Document:

<PAGE>

                                                                   EXHIBIT 10.12

                                AMENDMENT #1 TO
                                      THE
                             OEM PURCHASE AND SALE
                                   AGREEMENT
                                BY AND BETWEEN
                                NORTEL NETWORKS
                                      AND
                              CHORUM TECHNOLOGIES

This amendment (the "Amendment") is made this 12th day of October, 2000 (the
"Effective Date") by and between Nortel Networks, Ltd., having an office at 8200
Dixie Road, Brampton, Ontario L6T 5P6 ("Nortel") and Chorum Technologies, Inc.
("Seller") having an office at 1303 E. Arapaho Road, Richardson, Texas 75081.

     Whereas, Nortel and Seller entered into an OEM Purchase and Sale Agreement,
effective as of 1 January 2000 (the "OEM Agreement"), and,

     Whereas, the parties desire that this Amendment revise the OEM Agreement.

Now therefore, for good and valuable consideration, the receipt and sufficiency
of which the parties acknowledge, the parties hereby amend the OEM Agreement as
follows:

1.   Insert the following as Section 8.5.6:

     [*]

All capitalized terms herein will have the meaning set forth in the OEM
Agreement.  Except as specifically provided above, the OEM Agreement shall
remain in full force and effect without modification.

THE REST OF THIS PAGE IS INTENTIONALLY LEFT BLANK; THE NEXT PAGE IS THE
SIGNATURE PAGE.

* Certain information on this page has been omitted and filed separately with
the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

<PAGE>

IN WITNESS WHEREOF, the Parties hereto have executed this Amendment #1 on the
day and year last written below.

CHORUM TECHNOLOGIES INCORPORATED        NORTEL NETWORKS LIMITED

By:                                     By:
   ----------------------------            ----------------------------
        (Signature)                           (Signature)
Name:                                   Name:
     --------------------------              --------------------------

Title:                                  Title:
      --------------------------              -------------------------
        (Print)                               (Print)

Date:                                   Date:
     ---------------------------             --------------------------<PAGE>

                                                                   EXHIBIT 10.32

                             TWELFTH AMENDMENT TO
                             --------------------
                          LOAN AND SECURITY AGREEMENT
                          ---------------------------
                 AND AMENDMENT TO CERTAIN OTHER LOAN DOCUMENTS
                 ---------------------------------------------

          THIS TWELFTH AMENDMENT TO LOAN AND SECURITY AGREEMENT AND AMENDMENT TO
CERTAIN OTHER LOAN DOCUMENTS (the "Amendment") is made and entered into on this
                                   ---------
15/th/ day of October, 2000, to be effective (unless otherwise specified herein)
as of October 15, 2000 (the "Effective Date"), by and among FLEET CAPITAL
                             --------------
CORPORATION, a Rhode Island corporation, successor in interest by merger to
FLEET CAPITAL CORPORATION, a Connecticut corporation, formerly known as SHAWMUT
CAPITAL CORPORATION, successor in interest by assignment to BARCLAYS BUSINESS
CREDIT, INC. ("Lender"), LOWRANCE ELECTRONICS, INC., a Delaware corporation
               ------
("Lowrance"), LEI EXTRAS, INC., a Delaware corporation ("LEI"), LOWRANCE
  --------                                               ---
CONTRACTS, INC., a Delaware corporation ("Lowrance Contracts"), and SEA
                                          ------------------
ELECTRONICS, INC., an Oklahoma corporation ("Sea Electronics") (Lowrance, LEI,
                                             ---------------
Lowrance Contracts and Sea Electronics are herein individually and collectively
called "Borrower").
        --------

                                   RECITALS

          A.  Borrower, Lowrance Australia Pty Limited ("Lowrance Australia")
                                                         ------------------
and Lender have entered into that certain Loan and Security Agreement, dated
December 15, 1993, as amended by (i) that certain First Amendment to Loan and
Security Agreement, dated October 16, 1995, by and among Lender, Borrower and
Lowrance Australia, (ii) that certain Second Amendment to Loan and Security
Agreement, dated November 1, 1996 by and among Lender and Borrower, (iii) that
certain Third Amendment to Loan and Security Agreement, dated December 30, 1996,
by and among Lender and Borrower, (iv) that certain Fourth Amendment to Loan and
Security Agreement, entered into effective as of April 1, 1997, by and among
Lender and Borrower, (v) that certain Fifth Amendment to Loan and Security
Agreement, entered into effective as of August 25, 1997, by and between Lender
and Borrower ("Fifth Amendment"), (vi) that certain Sixth Amendment to Loan and
               ---------------
Security Agreement and Certain Other Loan Documents, entered into effective as
of August 28, 1997, by and between Lender and Borrower, (vii) that certain
Seventh Amendment to Loan and Security Agreement, entered into effective as of
November 1, 1996, by and between Lender and Borrower, (viii) that certain Eighth
Amendment to Loan and Security Agreement, made and entered into as of December
9, 1997, by and between Lender and Borrower, (ix) that certain Ninth Amendment
to Loan and Security Agreement made and entered into as of September 14, 1998,
by and between Lender and Borrower, (x) that certain Tenth Amendment to Loan and
Security Agreement and Amendment to Certain Other Loan Documents, executed in
November of 1998, by Lender and Borrower; and (xi) that certain Eleventh
Amendment to Loan and Security Agreement and Amendment to Certain Other Loan
Documents, executed March 14, 2000, by Lender and Borrower (as amended, the
"Loan Agreement").
 --------------

          B.  Borrower and Lender desire to amend the Loan Agreement and certain
of the other Loan Documents as hereinafter set forth.

                                       1
<PAGE>

          NOW, THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties, intending to be legally bound, agree as
follows:

                                   ARTICLE I
                                  Definitions
                                  -----------

          1.01 Capitalized terms used in this Amendment are defined in the Loan
Agreement, as amended hereby, unless otherwise stated.

                                  ARTICLE II
                                  Amendments
                                  ----------

          2.01 Amendment to Section 1.1 of the Loan Agreement; Addition of
               -----------------------------------------------------------
Certain Definitions.  Effective as of the Effective Date, Section 1.1 of the
-------------------                                       -----------
Loan Agreement is hereby amended by adding the following definitions thereto in
alphabetical order:

               "First Use - has the meaning set forth in the definition of
                ---------
          'Temporary Finished Goods Eligible Inventory Increased Amount'
          contained in this Agreement.

               Temporary Finished Goods Eligible Inventory Increased Amount -
               ------------------------------------------------------------
          the amount indicated below, during the time period indicated below:

       Time Period                     Maximum Amount
       -----------                     --------------

       (a)  First Use through the      (a) the lesser of (i) $1,500,000
            earlier to occur of the        or (ii) 20% of the value of
            68/th/ day after First         Finished Goods Eligible
            Use or January 18, 2001        Inventory at the relevant
                                           calculation date

       (b)  Seven day period           (b) the lesser of (i) $1,125,000
            beginning on the day           or (ii) 20% of the value of
            immediately succeeding         Finished Goods Eligible
            the end of the period          Inventory at the relevant
            described in (a) above         calculation date

       (c)  Seven day period           (c) the lesser of (i) $750,000 or
            beginning on the day           (ii) 20% of the value of
            immediately succeeding         Finished Goods Eligible
            the end of the period          Inventory at the relevant
            described in (b) above         calculation date

                                       2
<PAGE>

       (d)  Seven day period           (d) the lesser of (i) $375,000 or
            beginning on the day           (ii) 20% of the value of
            immediately succeeding         Finished Goods Eligible
            the end of the period          Inventory at the relevant
            described in (c) above         calculation date

       (e)  Earlier to occur of (i)    (e) $0.00
            February 12, 2001 or (ii)
            the day immediately
            succeeding the end of the
            period described in (d)
            above, and at all times
            thereafter

            Temporary Finished Goods Eligible Inventory Increased
            -----------------------------------------------------
     Amount Period - the period of time beginning on (i) the first day
     -------------
     after October 15, 2000, that the Borrower requests that the
     Temporary Finished Goods Eligible Inventory Increased Amount be
     included in the calculation of the Borrowing Base (the 'First
                                                             -----
     Use') and ending on (ii) the earlier to occur of February 12,
     ---
     2001 or the ninetieth day after the First Use."

     2.02  Amendment to Section 1.1 of the Loan Agreement; Amendment to
           ------------------------------------------------------------
Definition of "Borrowing Base."  Effective as of the Effective Date, clause
-----------------------------                                        ------
(iii) of paragraph (b) of the definition of "Borrowing Base" contained in
-----    -------------
Section 1.1 of the Loan Agreement is amended to read as follows:
-----------

          "(iii) the lesser of (a) the Inventory Commitment Amount, or
                 --- ------ --
     (b) the sum of (v) 30% of the value of Raw Materials Eligible
         --- --- --
     Inventory at such date, (w) 30% of the value of Mexican Raw
     Materials Eligible Inventory at such date, (x) 60% of the value
     of Finished Goods Eligible Inventory at such date, (y) 60% of the
     value of Australian Finished Goods Eligible Inventory at such
     date, and (z) as long as the Temporary Finished Goods Eligible
     Inventory Increased Amount Period is in existence, the Temporary
     Finished Goods Eligible Inventory Increased Amount at such date,
     all of the above as calculated on the basis of the lower of cost
     or market, with cost calculated on a first-in, first-out basis;"

     2.03  Amendment Fee.  In consideration for the agreements of Lender
           -------------
contained herein but subject to Section 3.1(D) of the Loan Agreement, Borrower
                                --------------
agrees to pay Lender a fee of $10,000.  Such fee shall be due and payable and
shall be fully earned as of the date of execution of this Amendment.

                                  ARTICLE III
                              Conditions Precedent
                              --------------------

          3.01  Conditions Precedent.  The effectiveness of this Amendment is
                --------------------
subject to the satisfaction of the following conditions precedent, unless
specifically waived in writing by Lender:

                                       3
<PAGE>

          (a)  Lender shall have received each of the following, each in form
     and substance satisfactory to Lender: (i) this Amendment, duly executed by
     Borrower; and (ii) such additional documents, instruments and information
     as Lender or its legal counsel may request;

          (b)  The representations and warranties contained herein, in the Loan
     Agreement and in the other Loan Documents, as each is amended hereby, shall
     be true and correct as of the date hereof, as if made on the date hereof;

          (c)  After giving effect to this Amendment, no Default or Event of
     Default shall have occurred and be continuing, unless such Default or Event
     of Default has been specifically waived in writing by Lender;

          (d)  All corporate proceedings taken in connection with the
     transactions contemplated by this Amendment and all documents, instruments
     and other legal matters incident thereto shall be satisfactory to Lender
     and its legal counsel; and

          (e)  Lender shall have received, in immediately available funds,
payment of the fee described in Section 2.03 of this Amendment.
                                ------------

                                  ARTICLE IV
                                   No Waiver
                                   ---------

     Nothing contained in this Amendment shall be construed as a waiver by
Lender of any covenant or provision of the Loan Agreement, the other Loan
Documents, this Amendment, or of any other contract or instrument between
Borrower and Lender, and the failure of Lender at any time or times hereafter to
require strict performance by Borrower of any provision thereof shall not waive,
affect or diminish any right of Lender to thereafter demand strict compliance
therewith. Lender hereby reserves all rights granted under the Loan Agreement,
the other Loan Documents, this Amendment and any other contract or instrument
between Borrower and Lender.

                                   ARTICLE V
                 Ratifications, Representations and Warranties
                 ---------------------------------------------

     5.01 Ratifications. The terms and provisions set forth in this Amendment
          -------------
shall modify and supersede all inconsistent terms and provisions set forth in
the Loan Agreement and the other Loan Documents, and, except as expressly
modified and superseded by this Amendment, the terms and provisions of the Loan
Agreement and the other Loan Documents are ratified and confirmed and shall
continue in full force and effect. Borrower and Lender agree that the Loan
Agreement and the other Loan Documents, as amended hereby, shall continue to be
legal, valid, binding and enforceable in accordance with their respective terms.

                                       4
<PAGE>

     5.02 Representations and Warranties. Borrower hereby represents and
          ------------------------------
warrants to Lender that (a) the execution, delivery and performance of this
Amendment and any and all other Loan Documents executed and/or delivered in
connection herewith have been authorized by all requisite corporate action on
the part of Borrower and will not violate the Certificate of Incorporation or
Bylaws of Borrower; (b) the representations and warranties contained in the Loan
Agreement, as amended hereby, and any other Loan Documents are true and correct
on and as of the date hereof and on and as of the date of execution hereof as
though made on and as of each such date; (c) no Default or Event of Default
under the Loan Agreement, as amended hereby, has occurred and is continuing; (d)
Borrower is in full compliance with all covenants and agreements contained in
the Loan Agreement and the other Loan Documents, as amended hereby; (e) the
Borrower's Certificate of Incorporation and Bylaws are in full force and effect
on and as of the date hereof without modification or amendment in any respect
since November 1, 1996; (f) as of the date hereof, (i) Borrower is in existence
and in corporate and tax good standing in the State of its organization, (ii)
the Borrower is qualified to do business as a foreign corporation and is in
corporate and tax good standing in each jurisdiction where Borrower is doing
business and is required to be so qualified, (iii) Borrower does not owe
franchise taxes or other taxes required to maintain its corporate existence and
no franchise tax reports are due, and (iv) no proceedings are pending for
forfeiture of the Borrower's charter or for its dissolution either voluntarily
or involuntarily; and (g) the officer of Borrower executing this Amendment has
been duly elected and is, at present, qualified and acting in the office
indicated below such officer's name and is duly authorized to execute this
Amendment on behalf of Borrower.

                                  ARTICLE VI
                           Miscellaneous Provisions
                           ------------------------

     6.01 Survival of Representations and Warranties. All representations and
          ------------------------------------------
warranties made in the Loan Agreement or any other Loan Document, including,
without limitation, any document furnished in connection with this Amendment,
shall survive the execution and delivery of this Amendment and the other Loan
Documents, and no investigation by Lender or any closing shall affect the
representations and warranties or the right of Lender to rely upon them.

     6.02 Reference to Loan Agreement. Each of the Loan Agreement and the other
          ---------------------------
Loan Documents, and any and all other agreements, documents or instruments now
or hereafter executed and delivered pursuant to the terms hereof or pursuant to
the terms of the Loan Agreement, as amended hereby, are hereby amended so that
any reference in the Loan Agreement and such other Loan Documents to the Loan
Agreement shall mean a reference to the Loan Agreement, as amended hereby.

     6.03 Expenses of Lender. As provided in the Loan Agreement, Borrower agrees
          ------------------
to pay on demand all costs and expenses incurred by Lender in connection with
the preparation, negotiation and execution of this Amendment and the other Loan
Documents executed pursuant hereto and any and all amendments, modifications,
and supplements thereto, including, without limitation, the costs and fees of
Lender's legal counsel, and all costs and expenses incurred by Lender in
connection with the enforcement or preservation of any rights under the Loan

                                       5
<PAGE>

Agreement, as amended hereby, or any other Loan Documents, including, without,
limitation, the costs and fees of Lender's legal counsel.

     6.04  Severability. Any provision of this Amendment held by a court of
           ------------
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

     6.05  Successors and Assigns. This Amendment is binding upon and shall
           ----------------------
inure to the benefit of Lender and Borrower and their respective successors and
assigns, except that Borrower may not assign or transfer any of its rights or
obligations hereunder without the prior written consent of Lender.

     6.06  Counterparts. This Amendment may be executed in one or more
           ------------
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.

     6.07  Effect of Waiver. No consent or waiver, express or implied, by Lender
           ----------------
to or for any breach of or deviation from any covenant or condition by Borrower
shall be deemed a consent to or waiver of any other breach of the same or any
other covenant, condition or duty.

     6.08  Headings. The headings, captions, and arrangements used in this
           --------
Amendment are for convenience only and shall not affect the interpretation of
this Amendment.

     6.09  Applicable Law. THIS AMENDMENT AND ALL OTHER LOAN DOCUMENTS EXECUTED
           --------------
PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE PERFORMABLE IN AND
SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF
TEXAS.

     6.10  Final Agreement. THE LOAN AGREEMENT AND THE OTHER LOAN DOCUMENTS,
           ---------------
EACH AS AMENDED HEREBY, REPRESENT THE ENTIRE EXPRESSION OF THE PARTIES WITH
RESPECT TO THE SUBJECT MATTER HEREOF ON THE DATE THIS AMENDMENT IS EXECUTED. THE
LOAN AGREEMENT AND THE OTHER LOAN DOCUMENTS, AS AMENDED HEREBY, MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS
OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. NO
MODIFICATION, RESCISSION, WAIVER, RELEASE OR AMENDMENT OF ANY PROVISION OF THIS
AMENDMENT SHALL BE MADE, EXCEPT BY A WRITTEN AGREEMENT SIGNED BY BORROWER AND
LENDER.

     6.11  Release. BORROWER HEREBY ACKNOWLEDGES THAT IT HAS NO DEFENSE,
           -------
COUNTERCLAIM, OFFSET, CROSS-COMPLAINT, CLAIM OR DEMAND OF ANY KIND OR NATURE
WHATSOEVER THAT CAN BE ASSERTED TO REDUCE OR ELIMINATE ALL OR ANY PART OF ITS
LIABILITY TO REPAY THE "OBLIGATIONS" OR TO SEEK AFFIRMATIVE RELIEF OR DAMAGES OF
ANY KIND OR NATURE FROM

                                       6
<PAGE>

LENDER. BORROWER HEREBY VOLUNTARILY AND KNOWINGLY RELEASES AND FOREVER
DISCHARGES LENDER, ITS PREDECESSORS, OFFICERS, DIRECTORS, AGENTS, EMPLOYEES,
SUCCESSORS AND ASSIGNS, FROM ALL POSSIBLE CLAIMS, DEMANDS, ACTIONS, CAUSES OF
ACTION, DAMAGES, COSTS, EXPENSES, AND LIABILITIES WHATSOEVER, KNOWN OR UNKNOWN,
ANTICIPATED OR UNANTICIPATED, SUSPECTED OR UNSUSPECTED, FIXED, CONTINGENT, OR
CONDITIONAL, AT LAW OR IN EQUITY, ORIGINATING IN WHOLE OR IN PART ON OR BEFORE
THE DATE THIS AMENDMENT IS EXECUTED, WHICH THE BORROWER MAY NOW OR HEREAFTER
HAVE AGAINST LENDER, ITS PREDECESSORS, OFFICERS, DIRECTORS, AGENTS, EMPLOYEES,
SUCCESSORS AND ASSIGNS, IF ANY, AND IRRESPECTIVE OF WHETHER ANY SUCH CLAIMS
ARISE OUT OF CONTRACT, TORT, VIOLATION OF LAW OR REGULATIONS, OR OTHERWISE, AND
ARISING FROM ANY "LOANS", INCLUDING, WITHOUT LIMITATION, ANY CONTRACTING FOR,
CHARGING, TAKING, RESERVING, COLLECTING OR RECEIVING INTEREST IN EXCESS OF THE
HIGHEST LAWFUL RATE APPLICABLE, THE EXERCISE OF ANY RIGHTS AND REMEDIES UNDER
THE LOAN AGREEMENT OR OTHER LOAN DOCUMENTS, AND THE NEGOTIATION OF AND EXECUTION
OF THIS AMENDMENT.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       7
<PAGE>

     IN WITNESS WHEREOF, this Amendment has been executed and is effective as of
the date first above-written.

                                 "LENDER"

                                 FLEET CAPITAL CORPORATION

                                 By:  /s/ E. James Beckemeier
                                 ----------------------------
                                 Name: E. James Beckemeier
                                 Title:  Vice President

                                 "BORROWER"

                                 LOWRANCE ELECTRONICS, INC.

                                 By:  /s/ Douglas J. Townsdin
                                 ----------------------------
                                 Name:  Douglas J. Townsdin
                                 Title:  Chief Financial Officer

                                 LEI EXTRAS, INC.

                                 By:  /s/ Jane M. Kaiser
                                 -----------------------
                                 Name:  Jane M. Kaiser
                                 Title:  President

                                 LOWRANCE CONTRACTS, INC.

                                 By:  /s/ Ronald G. Weber
                                 ------------------------
                                 Name:  Ronald G. Weber
                                 Title:  President

                                 SEA ELECTRONICS, INC.

                                 By:  /s/ Mark C. McQuown
                                 ------------------------
                                 Name:  Mark C. McQuown
                                 Title:  President

                                       8

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