1)
    , AuthorName NVARCHAR(100) NOT NULL
    )

CREATE TABLE dbo.Book
    (
    BookID INT NOT NULL PRIMARY KEY IDENTITY(1,1)
    , BookName NVARCHAR(100) NOT NULL
    , ISBN NVARCHAR(100) NOT NULL
    )

CREATE TABLE dbo.AuthorBook
    (
    AuthorBookID INT NOT NULL PRIMARY KEY IDENTITY(1,1)
    , AuthorID INT NOT NULL REFERENCES dbo.Author (AuthorID)
    , BookID INT NOT NULL REFERENCES dbo.Book (BookID)
    )